Targeting DNA damage response in cardiovascular diseases: from pathophysiology to therapeutic implications

Abstract

Cardiovascular diseases (CVDs) arise from a complex interplay among genomic, proteomic, and metabolomic abnormalities. Emerging evidence has recently consolidated the presence of robust DNA damage in a variety of cardiovascular disorders. DNA damage triggers a series of cellular responses termed DNA damage response (DDR) including detection of DNA lesions, cell cycle arrest, DNA repair, cellular senescence, and apoptosis, in all organ systems including hearts and vasculature. Although transient DDR in response to temporary DNA damage can be beneficial for cardiovascular function, persistent activation of DDR promotes the onset and development of CVDs. Moreover, therapeutic interventions that target DNA damage and DDR have the potential to attenuate cardiovascular dysfunction and improve disease outcome. In this review, we will discuss molecular mechanisms of DNA damage and repair in the onset and development of CVDs, and explore how DDR in specific cardiac cell types contributes to CVDs. Moreover, we will highlight the latest advances regarding the potential therapeutic strategies targeting DNA damage signalling in CVDs.

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1. Introduction

Cardiovascular diseases (CVDs) remain the leading cause of morbidity and mortality globally.¹ To date, multi-omics approaches have identified a multi-facet aetiology for CVDs, including genomic, proteomic, and metabolomic derrangements.^2,3 However, much focus has been geared towards impairment of proteostasis and metabolic harmony.^3,4 Possible genomic instability and DNA damage have been indicated in the pathophysiology of CVDs albeit remains largely unexplored.^5,6 Clinical and pre-clinical evidence has indicated the presence of DNA damage in CVDs.^7–9 Besides, DNA damage triggers unfavourable sequelae in mammalian cells, including cell senescence, apoptosis, and inflammation,^6,10 which are well perceived for the pathophysiology of CVDs. In this review, we outline the emerging role for DNA damage and repair mechanisms in CVDs, the DNA damage response (DDR) in various cardiac cell types, and potential therapies targeting DNA damage and DDR for the management of CVDs.

2. DNA damage and repair mechanism in the cardiovascular system

DNA damage can be provoked by intrinsic or extrinsic insults, including oxidative stress, metabolic stress, chemotherapy drugs, and radiotherapy.¹¹ Among these genomic insults, reactive oxygen species (ROS) represent the main endogenous culprit which leads to oxidative DNA damage, including a range of DNA lesions such as base oxidations, single-strand breaks (SSBs), double-strand breaks (DSBs), and telomere shortening.^12,13 DNA repair system is evolved to overcome various types of DNA damage, including homologous recombination (HR), non-homologous end joining (NHEJ), base excision repair (BER), nucleotide excision repair (NER), and mismatch repair (MMR). In general, DSBs are repaired through HR or NHEJ, while SSBs and individual base damage are revamped through BER, and large adducts through NER.¹²Figure 1 denotes perceived causes of DNA damage, DNA repair system, and cellular consequences in CVDs. Although mitochondrial DNA damage also contributes to the pathogenesis of CVDs,^14–16 such as heart failure (HF) and coronary heart disease, we will only focus on the nuclear DNA damage signalling in CVDs.

2.1 DSB signalling pathway in the cardiovascular system

In the HR modality, DSBs are detected by the MRE11-RAD50-NBS1 (MRN) complex which activates ataxia–telangiectasia mutated (ATM) kinase to transduce DDR signalling.¹⁷ HR repair is generally restricted to the S and G2 phases of the cell cycle, since this repair system uses sister-chromatid sequences as the template to execute the faithful repair.¹² Normally, HR is initiated by detection of the MRN complex, the 5′–3′ strand resection of exonuclease 1 (EXO1) and bloom syndrome heterodimer, leading to the generation of a 3′ single-stranded DNA (ssDNA) tail. The ssDNA is then rapidly coated by replication protein A (RPA), and the ssDNA–RPA complex recruits ATRIP, leading to activation of another primary kinase namely ataxia–telangiectasia and Rad3-related (ATR). RPA is subsequently displaced by Rad51 to form a nucleoprotein filament. In cellular processes catalysed by RAD51 and the breast-cancer susceptibility proteins BRCA1 and BRCA2, ssDNA invades undamaged template, helicases, and other components with the assistance of polymerases and nucleases.¹² Besides, BRCA1 interacts and co-localizes with RAD51 at the sites of DSBs to turn on RAD51-mediated HR repair. Notably, BRCA1-deficient cells exhibit deficiency in RAD51-mediated HR of DSBs along with hypersensitivity to genetic insults.¹⁸

In the NHEJ modality, DSBs are detected by the Ku70 and Ku80 proteins which bind and activate the protein kinase DNA-dependent protein kinase (DNA-PK) catalytic subunit (DNA-PKcs).¹² The DNA-PK complex recruits and activates DNA ligase IV and associated scaffolding factors XRCC4 (X-ray repair cross-complementing protein 4) and XLF (XRCC4-like factor) to repair DSBs.¹² In DSB signalling, the ATM, ATR, and DNA-PK complexes serve as major DDR mediators for phosphorylation of downstream substrates, including H₂AX, checkpoint kinase 1 (CHK1)/CHK2, and p53 to transduce DDR signals (i.e. cell cycle arrest, senescence, apoptosis, and inflammation).¹⁹ Notably, phosphorylation of H₂AX at serine 139 (termed γH₂AX) is perceived as a benchmark for DSBs.²⁰ The pathogenic and therapeutic value of ATM, ATR, and DNA-PK in the cardiovascular system will be discussed in Section 7.

DSBs are identified under genomic stress in nearly all cardiovascular cell types.^6,9,21,22 However, only limited studies directly assessed the role of DSB repair in cardiovascular cells. In theory, HR repair is unlikely to occur in post-mitotic cardiomyocytes due to the restriction of the cell cycle. However, up-regulated BRCA1 was observed in post-ischaemic human myocardium.⁹ BRCA1 depletion in cardiomyocytes led to impaired DSB repair (indicated by RAD51-foci formation) and cardiac function in myocardial ischaemia.⁹ However, no direct evidence was offered for possible HR in cardiomyocytes.⁹ Further study is warranted to discern the presence of HR in cardiac diseases. In another independent study, vascular smooth muscle cells (VSMCs) from human atherosclerotic plaques displayed DNA damage and up-regulated MRN complex, favouring the presence of HR in VSMCs.²³ Distinct from HR, a role for NHEJ in the cardiovascular system was only reported in endothelial cells.²⁴ The results revealed reduced lncRNA SNHG12 in atherosclerotic plaque endothelial cells, leading to reduced interaction between DNA-PKcs and Ku70/Ku80, compromised DNA repair, DDR activation, and vascular senescence.²⁴ These findings demonstrate that deficiency in DSB repair may lead to genomic instability, activation of DDR, and progression of CVDs.

2.2 SSB and excision repair in the cardiovascular system

The most common trigger for SSBs is oxidative attack evoked by ROS. SSBs can occur either by direct disintegration of oxidized sugar or indirectly during DNA BER of modified bases, such as oxidized bases, abasic sites (aka, apurinic, or apyrimidinic sites), or other base modifications.²⁵ Besides, SSBs can also be evoked due to the abortive or erroneous function of enzymes including DNA topoisomerase 1.²⁵ These base or nucleotide modifications and SSBs are repaired by excision repair mechanisms, including SSB repair, BER, and NER. The most likely consequence of SSBs in dividing cells is the blockage of DNA replication forks during the S phase, leading to DSB formation.²⁵ In non-proliferating cells such as post-mitotic cardiomyocytes, cell death induced by SSBs might involve RNA polymerase implemented during transcription, and overactivation of the SSB sensor protein poly(ADP-ribose) polymerase 1 (PARP1).²⁵

Compared to DSB repair, PARP enzymes play critical roles in various steps of SSB repair.^26,27 In brief, SSBs are rapidly recognized and bound with PARP1, followed by attachment of PAR onto PARP1, leading to PARP1 activation. During BER, PARP1 activates SSB repair through recruiting and stabilizing a series of repair components. PARP1 recruits a scaffold protein XRCC1 and assemblies with DNA polymerase β and DNA ligase III to foster the repair process.²⁸

NER pathway is conserved to repair bulky DNA lesions due to multiple sources of mutagenic agents, such as ultraviolet (UV) irradiation. This repair system includes the following processes namely (i) DNA damage detection by xeroderma pigmentosum group C-complementing protein (XPC) assisted by the UV-DDB1/2 (XPE) complex, (ii) local unwinding of DNA, (iii) damage verification by XPA, (iv) excision of damaged DNA by endonucleases ERCC1/XPF and XPG, and (v) replacement of excised DNA using intact strand as a template.²⁵ Notably, PARP1 was shown to play a vital role in NER by mediating the PARylation of NER proteins including XPA and XPC.²⁶

Although SSB is established in CVDs including HF, there is limited evidence for the precise role of SSB repair in given cardiovascular cells and CVDs.^29,30 It was previously shown that cardiomyocyte-specific depletion of XRCC1 led to SSB accumulation, DDR activation, cardiac inflammatory response, and exacerbated HF.²⁹ In addition, an essential role for NER in vascular disease was shown by two NER-defective mouse models, Ercc1^d/− and Xpd^TTD, where increased vascular senescence, stiffness, hypertension, and impaired vasodilator function were evident with ageing.³⁰ These findings further underline the importance of SSB repair machinery for the maintenance of genomic stability of the cardiovascular system and protection against CVDs.

2.3 Oxidative bases and OGG1-mediated BER in the cardiovascular system

DNA bases are especially vulnerable to oxidation damage evoked by ROS. 8-oxoguanine (8-oxoG) is the most abundant DNA lesion marker formed upon oxidative exposure. Accumulation of 8-oxoG is a cellular biomarker for oxidative stress.⁵ BER is the primary 8-oxoG repair machinery. Among these, 8-oxoguanine glycosylase (OGG1), the predominant form of DNA glycosylase, is deemed responsible for the removal of 8-oxoG.⁵

To date, ample studies have linked a deficiency in OGG1-mediated BER with the aetiology of CVDs.^5,7,31 Hearts from patients with end-stage cardiomyopathies exhibited a loss in OGG1 content.⁷ Besides, nutrient deprivation also contributed to impaired BER (8-oxoG accumulation) in cardiomyocytes in vitro, accompanied by loss of OGG1, while BER activity was rescued by recombinant OGG1. OGG1 was also verified in vascular cells in atherosclerosis progression. In particular, 8-oxoG accumulation in endothelial cells, VSMCs, and macrophages were closely linked with the onset of atherosclerosis.³¹ In this context, OGG1 deficiency in macrophages was shown to promote oxidative DNA damage and accelerated atherogenesis through induction of inflammation.³¹ Further investigations revealed reduced protein levels and activity of OGG1 in VSMCs from human plaques, leading to BER deficiency and 8-oxoG accumulation, en route to the facilitation of atherosclerosis.⁵ Thus, detrimental outcomes of oxidative stress on CVDs involve a vicious cycle among oxidative DNA damage, down-regulation of OGG1, and BER deficiency.

3. DDR in specific cardiovascular cell types

DDR encompasses a complex intertwined signalling network to prevent genomic instability. In particular, proteins undergo post-translational modifications to reconcile DNA damage, while DDR proteins are categorized into sensors, transducers, and effectors¹² (Figure 2). Normally, if DNA lesions are minor and properly repaired, cells will undergo a transient cell cycle arrest, and DDR inactivation ensues to restore normal function. Cells undergo excessive or permanent DDR activation triggering cellular senescence and apoptosis with severe unrepairable DNA damage.¹² Moreover, proteomics analysis has identified a variety of uncharacterized ATM/ATR-mediated phosphorylation sites,³² denoting more cellular processes as possible DDR regulatory targets.

DNA damage differentially affects cells depending on cell types. The cardiovascular system involves a wide range of cell types, including cardiomyocytes, VSMCs, fibroblasts, endothelial, immune, progenitor, and epithelial cells. In vivo and in vitro studies have shown that nearly all cell types undergo DNA damage and DDR activation with ageing or development of CVDs.^21,23,24,33 Therefore, possible contributions of DNA damage to CVD pathology can be originated from a variety of cell types. Although activation of DDR was initially thought to be a cell cycle arrest response unique to dividing cells, it became evident that DDR activation is also generalized in post-mitotic cells such as cardiomyocytes.³³

3.1 DDR in cardiomyocytes

The role of DDR activation in cardiomyocytes has been evaluated in only limited studies.^{21,29,33–35} Mammalian hearts possess a remarkable regenerative capacity for a brief period following birth, after which the majority of cardiomyocytes permanently exit the cell cycle. Notably, DDR serves as a mediator of physiological post-natal cell cycle arrest in cardiomyocytes. Post-natal exposure to environmental oxygen was shown to trigger mitochondrial oxidative metabolism, ROS production, oxidative DNA damage (8-oxoG level), and ATM-mediated DDR activation in the heart during the first post-natal week, triggering cell cycle arrest.³⁴ Intriguingly, post-natal exposure to mild hypoxia, ROS scavenging, and DDR inhibition promote cardiomyocyte proliferation and regenerative capacity.³⁴ Moreover, gradual exposure to systemic hypoxaemia after myocardial infarction (MI), where inspired oxygen was slowly dropped by 1% and was ultimately maintained at 7% for 2 weeks, contributed to a robust regenerative response in mice, along with reduced myocardial fibrosis and improved cardiac function.³⁵ Similarly, moderate hypoxia (blood oxygen saturation: 75–85%) was associated with increased cell cycle markers possibly through reduced oxidative DNA damage in post-natal human cardiomyocytes.³⁶

Under pathological stress, persistent DNA damage and DDR activation are evident in cardiomyocytes, prompting a shift from a non-dividing physiological to a non-dividing pathological state (e.g. hypertrophic growth). DNA damage in cardiomyocytes leads to up-regulation of several DDR markers such as phosphorylated ATM, ATR, PARP1, and p53, with increased cellular senescence and apoptosis.^21,37–39 DDR is shown to regulate pathological cardiomyocyte hypertrophy.^21,29 Pressure overload induces DSBs, DDR activation, ATM-dependent calcineurin activation, and protein synthesis, leading to cardiac hypertrophy.²¹ During telomeric DNA damage and DDR activation, cardiomyocytes acquire senescence-like phenotypes, characterized by p53, p21, and p16 activation, and a non-canonical SASP secretome including inflammatory cytokines TNF-α, IL-1, and IL-6, growth differentiation factor 15 (GDF15), TGFβ2, and endothelin 3 (EDN3), contributing to cardiac hypertrophy and interstitial fibrosis.³³

Cardiomyocytes usually display impaired contractile and electrical patterns in response to DDR activation, resulting in cardiomyopathies and arrhythmias.⁴⁰ For example, lamin A (LMNA) and TMEM43 (transmembrane protein 43) mutations led to dilated cardiomyopathy (DCM) and arrhythmogenic cardiomyopathy, associated with genomic instability, DDR and p53 activation in cardiomyocytes.^39,41 Besides, anthracyclines, a class of chemotherapeutic agents, trigger a DCM phenotype associated with cardiomyocyte DNA damage.⁴² These findings suggest an essential role of DNA damage and DDR activation, in particular through ATM signalling, in physiological cell cycle arrest and pathological hypertrophy in cardiomyocytes.

3.2 DDR in dividing cells in the cardiovascular system

In dividing cardiovascular cells, such as endothelial cells, VSMCs, cardiac fibroblasts (CFs), immune, and epithelial cells, DDR is characterized by ATM and p53 activation, reduced proliferation, cellular senescence, and apoptosis.⁶ Senescence is the major DDR consequence in dividing cardiovascular cells, characterized by cell cycle arrest, DNA damage, and up-regulated senescence markers (p16, p21, and p53), as well as elevated canonical SASP components, such as IL-6, CXC-chemokine ligand 1 (CXCL1) and CXCL2, TNF-α, vascular endothelial growth factor (VEGF), matrix metalloproteinase 1 (MMP1), MMP3, and plasminogen activator inhibitor 1 (PAI1).⁴³

In VSMCs, DNA damage due to defective 8-oxoG BER is involved in cell cycle arrest, lost proliferative capacity, and senescence, through an ATM/ATR-p53-p21-dependent pathway.^5,23 Abnormal processing of pre-lamin A compromised formation of the nuclear lamina, making VSMC more prone to DNA damage. Accumulation of pre-lamin A resulted from LMNA mutation was shown to promote VSMC senescence via DDR activation.⁴⁴ Activation of DDR such as in SIRT6 deficiency was shown to promote VSMC senescence and atherosclerosis.⁴⁵ Importantly, DDR activation in VSMC led to the progression and destabilization of atherosclerotic plaque.²³ In brief, DNA damage leads to loss of proliferative potential of VSMCs, while senescent VSMC triggers plaque instability directly through shrinkage of VSMC content in fibrous cap (reduced VSMC proliferation and collagen synthesis).⁴⁶ Further evidence also revealed a more proactive role for DNA damage from VSMC in plaque instability by fostering inflammation, secretion of MMPs, and inflammatory cytokines to favour matrix degradation.^45–47

Increased senescence and apoptosis have been shown in endothelial cells in response to DNA damage, in an ATM/Akt/p53/p21-dependent manner.^24,48 DDR activation in the endothelial cell leads to a pro-atherosclerotic, pro-thrombotic, and anti-angiogenic phenotype.⁴⁹ Under DNA damage stress, endothelial cells undergo premature senescence, and secret pro-inflammatory mediators (IL-6, IL-8, and TNF-α), endothelin-1 (ET-1), chemokines, MMPs, and growth factors, contributing to endothelial dysfunction, ultimately atherosclerosis, pulmonary hypertension, and cardiac diseases.⁴⁹

Several studies have reported a role for DDR in CFs.^50–52 Normally, activation of DDR and cellular senescence in CFs would suppress CF proliferation and limit cardiac fibrosis.⁵⁰ CCN1 (cellular communication network factor 1) belongs to SASP capable of inhibiting cardiac fibrosis through induction of CF senescence following MI, indicating a beneficial role from DDR and senescence of fibroblasts.⁵¹ Up-regulation of p53 following MI insult induces senescence of CFs. ATM activation was also noted in CFs in doxorubicin cardiotoxicity. ATM activation turns on Fas ligand in CF to interact with Fas and regulates cardiomyocyte apoptosis.⁵²

3.3 Crosstalk among various cells in the cardiovascular system during DDR and senescence

Recent studies have noted a rather complex interplay among various cardiovascular cells during DDR and senescence, through the paracrine SASP components, leading to unfavourable consequences such as fibroblast activation and fibrosis, prothrombotic phenotype in endothelial cells, and cardiomyocyte hypertrophy and death^33,53 (Figure 3). For example, telomeric DNA damage triggers cardiomyocyte secretion of EDN3, TGF-β, and GDF15, leading to myofibroblast activation and collagen accumulation.³³ Besides, inflammatory cytokines (IL-1, IL-6, and TNF-α) released by senescent cardiomyocytes induce local cardiac inflammation.⁵¹ CFs under DDR activation also communicate through paracrine signalling to regulate cardiomyocyte senescence and hypertrophic growth.⁴⁰ In heart injury, IGF-1 (insulin-like growth factor-1) is produced by CFs, leading to collagen synthesis and cardiomyocyte hypertrophy.⁵⁴ Senescent endothelial cells show decreased nitric oxide production and elevated ET-1 release, leading to crosstalk between surrounding cardiac cell populations.⁴⁰ This interaction contributes to vascular inflammation and impaired vasodilation. Taken together, DNA damage triggers cellular senescence in various cardiac cell types, while their crosstalk via SASP secretome leads to unfavourable consequences, including fibrosis, myofibroblast activation, collagen synthesis, hypertrophy, and inflammation, thereby drives the development of CVDs.

4. Evidence of DNA damage and DDR in cardiovascular pathology

Emerging evidence has depicted a vital role of DNA damage and DDR in the aetiology of CVDs. As demonstrated in Table 1, DNA damage and DDR occur in multiple cardiovascular pathologies, including HF, arrhythmia, ischaemic heart disease (IHD), metabolic cardiomyopathy, atherosclerosis, and hypertension. Besides, genetically engineered mouse models for genes involved in DDR display pathological cardiovascular phenotypes (Table 2), supporting a role for DNA damage and DDR in the pathogenesis of CVDs.

4.1 HF and cardiac remodelling

The involvement of DNA damage in the aetiology of HF has drawn some recent attention. Overt DNA damage (e.g. oxidative DNA damage, SSB, and DSB) or DDR activation is observed in patients with end-stage HF^55–57,89 and pressure overload-induced murine model of HF.^21,29,90 The end-stage cardiomyopathic human hearts presented marked DNA damage and DDR activation, as evidenced by increased 8-oxoG, γH₂AX, ATM phosphorylation, and NBS1.⁷ Besides, these DNA damage markers are found in not only heart tissues but also peripheral blood and urine. In a study including 56 HF patients and 20 healthy controls, elevated levels of 8-hydroxy-2′-deoxyguanosine (8-OHdG) were noted in both serum and myocardium of patients.⁵⁸ In another study, serum 8-OHdG levels were higher in HF patients, in particular advanced New York Heart Association classes.⁵⁵ Furthermore, the incidence of cardiac events was significantly higher in patients with high 8-OHdG levels during the follow-up. In a meta-analysis including six independent studies, 8-OHdG levels are drastically higher in urine and blood samples from HF patients.⁹¹ These findings suggest the presence of extensive oxidative stress and DNA damage in HF, and the extent of DNA damage correlates to the disease severity in human samples.

Mechanistically, current available evidence has revealed that DNA damage in HF is caused by deficiency of both OGG1-mediated BER and SSB repair.^7,29 ATM activation has recently garnered much attention as a critical DDR regulator closely related to myocardial inflammation, cardiac remodelling, and eventually HF development. ATM deletion was shown to suppress the activation of the nuclear factor-κB (NF-κB) pathway, cardiac inflammation, and HF progression.²⁹ In another parallel study, pressure overload led to DNA DSBs (specifically indicated by DNA-PKcs phosphorylation) in cardiomyocytes, triggering subsequent ATM-mediated DDR activation.²¹ Mechanistically, activated ATM phosphorylated and degraded Cain, leading to calcineurin activation. Besides, ATM also phosphorylated 4E-BP1 (eukaryotic translation initiation factor 4E-binding protein 1) to initiate protein synthesis, triggering cardiac hypertrophy. Both calcineurin and 4E-BP1 served as mediators of cardiomyocyte hypertrophy in response to DNA DSBs and ATM activation. Accordingly, genetic or pharmacological inhibition of ATM attenuated pressure overload-induced cardiomyocyte hypertrophy.²¹ These studies suggested that overwhelmed DNA damage triggers ATM activation in failing hearts. ATM-mediated DDR activation may represent a crucial pathway to initiate cardiac inflammation and remodelling, promoting HF development, by phosphorylation of key substrates related to cardiac pathologies.

4.2 Cardiac arrhythmia

A limited number of studies have shown the presence of DNA damage (mostly oxidative DNA damage) in arrhythmias, in particular atrial fibrillation (AF).^{37,59–61,92,93} DNA damage is noted in both tachypaced atrial cardiomyocytes and atrial tissue samples from persistent AF patients.³⁷ Importantly, 8-OHdG, a classical oxidative DNA damage marker, can be detectable in blood and urine samples, depicting their potential as biomarkers for AF.⁵⁹ Besides, 8-OHdG level was greatly reduced following rhythm restoration. In another recent study, serum 8-OHdG levels were gradually elevated in AF progression.⁶⁰ Notably, a significant rise in 8-OHdG levels was noted in patients with AF recurrence, as compared to those without AF recurrence. These clinical findings favour the utility of 8-OHdG as a diagnostic, severity, and recurrent biomarker for AF.

A recent study explored the potential mechanisms linking DDR to the pathogenesis of AF. PARP1 activation might foster cardiomyocyte dysfunction in an experimental AF model. Oxidative DNA damage was precipitated in atrial cardiomyocytes, leading to excess PARP1 activation, nicotinamide adenine dinucleotide (NAD⁺) depletion, and subsequent electrical and contractile impairment.³⁷ NAD⁺ loss was shown to cause a progressive decline in ATP levels, energy stress, and cell death during excessive PARP1 activation. Accordingly, PARP1 depletion or NAD⁺ replenishment was demonstrated to retard AF progression. Targeting PARP1 should represent a novel therapeutic approach to preserve cardiac function in clinical AF.

4.3 IHD

Infarcted hearts exhibit various types of DNA damage including oxidative DNA damage, SSB, and DSB. DDR activation plays an essential role in post-infarction remodelling through induction of cardiomyocyte apoptosis.^9,94–96 Corbucci et al.⁶² first noted DNA damage and ATM activation following acute myocardial ischaemia. In their study, myocardial ischaemia up-regulated p53 and γH₂AX levels as well as ATM activation in human left ventricular samples, indicating the presence of DSBs in ischaemic hearts. In a clinical study involving patients with stable angina and non-ST-segment elevation MI, peripheral blood mononuclear cells exhibited evident differences in DNA ligase activity and DDR genes.⁶³

Current evidence has suggested that BRCA1 and ATM represent the two most important DDR proteins regulating the development of MI. BRCA1 depletion in cardiomyocytes led to compromised HR repair and p53 activation, resulting in ventricular dysfunction, adverse cardiac remodelling, and increased mortality in response to ischaemic stress.⁹ In addition, post-MI ATM activation was shown to regulate cardiac remodelling, inflammation, and systolic function^79,80,97,98 (discussed in Section 7). Taken together, DDR activation is involved in the pathogenesis of IHD.

4.4 Metabolic cardiomyopathy

Ample evidence has noted the accumulation of DNA damage in metabolic disorders, including obesity⁹⁹ and diabetes mellitus.¹⁰⁰ Recently, a close interplay was noted between metabolic abnormalities and cardiovascular dysfunction through DNA damage.^101–103ob/ob and db/db mice demonstrated increased apoptosis in cardiomyocytes, associated with increased DNA damage and premature mortality.¹⁰¹ HF was reported to trigger DNA damage in both myocardial tissues and visceral fat, thereby promoting inflammation of adipose tissues and systemic insulin resistance.¹⁰² HF-related overactivation of the sympathetic nervous system led to oxidative stress and subsequent DNA damage via p53-dependent signalling. Interestingly, p53 deletion inhibited adipose tissue inflammation and improved metabolic and cardiac dysfunction, indicating a vicious circle between adipose tissues and hearts.¹⁰² In another study, high-caloric diet feeding led to up-regulated p53 in endothelial cells, due to DNA damage associated with metabolic stress.¹⁰³ Inhibition of endothelial p53 activation improved insulin resistance and obesity, suggesting a potential role of DNA damage linking diabetes to vascular function. These findings demonstrate the promises of suppressing DDR activation in the interruption of the vicious cycle between metabolic disorders and CVDs.

4.5 Cancer therapy-related cardiotoxicity

The field of cardio-oncology is evolved given the ever-rising prevalence of CVDs in cancer patients. Chemotherapeutic drugs and radiation therapy are tied with cardiotoxicity and risks of HF, coronary artery disease, and arrhythmia.¹⁰⁴ Besides, the recent advance has demonstrated a more complex relationship between cancer and CVDs, leading to a new concept of CVD-induced cancer incidence termed ‘reverse cardio-oncology’.^105,106 A number of mechanisms have been postulated to explain overtly increased cancer risk in CVD patients, including enrolment of inflammatory mediators, hypoxia, and secretion of circulating factors (e.g. extracellular vesicles, cardiokines, and microRNAs) from cardiovascular system.¹⁰⁷ Herein we only focus on the role of DNA damage in chemotherapy-related cardiotoxicity. The precise mechanisms of cardiotoxicity are complex and may involve (but not restrict to) oxidative stress, DNA damage, mitochondrial dysfunction, apoptosis, and other regulated cell deaths.¹⁰⁴ To date, compelling evidence suggests a cardinal role for DDR activation in radiation and chemotherapy-induced cardiomyopathy.^40,42,52,108 For example, heart samples from patients receiving doxorubicin exhibited DNA damage, cell senescence, cardiac progenitor cell (CPC) migration impairment, and increased ROS production in the majority of CPCs.¹⁰⁹

Several animal models have been explored to unveil the mechanisms underlying cardiac DNA damage and DDR in doxorubicin-challenged animals.^{42,52,110,111} Doxorubicin was shown to induce DSBs in cardiomyocytes via topoisomerase 2β, while cardiomyocyte-specific deletion of topoisomerase 2β protected cardiomyocytes from doxorubicin-induced DSBs, defective mitochondrial biogenesis, and ROS accumulation.⁴² Chronic doxorubicin-induced cardiotoxicity is mediated by the oxidative DNA damage-ATM-p53-apoptosis axis in cardiomyocytes.¹¹⁰ Further evidence revealed ATM activation in CFs, associated with elevated Fas ligand and cardiomyocyte apoptosis.⁵² In addition, doxorubicin increased the cardiac level of p53 which binds to the promoter of Ppargc1a (encoding PGC1α to regulate mitochondrial function), contributing to dampened Ppargc1a expression,¹¹² suggesting a role of DDR in regulating mitochondrial dysfunction after doxorubicin therapy.¹¹² These findings depict a crucial role for DDR activation in the complex interplay with oxidative stress and mitochondrial dysfunction, en route to the development of doxorubicin cardiotoxicity.

Given the essential role of DDR activation in doxorubicin cardiotoxicity, inhibition of DDR components may be a novel therapeutic approach for chemotherapy-related cardiotoxicity. At present, only one study showed that systemic administration of ATM inhibitor (KU55933) was able to prevent doxorubicin cardiotoxicity in animal models.⁵² Notably, genomic instability is a promising hallmark of cancer owing to defects in DDR and replication stress.¹³ A number of DDR inhibitors have been proven to be effective in various types of cancers from pre-clinical findings.¹³ Moreover, these drugs exhibited synergy with classical chemotherapy, radiotherapy, and immunotherapy.¹³ Therefore, the translational perspective may reside in that DDR inhibitors offer therapeutic advantage by simultaneously diminishing doxorubicin cardiotoxicity while boosting its anticancer effect. To the best of our knowledge, few studies have examined the role of DDR inhibition in animal models with concurrent cancer and cardiotoxicity.

4.6 Atherosclerosis

Ample evidence has revealed DNA damage and DDR in both plaques and circulating monocytes in atherosclerosis.^23,113 VSMCs and inflammatory cells within plaques exhibit various types of DNA damage, including oxidation of bases, strand breaks, and telomere shortening.^64,114,115 DNA damage and DDR activation increase in proportion to the disease severity. Besides, these cells within atherosclerotic plaques exhibit a series of consequences of DNA damage including premature senescence, apoptosis, and inflammation.^116–118 Human atherosclerotic VSMCs exhibit evident DNA DSBs and DDR activation as evidenced by increased MRN complex.²³ VSMC DNA damage was shown to alter plaque phenotype through inhibiting fibrous cap in advanced lesions. Thus, inhibition of DNA damage in atherosclerotic plaque may represent a novel approach to promote plaque stability.²³

Mechanistically, defective BER due to OGG1 deficiency is considered the major cause for DNA damage in atherosclerosis.^5,31 Overexpression of OGG1 in VSMCs alleviated DNA damage, cellular senescence, apoptosis, and NLRP3 inflammasome activation, thereby leading to reduced atherosclerotic plaque formation.⁵ These findings favour the presence of a vicious cycle among oxidative DNA damage, decreased OGG1 activity, and defective BER in the development of atherosclerosis. Moreover, PARP1 also serves as a critical DDR protein in atherogenesis.⁶⁹ Genetic and pharmacological inhibition of PARP1 was shown to interfere with plaque development and prevent plaque instability, through inhibition of NF-κB and inflammation in plaque dynamics. Collectively, DNA damage and DDR activation are involved in the onset and progression of atherosclerosis.

4.7 Hypertension and pulmonary artery hypertension

Only a handful of studies suggested a role for DNA damage in the aetiology of hypertension. Oxidative DNA damage is prominent in patients with hypertension.⁶⁶ Interestingly, DNA damage and oxidative stress were significantly attenuated following anti-hypertensive therapy. Urine 8-OHdG was elevated in hypertensive patients.⁶⁵ Thus, urine 8-OHdG levels may have promises as a marker for oxidative DNA damage in hypertension.

Although limited evidence favours a link between DNA damage and hypertension, possible roles of DNA damage and DDR activation in the pathogenesis of pulmonary artery hypertension (PAH) and associated right ventricular dysfunction have been unveiled.^{67,68,119,120} Genetic mutations were involved in PAH pathogenesis, as evidenced by a monoclonal origin of pulmonary artery endothelial cells (PAECs) in the majority of plexiform lesions in idiopathic PAH.^121,122 Subsequent studies showed that DNA damage and abnormal DNA repair provoked pulmonary vascular cell proliferation and vascular resistance in PAH progression.^67,119,120 DNA damage in PAECs, VSMCs, and peripheral blood mononuclear cells precedes the clinical manifestation of PAH, as shown by the elevated susceptibility to DNA damage prior to disease onset.⁶⁸ DNA damage may be attributable to ROS, inflammation, and hypoxia stress in PAH, and such damage persists for years even after the removal of the triggering exposure.¹²³

Among DDR machineries, PARP1 is the most extensively studied in PAH, as overactivation of PARP1 was noted in PAH and induced activation of inflammatory response and cell dysfunction. PARP1 inhibition was shown to reverse miR-204-mediated up-regulation of transcription factors nuclear factor of activated T cells (NFAT) and hypoxia-inducible factor 1-α (HIF-1α), contributing to the proliferation of pulmonary VSMCs. Genetic and pharmacological inhibition of PARP1 improved pulmonary vascular remodelling, endothelial function, and right ventricular hypertrophy and remodelling.^67,124

5. Relationship between DNA damage and CVDs in laminopathies

LMNA (lamin A/C) is a nuclear lamina protein that interacts with the genome to regulate gene expression. Mutations in LMNA cause a group of divergent tissue-specific disorders, including DCM, termed as laminopathies.¹²⁵ These disorders can also be caused by defects in the lamin interacting partners including TMEM43, and nesprins.¹²⁶ The linkers of the nucleoskeleton and cytoskeleton (LINC) complex are composed of nesprins 1–4 in the outer nuclear membrane, and SUN1/2 in the inner nuclear membrane. Disruption of these proteins is shown to evoke cardiomyopathies. Previous studies suggested an important role of DDR activation in pre-lamin A (Lamin A precursor protein) accumulation in VSMC senescence and vascular calcification.^44,127 Recent findings indicated a role for nuclear lamina in the DDR. Disruption of the nuclear lamina is closely tied with DCM.³⁹ Mice with cardiac-specific LMNA missense mutation p.Asp300Asn (LMNA^D300N), which is associated with DCM and progeroid syndrome in cardiomyocytes,³⁹ presented DCM phenotype including severe cardiac dysfunction, myocardial fibrosis, apoptosis, and premature death. Further cardiac transcriptome analysis revealed that these phenotypes were related to aberrant activation of the E2F transcription factor-DDR–p53 pathway. Targeted p53 deletion in cardiomyocytes rescued these phenotypes. This study suggested that DDR/p53 pathway is activated to drive the pathogenesis of DCM associated with Lamin A/C mutations.

Similar myopathies were noted in mice deficient in Lamin A/C interacting nuclear envelope protein TMEM43.⁴¹ Activation of DDR, p53, and SASP was observed in cardiomyocytes with TMEM43 haploinsufficiency, in association with increased mortality, apoptosis, and a pro-fibrotic cardiomyopathy phenotype in mice. In addition, nesprin-2, initially identified as a nuclear envelope Lamin A-binding protein, was shown to regulate DDR activation in pre-lamin accumulation and VSMC senescence.¹²⁸ A recent study noted a critical role of the cytoskeleton to maintain nuclear lamina structure in cardiomyocytes.¹²⁹ Acute loss of desmin or its LINC-binding partner nesprin-3, led to abnormal nuclear morphology in cardiomyocytes, accompanied with functional defects in Ca²⁺ cycling and contractility. Desmin depletion led to DNA damage and compromised key lamina-associated chromatin structures. These findings have demonstrated the key regulatory role of lamina-interacting LINC and cytoskeletal components in DNA damage, DDR, and nuclear homeostasis. Taken together, DNA damage and DDR may represent potential therapeutic targets in cardiomyopathies caused by the LMNA and associated gene mutations.

6. Therapeutic approach to combat DNA damage in CVDs

Given that accumulation of DNA damage greatly hampers cellular function and increases susceptibility for CVDs, therapeutic interventions should be targeted towards genomic instability and DNA damage. Alleviation of exogenous DNA damage, such as tobacco smoke and UV exposure, lowers morbidity and mortality of CVDs. Therapies including antioxidants and dietary intervention have been established to combat endogenous DNA damage. Emerging evidence has also unveiled efficacy towards DNA damage for multiple cardiovascular drugs including statins, angiotensin-converting enzyme inhibitors (ACEIs)/angiotensin II receptor blockers (ARBs), and β-blockers (Table 3). These findings further demonstrate the promises of targeting DNA damage in the management of CVDs.

6.1 Natural compounds and antioxidants

Several natural compounds capable of reducing DNA damage have displayed promises in the treatment of CVDs.^138–140 Cardiac benefits from fruits and vegetables have been attributed to polyphenols, classical natural antioxidants.¹⁴¹ Pre-clinical and clinical studies have shown that polyphenols mitigate endogenous DNA damage in various pathological conditions including CVDs,¹³⁸ in association with activation of antioxidant enzymes and scavenging ROS.¹⁴¹ In particular, the beneficial effects of polyphenols such as resveratrol in CVDs have been confirmed in clinical trials.¹⁴²

Excessive ROS-induced DNA damage is established in all types of CVDs, supporting the role of antioxidants in the therapeutics for CVDs. Antioxidants including vitamin C, vitamin E, and combinations are found therapeutically effective in pre-clinical studies of CVDs.^143,144 However, large clinical trials for dietary supplementation with antioxidants were disappointing. Randomized controlled trials (RCTs) have demonstrated the little additive cardiovascular benefit of antioxidants (such as vitamin C and E) in humans.^145,146 The discrepancy between experimental studies and RCTs might suggest the usage of antioxidants is intrinsically flawed. It is possible that RCTs were inadequately designed for methodological reasons. The cardiovascular benefit of antioxidants may depend on baseline antioxidant status, and reliable biomarkers of oxidative stress are still unavailable for large RCTs.

6.2 Statins

Statins exert proven benefits in patients with CVDs, mainly through cholesterol-lowering, anti-inflammatory, antioxidant, and anti-thrombotic properties. Many pharmacological effects of statins are attributed to abrogation of DNA damage in multiple CVDs including dyslipidemia,^130,147 atherosclerosis,^115,131 MI,¹³² and chemotherapy-induced cardiotoxicity.¹¹⁰ Statins can reduce oxidant stress-induced DNA damage, and inhibit DDR downstream signalling. For example, statins lead to phosphorylation of the ubiquitin ligase mdm2, promoting its nuclear localization and interaction with p300 and inhibiting its interaction with p19^ARF, favouring p53 degradation. In addition, statins were shown to improve telomere dysfunction by up-regulating telomere repeat-binding factor TRF2, thus enhancing the migratory capacity of endothelial progenitor cells.¹⁴⁸ In atherosclerosis, atorvastatin therapy reduced VSMC senescence, telomere shortening, and apoptosis, as well as inhibited ATM/ATR-mediated DDR activation.¹¹⁵ Mechanistically, statin treatment markedly accelerated NBS-1-induced DNA repair. Statin-induced accelerated DNA repair was mediated by NBS-1 and the human double minute protein Hdm2. In the presence of Statin, Hdm2 is phosphorylated, triggering dissociation of Hdm2 from NBS-1, thus inhibiting NBS-1 degradation. Moreover, statin therapy up-regulates a subset of DNA repair genes,¹⁴⁹ and inhibits ionizing radiation-induced DDR including activation of p53 and CHK1 in primary human endothelial cells.¹⁵⁰ In a clinical study involving 19 795 participants, statin users display a 4.3–6.0% lower urinary 8-oxoG level which represents oxidative DNA damage.¹⁵¹ Based on these findings, statin therapy for CVDs may be mediated by reduction of DNA damage and facilitation of DNA repair.

6.3 ACEIs/ARBs

Overactivation of the renin-angiotensin system with high levels of angiotensin II (Ang II) causes oxidative stress in CVDs including endothelial dysfunction and atherosclerosis.¹⁵² Previous findings showed that Ang II promotes ROS production and oxidative DNA damage via AT1 receptor in human VSMCs to accelerate vascular senescence.¹⁵³ The ARB losartan was shown to reduce oxidative stress-induced DNA damage and cell senescence through inhibition of telomere attribution-induced replicative senescence, or acute stress-induced premature senescence independent of the telomere.¹⁵³ Preceding studies also revealed that ACEI/ARB exerted cardiovascular protective effects by attenuation of oxidative stress, reduction of DNA damage, and improvement of endothelial function.^133,154 In an experimental MI model, administration of ramipril and valsartan decreased MI severity and attenuated DNA damage by reducing oxidative stress.¹³⁴ Similarly, oxidative stress and DNA damage (DSBs and mutagenic DNA base modification) were present in the hearts and kidneys of Ang II-induced hypertensive mice.¹⁵⁵ Furthermore, oxidative DNA damage was prevented by ARB in hypertensive mice.¹³⁵ These findings favour a role for the attention of oxidative stress and DNA damage in ACEI/ARB-offered cardiovascular benefits.

6.4 β-blockers

β-adrenergic receptor blockade prevents DNA damage, thereby protecting against CVDs.^58,136,137 In an experimental model of doxorubicin cardiomyopathy, early carvedilol therapy was shown to alleviate doxorubicin-induced DNA damage and cardiotoxicity.¹³⁶ Carvedilol therapy has been shown to reduce oxidative DNA damage indicated by 8-OHdG level in DCM patients, together with amelioration of HF.⁵⁸ Similarly, oxidative DNA damage was reduced by carvedilol in hypertensive patients.¹³⁷ These findings suggest that β-blockers may alleviate DNA damage by attenuating oxidative stress, although little is known with regards to the mechanistic insights behind β-blocker-induced response on DNA damage. These studies indicate that β-blockers may be a therapeutic medication to prevent DNA damage in CVDs.

7. DDR inhibition: novel therapeutic targets for CVDs

Given the cardinal role of DDR activation in CVDs, emerging strategies targeting DDR signalling components may be considered. Genetic and pharmacological inhibition of key DDR components has been confirmed beneficial in CVDs (Tables 2 and 4). In this section, we will focus on the inhibition of various DDR proteins, including PARP, ATM, ATR, DNA-PK, CHK1/2, and p53, in the management of CVDs.

7.1 PARP inhibition

PARP family denotes a major enzymatic group to catalyse poly(ADP-ribosyl)ation.²⁸ PARP activation in response to DNA damage mediates the assembly of a poly(ADP-ribose) chain through catalysing transfer of ADP-ribose residues from NAD⁺ onto target substrates. Recent work noted an essential role for PARP in cellular processes including DDR, gene transcription, and cell death.^27,176 In this context, PARP inhibition displays therapeutic promise for a variety of diseases, in particular cancers where potent PARP inhibitors have entered clinical trials and received approval for therapeutics.¹³ Emerging evidence has revealed aberrant activation of PARP in CVDs,^{70,71,77,157–160,162–164,177–179} and validated PARP inhibitors in pre-clinical studies and clinical trials for the treatment of CVDs (Table 5).

PARP enzymes play a critical role in the pathogenesis of CVDs including HF, MI and ischaemia and reperfusion (I/R) injury, atherosclerosis, and PAH. Inhibition of PARP was shown to exert cardioprotective effects in animal models of MI, chronic HF, and cardiopulmonary bypass.^73,94 Subsequent studies in patient specimens and pre-clinical samples demonstrated PARP activation in the heart and circulating leucocytes after MI.^180,181 The third-generation PARP inhibitor INO-1001 was shown to improve cardiac function and reduce infarct size in myocardial I/R.^182–184 Based on these studies, INO-1001 became the first PARP inhibitor to enter clinical trials.¹⁶² This trial displayed that PARP inhibition may inhibit the inflammatory response in MI patients, indicated by plasma C-reactive protein and IL-6 levels.

Ample pharmacological mechanisms have been postulated for the cardioprotective effects of PARP inhibitors.¹⁸⁵ DNA damage-triggered excessive PARP1 activation leads to unfavourable consequences including (i) NF-κB and activator protein 1-mediated inflammatory response; (ii) NAD⁺ and ATP depletion, down-regulation of cardioprotective SIRT1, as well as necrosis; (iii) acetyl-coenzyme A acetyltransferase 1-mediated foam cell death and oxidized LDL accumulation; (iv) decreased endothelial nitric oxide synthase (eNOS) activity; and (v) apoptosis-inducing factor translocation to the nucleus. PARP inhibitors suppress these detrimental consequences to protect against cardiovascular damage.¹⁸⁵

7.2 ATM inhibition

ATM is an apical activator of DDR in the face of DSBs.¹⁸⁶ ATM-mediated phosphorylation plays cardinal roles in response to genomic stress to preserve cellular homeostasis. Recently, ATM activation has garnered much attention as a DDR regulator in CVDs, in particular, HF (see Section 4).^21,22,29,98 Accordingly, ATM depletion or inhibitors preserves cardiac function. Genetic deletion of ATM and pharmacological inhibition using KU60019 exhibited protective effects in cardiac function in response to pressure overload.²¹ In another study, long non-coding RNA Caren was shown to maintain cardiac function under pressure overload through inactivation of ATM-mediated DDR and activation of mitochondrial bioenergetics.²² ATM inhibitor KU60019 partially rescues cardiac function in Caren loss-of-function mice. Taken together, these findings suggest inactivating DDR through genetic or pharmacological loss of ATM kinase function may become a new therapeutic strategy against HF.

Although promising therapeutic effects of ATM inhibition in preserving cardiac function in HF, discrepancies in the role of ATM in MI have been noted. Several reports also demonstrated aberrant activation of ATM kinase in MI.^79,80,97,98 ATM deficiency has shown to attenuate cardiac dysfunction and dilation post-MI with increased fibrosis and apoptosis.⁷⁹ Moreover, ATM promotes cardiac inflammation during myocardial ischaemia.⁸⁰ Post-MI cardiac remodelling was attenuated in ATM heterozygous knockout mice. A recent study also showed that KU60019 attenuated cardiac systolic dysfunction and reduced infarct size in MI.⁹⁸ These studies suggest the promises of ATM inhibition in post-MI remodelling. However, several studies showed that ATM deficiency exacerbated post-MI cardiac dysfunction and remodelling through impaired angiogenesis, and disturbed autophagy.^81–83 These studies have shown that ATM inhibition attenuated cardiac dysfunction, remodelling, and inflammation during the early post-MI period (1–7 days) while exacerbating cardiomyocyte dysfunction, fibrosis, apoptosis, and cardiac hypertrophy during late post-MI (14–28 days).

ATM inhibitors have been developed for the treatment of solid tumours. Besides, combination treatment with chemotherapy and ATM inhibitors are being tested in clinical trials.¹⁸⁷ At present, there is no clinical trial on ATM inhibitors in CVDs. Overall, modulating ATM represents a new therapeutic option in the management of CVDs.

7.3 ATR inhibition

ATR represents another logical therapeutic DDR target for CVDs, given its association with ATM and its central role in regulating DNA damage. To date, only a recent study demonstrated the essential role of ATR in sarcomeric cardiomyopathy.³⁸ In this study, increased DNA damage and selective ATR-p53 activation were found in Mybpc3^−/− cardiomyopathy, secondary to replication stress. Highly selective ATR inhibitor AZD6738 was shown to reduce pathological remodelling in Mybpc3^−/− cardiomyopathy. Besides, depletion of cardiomyocyte p53 mimicked the protective function of AZD6738. These findings suggest that replication stress-induced ATR activation regulates the remodelling of sarcomeric cardiomyopathy.

7.4 DNA-PK inhibition

DNA-PK, a heterotrimeric protein complex with a heterodimer of Ku proteins Ku70/Ku80, and a catalytic subunit DNA-PKcs, is a member of the phosphoinositide-3-kinase-related kinase family involved in NHEJ for DSB repair.^188–190 DNA-PK activation is noted in CVDs, including atherosclerosis,^24,64,166 DCM,¹⁹¹ cardiac hypertrophy,²¹ and myocardial I/R.⁸⁶

Genetic and pharmacological inhibition of DNA-PK demonstrated beneficial effects in atherosclerosis. DNA-PK and neuron-derived orphan receptor 1 activation were found within neointima of human atherosclerotic tissue specimens.¹⁶⁶ The specific DNA-PK inhibitors NU7024 and DMNB were shown to inhibit NOR-1-dependent proliferation of human aortic VSMCs.¹⁶⁶ Furthermore, DNA-PK inhibition attenuates neointimal lesion size following wire injury. Similarly, recent evidence from our laboratory suggested a role for DNA-PK inhibition in myocardial I/R.⁸⁶ DNA-PK is turned on in response to I/R stress to promote myocardial damage. Intriguingly, cardiomyocyte-specific DNA-PK depletion inhibited inflammatory response and apoptosis to preserve cardiac function under I/R injury. Therefore, targeting DNA-PK-mediated DDR may provide therapeutic promise in CVDs.

7.5 CHK1/2 inhibition

CHK1 and CHK2 are functionally overlapped serine/threonine kinases and immediate targets for ATR and ATM, respectively.¹⁹² CHK1 and CHK2 trigger cell cycle arrest and cellular senescence through phosphorylation of p53 and CDC25A, both with a vital role in the pathogenesis of CVDs. Recent studies identified a role for CHK1/2 kinases in CVDs including HF¹⁹³ and PAH.¹⁹⁴ In human HF, cardiomyocyte apoptosis is specifically related to down-regulated telomere repeat-binding factor TRF2, telomere shortening, and CHK2 activation.¹⁹³ In another study, patients with PAH exhibited up-regulated CHK1 expression in pulmonary VSMCs and distal pulmonary arteries.^167,194 CHK1 triggers VSMC proliferation and resistance to apoptosis. The CHK1 inhibitor MK8776, with a proven efficacy in clinical trials in cancer patients, attenuates vascular remodelling, and improves hemodynamic parameters in rodent models of PAH.¹⁹⁴ These findings argue the potential of CHK1 inhibitors in the management of PAH.

7.6 p53 inhibition

DDR-mediated p53 activation leads to cell cycle arrest, cellular senescence, and apoptosis.¹⁹⁵ A number of upstream kinases may mediate p53 phosphorylation and activation including ATM, ATR, DNA-PK, CHK1, and CHK2.¹⁹⁶ Mounting evidence has demonstrated DDR and p53 activation in CVDs, including HF, cardiac remodelling, myocardial I/R injury, diabetic cardiomyopathy, and chemotherapy-induced cardiotoxicity. Besides, p53 activation participates in the pathogenesis of CVDs, including anti-angiogenesis, apoptosis, autophagy, necrosis, metabolic alterations, and senescence. Genetic and pharmacological loss-of-function of p53 exerts cardioprotective effects. Currently, pifithrin, a small molecule inhibitor of p53, is used in animal models of CVDs, while further studies are required to test its clinical efficacy.

8. Future directions and conclusions

Many questions regarding DNA damage and DDR remain to be addressed in CVDs. While extensive attention was given for the involvement of DDR in HF, atherosclerosis or chemotherapy-evoked cardiovascular pathologies,^6,21,69,111 a role for DDR remains elusive in other crucial areas (e.g. arrhythmias and hypertension). In addition, susceptibilities and consequences of DNA damage in various cardiovascular cell types, including cardiomyocytes, CFs, endothelial cells, and immune cells, are poorly understood. A heterogeneity for DNA damage likely exists at the cellular level. Single-cell transcriptomics and spatial transcriptomics should be applied to better appreciate cell complexity in response to DNA damage, and to determine the impact of DDR in proliferative vs. non-proliferative cells.

DDR exerts both beneficial and detrimental effects on certain cardiovascular pathologies. For example, ATM inhibition may attenuate cardiac dysfunction and inflammation in the early post-MI period, while such inhibition exacerbates cardiac dysfunction and remodelling during late post-MI.^82,98 DDR components such as PARP and ATM may participate in DNA repair to maintain genome stability and promote cell survival in response to mild DNA damage.¹² Nonetheless, more studies have revealed rather detrimental roles of these molecules to promote DDR activation and cell death in the aetiology of CVDs.^21,22,29 Further clarification is needed with regards to the role of these proteins in either DNA repair or persistent DDR activation.

Although a number of compounds targeting DDR components have displayed therapeutic potential for CVDs, clinical trials evaluating these DDR inhibitors in CVDs are still lacking. Much of our knowledge on DNA damage is derived from animal studies which limit the translational value for DNA damage and DDR in human CVDs. However, it remains to be tested with regards to the efficacy and safety of DDR inhibitors in humans. Also, the safety and pharmacokinetics of PARP1 inhibitors were assessed in humans up to 2 weeks,¹⁶² lacking information for the long-term safety of PARP1 inhibitors. Thus, adverse consequences associated with the long-term application of DDR inhibitors would take longer observational periods, which cannot be simply evaluated using current models.

In conclusion, DNA damage and DDR have crucial roles in the pathogenesis of CVDs, while many classic cardiovascular drugs can modulate DNA damage. Understanding how DDR of individual cardiovascular cell types contributes to disease phenotypes will help to develop targeted therapies to prevent or delay DNA damage-associated CVDs. Such an approach should have a high impact in patients at risk of long-term DNA damage (e.g. chemotherapy). Overall, DDR-associated protein therapy is being recognized as an important therapeutic strategy for CVDs.

Authors’ contributions

L.W. and J.R.S. drafted the manuscript. All other authors edited the manuscript. All authors have approved the final version.

Acknowledgements

We wish to sincerely apologize to those authors whose important work cannot be included due to space limitations. Some of the icons and elements of diagrams were created with BioRender.com.

Funding

This work was supported in part by the National Key R&D Program of China (2017YFA0506000), the National Natural Science Foundation of China (82130011), and the Program of Shanghai Academic/Technology Research Leader (20XD1420900).

References

Author notes