INTRODUCTION: Vascular calcification (VC) is a common complication in chronic kidney disease (CKD) and has been shown to be associated with increased cardiovascular events and mortality. However, the mechanisms of CKD VC and how VC contributes to high mortality risk have not been well recognized. This study was to explore the role of Wnt-signaling pathway in CKD VC, and the association between VC and blood pressure variability (BPV) which is a risk factor of cardiovascular events.
METHODS: In this study, adult male Sprague-Dawley rats were divided into adenine-induced CKD group (n=5) and control group (n=5). Low-calcium and high-phosphate diets were introduced to induce vascular calcification. Both daytime (hour-to-hour during the day) and mid-term (day-to-day for 9 days) blood pressure (BP) were collected and analyzed for BPV metrics. At sacrifice, kidney, heart and aorta samples were taken for histological analyses. Calcium deposition in aorta was identified with Alizarin Red stain and graded. Immunohistochemistry stain was performed with antibodies against Wnt3a, Wnt5a, β-catenin, sclerostin, osteopontin and α-SMA.
RESULTS: Compared with control rats, CKD rats suffered from markedly severer VC (Grade 2.6±0.2 vs 0.0±0.0, p=0.0046, Fig A&B). The calcification deposition sites were mostly at the medial layer. VC was positively correlated with vascular Wnt3a and β-catenin expression (p= p=0.0090 and 0.0000), but not significantly associated with Wnta5a or sclerostin. There was no significant difference in BP between two groups at baseline. During follow-up, CKD group gained significantly higher systolic BP (SBP) and diastolic BP (DBP) than the control group (168±24 vs. 102±15, p=0.0000; 90±34 vs. 68±19, p=0.0008). CKD group showed more violent BP fluctuation than control (Fig C&D). Daytime SBP and DBP standard deviation (SD) in CKD group were significantly higher than that in control group (21±5 vs. 12±5, p=0.0000; 27±9 vs. 16±5, p=0.0000), as well as mid-term SBP and DBP SD (22±5 vs. 12±5, p=0.0000; 22±10 vs. 15±4, p=0.0004). Aorta calcification grade was positively correlated with both daytime (r=0.6963, p=0.0251) and mid-term SBP variability (r=0.6829, p=0.0295).
Fig legend. A. No vascular calcification in control group (Alizarin Red stain×100). B Vascular calcification in CKD group (Alizarin Red stain×100). C. Mid-term blood pressure variability. D. Daytime blood pressure variability.
CONCLUSIONS: In this study, we confirmed that CKD rats had enhanced Wnt-signaling in vascular tissue and severer aorta calcification together with increased BPV. Wnt pathway may be a potential target in future VC and BPV management in CKD.
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