FP331
ALPHA-SYNUCLEIN MAINTAINS THE EPITHELIAL PHENOTYPE AND PROTECTS FROM RENAL FIBROSIS Free

INTRODUCTION: Renal fibrosis is a complex disorder characterized by an extreme build-up and deposition of extracellular matrix components, subsequently leading to a loss of functional renal parenchyma. However, its pathogenesis and progression are still incompletely understood. Alpha (α)-synuclein (SNCA) is an actin-binding protein that has protective effects against various cellular injuries in the brain, but whether it has a protective role in the kidney is unknown. The aim of this study was to investigate the functional significance of endogenous levels of SNCA in renal proximal tubular epithelial cells (RPTECs) and its role in the pathogenesis of renal tubulointerstitial fibrosis.

METHODS: The expression of SNCA in the kidney was investigated in C57BL/6J mice subjected to unilateral ureteral obstruction (UUO) and in patients with chronic kidney disease. The physiological relevance of SNCA was assessed in C57BL/6J mice with the conditional deletion of SNCA in RPTECs (PEPCK-Cre+ SNCA fl/fl), as well as in the renal proximal tubular cells (HK-2) upon SNCA silencing or overexpression. The extent of kidney fibrosis in vivo was assessed after Sirius red staining. Expression of SNCA, markers of epithelial-mesenchymal transition, fibrosis and signaling molecules in vitro and in vivo was analyzed by qPCR, western blot and immunohistochemistry.

RESULTS: SNCA expression was significantly decreased in renal tubules of murine and human fibrotic kidneys. In vitro, TGF-β1 markedly downregulated SNCA expression in HK-2 in a dose- and time-dependent manner, which was attenuated with a MAPK-p38 kinase inhibitor. shRNA-mediated knockdown of SNCA in proximal tubular cells resulted in de novo expression of vimentin and α-SMA. Conversely, SNCA overexpression repressed TGF-β1-induced mesenchymal markers. PEPCK-Cre+ SNCA fl/fl mice subjected to UUO showed an exacerbated renal tubulointerstitial fibrosis, alongside an enhanced profibrotic gene expression, increased interstitial matrix deposition and myofibroblast activation, compared to PEPCK-Cre+ SNCA wt/wt control littermates. These effects were associated with an increased activation of MAPK-p38 and Akt pathways in vivo.

CONCLUSIONS: Our findings provide a novel evidence for an important role of endogenous SNCA levels in the maintenance of the epithelial phenotype of RPTECs and in protecting kidney against fibrotic injury. The results highlight the significance of preserving the basal SNCA levels in the kidney as a new therapeutic strategy to attenuate the progression of kidney fibrosis.