#2892 CRITICAL ROLE OF SERUM RESPONSE FACTOR IN PODOCYTE EPITHELIAL–MESENCHYMAL TRANSITION OF DIABETIC NEPHROPATHY

Abstract

Abstract Background and Aims To investigate the expression and function of serum response factor (SRF) in podocyte epithelial–mesenchymal transition (EMT) of diabetic nephropathy (DN). Method Expression of SRF, pSRF, synaptopodin, P-cadherin, ZO-1, α-SMA, FSP-1, fibronectin and collagen-1 were examined in podocytes or renal cortex following high glucose. SRF was upregulated by SRF plasmids and downregulated by CCG-1423 to investigate how SRF influence podocyte EMT in DN. Streptozocin was used to generate DM in rats. Results ① High glucose induced EMT and SRF upregulation in podocytes (Figure 1). High glucose suppressed synaptopodin and ZO-1 expression, and induced SRF, pSRF collagen-1, FSP-1 and α-SMA expression. SRF transferred from cytoplasm to nuclei obviously and the level of SRF was also increased in podocytes after high glucose treatment. ② SRF overexpression mediated EMT, migration and barrier dysfunction of podocytes (Figure 2). Overexpression of exogenous SRF reduced epithelial synaptopodin expression, and increased collagen-1, FSP-1, α-SMA and Snail expression in podocytes. Transwell chamber migration assay showed that overexpression of SRF significantly upregulated the migration of podocytes across the pores of transwell filters. Albumin filtration assay showed that albumin easily diffused across the monolayer of podocytes transfected with SRF cDNA. ③ Inhibition of SRF preserved phenotypes of podocytes in vitro (Figure 3). CCG-1423 selectively suppressed the expression of pSRF and SRF in podocytes after high glucose stimulation. Besides, simultaneous treatment of podocytes with CCG-1423 also significantly abolished the reduction of synaptopodin expression and the induction of collagen-1, FSP-1, α-SMA and Snail expression. CCG-1423 also reduced the transfer of SRF from cytoplasm to nucleus in podocytes treated with high glucose. ④ The effect of CCG-1423 in diabetic rats (Figure 4–-5). CCG-1423 significantly abrogated the reduction of synaptopodin expression and the induction of SRF, collagen-1, α-SMA and FSP-1 expression in renal cortex tissues. Masson and PAS staining demonstrated that renal glomerular fibrosis was present in DM group, and after 8 weeks treatment with CCG-1423, renal glomerular fibrosis was dramatically ameliorated. In addition, CCG-1423 significantly preserved P-cadherin expression and suppressed α-SMA and FN expression in DN rats. More importantly, CCG-1423 dramatically decreased 24-h urine protein excretion by about 50%, and increased serum albumin, compared with DM group. Conclusion Together, increased SRF activity provokes podocytes EMT and dysfunction in DN. Targeting SRF by small molecule inhibitor may be an attractive therapeutic strategy for DN.