High glucose-mediated tubular injury contributes to the development and progression of diabetic nephropathy through renal tubulointerstitial fibrosis. V-set immunoglobulin-domain-containing 4 (VSIG4), a B7 family-related protein, is a complement receptor. Although the role of epithelial-mesenchymal transition (EMT) has been reported in several diseases, little is known about its relationship with VSIG4 under diabetic conditions. This study aimed to investigate the role of VSIG4 in human tubule cells stimulated by high glucose (HG, 55 mM). HG upregulated both mRNA and protein levels of VSIG4 in proximal tubule cells (HK-2 cells) and Madin Darby Canine Kidney cells. These upregulations were accompanied by increased expression of mesenchymal markers such as fibronectin, N-cadherin, matrix metalloproteinase 9, and vimentin, and by decreased expression of the epithelial marker, E-cadherin. The siRNA-mediated inhibition of VSIG4 in HK-2 cells restored the dysregulation of EMT in cells. Interestingly, VSIG4 inhibition did not affect the expression of transforming growth factor (TGF)-β, whereas inhibition of TGF-β reduced VSIG4 expression, subsequently suppressing fibrosis markers. These findings suggest that VSIG4 plays an important role in mediating renal tubular EMT through the downstream action of HG-induced TGF-β activation.
Keywords: V-set immunoglobulin-domain containing 4 protein; diabetic nephropathies; fibrosis; kidney; transforming growth factor beta.