Gremlin Regulates Podocyte Apoptosis via Transforming Growth Factor-beta (TGF-beta) Pathway in Diabetic Nephropathy

Background: Gremlin has been reported to be up-regulated in glomerular mesangial cells in diabetic nephropathy (DN). However, the regulation of gremlin in podocytes is still rarely reported. This study aimed to investigate the underlying mechanisms by which gremlin mediates the pathogenesis of DN via transforming growth factor-beta (TGF-beta) signaling pathways. Material/Methods: Lentiviral and RNAi transfection were performed to increase and decrease gremlin expression in high-glucose conditions. Expression at the mRNA and protein level was detected by RT-qPCR and Western blotting. Results: The expression of gremlin was significantly higher in high-glucose (HG, 30 mM) than normal-glucose (NG, 5.5 mM) conditions. The gremlin overexpression significantly suppressed the expression of nephrin and synaptopodin. The phosphorylation of canonical TGF-b signaling pathway components, including Smad2/3 and MKK, was increased in the gremlin-overexpressing group. In addition, the expression levels of Bax and cleaved caspase-3 were also higher in the gremlin-overexpressing group. TGF-b pathway inhibitor (SB505124) significantly inhibited TGF-b pathway activity and enhanced the expression of nephrin and synaptopodin. Conclusions: These results indicate that gremlin can aggravate podocyte lesions through the TGF-b signaling pathway, providing a novel therapeutic target for DN.