Contraction of tubulointerstitial fibrosis tissue in diabetic nephropathy,as demonstrated in an in vitro fibrosis model

Tubulointerstitial fibrosis in diabetic nephropathy (DN) was investigated using an in vitro tissue model of remodeling, to determine the pathogenic mechanism of fibrosis that leads to renal atrophy, i.e., renal failure. The remodeling model consisted of a renal fibroblast-populated collagen lattice (FPCL). The overexpression of transforming growth factor (TGF)-β1 in the diabetic kidney gave rise to FPCL contraction. FPCL relaxation was induced by the subsequent addition of cytochalasin D. The FPCL failed to contract when exposed to TGF-β1 plus Y27632, a Rho kinase inhibitor. TGF-β1 induced the phosphorylation of myosin light chains, and Y27632 blocked this activity. TGF-β1-induced FPCL contraction was suppressed by the addition of 2,3-butanedione monoxime, a myosin ATPase inhibitor. As shown in the video, the contraction rate of the projections of the cells in the FPCL was significantly greater in the TGF-β1 group than in the control group. Collectively, these results indicate that TGF-β1-induced FPCL contraction is attributable to actin–myosin interactions in the fibroblasts through the activation of Rho kinase, the phosphorylation of myosin light chains, and the subsequent activation of myosin ATPase. We propose that via these mechanisms, tubulointerstitial fibrosis generates tissue contraction that leads to renal atrophy and renal failure in DN.