Sustained Wnt/β-Catenin Signaling Rescues High Glucose Induction of Transforming Growth Factor-β1-Mediated Renal Fibrosis

Introduction: Although diabetic nephropathy is attributable to transforming growth factor-beta 1 (TGF-beta 1) overproduction in glomer-ular mesangial cells, the biological role of Wnt/beta-catenin signaling in controlling high glucose-induced TGF-beta 1 has not yet been elucidated. Methods: This study found that sustained Wnt/beta-catenin signaling was required to protect glomerular mesangial cells from high glucose induction of TGF-beta 1-mediated fibrosis using in vitro and in vivo diabetic models. Results: High glucose down-regulated the Wnt signaling associated with increased TGF-beta 1 and fibronectin messenger RNA expression in glomerular mesangial cells. Restoring Wnt4, Wnt5a and cytosolic beta-catenin levels by transfecting Wnt4, Wnt5a and stable beta-catenin alleviated the stimulatory effect of high glucose on c-Jun mediated TGF-beta 1 fibrosis. Transfection of kinase-active glycogen synthase kinase-3 beta (GSK-3 beta) also abrogated high glucose promotion of nuclear c-Jun levels, TGF-beta 1 and fibronectin messenger RNA expression in mesangial cells. Pharmacological modulation of GSK-3 beta beta and beta beta-catenin signaling by recombinant Wnt5a or GSK-3 beta inhibitor (BIO or LiCl) suppressed high glucose promotion of TGF-beta 1-mediated fibrosis. Exogenous BIO and SB216763 alleviated TGF-beta 1-mediated fibrogenic expression in the kidneys of diabetic rats. Immunohistochemistry showed that GSK-3 beta inhibitor significantly reversed the diabetic attenuation of TGF-beta 1 and c-Jun coinciding with fibronectin immunoreactivity within glomeruli. Immunofluorescence demonstrated that cells within the glomeruli restored b-catenin expression after BIO and SB216763 treatment in cells within diabetic glomeruli colocalized with fragmented nuclei by 49,6-diamidino-2-phenylindole staining. Conclusions: Sustained Wnt signaling reduced c-Jun-dependent TGF-beta 1-mediated fibronectin accumulation in mesangial cells. These findings suggest that modulation of Wnt signaling is a viable alternative strategy to rescue the TGF-beta 1-mediated fibrotic signaling pathway in diabetic renal injury.