Inhibitor of MyoD family A increased fibronectin production by mesangial cells

Abstract

Overproduction of extracellular matrix proteins, including fibronectin by glomerular mesangial cells (MCs) contributes to the development of diabetic nephropathy. Inhibitor of myogenic differentiation family isoform a (I‐mfa) is a multifunctional cytosolic protein, functioning as a transcription modulator or plasma membrane channel protein regulator. However, its renal effects are unknown. The aim of the present study was to determine if I‐mfa regulated fibronectin production by MCs and the mechanisms involved. In cultured human MCs, I‐mfa expression levels were upregulated and downregulated by transiently transfecting I‐mfa expression plasmids and siRNA against I‐mfa, respectively. Western blot analysis was conducted to determine the abundance of fibronectin protein in human MCs with different treatments and in kidney tissues from rats with and without diabetic nephropathy. RT‐PCR analysis was performed to assess mRNA levels of I‐mfa and fibronectin in human MCs with various treatments and in glomeruli from mice with and without diabetic nephropathy, respectively. We found that overexpression of I‐mfa significantly increased fibronectin protein abundance in human MCs. Silencing I‐mfa significantly reduced the expression level of fibronectin mRNA and blunted TGF‐β1‐stimulated production of fibronectin protein. We further found that high glucose, a central pathogenic stimulus in diabetes increased I‐mfa protein content in a time (≥ 48 h) and concentration (≥ 25 mM) dependent manner. Although high glucose exposure increased fibronectin at the protein level, it did not significantly elevate transcript levels of fibronectin in MCs. In agreement with the data from cultured cells, the abundance of I‐mfa protein was significantly greater in the renal cortex of rats with diabetic nephropathy compared to non‐diabetic rats. However, there was no significant difference in the level of glomerular I‐mfa mRNA between the mice with and without diabetic nephropathy. Moreover, hydrogen peroxide significantly increased I‐mfa protein abundance in a dose‐dependent manner (≥ 100 μM) in cultured human MCs. Antioxidants polyethylene glycol‐catalase, ammonium pyrrolidithiocarbamate and N‐acetyl cysteine significantly blunted high glucose‐induced increase of I‐mfa protein abundance. Taken together, our study suggests that an increased level of I‐mfa induced by high glucose/diabetes through the production of reactive oxygen species stimulates fibronectin production by MCs.Support or Funding InformationNIH/NIDDK (1RO1 DK115424); AHA Southwest Affiliate (16GRNT27780043); Harry S. Moss Heart Trust Award