Aim: Determine the effect on fibrotic gene expression in Diabetic Nephropathy (DN) of miR-21 mediated SMAD7 and PTEN in proximal tubule epithelial cells (PTCs).
Introduction: TGFβ1 is known as a major contributor to DN and drives a number of fibrotic changes observed in both glomerular and tubular structures. These changes are mediated through regulation of a number of pathways including various coding and non-coding genes. Of these non-coding genes, miR-21 directly plays a role in fibrosis and also EMT-related events. Here we show that miR-21 mediated repression of SMAD7 and PTEN results in coordinated regulation of a number of genes in experimental and human diabetic nephropathy.
Methods: PTCs were grown in high glucose conditions with or without 10ng/µl TGFβ. miR-21 was over-expressed and knocked-down using miRNA mimics and locked-nucleic-acids (LNAs) respectively. The effect of miR-21-mediated SMAD7 and PTEN repression were investigated with SMAD3 siRNA and the PI3K inhibitor, LY294002, respectively.
Results: Fibrotic mRNA and miRNA, including miR-21, were pathogenically altered in PTCs following TGFβ treatment. Over-expression of miR-21 augmented TGFβ-induced gene expression changes whereas the effects of TGFβ were reduced in the absence of miR-21. Altering expression or activity levels of SMAD3 and/or PI3K revealed cooperative regulation of a number of genes and miRNA by these signalling pathways. Furthermore, miR-21 appears to play a central role in coordinating the flux through these fibrotic mediators.
Conclusion: These data provide further insight into the role of miR-21 in DN and how it mediates the pathogenic gene expression changes associated with its dysregulation. Undoubtedly, these findings add support to the notion of targeting miR-21 in a clinical setting with the aim of attenuating the progression of diabetic nephropathy.