Smad3-Mediated Upregulation of miR-21 Promotes Renal Fibrosis

Abstract

TGF-␤/Smad signaling plays a role in fibrogenesis, but therapies targeting TGF-␤ are ineffective in treating renal fibrosis. Here, we explored the therapeutic potential of targeting TGF-␤-induced microRNA in the progression of renal fibrosis. Microarray analysis and real-time PCR revealed upregulation of miR-21 in tubular epithelial cells (TECs) in response to TGF-␤. Lack of Smad3, but not lack of Smad2, prevented cells from upregulating miR-21 in response to TGF-␤. In addition, Smad3-deficient mice were protected from upregulation of miR-21 and fibrosis in the unilateral ureteral obstruction model. In contrast, conditional knockout of Smad2 enhanced miR-21 expression and renal fibrosis. Furthermore, ultrasound-microbubble-mediated gene transfer of a miR-21-knockdown plasmid halted the progression of renal fibrosis in established obstructive nephropathy. In conclusion, these data demonstrate that Smad3, but not Smad2, signaling increases expression of miR-21, which promotes renal fibrosis. Inhibition of miR-21 may be a therapeutic approach to suppress renal fibrosis.

microRNAs in Diabetic Kidney Disease

“…Smad3 physically interacts with Drosha to promote the processing of pri-miR-21 into mature miR-21. Our laboratory also demonstrates that TGF-/Smad3 signaling mediates the transcription of miR-21, miR-192, miR-433, and the miR-29 family during renal diseases [55,62,74,98,99]. TGF-inhibits miR-29 expression but stimulates miR-21 and miR-192 expression via the Smad3-dependent mechanism as demonstrated in MCs and TECs knocking down Smad2 or Smad3, or overexpressing Smad7, and in Smad2 or Smad3 KO mouse embryonic fibroblasts (MEF) [54,55,62,74].…”

“…Our laboratory also demonstrates that TGF-/Smad3 signaling mediates the transcription of miR-21, miR-192, miR-433, and the miR-29 family during renal diseases [55,62,74,98,99]. TGF-inhibits miR-29 expression but stimulates miR-21 and miR-192 expression via the Smad3-dependent mechanism as demonstrated in MCs and TECs knocking down Smad2 or Smad3, or overexpressing Smad7, and in Smad2 or Smad3 KO mouse embryonic fibroblasts (MEF) [54,55,62,74]. In addition, Smad3 physically interacts with Smad binding site (SBE) located in its promoters to regulate the expression of these microRNAs [55,62,74,98].…”

“…The ability to regulate TGF-/Smad3-mediated microRNAs via maintaining renal miR-29b but suppressing miR-192 and miR-21 is found to be one of the mechanism of how Smad7, an inhibitory Smad, protects kidneys from fibrosis [54,55,100]. This notion is also supported by the results from different mouse models of kidney diseases induced in mice lacking Smad3 or Smad7 or having conditional knockout (KO) for Smad2 or overexpressing renal Smad7 [54,55,62,74,98].…”

“…Recently miR-21 expression has been found to be increased in kidney biopsies from diabetic patients compared to healthy controls [66]. In addition, the pro-fibrotic property of miR-21 is further confirmed by functional analyses as miR-21 positively regulates expression of ECM and -SMA in TECs and MCs after treatment of TGF-1 or under diabetic condition [54,[62][63][64][65]. Overexpression of miR-21 in kidney cells also promotes but knockdown of miR-21 reduces renal inflammation under diabetic condition [63].…”

“…TGF-inhibits miR-29 expression but stimulates miR-21 and miR-192 expression via the Smad3-dependent mechanism as demonstrated in MCs and TECs knocking down Smad2 or Smad3, or overexpressing Smad7, and in Smad2 or Smad3 KO mouse embryonic fibroblasts (MEF) [54,55,62,74]. In addition, Smad3 physically interacts with Smad binding site (SBE) located in its promoters to regulate the expression of these microRNAs [55,62,74,98]. The ability to regulate TGF-/Smad3-mediated microRNAs via maintaining renal miR-29b but suppressing miR-192 and miR-21 is found to be one of the mechanism of how Smad7, an inhibitory Smad, protects kidneys from fibrosis [54,55,100].…”