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Diabetologia. 2015 Sep;58(9):2169-80. doi: 10.1007/s00125-015-3642-4. Epub 2015 Jun 11.

MicroRNA-26a inhibits TGF-β-induced extracellular matrix protein expression in podocytes by targeting CTGF and is downregulated in diabetic nephropathy.

Author information

1
Department of Nephrology, Kyoto University Graduate School of Medicine, 54 Shogoin Kawahara-cho, Sakyo-ku, Kyoto, 606-8507, Japan.

Abstract

AIMS/HYPOTHESIS:

The accumulation of extracellular matrix (ECM) is a characteristic of diabetic nephropathy, and is partially caused by profibrotic proteins TGF-β and connective tissue growth factor (CTGF). We aimed to identify microRNAs (miRNAs) targeting CTGF on podocytes in diabetic nephropathy.

METHODS:

We investigated miRNAs targeting CTGF on podocytes with miRNA array analysis and identified a candidate miRNA, miR-26a. Using overexpression and silencing of miR-26a in cultured podocytes, we examined changes of ECM and its host genes. We further investigated glomerular miR-26a expression in humans and in mouse models of diabetic nephropathy.

RESULTS:

miR-26a, which was downregulated by TGF-β1, was expressed in glomerular cells including podocytes and in tubules by in situ hybridisation. Glomerular miR-26a expression was downregulated by 70% in streptozotocin-induced diabetic mice. Transfection of miR-26a mimics in cultured human podocytes decreased the CTGF protein level by 50%, and directly inhibited CTGF expression in podocytes, as demonstrated by a reporter assay with the 3'-untranslated region of the CTGF gene. This effect was abolished by a mutant plasmid. miR-26a mimics also inhibited TGF-β1-induced collagen expression, SMAD-binding activity and expression of its host genes CTDSP2 and CTDSPL. Knockdown of CTDSP2 and CTDSPL increased collagen expression in TGF-β-stimulated podocytes, suggesting that host genes also regulate TGF-β/SMAD signalling. Finally, we observed a positive correlation between microdissected glomerular miR-26a expression levels and estimated GFR in patients with diabetic nephropathy.

CONCLUSIONS/INTERPRETATION:

The downregulation of miR-26a is involved in the progression of diabetic nephropathy both in humans and in mice through enhanced TGF-β/CTGF signalling.

PMID:
26063197
DOI:
10.1007/s00125-015-3642-4
[Indexed for MEDLINE]

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