title: MicroRNA-26a inhibits TGF-β-induced extracellular matrix protein expression in podocytes by targeting CTGF and is downregulated in diabetic nephropathy.
abstract: OBJECTIVE
  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
  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.
authors.affiliation: Department of Nephrology, Kyoto University Graduate School of Medicine, 54 Shogoin Kawahara-cho, Sakyo-ku, Kyoto, 606-8507, Japan.
authors.forename: Kenichi
authors.initials: K
authors.lastname: Koga
authors.forename: Hideki
authors.initials: H
authors.lastname: Yokoi
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Mori
authors.forename: Masato
authors.initials: M
authors.lastname: Kasahara
authors.forename: Takashige
authors.initials: T
authors.lastname: Kuwabara
authors.forename: Hirotaka
authors.initials: H
authors.lastname: Imamaki
authors.forename: Akira
authors.initials: A
authors.lastname: Ishii
authors.forename: Keita P
authors.initials: KP
authors.lastname: Mori
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Kato
authors.forename: Shoko
authors.initials: S
authors.lastname: Ohno
authors.forename: Naohiro
authors.initials: N
authors.lastname: Toda
authors.forename: Moin A
authors.initials: MA
authors.lastname: Saleem
authors.forename: Akira
authors.initials: A
authors.lastname: Sugawara
authors.forename: Kazuwa
authors.initials: K
authors.lastname: Nakao
authors.forename: Motoko
authors.initials: M
authors.lastname: Yanagita
authors.forename: Masashi
authors.initials: M
authors.lastname: Mukoyama
mesh_terms: D020413:3' Untranslated Regions; D000818:Animals; D001483:Base Sequence; D001706:Biopsy; D055513:Connective Tissue Growth Factor / Q000378:metabolism*; D003921:Diabetes Mellitus, Experimental; D003928:Diabetic Nephropathies / Q000378:metabolism*; D018450:Disease Progression; D015536:Down-Regulation; D005109:Extracellular Matrix / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation; D020868:Gene Silencing; D005919:Glomerular Filtration Rate; D006801:Humans; D007678:Kidney Glomerulus / Q000378:metabolism; D008297:Male; D051379:Mice; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism*; D042282:Microdissection; D008875:Middle Aged; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D050199:Podocytes / Q000378:metabolism*; D051785:Smad Proteins / Q000378:metabolism; D013311:Streptozocin; D053773:Transforming Growth Factor beta1 / Q000037:antagonists & inhibitors*; D025521:Tumor Suppressor Proteins / Q000378:metabolism
chemical_list: D020413:3' Untranslated Regions; D055513:Connective Tissue Growth Factor; D035683:MicroRNAs; D009687:Nuclear Proteins; D010749:Phosphoprotein Phosphatases; D051785:Smad Proteins; D013311:Streptozocin; D053773:Transforming Growth Factor beta1; D025521:Tumor Suppressor Proteins; C526317:CCN2 protein, human; C526318:CCN2 protein, mouse; C486483:CTDSPL protein, human; C528163:MIRN26 microRNA, human; C543693:Mirn26 microRNA, mouse; C508960:TGFB1 protein, human; C508961:Tgfb1 protein, mouse; C108580:CTDSP2 protein, human