Abstract
Abstract Background and Aims Reduced peroxisome proliferator-activated receptor-γ (PPARγ) activity has been observed in chronic kidney disease and fibrosis. We have recently shown that the PPARγ agonist pioglitazone dampens TGF-β induced renal pro-fibrotic transcription factors in vivo. Several studies have shown that renal complement expression is associated with fibrosis, yet the role of galectin-3 (Lgals3) remains controversial. However, the effect of PPARγ agonists on renal complement (C3, C4b) and Lgals3 expression has not been studied. We investigated how pioglitazone treatment affects TGF-β–driven renal inflammatory molecule expression in transgenic mice and in primary tubular epithelial cell (PTEC) culture. Method Ten weeks-old male C57Bl6 control (CTL) and TGF-β transgenic mice (with elevated circulating TGF-β1 level) were divided in two sets. The first set of mice received regular chow (CTL and TGFβ, n=4/group). The second set of mice were treated orally with pioglitazone (20mg/kg/day) for 5 weeks (CTL+Pio and TGFβ+Pio, n=5/group), when the kidneys were analyzed for mRNA and protein expression. PTEC were isolated from 4-weels old CTL mouse kidneys using graded sieving and characterized by immunoblot. Isolated cells were maintained in DMEM/F12 medium supplemented with 2% FBS and insulin/transferrin/selenium, and cells of passage 4-6 were used in triplicate for the experiments. Cells were treated for 24h with 10 ng/ml TGF-β and/or 5 µM pioglitazone, then mRNA expression levels were assessed. Statistical significance was verified using Mann-Whitney test. Results TGFβ kidneys depicted 13-fold and 4-fold overexpression of C3 and C4b mRNA (p<0.05), respectively, accompanied by a 1.7-fold Lgals3 expression (p<0.05). Oral treatment with the PPARγ agonist pioglitazone inhibited the TGF-β1 induced overexpression of C3, C4b, Lgals3, as well as IL-6 and CCL2 (MCP-1) mRNA (p<0.01). This was accompanied by reduced alfa-SMA (Actca2) and fibronectin mRNA expression. Renal Lgals3 showed significant correlation with alfa-SMA expression (p<0.01, see Figure). PTEC treated with TGF-β also depicted increased C3aR, alfa-SMA and collagen-1 mRNA expression by 1.7-fold, 2-fold and 2.1-fold, respectively (p<0.01), that were reduced to control levels by pioglitazone treatment (p<0.05). Conclusion Our data indicate that PPARγ activation exert strong anti-inflammatory effects in the renal tubular epithelial cells, implicating its possible therapeutic benefit by attenuating renal EMT and fibrosis in CKD patients.
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