Restoration of PGC-1α activity by deletion of Smad3 protects against kidney injury in CRP TG mice with unilateral ureteral obstruction (UUO)

Abstract

Introduction: Sustained elevated plasma levels of C-reactive protein (CRP) is closely associated with increased risk of chronic kidney disease. Studies have shown that kidney injury is exacerbated in CRP transgenic mice (CRP Tg) with UUO and attenuated in Samd3 deficiency mice (Smad3 KO). In this study, we investigated the signalling mechanisms of CRP promoting renal fibrosis and inflammation in UUO by using CRP Tg, Smad3 KO, and CRP Tg/ Smad3 KO mice. Methods: CRP Tg/ Smad3 KO mice and wild type littermates were generated by Smad3 heterozygous X CRP Tg mice. UUO was induced in CRP wild-type (Wt)/Smad3 Wt; CRP Wt/Smad3 KO, CRP Tg/Smad3 Wt, and CRP Tg/Smad3 KO mice.A rat tubular epithelia cell line with stable Smad3 knockdown (NRK52E) was used for in vitro study. Results: Our results show that renal inflammation and fibrosis induced by UUO was greater for CRP Tg than Wt. In contrast in Smad3 KO mice, whether CRP Wt or CRP Tg, exhibited attenuated kidney injury including: 1) obviously reduced histological injury revealed by Masson‘s Trichrome &HEStaining; 2) marked down-regulation of pro-inflammatory cytokines (IL-1ß and TNF-a); 3) reduced renal fibrosis as demonstrated by significantly down-regulation of extracellular matrix deposition, such as a-smooth muscle actin (a-SMA) ,collagen 1 and fibronectin. Exacerbation of UUO-induced kidney injury in CRP Tg was associate with increased TGF-ß/Smad3 signaling and decreased expression of peroxisomal proliferation-coactivator (PGC-1a). On the other hand, protection from UUO-induced kidney injury in Smad3 KO mice was associated with restored expression of PGC-1a. In vitrostudies using Smad3 KO NRK52E TECs showed that CRP activates CD32-Smad3 and inhibits PGC-1a expression, restored activity of PGC-1a by deletion of Smad3 protects against CRP-induced extracellular matrix deposition (collagen I, and fibronectin). Conclusions: In conclusion, deletion of Smad3 can protect against CRP exacerbated kidney injury after UUO, at least partly the results of CD32-Smad3 driven inhibition of the PGC-1a expression. Targeting Smad3-regulating PGC-1a activity may offer a new treatment approach for obstructive nephropathy.