The Attenuation Of Renal Fibrosis By Nicotinamide Through Activation Of Sirtuins

Background:Chronic kidney disease(CKD)has become the sixth leading cause of death in the world.Progressive tubulointerstitial fibrosis(TIF)is the final common pathway that leading to end stage renal disease(ESRD).At present,treating ESRD still mainly depends on dialysis and renal replacement therapy,which bring the huge economic burden to patients.There is an urgent need to deeply understand the pathogenesis of CKD and develop effective approaches slowing down the progress of TIF.It has been elaborated that the content of NAD+in renal tubular epithelial cells is decreased,and energy source of renal cells mainly depends on the glycolysis during the process of acute kidney injury(AKI)and CKD.Previous studies showed that systemic supplementation of nicotinamide(NAM)could increase renal NAD+,and could reverse acute renal injury induced by ischemic reperfusion.However,the role and mechanism of NAM in TIF has been unclear.Methods:In vivo,we injected NAM(0.25mg/g)3 days before mice unilateral ureter obstruction(UUO)till day 7 post-operation.In vitro,mouse primary proximal tubular epithelial cells(PTCs),rat renal fibroblast cells(NRK-49F)and human renal proximal tubular epithelial cells(HK-2)were pretreated with different concentration of NAM 1 hour before incubation with TGF-β1(10ng/ml)or aristolochic acid(AA)for 24 or 48 hours.Results:We demonstrated that NAM supplementation prevented UUO-induced TIF,which was shown by Masson trichrome and Sirius staining of collagen fibrils or deposition.NAM also decreased the expression of pro-inflammatory cytokines(IL-6 and TNF-α),attenuated interstitial inflammation.In vivo and in vitro experiments showed that,NAM inhibited G2/M arrest of proximal tubular epithelial cells by downregulating the expression of CG1,a target gene of p53.In addition,NAM inhibited TGF-β1 induced fibroblast proliferation and activation,shown as downregulated expression of collagen I,Fibronectin(FN),PCNA,cyclin D1,IL-6 and TNF-α.Mechanistically,NAM decreased the acetylation of Smad3 and p53 via boosting the activity of sirtuins.Conclusions:Taken together,these data indicate that NAM supplementation could inhibit TIF at least partially by activating sirtuins.Our study provides experimental evidence for NAM applicated in the treatment of renal fibrosis.