Vitamin C Ameliorates Diabetic Nephropathy Through Protein Kinase B Mediated Suppression Of Transform Growth Factor-? Signaling

Background and Objective:Diabetic nephropathy(DN)is one of chronic microvascular complications in diabetic mellitus(DM)and is a leading cause of end-stage renal disease(ESRD)globally.As the improvement of diabetes treatment,the patient's survival time is prolonged,making the incidence of diabetes complications significantly increased.Up to date,DN pathogenesis is not clear,hemodynamics,metabolic abnormalities and interactions between vasoactive substances lead to glomerulosclerosis and tubulointerstitial fibrosis,which are closely related with DN.Especially,excess mesangial extracelluar matrix is the main reason of DN.Non-specific drugs in the treatment of DN,current guidelines recommend controlling blood glucose,blood pressure,and the application of ACEI or angiotensin II receptor blockers in order to reduce the progression of DN.It is an urgent task for human health to a better understanding of the pathogenesis of DN and new therapeutic prevention of DN.The hyperglycemia and hyperoxidation that characterize diabetes lead to reduced serum vitamin C(VC)in diabetic humans and experimentally diabetic animals.Herein,we compare the effectiveness of VC and vitamin E(VE)supplements in diabetic nephropathy(DN)and explore the underlying mechanism.Method and Results:1.The effect and underlying mechmism of VC deprivation in STZ-induced Gulo-/-mice on DNHumans lack the ability to synthesize VC because of a loss of function in the gene(Gulo)coding for a key synthetic enzyme,L-gulono-?-lactone oxidase.But rat and mice have the functional gene.Using TALEN technology successfully,we have generated Gulo-/-mice,which require VC supplemented in their drinking water(4g/L),is able to support the growth.VC deprivation aggravate the urinary albumin,mesangial expansion and extracellura matrix deposition in STZ-induced Gulo-/-mice.VC deprivation increase streptozotocin-induced ?-SMA and ECM deposition.VC deprivation exacerbates morphologically and functionally glomerular injury.2.The effect and underlying mechanism of VC and VE supplement in STZ-induced ratsVC and VE supplement to determine the role of VC and specificity in STZ-induced rats.VC supplement significantly decrease urinary albumin,whereas VE exhibits no significant effect.To determine the target site of VC is glomeruli or renal tubules by glomerular filtration rate,glomerular reabsorption and urine osmotic pressure experinents.VC supplement reduced creatinine clearance(glomerular filtration rate),while VE exhibits no significant effect.VC and VE supplement have no effect on glomerular reabsorption and urine osmolality.VC supplement decrease ?-SMA expression and induce nephrin expression.VC supplement not only ameliorate renal function,but also glomerulosclerosis,while VE exhibits no significant effect.3.The effect and underlying mechanism of VC and VE supplement in db/db miceVC and VE supplement to determine the role of VC and specificity in db/db mice with type 2 diabetes.VC supplement significantly reduce urinary albumin,while VE supplement exhibits no significant effect.VC supplement decrease ?-SMA expression and extracellular matrix accumulation,while VE exhibits no significant effect.5.To explore the potential mechnisms in the rat mesangial cellsIn rat mesangial cells,VC reduced TGF-?1-induced the mRNA levels of a-SMA,FN and COL4,and robustly decrease phospho-Smad2 expression after added 16-h pretreatment.Specifically,VC but not VE and glutathione activates protein kinase B(Akt)to destabilize Ski and thereby induce the expression of Smad7,resulting in suppression of TGF-?/Smad signaling and extracellular matrix deposition.Further,VC deprivation reduce Smad7 expression and increase Ski expression in glomeruli in STZ-induced Gulo-/-mice.Conclusions:VC deprivation aggravate glomerular injury in STZ-induced Gulo-/-mice.VC but not VE supplement ameliorates glomerular fribrosis in STZ-induced rats.VC but not VE supplement ameliorates glomerular fribrosis in db/db mice.VC via AKT/Ski/Smad7 signaling cascade in negating TGF-? signaling and ameliorating mesangial expansion and extracellular matix deposition.VC prevents the DN possibly through direct rather than anti-oxidation resulted blockage of the inflammation in glomeruli,and compensation for the loss of VC in diabetes should be an effective means for therapeutic intervention of DN...