Renal Hypertrophy Inhibited By FK506 And Its Mechanism In Early Experimental Diabetic Rats

Background and objective Diabetic nephropathy ( DN ) is the principal cause of end-stage renal failure ,the distinctive pathological changes in the early stage of DN is characterized by glomerular hypertrophy,extracellular matrix ( ECM ) accumulation and glomerular basement membrane thickening and most result in glomerulosclerosis gradually,further induce ESRD. An interaction of glucose metabolic,hemodynamic factors,oxidative stress and inflammatory have been considered a traditional aspect involved in the development of renal lesions in patients with diabetes. Experimental study has shown that the development and maintenance of renal hypertrophy and matrix expansion are controlled by a variety of hormones, cytokines, and peptide growth factors such as transforming growth factor-β1 ( TGF-β1 ) and insulin-like growth factor-I ( IGF-I ) in diabetes. although IGF-I activates wellknown signaling pathways , these signaling mechanisms appear not to be required for hypertrophy or accumulation of ECM proteins . Instead, IGF-I-mediated hypertrophy and ECM synthesis requires activation of the calcium-dependent, serine/threonine phosphatase calcineurin. The purpose of the study was to investigate inhibiting effect of the inhibitor FK506 for calcineurin on renal hypertrophy and its mechanism in early diabetic rats. Methods Diabetes was induced with streptozotocin in Sprague-Dawley rats.The rats were separated into four groups at random: control group (n=10), model group (n=10), model group treated with FK506 ( 0.5 or 1.0 mg/kg ) (n=10). FK506 was orally administered. Control group and model group treated with the same vehicle alone.After 4 weeks, the following determinations were done in samples: plasma glucose ( BG ),liver function,kidney function and plasma lipid were determined according to standard methods. 24 hours urinary albumin excretion rate ( AER ) was determined by Enzyme Immunoassay ( EIA ). Relative kidney weight ( RKW ) and Creatinine clearance rate ( Ccr ) were measured. Kidney pathologic injury was observed by light microscopy. The expression of calcineurin ( CaN ),1αtypeⅣcollagen,α-smooth muscle actin (α-SMA ) and transforming growth factorβ1 ( TGFβ1 ) were determined by Western blot analysis or immunohistochemistry. Results 1. Clinical and metabolic parameters: There was a significant increase in fasting BG and plasma lipid ( P<0.01 ) ,but body weight ( BW ) was significantly decrease ( P<0.01 ) in model group and FK506 group compared with control group .The BG,plasma lipid and liver function of FK506 group were not differnt with model group. Increased RKW was significantly reduced by FK506 treatment with 1.0 mg/ kg ( P<0.05 ) , elevated AER was markedly attenuated by FK506 treatment with 0.5 and 1.0 mg/ kg ( P<0.05, 0.01 ) . Ccr was not changed by FK506 treatment with 0.5 or 1.0 mg/kg. 2. Renal pathologic morphology: Comparaed with control group, indices for tubulointerstitial injury ( TII ) and glomerular volume ( VG ) were significantly increased in model group ( P<0.05, 0.01 ). Elevated glomerular volume was significantly attenuated by FK506 treatment with 0.5 and 1.0 mg/ kg (P<0.05), and increased indices for tubulointerstitial injury were only ameliorated by FK506 treatment with 1.0 mg/ kg (P<0.01).3. CaN protein expression in renal tissue: Western blot analysis noted that the expression of CaN protein was increased 2.4 fold in the kidney in model group, FK506 treatment with 0.5 and 1.0 mg/kg could reduced increased expression of CaN protein by 38.0% and 73.2%. 4. 1αtypeⅣcollagen expression in renal tissue: The expression of 1αtypeⅣcollagen in kidney were significantly increased in model group and reduced by FK506 treatment (P<0.05, 0.01). 5. TGFβ1 andα-SMA expression in renal tissue: TGFβ1 immunostaining was found in grestest aboundance in the glomerular and tubulointerstitial of model group Comparaed with control group(P<0.01),TGFβ1 expression in FK506 treatment with 0.5 and 1.0 mg/ kg were significantly lower than that in model group(P<0.05, 0.01). Western blot analysis noted that the expression ofα-SMA protein was increased 3.5 fold in the kidney in model group, FK506 treatment with 0.5 and 1.0 mg/kg could reduced increased expression ofα-SMA protein by 40.7% and 69.1%. Conclusion: FK506 could inhibit early renal hypertrophy in diabetic rats, which mechanism may be at least partly correlated with downregulation on increased expression of CaN in the kidney in diabetic rats.