| Diabetic nephropathy (DN) is one of the major chronic complications of diabetes. The early signs of DN are renal hypertrophy, hyperperfusion, high transmembrane pressure, and thickened glomerular and tubular basement membranes. Following the progress of the disease, renal interstitial fibrosis, which was resulted by over intracellular matrix accumulation, and glomerular sclerosis occurs. The end stage of DN is renal failure, one of the major causes of death in diabetic patients.The mechanism of DN has not been completely clear. Multiple factors are considered contribute to the development of DN, such as abnormal glucose metabolism, change in renal hemodynamics, cytokines and so on. Among those reasons, hyperglycemia is considered the most important trigger of DN.Available evidences indicate that over activation of RAS system plays important role in the development of DN. Suppress RAS elevation has been the major clinical strategy in treatment of DN. Also there is evidence suggest over production of ROS, which was induced by hyperglycemia, was also related to DN. Elevated ROS upregulates TGF-β1, leads to cell proliferation and ECM overexpression are all contributed to the renal injury.Recent reports suggest hydrogen sulfide (H2S) exhibits different physiological functions in the body. H2S was even considered as the third gasotransmitter after nitric oxide (NO) and carbon monoxide (CO). Most tissues produce significant amount of H2S, while the brain, cardiovascular system, liver and kidney are believe having the highest H2S generation rate.The formation of endogenous H2S was mainly from catalyzing pyridoxal 5'-phosphate(vitamin B6) -dependent by cystathionine-β-synthase(CBS), cystathionine-γ-lyase (CSE) or cysteine transferase. The three enzymes have different distributions in the body. In kidney, it was reported that both CSE and CBS are expressed. But little was known about the physiological role of H2S in kidney.In the present study, we aimed to observe the effect of high glucose on H2S synthesis, the role of H2S in DN and its relative pathway.Sprague Dawley rats were used in the experiment. Streptozotocin (STZ, 65mg/kg bw) was given intraperitoneally to induce diabetic syndrome. The distributions of CSE and CBS in kidney were identified by RT-PCR and Western blot. The result showed that the rat kidney expresses both CSE and CSE, which was consistent with previous study. In STZ-induced diabetic rat, CSE, but not CBS expression was significantly decreased, which indicated that the synthesis of H2S was decreased in STZ-induced diabetic rats. Meanwhile, in STZ-induced diabetic rats, increased TGF-β1 and angiotensinogen, decreased angiotensin AT1 receptor expressions were observed. Supplementary of H2S by intraperitoneal injection of HaHS reversed the changes in TGF-β1, angiotensinogen and angiotensin AT1 receptor expressions.Mesangial cell (MC) is an inherent vascular peripheral cell in kidney. Abnormality in MC functions, including over proliferation and excessive synthesis and secretion of ECM, contribute to DN. So in the experiment, we also observed the effect of H2S on regulating the function of mesangial cells.The results showed that there is CSE expression in cultured rat renal mesangial cells. High glucose stimulation inhibited the expression of CSE, further lead to the increasing in angiotensinⅡsecretion, intracellular ROS level and TGF-β1 expression. All of those changes were related to upregulating the cell proliferation, collagenⅣsynthesis and secretion. Exogenous H2S donor NaHS inhibited the increased expression of AGT, angiotensinⅡ, angiotensin AT1 receptor, TGF-β1 and CollagenⅣ, as well as the production of ROS and cell proliferation. Treatment of the cell with PAG, a CSE inhibitor to block the endogenous H2S production, induced similar effects of high glucose stimulation, including the over expression of AGT, angiotensinⅡ, angiotensin AT1 receptor, TGF-β1 and collagenⅣ, also over production of intracellular ROS and cell proliferation. In addition, pretreatment of the cell by angiotensin AT1 receptor, blocker Losartan or NADPH oxidase inhibitor DPI blocked the production of ROS, and increase in TGF-β1 expression, collagenⅣsynthesis and cell proliferation.All our results indicated that the endogenous H2S participated in DN. Hyperglycemia suppressed the expression of CSE, decreased the endogenous synthesis of H2S. Decrease in H2S may result in activation of RAS, then stimulates intracellular ROS generation, further results in mesangial cell over proliferation and extracellular matrix secretion. So restore H2S level under diabetic condition might be a new target in management of diabetic nephropathy. |
PDF Full Text Request