Expression Of Endoplasmic Reticulum Stress And Significance In The Diabetic Renal Tissue Podocyte Injury

BACKGROUD;Diabetic Nephropathy (DN) is one of the most common microvessel complication of diabetes, the primary clinical presentation of intermediate and advanced DN includes massive proteinuria and diffuse glomerular sclerosis. DN is one of the most important cause of end stage renal disease (ESRD).It’s reported that accompanied with the progression of DN, the number of podocyte decreased, and the extent of decreasing is positive related to proteinuria. The less podocyte left, the faster patients develops ESRD. Podocyte is highly differentiated, without regeneration capacity. Therefore, the impairment of glomerular filtration barrier caused by the decreasing of podocyte is unrepairable. Synaptopodin is the specific synaptic connexin of podocyte, which mainly expressed in the surface of cell membrane. Wilms-tumor protein1(WT-1) is the specific nuclear protein of podocyte. According to the observation of these two protein, we can investigate the impairment condition of podocyte. Endoplasmic reticulum stress (ERS) is one of the adaptive responsiveness of cell. When outside stimulation exists, endoplasmic reticulum tends to up-regulate the degradation and transportation of protein to enhance the resistant ability of harmful stimulation. GRP78is a kind of molecular chaperone of ERS. To some extent, the expression of GRP78reflected the intensity of endoplasmic reticulum regulate stress. It has been reported that ERS related to renal tissue impairment, however, it still lack of further study of the relationship between ERS and podoctye of DN renal tissue.Our associate professor Jian-ling Tao [22] observed the relationship between ERS and the impairment of renal podocyte in early stage DN animal model. However, there is little in vivo study about the relationship between ERS and podocyte impairment in intermediate and advanced DN and prediabetic state. Here, we performed clinical and animal experiment to study the intermediate and advanced DN and prediabetic state respectively, trying to find out the expression and significance of ERS in podocyte impairment of DN.Objectives:1. To investigate whether ERS is persisted along podocyte damage in advanced stage of DN.2. To investigate the activation of ER stress in the early stage of Pre-diabetes.Methods:1.Forty-eight patients diagnosed as DN by renal biopsy were reviewed. All patients were divided into two groups according to proteinuria (>3.5g/d n=31and<3.5g/d n=17).The density of podocytes in DN patients was illustrated by Immunohistochemistry staining of WT1and Immunmoflourescence double-staining of synaptopodin and GRP78in podocytes were also detected.2. Thirty-six male wista rats were randomly divided into two groups, the control groups(n=18)were fed with normal diet, the high fat group (n=18)were fed with high fat diet, the quantitative of urine protein in24h, the serum cholesterol and triglycerides levels were tested, the pathological changes of renal tissue were observed under optic microscope, the expression of WT-1in renal tissue were examined by immunohistochemistry, the expression of GRP78and synaptopodin were examined by Western blotting.Results:1. The mean age of patients was45.4+11.2years, with male to female ratio of1:1.22patients (46%) presented with diffusive glomerulosclerosis,26patients (54%) presented with nodular glomerulosclerosis. There is a statistically significant difference in podocyte density between two groups (P=0.003), and it was negatively correlated with proteinuria (P=0.005). The expressions of synaptopodin and GRP78in podocytes were also negatively correlated with proteinuria (P=0.004and P=0.001).2. All rats were randomly divided into normal control group and test group.(1) the levels of insulin were not significantly changed the first six weeks (P>0.05), the levels of insulin were significantly increased in rats at the end of6,9weeks (P<0.05).(2) Compared with contral group, the levels of BUN, TC and TG were not significantly increased in test group at the end of3、6and9weeks.(3) Compared with control group, renal protein expressions of WT-1were not significantly decreased in test group at the end of3、6and9weeks. renal protein expressions of GRP78were significantly increased in test rats at the end of6,9weeks (P<0.05).Conclusion:1. The podocyte injury was aggravated with increased proteinuria in DN patients and the adaptive ability of endoplasmic reticulum to stress was decreased.2. Endoplasmic reticulum stress in pre-diabetic renal tissue has been activated, but renal protein expressions of WT-1and synaptopodin were significantly decreased in rats at the end of3,6and9weeks.