The Effect And Mechanism Of Sp1 On High Glucose Induced Glomerular Podocyte Apoptosis

Background:Diabetic nephropathy(DN)is a common and important complication of diabetes patients,the incidence of disease is increasing in our country.With the progress of the disease it can become end-stage renal disease(ESRD).As a result,the researchers tried to investigate the mechanism of glomerular damage in DN and want to find new treatment strategies.Podocytes are highly branched,terminally differentiated visceral epithelial cells of the renal glomerulus that cover the urinary side of the Glomerular basement membrane(GBM)and play a crucial role in the regulation of glomerular function.At present,it is believed that podocytes play an important role in the Pathogenesis of DN.It was shown that high glucose induces podocyte apoptosis and contributes to reduced podocyte number both in vivo and in vitro.But the mechanism remains unclear.It is necessary for the mechanism of podocyte apoptosis of DN-induced in further research,and provide a theoretical basis for clinical prevention and treatment of DN.Transcription factor specificity protein 1(Sp1)is a member of the SP/KLF family of transcription factors and is thought to function as a metastasis promoter.Previous data indicate that Spl is over-expressed in various human cancers including thyroid,pancreatic,hepatocellular,colorectal and gastric cancers,and this could be a critical factor for tumour development or maintenance.Recently,increasing evidences have accumulated to suggest that Spl were implicated in cell apoptosis.Recent studies have also shown that Spl is also involved in the pathogenesis of DN.Meanwhile,some studies has also demonstrated that Spl was essential for maintaining podocyte integrity,but it was still unknown whether high glucose(HG)activates Spl in cultured podocyte and whether this leads to podocyte apoptosis.The aim of the present study was to investigate if HG activated Spl and its function in hyperglycaemia-induced podocyte apoptosis.Methods:Immortalized mouse podocytes were cultured in media containing normal glucose(NG),or high glucose(HG)or Spl siRNA.The expression of Spl in podocytes was detected by real-time RCR,western blotting and immunofluorescence assay.The role of Spl in hyperglycaemia-induced podocyte apoptosis was further evaluated by observing the inhibition of Sp1 expression by Sp1 siRNA using flow cytometer.The mRNA and protein expression of apoptosis gene Bax were measured by real-time RCR and western blotting.The statistical analyses were performed using the SPSS for windows software(version 17.0).Data are presented as mean±standard deviation(SD).Multiple comparisons among the groups were conducted by one-way analysis of variance with Bonferonni's/Turkey test or Dunnett's T3-test.P<0.05 were considered significant.Results:In cultured podocyte,HG significantly increased Spl expression in a time and dose-dependent manner.Pretreatment with Spl siRNA(50 nm)significantly decreased the expression of Spl.Meanwhile,the apoptosis effects induced by HG were also abrogated by Sp1 knock down in cultured podocytes.In addition,we further found that HG also increased Bax expression in cultured podocytes,and this effect was blocked by Spl siRNA.Conclusions:Sp1/Bax signaling pathway plays an important role in HG induced podocyte apoptosis.Blocking Sp1/Bax signaling pathway can reduce the apoptosis of podocytes induced by HG.