Effects Of Vitamin D On The Lipid Metabolism In Glomerular Epithelial Cells

Objective:Vitamin D is believed to play an important role in the development and complications of diabetes mellitus(DM).Published reports have indicated that vitamin D ameliorates diabetes-induced glucose metabolism disorders by stimulating insulin secretion and increasing insulin sensitivity.Previous results from our laboratory indicated that 1?,25(OH)2D3 could decrease the renal damage based on decreasing levels of serum creatinine and proteinuria in diabetic mice and protect against the high glucose-induced damage to glomerular podocytes.However,the role that 1?,25(OH)2D3,the active vitamin D metabolite,plays in the dyslipidemias associated with DM is unclear.The purpose of the present study was to explore the effects of 1?,25(OH)2D3 on lipid metabolism and palmitic acid-induced lipid disorder associated with diabetic nephropathy using human podocytes.Methods:The study was divided into three experiments.(1)Effects of la,25(OH)2D3 on glomerular podocytes:podocytes were treated with RPMI 1640 medium or absolute ethyl alcohol as the negative control,or 1?,25(OH)2D3 at 10-7 M or 10-8 M concentrations in medium for 48 hours.The CCK-8 assay was used to determine cell viability,and a flow cytometer was used to detect the apoptosis rate of podocytes.Oil red 0 staining was used to detect lipid droplets in cells.Realted standard assay kits were used to detect the concentrations of triglyceride(TG),cholesteryl esters(CE)and the total cholesterol(TC)in the cells.At the same time,the expression of relative fatty acid synthesis protein(FASN)and cholesterol metabolism protein(SCAP and SREBP-2)were detected using Western Blotting and Real-time PCR.(2)Effects of palmitic acid(PA)on podocytes:Podocytes were treated with palmitic acid at different concentrations to create the DN lipid disorders model for 48 hours(0,50,75,100 ?M).CCK-8 was used to assess cell viability and oil red O staining was used to detect the lipid droplets in podocytes.Triglycerides and the expressions of relative fatty acid synthesis and cholesterol metabolism proteins were measured as previously described.(3)Effects of 1?,25(OH)2D3 on palmitic acid-induced injury and disorders of lipid metabolism in podocytes:Podocytes were treated with RPMI 1640 medium as control,50 ?M palmitic acid,PA plus la,25(OH)2D3 at 10-7 M or 10-8 M concentrations in medium for 48 hours.CCK-8 was used to determine cell viability.Oil red O staining and the triglyceride assay kit were used to detect the lipid accumulation as described previously.Results:(1)Effects of la,25(OH)2D3 on lipid metabolism in podocytes:1?,25(OH)2D3 decreased cell viability and increased the apoptosis rate of podocytes(P<0.05).1?,25(OH)2D3 reduced the accumulation of lipid droplets and the concentrations of TG and EC(P<0.05).The expression of FASN,SCAP and SREBP-2 significantly decreased after treatment with 1?,25(OH)2D3(P<0.05).At the same time,the level of total cholesterol in podocytes were significant increased after la,25(OH)2D3 treated(P<0.05).(2)Effects of palmitic acid on lipid metabolism in podocytes:Cell viability were significant decreased with PA treated(P<0.05)and the response dose was related,PA increased lipid droplets accumulation and significantly increased the TG concentration in podocytes(P<0.05).There was no significant change after treatment in the expression of protein FASN,however,there were some changes in the levels of FASN mRNA(P<0.05).Both SCAP and SREBP-2 were significantly decreased after treatment with PA(P<0.05).(3)Effect of 1?,25(OH)2D3 on palmitic acid-induced injury and disorder of lipid metabolism in podocytes:1?,25(OH)2D3 had no significant influence on reversing the cell viability decline induced by PA.Furthermore,1?,25(OH)2D3 had no significant effect on PA-induced lipid droplets accumulation and increased TG concentration.Conclusions:(1)la,25(OH)2D3 decreased the fatty acid accumulation in podocytes and increased the total cholesterol level.To sum up,la,25(OH)2D3 influenced the lipid metabolism in podocytes.(2)Palmitic acid increased the lipids accumulation and affectted the lipids metabolism.(3)1?,25(OH)2D3 did not protect from the injury and lipid metabolism disorder induced by palmitic acid.