磷酸化FOXO1对高糖刺激的人肾小管上皮细胞脂质沉积的影响

Effect of phospho-FOXO1 on lipid deposit in high glucose-stimulated human renal tubular cells

目的:研究叉头框蛋白O1(FOXO1)表达和磷酸化过程对高糖刺激下人肾小管上皮细胞脂质沉积的影响。方法:体外培养人肾小管上皮细胞株HKC,给予高糖刺激后免疫荧光及Western blotting检测总FOXO1、磷酸化FOXO1和固醇调节元件结合蛋白1(SREBP1)的表达,油红O染色测定细胞内脂质沉积;构建野生型和磷酸化位点突变型FOXO1质粒,转染入HKC细胞后给予高糖刺激,采用免疫荧光、Western blotting和油红O染色确定FOXO1磷酸化位点突变对肾小管上皮细胞脂质代谢的影响。结果:高糖刺激HKC细胞48 h后,总FOXO1在正常糖组和高糖组的表达未见差异,而磷酸化FOXO1及SREBP-1表达明显上调,细胞内脂滴显著增加。将构建的野生型FOXO1质粒转染人细胞后,上调了总FOXO1和磷酸化FOXO1的表达,增加了SREBP-1表达和细胞内脂滴含量;而磷酸化位点突变的FOXO1质粒避免了高糖诱导引起的SREBP-1上调和细胞内脂质沉积。结论:磷酸化FOXO1参与了高糖诱导的肾小管上皮细胞SREBP-1上调和细胞内脂质聚集;磷酸化位点的突变可避免高糖引起的肾小管上皮细胞SREBP-1上调和脂质沉积。

AIM： To study the effect of forkhead box O1 （FOXO1） expression and phosphorylation on lipid accumulation in high glucose-stimulated human renal tubular cell line HKC. METHODS： HKC cells were stimulated with high glucose. The total FOXO1, phospho-FOXO1 and sterol-regulatory element-binding protein 1 （SREBP-1） were detected by the methods of immunofluorescence and Western blotting. The cellular lipid deposit was measured by oil red O staining. Moreover, the wild-type FOXO1 vector or mutant FOXO1 vector was transfectcd into HKC cells followed by the treatment with high glucose. Immunofluorescence, Western blotting and oil red O staining were used to determine the effect of the phosphorylation site mutation on the lipid metabolism in renal tubular cells. RESULTS： No difference in total FOXO1 expression between normal glucose group and high glucose group was observed 48 h after HKC cells were stimulated with high glucose. However, phospho-FOXO1 was significantly increased in high glucose-treated HKC cells. Subsequently, SREBP-1 and cellular lipid deposit were up-regulated. The wild-type FOXO1 vector increased total FOXO1, phosphoFOXO1, SREBP-1 and cellular triglyceride in high glucose-treated HKC cells. However, mutant FOXO1 vector at the phosphorylation site attenuated the effect of high glucose on SREBP-1 and cellular lipid deposit. CONCLUSION： The phosphorylation of FOXO1 is involved in high glucose-induced up-regulation of SREBP-1 and cellular lipid accumulation in renal tubular cells. In addition, the mutation at the phosphorylation site prevents high glucose-induced enhancement of SREBP-1 and lipid deposit.