Kruppel-like factor 4 promotes autophagy in human monocytes leukemia cells under high glucose conditions by inhibiting AKT/mTOR signaling pathway

Abstract

Abstract Background Diabetic atherosclerosis (AS) is the main cause of disability and death in diabetes. In the progression of AS, autophagic activity plays an important role. Kruppel-like factor 4 (KLF4) is a member of zinc finger protein transcription factor family and is believed to play a protective role in the pathogenesis of atherosclerosis. This study aimed to explore the role of KLF4 in diabetic atherosclerosis and the autophagic mechanism. Methods After the diabetic mouse model induced by streptozotocin (STZ), we gave mice a high-fat and sugar diet. Aortic arches were dissected from the iliac bifurcation to remove external fatty deposits and detected the level of KLF4 protein expression in diabetic group compared to the non-diabetic group. On the other hand, KLF4 lentiviral vector and small interfering RNA (siRNA) were constructed for in vitro experiments. Oil red staining and cholesterol content assay was used to determinate the cholesterol content in human monocytes leukemia cells (THP-1). Cell apoptosis was determined using TUNEL assay. Immunofluorescence staining, western blotting and reverse transcription-PCR analysis were utilized to evaluate the expressions of autophagy-related proteins as well as AKT/mTOR signaling pathway-related proteins after the transfection of KLF4 siRNA or lentiviral vector. Results The expression level of KLF4 protein was decreased in the aorta of diabetic mice, while KLF4 overexpression in THP-1 cells under high glucose can significantly decrease cellular cholesterol accumulation, increase beclin-1 expression and decrease P62/SQSTM1 expression, respectively. Meanwhile, microtubule-associated protein 1 light chain 3 (LC3) fluorescence intensity in KLF4 lentiviral vector group is significantly enhanced with increased cell apoptosis. Phosphorylated mammalian target of rapamycin (p-mTOR) and phosphorylated AKT (p-AKT) expression was decreased in KLF4 overexpressed group. On the contrary, after transfection of KLF4 siRNA, the expression levels of p-mTOR and p-AKT were increased in THP-1 cells. Conclusion KLF4 can decrease cellular cholesterol accumulation and induce autophagy in THP-1 cells under high glucose conditions by inhibiting the AKT/mTOR pathway, which may slow the progression of diabetic atherosclerosis.