Role of TFEB-autophagy lysosomal pathway in palmitic acid induced renal tubular epithelial cell injury.

Lysosomal dysfunction and impaired autophagic flux are involved in the pathogenesis of lipotoxicity in the kidney. Here, we investigated the role of transcription factor EB (TFEB), a master regulator of autophagy-lysosomal pathway, in palmitic acid induced renal tubular epithelial cells injury. We examined lipid accumulation, autophagic flux, expression of Ps211-TFEB, and nuclear translocation of TFEB in HK-2 cells overloaded with palmitic acid (PA). By utilizing immunohistochemistry, we detected TFEB expression in renal biopsy tissues from patients with diabetic nephropathy and normal renal tissue adjacent to surgically removed renal carcinoma (controls), as well as kidney tissues from rat fed with high-fat diet (HFD) and low-fat diet (LFD). We found significant lipid accumulation, increased apoptosis, accompanied with elevated Ps211-TFEB, decreased nuclear TFEB, reduced lysosome biogenesis and insufficient autophagy in HK-2 cells treated with PA. Kidney tissues from patients with diabetic nephropathy had lower nuclear and total levels of TFEB than that in control kidney tissues. Level of renal nuclear TFEB in HFD rats was also lower than that in LFD rats. Exogenous overexpression of TFEB increased the nuclear TFEB level in HK-2 cells treated with PA, promoted lysosomal biogenesis, improved autophagic flux, reduced lipid accumulation and apoptosis. Our results collectively indicate that PA is a strong inducer for TFEB phosphorylation modification at ser211 accompanied with lower nuclear translocation of TFEB. Impairment of TFEB-mediated lysosomal biogenesis and function by palmitic acid may lead to insufficient autophagy and promote HK-2 cells injury.

Activation of the Nrf2/ARE signaling pathway protects against palmitic acid-induced renal tubular epithelial cell injury by ameliorating mitochondrial reactive oxygen species-mediated mitochondrial dysfunction.

Chronic kidney disease (CKD) is often accompanied by dyslipidemia, and abnormal lipid metabolism in proximal tubule cells is considered closely related to the dysfunction of proximal tubule cells and eventually leads to accelerated kidney damage. Nuclear factor E2-related factor 2 (Nrf2), known as a redox-sensitive transcription factor, is responsible for regulating cellular redox homeostasis. However, the exact role of Nrf2 in dyslipidemia-induced dysfunction of proximal tubule cells is still not fully elucidated. In the present study, we showed that palmitic acid (PA) induced mitochondrial damage, excessive mitochondrial reactive oxygen species (ROS) (mtROS) generation, and cell injury in HK-2 cells. We further found that mtROS generation was involved in PA-induced mitochondrial dysfunction, cytoskeletal damage, and cell apoptosis in HK-2 cells. In addition, we demonstrated that the Nrf2/ARE signaling pathway was activated in PA-induced HK-2 cells and that silencing Nrf2 dramatically aggravated PA-induced mtROS production, mitochondrial damage, cytoskeletal damage and cell apoptosis in HK-2 cells. However, the mitochondrial antioxidant MitoTEMPOL effectively eliminated these negative effects of Nrf2 silencing in HK-2 cells under PA stimulation. Moreover, activation of the Nrf2/ARE signaling pathway with tBHQ attenuated renal injury, significantly reduced mtROS generation, and improved mitochondrial function in rats with HFD-induced obesity. Taken together, these results suggest that the Nrf2/ARE-mediated antioxidant response plays a protective role in hyperlipidemia-induced renal injury by ameliorating mtROS-mediated mitochondrial dysfunction and that enhancing Nrf2 antioxidant signaling provides a potential therapeutic strategy for kidney injury in CKD with hyperlipidemia.