High glucose induces renal tubular epithelial cell senescence by inhibiting autophagic flux

Autophagy, a cellular degradation process involving the formation and clearance of autophagosomes, is mediated by autophagic proteins, such as microtubule-associated protein 1 light chain 3 (LC3) and sequestosome 1 (p62), and modulated by 3-methyladenine (3-MA) as well as chloroquine (CQ). Senescence, characterised by permanent cell cycle arrest, is marked by proteins such as cyclin-dependent kinase inhibitor 1 (p21) and tumour protein 53 (p53). This study aims to investigate the relationship between cell senescence and renal function in diabetic kidney disease (DKD) and the effect of autophagy on high-glucose-induced cell senescence. We categorised 46 patients with DKD diagnosed by renal biopsy into classes I, IIa, IIb, III and IV and used four normal kidney specimens from patients with renal trauma as controls. We evaluated pathological changes, LC3 and p21. We used streptozotocin-induced DKD models in rats and 35 mM glucose-cultured human proximal tubular epithelial cells (HK-2) with or without 3-MA and CQ. We assessed p53, p21, LC3 and p62. We observed autophagosomes and detected senescence-associated galactosidase (SA-beta-gal) activity. In patients with DKD, p21 and LC3 expression levels increased over time and correlated positively with blood creatinine and proteinuria. In DKD rats and HK-2 cells, p21, p53, LC3 and p62 expression levels were higher than in the controls, as were SA-beta-gal-positive cells, renal tubular autophagosomes and co-expression of p21 and LC3. The 3-MA reduced p16, p21 and p53 expression compared with the high glucose group, whereas CQ had the opposite effect. These results suggest that renal tubular cell senescence is associated with the progression of DKD. Additionally, autophagic flux may play a role in mediating high-glucose-induced senescence in renal tubular cells.