Aging-Associated Decline in Cell Growth, Tubulogenic Capability, and Stress Resistance in Human Proximal Tubule Cells

Background: The kidney consists mainly of tubular epithelial cells, which play a critical role in the reabsorption and secretion of electrolytes, amino acids, and various drugs through a range of transporters and channels. These cells can regenerate after acute injury, but in the elderly, recovery is often delayed, causing prolonged renal dysfunction. Although aging is associated with increased susceptibility to injury and diminished regenerative capacity, the underlying mechanisms of tubular senescence remain poorly understood. Methods: To investigate renal tubular aging mechanisms, we utilized primary cultured human proximal tubular epithelial cells (RPTEC). Early-passage cells (Passage 2–5) were designated as Young RPTEC, and late-passage cells (Passage 10–17) as Aged RPTEC. We compared these groups for cellular proliferation (MTT assay), DNA synthesis (BrdU incorporation), cell adhesion (cell attachment assay), responses to hypoxia-induced injury and cisplatin-induced cytotoxicity. Additionally, a three-dimensional in vitro tubulogenesis assay was used to evaluate tubular formation capacity. Protein array analysis was performed to identify differentially expressed factors between Young and Aged RPTEC. Results: Aged RPTEC showed significantly increased senescence-associated β-galactosidase (SA-β-gal) activity and markedly reduced proliferation capacity compared to Young RPTEC. While no significant differences in adhesion to various extracellular matrices were detected, Aged RPTEC exhibited greater susceptibility to both hypoxic injury and cisplatin-induced cytotoxicity. In the 3D tubulogenesis model, hepatocyte growth factor (HGF) induced the formation of morphologically polarized tubular structures in Young RPTEC, whereas Aged RPTEC showed a significantly impaired ability to form tubular lumens. Protein array analysis revealed decreased insulin-like growth factor-I (IGF-I) and vascular endothelial growth factor (VEGF) expression in Aged RPTEC. Supplementation with IGF-I and VEGF partially restored the proliferation capacity of Aged RPTEC. Conclusion: Our findings suggest that reduced production of IGF-I and VEGF in aged renal tubules may contribute to the development of a senescent phenotype, providing insight into the molecular basis of impaired renal repair associated with aging.