High glucose alters tubular epithelial cell expression of molecules in the renin‐angiotensin axis

Abstract

Purpose: Aminopeptidase N (APN), a type II membrane ectoenzyme also known as CD13, is a major component of Glut‐4 containing vesicles. It has been postulated to regulate secretory function in general and glucose transport in particular. The present study was performed to determine the effect of glucose and insulin on the expression and activity of APN in renal epithelial cells.Methods: A heightened glucose milieu was created by culturing immortalized HK‐2 cells in 25 mM glucose as compared to the normal 5 mM glucose and a control for hyperosmolality (cells grown in 5 mM glucose with 20 mM mannitol)(OC). The model was validated by studying the altered growth and adhesion characteristics of the HK‐2 cells in the three conditions. Assays for APN activity and APN transcript abundance were performed on cells cultured in the three conditions. The effect of insulin and lisinopril on glucose‐induced changes APN activity was examined.Results: APN transcript, protein, and activity were greater in cells treated with 25 mM vs 5 mM glucose and the same in cells treated with OC vs 5 mM glucose. Insulin reduced APN activity to that observed in low glucose (5mM) levels (p<0.05).Conclusions: Glucose is capable of stimulating APN in renal epithelial cells. This stimulation was blocked by insulin, raising the possibilities that APN plays a role in glucose homeostasis in general and in the pathogenesis of diabetes specifically.