Elevated Glucose Negatively Regulates Nkx6.1 Protein Level in the Pancreatic Beta Cell.

Millions of people suffer from T2D. A key characteristic of T2D is damage to the pancreatic beta cell. This damage affects the beta cell's ability to sense glucose, produce insulin, and release insulin in response to elevated blood glucose levels. Homeobox protein Nkx6.1 is a beta cell transcription factor essential for beta cell differentiation, proliferation, and insulin secretion. To test the effect of hyperglycemia on the beta cell, INS-1 832/13 beta cells were cultured under hyperglycemic conditions (20mM glucose) for 24 and 48 hours. This treatment significantly increased cellular ROS levels and impairs beta cell insulin secretion. Similarly, 20mM culture resulted in decreased nuclear localization of Nkx6.1, decreased overall Nkx6.1 protein levels, and decreased Nkx6.1 mRNA levels. We demonstrate that culturing beta cells in 20mM glucose increase Nkx6.1 ubiquitination and appears to impair new Nkx6.1 translation. Our data suggest that beta cells cultured in 20mM glucose result in increased ROS levels that result in Nkx6.1 relocalization and degradation, thus changing the ability of the beta cell to properly secrete insulin.