MEF2A is a negative regulator of β-Cell maturation and function
Pancreatic beta cells produce and secrete insulin to maintain glucose homeostasis. Due to their high secretory activity, beta cells rely heavily on endoplasmic reticulum (ER) function and are particularly susceptible to ER stress, which contributes to beta cell dysfunction in diabetes. However, the transcriptional mechanisms linking ER stress to beta cell failure remain poorly understood. In this study, we investigated the role of the transcription factor Mef2a in ER stress-mediated beta cell dysfunction using primary mouse islet cells. ER stress induced by thapsigargin increased Mef2a expression and activated canonical unfolded protein response (UPR) pathways. Overexpression of Mef2a reduced beta cell proliferation, suppressed expression of key beta cell transcription factors including Pdx1, MafA, NeuroD1, and Nkx6.1, and impaired glucose-stimulated insulin secretion. Mef2a overexpression also altered mitochondrial respiration, characterized by reduced glucose-coupled respiration and increased maximal respiratory capacity. In contrast, Mef2a knockdown attenuated ER stress induced activation of ATF6 and IRE1/XBP1 dependent UPR genes. Importantly, reducing Mef2a expression preserved beta cell identity gene expression and improved insulin secretion during ER stress induced by thapsigargin or tunicamycin. Together, these findings identify Mef2a as a stress-responsive regulator that contributes to ER stress-mediated beta cell dysfunction and suggest that modulating Mef2a activity may help preserve beta cell function during metabolic stress.