MEF2D impairs mitochondrial respiration, glucose-stimulated insulin secretion, and survival in INS-1 β-cells.

Myocyte Enhancer Factor 2D (Mef2D) is a member of the Mef2 family. As a transcription factor, Mef2D regulates the expression of genes that impinge on cellular viability, tissue development, and fuel metabolism in a tissue dependent manner. Mef2D is expressed in the beta-cell, and overexpression and knockdown have been shown to modulate glucose stimulated insulin secretion. We sought to understand the role of Mef2D on beta-cell function and survival. To determine the function of Mef2D in the beta-cell, we built overexpression and knockdown INS-1 832/13 cell lines. We determined the effect of Mef2D overexpression or knockdown on mitochondrial respiration, insulin secretion, cell survival, and gene expression. Our data demonstrates that Mef2D knockdown enhances mitochondrial respiration, insulin secretion, and cell survival. Conversely, Mef2D overexpression inhibits mitochondrial respiration, insulin secretion, and cell survival. We demonstrate that some of this effect is due to modulated expression of the mitochondrial gene mtND6. These findings demonstrate that Mef2D overexpression is detrimental to beta-cell function and that Mef2D knockdown is beneficial. These data suggest that Mef2D may be a viable target to enhance functional beta-cell mass as a treatment for Type 1 and Type 2 Diabetes.