MCU and obesity due to melanocortin 4 receptor deficiency: Moreover, the Sirtuin family member SIRT3 has recently been shown to be an inhibitor of mitochondrial calcium overload via a mechanism of lowering the H3K27ac level on the mitochondrial calcium uniporter (MCU) promoter in an AMPK-dependent manner, thereby preventing obesity or age-related whitening of brown adipose tissue (48).