Loss of BIM increases mitochondrial oxygen consumption and lipid oxidation, reduces adiposity and improves insulin sensitivity in mice

BCL-2 proteins are known to engage each other to determine the fate of a cell after a death stimulus. However, their evolutionary conservation and the many other reported binding partners suggest an additional function not directly linked to apoptosis regulation. To identify such a function, we studied mice lacking the BH3-only protein BIM. BIM^-/- cells had a higher mitochondrial oxygen consumption rate that was associated with higher mitochondrial complex IV activity. The consequences of increased oxygen consumption in BIM^-/- mice were significantly lower body weights, reduced adiposity and lower hepatic lipid content. Consistent with reduced adiposity, BIM^-/- mice had lower fasting blood glucose, improved insulin sensitivity and hepatic insulin signalling. Lipid oxidation was increased in BIM^-/- mice, suggesting a mechanism for their metabolic phenotype. Our data suggest a role for BIM in regulating mitochondrial bioenergetics and metabolism and support the idea that regulation of metabolism and cell death are connected.