Coenzyme Q (CoQ, aka ubiquinone) is an important component of the mitochondrial electron transport chain (ETC) as well as a membrane-incorporated antioxidant and a co-factor for redox processes outside the mitochondria. CoQ deficiencies can be caused by hereditary mutations in the biosynthesis pathway but are also associated with aging, chronic diseases such as Type-2 Diabetes, and the pharmacological use of HMGCoA inhibitors (statins). Due to the complexities of inter-organ communication, it has been difficult to dissect the tissue specific effects of CoQ deficiencies and to identify primary metabolic alterations. Since non-shivering thermogenesis heavily relies on mitochondrial function and mitochondria-rich brown adipose tissue (BAT), we hypothesize that this tissue will be disproportionately affected by CoQ deficiencies and have generated BAT specific CoQ deficiency models both in vitro (pharmacological inhibition of CoQ synthesis) and in vivo (UCP1-cre driven deletion of the CoQ biosynthetic enzyme PDSS2). Indeed, we find that BAT CoQ deficiency from diminished de novo synthesis within BAT results in tissue dysfunction and cold sensitivity. Interestingly, we find that the primary mitochondrial defect in both pharmacological and genetic models of CoQ deficiency appears not to be a decline in maximal mitochondrial respiration capacity but a rapid down regulation of UCP1 expression and function. RNAseq data reveal a transcriptional signature of CoQ deficiency in BAT that involves key regulators of the mitochondrial unfolded protein response (UPRmt) and the integrated stress response (ISR). We propose that activation of the IRS in BAT triggers metabolic adaptations including decreased UCP1 expression and enhanced UCP1-independent thermogenesis, in BAT and other tissues, via increased secretion of BAT para/autocrine factors such as FGF21.
Activating heat production in a tissue termed brown fat might offer new ways to combat obesity, however, availability of coenzyme Q (CoQ) might limit brown fat activity. Here we will investigate the consequences of CoQ deficiency in brown fat and how the tissue adapts to the scarcity of this important metabolite.
