Mechanisms of mitochondrial energetics
in health and disease
Background and Significance: White fat stores energy. In contrast, brown fat burns energy through thermogenic mitochondrial respiration and is thus powerfully anti-obesogenic and anti-diabetic. By elucidating the genetic and metabolic pathways that control thermogenesis, we aim to recapitulate the positive effects of brown fat energy expenditure on health. We have recently taken steps towards this goal through the discovery that creatine energetics combats obesity through activation of brown fat thermogenesis, and we are now focused on identifying the molecular mechanism underlying this process. In addition, mitochondrial energetics leverages creatine metabolism in cell types that require rapid energetic sensing for diverse biological outcomes. Because cancer cells are especially metabolically flexible, it is not surprising that altered creatine metabolism is associated with many cancers. However, the mechanistic role of creatine in cancer is poorly understood. The Kazak lab is developing molecular tools to investigate the role of creatine metabolism in cancer.
The Kazak lab is focused on the following research aims:
1. Determine the metabolic intermediates controlling creatine-dependent thermogenesis. Creatine drives energy expenditure in adipose tissue by stimulating a futile cycle of mitochondrial ATP turnover (Kazak L et al., Cell, 2015), and this process powerfully combats obesity in pre-clinical models (Kazak L et al., Cell Metabolism, 2017). However, the metabolic intermediates that drive creatine cycling are unknown. The Kazak lab is utilizing mass spectrometry-based metabolic tracing to identify creatine-dependent metabolite signatures in thermogenic fat. We are combining this approach with genetic manipulations and bioenergetic analyses in primary adipocytes and mouse models to determine the effects of these novel metabolites on thermogenic respiration and body mass/composition.
2. Identify the composition of the creatine-dependent thermogenic protein complex. Mitochondrial synthesis of phosphocreatine and its use in ATP-requiring reactions involves a close physical association between mitochondrial Creatine Kinase (Mi-CK) and the enzymes that generate and consume ATP. Given the unique function for creatine in thermogenic adipose tissue, we hypothesize that Mi-CK physically interacts with proteins that support creatine cycling. We are using unbiased quantitative proteomics to discover novel MiCK-interacting partners, which can be studied in vivo and may potentially be exploited therapeutically to combat obesity.
3. Generate novel genetically-engineered mouse models to study thermogenesis. To continue our work on elucidating the role of adipocyte thermogenesis in obesity and metabolic disease, we are generating new mouse models where we can inactivate thermogenic genes selectively in fat, in an inducible manner.
4. Identify the role of creatine in tumorigenesis. Creatine is intimately linked with mitochondrial metabolism and is critical for cell types that require rapid energetic sensing for diverse biological outcomes. Genes of creatine metabolism drive malignancies such as breast cancer, colorectal cancer, pancreatic cancer, and acute myeloid leukemia. However, the molecular mechanism underlying this pro-cancer property of creatine is unknown. We are generating biochemical and genetic tools to systematically examine the molecular mechanisms underlying the role of creatine energetics in cancer metabolism.