Goal: The major focus of the Kazak lab is to identify the molecular mechanisms that drive adipocyte energy expenditure (thermogenesis). Activation of thermogenic (brown and beige) adipocytes can combat obesity and promote cardiometabolic health. By elucidating the genetic and metabolic pathways that control thermogenesis, we aim to recapitulate the positive effects of brown fat energy expenditure on health.
Some ongoing projects:
1. Delineating the acute triggers of the futile creatine cycle. Creatine drives energy expenditure in adipose tissue by stimulating a futile creatine cycle [i], and this process can counter obesity and glucose dysregulation in pre-clinical models [ii], [iii], and [iv]. Our experimental evidence points to a two-enzyme system that uses mitochondrial-derived ADP phosphorylation to support cycling between creatine and phosphocreatine. We have defined creatine kinase, brain-type (CKB) as a key protein that regulates the first step of the futile creatine cycle [iv]. CKB, known primarily as a non-mitochondrial enzyme, is surprisingly the major mitochondrial creatine kinase isoenzyme in brown adipocytes. We find that due to a unique internal mitochondrial targeting signal, CKB traffics to mitochondria. Once translocated to these organelles, CKB triggers the initial reaction of a creatine phosphorylation cycle and simultaneously liberates mitochondrial ADP to increase the rate of mitochondrial respiration. We have constructed a new mouse model, wherein a Flag epitope tag has been inserted at the carboxy-terminus of the endogenous CKb locus (Ckb.Flag mice). We are combining Ckb.Flag mice with quantitative TMT-based proteomics to identify covalent modifications on CKB in response to acute thermogenic triggers. This work may lead to the identification of acute regulation of the futile creatine cycle.
2. Thermogenic signals that control BAT-selective increase in CKB expression. We have recently identified that thermogenic signals (cold exposure, cAMP signaling) powerfully activate CKB expression in a BAT-selective manner. We are using functional genomics (RNA-seq, ATAC-seq, ChIP-seq) approaches to identify the signaling pathways and transcriptional networks that regulate CKB expression in response to thermogenic cues.
3. Determine the role of thermogenic effectors on combating obesity. We have shown that the constitutive
uncoupling protein 1 knockout mouse (UCP1KO) acquires a substantial number of downstream alterations that make it an unsuitable model to study the role of UCP1 in physiology [i]. To continue our work on elucidating the role of adipocyte thermogenesis (UCP1 and beyond) in combating obesity and metabolic disease, we are generating new genetically-engineered mouse models where we can inactivate thermogenic genes selectively in fat, in an inducible manner.
[i] Kazak L (2017) PNAS
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 [i]. 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.
[i] Kazak L and Cohen P (2020) Nature Reviews Endocrinology
Sources of Funding