👤 T A Rouault

White adipocyte differentiation or adipogenesis requires coordination of metabolic sensing and transcriptional modifications to orchestrate lipid storage. Creatine and its kinases are implicated in adipose energy buffering, but the roles of cytosolic (CKB) and mitochondrial (CKMT2) creatine kinases in adipogenesis are unclear. We find that both CKB and CKMT2 are progressively upregulated during differentiation. Functional studies show that CKB restrains de novo lipogenesis (DNL) by limiting activation of carbohydrate-responsive element-binding protein (ChREBP), a key regulator of lipogenic genes. Mechanistically, CKB interacts with AKT and regulates its activation in response to insulin. Loss of CKB causes persistent AKT-mTORC1 signaling, increases glycolytic flux, and enhances ChREBP activation, thereby promoting glucose-derived lipid synthesis. Thus, CKB acts as a metabolic rheostat linking creatine-kinase activity to insulin signaling and nutrient-responsive transcription. We propose a CKB-AKT-ChREBP regulatory axis that contributes to metabolic remodeling and lipid homeostasis during adipocyte differentiation. Show less

The melanocortin-3 receptor (MC3R) regulates GABA release from agouti-related protein (AgRP) nerve terminals and thus tonically suppresses multiple circuits involved in feeding behavior and energy homeostasis. Here, we examined the role of the MC3R and the melanocortin system in regulating the response to various anorexigenic agents. The genetic deletion or pharmacological inhibition of the MC3R, or subthreshold doses of an MC4R agonist, improved the dose responsiveness to glucagon-like peptide 1 (GLP1) agonists, as assayed by inhibition of food intake and weight loss. An enhanced anorectic response to the acute satiety factors peptide YY (PYY3-36) and cholecystokinin (CCK) and the long-term adipostatic factor leptin demonstrated that increased sensitivity to anorectic agents was a generalized result of MC3R antagonism. We observed enhanced neuronal activation in multiple hypothalamic nuclei using Fos IHC following low-dose liraglutide in MC3R-KO mice (Mc3r-/-), supporting the hypothesis that the MC3R is a negative regulator of circuits that control multiple aspects of feeding behavior. The enhanced anorectic response in Mc3r-/- mice after administration of GLP1 analogs was also independent of the incretin effects and malaise induced by GLP1 receptor (GLP1R) analogs, suggesting that MC3R antagonists or MC4R agonists may have value in enhancing the dose-response range of obesity therapeutics. Show less

Although iron is an essential nutrient, it is also a potent cellular toxin, and the acquisition of iron is a highly regulated process in eukaryotes. In yeast, iron uptake is homeostatically regulated by the transcription factor encoded by AFT1. Expression of AFT1-1(up), a dominant mutant allele, results in inappropriately high rates of iron uptake, and AFT1-1(up) mutants grow slowly in the presence of high concentrations of iron. We present evidence that when Aft1-1(up) mutants are exposed to iron, they arrest the cell division cycle at the G1 regulatory point Start. This arrest is dependent on high-affinity iron uptake and does not require the activation of the DNA damage checkpoint governed by RAD9. The iron-induced arrest is bypassed by overexpression of a mutant G1 cyclin, cln3-2, and expression of the G1-specific cyclins Cln1 and Cln2 is reduced when yeast are exposed to increasing amounts of iron, which may account for the arrest. This reduction is not due to changes in transcription of CLN1 or CLN2, nor is it due to accelerated degradation of the protein. Instead, this reduction occurs at the level of Cln2 translation, a recently recognized locus of cell-cycle control in yeast. Show less