The Role of Copper and CTR1 in the Regulation of Adipose Function

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Copper (Cu) is an essential trace element and Cu imbalance is the underlying etiology of several human diseases, including Menkes disease, Wilsonʼs disease, myeloneuropathy, and cardiomyopathy. Menkes disease, caused by mutations in the ATP7A Cu transporter, leads to organismal Cu deficiency that results in connective tissue defects and severe lethal neurodegeneration. Menkes patients also exhibit hypothermia, suggesting a link between Cu metabolism and mammalian thermogenic pathways. Thermogenesis is supported by several layers of metabolism coordinately regulated in multiple tissues. The major location for heat generation is adipose tissue, which responds to hormones generated by the sympathetic nervous system. For example, noradrenaline (NE) stimulation activates β3 adrenergic receptors expressed in adipose tissue, which in turn upregulates lipolysis, mitogenesis, and uncoupling protein 1 (Ucp1), culminating in a thermogenic response. It has generally been assumed that the hypothermia observed in Menkes patients is at least partly due to Cu deficiency in adipose tissue, where inadequate levels of any metal cofactor for the electron transport chain would impair the mitochondrial activity required for heat generation. However, the underlying mechanisms linking Cu homeostasis to adaptive thermogenesis have not yet been elucidated. The current proposal seeks to clarify the nature of this connection and improve our understanding of how Cu metabolism and adipose biology intersect. We plan to use genetic, pharmacological, and cell biological methods to study parallel thermogenesis models, including adipose-specific knockout mice, and cultured primary and immortalized adipocytes. Preliminary studies have shown a unique role for Cu in adaptive thermogenesis, as mice exposed to cold or adrenergic stimulators specifically import Cu (rather than both Cu and iron) into adipose tissue and mice lacking adipose expression of the high affinity Cu importer Ctr1 are more sensitive to cold exposure than mice lacking the iron importer Tfr1. We outline three specific aims to uncover how Cu homeostasis pathways intersect with thermogenic pathways in adipose tissue, and in doing so, uncover how Cu metabolism interacts with global energy regulation: (1) Establish a role for Cu in adipose thermoregulation and systemic energy homeostasis using tissue-specific Ctr1 and Atp7a mutant mice, (2) Determine how coordinated regulation of Ctr family proteins controls Cu availability in adipocytes upon β3-AR stimulation, and (3) Uncover mechanisms for CTR1-mediated thermogenesis and adipocyte browning.