Erythropoietin and Hypothalamic-Pituitary Axis.

Erythropoietin (EPO), known primarily for its erythropoietic activity, is commonly used clinically to treat anemia of chronic kidney disease. However, the expression of EPO receptor (EpoR) beyond erythroid tissue provides for potential extrahematopoietic effects of EPO, including EPO regulation of metabolic homeostasis (Zhang et al., 2014). Small clinical studies have shown that EPO treatment in patients with end-stage renal disease improved glycemic control and insulin sensitivity. Studies in animal models have shown that EPO regulation of metabolism is mainly attributed to its response in fat, and the hypothalamus-pituitary axis (Dey et al., 2016; Dey, Scullen, & Noguchi, 2015; Teng, Gavrilova, et al., 2011; Wang et al., 2013) and is not dependent on its hematopoietic activity. EpoR expression in the hypothalamus is localized to the neurons expressing proopiomelanocortin (POMC) in the arcuate nucleus region, the most important site in the brain for the regulation of physiological energy expenditure. EPO treatment increases POMC production in anorexigenic POMC neurons in the hypothalamus. In the pituitary, EPO modulates the secretion of the POMC-derived peptide, adrenocorticotropic hormone (ACTH) that regulates physiological and metabolic stress response. With EPO produced by cells in the brain, such as astrocytes, and with EPO-stimulated POMC expression in the hypothalamus and EPO-inhibited ACTH secretion in the pituitary, EPO signaling contributes to the hypothalamic-pituitary axis as a major regulator of glucose metabolism and energy homeostasis.