Both NPY-Expressing and CART-Expressing Neurons Increase Energy Expenditure and Trabecular Bone Mass in Response to AP1 Antagonism, But Have Opposite Effects on Bone Resorption.

Energy metabolism and bone homeostasis share several neuronal regulatory pathways. Within the ventral hypothalamus (VHT), the orexigenic neurons co-express Agouti-related peptide (AgRP) and neuropeptide Y (NPY) and the anorexigenic neurons co-express, α-melanocyte stimulating hormone derived from proopiomelanocortin (POMC), and cocaine and amphetamine-regulated transcript (CART). These neurons regulate both processes, yet their relative contribution is unknown. Previously, using genetically targeted activator protein (AP1) alterations as a tool, we showed in adult mice that AgRP or POMC neurons are capable of inducing whole-body energy catabolism and bone accrual, with different effects on bone resorption. Here, we investigated whether co-residing neurons exert similar regulatory effects. We show that AP1 antagonists targeted to NPY-producing or CART-producing neurons in adult mice stimulate energy expenditure, reduce body weight gain and adiposity and promote trabecular bone formation and mass, yet again via different effects on bone resorption, as measured by serum level of carboxy-terminal collagen type I crosslinks (CTX). In addition, AP1 antagonists promote neurite expansion, increasing neurite number, length, and surface area in primary hypothalamic neuronal cultures. Overall, our data demonstrate that the orexigenic NPY and anorexigenic CART neurons both have the capacity to stimulate energy burning state and increase bone mass. © 2020 American Society for Bone and Mineral Research.