Molecular Metabolism (Oct 2016)

α-Melanocyte stimulating hormone promotes muscle glucose uptake via melanocortin 5 receptors

  • Pablo J. Enriori,
  • Weiyi Chen,
  • Maria C. Garcia-Rudaz,
  • Bernadette E. Grayson,
  • Anne E. Evans,
  • Sarah M. Comstock,
  • Ursel Gebhardt,
  • Hermann L. Müller,
  • Thomas Reinehr,
  • Belinda A. Henry,
  • Russell D. Brown,
  • Clinton R. Bruce,
  • Stephanie E. Simonds,
  • Sara A. Litwak,
  • Sean L. McGee,
  • Serge Luquet,
  • Sarah Martinez,
  • Martin Jastroch,
  • Matthias H. Tschöp,
  • Matthew J. Watt,
  • Iain J. Clarke,
  • Christian L. Roth,
  • Kevin L. Grove,
  • Michael A. Cowley

Journal volume & issue
Vol. 5, no. 10
pp. 807 – 822

Abstract

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Objective: Central melanocortin pathways are well-established regulators of energy balance. However, scant data exist about the role of systemic melanocortin peptides. We set out to determine if peripheral α-melanocyte stimulating hormone (α-MSH) plays a role in glucose homeostasis and tested the hypothesis that the pituitary is able to sense a physiological increase in circulating glucose and responds by secreting α-MSH. Methods: We established glucose-stimulated α-MSH secretion using humans, non-human primates, and mouse models. Continuous α-MSH infusions were performed during glucose tolerance tests and hyperinsulinemic-euglycemic clamps to evaluate the systemic effect of α-MSH in glucose regulation. Complementary ex vivo and in vitro techniques were employed to delineate the direct action of α-MSH via the melanocortin 5 receptor (MC5R)–PKA axis in skeletal muscles. Combined treatment of non-selective/selective phosphodiesterase inhibitor and α-MSH was adopted to restore glucose tolerance in obese mice. Results: Here we demonstrate that pituitary secretion of α-MSH is increased by glucose. Peripheral α-MSH increases temperature in skeletal muscles, acts directly on soleus and gastrocnemius muscles to significantly increase glucose uptake, and enhances whole-body glucose clearance via the activation of muscle MC5R and protein kinase A. These actions are absent in obese mice, accompanied by a blunting of α-MSH-induced cAMP levels in skeletal muscles of obese mice. Both selective and non-selective phosphodiesterase inhibition restores α-MSH induced skeletal muscle glucose uptake and improves glucose disposal in obese mice. Conclusion: These data describe a novel endocrine circuit that modulates glucose homeostasis by pituitary α-MSH, which increases muscle glucose uptake and thermogenesis through the activation of a MC5R-PKA-pathway, which is disrupted in obesity. Keywords: α-MSH, Pituitary, Skeletal muscles, MC5R, PKA, Glucose homeostasis