Role of the Mrg family of GPCRs in nociception

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Chronic pain is a serious health problem that has remained largely refractory to therapeutic intervention. The development of new pain therapeutics would be aided by a better understanding of the molecular and cellular mechanisms mediating nociception. The Mas-related genes (Mrgs) are a recently discovered, large family of G-protein coupled neuropeptide receptors (GPCRs) that are expressed with exquisite specificity in highly restricted subsets of nociceptive sensory neurons. The goal of this Program Project gram is to mount a concerted, interdisciplinary effort to understand the molecular function of differem Mrgs, the function of the neurons that express them, and the nature of the circuits in which these neurons participate. The project integrates the efforts of three laboratories with complementary expertise. The laboratory of David Anderson, which discovered the Mrgs, will utilize state-of-the art methods of mouse molecular genetics to generate and analyze strains of mice in which different Mrg genes have been deleted, and in which Mrg-expressing neurons can be inducibly ablated or silenced, or their second- and higher-order projections traced. These mice can also be used to prospectively identify Mrg-expressing neurons for physiological and molecular genetic analyses. The laboratory of Allan Basbaum is experienced in the behavioral, neuroanatomical, physiological and pharmacological analysis of nociception, and will collaborate with Anderson's group to thoroughly characterize the phenotypes of mice lacking different Mrg genes, or Mrg-expressing neurons, as well as in the analysis of Mrg synaptic connectivity. Because all Mrg-expressing cells are contained within the IB4-positive subset of nociceptive neurons, this project dovetails with the Basbaum laboratory's ongoing interest in understanding the function of this subpopulation in pain. The laboratory of Melvin Simon has expertise in the molecular genetic analysis of signal transduction by GPCRs and G-proteins. They will apply this expertise to characterize the pharmacology and mechanism of action of Mrgs, as well as to identify both endogenous and surrogate ligands for these receptors. In vitro culture of Mrg-expressing neurons will be employed to analyze and mechanistically dissect the influence of different candidate Mrg ligands, and idemify components of the intracellular signaling circuit. These studies may eventually lead to novel Mrg-based therapeutics for the treatment of pain in humans.