Regulatory Role of Growth Hormone Secretagogue Receptor

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DESCRIPTION: (Scanned from the applicant's abstract) The long-term objective is to understand the role of the Growth Hormone Secretagogue Receptor (GHS-R) in endocrinology. This G-protein coupled receptor has been characterized, cloned, and established as an important regulator of pulsatile Growth Hormone (GH) release. In humans, daily treatment with the synthetic GHS-R ligand MK-0677 reverses the age-related decline in both pulsatile GH release and serum IGF-1 levels. Functional benefits of this rejuvenation include improvements in quality of sleep, improved body composition and modest improvements in strength. Hence, the GHS-R pathway is an important factor in the endocrinology of aging. This proposal focuses on the role of GHS-R on hypothalamic regulation of GH release. The interplay between GHS-R, growth hormone releasing hormone (GHRH) neurons, GH, somatostatin (sst) and neuropeptide Y (NPY) in regulating the entrainment of GH pulsatility will be evaluated. The roles of NPY and sst will be evaluated using NPY null mice and sstr2 null mice. Specificity of NPY effects will be determined using NPY-receptor null mice and antagonists selective for NPY-receptor subtypes. Effects of MK-0677 on GHRH expressing arcuate neurons will be identified visually by exploiting transgenic mice where enhanced green fluorescent protein is expressed under the control of the GHRH promoter. These GHRH neurons will be characterized for ion channel expression using real time RT-PCR and activity by electro physiology and pharmacology. Modification of specific channel activity by MK-0677 will be tested. To directly determine the mechanism and phosphorylation of substrates involved in GHS-R signaling, such as a Kvl.2 and PYK2, the components will be reconstituted in Xenopus oocytes and in pituitary derived GC cells that stably express GHS-R. To investigate signaling pathways between GHS-R and other hypothalamic neurons in vivo, the projections of hypothalamic GHS-R neurons will be mapped. This will be accomplished by integrating IREStau-lacZ into the mouse GHS-R locus by homologous recombination. The wiring of GHS-R hypothalamic neurons will be characterized by immunostaining for beta-galactosidase. The results of these experiments will provide important information in central mechanisms involved in the endocrinology of aging.