Our objective is to provide therapeutic intervention that will extend health span during aging. The discovery of the ghrelin mimetic MK-0677 was a milestone discovery in aging research. MK-0677 rejuvenated the growth hormone (GH) axis in the frail elderly which was accompanied by increased bone density, lean mass and strength. It appears that MK-0677 rescued an age-dependent deficit in endogenous ghrelin signaling;evidence continues to emerge in support of this conclusion. Besides restoring neurons regulating the GH axis, the GHS-R (ghrelin receptor) localizes to neurons regulating mood and cognitive function. The dopamine receptor subtype-1 (D1R) is coexpressed in these neurons, implicating ghrelin as a modulator of dopamine signaling. In vitro studies support this notion and show that ghrelin amplifies dopamine-induced accumulation of cAMP by formation of GHS-R/D1R heterodimers. Because learning and memory are improved by augmentation of cAMP accumulation in neurons, rescuing impaired endogenous ghrelin signaling by selectively increasing cAMP in D1R neurons with ghrelin mimetics has potential benefit for the elderly. The hypothesis that ghrelin augmentation of D1R signaling and formation of GHS-R/D1R heterodimers occurs in vivo and manifests behavioral effects will be tested using ghrelin-/- and Ghsr-/- mice. Ghrelin has neuroprotective properties and is a positive regulator of uncoupling protein-2 (UCP2) expression. UCP2 protects dopamine neurons from oxidative damage and death induced by 1-methyl-4-phenyl-1,2,5,6 tetrahydropyridine (MPTP). Therefore, the hypothesis that ghrelin prevents loss of D1R neurons by increasing UCP2 expression will also be tested. Crosstalk between GHS-R and D1R causing amplification of cAMP production in selective neurons that coexpress GHS-R and D1R is of fundamental importance. Hence, the signal transduction pathways involved will be elucidated to test the hypothesis that amplification of cAMP accumulation is mediated by augmentation of G1s (derived from D1R coupling) stimulated adenylyl cyclase subtype-2 activity by 23 subunits liberated by GHS-R coupling to G1i.
Specific Aims : 1.Test the hypothesis in wildtype, ghrelin-/- and ghrelin receptor knockout mice (Ghsr-/-) that ghrelin-mediated amplification occurs in vivo to enhance signaling in D1R and GHS-R expressing neurons resulting in behavioral changes;2. Test the hypothesis that expression of GHS-R in D1R containing neurons provides a mechanism by which ghrelin protects neurons from oxidative damage by maintaining UCP2 expression;3: Define the molecular mechanism of amplification of dopamine D1R-induced cAMP accumulation caused by co-activation of the ghrelin receptor (GHS-R): a.) signal transduction pathway;b.) stoichiometry of agonist and G-protein interaction with GHS-R homoligomers. These studies have near-term clinical applications because of the availability of orally active long-acting ghrelin mimetics shown to be safe and well tolerated.

Agency
National Institute of Health (NIH)
Institute
National Institute on Aging (NIA)
Type
Research Project (R01)
Project #
5R01AG019230-11
Application #
8225189
Study Section
Molecular and Cellular Endocrinology Study Section (MCE)
Program Officer
Mackiewicz, Miroslaw
Project Start
2001-04-01
Project End
2014-01-31
Budget Start
2012-02-15
Budget End
2014-01-31
Support Year
11
Fiscal Year
2012
Total Cost
$382,473
Indirect Cost
$189,305
Name
Scripps Research Institute
Department
Type
DUNS #
781613492
City
La Jolla
State
CA
Country
United States
Zip Code
92037
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Kern, Andras; Albarran-Zeckler, Rosie; Walsh, Heidi E et al. (2012) Apo-ghrelin receptor forms heteromers with DRD2 in hypothalamic neurons and is essential for anorexigenic effects of DRD2 agonism. Neuron 73:317-32
Park, Seongjoon; Jiang, Hong; Zhang, Hongjie et al. (2012) Modification of ghrelin receptor signaling by somatostatin receptor-5 regulates insulin release. Proc Natl Acad Sci U S A 109:19003-8
Albarran-Zeckler, Rosie G; Brantley, Alicia Faruzzi; Smith, Roy G (2012) Growth hormone secretagogue receptor (GHS-R1a) knockout mice exhibit improved spatial memory and deficits in contextual memory. Behav Brain Res 232:13-9
Rogers, Nicole H; Landa, Alejandro; Park, Seongjoon et al. (2012) Aging leads to a programmed loss of brown adipocytes in murine subcutaneous white adipose tissue. Aging Cell 11:1074-83

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