Ghrelin-Related Peptides Exert Protective Effects in the Cerebral Circulation of Male Mice Through a Nonclassical Ghrelin Receptor(s)

Jacqueline M. Ku, Zane B. Andrews, Tom Barsby, Alex Reichenbach, Moyra B. Lemus, Grant R. Drummond, Mark W. Sleeman, Sarah J. Spencer, Christopher G. Sobey, Alyson A. Miller

The ghrelin-related peptides, acylated ghrelin, des-acylated ghrelin, and obestatin, are novel gastrointestinal hormones. We firstly investigated whether the ghrelin gene, GOAT, and the ghrelin receptor (growth hormone secretagogue receptor 1a [GHSR1a]) are expressed in mouse cerebral arteries. Secondly, we assessed the cerebrovascular actions of ghrelin-related peptides by examining their effects on vasodilator nitric oxide (NO) and superoxide production. Using RT-PCR, we found the ghrelin gene and GOAT to be expressed at negligible levels in cerebral arteries from male wild-type mice. mRNA expression of GHSR1a was also found to be low in cerebral arteries, and GHSR protein was undetectable in GHSR-eGFP mice. We next found that exogenous acylated ghrelin had no effect on the tone of perfused cerebral arteries, or superoxide production. By contrast, exogenous des-acylated ghrelin or obestatin elicited powerful vasodilator responses (EC50 values <10 pmol/L) that were abolished by the NO synthase inhibitor L-NAME. Furthermore, exogenous des-acylated ghrelin suppressed superoxide production in cerebral arteries. Consistent with our GHSR expression data, vasodilator effects of des-acylated ghrelin or obestatin were sustained in the presence of YIL-781 (GHSR1a antagonist) and in arteries from Ghsr-deficient mice. Using ghrelin-deficient (Ghrl(-/-)) mice, we also found that endogenous production of ghrelin-related peptides regulates NO bioactivity and superoxide levels in the cerebral circulation. Specifically, we show that NO bioactivity was markedly reduced in Ghrl(-/-) versus WT mice, and superoxide levels were elevated. These findings reveal protective actions of exogenous and endogenous ghrelin-related peptides in the cerebral circulation, and show the existence of a novel ghrelin receptor(s) in the cerebral endothelium.