Developmental Changes in the Pattern of Ghrelin’s Acyl Modification and the Levels of Acyl-Modified Ghrelins in Murine Stomach

Abstract

Ghrelin is an acylated peptide hormone secreted primarily from endocrine cells in the stomach. The major active form of ghrelin is a 28-amino acid peptide with an n-octanoyl modification at Ser(3) (n-octanoyl ghrelin), which is essential for its activity. In addition to n-octanoyl ghrelin, other forms of ghrelin peptide exist, including des-acyl ghrelin, which lacks an acyl modification, and other minor acylated ghrelin species, such as n-decanoyl ghrelin, whose Ser(3) residue is modified by n-decanoic acid. Multiple reports have identified various physiological functions of ghrelin. However, until now, there have been no reports that explore the process of ghrelin acyl modification, and only a few studies have compared the levels of des-acyl, n-octanoyl, and/or other minor populations of acylated ghrelin peptides. In this study we report that the amount of n-octanoyl ghrelin in murine stomachs increases gradually during the suckling period to a maximal level at 3 wk of age and falls sharply after the initiation of weaning. However, the concentration (picomoles per milligram of wet weight tissue) of total ghrelin, which includes des-acyl and all acylated forms of ghrelin peptides with intact C termini in murine stomach, remains unchanged across this suckling-weaning transition. Prematurely weaned mice exhibited a significant decrease in the amount of n-octanoyl or n-decanoyl ghrelin in the stomach. Orally ingested glyceryl trioctanoate, a medium-chain triacylglyceride rich in milk lipids, significantly increased the level of n-octanoyl-modified ghrelin in murine stomach. Fluctuations in the proportion of this biologically active, acyl-modified ghrelin could contribute to or be influenced by the change in energy metabolism during the suckling-weaning transition.

Identification of a mouse ghrelin gene transcript that contains intron 2 and is regulated in the pituitary and hypothalamus in response to metabolic stress

“…2003, Nishi et al 2005, Zhang et al 2005, Gualillo et al 2006. Consistent with the alternative usage of In2 observed in the current report, utilization of an alternative splice site in In2 has previously been reported to yield 'des-Gln 14 -ghrelin' in several species (Hosoda et al 2000b, Kawamura et al 2003Genbank #: AB089202).…”

“…Non-acylated ghrelin does not bind to the GHS-R1a, but does have biological activities in multiple tissues, through a yet to be identified receptor that is distinct from GHS-R1a (Muccioli et al 2004, Gauna et al 2005, Toshinai et al 2006. In addition to the modification by acylation, the preproghrelin peptide can be differentially processed by enzymatic cleavage (Hosoda et al 2000a, Pemberton et al 2003, Nishi et al 2005, Zhang et al 2005. For example, it is now appreciated that preproghrelin can be enzymatically cleaved to yield both ghrelin and obestatin, where obestatin is a 23 amino acid peptide that may act through distinct receptors to oppose the actions of ghrelin (Zhang et al 2005).…”

Analysis of plasma ghrelin in patients with medium-chain acyl-CoA dehydrogenase deficiency and glutaric aciduria type II

“…In addition to n-octanoylated ghrelin, other molecular forms of the ghrelin peptide exist, including des-acyl ghrelin lacking an acyl modification and such minor acylated ghrelin species as n-decanoylated ghrelin (Ser3 is modified by n-decanoic acid) (4,5). Serum from a patient with GA2 showed the presence of acylated ghrelin that was not octanoylated and was possibly decanoylated (16).…”

“…Reverse-phase HPLC (RP-HPLC) was performed as described previously (4,5,14). Briefly, plasma diluted 50% with 0.9% saline was applied to a Sep-Pak C18 cartridge pre-equilibrated with 0.9% saline.…”

“…Octanoylation of the Ser3 residue is essential for ghrelin-mediated stimulation of GH secretion and regulation of energy homeostasis via increased food intake and adiposity (2,3). Other than octanoylation (C8:0), the hormone is subject to other types of acyl modification, decanoylation (C10:0), and possibly decenoylation (C10:1) (4,5). Recently, ghrelin Oacyltransferase (GOAT), which octanoylates ghrelin, was identified (6,7).…”