Endocrine Abstracts (2002) 3 OC31

An interaction between ghrelin and a species of high-density lipoprotein

NJ Beaumont1, TM-M Tan2, VO Skinner1, BS Ramesh1, DJ Byrne3, DP Mikhailidis3, PM Bouloux2, SK Srai1 & MP Vanderpump2

1Department of Biochemistry & Molecular Biology, Royal Free & University College Medical School, London, UK; 2Department of Endocrinology, Royal Free Hospital Trust, London, UK; 3Department of Clinical Biochemistry, Royal Free Hospital Trust, London, UK.

Ghrelin is an acylated peptide hormone that is expressed by a variety of tissues including the stomach, hypothalamus and kidney. Ghrelin produces a range of effects, including stimulating the release of growth hormone from the pituitary gland, and inducing feeding and obesity.

The effects of some hormones can be altered by interactions with other proteins; so the aim of this project was to screen plasma for proteins that can bind ghrelin, as part of an investigation into factors that modulate the activity of ghrelin.

Ghrelin was engineered to bind it to a resin. Plasma was incubated with this matrix and also a control matrix without the peptide. The matrices were then washed with 2M sodium chloride, and then bound proteins were eluted with 100mM glycine (pH 2.5). Several proteins were only eluted from the ghrelin affinity matrix. A band of approximately 28 kDa was identified as apolipoprotein A-I (Apo A-I) by Edman degradation and Western blotting. Apo A-I is present on high-density lipoprotein (HDL) and is involved in lipid transport from peripheral tissues to the liver.

The interaction between ghrelin and HDL was corroborated by gel filtration. I125Ghrelin was incubated with HDL, LDL or buffer. The labeled ghrelin migrated slowly through Sephadex G50, as did the peptide that had been incubated with LDL, indicating that the peptide was a species of less than 10 kDa. However, ghrelin that had been incubated with HDL produced a peak that migrated with the HDL, indicating that some ghrelin was bound to a higher molecular weight species.

These findings suggest there is a novel interaction between ghrelin and a fraction of HDL. This interaction links lipid physiology to feeding and growth hormone release. Further work is being undertaken to establish the physiological effects of this interaction and the conditions under which it naturally occurs.

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