The peripheral actions of the des-acyl and octanoylated ghrelin on leptin in human abdominal subcutaneous adipocytes
Steve Goodyear1, Nancy Fernandez da Silva1, Katarina Kos1, Alison Harte1, Ed Sung2, Ling Wong3, Joseph OHare1, Sudhesh Kumar1, Chuka Nwokolo2 & Philip McTernan1
The anorexigenic leptin and orexigenic ghrelin, are peripheral signals that control appetite via the hypothalamic neuropeptide Y (NPY) system. Ghrelin exists in an inactive (des-acyl) and active (octanoylated) form which acts via the GHS-R1a. Whilst a great deal is understood about central interaction of these peptides their peripheral pathways remain uncertain. Adipose tissue (AT) produces several neuropeptides. Due to the importance of AT in the control of energy homeostasis we examined 1) AT expression of ghrelin; 2) the effect of human recombinant (hr) octanoylated ghrelin (OctGhr) and des-acyl ghrelin (DesGhr) on leptin secretion; 3) and the mechanism of action, involving NFκB protein expression and activity studies. Ex vivo human abdominal and omental AT was taken from women undergoing elective surgery (BMI:26.2(mean±S.D.)±1.6 kg/m2, Age:42.7±1.6 yrs, n=38). Western blot analysis determined ghrelin protein expression. Isolated AbdSc adipocytes were treated with 1, 10 and 100 nM of des-acyl or octanoylated ghrelin. Following 48 hours incubation, leptin secretion from conditioned media was measured by ELISA. Ghrelin was expressed in AT and adipocytes in a depot-specific manner. HrOctGhr (Control 5.2±1.4 ng/mL; OctGhr 1 nM:4.7±1.7 ng/ml, OctGhr 10 nM 5.0±1.6 ng/mL, OctGhr 100 nM: 4.4±1.3 ng/ml) as well as DesGhr (DesGhr1 nM 5.3±1.7 ng/mL; DesGhr 10 nM 4.9±1.4; DesGhr 100 nM: 4.1±1.5 ng/ml) reduced leptin secretion and remained significant after BMI adjustment for OctGhr (P=0.029, n=5). Further studies assessed translocation of NFκB to the nucleus (expressed as a % of NFκB activity/protein expression). This showed a dose dependent increase with octanoyl-ghrelin (OctGhr 1 nM 21%, 100 nM 66% P=0.01) and des-acyl ghrelin (DesGhr: 1 nM 29%, 100 nM 113% P=0.03). Contrary to the central feedback where leptin antagonises ghrelin action, our data suggests that both forms of ghrelin, partly produced in the human fat itself, inhibit leptin production in the human adipocyte as part of a feedback loop. This highlights AT as a site of neuropeptide production and energy homeostatic regulation.