Involvement of AMP-activated protein kinase in differential regulation of appetite between lines of chickens selected for low or high juvenile body weight
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This study was to determine (1) if genetic selection for high (HWS) or low (LWS) body weight in chickens has altered the hypothalamic AMP-activated protein kinase (AMPK) system and (2) if this alteration contributes to the dissimilar feeding response to various appetite modulators between HWS and LWS lines. Compared to HWS, LWS chickens had higher levels of AMPK Î± and acetyl-CoA carboxylase (ACC) phosphorylation, which was caused by upregulation of the upstream factor calcium/calmodulin-dependent protein kinase kinase 2 (CAMKK Î²). There was greater mRNA expression of carnitine palmitoyltransferase I (CPT1), leptin receptor (LEPR) and neuropeptide Y (NPY) and less mRNA expression of ACC Î±, fatty acid synthase (FAS), fat mass and obesity associated gene (FTO), pro-opiomelanocortin (POMC) and orexin in LWS than HWS chickens. At 5 days of age, intracerebroventricular (ICV) injection of AICAR, 5-amino- 4-imidazolecarboxamide riboside, caused a quadratic dose-dependent decrease in food intake in LWS but not HWS chicks. Compound C, (6-(4-(2-piperidin-1-yl-ethoxy)- phenyl))-3-pyridin-4-yl-pyrazolo(1,5-a)-pyrimidine, caused a quadratic dose-dependent increase in food intake in HWS but not LWS chicks. The anorexigenic effect of AICAR in LWS chicks and orexigenic effect of Compound C in HWS chicks resulted from either activation or inhibition of other kinase pathways separate from AMPK. There is a lower threshold for the anorexigenic effect of ghrelin in LWS than HWS chicks, which was associated with differential hypothalamic AMPK signaling. ICV injection of ghrelin iii inhibited corticotrophin-releasing hormone (CRH), 20-hydroxysteroid dehydrogenase (20HSD), glucocorticoid receptor (GR), CPT1 and FTO expression in LWS but not HWS chicks. Additionally, the hypothalamic mRNA level of ghrelin was significantly higher in LWS than HWS chicks, which may also contribute to the differential threshold response to ghrelin in these two lines. Obestatin caused a linear dose-dependent increase in food intake in HWS but not LWS chicks. The orexigenic effect of obestatin in HWS chicks was not associated with altered AMPK. Obestatin inhibited LEPR and FTO expression in HWS but not LWS chicks. Thus, selection for body weight may alter the hypothalamic response to ghrelin by the AMPK pathway, CRH pathway, CPT1 and FTO, and to obestatin by LEPR and FTO.
- Doctoral Dissertations