Proceedings of The Physiological Society
University College Dublin (2009) Proc Physiol Soc 15, C118
Involvement of both AMPK and mTOR pathways in the arcuate nucleus of rat hypothalamus during ambient hypoxia
N. Simler1, T. Chaillou1, X. Bigard1
1. CRSSA, La Tronche, France.
Acute environmental hypoxia is known to promote reduction of body weight and marked decrease in food intake, as a result of hypoxia per se. This alteration in feeding behavior is known as altitude-induced anorexia but the molecular mechanisms underlying such alterations remain unclear. AMP-activated protein kinase (AMPK) functions as a major regulator of cellular metabolism and recent data demonstrated that together with the mammalian target of rapamycin (mTOR), AMPK plays a critical role in regulating food intake. Decreased AMPK activity in the hypothalamus reduces food intake and body weight, whereas mTOR activation is required for the appetite-suppressing response to a variety of anorexigenic signals. We previously reported that hypothalamic AMPK activity was reduced by hypoxic stimulus concomitant to hypophagia in rats, response which could be linked to the transient hyperglycemia observed at the same time (Simler et al). Here we determine whether this reduction occurs specifically in the arcuate nucleus of the hypothalamus and if the mTOR signaling could contribute to the mechanisms of altitude-induced anorexia. Adult male wistar rats were either submitted to normobaric hypoxia (10% O2) during 2 or 6 h, or maintained in normoxia. At the end of experimental conditioning, animals were anesthetized with pentobarbital (70 mg/kg body weight)and brains were quickly removed. The arcuate nucleus and the paraventricular nucleus (PVN) were extracted from 1mm slices with a punch needle. Activity of the AMPK pathway was assessed by measuring the phosphorylation levels of both AMPK and acetylCoA-carboxylase (ACC). Activity of the mTOR pathway was examined by the phosphorylation level of p70 S6 kinase (p70 S6K) and the S6 ribosomal protein. Results: The AMPK pathway in the arcuate nucleus was progressively affected during hypoxia, as a result of diminished levels of both AMPK and ACC. This confirmed what we previously reported on the whole hypothalamus after 6h of hypoxia. Conversely, in the arcuate nucleus, the activity of the p70 S6K and of it’s target S6 ribosomal protein were markedly enhanced after exposure to hypoxia affording for an increased activity of the mTOR pathway. A cross-regulation between AMPK and mTOR seemed to proceed to control food intake in the arcuate nucleus, which is consistent with anorexigenic signals led by ambient hypoxia. Such modifications were not observed in the PVN, suggesting a specific response of the AMPK and mTOR pathways within the hypothalamus during environmental hypoxia. Icv injections of the AMPK activator AICAR and of an inhibitor of mTOR (rapamycin) will provide further knowledge of the molecular mechanisms that drive this hypoxia-induced anorexia. Conclusion: These findings provide support for the hypothesis that AMPK and mTOR interact in the arcuate nucleus to regulate feeding during acute environmental hypoxia.
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