Proceedings of The Physiological Society
AstraZeneca (2010) Proc Physiol Soc 18, PC27
Hypothalamic expression pattern and molecular and physiological markers indicate elevated sympathetic stimulation of metabolism in XLαs-deficient mice
K. Burton1, N. Nunn1, S. Krechowec1, R. Barrett-Jolley2, A. Plagge1
1. Physiological Laboratory, University of Liverpool, Liverpool, United Kingdom. 2. Veterinary Preclinical Sciences, University of Liverpool, Liverpool, United Kingdom.
XLαs constitutes an NH2-terminal splice variant of the stimulatory G-protein α-subunit Gsα, which is encoded by the imprinted Gnas locus. We previously generated a knock-out specific for the Gnasxl transcript (XLαs) , which exhibits a lean, hypermetabolic, glucose tolerant and insulin sensitive phenotype . Increased catecholamines in urine and increased cAMP in brown adipose tissue (BAT) suggest elevated sympathetic nervous system (SNS) activity in XLαs deficient mice. To further define the causes of this phenotype, particularly in relation to the SNS, we are investigating the brain expression pattern, as well as additional molecular and physiological parameters. Immunohistochemistry in adult brain shows XLαs to be expressed in areas associated with SNS activity, including the paraventricular nucleus of the hypothalamus, the raphe magnus and the raphe pallidus. Other areas involved in feeding regulation and energy metabolism are also positive for XLαs, including the arcuate nucleus, the lateral and dorsomedial hypothalami, the zona incerta, the amygdala and the locus coeruleus. Co-localisation studies show that XLαs is expressed in a subgroup of Orexin positive neurons in the lateral and dorsomedial hypothalamus and in tyrosine hydroxylase positive neurones in the arcuate nucleus, but this does not account for all XLαs neurons in these regions. Q-RTPCR results of adult knock-out hypothalami show decreased expression of the ghrelin receptor, MCH receptor 1 and malonyl CoA decarboxylase, which is in line with their increased energy expenditure. We also assessed additional peripheral markers of SNS outflow. Western blotting of BAT shows increased hormone-sensitive lipase (HSL) phosphorylation in XLαs knock-outs, indicating increased sympathetic stimulation. Uncoupling protein 1 (UCP1) expression, as determined by Q-RTPCR, was also found to be increased in adult BAT . However, in neonatal BAT no correlation of HSL phosphorylation (increased) and UCP1 expression (decreased) was found. This might indicate an additional cell-autonomous role of XLαs, which is transiently expressed in the neonatally developing BAT. Furthermore, using tail plethysmography under anaesthesia (1.3-2.15 g/kg urethane i.p.), adult knock-outs were found to have increased blood pressure. These results support the suggestion of increased SNS outflow in XLαs-deficient mice and provide further hints as to which central nervous system mechanisms may be involved.
Where applicable, experiments conform with Society ethical requirements