PROTRH GENE TRANSCRIPTION AND BIOSYNTHESES BY LEPTIN

描述（由申请人提供）：瘦素主要在脂肪组织中产生，在向调节食欲、能量消耗和神经内分泌功能的大脑中心提供能量储存和能量平衡信息方面具有重要的生理作用。瘦素的作用之一是通过促甲状腺素释放激素（TRH）肽激活下丘脑-垂体-甲状腺（HPT）轴，从而增加能量消耗。在过去三年的资助中，我们能够提供强有力的证据，证明瘦素在调节TRH激素原生物合成中的直接（室旁核，PVN）和间接（弓形核，ARC）途径的存在。我们证明瘦素可以独立于黑素皮质素（α -黑色素细胞刺激激素，α - msh）的输入，直接调节培养下丘脑神经元中突起细胞的生物合成和TRH的分泌。我们还观察到瘦素受体（ObRb）与PVN神经元中突起的共定位，强烈提示瘦素对TRH神经元的直接作用。这一假设进一步得到了PVN内ObRb mRNA表达的证实，以及大鼠给药瘦素后TRH神经元表达SOCS-3 mRNA（这是瘦素直接作用的敏感标志物）的证实。最近，我们首次在体内证明了瘦素在TRH神经元中激活STATS，进一步证明了STAT3转录因子在瘦素调节promh启动子活性中的潜在关键作用。我们最近还证明，瘦素作用导致的TRH生物合成的增加与加工酶PCI和PC2的上调有关，这些酶参与了TRH和其他肽的成熟。

DESCRIPTION (provided by applicant): Leptin, principally produced in adipose tissue, has a central physiologic role in providing information on energy stores and energy balance to brain centers that regulate appetite, energy expenditure and neuroendocrine function. One of the actions of leptin is to activate the Hypothalamic-Pituitary-Thyroid (HPT) axis through the thyrotropin-releasing hormone (TRH) peptide thereby increasing energy expenditure. During the last three years of funding, we were able to provide strong evidence for the existence of a direct (paraventricular nucleus, PVN) and an indirect (arcuate nucleus, ARC) pathway of leptin action on the regulation of the TRH prohormone biosynthesis. We demonstrated that leptin could directly regulate proTRH biosynthesis and TRH secretion in cultured hypothalamic neurons independently of the melanocortin (alpha-melanocyte-stimulating-hormone, alpha-MSH) input. We also observed the colocalization of the leptin receptor (ObRb) with proTRH in neurons of the PVN, strongly suggesting direct effects of leptin on TRH neurons. This hypothesis was further supported by the demonstration of ObRb mRNA expression within the PVN, and by showing that TRH neurons express SOCS-3 mRNA (which is the sensitive marker of direct leptin action) after leptin administration to rats. Recently, we demonstrated for the first time activation of STATS in TRH neurons by leptin in vivo, providing further evidence of a potential key role of the STAT3 transcription factor to regulate the activity of the proTRH promoter by leptin. We also recently demonstrated that the increase in TRH biosynthesis due to leptin action was associated with an up-regulation of the processing enzymes PCI and PC2, involved in the maturation of TRH and other proTRH peptides. Aim #1 We will test the hypothesis that there are two different or overlapping groups of PVN-TRH neurons carrying the ObRb (direct pathway) and the MC4R (indirect pathway) that are targeted by leptin and alpha-MSH to regulate the energy balance by increasing energy expenditure through the HPT axis, and potentially inhibiting food intake by sending synapses to the LH and DMH. Aim #2 We will test the hypothesis that leptin regulates the HPT axis primarily through the direct pathway. AIM #3 A) Because we found that leptin regulates proTRH and coordinates its processing by also up-regulating PCI and PC2 biosynthesis, we hypothesize that leptin might also regulate the other enzymes, co-chaperones, and inhibitors necessary for full prohormone processing and maturation. B) Since the melanocortin system represents the indirect pathway of action on TRH neurons, we will also determine whether alpha- MSH affects the biosynthesis, maturation and activity of PCI, PC2, proSAAS, 7B2 and CPE.