Molecular mechanisms of leptin receptor/Jak2 action

描述（由申请人提供）：本提案标题为“瘦素受体/Jak 2作用的分子机制”，是DK 56731的竞争性更新申请。我们以前和未来的研究的长期前景是了解LepRb信号传导的机制，并确定LepRb信号如何有助于调节神经功能，从而控制能量平衡，葡萄糖稳态和神经内分泌功能。LepRb通过相关的Jak 2酪氨酸激酶介导酪氨酸磷酸化（Tyr（P））依赖性信号传导。瘦素结合刺激Jak 2的Tyr（P）和LepRb上的酪氨酸残基;每个Tyr（P）位点介导细胞内信号的独特互补。为此，我们已经确定了LRb/Jak 2相互作用的机制，确定了Jak 2 Tyr（P）位点的功能，并检查了LepRb Tyr 1138 AESTAT 3信号传导和LepRb Tyr 985 AESHP 2/SOCS 3信号传导的生物学。最近，我们定义了LepRb上的第三个Tyr（P）位点（Tyr 1077），其调节STAT 5信号传导和潜在的其他LepRb信号，并且已经产生了新的小鼠模型来探测Jak 2和Tyr 1077在体内LepRb作用中的功能。初步数据表明，从LepRb磷酸化位点的贡献是必需的最已知的瘦素的影响，包括一些行动是独立的Tyr 1138和Tyr 985。相反，Tyr 1077对血糖控制和潜在的其他生理性瘦素效应的调节至关重要。在各种数据的背景下，表明瘦素的急性（非转录）的影响，在短期调节能量平衡和血糖控制的重要性，这些数据表明的假设，LepRb Tyr 1077介导的瘦素的急性效应所需的细胞信号。除了测试这一核心假设，拟议的研究将定义瘦素介导的各种生理效应和瘦素调节血糖水平的信号和机制。我们的研究目标是：（1）了解LepRb信号在生理调节中的作用，重点是Jak 2和Tyr 1077。(2)在LepRb信号改变的小鼠模型中定义瘦素介导的神经功能调节。(3)确定LepRb Tyr 1077和/或其他Jak 2和LepRb Tyr（P）位点控制生理和神经功能的信号传导机制。这种方法将揭示瘦素作用的分子基础，并描绘瘦素在神经和生物生理学调节中的每个瘦素信号的作用。从这些研究中获得的机制见解将为代谢性疾病的治疗干预提供潜在的分子靶点。公共卫生相关性：瘦素是机体能量平衡和代谢的关键调节因子，瘦素作用受损可能导致多种代谢性疾病。因此，了解瘦素作用的分子机制对于我们理解代谢疾病中可能失调的过程以及确定治疗干预的潜在靶点至关重要。因此，我们一直致力于定义瘦素受体LepRb介导细胞信号传导的机制，并了解这些信号中的每一个如何有助于瘦素在体内的生理作用。虽然LepRb Tyr 1138/STAT 3信号通路对于长期能量平衡至关重要，但该信号通路未能解释瘦素作用的许多重要方面。LepRb Tyr 985介导对LepRb的反馈抑制以减弱体内瘦素作用，但不能解释残余瘦素作用。我们正在进行的分析的最新数据表明LepRb Tyr 1077在体内瘦素作用中的重要作用;直接从Jak 2发出的信号也可能有贡献。因此，我们将分析Jak 2和LepRb Tyr 1077在瘦素的神经和生理作用中的作用，通过利用小鼠模型，我们已经改变了LepRb特异性地影响这些信号。我们将进一步利用一组体内系统来定义位于Jak 2和/或LepRb Tyr 1077下游的分子介质，以调节这些过程。总之，这些研究将定义瘦素作用的关键介质，并揭示瘦素控制特定生理终点的特定机制。

DESCRIPTION (provided by applicant): This proposal, entitled, "Molecular Mechanisms of Leptin Receptor/Jak2 Action," is an application for competitive renewal of DK56731. The long-term outlook of our previous and future studies is to understand mechanisms of LepRb signaling and to determine how LepRb signals contribute to the regulation of neural function and thence to the control of energy balance, glucose homeostasis, and neuroendocrine function. LepRb mediates tyrosine phosphorylation (Tyr(P))-dependent signaling by means of an associated Jak2 tyrosine kinase. Leptin binding stimulates the Tyr(P) of Jak2 and tyrosine residues on LepRb; each Tyr(P) site mediates a unique complement of intracellular signals. To this point, we have defined the mechanisms of LRb/Jak2 interaction, defined the function of Jak2 Tyr(P) sites, and examined the biology of LepRb Tyr1138AESTAT3 signaling and LepRb Tyr985AESHP2/SOCS3 signaling. Recently, we defined a third Tyr(P) site on LepRb (Tyr1077), which regulates STAT5 signaling and potentially other LepRb signals, and have generated novel mouse models to probe the function of Jak2 and Tyr1077 in LepRb action in vivo. Preliminary data suggest that contributions from LepRb phosphorylation sites are required for most known leptin effects, including some actions that are independent of Tyr1138 and Tyr985. In contrast, Tyr1077 is crucial to the regulation of glycemic control and potentially other physiologic leptin effects. In the context of a variety of data that suggest the importance of the acute (non-transcriptional) effects of leptin in the short-term regulation of energy balance and glycemic control, these data suggest the hypothesis that LepRb Tyr1077 mediates cellular signals required for the acute effects of leptin. In addition to testing this core hypothesis, the proposed research will define the signals and mechanisms by which leptin mediates a variety of physiologic effects and by which leptin modulates blood glucose levels. We propose to: (1) Understand the roles for LepRb signals in the regulation of physiology, focusing on Jak2 and Tyr1077. (2) Define the leptin-mediated regulation of neural function in mouse models of altered LepRb signaling. (3) Determine the signaling mechanisms by which LepRb Tyr1077 and/or other Jak2 and LepRb Tyr(P) sites control physiology and neural function. This approach will reveal the molecular underpinnings of leptin action and delineate the role of each leptin signal in the regulation of neural and organismal physiology by leptin. The mechanistic insights derived from these studies will suggest potential molecular targets for therapeutic intervention in metabolic disease. PUBLIC HEALTH RELEVANCE: Leptin is a key regulator of body energy homeostasis and metabolism, and impaired leptin action may contribute to a variety of metabolic diseases. Understanding the molecular mechanisms of leptin action is thus crucial for our understanding of processes that may be dysregulated in metabolic diseases, as well as for defining potential targets for therapeutic intervention. We have thus been working to define the mechanisms by which the leptin receptor, LepRb, mediates cellular signaling and to understand how each of these signals contributes to the physiologic actions of leptin in vivo. While LepRb Tyr1138/STAT3 signaling is crucial for long-term energy balance, this signaling pathway fails to explain many important aspects of leptin action. LepRb Tyr985, which mediates feedback inhibition on LepRb to attenuate leptin action in vivo, cannot account for residual leptin action. Recent data from our ongoing analysis suggests important roles for LepRb Tyr1077 in leptin action in vivo; signals emanating directly from Jak2 may contribute, as well. We will thus analyze the role of Jak2 and LepRb Tyr1077 in the neural and physiologic actions of leptin by utilizing mouse models in which we have altered LepRb to specifically affect those signals. We will furthermore utilize a set of in vivo systems to define the molecular mediators that lie downstream of Jak2 and/or LepRb Tyr1077 in the regulation of these processes. Overall, these studies will define crucial mediators of leptin action and reveal specific mechanisms by which leptin controls particular physiologic endpoints.