Molecular mechanisms of leptin receptor/Jak2 action

描述（由申请人提供）：该提案题为“Leptin受体/Jak2作用的分子机制”，是DK56731竞争性续期申请。我们之前和未来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Jak2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Jak2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补充。至此，我们定义了LRb/Jak2相互作用的机制，定义了Jak2 Tyr(P)位点的功能，并检测了LepRb Tyr1138AESTAT3信号通路和LepRb Tyr985AESHP2/SOCS3信号通路的生物学特性。最近，我们在LepRb上定义了第三个Tyr(P)位点（Tyr1077），它调节STAT5信号和其他潜在的LepRb信号，并建立了新的小鼠模型来探测Jak2和Tyr1077在体内LepRb作用中的功能。初步数据表明，LepRb磷酸化位点的贡献是大多数已知瘦素作用所必需的，包括一些独立于Tyr1138和Tyr985的作用。相反，Tyr1077对调节血糖控制和潜在的其他生理性瘦素作用至关重要。在各种数据表明瘦素在能量平衡和血糖控制的短期调节中的急性（非转录）作用的重要性的背景下，这些数据提出了LepRb Tyr1077介导瘦素急性作用所需的细胞信号的假设。除了验证这一核心假设外，拟议的研究还将确定瘦素介导各种生理效应的信号和机制，以及瘦素调节血糖水平的信号和机制。我们建议：(1)了解LepRb信号在生理调控中的作用，重点关注Jak2和Tyr1077。(2)在LepRb信号改变的小鼠模型中，明确瘦素介导的神经功能调节。(3)确定LepRb Tyr1077和/或其他Jak2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，并描述每个瘦素信号在瘦素调节神经和生物体生理中的作用。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：瘦素是人体能量稳态和代谢的关键调节因子，瘦素作用受损可能导致多种代谢疾病。因此，了解瘦素作用的分子机制对于我们理解代谢性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，并了解这些信号如何促进瘦素在体内的生理作用。虽然LepRb Tyr1138/STAT3信号通路对长期能量平衡至关重要，但该信号通路无法解释瘦素作用的许多重要方面。LepRb Tyr985在体内介导LepRb的反馈抑制以减弱瘦素的作用，但不能解释瘦素的残留作用。我们正在进行的分析的最新数据表明LepRb Tyr1077在体内瘦素作用中起重要作用；直接从Jak2发出的信号也可能起作用。因此，我们将利用小鼠模型分析Jak2和LepRb Tyr1077在瘦素的神经和生理作用中的作用，我们在小鼠模型中改变了LepRb以特异性影响这些信号。我们将进一步利用一组体内系统来确定Jak2和/或LepRb Tyr1077下游调控这些过程的分子介质。总的来说，这些研究将确定瘦素作用的关键介质，并揭示瘦素控制特定生理终点的具体机制。

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.