Leptin Production and Action in Adipocytes

描述（由申请人提供）：瘦素在调节全身能量平衡中起关键作用。这种激素在向中枢神经系统发送外周脂肪储存状态的信号以及调节能量摄入和消耗方面的作用已得到充分证明。本提案的目标是解决瘦素生物学中两个定义不太明确但关键相关的方面。具体目的一：探讨瘦素基因表达、脂肪细胞大小和脂肪细胞代谢状态密切相关的分子机制。具体目的II是研究瘦素直接作用对脂肪细胞代谢和基因表达的长期影响，以及瘦素在脂肪细胞中的直接作用对全身能量稳态的贡献。在Specific Aim I中，正在测试的假设是，脂肪细胞的代谢状态是瘦素基因表达的主要决定因素，这是一种统一的机制，负责在进食状态（长期能量平衡）和禁食状态（短期能量平衡）的脂肪细胞大小信号。脂肪细胞的代谢状态将通过营养、药理学和分子遗传学工具进行调控，并确定瘦素基因表达与脂肪细胞代谢状态和大小之间的关系。将确定负责调节瘦素基因表达的代谢中间体，以反映脂肪细胞大小和急性全身热量平衡的变化。在Specific Aim II中，正在验证的假设是瘦素在脂肪细胞中的直接作用在调节脂肪细胞局部代谢和基因表达方面发挥重要作用。瘦素的这种局部作用可能影响体脂分布和脂肪细胞功能的储存库特异性差异。脂肪细胞前植入系统将用于研究瘦素在体内对局部脂肪细胞功能的直接作用。腺病毒介导的基因转移将用于改变培养的前脂肪细胞中瘦素受体的功能或瘦素产生的速度，然后将其植入胸腺裸鼠。这些修饰对来自这些移植前脂肪细胞的成熟脂肪细胞的脂肪细胞功能（代谢和分泌蛋白的表达）的影响将被确定。在组织特异性转基因小鼠模型中，瘦素的直接作用对解剖学上不同脂肪库中脂肪细胞功能的影响也将被研究。更好地了解脂肪细胞对全身能量平衡变化的瘦素产生的调节，将为预防节食或减肥引起的瘦素产生减少提供基础，从而阻断干扰临床减肥成功的反馈调节机制。研究瘦素直接作用在调节脂肪细胞局部功能中的作用，将有助于深入了解机体脂肪分布调控的机制和分子，以及脂肪细胞代谢的储存库特异性差异的形成，并为腹部肥胖及其代谢合并症（如胰岛素抵抗、血脂异常、高血压、糖尿病和心血管疾病）的预防和治疗提供依据。

DESCRIPTION (provided by applicant): Leptin plays a critical role in regulating systemic energy balance. This hormone's role in signaling the status of peripheral fat stores to the central nervous system, and in regulating energy intake and expenditure are well documented. The goal of this proposal is to address two less-well defined, but critically related, aspects of the biology of leptin. Specific Aim I is to investigate the molecular mechanisms responsible for the close correlation between leptin gene expression, adipocyte size and the metabolic status of adipocytes. Specific Aim II is to investigate the long-term effects of direct leptin action on metabolism and gene expression in adipocytes, and the contribution of direct leptin action in adipocytes to systemic energy homeostasis. In Specific Aim I, the hypothesis being tested is that the metabolic status of adipocytes is a primary determinant of leptin gene expression, a unifying mechanism responsible for signaling adipocyte size in fed states (long term energy balance) and acute caloric deficit in fasting states (short-term energy balance). The metabolic status of adipocytes will be manipulated using nutritional, pharmacological and molecular genetic tools, and the effects of such manipulations on relationships of leptin gene expression with the metabolic status and size of adipocytes will be determined. Metabolic intermediates responsible for regulating leptin gene expression to reflect changes in adipocyte size and acute systemic caloric balance will be identified. In Specific Aim II, the hypothesis being tested is that direct leptin actions in adipocytes play a significant role in regulating local adipocyte metabolism and gene expression. Such local action of leptin may affect body fat distribution and depot-specific differences in adipocyte functions. A preadipocyte implantation system will be used to study direct leptin actions on local adipocyte functions in vivo. Adenovirus-mediated gene transfer will be used to modify leptin receptor function or the rate of leptin production in cultured preadipocytes, which will then be implanted in athymic nude mice. The effects of these modifications on adipocyte functions (metabolism and expression of secreted proteins) in the mature adipocytes derived from these implanted preadipocytes will be determined. The effects of direct leptin actions on the adipocyte functions in anatomically distinct fat depots will also be investigated in tissue-specific transgenic mouse models. A better understanding of the regulation of leptin production in adipocytes in response to changes in systemic energy balance will provide a basis for preventing the decrease of leptin production induced by dieting or weight loss, thus blocking a feedback regulatory mechanism that interferes with success in clinical weight loss efforts. The work on the role of direct leptin actions in regulating local adipocyte functions will provide insights into the mechanisms and molecules involved in the regulation of body fat distribution and development of depot-specific differences in adipocyte metabolism, and provide a basis for rationalizing the prevention and treatment of abdominal obesity and its metabolic co-morbidities, such as insulin resistance, dyslipidemia, hypertension, diabetes and cardiovascular diseases.