Mouse model of adult-onset, isolated, GH-deficiency

描述（由申请人提供）：理由：在成人中，生长激素（GH）已被证明具有抗脂肪生成、促脂肪分解和蛋白质合成代谢作用，而胰岛素样生长因子I （IGF-I）的代谢作用类似于胰岛素。据报道，生长激素和igf - 1对胰腺2细胞质量、心血管功能、骨重塑和免疫功能也有积极作用。因此，随着年龄的增长，循环GH/IGF-I水平的下降被预测在各种年龄相关疾病的病理生理和进展中发挥作用，包括肥胖/糖尿病、肌肉减少症、心肌病和骨质疏松症。尽管生长激素/ igf - 1对成人有潜在的积极作用，但也有证据表明生长激素/ igf - 1会加剧癌症并缩短寿命。因此，在正常衰老过程中观察到的GH/ igf - 1的下降实际上可能是一种保护机制。问题：很难准确地确定生长激素在成人生理学中的重要性，因为我们的大部分知识都来自人类和啮齿动物模型：1)发育性GH缺乏，这可能与性成熟后发生的GH缺乏不同；2)成人发病的GH缺乏，这通常与全垂体功能减退症有关。由于这些原因，成人发病的孤立GH缺乏症（AOiGHD）模型将是一种独特的信息工具，可以更准确地定义内源性GH在年龄相关的健康和疾病变化中的重要性。解决方案：我们的实验室最近开发并验证了一种转基因小鼠系，该小鼠系在垂体前叶（rGHp-Cre）的gh产生细胞（somatotropes）中表达Cre重组酶（Cre）。rGHp-Cre小鼠代表了一种多功能工具，可以研究生长性状功能的各个方面，因为它可以与携带基因工程等位基因的小鼠杂交，这些等位基因含有由独特的Cre识别序列（称为loxP位点）组成的关键DNA元件；因此，cre介导的这些基因的改变（激活或失活）仅在垂体前叶的生长性状群体中发生。为了产生成年发病的分离gh缺乏模型，将rGHp-Cre小鼠与携带re诱导白喉毒素受体转基因（iDTR）的现有小鼠模型杂交。初步结果表明，双转基因子代（Cre、iDTR）正常。性成熟后，这些小鼠被注射低剂量的白喉毒素（DT），该毒素与生长斜体上表达的DTR结合，允许毒素内化和随后的生长斜体细胞凋亡，导致AOiGHD。具体目的：1 .完成对经dt处理的“部分”AOiGHD的Cre、iDTR雄性和雌性成年小鼠的组织分析，以便a)确认生长激素破坏的特异性，b)初步评估GH/IGF-I减少对代谢基因表达的影响。2。测试替代策略，以最大限度地发挥dt介导的生长斜体破坏，以实现“完全”AOiGHD模型，III。提供AOiGHD对代谢终点影响的更详细的体内分析。评估AOiGHD对寿命的影响。公共卫生相关性：本提案将描述一种新的成年发病的孤立性GHD （AOiGHD）小鼠模型，并研究AOiGHD对身体成分、代谢和寿命的影响。该模型将为更准确地定义内源性生长激素在与年龄相关的健康和疾病变化中的重要性提供一个独特的信息工具。

DESCRIPTION (provided by applicant): Rationale: In adults, growth hormone (GH) has been shown to have anti-lipogenic, pro-lipolytic and protein anabolic effects, while the metabolic actions of insulin-like growth factor I (IGF-I) resemble those of insulin. GH and IGF-I are also reported to have positive effects on pancreatic 2-cell mass, cardiovascular performance, bone remodeling and immune function. Therefore, the fall in circulating GH/IGF-I levels observed with age is predicted to play a role in the pathophysiology and progression of a variety of age-associated diseases including obesity/diabetes, sarcopenia, cardiomyopathy and osteoporosis. Despite the potential positive effects of GH/IGF-I in adults, there is also evidence that GH/IGF-I can exacerbate cancer and reduce lifespan. Therefore the fall in GH/IGF-I observed with normal aging might, in fact, serve a protective mechanism. Problem: It is difficult to accurately determine the importance of GH in adult physiology because the bulk of our knowledge has been derived from humans and rodent models of 1) developmental GH-deficiency, which may differ from that resulting in GH-deficiency occuring after sexual maturation and 2) adult-onset, GH- deficiency, which is typically associated with panhypopituitarism. For these reasons, a model of adult-onset, isolated GH-deficiency (AOiGHD) would be a unique and informative tool to more accurately define the importance of endogenous GH in age-associated changes in health and disease. Solution: Our laboratory has recently developed and validated a transgenic mouse line that expresses Cre recombinase (Cre) in the GH-producing cells (somatotropes) of the anterior pituitary gland (rGHp-Cre). The rGHp-Cre mouse represents a versatile tool to study various aspects of somatotrope function in that it can be crossbred to mice carrying genetically engineered alleles that contained critical DNA elements flanked by unique Cre recognition sequences referred to as loxP sites; thereby allowing for the Cre-mediated alteration of these genes (activation or inactivation) only in the somatotrope population of the anterior pituitary gland. To generate a model of adult-onset, isolated, GH-deficiency, the rGHp-Cre mice have been crossbred to an existing mouse model carrying a Cre-inducible diphtheria toxin receptor transgene (iDTR). Preliminary results demonstrate that the double transgenic offspring (Cre,iDTR) are normal. After sexual maturation, these mice were injected with a low dose of diphtheria toxin (DT), which binds to the DTR expressed on somatotropes allowing for internalization of the toxin and subsequent apoptosis of the somatotrope population, resulting in AOiGHD. Specific Aims: I. Finalize the analysis of tissues taken from DT-treated Cre,iDTR male and female adult mice with "partial" AOiGHD, in order to a) confirm the specificity of somatotrope destruction, and b) provide an initial assessment of the impact of GH/IGF-I reduction on metabolic gene expression. II. Test alternative strategies to maximize DT-mediated somatotrope destruction, to achieve a model of "complete" AOiGHD, III. Provide a more detailed in vivo analysis of the impact of AOiGHD on metabolic endpoints. IV. Assess the impact of AOiGHD on lifespan. PUBLIC HEALTH RELEVANCE: This proposal will characterize a novel mouse model of adult-onset, isolated GHD (AOiGHD) and examine the effect of AOiGHD on body composition, metabolism and longevity. This model will provide a unique and informative tool to more accurately define the importance of endogenous GH in age-associated changes in health and disease.