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

描述（由申请方提供）：依据：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）的代谢作用与胰岛素相似。据报道，GH和IGF-I对胰腺2细胞质量、心血管性能、骨重建和免疫功能也有积极影响。因此，预计随着年龄的增长观察到的循环GH/IGF-I水平的下降在各种年龄相关疾病的病理生理学和进展中发挥作用，包括肥胖症/糖尿病、肌肉减少症、心肌病和骨质疏松症。尽管GH/IGF-I对成人有潜在的积极影响，但也有证据表明GH/IGF-I会加剧癌症并缩短寿命。因此，在正常衰老中观察到的GH/IGF-I下降实际上可能是一种保护机制。问题：很难准确确定GH在成人生理学中的重要性，因为我们的大部分知识来自人类和啮齿动物模型：1）发育性GH缺乏症，可能与性成熟后导致GH缺乏症的模型不同; 2）成人发作性GH缺乏症，通常与全垂体功能减退症相关。由于这些原因，成人发病，孤立的GH缺乏症（AOiGHD）的模型将是一个独特的和信息丰富的工具，更准确地定义内源性GH在年龄相关的健康和疾病的变化的重要性。解决方法：我们的实验室最近开发并验证了一种转基因小鼠系，表达Cre重组酶（Cre）的生长激素产生细胞（生长激素）的垂体前叶（rGHp-Cre）。rGHp-Cre小鼠代表了研究生长激素功能的各个方面的通用工具，因为它可以与携带基因工程等位基因的小鼠杂交，所述基因工程等位基因含有侧翼有称为loxP位点的独特Cre识别序列的关键DNA元件;从而仅在垂体前叶的生长激素群体中允许Cre介导的这些基因的改变（激活或失活）。为了产生成年发作的、孤立的GH缺乏症的模型，将rGHp-Cre小鼠与携带Cre诱导型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，双转基因后代（Cre，iDTR）正常。在性成熟后，这些小鼠注射低剂量的白喉毒素（DT），其结合在生长激素上表达的DTR，允许毒素的内化和随后的生长激素群体的凋亡，导致AOiGHD。具体目标：一。完成对DT处理的Cre、iDTR雄性和雌性“部分”AOiGHD成年小鼠的组织分析，以a）确认生长激素破坏的特异性，和B）提供GH/IGF-I减少对代谢基因表达影响的初步评估。二.测试替代策略以最大化DT介导的生长激素破坏，以实现“完全”AOiGHD的模型，III.提供AOiGHD对代谢终点影响的更详细体内分析。四.评估AOiGHD对寿命的影响。公共卫生相关性：该提案将描述一种新的成年发病的孤立GHD小鼠模型（AOiGHD），并研究AOiGHD对身体组成，代谢和寿命的影响。这个模型将提供一个独特的和翔实的工具，更准确地定义内源性生长激素的重要性，在年龄相关的健康和疾病的变化。

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.