Depot-specific Adipogenesis in a Novel Mouse Model of Extended Lifespan

描述（由申请人提供）：妊娠相关血浆蛋白-A（PAPP-A）是一种锌金属蛋白酶，发现其在妊娠期外发挥作用，以增强局部胰岛素样生长因子（IGF）的生物利用度。与野生型同窝仔相比，PAPP-A（基因敲除）缺陷小鼠的中位寿命和最长寿命均增加30-40%，没有内分泌异常或热量限制的证据。然而，这种长寿表型的具体机制知之甚少。在初步实验中，我们观察到高脂肪饮食的PAPP-A敲除小鼠对肠系膜脂肪储库（小鼠相当于人类内脏脂肪）中的脂肪积累具有抗性，其中细胞大小显著减小。这些前脂肪细胞是否由于缺乏PAPP-A而降低了IGF-I的生物利用度而没有被刺激分化？还是成熟脂肪细胞抑制了脂质的积累？此外，为什么在全球PAPP-A基因敲除模型中，肠系膜脂肪库的缺陷相对特异？这与PAPP-A的差异表达有关吗？来自人类和非人类灵长类前脂肪细胞的RNA的微阵列分析可能与最后一个问题有关。在这些实验中，PAPP-A是被发现过表达的最独特的基因，其在来自内脏脂肪库的前脂肪细胞中的水平大大超过皮下脂肪中的水平。此外，PAPP-A表达的最有效的刺激物是促炎性的，其与衰老和肥胖两者相关。我们的主要假设是PAPP-A以IGF依赖的方式刺激脂肪形成，并对前脂肪细胞增殖和分化具有储库特异性作用。推论是PAPP-A的抑制将优先在内脏脂肪中调节脂肪形成。这具有潜在的重要性，因为主要的临床后果是内脏脂肪相对于皮下脂肪增加。我们的第二个假设是，即使在高脂肪饮食的动物中，抑制PAPP-A也会延长寿命。具体目标：（1）确定贮库特异性脂肪形成的年龄相关变化和PAPP-A在该调节中的作用，（2）确定喂食高脂肪饮食的PAPP-A敲除小鼠和野生型小鼠的寿命，和（3）确定成年小鼠中条件性PAPP-A基因敲除对贮库特异性脂肪形成和寿命的影响。所有的专业知识和模型系统都在进行这项研究。重要性：这些研究将为脂肪分布和功能的调节提供新的见解，并阐明PAPP-A缺乏促进长寿的机制。影响：我们的研究结果可能对使用PAPP-A作为内脏脂肪积累及其缩短寿命的发病率的预防目标的新策略具有临床意义。

DESCRIPTION (provided by applicant): Pregnancy-associated plasma protein-A (PAPP-A) is a zinc metalloprotease that was discovered to function outside of pregnancy to enhance local insulin-like growth factor (IGF) bioavailability. Mice deficient in PAPP-A (gene knock-out) have a 30-40% increase in both median and maximum lifespan compared to wild-type littermates, without evidence of endocrine abnormalities or caloric restriction. However, the particular mechanisms underlying this longevity phenotype are poorly understood. In preliminary experiments, we observed that PAPP-A knock-out mice on a high fat diet were resistant to fat accumulation in the mesenteric fat depot (mouse equivalent to human visceral fat) where there was a significant reduction in cell size. Were these pre-adipocytes that were not being stimulated to differentiate due to decreased IGF-I bioavailability in the absence of PAPP-A? Or was there suppressed lipid accumulation by mature adipocytes? Moreover, why was the defect relatively specific for the mesenteric fat depot in the global PAPP-A knock-out model? Did it have anything to do with differential PAPP-A expression? Micro-array analyses of RNA from human and non-human primate pre-adipocytes may be relevant to the last question. In these experiments, PAPP-A was the most distinctive gene found to be overexpressed, with levels in pre-adipocytes from visceral fat depots greatly exceeding those in subcutaneous fat. Furthermore, the most potent stimulators of PAPP-A expression are pro- inflammatory, which are associated with both aging and obesity. Our primary hypothesis is that PAPP-A stimulates adipogenesis in an IGF-dependent manner and with depot-specific effects on pre-adipocyte proliferation and differentiation. The corollary is that inhibition of PAPP-A will moderate adipogenesis preferentially in visceral fat. This has potential importance since major clinical consequences occur with increased visceral fat relative to subcutaneous fat. Our secondary hypothesis is that inhibition of PAPP-A will prolong lifespan even in animals on a high fat diet. Specific Aims: (1) Determine age-related changes in depot- specific adipogenesis and the role of PAPP-A in this regulation, (2) Determine the lifespan of PAPP-A knock- out and wild-type mice fed a high fat diet, and (3) Determine the effect of conditional PAPP-A gene knock-out in adult mice on depot-specific adipogenesis and lifespan. All expertise and model systems are in hand to conduct this research. Significance: These studies will provide new insight into regulation of fat distribution and function and elucidate mechanisms by which PAPP-A deficiency promotes longevity. Impact: Our findings could have clinical implications for novel strategies using PAPP-A as a preventive target for visceral fat accumulation and its life-shortening morbidities.