Role of FSH in Osreoclast Formation and Function

描述(申请人提供)：绝经后骨质疏松症是一个全球性的公共健康问题，几十年来一直被完全归因于雌激素水平的下降，尽管卵泡刺激素(FSH)水平同时急剧上升，但FSH对骨骼的直接影响从未被探索过。卵泡刺激素的唯一功能是分泌卵巢雌激素。我们推测，除了雌激素下降外，FSH还通过刺激破骨细胞(吸收骨的细胞)来推动绝经早期骨量的减少。缺乏FSH或其受体的小鼠，即使性腺严重减退，也不会表现出高吸收或骨丢失。破骨细胞上的G蛋白偶联FSH受体(FSHR)的体外证据支持FSH是促吸收的。FSH还能促进破骨细胞前体释放破骨细胞因子TNFa，此外，还能促进破骨细胞存活。从我们的研究中得出的假说是，循环中的FSH直接刺激破骨细胞性骨吸收，这一假说得到了人类骨量和血清FSH密切相关的支持。因此，我们将在特定的目标1中研究FSH是否会导致体内的骨丢失，而不依赖于雌激素水平的降低。为此，我们将在缺乏两种雌激素受体ER？？-/-的小鼠以及GnRH缺陷的HPG小鼠中应用或过度表达FSH。我们还将研究在破骨细胞中选择性地删除FSHR是否可以防止卵巢切除引起的骨丢失，以及在FSHR-/-破骨细胞中转基因重建FSHR是否可以恢复吸收活性。在特定的目标2中，我们确定了FSH效应的机制。我们将首先研究FSH诱导TNFa表达的机制，然后利用TNFa-/-小鼠，阐明FSH的整个作用是否依赖于TNFa。最后，利用Akt缺陷细胞，我们还将确定FSH的促生存作用是否由Akt介导。如果FSH在体内被证实是促吸收的，我们设想可以在不损害卵巢功能的情况下减轻人类的FSH，使其具有骨骼优势，例如通过单抗。后一个前提来自我们的观察，即小鼠的FSH单倍性不足增加了骨量，而保留了卵巢。因此，这项工作的意义不仅在于我们挑战了雌激素缺乏这一原型范式，将其作为绝经期骨质丢失的完全解释，而且还在于确立了垂体激素，如促卵泡刺激素(FSH)，其作用超出了传统的靶内分泌器官。

DESCRIPTION (provided by applicant): Post-menopausal osteoporosis, a global public health problem, has for decades been attributed solely to declining estrogen levels, and although follicle stimulating hormone (FSH) levels rise sharply in parallel, a direct effect of FSH on the skeleton has never been explored. The only ascribed function of FSH is ovarian estrogen secretion. We speculate that, in addition to declining estrogen, FSH drives the decreases in bone mass during the early menopause by stimulating the osteoclast, the cell that resorbs bone. Mice devoid of FSH or its receptor do not display hyper-resorption or bone loss despite being severely hypogonadal. That FSH is pro-resorptive is supported by in vitro evidence for a G-protein coupled FSH receptor (FSHR) on the osteoclast. FSH also enhances the release of the osteoclastogenic cytokine TNFa from osteoclast precursors, and additionally, promotes osteoclast survival. The hypothesis emerging from our study, supported by the tight correlations between bone mass and serum FSH in humans, is that circulating FSH directly stimulates osteoclastic bone resorption. We will therefore investigate in Specific Aim 1 whether FSH causes bone loss in vivo independently of lowered estrogen. For this, we will administer or over-express FSH in mice lacking the two estrogen receptors, ER??-/-, as well as GnRH-deficient hpg mice. We will also examine whether selective FSHR deletion in the osteoclast will prevent ovariectomy-induced bone loss, and whether transgenic reconstitution of the FSHR in FSHR-/- osteoclasts will restore resorptive activity. In Specific Aim 2 we determine the mechanism of the FSH effect. We will first study the mechanism of FSH-induced TNFa expression, and then, using TNFa-/- mice, elucidate if the entire effect of FSH is TNFa-dependent. Finally, using Akt-deficient cells, we will also determine whether the pro-survival action of FSH is Akt-mediated. If FSH is proven to be pro-resorptive in vivo, we envisage attenuating FSH in humans to a skeletal advantage without compromising ovarian function, for example by a monoclonal antibody. The latter premise arises from our observation that FSH haploinsufficiency in mice increases bone mass, while sparing the ovaries. The significance of this work thus lies not only in our challenging an archetypal paradigm, estrogen deficiency, as being the full explanation for menopausal bone loss, but also in establishing that pituitary hormones, such as FSH, act beyond traditional target endocrine organs.