Role of FSH in Osreoclast Formation and Function

描述（由申请人提供）：绝经后骨质疏松症是一个全球性的公共卫生问题，几十年来一直仅归因于雌激素水平下降，尽管促卵泡激素（FSH）水平平行急剧上升，但FSH对骨骼的直接影响从未被探索过。FSH的唯一功能是分泌卵巢雌激素。我们推测，除了雌激素下降，FSH通过刺激破骨细胞（骨吸收细胞）导致绝经早期骨量减少。缺乏FSH或其受体的小鼠尽管有严重的性腺功能减退，但不显示高吸收或骨丢失。破骨细胞上的G蛋白偶联FSH受体（FSHR）的体外证据支持FSH具有促吸收作用。FSH还促进破骨细胞前体释放破骨细胞生成细胞因子TNF α，此外，促进破骨细胞存活。从我们的研究中出现的假设，支持在人类骨量和血清FSH之间的紧密相关性，是循环FSH直接刺激骨细胞骨吸收。因此，我们将在特定目标1中研究FSH是否独立于降低的雌激素而导致体内骨丢失。为此，我们将在缺乏两种雌激素受体ER？？-/-的小鼠中给予或过度表达FSH，以及GnRH缺陷型hpg小鼠。我们还将研究是否选择性FSHR删除破骨细胞将防止卵巢切除术诱导的骨丢失，以及是否转基因重建FSHR-/-破骨细胞中的FSHR将恢复再吸收活性。在具体目标2中，我们确定了FSH作用的机制。我们将首先研究FSH诱导TNF α表达的机制，然后使用TNF α-/-小鼠，阐明FSH的整个作用是否是TNF α依赖性的。最后，使用Akt缺陷细胞，我们还将确定FSH的促存活作用是否是Akt介导的。如果FSH在体内被证明是促吸收的，我们设想在不损害卵巢功能的情况下，例如通过单克隆抗体来减弱人类的FSH以获得骨骼优势。后一个前提来自我们的观察，即FSH单倍不足小鼠骨量增加，而卵巢保留。因此，这项工作的意义不仅在于我们挑战了一个典型的范例，雌激素缺乏，作为绝经期骨质流失的充分解释，而且还建立了垂体激素，如FSH，作用于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.