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，几十年来一直认为雌激素水平下降是唯一的原因，尽管促卵泡激素（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。FSH的唯一功能是卵巢雌激素分泌。我们推测，除了雌激素下降外，FSH还通过刺激破骨细胞（一种吸收骨骼的细胞），在更年期早期导致骨量减少。缺乏FSH或其受体的小鼠尽管性腺功能严重低下，但不会表现出过度吸收或骨质流失。破骨细胞上g蛋白偶联FSH受体（FSHR）的体外证据支持FSH具有促进骨吸收的作用。FSH还能促进破骨细胞前体中破骨细胞因子TNFa的释放，并促进破骨细胞的存活。在我们的研究中，骨量和血清促卵泡刺激素之间的紧密相关性支持了我们的假设，即循环的促卵泡刺激素直接刺激破骨细胞骨吸收。因此，我们将在Specific Aim 1中研究FSH是否独立于雌激素降低而导致体内骨质流失。为此，我们将在缺乏雌激素受体（ER??）的小鼠中施用或过度表达FSH。-/-，以及缺乏gnrh的hpg小鼠。我们还将研究破骨细胞中FSHR的选择性缺失是否会防止卵巢切除引起的骨丢失，以及FSHR-/-破骨细胞中FSHR的转基因重组是否会恢复骨吸收活性。在特异性目标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，使用TNFa-/-小鼠，阐明FSH的整个作用是否依赖于TNFa。最后，使用缺乏akt的细胞，我们还将确定FSH的促生存作用是否由akt介导。如果FSH在体内被证明具有促进吸收的作用，我们设想在不损害卵巢功能的情况下，通过单克隆抗体等方法，在人体中降低FSH对骨骼有利。后一个前提源于我们的观察，即小鼠FSH单倍体不足会增加骨量，同时保留卵巢。因此，这项工作的意义不仅在于我们挑战了雌激素缺乏作为绝经期骨质流失的完整解释的原型范式，而且还在于确立了垂体激素，如FSH，在传统的目标内分泌器官之外起作用。

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.