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Mechanisms of Female Germline Stem Cell Senescence

女性生殖干细胞衰老的机制

基本信息

批准号：
7093142
负责人：
Jonathan Lee Tilly
金额：
$ 28.2万
依托单位：
MASSACHUSETTS GENERAL HOSPITAL
依托单位国家：
美国
项目类别：
财政年份：
2004
资助国家：
美国
起止时间：
2004-09-30 至 2008-01-31
项目状态：
已结题

来源：
https://reporter.nih.gov/project-details/7093142
关键词：
aging cell cycle proteins cell proliferation cell senescence female gene expression genetic regulation genetically modified animals germ cells laboratory mouse molecular biology ovary disorder stem cells transcription factor

项目摘要

DESCRIPTION (provided by applicant): Recently, we reported that female mice possess germline stem cells (GSC) that replenish the ovaries with new oocytes during postnatal life. Elimination of GSC with busulfan, a chemical known to impair male GSC and hematopoietic stem cell (HSC) function, results in loss of the primordial follicle pool within 3 weeks. Although busulfan is thought to cause spermatogenic failure by eliminating GSC through cytotoxic actions, no studies have been published that have directly proven this. Indeed, very recently busulfan has been shown to suppress HSC function by inducing premature senescence rather than by activating apoptosis. Further, busulfan-induced 'aging' in HSC was accompanied by increased levels of two proteins linked with replicative senescence, both of which are encoded by the Ink4a locus. Expression of Ink4a is actively repressed in non-senescent cells by the polycomb gene product, Bmi-I. In fibroblasts, Bmi-1 expression is downregulated coincident with senescence, and overexpression of Bmi-I extend replicative lifespan by suppressing Ink4a expression. Studies of Bmi-1 mutant mice have shown that neural and hematopoietic stem cells exhibit a reduced rate of self-renewal. These defects are partially rescued by loss of Ink4a, confirming that the Ink4a locus is a critical target for Bmi-I to maintain replicative potential of stem cells in vivo. We hypothesize that GSC are present and required for regenerating the ovarian follicle pool during prepubertal and reproductive life in the mouse. However, with advancing chronological age female GSC activate a program of replicative senescence involving increased expression of Ink4a, due to a loss of Bmi-I . As a consequence, depletion of follicles through atresia is no longer offset by primordial follicle renewal, ultimately resulting in exhaustion of the follicle reserve and ovarian senescence. To test these hypotheses, the following Specific Aims are proposed: l) to characterize age-related changes in the number and proliferative potential of GSC, as well as in Bmi-I and lnk4a expression, in the mouse ovary from neonatal through reproductive life; 2) to evaluate if mutant mice lacking Bmi-1 possess a reduced follicle reserve due to failed primordial follicle renewal resulting from premature replicative senescence of Bmi-I deficient GSC; and 3) to determine if mutant mice lacking expression of Ink4a gene products exhibit extended ovarian function due to impaired activation of GSC senescence with advancing age.

描述（由申请人提供）：最近，我们报道了雌性小鼠拥有生殖系干细胞（GSC），可以在出生后为卵巢补充新的卵母细胞。用一种已知会损害男性GSC和造血干细胞（HSC）功能的化学物质丁硫丹（busulfan）消除GSC，会导致原始卵泡池在3周内消失。虽然人们认为丁硫丹通过细胞毒性作用消除GSC而导致生精失败，但目前还没有发表的研究直接证明这一点。事实上，最近已经证明，busulfan通过诱导过早衰老而不是激活细胞凋亡来抑制HSC功能。此外，在HSC中，busulan诱导的“衰老”伴随着两种与复制性衰老相关的蛋白质水平的增加，这两种蛋白质都是由Ink4a基因座编码的。在非衰老细胞中，Ink4a的表达被多梳基因产物bmi - 1积极抑制。在成纤维细胞中，Bmi-1表达下调与衰老同时发生，Bmi-1过表达通过抑制Ink4a表达延长复制寿命。对Bmi-1突变小鼠的研究表明，神经和造血干细胞的自我更新速度降低。这些缺陷通过Ink4a的缺失得到部分修复，证实Ink4a位点是bmi - 1在体内维持干细胞复制潜能的关键靶点。我们假设在小鼠的青春期前和生殖期，GSC存在并且是卵巢卵泡池再生所必需的。然而，随着年龄的增长，由于bmi - 1的缺失，女性GSC激活了涉及Ink4a表达增加的复制性衰老程序。因此，通过闭锁的卵泡消耗不再被原始卵泡更新所抵消，最终导致卵泡储备的耗尽和卵巢衰老。为了验证这些假设，我们提出了以下具体目标：1)表征小鼠卵巢中从新生儿到生殖期GSC数量和增殖潜力以及bmi - 1和lnk4a表达的年龄相关变化；2)评估缺乏Bmi-1的突变小鼠是否由于缺乏Bmi-1的GSC过早复制衰老导致原始卵泡更新失败而导致卵泡储备减少；3)确定缺乏Ink4a基因产物表达的突变小鼠是否由于GSC衰老激活受损而表现出卵巢功能延长。