Mechanisms of Female Germline Stem Cell Senescence

女性生殖干细胞衰老的机制

• 批准号: 6847621
• 负责人: Jonathan Lee Tilly
• 金额: $ 28.82万
• 依托单位: MASSACHUSETTS GENERAL HOSPITAL
• 依托单位国家: 美国
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-09-30 至 2007-07-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6847621
• 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

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(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)，在出生后生活中用新的卵母细胞补充卵巢。用白消丹清除GSC，一种已知会损害男性GSC和造血干细胞(HSC)功能的化学物质，会在3周内导致原始卵泡池的丧失。尽管白丹被认为通过细胞毒作用消除GSC而导致生精功能障碍，但还没有发表直接证明这一点的研究。事实上，最近有研究表明，白花丹通过诱导HSC过早衰老而不是通过激活细胞凋亡来抑制HSC的功能。此外，丁硫丹诱导的HSC“衰老”伴随着与复制衰老相关的两种蛋白质水平的增加，这两种蛋白质都由INK4A基因编码。在非衰老细胞中，Ink4a的表达受到多梳基因产物BMI-I的积极抑制。在成纤维细胞中，BMI-1的表达下调与衰老一致，BMI-I的过表达通过抑制Ink4a的表达来延长复制寿命。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率降低。Ink4a的缺失部分挽救了这些缺陷，证实了Ink4a基因是BMI-I在体内维持干细胞复制能力的关键靶点。我们假设，在小鼠的青春期前和生殖期间，GSC存在，并且是再生卵泡池所必需的。然而，随着年龄的增长，女性GSC启动了一个复制衰老程序，由于BMI-I的丢失，Ink4a的表达增加。因此，闭锁导致的卵泡衰竭不再被原始卵泡的更新所抵消，最终导致卵泡储备的耗尽和卵巢的衰老。为了验证这些假说，提出了下列具体目标：L)表征从新生到生殖生命，小鼠卵巢中GSC数量和增殖能力以及Bmi-I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Bmi-I缺陷的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；以及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延长的卵巢功能。