Impact of ageing on the human male germline

近几十年来，父母的年龄一直在稳步增长，特别是在西方社会。虽然女性生殖老龄化得到了更多的关注，但父系老龄化的后果很容易从老年男性后代生育率下降、单胎和复杂疾病发生率增加以及围产期结局较差中观察到。这些不良结果不能仅仅基于男性生殖系中突变率的增加来解释，而可能是由于年龄相关的DNA稳定性变化和精子中的表观遗传标记造成的。为了完全区分年龄和与年龄相关的疾病对男性生殖系的影响，在上一个资助期间，我们建立了健康男性生育和老龄化(FAME)队列，其中包括197名年龄在18岁至84岁之间的男性。我们发现，在这个年龄段，健康的老龄化与良好的生殖健康有关。然而，我们在生殖系中发现了与年龄相关的特定变化，这与体细胞老化明显不同。也就是说，我们发现随着年龄的增长，精子DNA的不稳定性急剧增加，精子DNA甲基化发生了深刻的变化。此外，我们确定了一种代偿机制，允许以通常处于静止状态的储备精原干细胞为代价，维持老年男性的正常精子产生。然而，我们对男性生殖系老化的途径和机制以及它们与老年男性生殖不良结局的关系的了解仍然非常有限。我们假设，为了维持正常的精子产生，老年男性激活了他们生殖系和生殖细胞利基中的分子通路，有利于储备干细胞的激活和增殖，但牺牲了生殖细胞的完整性。在这个项目中，我们的目标是了解人类生殖细胞中衰老的分子标记物，这些标记物最终可能与年长父亲的生殖结果和后代健康有关。我们建议通过评估年龄与人类睾丸的转录漂移、精子的表观遗传漂移(在甲基组水平上)以及男性生殖系中DNA不稳定和DNA断裂的发生之间的关联来解决这个问题。为此，知名度队列发挥了重要作用，因为现在已经通过评估并在参与者最初评估5至6年后从他们那里获取样本来扩大知名度队列。这使得可以纵向分析人类男性生殖系随着年龄的增长而发生的分子变化。使用计划的多层方法，我们将形成一个框架，用于识别与人类男性衰老表型有关的基因和途径，建立一个前所未有的关于年龄对男性生殖系影响的图像。

The age of parents has been steadily increasing in recent decades, especially in western societies. Although female reproductive ageing has received more attention, the consequences of paternal ageing can be readily observed in the reduced fertility rates, increased rates of monogenic and complex disorders and poorer perinatal outcomes in the offspring of older men. These adverse outcomes cannot be explained solely based on an increased mutation rate in the male germline, but likely stem from age-dependent changes in DNA stability and epigenetic marks in sperm. To fully separate the effects of age from those of age-associated morbidities on the male germline, in the previous funding period we established the Fertility and Ageing in Healthy Men (FAMe) cohort, which included 197 men aged 18 to 84 years. We found that healthy ageing was associated with good reproductive health over this age period. However, we found specific age-associated changes in the germline, which are clearly distinguishable from somatic cell ageing. Namely, we found a sharp increase in sperm DNA instability and profound alterations in sperm DNA methylation with increasing age. Moreover, we identified a compensatory mechanism that allows the maintenance of normal sperm production in older men at the expense of usually quiescent reserve spermatogonial stem cells. Nevertheless, our understanding of the pathways and mechanisms involved in male germline ageing and how they relate to poor reproductive outcomes in older men is still very limited. We hypothesize that, in order to maintain normal sperm production, older men activate molecular pathways in their germline and germ cell niche favouring the activation and proliferation of reserve stem cells, at the expense of germ cell integrity. In this project, we aim to understand the molecular markers of ageing in human germ cells, which ultimately might be associated with reproductive outcome and offspring health of older fathers. We propose to address this by evaluating the association between age and transcriptional drift in human testis, epigenetic drift (at methylome level) in sperm, and the DNA instability and occurrence of DNA breaks in the male germline. For this, the FAMe cohort takes an important role, as it has now been extended by evaluating and obtaining samples from the involved participants 5 to 6 years after their original evaluation. This allows longitudinal analyses of molecular changes in the human male germline with increasing age. Using the planned-for multi-layered approach, we will form a framework for the identification of genes and pathways involved in the human male aged phenotype, building an unprecedented image of the effects of age on the male germline.