Sperm microRNA Content Is Altered in a Mouse Model of Male Obesity, but the Same Suite of microRNAs Are Not Altered in Offspring’s Sperm

The prevalence of obesity is increasing worldwide and has tripled in men of reproductive age since the 1970s. Concerningly, obesity is not only comorbid with other chronic diseases, but there is mounting evidence that it increases the non-communicable disease load in their children (eg mortality, obesity, autism). Animal studies have demonstrated that paternal obesity increases the risk of metabolic (eg glucose metabolism defects, obesity) and reproductive disorders in offspring. Epigenetic changes within sperm are clear mechanistic candidates that are associated with both changes to the father’s environment and offspring phenotype. Specifically there is emerging evidence that a father’s sperm microRNA content both responds to paternal environmental cues and alters the gene expression profile and subsequent development of the early embryo. We used a mouse model of high fat diet (HFD) induced obesity to investigate whether male obesity could modulate sperm microRNA content. We also investigated whether this alteration to a father’s sperm microRNA content lead to a similar change in the sperm of male offspring. Our investigations were initially guided by a Taqman PCR array, which indicated the differential abundance of 28 sperm borne microRNAs in HFD mice. qPCR confirmation in a much larger cohort of founder males demonstrated that 13 of these microRNAs were differentially abundant (11 up-regulated; 2 down-regulated) due to HFD feeding. Despite metabolic and reproductive phenotypes also being observed in grand-offspring fathered via the male offspring lineage, there was no evidence that any of the 13 microRNAs were also dysregulated in male offspring sperm. This was presumably due to the variation seen within both groups of offspring and suggests other mechanisms might act between offspring and grand-offspring. Thus 13 sperm borne microRNAs are modulated by a father’s HFD and the presumed transfer of this altered microRNA payload to the embryo at fertilisation potentially acts to alter the embryonic molecular makeup post-fertilisation, altering its growth trajectory, ultimately affecting adult offspring phenotype and may contribute to paternal programming.

全球肥胖患病率持续攀升，自20世纪70年代以来，育龄男性的肥胖率已增长至原先的三倍。值得警惕的是，肥胖不仅与多种慢性疾病共病，越来越多的研究证据表明，肥胖会增加其子女罹患非传染性疾病的风险，例如死亡、肥胖症以及孤独症。动物实验已证实，父代肥胖会增加子代发生代谢紊乱（如葡萄糖代谢异常、肥胖）与生殖功能障碍的风险。精子内的表观遗传改变是连接父代环境变化与子代表型异常的明确潜在机制靶点。具体而言，越来越多的新证据表明，父代精子中的微小RNA（microRNA）含量不仅会响应父代的环境信号，还会改变早期胚胎的基因表达谱与后续发育进程。本研究采用高脂饮食（high fat diet, HFD）诱导的肥胖小鼠模型，探究雄性肥胖是否会调控精子中的微小RNA含量。同时，本研究还探究了父代精子微小RNA含量的改变，是否会在其子代雄性个体的精子中产生类似的变化。本研究最初通过Taqman聚合酶链式反应（PCR）芯片开展预实验，结果显示高脂饮食小鼠的精子中存在28种差异表达的微小RNA。随后，在更大规模的初代雄性小鼠队列中通过实时定量PCR（qPCR）验证发现，其中13种微小RNA的表达丰度因高脂饮食喂养发生显著改变（11种上调，2种下调）。尽管通过雄性子代谱系繁育的孙代个体中同样观察到了代谢与生殖相关的表型异常，但未发现上述13种微小RNA在子代雄性个体的精子中存在表达失调的情况。这一现象可能源于两组子代个体间存在的个体差异，同时也提示在子代与孙代之间可能存在其他表观遗传调控机制发挥作用。综上，父代高脂饮食会调控13种精子源性微小RNA的表达；受精时，这种改变的微小RNA负载被传递至胚胎，可能会改变受精后胚胎的分子组成，进而改变其生长轨迹，最终影响成年子代表型，这或许是父系表观遗传程序化调控的重要机制之一。