Liver sexual dimorphism in key signaling pathways across the rat life course

Introduction: At the molecular level, cellular aging involves changes in multiple gene pathways, which can produce many aging phenotypes. In the liver, senescence changes lead to impaired hepatic function. We hypothesized that the natural hepatic aging process is driven by sex-dependent mechanisms. Purpose: We studied our well-established model of aging in which we have previously determined aging of metabolism, reproduction and endocrine systems. We performed liver transcriptomics (RNA-seq) on male and female rats at 110 and 650 days (d) fed with normal rat chow to determine changes key signaling pathways related to senescence processes. Methods: To identify the functional F1 liver changes due to natural aging processes, we evaluated the differentially expressed genes (DEGs) between 650d and 110d in males and females, with separate pairwise comparisons due to the marked differences. Genes were filtered based on ?1.4 fold change (FC) and nominal P value <0.05 (Studentｴs t-test). Results: We found that the natural liver aging process shows sex-differences. RNA-seq revealed more male (3,967) than female (283) differentially expressed genes (DEG) and pathways over the 110d to 650d period studied. Cell cycle pathway signaling in males was accompanied by decreased protein and gene expression of key genes (CDK2, CDK4, Cycd and PCNA) and an increase of p57 at 650d vs. 110d. In females, protein and gene expression of cell growth regulators such as p15 and p21, that inhibit cell cycle G1 progression were increased. Moreover, additionally the cell senescence pathway showed sexual dimorphism in liver gene regulation. Conclusions: Our results demonstrate how the natural aging process affects the liver transcriptome signature in a sex-dependent manner, specifically in cell cycle and cell senescence pathways, pathways that contribute in a major fashion to the development of aging-induced liver diseases. Understanding cellular senescence pathways involved in the natural aging process will aid evaluation of mechanisms associated with altered aging and frailty trajectories.引言：在分子层面，细胞衰老涉及多条基因通路的改变，进而催生诸多衰老表型。在肝脏中，衰老相关变化会导致肝功能受损。我们提出假说：肝脏的自然衰老过程由性别依赖型机制驱动。 研究目的：我们采用已成熟的衰老模型开展研究——此前我们已借助该模型明确了代谢、生殖及内分泌系统的衰老情况。我们对正常饲料喂养的110日龄与650日龄雌雄大鼠进行肝脏转录组（RNA-seq）测序，以解析与衰老过程相关的关键信号通路变化。 研究方法：为识别自然衰老过程引发的功能性F1肝脏改变，我们分别对雄性与雌性大鼠中650日龄与110日龄的样本进行差异表达基因（differentially expressed genes, DEGs）分析，鉴于二者存在显著差异，故采用独立的两两比较策略。基因筛选标准为倍数变化（fold change, FC）≥1.4且名义P值<0.05（学生t检验，Student's t-test）。 研究结果：我们发现肝脏自然衰老过程存在性别差异。RNA-seq结果显示，在本次研究的110日龄至650日龄阶段，雄性大鼠的差异表达基因（3967个）与显著富集通路数量均多于雌性大鼠（283个）。雄性大鼠的细胞周期通路信号伴随关键基因（CDK2、CDK4、Cycd及PCNA）的蛋白与基因表达水平下调，且650日龄时p57的表达水平较110日龄有所升高。雌性大鼠中，抑制细胞周期G1期进展的细胞生长调节因子如p15与p21的蛋白及基因表达水平均出现上调。此外，细胞衰老通路在肝脏基因调控层面同样表现出性别二态性。 研究结论：本研究结果证实，自然衰老过程会以性别依赖的方式影响肝脏转录组特征，尤其体现在细胞周期与细胞衰老通路中——这两类通路在衰老相关肝脏疾病的发生发展中发挥核心作用。明确自然衰老过程中涉及的细胞衰老通路，将有助于解析衰老进程改变与衰弱轨迹相关的机制。