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. Liver transcriptomic profiles from 110d and 650d male and female Wistar rats were analyzed by RNA-seq. 24 samples, 6 animals per group: 1) 110 d MALE n=6, 2) 650d MALE,n=6; 3) 110d FEMALE, n=6 and 4) 650d FEMALE n=6

【引言】在分子水平上，细胞衰老涉及多条基因通路的改变，进而催生多种衰老表型。在肝脏组织中，衰老相关变化会导致肝功能受损。我们提出假说：自然肝脏衰老过程由性别依赖的分子机制所驱动。【研究目的】本研究采用已成熟的衰老模型开展实验，该模型此前已被用于阐明代谢、生殖及内分泌系统的衰老特征。我们对110日龄与650日龄的雌雄大鼠进行了肝脏转录组学（RNA-seq）分析，所有受试大鼠均饲喂正常大鼠饲料，旨在明确与衰老过程相关的关键信号通路的变化情况。【研究方法】为探究自然衰老过程引发的F1代肝脏功能性变化，我们分别评估了雄性与雌性大鼠在650日龄与110日龄时的差异表达基因（differentially expressed genes, DEGs），并基于组间显著差异开展了独立的两两比较。基因筛选标准为折叠变化（fold change, FC）≥1.4，且名义P值<0.05（学生t检验）。【研究结果】我们发现自然肝脏衰老过程存在显著的性别差异。RNA-seq分析显示，在所研究的110日龄至650日龄阶段，雄性大鼠的差异表达基因（3967个）数量多于雌性大鼠（283个），相关信号通路也更为丰富。雄性大鼠的细胞周期信号通路伴随关键基因（CDK2、CDK4、Cycd及PCNA）的蛋白与基因表达水平下调，且在650日龄时，p57的表达水平相较于110日龄出现显著升高。在雌性大鼠中，抑制细胞周期G1期进展的细胞生长调节因子（如p15与p21）的蛋白与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中表现出明显的性别二态性。【结论】本研究结果证实，自然衰老过程以性别依赖的方式影响肝脏转录组特征，这种影响尤其体现在细胞周期与细胞衰老通路中——这两类通路在衰老诱导的肝脏疾病发生发展过程中发挥关键作用。阐明自然衰老过程中的细胞衰老通路，将有助于评估与衰老进程及虚弱轨迹改变相关的潜在机制。本研究通过RNA-seq分析了110日龄与650日龄的雌雄Wistar大鼠的肝脏转录组图谱。实验共包含24个样本，每组6只动物：1）110日龄雄性大鼠（n=6）；2）650日龄雄性大鼠（n=6）；3）110日龄雌性大鼠（n=6）；4）650日龄雌性大鼠（n=6）