XCI and sex-biased expression in AT2 cells. XCI and sex-biased expression in AT2 cells

Significant sex differences exist for many lung pathologies, including SARS-CoV-2 related disease (COVID-19) and pulmonary fibrosis, but the mechanistic basis for this remains unclear. Notably, Ace2, the gene encoding angiotensin-converting enzyme 2, an enzyme that plays multiple roles in SARS-CoV-2 pathogenesis, including acting as the major viral receptor, is localized on the X-chromosome. Moreover, prior work in fibroblasts suggested that Ace2 may escape X-Chromosome Inactivation (XCI), which normalizes X-lined gene expression between sexes. Alveolar type 2 cells (AT2s), which play a key role in alveolar lung regeneration, express Ace2, suggesting that aberrant XCI in AT2s could potentially impact sex-biased lung pathology. To that end, we performed RNA-seq on AT2 cells isolated from 4 male and 4 female F1 mus/cast mice. Utilizing allele-specific transcriptomics, we demonstrate that about 50% of expressed X-linked genes in mouse AT2s, including Ace2, escape XCI, the highest levels reported to date. Moreover, we observe dramatic genome-wide expression differences between male and female AT2s, likely influencing both lung physiology and pathophysiologic responses. Taken together, these studies support a renewed focus on AT2s as potential contributor to sex-biased differences in lung disease. Overall design: Comparative gene expression profiling analysis of RNA-seq data for Alveolar Type 2 (AT2) cells from 4 male and 4 female F1 mus/cast mice.

多种肺部病变均存在显著的性别差异，包括与严重急性呼吸综合征冠状病毒2（SARS-CoV-2）相关的疾病（COVID-19）以及肺纤维化，但其潜在的分子机制仍未阐明。值得注意的是，编码血管紧张素转换酶2（Angiotensin-converting enzyme 2，ACE2）的基因Ace2定位于X染色体；该酶在SARS-CoV-2的致病过程中发挥多重作用，包括作为病毒的主要受体。此外，此前在成纤维细胞中的研究表明，Ace2可能逃避X染色体失活（X-Chromosome Inactivation，XCI）——后者可平衡两性间的X连锁基因表达水平。肺泡Ⅱ型细胞（Alveolar type 2 cells，AT2s）在肺泡肺组织再生中发挥关键作用，且表达Ace2，这提示AT2s中异常的XCI可能会影响性别偏向性肺部病变的发生。鉴此，我们对从4只雄性和4只雌性F1 mus/cast小鼠中分离得到的AT2细胞开展了RNA-seq分析。通过等位基因特异性转录组学技术，我们证实小鼠AT2中约50%的表达X连锁基因（包括Ace2）可逃避XCI，这是目前已报道的最高逃逸水平。此外，我们还观察到雄性与雌性AT2之间存在显著的全基因组表达差异，这可能同时影响肺部生理与病理生理应答。综上，本研究支持将AT2作为肺部疾病性别偏向性差异的潜在贡献因素，重新予以关注。整体实验设计：对来自4只雄性和4只雌性F1 mus/cast小鼠的肺泡Ⅱ型细胞（AT2s）的RNA-seq数据进行比较基因表达谱分析。