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Activation of alveolar epithelial ER stress by b-coronavirus infection disrupts surfactant homeostasis in mice: implications for COVID-19 respiratory failure

ABSTRACT: Covid-19 syndrome is characterized by an acute lung injury phenotype marked by hypoxemic respiratory failure and high mortality. Alveolar Type 2 (AT2) cells are essential for gas exchange, repair, and regeneration of distal lung epithelium. We have shown that the causative agent, SARS-CoV-2 and other members of the b coronavirus genus induces an ER stress response in vitro however the consequences for host AT2 cell function in vivo are less understood. To study this, two murine models of coronavirus infection were employed– mouse hepatitis virus-1 (MHV-1) in A/J mice and a C57BL6/j adapted SARS-CoV-2 strain. MHV-1 infected mice exhibited dose-dependent weight loss through Day 8 (8dpi) with histological evidence of distal lung injury accompanied by elevated BALF cell counts and total protein. AT2 cells isolated at 4dpi and 8dpi showed evidence of both viral infection and increases in Bip /GRP78 expression, consistent with activation of the unfolded protein response (UPR). AT2 UPR signaling included elevations in spliced XBP-1 indicating activation of IRE1a signaling as well as a biphasic response in PERK signaling mark by phosphorylated eIF2a protein levels and expression of Atf4, Ppp1r15a, and Ddit3. Viral UPR activation was accompanied by marked reductions in AT2 and BALF surfactant protein (SP-B, SP-C) content, increases in surfactant surface tension, and emergence of a re-programmed epithelial cell population (Krt8+, Cldn4+, and Gdf15+) which was attenuated by treatment with the IRE1a inhibitor OPK711. As proof-of-concept, C57BL6 mice infected with mouse-adapted SARS-CoV-2 demonstrated similar lung injury and evidence of disrupted surfactant homeostasis. We conclude that hypoxic respiratory failure from b-coronavirus infection results from an aberrant AT2 cell host response activating multiple ER stress pathways, altering surfactant metabolism / function, and changing AT2 endophenotypes offering a mechanistic link between SARS-CoV-2 infection, AT2 cell biology, and hypoxemic respiratory failure.

ORGANISM(S): Mus musculus

PROVIDER: GSE244820 | GEO | 2024/06/27

REPOSITORIES: GEO

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Project description:The coronavirus disease 2019 (COVID-19) pandemic has affected nearly 700 million and claimed more than 6 million lives. However, the large heterogeneity in disease susceptibility and severity of illness (SOI) remains poorly understood. A growing body of evidence suggests that alveolar epithelial cell type 2 (AT2), which constitute 10-15% of all alveolar cells and are critical for alveolar homeostasis, are the primary targets of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection and damage to AT2s may directly contribute to disease severity and poor prognosis in COVID-19 patients. Our in-vitro modeling of SARS-CoV-2 infection, in well-characterized, highly uniform, (r2 at 95% CI = 0.92 ± 0.03), induced pluripotent stem cell (iPSC) derived AT2s from 10 participants of our Mexican American Family Study, showed interindividual variability in infection susceptibility and the post-infection cellular viral load. To understand the underlying mechanism of the AT2’s capacity to regulate SARS-CoV-2 infection and cellular viral load, we performed a systematic characterization of the pre- and post-SARS-CoV-2 challenged AT2 transcriptomes. A total of 1,393 genes were found significantly (Oneway ANOVA FDR corrected p ≤ 0.05; FC abs ≥ 2.0) differentially expressed (DE) between pre- and post-SARS-CoV-2 infection-challenged AT2 and suggest significant upregulation of viral infection-related cellular innate immune response pathways (p-value ≤ 0.05; activation z-score ≥ 3.5), whilst the cholesterol and xenobiotic related metabolic pathways were significantly downregulated (p-value ≤ 0.05; activation z-score ≤ - 3.5). Interestingly, pre-infection expression of 238 DE genes showed a high correlation with the post-infection SARS-CoV-2 viral load (FDR corrected p-value ≤ 0.05, and r2-absolute ≥ 0.57). The 85 genes whose expression was negatively correlated with the viral load showed significant enrichment in viral recognition and cytokine-mediated innate immune GO biological processes (p-value range: 4.65x10-10 to 2.24x10-6). The 153 genes whose expression was positively correlated with the viral load showed significant enrichment in cholesterol homeostasis, extracellular matrix, and MAPK/ERK pathway-related GO biological processes (p-value range: 5.06x10-5 to 6.53x10-4). Overall, our results strongly suggest that AT2s pre-infection innate immunity and metabolic state affects their susceptibility to SARS-CoV-2 infection and viral load.

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Activation of alveolar epithelial ER stress by b-coronavirus infection disrupts surfactant homeostasis in mice: implications for COVID-19 respiratory failure

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