Murthy, et al_AJP Lung L-00324-2023-R2_SUPPLEMENTAL TABLES AND FIGURES.pdf

COVID-19 syndrome is characterized by acute lung injury, 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 induce an ER stress response<i> in vitro</i>, however the consequences for host AT2 cell function <i>in vivo</i> 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 mouse adapted SARS-CoV-2 strain. MHV-1 infected mice exhibited dose-dependent weight loss with histological evidence of distal lung injury accompanied by elevated bronchoalveolar lavage fluid (BALF) cell counts and total protein. AT2 cells showed evidence of both viral infection and increased BIP/GRP78 expression, consistent with activation of the unfolded protein response (UPR). The AT2 UPR included increased IRE1a signaling and a biphasic response in PERK signaling accompanied 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 (<i>Krt8+</i>, <i>Cldn4+</i>). The loss of a homeostatic AT2 cell state 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 lung injury from b-coronavirus infection results from an aberrant host response activating multiple AT2 UPR stress pathways, altering surfactant metabolism/function, and changing AT2 cell state offering a mechanistic link between SARS-CoV-2 infection, AT2 cell biology, and acute respiratory failure.