Chronic airway epithelial hypoxia exacerbates injury in muco-obstructive lung disease through mucus hyperconcentration

Unlike solid organs, human airway epithelia derive their oxygen from inspired air rather than the vasculature. Many pulmonary diseases are associated with intraluminal airway obstruction caused by aspirated foreign bodies, virus infection, tumors, or mucus plugs intrinsic to airway disease, including cystic fibrosis (CF). Consis-tent with requirements for luminal O2, airway epithelia surrounding mucus plugs in chronic obstructive pulmo-nary disease (COPD) lungs are hypoxic. Despite these observations, the effects of chronic hypoxia (CH) on airway epithelial host defense functions relevant to pulmonary disease have not been investigated. Molecular charac-terization of resected human lungs from individuals with a spectrum of muco-obstructive lung diseases (MOLDs) or COVID-19 identified molecular features of chronic hypoxia, including increased EGLN3 expression, in epithelia lining mucus-obstructed airways. In vitro experiments using cultured chronically hypoxic airway epithelia re-vealed conversion to a glycolytic metabolic state with maintenance of cellular architecture. Chronically hypoxic airway epithelia unexpectedly exhibited increased MUC5B mucin production and increased transepi-thelial Na+ and fluid absorption mediated by HIF1 alpha/HIF2 alpha-dependent up-regulation of beta and gamma ENaC (epithelial Na+ channel) subunit expression. The combination of increased Na+ absorption and MUC5B production gener-ated hyperconcentrated mucus predicted to perpetuate obstruction. Single-cell and bulk RNA sequencing anal-yses of chronically hypoxic cultured airway epithelia revealed transcriptional changes involved in airway wall remodeling, destruction, and angiogenesis. These results were confirmed by RNA-in situ hybridization studies of lungs from individuals with MOLD. Our data suggest that chronic airway epithelial hypoxia may be central to the pathogenesis of persistent mucus accumulation in MOLDs and associated airway wall damage.

Automated summary

Unlike solid organs, human airway epithelia rely on inspired air rather than the vasculature for oxygen supply. Chronic hypoxia in the airway epithelia plays a central role in the pathogenesis of persistent mucus accumulation and airway wall damage in muco-obstructive lung diseases (MOLDs). Chronic hypoxia leads to glycolytic metabolic state, increased MUC5B mucin production, and up-regulation of ENaC subunits, resulting in hyperconcentrated mucus and perpetuated obstruction. Transcriptional changes in airway wall remodeling, destruction, and angiogenesis are also observed in chronically hypoxic airway epithelia.