Tryptase activates calcium-independent phospholipase A2 and releases PGE2 in airway epithelial cells

Human small airway epithelial cells (HSAEC) form the boundary between the external environmental allergens and the internal lung milieu. Mast cells are present in human lung tissue interspersed within the pulmonary epithelium and can secrete a host of pre- and newly formed mediators from their granules, which may propagate small airway inflammation. In this study, tryptase stimulation of HSAEC increased membrane-associated, calcium-independent phospholipase A2γ (iPLA2γ) activity, resulting in increased arachidonic acid and PGE2 release. These responses were inhibited by pretreating HSAEC with the iPLA2-selective inhibitor bromoenol lactone. The tryptase-stimulated PGE2 production was inhibited by treating HSAEC with the cyclooxygenase (COX)-1-selective inhibitor SC-560 and the nonselective COX inhibitor aspirin but not by the COX-2-selective inhibitor CAY10404 , indicating that the early release of arachidonic acid is metabolized by constitutive COX-1 to form PGE2 in tryptase-stimulated HSAEC. Additionally, platelet-activating factor production and neutrophil adherence to tryptase-stimulated HSAEC was also increased. This complex response can set up a cascade of inflammatory mediator production in small airways. We speculate that selective inhibition of iPLA2γ-mediated phospholipid hydrolysis may prove beneficial in inflammatory airway diseases.

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Influenza virus infection increases ACE2 expression and shedding in human small airway epithelial cells

European Respiratory Journal ◽

10.1183/13993003.03988-2020 ◽

2021 ◽

pp. 2003988

Author(s):

Kelly S. Schweitzer ◽

Taylor Crue ◽

Jordan M. Nall ◽

Daniel Foster ◽

Satria Sajuthi ◽

...

Keyword(s):

Epithelial Cells ◽

Lung Injury ◽

Influenza A ◽

Viral Infections ◽

Influenza Virus Infection ◽

Airway Epithelial Cells ◽

Small Airway ◽

Small Airways ◽

Airway Epithelial ◽

Small Airway Epithelial Cells

Patients with COVID-19 caused by severe acute respiratory syndrome coronavirus (SARS-Co-V)-2 demonstrate high rates of co-infection with respiratory viruses, including influenza A (IAV), suggesting pathogenic interactions. We investigated how IAV may increase the risk for COVID-19 lung disease, focusing on the receptor Angiotensin Convertase Enzyme 2 (ACE2) and the protease TMPRSS2, which cooperate to uptake SARS-CoV-2 intracellular. We found, using single cell RNA sequencing of distal human non-diseased lung homogenates, that at baseline, ACE2 is minimally expressed in basal, goblet, ciliated, and secretory epithelial cells populating small airways. We focused on human small airway epithelial cells (SAEC), central to the pathogenesis of lung injury following viral infections. Primary SAEC from non-diseased donor lungs apically infected (at air-liquid interface) with IAV (up to 3×105 pfu; ∼1 MOI) markedly (8-fold) boosted the expression of ACE2, paralleling that of STAT1, a transcription factor activated by viruses. IAV increased the apparent electrophoretic mobility of intrac¬ellular ACE2 and generated an ACE2 fragment (90 kDa) in apical secretions, suggesting cleavage of this receptor. IAV also increased the expression of two proteases known to cleave ACE2, sheddase ADAM17 (TACE) and TMPRSS2 and increased the TMPRSS2 zymogen and its mature fragments, implicating proteolytic autoactivation. These results indicate that IAV amplifies the expression of molecules necessary for SARS-CoV-2 infection of the distal lung. Further, posttranslational changes in ACE2 by IAV may increase the vulnerability to lung injury such as ARDS during viral co-infections. These findings support prevention and treatment efforts of influenza infections during the COVID-19 pandemic.

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