NLRP6 plays a key role in pulmonary inflammation to chronic ozone through activation of pyroptotic and necroptotic pathways - 20/03/24

Ground-level ozone is an important gaseous constituent of air pollution that contributes to lung disease progression and mortality. Ozone exposure in mice causes pulmonary inflammation evolving into lung emphysema and/or fibrotic patterns but the mechanisms are not well understood [1Sokolowska M., Quesniaux V.F.J., Akdis C.A., Chung K.F., Ryffel B., Togbe D. Acute respiratory barrier disruption by ozone exposure in mice Front Immunol 2019 ;  10 : 2169

Cliquez ici pour aller à la section Références]. We investigated the role of the poorly characterized innate receptor nucleotide-binding domain and leucine-rich repeat containing protein 6 (NLRP6) involved in inflammasome scaffold [2Ghimire L., Paudel S., Jin L., Jeyaseelan S. The NLRP6 inflammasome in health and disease Mucosal Immunol 2020 ;  13 : 388-398 [cross-ref]

Cliquez ici pour aller à la section Références], in ozone exposure-induced in the context of immunogenic cell death [3Kesavardhana S., Malireddi R.K.S., Kanneganti T.D. Caspases in cell death, inflammation, and pyroptosis Annu Rev Immunol 2020 ;  38 : 567-595 [cross-ref]

Cliquez ici pour aller à la section Références].

Using a chronic ozone exposure model of chronic obstructive pulmonary disease (COPD) in mice, we investigated the role of the NLRP6 receptor in pulmonary inflammation, emphysema and fibrosis by exposing wild-type, Nlrp6 deficient mice and mice deficient for Nlrp6 specifically in lung epithelial cells. In addition, we analyzed NLRP6 expression in lung using NLRP6 FLAG-tagged mice. NLRP6-dependent expression and/or activation of proteins characteristic of immunological cell deaths such as pyroptosis, apoptosis and necroptosis were analyzed by western blotting and immunofluorescence.

We observed that mouse chronic ozone exposure increased NLRP6 expression in bronchial and alveolar epithelial cells and in a lesser extend in airway macrophages. Interestingly Nlrp6 deficiency dampened pulmonary inflammation and alveolar damage with reduced neutrophil and eosinophil influxes, attenuated chemokine/cytokine and remodeling factor production, collagen deposition and lung fibrosis. Chronic ozone-induced a loss of alveolar type 1 pneumocytes that was attenuated in Nlrp6 deficient mice. Mechanistically, we report that chronic ozone exposure promoted NLRP6-dependent caspase-1, caspase-11 and gasdermin D activation in alveolar type 1 pneumocytes. Chronic ozone exposure also induced NLRP6-dependent expression of apoptotic and necroptotic markers in lung tissue.

We identified NLRP6 as a new innate sensor of chronic ozone-induced lung injury promoting pulmonary inflammation leading to emphysema and fibrosis in mice. Our results suggest that chronic ozone induces pulmonary inflammation through NLRP6 inflammasome-dependent pyroptosis and necroptosis of alveolar type 1 pneumocytes. Understanding the mechanisms of pollutant-induced alveolar cell death, lung inflammation and repair might help fight COPD and lung fibrosis.