Inflammasome Hyperactivation Disrupts Construction of the Gas Exchange Surface through the NLRP3-IL-18-TNFa Axis [RNA-seq]

Inflammation is a prominent feature of tissue injury, and a driver of chronic disease. However, the precise molecular mechanisms underlying the impact of inflammation remains unclear in many injury settings including in alveolar development to build the gas exchange surface in lung. Here we show that in mice, overexpression of patient-derived activated variants of Nlrp3 (Nlrp3act), a central sensor within the inflammasome, resulted in severe simplification of alveoli. Such histology is accompanied by a striking decrease of cell proliferation and marker expression of secondary crest myofibroblasts (SCMFs) whose contractility is essential for septa formation. Such a drastic effect on lung structure was only observed when the variants were overexpressed in the first two weeks after birth, but not later. While both downstream proinflammatory cytokines IL-1β and IL-18 are upregulated, inactivation of Il18, but not Il1b in the Nlrp3act background reversed simplification. Also unlikely in other tissue settings where Mmp9 is a critical mediator downstream of the inflammasome, inactivation of Mmp9 also did not reverse Nlrp3act phenotypes, suggesting context-dependent mechanisms. scRNAseq followed by validation revealed IL-18-dependent increase of Tnfα in myeloid cells, capable of signaling through its widely-expressed receptors to all structural cells including SCMFs. Addition of recombinant TNFα to mesenchymal cells enriched for SCMFs led to reduced contractile gene expression. Finally, inactivation of Tnfα in the Nlrp3act background led to a robust reversal of simplification. These findings together demonstrate an inflammasome-IL-18-TNFα axis that dictate lung mesenchymal cell states, thereby control the building of the gas exchange surface.