Impact of cigarette smoke on caspases activation and gasdermin D cleavage in human macrophages

Cigarette smoke (CS) contributes to alveolar macrophage (AM) dysfunction. We previously showed that cigarette smoke extract (CSE) inhibits the NLRP3 inflammasome while activating caspase-1 via TRIF-caspase-8 axis in human monocyte-derived macrophages (hMDMs). Active caspase-1 cleaves gasdermin D (GSDMD) that, once activated, leads to pore formation and eventually cell death. Caspase-4, which is activated by intracellular lipopolysaccharide (LPS), and caspase-8 can also cleave GSDMD. The impact of CS on GSDMD cleavage in human macrophages is unknown. Herein, we investigated the effects of CSE±LPS on GSDMD activation, cell permeability, and cell death in hMDMs and distal lung tissue sections from patients (controls, ex-smokers/COPD, smokers/COPD). In hMDMs CSE ± LPS did not alter GSDMD expression (RT-qPCR and western blot, WB) while increasing cleaved GSDMD (WB and immunofluorescence, IF) and cell permeability, with no cell death. Of note, GSDMD cleavage was higher when CSE was combined with LPS. Thus, the hypothesis that exposure of hMDMs to LPS+CSE promoted caspase-4-dependent GSDMD cleavage, in addition to caspase-1 and -8, was tested. Presented data show that CSE promoted LPS internalization (IF) leading to caspase-4 activation (enzymatic assay and WB), thus enhancing GSDMD cleavage. To support the relevance of our data, increased cleaved GSDMD was found in AMs of smokers compared to ex-smokers and controls. For the first time to our knowledge, we show that CS promotes caspase-dependent GSDMD cleavage in hMDMs and AMs. Being GSDMD a driver of inflammation, these findings unveil novel mechanisms contributing to chronic lung diseases paving the way for the development of new therapies.