Cigarette smoke activates caspase (casp)-8/-1/Gasdermin D axis via TLR4 in human macrophages. Casp-8 is central both in cell death and inflammation; casp-3/7, as casp-8 effector, mediates apoptosis and cleaves Gasdermin E (GSDME), inducing the highly inflammatory pyroptosis secondary to apoptosis.

Herein, hypothesizing a role of casp-8/-3/7/GSDME axis, the effect of cigarette smoke extract (CSE) on cell death and inflammation was evaluated in LPS-treated human monocyte-derived macrophages (hMDMs). Apoptosis was evaluated by analyzing casp-8, and -3/7 activity, nuclear fragmentation, and mitochondrial membrane potential (MMP). Pyroptosis was evaluated by measuring GSDME cleavage and LDH release. TNF? and IL6 gene expression and release were also measured. Casp-3 cleavage was assessed in human lung tissue sections from smokers (S, n=4) and non-smoker controls (NS, n=5).

LPS induced a quick inflammatory response at 6h, which declined at 24h; no lytic cell death occurred at 24h, despite a slight activation of casp-8 and -3/7. Conversely, hMDMs exposed to CSE/LPS for 24h underwent lytic cell death, indicated by LDH release, associated with stronger activation of casp-8 and -3/7, nuclear fragmentation, loss of MMP, and a casp-3/7-dependent cleavage of GSDME. The inflammatory response, indicated by TNF? and IL6 gene expression and release, was delayed and weaker than LPS-treated hMDMs. Of note, cleaved casp-3 increased in alveolar macrophages of S compared to NS controls. 

The inflammatory lytic cell death, with a dysregulated inflammatory response, may represent a key alteration of lung macrophages exposed to CS in the context of infections associated with chronic inflammation.