Extracellular Hsp70 modulates the inflammatory response of cigarette smoke extract in NCI-H292 cells

What is the central question of this study? Does extracellular heat shock protein 70 (eHsp70) alter cigarette smoke extract (CSE)-induced inflammatory responses in NCI-H292 bronchial epithelial cells? What is the main finding and its importance? eHsp70 modulates inflammatory responses and TLR2, TLR4 and Hsp70 gene expression, and protects NCI-H292 cells against CSE-induced cytotoxicity. eHsp70 might be implicated in development of inflammatory diseases affected by cigarette smoke, such as COPD.

One of the major risk factors for development of chronic obstructive pulmonary disease (COPD) is cigarette smoke. Extracellular Hsp70 (eHsp70) is increased in sera of COPD patients, and can act as damage-associated molecular pattern (DAMP). In this study, we explored inflammatory parameters (cytokine concentrations, Toll-like receptor (TLR) 2 and 4 and Hsp70 expression, mitogen-activated protein kinases (MAPKs) and nuclear factor κB (NF-κB) activation, and cytotoxicity) after exposure of bronchial-epithelial NCI-H292 cells to cigarette smoke extract (CSE) alone (2.5 and 15%) and in combinations with recombinant human (rh) Hsp70 (0.3, 1 and 3 μg ml^-1 ). We applied specific MAPKs, NF-κB and Hsp70 inhibitors to elucidate rhHsp70 inflammation-associated responses. CSE alone and combinations of 15% CSE with rhHsp70 stimulated IL-1α, IL-6 and IL-8 release. However, rhHsp70 applied with 2.5% CSE decreased secretion of cytokines indicating antagonistic effects. Individual and combined treatments with 2.5% CSE suppressed TLR2 expression. CSE at 15% induced TLR2 and TLR4 gene expression, whereas rhHsp70 abolished that effect. rhHsp70 and 15% CSE alone reduced, while their combination increased, intracellular Hsp70 mRNA level. CSE alone and in combination with rhHsp70 activated extracellular signal-regulated kinase and p38 MAPKs, while inhibition of MAPKs, NF-κB and Hsp70 attenuated IL-6 and IL-8 secretion. CSE at 15% reduced cell viability and induced apoptosis, as shown by MTS and caspases-3/7 assays. CSE at 2.5% alone stimulated lactate dehydrogenase release, but cellular membrane integrity remained intact in co-treatments with rhHsp70. rhHsp70 might modulate the inflammatory response of CSE and could also protect NCI-H292 cells against CSE cytotoxicity. Those effects are implemented via MAPK and NF-κB signalling pathways.