Abstract
BackgroundIn vivo studies have demonstrated the ability of multi-walled carbon nanotubes (MWCNT) to induce airway remodeling, a key feature of chronic respiratory diseases like asthma and chronic obstructive pulmonary disease. However, the mechanism leading to remodeling is poorly understood. Particularly, there is limited insight about the role of airway epithelial injury in these changes.ObjectivesWe investigated the mechanism of MWCNT-induced primary human bronchial epithelial (HBE) cell injury and its contribution in inducing a profibrotic response.MethodsPrimary HBE cells were exposed to thoroughly characterized MWCNTs (1.5-24 μg/mL equivalent to 0.37-6.0 μg/cm2) and MRC-5 human lung fibroblasts were exposed to 1:4 diluted conditioned medium from these cells. Flow cytometry, ELISA, immunostainings/immunoblots and PCR analyses were employed to study cellular mechanisms.ResultsMWCNT induced NLRP3 inflammasome dependent pyroptosis in HBE cells in a time- and dose-dependent manner. Cell death and cytokine production were significantly reduced by antioxidants, siRNA to NLRP3, a caspase-1 inhibitor (z-WEHD-FMK) or a cathepsin B inhibitor (CA-074Me). Conditioned medium from MWCNT-treated HBE cells induced significant increase in mRNA expression of pro-fibrotic markers (TIMP-1, Tenascin-C, Procollagen 1, and Osteopontin) in human lung fibroblasts, without a concomitant change in expression of TGF-beta. Induction of pro-fibrotic markers was significantly reduced when IL-1β, IL-18 and IL-8 neutralizing antibodies were added to the conditioned medium or when conditioned medium from NLRP3 siRNA transfected HBE cells was used.ConclusionsTaken together these results demonstrate induction of a NLRP3 inflammasome dependent but TGF-beta independent pro-fibrotic response after MWCNT exposure.
Highlights
In vivo studies have demonstrated the ability of multi-walled carbon nanotubes (MWCNT) to induce airway remodeling, a key feature of chronic respiratory diseases like asthma and chronic obstructive pulmonary disease
We found that MWCNT induce pyroptosis and inflammasome activation in primary human bronchial epithelial cells
Our study differs from above mentioned work in four important aspects: 1) We used primary human bronchial epithelial cells; 2) We uncovered the molecular mechanism of pyroptosis in HBE cells; 3) We observed inflammasome activation without prior priming with LPS; and 4) We uncovered the biological significance of the inflammasome activation after MWCNT exposure as a trigger for a pro-fibrotic response
Summary
In vivo studies have demonstrated the ability of multi-walled carbon nanotubes (MWCNT) to induce airway remodeling, a key feature of chronic respiratory diseases like asthma and chronic obstructive pulmonary disease. Multi-walled carbon nanotubes (MWCNT) exhibit unique electrical, mechanical, thermal and optic properties, which make them the material of choice for a variety of industrial and consumer product applications. Apart from their conventional utilizations in electronics, composite materials and optics, more recent applications of MWCNT include biomedical engineering, biosensors, drug delivery and gene therapy [1,2,3,4,5]. Given their tremendous potential, it is expected that their applications will continue to grow over the coming years [6]. Recent estimates indicate that more than 6 million workers will be involved with nanotechnology by 2020, one third of whom will reside in the US [23]
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