Lysosomal BK channels facilitate silica-induced inflammation in macrophages

Abstract

Background

Lysosomal ion channels are proposed therapeutic targets for a number of diseases, including those driven by NLRP3 inflammasome-mediated inflammation. Here, the specific role of the lysosomal big conductance Ca²⁺-activated K⁺ (BK) channel was evaluated in a silica model of inflammation in murine macrophages. A specific-inhibitor of BK channel function, paxilline (PAX), and activators NS11021 and NS1619 were utilized to evaluate the role of lysosomal BK channel activity in silica-induced lysosomal membrane permeabilization (LMP) and NLRP3 inflammasome activation resulting in IL-1β release.

Methods

Murine macrophages were exposed in vitro to crystalline silica following pretreatment with BK channel inhibitors or activators and LMP, cell death, and IL-1β release were assessed. In addition, the effect of PAX treatment on silica-induced cytosolic K⁺ decrease was measured. Finally, the effects of BK channel modifiers on lysosomal pH, proteolytic activity, and cholesterol transport were also evaluated.

Results

PAX pretreatment significantly attenuated silica-induced cell death and IL-1β release. PAX caused an increase in lysosomal pH and decrease in lysosomal proteolytic activity. PAX also caused a significant accumulation of lysosomal cholesterol. BK channel activators NS11021 and NS1619 increased silica-induced cell death and IL-1β release. BK channel activation also caused a decrease in lysosomal pH and increase in lysosomal proteolytic function as well as a decrease in cholesterol accumulation.

Conclusion

Taken together, these results demonstrate that inhibiting lysosomal BK channel activity with PAX effectively reduced silica-induced cell death and IL-1β release. Blocking cytosolic K⁺ entry into the lysosome prevented LMP through the decrease of lysosomal acidification and proteolytic function and increase in lysosomal cholesterol.

Keywords:

• Macrophage
• silica
• inflammation
• lysosome
• ion channels
• cholesterol
• LMP

Acknowledgements

The authors thank Britten Postma of the University of Montana’s Inhalation and Pulmonary Physiology Core for assistance in alveolar macrophage isolation and bone marrow collection and Dr. Jessica Ray of the University of Montana’s Fluorescence Cytometry Core for assistance and training on the use of the Attune fluorescence cytometer.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Data available upon request.

Additional information

Funding

This research was supported by the National Institute of Environmental Health Sciences R21ES033511 and F31ES033562. The Fluorescence Cytometry Core and Inhalation and Pulmonary Core at the University of Montana are supported by National Institutes of General Medical Sciences P30GM103338. The content herein is solely the responsibility of the authors and does not necessarily represent the official views of the National Institute of Health.