Research ArticleInflammation

Manganese activates NLRP3 inflammasome signaling and propagates exosomal release of ASC in microglial cells

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Sci. Signal.  08 Jan 2019:
Vol. 12, Issue 563, eaat9900
DOI: 10.1126/scisignal.aat9900

Exosomes transfer inflammasome activation

Chronic occupational exposure to manganese is associated with the development of Parkinson’s disease. Sarkar et al. found that exposure of primed microglial cells or mice to manganese increased NLRP3 inflammasome expression and activation. Manganese caused mitochondrial dysfunction in treated microglial cells and stimulated their release of exosomes containing the inflammasome adaptor protein ASC. The effects of manganese on inflammasome activation were sensitive to reduced endocytosis and transferable by exposure of cells to purified exosomes from ASC-sufficient cells. Similarly, serum exosomes from welders contained more ASC and were more inflammatory than those from normal donors, suggesting that occupational manganese exposure may increase systemic inflammasome activation due to exosome-mediated transfer of ASC.

Abstract

Chronic, sustained inflammation underlies many pathological conditions, including neurodegenerative diseases. Divalent manganese (Mn2+) exposure can stimulate neurotoxicity by increasing inflammation. In this study, we examined whether Mn2+ activates the multiprotein NLRP3 inflammasome complex to promote neuroinflammation. Exposing activated mouse microglial cells to Mn2+ substantially augmented NLRP3 abundance, caspase-1 cleavage, and maturation of the inflammatory cytokine interleukin-1β (IL-1β). Exposure of mice to Mn2+ had similar effects in brain microglial cells. Furthermore, Mn2+ impaired mitochondrial ATP generation, basal respiratory rate, and spare capacity in microglial cells. These data suggest that Mn-induced mitochondrial defects drove the inflammasome signal amplification. We found that Mn induced cell-to-cell transfer of the inflammasome adaptor protein ASC in exosomes. Furthermore, primed microglial cells exposed to exosomes from Mn-treated mice released more IL-1β than did cells exposed to exosomes from control-treated animals. We also observed that welders exposed to manganese-containing fumes had plasma exosomes that contained more ASC than did those from a matched control group. Together, these results suggest that the divalent metal manganese acts as a key amplifier of NLRP3 inflammasome signaling and exosomal ASC release.

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