Propionibacterium acnes induces IL-1β secretion via the NLRP3 inflammasome in human monocytes

Propionibacterium acnes induction of inflammatory responses is a major etiologic factor contributing to the pathogenesis of acne vulgaris. In particular, the IL-1 family of cytokines plays a critical role in both initiation of acne lesions and in the inflammatory response in acne. In this study, we demonstrated that human monocytes respond to P. acnes and secrete mature IL-1β partially via NLRP3 mediated pathway. When monocytes were stimulated with live P. acnes, caspase-1 and caspase-5 gene expression was upregulated; however, IL-1β secretion required only caspase-1 activity. P. acnes induced key inflammasome genes including NLRP1 and NLPR3. Moreover, silencing of NLRP3, but not NLRP1, expression by siRNA attenuated P. acnes-induced IL-1β secretion. The mechanism of P. acnes-induced NLRP3 activation and subsequent IL-1β secretion was found to involve potassium efflux. Finally, in acne lesions, mature caspase-1 and NLRP3 were detected around the pilosebaceous follicles and co-localized with tissue macrophages. Taken together, our results indicate that P. acnes triggers a key inflammatory mediator, IL-1β, via NLRP3 and caspase-1 activation, suggesting a role for inflammasome-mediated inflammation in acne pathogenesis.