FP04 Distinguishing roles of Cutibacterium acnes secretome and live bacteria on inflammasome activation in acne vulgaris
Meri Goff, Dave Boucher, Kim RobinsonAbstract
Introduction and aims
Acne vulgaris is the eighth most prevalent disease worldwide, yet its pathogenesis remains incompletely defined. Acne is a multifactorial condition, characterized by Cutibacterium acnes colonization with type IA1 strains, contributing towards cutaneous inflammatory responses. Evidence suggests that inflammasomes play a role in acne inflammation, with C. acnes shown to activate NOD-like-receptor-3 (NLRP3). Inflammasomes are multiprotein complexes that cleave caspases to release proinflammatory cytokines, such as interleukin (IL)-1β. We aim to examine the role of C. acnes in inflammasome activation to see whether the secretome or bacteria itself is responsible for inflammatory effects.
Methods
Normal human epidermal keratinocytes and macrophages from two donors were stimulated with clinically isolated C. acnes strains (04D7, 07H6, hdn-1, prp-38, ATCC 6919 and 1.5.4) and Staphylococcus aureus (JE2). Stimulation was done with supernatant, heat-inactivated cultures and live bacteria. Inflammasome activation was measured via Western blot analysis and interleukin (IL)-1β enzyme-linked immunosorbent assay.
Results
Keratinocytes stimulated with C. acnes supernatant, heat-inactivated or live bacteria does not activate NLRP1 or NLRP3. Macrophages stimulated with C. acnes supernatant does not activate NLRP3, but does secrete high amounts of IL-1β when stimulated with heat-inactivated bacteria. Live bacteria stimulated macrophages activate caspase 4, but does not lead to IL-1β secretion. MCC950-treated macrophages express full-length caspase 1 and cleaved caspase 4 but with low levels of IL-1β secretion. Interestingly some strains secrete similar levels of IL-1β to nontreated MCC950 macrophages. Live bacteria stimulation caused a significant increase of IL-1β secretion in 04D7 and 07H6 strains.
Conclusions
C. acnes has intrinsic inflammatory factors, independent of its secretome. C. acnes supernatant does not activate NLRP1 in keratinocytes and only partially works via NLRP3 in macrophages, suggesting involvement of alternative mechanisms. Better defining acne inflammatory mechanisms will advance our understanding of acne pathophysiology. This may inform better therapeutic strategies, particularly in light of increasing antimicrobial resistance.