Anti-inflammatory activity of calmodulin-lysine N-methyltransferase through suppressing the caspase-11 non-canonical inflammasome

Maclurin inhibits caspase-11 non-canonical inflammasome in macrophages and ameliorates acute lethal sepsis in mice

Maclurin is a natural phenolic compound isolated from Morus alba(white mulberry) andGarcinia mangostana (purple mangosteen) and has been reported to regulate cancer progression, oxidative stress, and melanogenesis. The regulatory role of maclurin, however, has never been demonstrated. This study investigated in vitro and in vivo anti-inflammatory roles of maclurin and the underlying mechanism in caspase-11 non-canonical inflammasome-stimulated inflammatory responses in macrophages and an animal model of acute lethal sepsis. Maclurin protected J774A.1 macrophages from LPS-induced cytotoxicity and suppressed caspase-11 non-canonical inflammasome-stimulated pyroptosis. Maclurin decreased the secretion and mRNA expression of pro-inflammatory cytokines and inflammatory mediators, such as IL-1β, IL-18, TNF-α, IL-6, nitric oxide (NO), and inducible NO synthase (iNOS) in caspase-11 non-canonical inflammasome-stimulated J774A.1 macrophages. Mechanistic studies revealed that maclurin markedly suppressed the proteolytic activation of caspase-11 and gasdermin D (GSDMD) in caspase-11 non-canonical inflammasome-stimulated J774A.1 macrophages, while it did not inhibit caspase-11-mediated direct sensing of LPS. In vivo study revealed that maclurin ameliorated acute lethal sepsis in mice by increasing the survival rate and decreasing the serum levels of IL-1β and IL-18 without significant toxicity. In conclusion, this study suggests that maclurin is a novel anti-inflammatory agent in inflammatory responses and against acute lethal sepsis via the inhibition of the caspase-11 non-canonical inflammasome in macrophages, which justifies its potential as an anti-inflammatory therapeutic agent in traditional medicine.

Roles of the Caspase-11 Non-Canonical Inflammasome in Rheumatic Diseases

Inflammasomes are intracellular multiprotein complexes that activate inflammatory signaling pathways. Inflammasomes comprise two major classes: canonical inflammasomes, which were discovered first and are activated in response to a variety of pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs), and non-canonical inflammasomes, which were discovered recently and are only activated in response to intracellular lipopolysaccharide (LPS). Although a larger number of studies have successfully demonstrated that canonical inflammasomes, particularly the NLRP3 inflammasome, play roles in various rheumatic diseases, including rheumatoid arthritis (RA), infectious arthritis (IR), gouty arthritis (GA), osteoarthritis (OA), systemic lupus erythematosus (SLE), psoriatic arthritis (PA), ankylosing spondylitis (AS), and Sjögren's syndrome (SjS), the regulatory roles of non-canonical inflammasomes, such as mouse caspase-11 and human caspase-4 non-canonical inflammasomes, in these diseases are still largely unknown. Interestingly, an increasing number of studies have reported possible roles for non-canonical inflammasomes in the pathogenesis of various mouse models of rheumatic disease. This review comprehensively summarizes and discusses recent emerging studies demonstrating the regulatory roles of non-canonical inflammasomes, particularly focusing on the caspase-11 non-canonical inflammasome, in the pathogenesis and progression of various types of rheumatic diseases and provides new insights into strategies for developing potential therapeutics to prevent and treat rheumatic diseases as well as associated diseases by targeting non-canonical inflammasomes.