Oral StreptococciS. anginosusandS. mitisinduce distinct morphological, inflammatory, and metabolic signatures in macrophages

Abstract

AbstractOral streptococci are the pioneer colonizer and structural architect of the complex oral biofilm. Disruption of this architectural framework causes oral dysbiosis associated with various clinical conditions, including dental caries, gingivitis, and oral cancer. Among the genusStreptococcus,S. anginosusis associated with esophageal, gastric, and pharyngeal cancer tissues, whileS. mitisis correlated with oral cancer. However, no study has investigated mechanistic links between theseStreptococcus speciesand cancer-related inflammatory responses. To explore the underlying involvement ofS. anginosus and S. mitisin inflammation-associated cancer development, we investigated the innate immune response elicited byS. anginosusversusS. mitisusing the RAW264.7 macrophage cell line. Compared to untreated orS. mitisinfected macrophages,S. anginosusinfected macrophages exhibited a robust proinflammatory response characterized by significantly increased levels of inflammatory cytokines and mediators, including TNF, IL-6, IL-1β, NOS2, and COX2, accompanied by enhanced NF-κB activation. Mitostress analysis revealed an increased extracellular acidification rate in macrophages infected withS. anginosuscompared toS. mitis.Further, macrophages infected withS. anginosusfor 6h displayed upregulated aconitate decarboxylase, which catalyzes itaconate production. In contrast, no significant alterations were observed in succinate dehydrogenase that converts succinate to fumarate. At 24h,S. anginosusinduced significant shifts in succinate and itaconate, emphasizing a unique macrophage metabolic profile, and an augmented inflammatory response in response toS. anginosus.This study underscores the capacity ofS. anginosusto elicit a robust proinflammatory response in macrophages and opens new avenues of secretory immune metabolites in response to oral streptococci.ImportanceThe surge in head and neck cancer cases among individuals devoid of typical risk factors such as HPV infection, tobacco and alcohol use sparks an argumentative discussion around the emerging role of oral microbiota as a novel risk factor in oral squamous cell carcinoma (OSCC). While substantial research has dissected the gut microbiome’s influence on physiology, the oral microbiome, notably oral streptococci, a gatekeeper of systemic health, has been underappreciated in mucosal immunopathogenesis.S. anginosus,a viridans streptococci group, has been linked to abscess formation and an elevated presence in esophageal cancer and OSCC. The current study aims to probe the innate immune response toS. anginosuscompared to the early colonizerS. mitisas an initial ride towards understanding the impact of distinct oralStreptococcusspecies on the host immune response in the progression of OSCC.