miR-7a-5p Contributes to Suppressing NLRP3/Caspase-1 Signaling Pathway in Response to Streptococcus suis Type 2 Infection

<i>Streptococcus suis</i> type 2 (SS2) is a pathogen causing diseases like meningitis and septicaemia worldwide. While microRNAs (miRNAs) are acknowledged for their role in post-transcriptional regulation of gene expression and influence on immune responses, their exact functions in hosts during SS2 infection remain elusive. This study aims to explore the role of miR-7a-5p in macrophages during SS2 infection. Our findings reveal that SS2 infection in J774A.1 cells triggers upregulation of the NLRP3 inflammasome signaling pathways, evidenced by enhanced mRNA expression of pro-inflammatory cytokines (IL-6, IL-18, IL-23, TNF-α) and elevated protein levels of NLRP3, caspase-1, and IL-1β. Concurrently, SS2 infection reduces miR-7a-5p expression. Dual-luciferase reporter assays confirm that miR-7a-5p directly targets the 3'UTR of NLRP3 mRNA. Notably, miR-7a-5p overexpression in SS2-infected J774A.1 cells suppresses NLRP3 inflammasome activation and downstream signaling, as demonstrated by reduced mRNA levels of inflammatory mediators and decreased protein levels of NLRP3, caspase-1, IL-1β, and IL-18. Conversely, miR-7a-5p inhibition produces effects opposite to those of overexpression. In mice, administration of miR-7a-5p mimics mitigates SS2-induced lung, liver, and spleen damage, reducing histological scores in these organs. Collectively, these results show that miR-7a-5p alleviates SS2-induced inflammation by inhibiting the NLRP3 inflammasome, underscoring its potential as a therapeutic target for SS2-associated diseases.