Gut microbe-derived short-chain fatty acids regulate joint inflammation and osteoclast activation after alphavirus infection

Although oral antibiotics can predispose to joint inflammation, this phenomenon remains poorly understood. Here, we leverage mouse models of alphavirus arthritis to investigate the gut commensals, metabolites, and host mechanisms that promote musculoskeletal inflammation. Mice treated with a short course of oral antibiotics exhibited worsened arthritis after chikungunya virus (CHIKV) infection. This phenotype was associated with loss of short chain fatty acids (SCFA) and greater intestinal permeability, and required TLR4 signaling, MyD88 expression, monocytes, antigen-specific and bystander CD4+ T cells, and pro-inflammatory cytokines. Administration of exogenous SCFA or colonization of mice with bacterial species that generate SCFA mitigated CHIKV-induced joint inflammation. Single cell RNA sequencing revealed that gut-derived SCFA restrain the inflammatory phenotype of synovial CD4+ T cells and limit activation of monocytes and osteoclast-like cells. Thus, antibiotic-triggered gut dysbiosis exacerbates alphavirus arthritis by shaping the inflammatory profile of both infiltrating and resident immune cells in joint tissues. 3-4-week-old mice were treated with either water, antibiotics (vancomycin and ampicillin [AV]), AV supplemented with propionate, or AV after CD4+ T cell depletion (4 mice per group), prior to infection with Mayaro virus. At 5 days post infection, tissues from the ipsilateral feet were grossly dissected and single cell suspensions were obtained. Cells were labeled with TotalSeq anti-mouse hashtag antibodies (one distinct hastag per mouse sample in each group) and fluorescently conjugated antibodies against cell surface antigens, and individual samples were pooled according to experimental treatment group. CD4+ T cells and myeloid cells were then sorted, pooled by experimental group, and submitted for single cell RNA sequencing.