OA susceptibility in mice is partially mediated by the gut microbiome, is transferrable via microbiome transplantation and is associated with immunophenotype changes.

OBJECTIVES: The Murphy Roths Large (MRL)/MpJ 'superhealer' mouse strain is protected from post-traumatic osteoarthritis (OA), although no studies have evaluated the microbiome in the context of this protection. This study characterised microbiome differences between MRL and wild-type mice, evaluated microbiome transplantation and OA and investigated microbiome-associated immunophenotypes. METHODS: Cecal material from mixed sex C57BL6/J (B6) or female MRL/MpJ (MRL) was transplanted into B6 and MRL mice, then OA was induced by disruption of the medial meniscus surgery (DMM). In other experiments, transplantation was performed after DMM and transplantation was performed into germ-free mice. Transplanted mice were bred through F2. OARSI, synovitis and osteophyte scores were determined blindly 8 weeks after DMM. 16S microbiome sequencing was performed and metagenomic function was imputed. Immunophenotypes were determined using mass cytometry. RESULTS: MRL-into-B6 transplant prior to DMM showed reduced OA histopathology (OARSI score 70% lower transplant vs B6 control), synovitis (60% reduction) and osteophyte scores (30% reduction) 8 weeks after DMM. When performed 48 hours after DMM, MRL-into-B6 transplant improved OA outcomes but not when performed 1-2 weeks after DMM. Protection was seen in F1 (60% reduction) and F2 progeny (30% reduction). Several cecal microbiome clades were correlated with either better (eg, Lactobacillus, R=-0.32, p=0.02) or worse (eg, Rikenellaceae, R=0.43, p=0.001) OA outcomes. Baseline immunophenotypes associated with MRL-into-B6 transplants and MRL included reduced double-negative T cells and increased CD25+CD4+ T cells. CONCLUSION: The gut microbiome is responsible in part for OA protection in MRL mice and is transferrable by microbiome transplantation. Transplantation induces resting systemic immunophenotyping changes that correlate with OA protection.

Murine cartilage microbial DNA deposition occurs rapidly following the introduction of a gut microbiome and changes with obesity, aging, and knee osteoarthritis.

Cartilage microbial DNA patterns have been recently characterized in osteoarthritis (OA). The objectives of this study were to evaluate the gut origins of cartilage microbial DNA, to characterize cartilage microbial changes with age, obesity, and OA in mice, and correlate these to gut microbiome changes. We used 16S rRNA sequencing performed longitudinally on articular knee cartilage from germ-free (GF) mice following oral microbiome inoculation and cartilage and cecal samples from young and old wild-type mice with/without high-fat diet-induced obesity (HFD) and with/without OA induced by destabilization of the medial meniscus (DMM) to evaluate gut and cartilage microbiota. Microbial diversity was assessed, groups compared, and functional metagenomic profiles reconstructed. Findings were confirmed in an independent cohort by clade-specific qPCR. We found that cartilage microbial patterns developed at 48 h and later timepoints following oral microbiome inoculation of GF mice. Alpha diversity was increased in SPF mouse cartilage samples with age (P = 0.013), HFD (P = 5.6E-4), and OA (P = 0.029) but decreased in cecal samples with age (P = 0.014) and HFD (P = 1.5E-9). Numerous clades were altered with aging, HFD, and OA, including increases in Verrucomicrobia in both cartilage and cecal samples. Functional analysis suggested changes in dihydroorotase, glutamate-5-semialdehyde dehydrogenase, glutamate-5-kinase, and phosphoribosylamine-glycine ligase, in both cecum and cartilage, with aging, HFD, and OA. In conclusion, cartilage microbial DNA patterns develop rapidly after the introduction of a gut microbiome and change in concert with the gut microbiome during aging, HFD, and OA in mice. DMM-induced OA causes shifts in both cartilage and cecal microbiome patterns independent of other factors.