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Single cell level characterization of injury-induced immune changes in MRL/MpJ knee joints

ABSTRACT: Post traumatic osteoarthritis (PTOA) is a painful joint disease characterized by the degradation of bone, cartilage, and connective tissues. PTOA is initiated by trauma to joint-stabilizing tissues, such as the anterior cruciate ligament, medial meniscus or by intra-articular fractures. In humans, ~50% of joint injuries progress to chronic PTOA, while the rest spontaneously resolve. To understand molecular programs contributing to PTOA development, we examined injury-induced fluctuations in immune cell populations and transcriptional shifts by single-cell sequencing of synovial joints in PTOA -susceptible C57BL6/J (B6) and -resistant MRL/MpJ (MRL) mice. A potent myeloid driven anti-inflammatory response was discovered in MRL injured joints that significantly contrasted the pro-inflammatory signaling seen in B6 joints. We found Trem2+ macrophages classically described as M2 (CD206+Trem2+) to be enriched in the uninjured joints of MRL mice, and these populations were consistently elevated in this strain, post injury. To evaluate whether Trem2 is essential to macrophage-mediated homeostasis in the joint, we examined Trem2 deficient mice and determined that these mice develop spontaneous OA. Overall, these data suggest that the PTOA resistant MRL mouse strain displays enhanced capacity of clearing debris and apoptotic cells induced by inflammation after injury due to an increase in activated macrophages within the synovial tissue and joint space. Furthermore, we showed that Trem2 is essential for preserving cartilage homeostasis in B6, and we postulate that the elevated levels of Trem2+ joint-resident macrophages in MRL are in part responsible for the PTOA-resistant phenotype in this strain.

ORGANISM(S): Mus musculus

PROVIDER: GSE220167 | GEO | 2024/12/31

REPOSITORIES: GEO

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Project description:Objective: To quantify gene expression changes in the synovium of osteoarthritis-affected joints in an equine metacarpophalangeal joint (MCPJ) chip model specifically designed to recapitulate early post-traumatic osteoarthritis (PTOA). Design: Synovial samples were collected arthroscopically from the MCPJ of 11 adult horses before (pre-OA) and after (OA) surgical induction of osteoarthritis and from sham-operated joints. Briefly, in this model, an osteochondral fragment is created in one randomly chosen MCPJ at the proximal dorsomedial aspect of the first phalanx. The fragment is replaced in the fragment bed after creation so that subchondral bone is not exposed to the opposing cartilage surface. The opposite MCPJ is sham-operated. After a two week recover period, the horses are treadmill-exercised for 14 weeks and then the osteochondral fragment is removed (16 weeks after creation). Synovial tissue samples were collected arthroscopically from the MCPJ of eleven adult horses before (pre-OA) and 16 weeks after (OA) experimental induction of OA as well as from the sham-operated joints (sham). After sequencing of synovial RNA, Salmon was used to quasi-map reads to the reference genome and quantify transcript abundances. Differential expression analysis was performed with the limma-treat method using a fold-change cutoff of 1.1. Functional annotation was performed with PANTHER and Reactome at FDR < 0.05. Results: RNA was successfully extracted from 28 samples (6 pre-OA, 11 OA, 11 sham). Sequencing yielded 15.7-29.4 million paired-end reads per sample. “Sham” and “pre-OA” were not different and were grouped. 321 genes were upregulated and 351 genes were downregulated in OA synovium compared to unaffected. Gene ontology (GO) terms related to extracellular matrix (ECM) organization and growth factor binding were overrepresented among differentially expressed genes. There were 20 significantly enriched pathways; these included pathways involved in ECM turnover, O-glycosylation of TSR domain-containing proteins, and growth factor signaling. Conclusions: Most enriched pathways and overrepresented GO terms reflect a state of high metabolic activity and tissue turnover in OA-affected tissue, suggesting efforts at healing and restoring homeostasis. Limitations of this study include a small sample size and capture of a single point post-injury. Differentially expressed genes falling within key pathways may represent potential diagnostic markers or therapeutic targets for PTOA.

Project description:Ectopic calcification in synovial tissues is devastating to diarthrodial joints. While some forms of synovial ectopic calcification have genetically simple basis, most cases manifest as complex traits with environmental and multigenic components. The location of causal loci or the physiological processes affected by allelic variants is poorly understood. Here, we report on genetic susceptibility to ectopic calcification in the LG/J and SM/J advanced intercross mice. Using 347 mice in 98 full-sibships, destabilization of medial meniscus was performed to induce joint injury. We performed quantitative trait locus (QTL) analysis to map calcification phenotypes to discrete genomic locations. To validate the functional significance of the selected QTL candidate genes, we compared mRNA expression between parental LG/J and SM/J inbred strains. Our findings showed that joint destabilization instigated ectopic calcifications as detected and quantified by micro-CT. Overall, we detected 20 QTLs affecting synovial and meniscus calcification phenotypes with 11 QTLs linked to synovial calcification. Functional and bioinformatic analyses of single nucleotide polymorphism identified functional classifications relevant to angiogenesis (Myo1e, Kif26b, Nprl3, Stab2, Fam105b), bone metabolism/calcification (Tle3, Tgfb2, Lipc, Nfe2l1, Ank, Fam105b), arthritis (Stab2, Tbx21, Map4k4, Hoxb9, Larp6, Col1a2, Adam10, Timp3, Nfe2l1, Trpm3), and ankylosing-spondylitis (Ank, Pon1, Il1r2, Tbkbp1) indicating that ectopic calcification involves multiple mechanisms. Furthermore, the expression of 11 candidate genes was significantly different between LG/J and SM/J. Correlation analysis showed that Aff3, Fam81a, Syn3, and Ank were correlated with synovial calcification. Our findings of multiple genetic loci affecting the phenotype suggest the involvement of multiple genes contributing to its pathogenesis. We collected tissue lysates from the formalin-fixed paraffin-embedded sections from mouse knee joints and analyzed the expression of several genes by Affymetrix QuantiGene Plex assay.