Alford, A. I. | bioRxiv Science

bioRxiv2026

Thrombospondin-2 deficiency primes the synovial joint for aberrant tissue remodeling and injury response

ObjectiveThis study investigates joint injury-induced angiogenesis and the effects of genetic deficiency of thrombospondin-2 (TSP2), an anti-angiogenic factor, in joint homeostasis and post-traumatic osteoarthritis (PTOA). MethodWe utilized a murine non-invasive anterior cruciate ligament rupture (ACLR) model of PTOA and mined published synovial transcriptomics datasets to investigate injury-induced synovial angiogenesis. Spatial transcriptomics and flow cytometry of TSP2-GFP reporter mice were used to assess injury-induced thrombospondin-2 and its cellular origins in synovium. Global TSP2 knockout mice (TSP2-KO) were used to assess the effect of TSP2 deficiency on early and late stages of PTOA development via molecular imaging of inflammation and angiogenesis, histopathology, micro-computed tomography, Raman spectroscopy, and synovium bulk RNA-sequencing. ResultsIntra-articular angiogenesis peaked at 7d post-ACLR and declined but remained elevated above baseline at 28d post-ACLR. We identified synovial crosstalk between endothelial cells and sublining fibroblasts as a key driver of angiogenesis and source of thrombospondin-2 signaling, with TSP2 primarily upregulated in sublining fibroblasts. TSP2-KO mice exhibited increased peri-articular inflammation at 7d post-ACLR and inferior bone quality. Histopathology revealed greater PTOA severity but paradoxically lower synovitis in TSP2-KOs. Additionally, aberrant structural remodeling of the entire knee joint was observed in uninjured and ACLR TSP2-KO limbs. The uninjured TSP2-KO synovial transcriptome demonstrated elevated immune, fibrotic, and angiogenic activation; however, TSP2-KO and WT synovial transcriptomes partially converged upon injury. ConclusionTSP2 is essential for joint homeostasis and trauma response. Global TSP2 deficiency causes premature OA and worsened PTOA, suggesting that therapeutic targeting with TSP2 mimetic could be used to prevent OA.

physiology↗

bioRxiv2018

Thrombospondins 1 and 2 affect lysyl oxidase protein and collagen matrix maturation in cortical bone of growing male and female mice via non-redundant pathways

Thrombospondin-2-deficiency is associated with impaired matrix maturation in osteoblasts and cortical bone of growing mice. Here we addressed the possibility that lysyl oxidase (LOX) contributes to this phenotype. After overnight serum starvation, pro-LOX levels were elevated compared to wild-type in marrow-derived osteoblasts from male and female TSP2-/- mice. The liberated LOX pro-peptide (LOPP) was faintly visible in serum-starved cultures. When serum was maintained, pro-LOX content was not affected by TSP2 status, but relative LOPP levels were elevated in cultures from female TSP2-/- mice. Two isoforms of pro-LOX at 75 kDa and 50 kDa were detected in detergent soluble protein extracts of diaphyseal tissue from growing mice. In female mice, TSP2 status did not affect detergent soluble pro-LOX content or the relative contribution of each band to the total signal. Instead, levels of the 50 kDa band were reduced in female TSP1-/- samples. In male diaphyseal tissue, total pro-LOX content and the contribution each isoform made to the total signal was not affected by TSP1 or TSP2 status. We did not detect 32 kDa mature LOX in detergent soluble preparations of cells or whole bone tissue. Detergent insoluble hydroxyproline content was reduced in diaphyseal tissue obtained from female TSP1-/- and TSP2-/- mice. In male diaphyseal cortical samples, TSP2 but not TSP1 deficiency was associated with reduced insoluble hydroxyproline content. Our data suggest that the trimeric thrombospondins contribute to bone matrix quality via non-redundant mechanisms that are dependent on the unique tissue milieu of the male and female skeleton.

cell biology↗