Concurrent Joint Contact in Anterior Cruciate Ligament Injury induces cartilage micro-injury and subchondral bone sclerosis, resulting in knee osteoarthritis.

Objective: Anterior Cruciate Ligament (ACL) injury develops the Osteoarthritis (OA) via two distinct processes: initial direct micro-injury of the cartilage surface by compressive force during ACL injury, and secondary joint instability due to the deficiency of the ACL. Using the conventional Compression-induced ACL-R and novel Non-Compression ACL-R models, we aimed to reveal the individual effects on OA progression after ACL injury. Methods: Twelve-week-old C57BL/6 male were randomly divided to three experimental groups: Compression ACL-R, Non-Compression ACL-R, and Intact. We performed the joint laxity test and microscope analysis at 0 days, in vivo imaging with matrix-metalloproteinases (MMPs) at 3 and 7 days, histological and micro-CT analysis at 0, 7, 14, and 28 days. Results: Although no differences in the joint laxity were observed between both ACL-R groups, the Compression ACL-R group exhibited a significant increase of cartilage roughness immediately after injury compared with the Non-Compression group. At 7 days, Compression group increased MMPs-induced fluorescence intensity slightly and MMP-13 positive cell ratio of chondrocytes significantly than that in the Non-Compression group. Moreover, histological cartilage degeneration initiated in the whole joint level of the Compression group at the same time point. Micro-CT analysis revealed that sclerosis of tibial Subchondral bone in the Compression group developed significantly more than in the Non-Compression group at 28 days, especially in the medial tibial compartment. Conclusions: Concurrent joint contact during ACL rupture caused initial micro-damage on the cartilage surface and early cartilage degeneration with MMP-13 production, leading to later bone formation in the subchondral bone.

Effect of Suppression of Rotational Joint Instability on Cartilage and Meniscus Degeneration in Mouse Osteoarthritis Model.

OBJECTIVE: Joint instability and meniscal dysfunction contribute to the onset and progression of knee osteoarthritis (OA). In the destabilization of the medial meniscus (DMM) model, secondary OA occurs due to the rotational instability and increases compressive stress resulting from the meniscal dysfunction. We created a new controlled abnormal tibial rotation (CATR) model that reduces the rotational instability that occurs in the DMM model. So, we aimed to investigate whether rotational instability affects articular cartilage degeneration using the DMM and CATR models, as confirmed using histology and immunohistochemistry. DESIGN: Twelve-week-old male mice were randomized into 3 groups: DMM group, CATR group, and INTACT group (right knee of the DMM group). After 8 and 12 weeks, we performed the tibial rotational test, safranin-O/fast green staining, and immunohistochemical staining for tumor necrosis factor (TNF)-α and metalloproteinase (MMP)-13. RESULTS: The rotational instability in the DMM group was significantly higher than that of the other groups. And articular cartilage degeneration was higher in the DMM group than in the other groups. However, meniscal degeneration was observed in both DMM and CATR groups. The TNF-α and MMP-13 positive cell rates in the articular cartilage of the CATR group were lower than those in the DMM group. CONCLUSIONS: We found that the articular cartilage degeneration was delayed by controlling the rotational instability caused by meniscal dysfunction. These findings suggest that suppression of rotational instability in the knee joint may be an effective therapeutic measure for preventing OA progression.

RUNX1 regulates site specificity of DNA demethylation by recruitment of DNA demethylation machineries in hematopoietic cells.

RUNX1 is an essential master transcription factor in hematopoietic development and plays important roles in immune functions. Although the gene regulatory mechanism of RUNX1 has been characterized extensively, the epigenetic role of RUNX1 remains unclear. Here, we demonstrate that RUNX1 contributes DNA demethylation in a binding site-directed manner in human hematopoietic cells. Overexpression analysis of RUNX1 showed the RUNX1-binding site-directed DNA demethylation. The RUNX1-mediated DNA demethylation was also observed in DNA replication-arrested cells, suggesting an involvement of active demethylation mechanism. Coimmunoprecipitation in hematopoietic cells showed physical interactions between RUNX1 and DNA demethylation machinery enzymes TET2, TET3, TDG, and GADD45. Further chromatin immunoprecipitation sequencing revealed colocalization of RUNX1 and TET2 in the same genomic regions, indicating recruitment of DNA demethylation machinery by RUNX1. Finally, methylome analysis revealed significant overrepresentation of RUNX1-binding sites at demethylated regions during hematopoietic development. Collectively, the present data provide evidence that RUNX1 contributes site specificity of DNA demethylation by recruitment of TET and other demethylation-related enzymes to its binding sites in hematopoietic cells.