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EphrinB2, a member of the Ephrin family, has been linked to several orthopaedic conditions. Nevertheless, the correlation between ephrinB2 and post-traumatic arthritis (PTOA) remains unclear. Human PTOA cartilage from human and mouse knee joints was systematically analysed to investigate the relationship between EphrinB2 and PTOA using SO-FG and toluidine blue staining, micro-CT, histomorphometry, immunohistochemistry, immunofluorescence, lentiviral articular injection and in situ end labeling (TUNEL) assays. EphrinB2 expression was significantly downregulated in PTOA chondrocytes. Blocking EphrinB2 increased the breakdown of cartilage matrix in mice with PTOA via reducing the process of chondrocyte autophagy. The presence of severe cartilage damage was evident, as indicated by a considerable decrease in both cartilage thickness and area, accompanied by an increase in chondrocyte death. Altogether, EphrinB2 is required for the maintenance of cartilage homeostasis in post-traumatic arthritis, and EphrinB2 ablation is associated with accelerated chondrocyte matrix degeneration, finally causing damage to the articular cartilage., (© 2024 The Author(s). Journal of Cellular and Molecular Medicine published by Foundation for Cellular and Molecular Medicine and John Wiley & Sons Ltd.)

Gut mucosal layers are crucial in maintaining the gut barrier function. Gut microbiota regulate homeostasis of gut mucosal layer via gut immune cells such as RORγt (+) IL-22(+) ILC3 cells, which can influence the proliferation of mucosal cells and the production of mucin. However, it is unclear how gut microbiota execute this regulation. Here we show that lactobacilli promote gut mucosal formation by producing L-Ornithine from arginine. L-Ornithine increases the level of aryl hydrocarbon receptor ligand L-kynurenine produced from tryptophan metabolism in gut epithelial cells, which in turn increases RORγt (+)IL-22(+) ILC3 cells. Human REG3A transgenic mice show an increased proportion of L-Ornithine producing lactobacilli in the gut contents, suggesting that gut epithelial REG3A favors the expansion of L-Ornithine producing lactobacilli. Our study implicates the importance of a crosstalk between arginine metabolism in Lactobacilli and tryptophan metabolism in gut epithelial cells in maintaining gut barrier. Qi, Li, Yun, Zhang et al.show that lactobacilli promote the generation of gut mucosa by facilitating the conversion of arginine to L-Ornithine. This study highlights the importance of a crosstalk between arginine metabolism in Lactobacilli and tryptophan metabolism in gut epithelial cells in maintaining a healthy gut barrier. [ABSTRACT FROM AUTHOR]