Human PRG4 blocking peptide

Purpose of this study: To elucidate the origin of cell populations that contribute to rotator cuff healing, we developed a mouse surgical model where a full-thickness, central detachment is created in the supraspinatus. Materials and methods: Three different inducible Cre transgenic mice with Ai9-tdTomato reporter expression (PRG4-9, aSMA-9, and AGC-9) were used to label different cell populations in the shoulder. The defect was created surgically in the supraspinatus. The mice were injected with tamoxifen at surgery to label the cells and sacrificed at 1, 2, and 5 weeks postoperatively. Frozen sections were fluorescently imaged then stained with Toluidine Blue and re-imaged. Results: Three notable changes were apparent postoperatively. (1) A long thin layer of tissue formed on the bursal side overlying the supraspinatus tendon. (2) The tendon proximal to the defect initially became hypercellular and disorganized. (3) The distal stump at the insertion underwent minimal remodeling. In the uninjured shoulder, tdTomato expression was seen in the tendon midsubstance and paratenon cell on the bursal side in PRG4-9, in paratenon, blood vessels, and periosteum of acromion in SMA-9, and in articular cartilage, unmineralized fibrocartilage of supraspinatus enthesis, and acromioclavicular joint in AGC-9 mice. In the injured PRG4-9 and SMA-9 mice, the healing tissues contained an abundant number of tdTomato+ cells, while minimal contribution of tdTomato+ cells was seen in AGC-9 mice. Conclusions: The study supports the importance of the bursal side of the tendon to rotator cuff healing and PRG4 and aSMA may be markers for these progenitor cells.

Intravenous infusion of mesenchymal stromal cells (MSCs) is thought to be a viable treatment for numerous disorders. Although the intrinsic immunosuppressive ability of MSCs has been credited for this therapeutic effect, their exact impact on endogenous tissue-resident cells following delivery has not been clearly characterized. Moreover, multiple studies have reported pulmonary sequestration of MSCs upon intravenous delivery. Despite substantial efforts to improve MSC homing, it remains unclear whether MSC migration to the site of injury is necessary to achieve a therapeutic effect. Using a murine excisional wound healing model, we offer an explanation of how sequestered MSCs improve healing through their systemic impact on macrophage subpopulations. We demonstrate that infusion of MSCs leads to pulmonary entrapment followed by rapid clearance, but also significantly accelerates wound closure. Using single-cell RNA sequencing of the wound, we show that following MSC delivery, innate immune cells, particularly macrophages, exhibit distinctive transcriptional changes. We identify the appearance of a pro-angiogenic CD9(+) macrophage subpopulation, whose induction is mediated by several proteins secreted by MSCs, including COL6A1, PRG4, and TGFB3. Our findings suggest that MSCs do not need to act locally to induce broad changes in the immune system and ultimately treat disease.