Enhanced healing outcomes in MRL/MpJ mouse tissues conserved in insertion site following surgical repair

Background: Surgical repair of supraspinatus tendons (SSTs) has a high failure rate at the insertion site. A significant hurdle to ther-apeutic development is that effective intrinsic healing mechanisms are unknown. The MRL/MpJ (MRL) mouse exhibits tissue-specific enhanced healing; however, these tissues exhibit disparate properties from the complex SST. The extent of SST healing in the complex environment of the rotator cuff is unknown. We hypothesized that MRL mice would exhibit enhanced restoration of the structurally complex insertion site, resulting in functional improvements. Methods: B6 and MRL mice underwent SST detachment and immediate surgical repair. Mice were analyzed for gait assessment after either 2 or 6 weeks and were then killed humanely for immunohistologic analysis.Results: MRL SSTs demonstrated enhanced recovery of zonal architecture and bone structure compared with B6 SSTs. MRL SSTs exhibited decreased levels of type III collagen at 2 weeks and increased levels of type I procollagen at 6 weeks compared with B6 SSTs. MRL mice experienced initial gait deficits at 2 weeks that had recovered by 6 weeks.Discussion: The temporal balance of collagen in MRL mice suggests recovery toward naive composition. Initial gait deficits in MRL mice may provide a protective loading environment that is ultimately beneficial. The mechanisms of enhanced healing observed pre-viously in MRL mice may be conserved in the complex SST, providing a platform to interrogate specific aspects of improved healing.Level of evidence: Basic Science Study (c) 2022 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.

Automated summary

The study found that MRL mice exhibited enhanced healing in the repair of supraspinatus tendons compared to B6 mice. They showed improved zonal architecture and bone structure recovery, as well as a temporal balance of collagen levels. The initial gait deficits observed in MRL mice may have provided a protective loading environment that ultimately contributed to better healing.