Role of lysyl oxidase like-2 in post-traumatic osteoarthritis and cartilage regeneration
OA Version
Citation
Abstract
INTRODUCTION: While the progressive joint disease osteoarthritis (OA) affects a significant portion of the US population, there remain a few therapeutic options. Identifying agents that promote cartilage regeneration and protect against cartilage damage could provide breakthroughs for OA prevention and treatment. However, there are no chondroprotective agents approved for clinical application. In the previous studies from our lab, we showed that lysyl oxidase like-2(LOXL2) is elevated in the regenerative response during fracture healing in mice and has a critical role in chondrogenic differentiation. Indeed, LOXL2 is an anabolic effector that attenuates proinflammatory signaling in OA cartilage of the TMJ and knee joint, and induces chondroprotective and regenerative responses (Alshenibr, Tashkandi et al. 2017). The goal of the present study is to evaluate the role of LOXL2 in post-traumatic OA in destabilized medial meniscus mouse (DMM) model.
MATERIALS AND METHODS: The approval to obtain human tissues was obtained from Institutional Review Board, and animal experiments were approved by Institutional Animal Care and Use Committee, Boston University. In order to evalute loss of LOXL2 function, Tamoxifen inducible cartilage-specific LOXL2 mice were generated. At 5-6 months of age, the destabilized medial meniscus (DMM) surgeries to induce OA was performed (n=48 mice).Tamoxifen injection was administered to delete LOXL2 (LOXL2-cKO) and vehicle injection (LOXL2-VC) was performed, The gain of LOXL2 function were performed in by administering intra-articular injections of adenoviral-LOXL2 (Adv-RFP-LOXL2) and respective control (Adv-RFP-Empty) followed by an treadmill exhaustion test, allodynia, immunostaining, safranin-O staining, and RT-qPCR to determine knee joint functional and structural analysis.
RESULTS: The analysis of data from LOXL2-cKO group compared to the respective control (LOXL2-VC) showed that LOXL2 and aggrecan have reduced levels in DMM LOXL2-cKO mouse model. The comparison of sham surgery group showed LOXL2-cKO has reduction of ACAN and LOXL2 compared to LOXL2-VC . Thus, LOXL2-cKO mice with DMM-operated knee joint has severe changes compared to LOXL2-VC. Safranin-O-staining for proteogylcan and immunostaining and its quantification data shows that DMM surgery in LOXL2-cKO knee cartilage reduced proteoglycan, aggrecan, LOXL2, lubricin whereas elevated MMP13 and IL-1 β compared to LOXL2-VC. In another study the role of adenovirus delivered LOXL2 in the knee joint, the treadmill exhaustion test showed that the treadmill running for time and distance are impaired in the group with Adv-RFP-EMPTY injected group and rescued in Adv-RFP-LOXL2 injected group.
CONCLUSION: LOXL2 appears to protect mice from DMM-OA-induced impaired functional changes. Cartilage-specific deletion of LOXL2 shows defects in proteoglycan and aggrecan expression. As expected, LOXL2 overexpression restored knee joint function and impaired structural changes. Earlier studies from our laboratory showed that LOXL2 could have interaction with epigenetic regulators such as lysine-specific demethylase 1. We showed in the current study that LOXL2 could restore structure and function in Lsd1 knockout mice knee joint, and the mechanism must be through LSD1. We have identified novel role of LOXL2 in the mechanism of OA; our studies will provide more information for therapeutic application.