Receptor activator of nuclear factor-kappa B ligand-derived microglia healing peptide 1-AcN inhibits osteoarthritis progression in mice

Osteoarthritis (OA) is a degenerative disease characterized by subchondral bone sclerosis, chronic inflammation, and cartilage degradation. Abnormal mechanical stress by meniscal deviation activates osteoclasts and induces the release of transforming growth factor-beta (TGF-β), which promotes mesenchymal stem cell (MSC)-mediated type H angiogenesis and osteogenesis, contributing to bone sclerosis and cartilage damage. Subsequently, macrophages recognize cartilage-derived damage-associated molecular patterns (DAMPs) via Toll-like receptor 4 (TLR4), polarizing into the pro-inflammatory M1 phenotype, thereby exacerbating synovitis and cartilage loss. We developed Microglia Healing Peptide 1 with N-terminal acetylation and C-terminal amidation (MHP1-AcN), a modified peptide derived from receptor activator of nuclear factor-kappa B ligand (RANKL), exhibiting both anti-osteoclastic and anti-inflammatory properties. This study aimed to evaluate the therapeutic potential of MHP1-AcN in a murine OA model and elucidate its underlying mechanisms. OA was induced in mice via destabilization of the medial meniscus (DMM) surgery. Mice were randomly assigned to three groups (n = 8/group): Sham (sham surgery + saline), Vehicle (DMM + saline), and MHP1-AcN (DMM + MHP1-AcN). MHP1-AcN (600 µg) was administered intraperitoneally five times per week from a day after surgery. Knee joints were harvested at 2, 4, and 8 weeks post-surgery. In vitro, the effects of MHP1-AcN were assessed on osteoclast differentiation, inflammatory cytokine expression, and M1/M2 macrophage polarization using mouse bone marrow-derived macrophages. Additionally, its effects on TGF-β-induced osteogenic differentiation of bone marrow-derived MSCs (BMMSCs) and angiogenesis of human umbilical vein endothelial cells (HUVECs) were evaluated. MHP1-AcN markedly suppressed key pathological features of OA in vivo, including synovial inflammation, osteoclast-driven subchondral bone remodeling, aberrant angiogenesis, and cartilage degeneration. In vitro, MHP1-AcN effectively inhibited TLR4-mediated inflammatory cascades by reducing M1 macrophage polarization and inflammasome activation. Despite being derived from RANKL, MHP1-AcN supressed RANKL-induced osteoclastogenesis through NF-κB pathway suppression. Furthermore, MHP1-AcN attenuated TGF-β-induced osteogenic and angiogenic activities via Smad2 signaling inhibition in BMMSCs and HUVECs. MHP1-AcN attenuates OA progression by modulating multi-pathways including aberrant bone remodeling, angiogenesis, and macrophage polarization, representing a promising disease-modifying therapeutic candidate for OA.