Leucine Attenuates Osteoarthritis via mTORC1/LXRα-Mediated Macrophage Reprogramming and Rspo2/β-Catenin Axis Suppression.

BackgroundTo investigate the role and regulatory mechanisms of fargesin, one of the main components of Magnolia fargesii, in macrophage reprogramming and crosstalk across cartilage and synovium during osteoarthritis (OA) development.MethodsTen-week-old male C57BL/6 mice were randomized and assigned to vehicle, collagenase-induced OA (CIOA), or CIOA with intra-articular fargesin treatment groups. Articular cartilage degeneration was evaluated using the Osteoarthritis Research Society International (OARSI) score. Immunostaining and western blot analyses were conducted to detect relative protein. Raw264.7 cells were treated with LPS or IL-4 to investigate the role of polarized macrophages. ADTC5 cells were treated with IL-1β and conditioned medium was collected to investigate the crosstalk between chondrocytes and macrophages.ResultsFargesin attenuated articular cartilage degeneration and synovitis, resulting in substantially lower Osteoarthritis Research Society International (OARSI) and synovitis scores. In particular, significantly increased M2 polarization and decreased M1 polarization in synovial macrophages were found in fargesin-treated CIOA mice compared to controls. This was accompanied by downregulation of IL-6 and IL-1β and upregulation of IL-10 in serum. Conditioned medium (CM) from M1 macrophages treated with fargesin reduced the expression of matrix metalloproteinase-13, RUNX2, and type X collagen and increased Col2a1 and SOX9 in OA chondrocytes, but fargesin alone did not affect chondrocyte catabolic processes. Moreover, fargesin exerted protective effects by suppressing p38/ERK MAPK and p65/NF-κB signaling.ConclusionsThis study showed that fargesin switched the polarized phenotypes of macrophages from M1 to M2 subtypes and prevented cartilage degeneration partially by downregulating p38/ERK MAPK and p65/NF-κB signaling. Targeting macrophage reprogramming or blocking the crosstalk between macrophages and chondrocytes in early OA may be an effective preventive strategy.

The role of macrophages in osteoarthritis and cartilage repair

LDL receptor deficiency results in increased osteophyte formation during experimental osteoarthritis both under low and high cholesterol conditions

Background Knee osteoarthritis (KOA) is characterized by cartilage degradation, osteophyte formation, and synovitis. Cartilage degradation in KOA begins with the loss of aggrecan, primarily due to A Disintegrin and Metalloproteinase with Thrombospondin Motif 5 (ADAMTS5), which is produced by chondrocytes and synovial cells and a key target for therapeutic intervention. Current treatments for KOA primarily focus on pain relief, as disease-modifying osteoarthritis drugs (DMOADs) remain unavailable. Electroacupuncture (EA), applying electrical stimulation to acupoints, has been investigated for its potential to alleviate KOA symptoms; however, the specific effects of different acupoint combinations remain unclear. This study investigates the effect of EA on pain and cartilage degeneration in a KOA rat model by examining ADAMTS5 expression in synovial tissue. Materials and methods Male Wistar rats were divided into five groups: control, sham-operated, KOA model, KOA treated with EA at ST36 (Zusanli)-LR8 (Ququan) (KOA+LR8), and KOA treated at ST36-Ex-LE2 (Heding) (KOA+Ex-LE2). The DMM (destabilization of the medial meniscus) procedure induced KOA, and EA was applied thrice weekly for four weeks. The rotarod test was used to assess motor coordination, and samples were collected for immunofluorescence, Western blot, and histological analysis. Pain was assessed via c-fos expression in the spinal cord, while Safranin O-Fast Green staining was used to evaluate cartilage degeneration via the Osteoarthritis Research Society International (OARSI) scoring system. Results The KOA group post-surgery showed reduced motor coordination, while EA at both ST36-LR8 and ST36-Ex-LE2 enhanced performance (day 28: control: 28.8 ± 0.6, sham: 28.4 ± 3.7, KOA: 19.7 ± 0.9, KOA+LR8: 24.8 ± 1.5, KOA+Ex-LE2: 26.9 ± 1.2). Expression of c-fos, elevated in the KOA group, was significantly suppressed by EA (control: 7.6 ± 0.9, sham: 13.6 ± 2.8, KOA: 24.5 ± 2.1, KOA+LR8: 12.8 ± 0.9, KOA+Ex-LE2: 17.0 ± 1.2). Histologically, KOA rats showed severe cartilage degradation and osteophyte formation, while EA at ST36-Ex-LE2 significantly reduced these changes (control: 0.2 ± 0.1, sham: 0.4 ± 0.2, KOA: 1.8 ± 0.4, KOA+LR8: 1.0 ± 0.2, KOA+Ex-LE2: 0.5 ± 0.2). The ST36-LR8 group also showed improvements, although less pronounced than the ST36-Ex-LE2 group. Western blotting revealed that DMM-induced ADAMTS5 expression was significantly inhibited by EA at ST36-Ex-LE2 but not at ST36-LR8 (control: 1.0 ± 0, sham: 1.2 ± 0.4, KOA: 3.0 ± 0.3, KOA+LR8: 2.1 ± 0.3, KOA+Ex-LE2: 1.4 ± 0.4). Conclusion EA at ST36-Ex-LE2 showed a remarkable protective effect on articular cartilage by inhibiting ADAMTS5 expression from synovium, suggesting that it can break the vicious cycle of synovitis and cartilage destruction. In contrast, EA at ST36-LR8 had a moderate effect on cartilage degeneration and ADAMTS5 expression. The difference in efficacy may be due to the anatomical differences between acupoints. ST36-Ex-LE2 coincides with an area rich in synovial fibroblasts and mast cells involved in inflammation and pain. This highlights the importance of acupoint selection to maximize the therapeutic effect of EA. The specificity of this acupoint combination provides a potential strategy for managing KOA and slowing the progression of the disease. Further studies are needed to elucidate the detailed mechanisms behind the effects of EA and explore its potential as an alternative or complementary treatment for KOA.

BackgroundSynovial macrophages have previously shown to be involved in joint destruction during experimental collagenase-induced osteoarthritis (OA). The low density lipoprotein (LDL) receptor expressed by synovial macrophages is involved in transport...

Pain highly correlates to collagenase-induced oa-like damage in female mice but not in males.

BackgroundSynovial macrophages have previously shown to play a significant role in the etiopathology of experimental collagenase-induced osteoarthritis (OA)1. In addition to production of the pro-inflammatory protein S100A8/9 in early OA2,...

Gremlin1 induced by excessive mechanical stress loading enhances cartilage degradation

Are the inflammatory mechanism differentialy regulated across different osteoarthritic joints

Synovial lining macrophages mediate osteophyte formation during experimental osteoarthritis

MRI of articular cartilage in OA: novel pulse sequences and compositional/functional markers

More severe OA pathology in a humanized mouse model for APOE-ε4 as compared to APOE-ε3: APOE-isoforms as possible risk factor for inflammatory osteoarthritis development?

<h3>Background and Objectives</h3> Osteophyte formation is an important hallmark of osteoarthritis (OA) causing limited joint movement and pain. There is increasing belief that synovial activation contributes to OA pathology. As shown recently in our lab, alarmins S100A8 and S100A9 (major products of synovial macrophages) are involved in cartilage degradation and synovial activation during human and murine OA. In the current study, we explored the involvement of S100A8/A9 in osteophyte formation in experimental OA. <h3>Methods</h3> Experimental OA was elicited in C57Bl/6 (WT) mice and S100A9^-/- mice, which also lack functional S100A8. Collagenase induced OA (CIOA) was induced by two times intra-articular injection of 1U collagenase, DMM was induced by transsection of the medial anterior meniscotibial ligament leading to destabilisation of the medial meniscus (DMM). Osteophyte size was assessed by a blind observer using Leica Application Suite (LAS) imaging software. Chondrogenesis was induced by bringing human foetal mesenchymal stem cells (MSCs) in pellet and stimulating for 5 days with BMP-2 and TGFβ1, with or without human recombinant S100A8. Proteoglycan content was quantified using the LAS imaging software on SafO stained sections. <h3>Results</h3> First, we measured osteophyte size in S100A9^-/- mice at day 42 of CIOA. Synovial activation is high in CIOA and this is significantly reduced in S100A9^-/- mice. Osteophyte size was dramatically reduced in the S100A9^-/- compared to WT in the medial collateral ligament (92.5% reduction) but also significantly at the medial side of both tibia and femur (68.2% and 64.6% reduction) (n = 10). One explanation for the reduced osteophyte size in S100A9^-/- mice may be a direct effect of S100-proteins on chondrogenesis. To investigate this, we stimulated MSCs in pellet culture with BMP-2 and TGFβ1, supplemented with 1 and 5 µg/ml S100A8. Proteoglycan deposition as measured by redness in SafO staining was increased 27% and 71% respectively, indicating that S100A8 stimulates chondrogenesis. Finally, we determined osteophyte size in the DMM model, in which synovial involvement is very low. At day 56, we observed no significant differences in osteophyte size between the S100A9^-/- and WT at the medial femur and tibia (105% and 136% of WT, n = 8). This confirms the importance of the synovium in the S100-effect on osteophyte development. <h3>Conclusions</h3> S100A8/S100A9 play a crucial role in osteophyte formation in an OA model that shows clear synovial involvement, probably by stimulating chondrogenesis. Considering also the deleterious effect of S100A8/A9 on joint destruction in OA, targeting these alarmins during OA may be very promising.

An imbalance between M1 and M2 macrophage polarization is critical in osteoarthritis (OA) development. We investigated the effect of M2 macrophage-derived extracellular vesicles (M2-EVs) to reprogramme macrophages from the M1 to M2 phenotype for OA treatment. M1 macrophages and mouse OA models were treated with M2-EVs. Proteomic analysis was performed to evaluate macrophage polarization in vitro. The OA models were as follows: destabilization of the medial meniscus (DMM) surgery-induced OA and collagenase-induced OA (CIOA). Hyaluronic acid (HA) was used to deliver M2-EVs. M2-EVs decreased macrophage accumulation, repolarized macrophages from the M1 to M2 phenotype, mitigated synovitis, reduced cartilage degradation, alleviated subchondral bone damage, and improved gait abnormalities in the CIOA and DMM models. Moreover, HA increased the retention time of M2-EVs and enhanced the efficiency of M2-EVs in OA treatment. Furthermore, proteomic analysis demonstrated that M2-EVs exhibited a macrophage reprogramming ability similar to IL-4, and the pathways might be the NOD-like receptor (NLR), TNF, NF-κB, and Toll-like receptor (TLR) signaling pathways. M2-EVs reprogrammed macrophages from the M1 to M2 phenotype, which resulted in beneficial effects on cartilage and attenuation of OA severity. In summary, our study indicated that M2-EV-guided reprogramming of macrophages is a promising treatment strategy for OA.

BackgroundThickening of the synovial lining layer comprising macrophages expressing an activated phenotype is evident in a substantial subpopulation of patients with early OA and has been associated with pathophysiology and...