Objective: Obesity is one of the greatest risk factors for osteoarthritis (OA) and evidence is accumulating that inflammatory mediators and innate immunity play an important role. The infrapatellar fat pad (IPFP) could be a potential local source of inflammatory mediators in the knee. Here, we combine surgical joint damage with high-fat feeding in mice to investigate inflammatory responses in the IPFP during OA development. Design: Mice (n ¼ 30) received either a low-fat diet (LFD), high-fat diet (HFD) for 18 weeks or switched diets (LFD > HFD) after 10 weeks. OA was induced by surgical destabilization of the medial meniscus (DMM), contralateral knees served as sham controls. An additional HFD-only group (n ¼ 15) received no DMM. Results: The most pronounced inflammation, characterized by macrophage crown-like structures (CLS), was found in HFD þ DMM mice, CLS increased compared to HFD only (mean difference ¼ 7.26, 95%CI [1.52e13.0]) and LFD þ DMM (mean difference ¼ 6.35, 95%CI [0.53e12.18). The M1 macrophage marker iNOS increased by DMM (ratio ¼ 2.48, 95%CI [1.37e4.50]), while no change in M2 macrophage marker CD206 was observed. Fibrosis was minimal by HFD alone, but in combination with DMM it increased with 23.45% (95%CI [13.67e33.24]). Conclusions: These findings indicate that a high-fat diet alone does not trigger inflammation or fibrosis in the infrapatellar fat pad, but in combination with an extra damage trigger, like DMM, induces inflammation and fibrosis in the infrapatellar fat pad. These data suggest that HFD provides a priming effect on the infrapatellar fat pad and that combined actions bring the joint in a metabolic state of progressive OA.

In animal models, joint degeneration observed in response to obesogenic diet varies in nature and severity. In this study, we compare joint damage in Sprague Dawley and Wistar-Han rats in response to a high-fat, high-sucrose (HFS) diet groove model of osteoarthritis (OA). Wistar Han (n = 5) and Sprague Dawley (n = 5) rats were fed an HFS diet for 24 weeks. OA was induced 12 weeks after the diet onset by groove surgery in the right knee joint. The left knee served as a control. Outcomes were OARSI histopathology scoring, bone changes by µCT imaging, local (synovial and fat pad) and systemic (blood cytokine) inflammation markers. In both rat strains, the HFS diet resulted in a similar change in metabolic parameters, but only Sprague Dawley rats showed a large, osteoporosis-like decrease in trabecular bone volume. Osteophyte count and local joint inflammation were higher in Sprague Dawley rats. In contrast, cartilage degeneration and systemic inflammatory marker levels were similar between the rat strains. The difference in bone volume loss, osteophytosis and local inflammation suggest that both rat strains show a different joint damage phenotype and could, therefore, potentially represent different OA phenotypes observed in humans.

Objective Folate receptor beta (FR-β) has been used as a clinical marker and target in multiple inflammatory diseases, including osteoarthritis (OA) and rheumatoid arthritis (RA). However, the conditions under which FR-β+ macrophages arise remain unclear and could be affected by corticosteroids. Therefore, we studied FR-β expression in vitro in macrophage subtypes and determined their response to triamcinolone acetonide (TA), a clinically often-used corticosteroid. Design Human monocyte–derived macrophages were differentiated to the known M0, M1, or M2 macrophage phenotypes. The phenotype and FR-β expression and plasticity of the macrophage subtypes were determined using flow cytometry, reverse transcription-quantitative polymerase chain reaction (RT-qPCR), and enzyme-linked immunosorbent assay (ELISA). Results FR-β expression was low in granulocyte-macrophage colony-stimulating factor (GM-CSF)-generated (M1-like) macrophages and high in macrophage colony-stimulating factor (M-CSF)-generated (M0 and M2-like) macrophages. FR-β expression remained high once the M0 or M2 macrophages were stimulated with pro-inflammatory stimuli (interferon-γ plus lipopolysaccharide) to induce M1-like macrophages. On the contrary, anti-inflammatory TA treatment skewed GM-CSF macrophage differentiation toward an M2 and FR-β+ phenotype. Conclusions As corticosteroids skewed monocytes toward an FR-β-expressing, anti-inflammatory phenotype, even in an M1 priming GM-CSF environment, FR-β has potential as a biomarker to monitor success of treatment with corticosteroids. Without corticosteroid treatment, M-CSF alone induces high FR-β expression which remains high under pro-inflammatory conditions. This explains why pro-inflammatory FR-β+ macrophages (exposed to M-CSF) are observed in arthritis patients and correlate with disease severity.

expression of COL10A1 in OA chondrocytes in alginate, suggesting a reduction in hypertrophy (Fig. 1A). ALW-41-27 significantly decreased the production of nitric oxide and IL-6 at the protein and gene level in OA chondrocytes stimulated with TNFa. MMP1 and MMP13, genes encoding catabolic enzymes were significantly reduced as well (Fig.1B). Conclusions: These results identify EphA2 to be associated with osteoarthritic cartilage, chondrocyte hypertrophy and inflammation. ALW-41-27 attenuates the hypertrophic differentiation of human chondrocytes and reduces inflammatory markers. Therefore, the use of ALW-41-27 may constitute a new approach for the treatment of OA.

Background Mesenchymal stromal/stem cells (MSCs) and MSC-derived extracellular vesicles (MSC-EVs) hold promise as a disease modifying treatment in osteoarthritis (OA). Obesity, and its associated inflammation, contribute to OA development and metabolic OA represents a specific and significant group of the OA patient population. Given their immunomodulatory properties, MSC and MSC-EVs are especially interesting for this group of patients as a therapeutic option. Here, we were the first to compare the therapeutic efficacy of MSCs and MSC-EVs in a mild OA model taking these metabolic aspects into consideration. Methods Male Wistar-Han rats (Crl:WI(Han) (n = 36) were fed a high fat diet for 24 weeks, with unilateral induction of OA by groove surgery after 12 weeks. Eight days after surgery rats were randomized in three treatment groups receiving MSCs, MSC-EVs or vehicle injection. Pain-associated behavior, joint degeneration, and local and systemic inflammation were measured. Results We demonstrated that despite not having a significant therapeutic effect, MSC-EV treatment results in lower cartilage degeneration, less pain behaviour, osteophytosis and joint inflammation, than MSC treatment. Suggesting that MSC-EVs could be a more promising therapeutic strategy than MSCs in this mild metabolic OA model. Conclusion In summary, we find that MSC treatment has negative effects on the joint in metabolic mild OA. This is an essential finding for the significant group of patients with metabolic OA phenotype, and might help to understand why clinical translation of MSC treatment shows varying therapeutic efficacy thus far. Our results also suggest that MSC-EV-based treatment might be a promising option for these patients, however MSC-EV therapeutic efficacy will need improvement.

Background: Mesenchymal stromal/stem cells (MSCs) and MSC-derived extracellular vesicles (MSC-EVs) hold promise as a disease modifying treatment in Osteoarthritis (OA). Obesity, and its associated inflammation, contribute to OA development and metabolic OA represents a specific and significant group of the OA patient population. Given their immunomodulatory properties, MSC and MSC-EVs are especially interesting for this group of patients as a therapeutic option. Here, we were the first to compare the therapeutic efficacy of MSCs and MSC-EVs in a mild OA model taking these metabolic aspects into consideration. Methods: Male Wistar-Han rats (Crl:WI(Han) (n=36) were fed a high fat diet for 24 weeks, with unilateral induction of OA by groove surgery after 12 weeks. Eight days after surgery rats were randomized in three treatment groups receiving MSCs, MSC-EVs or vehicle injection. Pain-associated behavior, joint degeneration, and local and systemic inflammation were measured. Results: We demonstrated that despite not having a significant therapeutic effect, MSC-EV treatment results in lower cartilage degeneration, less pain behaviour, osteophytosis and joint inflammation, than MSC treatment. Suggesting that MSC-EVs could be a safer therapeutic strategy than MSCs in this mild metabolic OA model. Conclusions: In summary, we find that MSC treatment has negative effects on the joint in metabolic mild OA. This is an essential finding for the significant group of patients with metabolic OA phenotype, and might help to understand why clinical translation of MSC treatment shows varying therapeutic efficacy thus far. Our results also suggest that MSC-EV-based treatment might be a safer option for these patients, however MSC-EV therapeutic efficacy will need improvement.

No abstract

LPS/HA treatment for 4 hours did not alter the number or relative proportions of the three major immune cell populations of the FR þ subset, total neutrophils or total T cells, the total number of macrophages (mean 22% reduction) declined (Figure 1A). Both macrophages and neutrophils expressed functional FR; in contrast, the low amount of folate taken up by T cells was not specifically mediated by FR (not competed by label-free folate) (Figure 1B). Despite the reduction in macrophage numbers, incubation of primary SF cells with LPS/HA for 2 hours resulted in a dramatic increase in the number of IL-1b producing macrophages (p¼0.045, 34-fold increase by intracellular detection); the number of IL-1b producing T cells and neutrophils did not change. Compared to the negative control, LPS/HA treatment statistically significantly increased IL-1b production by the FR þ (p¼0.029) but not the FR-(p¼0.22) sub-populations (Figure 1C&D). Incubation of primary SF cells with LPS/HA did not increase the number of IL-6 producing immune cells. Conclusions: We have identified macrophages, neutrophils, and T cells as the three major cell populations in primary human OA SF. Both activated macrophages and neutrophils from knee OA SF express functional folate receptors. The addition of LPS/HA did not affect the viability of the FR þ cell sub-populations of primary human SF cells. The inflammatory responses induced by LPS/HA mainly affected macrophages and predominantly the FR þ macrophages. Taken together, these results suggest that FR þ macrophages may be important in the pathogenesis of OA and might be targeted by means of folate-drug conjugates.