Objective: In osteoarthritis, chondrocytes tend to acquire a hypertrophic phenotype, which contributes to the modification of the extracellular matrix, resulting in permanent cartilage changes. In mouse chondrocytes, pro-inflammatory macrophages and pro-inflammatory cytokines have been shown to stimulate hypertrophy via the activation of the nuclear factor kappa B (NF-κB) pathway. Whether or not this also occurs in human chondrocytes remains unclear. We therefore aimed to investigate whether hypertrophy-like responses in human cartilage are driven mainly by intrinsic inflammatory signaling or shaped by specific macrophage populations. Design: Human articular chondrocytes were cultured with pro-inflammatory cytokines or medium conditioned by defined macrophage subsets. Furthermore, the effect of inhibition of NF-κB-dependent gene expression was evaluated using the NF-κB inhibitor SC-514. Hypertrophy was assessed by measuring the transcription level of alkaline phosphatase (ALPL), type X collagen (COL10A1), Indian hedgehog (IHH), and runt-related transcription factor 2 (RUNX2). Results: The expression of hypertrophic genes was not promoted in human chondrocytes by pro-inflammatory cytokines neither pro-inflammatory M(IFNγ + TNFα) macrophages. Inhibition of the NF-κB-dependent gene expression did not affect human articular chondrocyte hypertrophy. However, tissue repair M(IL4) macrophages induced hypertrophy by promoting the expression of COL10A1, RUNX2, and IHH. Conclusion: Intrinsic inflammatory signaling activation is not involved in the hypertrophic shift observed in human articular chondrocytes cultured in vitro. However, tissue repair macrophages may contribute to the onset of this detrimental phenotype in human osteoarthritic cartilage, given the effect observed in our experimental models.@en

Background: Cartilage defects result in joint inflammation. The presence of proinflammatory factors has been described to negatively affect cartilage formation. Purpose: To evaluate the effect and timing of administration of triamcinolone acetonide (TAA), an anti-inflammatory drug, on cartilage repair using a mouse model. Study Design: Controlled laboratory study. Methods: A full-thickness cartilage defect was created in the trochlear groove of 10-week-old male DBA/1 mice (N = 80). Mice received an intra-articular injection of TAA or saline on day 1 or 7 after induction of the defect. Mice were euthanized on days 10 and 28 for histological evaluation of cartilage defect repair, synovial inflammation, and synovial membrane thickness. Results: Mice injected with TAA had significantly less synovial inflammation at day 10 than saline-injected mice independent of the time of administration. At day 28, the levels of synovitis dropped toward healthy levels; nevertheless, the synovial membrane was thinner in TAA- than in saline-injected mice, reaching statistical significance in animals injected on day 1 (70.1 ± 31.9 µm vs 111.9 ± 30.9 µm, respectively; P =.01) but not in animals injected on day 7 (68.2 ± 21.86 µm vs 90.2 ± 21.29 µm, respectively; P =.26). A thinner synovial membrane was moderately associated with less filling of the defect after 10 and 28 days (r = 0.42, P =.02; r = 0.47, P =.01, respectively). Whereas 10 days after surgery there was no difference in the area of the defect filled and the cell density in the defect area between saline- and TAA-injected knees, filling of the defect at day 28 was lower in TAA- than in saline-injected knees for both injection time points (day 1 injection, P =.04; day 7 injection, P =.01). Moreover, there was less collagen type 2 staining in the filled defect area in TAA- than in saline-injected knees after 28 days, reaching statistical significance in day 1–injected knees (2.6% vs 18.5%, respectively; P =.01) but not in day 7–injected knees (7.4% vs 15.8%, respectively; P =.27). Conclusion: Intra-articular injection of TAA reduced synovial inflammation but negatively affected cartilage repair. This implies that inhibition of inflammation may inhibit cartilage repair or that TAA has a direct negative effect on cartilage formation. Clinical Relevance: Our findings show that TAA can inhibit cartilage defect repair. Therefore, we suggest not using TAA to reduce inflammation in a cartilage repair setting.@en

OBJECTIVE: Inflammation is known to negatively affect cartilage repair. However, it is unclear how inflammation influences the migration of mesenchymal stromal cells (MSCs) from the underlying bone marrow into the defect. We therefore aimed to investigate how synovial inflammation influences MSC migration, and whether modulation of inflammation with triamcinolone acetonide (TAA) may influence migration. DESIGN: Inflamed human osteoarthritic synovium, M(IFNγ+TNFα) pro-inflammatory macrophages, M(IL4) repair macrophages, M(IL10) anti-inflammatory macrophages, or synovial fibroblasts were cultured with/without TAA. Conditioned medium (CM) was harvested after 24 hours, and the effect on MSC migration was studied using a Boyden chamber assay. Inflammation was evaluated with gene expression and flow cytometry analysis. RESULTS: Synovium CM increased MSC migration. Modulation of synovial inflammation with TAA further increased migration 1.5-fold (P < 0.01). TAA significantly decreased TNFA, IL1B, and IL6 gene expression in synovium explants and increased CD163, a gene associated with anti-inflammatory macrophages. TAA treatment decreased the percentage of CD14+/CD80+ and CD14+/CD86+ pro-inflammatory macrophages and increased the percentage of CD14+/CD163+ anti-inflammatory macrophages in synovium explants. Interestingly, MSC migration was specifically enhanced by medium conditioned by M(IL4) macrophages and by M(IL10) macrophages treated with TAA, and unaffected by CM from M(IFNγ+TNFα) macrophages and synovial fibroblasts. CONCLUSION: Macrophages secrete factors that stimulate the migration of MSCs. Modulation with TAA increased specifically the ability of anti-inflammatory macrophages to stimulate migration, indicating that they play an important role in secreting factors to attract MSCs. Modulating inflammation and thereby improving migration could be used in approaches based on endogenous repair of full-thickness cartilage defects.@en

Background and purpose: Corticosteroids such as triamcinolone acetonide (TAA) are potent drugs administered intra-articularly as an anti-inflammatory therapy to relieve pain associated with osteoarthritis (OA). However, the ability of early TAA intervention to mitigate OA progression and modulate immune cell subsets remains unclear. Here, we sought to understand the effect of early intra-articular injection of TAA on OA progression, local macrophages, and peripheral blood monocytes. Experimental approach: Degenerative joint disease was induced by intra-articular injection of collagenase into the knee joint of male C57BL/6 mice. After 1 week, TAA or saline was injected intra-articularly. Blood was taken throughout the study to analyse monocyte subsets. Mice were killed at days 14 and 56 post-induction of collagenase-induced OA (CiOA) to examine synovial macrophages and structural OA features. Key results: The percentage of macrophages relative to total live cells present within knee joints was increased in collagenase- compared with saline-injected knees at day 14 and was not altered by TAA treatment. However, at day 56, post-induction of CiOA, TAA-treated knees had increased levels of macrophages compared with the knees of untreated CiOA-mice. The distribution of monocyte subsets present in peripheral blood was not altered by TAA treatment during the development of CiOA. Osteophyte maturation was increased in TAA-injected knees at day 56. Conclusion and implications: Intra-articular injection of TAA increases long-term synovial macrophage numbers and osteophytosis. Our findings suggest that TAA accentuates the progression of osteoarthritis-associated features when applied to an acutely inflamed knee.@en