Enhancement of the synthesis of n-3 PUFAs in fat-1 transgenic mice inhibits mTORC1 signalling and delays surgically induced osteoarthritis in comparison with wild-type mice

Intra-articular Delivery of Antago-miR-483-5p Inhibits Osteoarthritis by Modulating Matrilin 3 and Tissue Inhibitor of Metalloproteinase 2

MicroRNAs (miRNAs) are emerging as important regulators in osteoarthritis (OA) pathogenesis. In our study, a real-time PCR assay revealed that miR-483-5p was upregulated in articular cartilage from OA patients and experimental OA mice induced by destabilization of the medial meniscus compared to their controls. Overexpression of miR-483-5p by intra-articular injection of lentivirus LV3-miR-483-5p significantly enhanced the severity of experimental OA. Consequently, we synthesized antago-miR-483-5p to silence the endogenous miR-483-5p and delivered it intra-articularly, which revealed that antago-miR-483-5p delayed the progression of experimental OA. To investigate the functional mechanism of miR-483-5p in OA development, we generated doxycycline-inducible miR-483 transgenic (TG483) mice. TG483 mice exhibited significant acceleration and increased severity of OA, and age-related OA occurred with higher incidence and greater severity in TG483 mice compared with their controls. Furthermore, our results revealed miR-483-5p directly targeted to the cartilage matrix protein matrilin 3 (Matn3) and tissue inhibitor of metalloproteinase 2 (Timp2) to stimulate chondrocyte hypertrophy, extracellular matrix degradation, and cartilage angiogenesis, and it consequently initiated and accelerated the development of OA. In conclusion, our findings reveal an miRNA functional pathway important for OA development. Targeting of miR-483-5p by intra-articular injection of antago-miR-483-5p represents an approach that could prevent the onset of OA and delay its progression.

A low ratio of n-6/n-3 polyunsaturated fatty acids suppresses matrix metalloproteinase 13 expression and reduces adjuvant-induced arthritis in rats

Increased expression of matrix metalloproteinase 13 (MMP13) in chondrocytes contributes to the development of osteoarthritis. The hypothesis of this study was that diet with a low ratio of n-6/n-3 polyunsaturated fatty acids (PUFAs) is associated with reduced MMP13 expression in inflammatory chondrocytes in vitro and in vivo. Human chondrocytes were cultured with different ratios of linoleic acid (LA, n-6 PUFA) to α-linolenic acid (n-3 PUFA) from 1:1 to 10:1. Proliferation of chondrocytes, MMP13 protein and mRNA levels were detected, respectively. Sprague-Dawley rats (n=30) were fed diets containing different ratios of n-6/n-3 PUFA. Freund's complete adjuvant was injected to make the model of arthritis. Paw swelling rate was measured and all rats were euthanized after 6 weeks of treatment. Serum MMP13 and IL-1 were measured by enzyme-linked immunosorbent assay. Joint histological sections were stained with safranin-O Fast Green to evaluate cartilage damage. Low ratio of LA/α-linolenic acid decreased the mRNA and protein levels of MMP13 but did not affect chondrocytes proliferation. Ratios of PUFA such as 1:1 and 2:1 significantly reduced paw swelling rate, and serum MMP13 and IL-1 levels in a rat model. Histological staining showed that ratios of 1:1 and 2:1 PUFA significantly alleviated cartilage damage in adjuvant-induced arthritis. A ratio of n-6/n-3 PUFA of 1:1 showed the strongest inhibitory effect on MMP13. Our results indicate that a low ratio of n-6/n-3 PUFA at 1:1 significantly suppressed MMP13 expression both in vitro and in vivo and reduced adjuvant-induced arthritis in rats could be a means to control and reduce the symptoms of osteoarthritis.

Endogenous conversion of n-6 to n-3 polyunsaturated fatty acids attenuates K/BxN serum-transfer arthritis in fat-1 mice

It is suggested that n-3 polyunsaturated fatty acids (PUFAs) can be used in the preventive or therapeutic management of rheumatoid arthritis (RA); however, controversial results have been reported. Here, we examined the effects of a decrease in the n-6/n-3 PUFA ratio on RA using fat-1 transgenic mice. First, we tested whether fat-1 expression modulated signaling pathways in fibroblast-like synoviocytes (FLSs) stimulated with tumor necrosis factor α (TNF-α). TNF-α activated p38 mitogen-activated protein kinase and increased phosphorylation of the signal transducer and activator of transcription 3 in wild type (WT) FLSs but not in fat-1 FLSs. Arthritis was induced by injection of K/BxN serum. Based on clinical scores, ankle thickness and pathological severity, we showed that WT mice developed clinically overt arthritis, whereas fat-1 mice showed attenuated arthritis. Moreover, fat-1 mice exhibited down-regulated local and systemic levels of inflammatory cytokines. Lastly, bone marrow-derived macrophages (BMMs) of WT mice differentiated into tartrate-resistant acid phosphatase-positive multinucleated osteoclasts, whereas the osteoclastogenenic process was suppressed in BMMs of fat-1 mice. The endogenous conversion of n-6 to n-3 PUFAs via fat-1 plays a key role in attenuation of RA; therefore, dietary supplementation of n-3 PUFAs may have therapeutic potential for the management of RA.

mTOR: a potential therapeutic target in osteoarthritis?

Osteoarthritis (OA) is a chronic degenerative joint disease characterized by the progressive loss of articular cartilage, remodeling of the subchondral bone, and synovial inflammation. Mammalian target of rapamycin (mTOR) is a serine/threonine protein kinase that controls critical cellular processes such as growth, proliferation, and protein synthesis. Recent studies suggest that mTOR plays a vital role in cartilage growth and development and in altering the articular cartilage homeostasis as well as contributing to the process of cartilage degeneration associated with OA. Both pharmacological inhibition and genetic deletion of mTOR have been shown to reduce the severity of OA in preclinical mouse models. In this review article, we discuss the roles of mTOR in cartilage development, in maintaining articular cartilage homeostasis, and its potential as an OA therapeutic target.

Deficiency of G-protein coupled receptor 40, a lipid-activated receptor, heightens in vitro- and in vivo-induced murine osteoarthritis

Osteoarthritis (OA) is an age-related degenerative joint disease. To date, its management is focused on symptoms (pain and inflammation). Studies suggest that fatty acids can reduce the expression of inflammatory and catalytic mediators, and improve in vivo joint function. Free fatty acid receptors (FFARs) such as G-protein coupled receptor 40 (GPR40) are proposed as attractive therapeutic targets to counteract inflammation and cartilage degradation observed in OA. This study aims to elucidate the involvement of GPR40 in OA. In this study, we used an in vitro model of OA, and surgically induced OA by ligament transection and partial meniscectomy in wild-type and GPR40 deficient mice. OA phenotype was investigated in vivo by histology and genes expression. We demonstrate that IL-1β-treated GPR40(-/-) chondrocytes secret more inflammatory mediators (nitric oxide, interleukin-6, prostaglandin E2) and active catabolic enzymes (metalloproteinase-2, -9 [MMP-2, MMP-9]), and show decreased anabolism (glycoaminoglycan) compared to GPR40(+/+) cells. In accordance with these results, we show that GPR40(-/-) mice exhibit an aggravated OA-induced phenotype characterized by higher tidemark exposure, frequency of osteophyte formation and subchondral bone sclerosis. Altogether our results demonstrate that GPR40 deficiency leads to an extended OA phenotype, providing evidence that increasing GPR40 activity, by natural or synthetic ligands, could be a new strategy in the management of OA.

Metabolic enrichment of omega-3 polyunsaturated fatty acids does not reduce the onset of idiopathic knee osteoarthritis in mice

OBJECTIVE

We evaluated the effect of a reduction in the systemic ratio of n-6:n-3 polyunsaturated fatty acids (PUFAs) on changes in inflammation, glucose metabolism, and the idiopathic development of knee osteoarthritis (OA) in mice. We hypothesized that a lower ratio of n-6:n-3 PUFAs would protect against OA markers in cartilage and synovium, but not bone.

DESIGN

Male and female fat-1 transgenic mice (Fat-1), which convert dietary n-6 to n-3 PUFAs endogenously, and their wild-type (WT) littermates were fed an n-6 PUFA enriched diet for 9-14 months. The effect of gender and genotype on serum PUFAs, interleukin (IL)-6, tumor necrosis factor (TNF)-α, and glucose tolerance was tested by 2-factor analysis of variance (ANOVA). Cortical and trabecular subchondral bone changes were documented by micro-focal computed tomography (CT), and knee OA was assessed by semi-quantitative histomorphometry grading.

RESULTS

The n-6:n-3 ratio was reduced 12-fold and 7-fold in male and female Fat-1 mice, respectively, compared to WT littermates. IL-6 and TNF-α levels were reduced modestly in Fat-1 mice. However, these systemic changes did not reduce osteophyte development, synovial hyperplasia, or cartilage degeneration. Also the fat-1 transgene did not alter subchondral cortical or trabecular bone morphology or bone mineral density.

CONCLUSIONS

Reducing the systemic n-6:n-3 ratio does not slow idiopathic changes in cartilage, synovium, or bone associated with early-stage knee OA in mice. The anti-inflammatory and anti-catabolic effects of n-3 PUFAs previously reported for cartilage may be more evident at later stages of disease or in post-traumatic and other inflammatory models of OA.

Dietary fatty acid content regulates wound repair and the pathogenesis of osteoarthritis following joint injury

OBJECTIVE

The mechanisms linking obesity and osteoarthritis (OA) are not fully understood and have been generally attributed to increased weight, rather than metabolic or inflammatory factors. Here, we examined the influence of fatty acids, adipokines, and body weight on OA following joint injury in an obese mouse model.

METHODS

Mice were fed high-fat diets rich in various fatty acids (FA) including saturated FAs (SFAs), ω-6 polyunsaturated FAs (PUFAs), and ω-3 PUFAs. OA was induced by destabilising the medial meniscus. Wound healing was evaluated using an ear punch. OA, synovitis and wound healing were determined histologically, while bone changes were measured using microCT. Activity levels and serum cytokines were measured at various time-points. Multivariate models were performed to elucidate the associations of dietary, metabolic and mechanical factors with OA and wound healing.

RESULTS

Using weight-matched mice and multivariate models, we found that OA was significantly associated with dietary fatty acid content and serum adipokine levels, but not with body weight. Furthermore, spontaneous activity of the mice was independent of OA development. Small amounts of ω-3 PUFAs (8% by kcal) in a high-fat diet were sufficient to mitigate injury-induced OA, decreasing leptin and resistin levels. ω-3 PUFAs significantly enhanced wound repair, SFAs or ω-6 PUFAs independently increased OA severity, heterotopic ossification and scar tissue formation.

CONCLUSIONS

Our results indicate that with obesity, dietary FA content regulates wound healing and OA severity following joint injury, independent of body weight, supporting the need for further studies of dietary FA supplements as a potential therapeutic approach for OA.

Lipid transport and metabolism in healthy and osteoarthritic cartilage

Cartilage is an avascular tissue and cartilage metabolism depends on molecule diffusion from synovial fluid and subchondral bone. Thus, nutrient availability is limited by matrix permeability according to the size and charge of the molecules. Matrix composition limits the access of molecules to chondrocytes, determining cell metabolism and cartilage maintenance. Lipids are important nutrients in chondrocyte metabolism and are available for these cells through de novo synthesis but also through diffusion from surrounding tissues. Cartilage status and osteoarthritis development depend on lipid availability. This paper reviews lipid transport and metabolism in cartilage. We also analyze signalling pathways directly mediated by lipids and those that involve mTOR pathways, both in normal and osteoarthritic cartilage.