Introduction: Likely due to ignored heterogeneity in disease pathophysiology, osteoarthritis (OA) has become the most common disabling joint disease, without effective disease-modifying treatment... Show moreIntroduction: Likely due to ignored heterogeneity in disease pathophysiology, osteoarthritis (OA) has become the most common disabling joint disease, without effective disease-modifying treatment causing a large social and economic burden. In this study we set out to explore responses of aged human osteochondral explants upon different OA-related perturbing triggers (inflammation, hypertrophy and mechanical stress) for future tailored biomimetic human models.Methods: Human osteochondral explants were treated with IL-1 beta (10 ng/ml) or triiodothyronine (T3; 10 nM) or received 65% strains of mechanical stress (65% MS). Changes in chondrocyte signalling were determined by expression levels of nine genes involved in catabolism, anabolism and hypertrophy. Breakdown of cartilage was measured by sulphated glycosaminoglycans (sGAGs) release, scoring histological changes (Mankin score) and mechanical properties of cartilage.Results: All three perturbations (IL-1 beta, T3 and 65% MS) resulted in upregulation of the catabolic genes MMP13 and EPAS1. IL-1 beta abolished COL2A1 and ACAN gene expression and increased cartilage degeneration, reflected by increased Mankin scores and sGAGs released. Treatment with T3 resulted in a high and significant upregulation of the hypertrophic markers COL1A1, COL10A1 and ALPL. However, 65% MS increased sGAG release and detrimentally altered mechanical properties of cartilage.Conclusion: We present consistent and specific output on three different triggers of OA. Perturbation with the pro-inflammatory IL-1 beta mainly induced catabolic chondrocyte signalling and cartilage breakdown, while T3 initiated expression of hypertrophic and mineralization markers. Mechanical stress at a strain of 65% induced catabolic chondrocyte signalling and changed cartilage matrix integrity. The major strength of our ex vivo models was that they considered aged, preserved, human cartilage of a heterogeneous OA patient population. As a result, the explants may reflect a reliable biomimetic model prone to OA onset allowing for development of different treatment modalities. Show less
Immunometabolism focusses on the interplay between immunological and metabolic processes, both at a systemic and a cellular level. This thesis is divided into two parts based on these two... Show moreImmunometabolism focusses on the interplay between immunological and metabolic processes, both at a systemic and a cellular level. This thesis is divided into two parts based on these two levels. The first part focusses on the infrapatellar fat pad (IFP), an adipose tissue located in the knee, and the potential role in the pathophysiology of osteoarthritis. Therefore, we characterized the IFP based on a cellular and molecular level and found that the inflammatory state of the joint does affect the cellular load of the IFP, however, the secretory profile of the IFP does not seem to be affected. Furthermore, obesity-related changes normally found in adipose tissue were not present in the IFP. When characterizing the IFP we found two interesting cell populations, IL-6-secreting T cells and macrophages with an anti-inflammatory phenotype secreting pro-inflammatory cytokines. Both populations could be involved in the pathophysiology of the osteoarthritic joint. Furthermore, in the second part we focussed on cellular metabolism where we determined the mechanism by which fatty acids exert their effect on T cells. We found that fatty acids are not served as energy, however, whether it is used for daughter cells or influencing cell signalling remains to be elucidated. Show less
This thesis investigates the role of adipose tissue inflammation in joint diseases such as osteoarthritis (OA) and rheumatoid arthritis (RA) . In the first part, we show that baseline levels of... Show moreThis thesis investigates the role of adipose tissue inflammation in joint diseases such as osteoarthritis (OA) and rheumatoid arthritis (RA) . In the first part, we show that baseline levels of circulating adiponectin can predict radiographic progression in patients with early RA. In contrast, in patients with hand OA, this association appears protective. Therefore, to obtain insight into the mechanisms underlying these associations, we investigated the high-molecular-weight isoform of adiponectin (hmwAPN), which is one of the most biologically active isoforms of adiponectin. We show that the associations of total adiponectin with radiographic progression are not mediated by hmwAPN, in either RA or HOA. In the second part, we present the immunological characterization of the infrapatellar fat pad (IFP), a joint associated adipose tissue, in patients with advanced knee OA. We observed profound differences in secreted inflammatory factors and immune cell composition between the IFP and paired subcutaneous adipose tissue samples. Interestingly, we observed obesity-related changes in the IFP phenotype, and in macrophages and adipocytes, Therefore, we investigated the modulatory effects of adipocytes on the phenotype of human macrophages in vitro and we observed that adipocyte-derived lipids can mediate the obesity-related changes in the phenotype of adipose tissue macrophages in humans Show less
Kortekaas, M.C.; Kwok, W.Y.; Reijnierse, M.; Huizinga, T.W.J.; Kloppenburg, M. 2014
Osteoarthritis (OA) is a frequently occurring joint disorder with great impact on the quality of life. In general, OA is described as a heterogeneous disease with degeneration of articular... Show moreOsteoarthritis (OA) is a frequently occurring joint disorder with great impact on the quality of life. In general, OA is described as a heterogeneous disease with degeneration of articular cartilage as main outcome. Despite extensive research on the pathogenesis of OA, there is until now no cure and treatments are primarily aimed at reducing pain. Evidence starts to appear that mild inflammation and obesity-related biochemical changes are involved in OA pathology. It is uncertain what the relative contribution of these processes is and if they characterize a certain type of OA patients. We identified obesity, high cholesterol and systemic inflammation associated with these conditions as major players in OA development, which may activate joint tissues to secrete inflammatory mediators and contribute to the initiation and progression of OA. Our work suggests that a stratification of OA patients with (features of) the metabolic syndrome as underlying mechanism is recommendable, to optimize the efficacy of clinical trials. Approaching OA as a disease induced by whole body metabolism, and integrating knowledge about different potentially active tissues in the OA process, will provide new insights for possible pharmacological interventions. Show less
Osteoarthritis (OA) mainly affects the articular cartilage covering the bones. In this thesis we investigated the relation between levels of inflammatory mediators, genes involved in their... Show moreOsteoarthritis (OA) mainly affects the articular cartilage covering the bones. In this thesis we investigated the relation between levels of inflammatory mediators, genes involved in their regulation and the disease status of OA. We investigated the role of genetic variation at the interleukin(IL)-1 gene cluster in the innate bio-availability of IL-1beta. A haplotype that associated to low innate bio-availability also associated to higher hand OA scores. Although this is counterintuitive with respect to the generally accepted hypothesis that a pro-inflammatory status is detrimental to the cartilage it underlines a complex relationship between inflammation and OA. For the C-reactive protein we identified a haplotype associated to high CRP levels as well as to severe hand OA, which is more in line with expected directions of associations. Analysis of baseline cytokine and chemokine levels indicated that chemokine levels associated to hand OA scores, again with low levels associated to high OA scores. In a follow up functional genomic analysis of a previously identified OA susceptibility gene (DIO2) in our studies we show that the risk allele of this gene is transcribed at higher levels as compared to the non-risk allele. Furthermore, we showed increased DIO2 protein presence in OA affected cartilage. Show less
