Le potentiel thérapeutique du GDF-5 dans l’arthrose : une étude in vitro des facteurs anaboliques et cataboliques du cartilage

Introduction: Le principal objectif de cette étude est de mesurer l’effet du GDF-5 sur l’homéostasie du cartilage. Le GDF-5 est un gène de susceptibilité de l’OA faisant partie de la famille des BMPs et qui favorise la synthèse du cartilage. Le but de notre étude a été de déterminer l’effet du GDF-5 sur le métabolisme catabolique ainsi que sur l’équilibre global des chondrocytes, principalement au niveau de l’Aggrécan. Méthode : Des chondrocytes arthrosiques canins et humains OA ont été exposés au GDF-5. L’expression des ARNm et des protéines a été analysée afin d’évaluer la production de l’Aggrécan et le ratio Col-II/Col-I au niveau des facteurs anaboliques et du phénotype. Pour le catabolisme, l’expression et l’activité des aggrécanases ADAMTS-4 et ADAMTS-5 ont été mesurées. Les épitopes NITEGE et CTX-II ont aussi été quantifiés dans le liquide synovial canin après des injections intraarticulaires de GDF-5. Résultats : Le GDF-5 provoque une augmentation de l’activité cellulaire des chondrocytes canins et humains. Pour les ARNm et l’expression protéique, le GDF-5 augmente l’expression de l’Aggrécan alors que les facteurs cataboliques le diminuent. Le phénotype reste inchangé en présence du produit, sauf à haute dose où on augmente le ColI. L’activité des aggrécanases diminue puisque l’épitope NITEGE diminue alors que le CTX-II augmente dans l’articulation. Conclusion : En somme, les facteurs anaboliques du cartilage sont favorisés, alors que les facteurs cataboliques sont diminués par le GDF-5. Cette action double permet d’illustrer l’effet du GDF-5, le classant comme un potentiel médicament modifiant la maladie de l’OA qui mérite d’être étudiée.

The Role of ULK1 in the Pathophysiology of Osteoarthritis

L'arthrose est la maladie musculo-squelettique la plus commune dans le monde. Elle est l'une des principales causes de douleur et d’incapacité chez les adultes, et elle représente un fardeau considérable sur le système de soins de santé. L'arthrose est une maladie de l’articulation entière, impliquant non seulement le cartilage articulaire, mais aussi la synoviale, les ligaments et l’os sous-chondral. L’arthrose est caractérisée par la dégénérescence progressive du cartilage articulaire, la formation d’ostéophytes, le remodelage de l'os sous-chondral, la détérioration des tendons et des ligaments et l'inflammation de la membrane synoviale. Les traitements actuels aident seulement à soulager les symptômes précoces de la maladie, c’est pour cette raison que l'arthrose est caractérisée par une progression presque inévitable vers la phase terminale de la maladie. La pathogénie exacte de l'arthrose est encore inconnue, mais on sait que l'événement clé est la dégradation du cartilage articulaire. Le cartilage articulaire est composé uniquement des chondrocytes; les cellules responsables de la synthèse de la matrice extracellulaire et du maintien de l'homéostasie du cartilage articulaire. Les chondrocytes maintiennent la matrice du cartilage en remplaçant les macromolécules dégradées et en répondant aux lésions du cartilage et aux dégénérescences focales en augmentant l'activité de synthèse locale. Les chondrocytes ont un taux faible de renouvellement, c’est pour cette raison qu’ils utilisent des mécanismes endogènes tels que l'autophagie (un processus de survie cellulaire et d’adaptation) pour enlever les organelles et les macromolécules endommagés et pour maintenir l'homéostasie du cartilage articulaire. i L'autophagie est une voie de dégradation lysosomale qui est essentielle pour la survie, la différenciation, le développement et l’homéostasie. Elle régule la maturation et favorise la survie des chondrocytes matures sous le stress et des conditions hypoxiques. Des études effectuées par nous et d'autres ont montré qu’un dérèglement de l’autophagie est associé à une diminution de la chondroprotection, à l'augmentation de la mort cellulaire et à la dégénérescence du cartilage articulaire. Carames et al ont montré que l'autophagie est constitutivement exprimée dans le cartilage articulaire humain normal. Toutefois, l'expression des inducteurs principaux de l'autophagie est réduite dans le vieux cartilage. Nos études précédentes ont également identifié des principaux gènes de l’autophagie qui sont exprimés à des niveaux plus faibles dans le cartilage humain atteint de l'arthrose. Les mêmes résultats ont été montrés dans le cartilage articulaire provenant des modèles de l’arthrose expérimentaux chez la souris et le chien. Plus précisément, nous avons remarqué que l'expression d’Unc-51 like kinase-1 (ULK1) est faible dans cartilage humain atteint de l'arthrose et des modèles expérimentaux de l’arthrose. ULK1 est la sérine / thréonine protéine kinase et elle est l’inducteur principal de l’autophagie. La perte de l’expression de ULK1 se traduit par un niveau d’autophagie faible. Etant donné qu’une signalisation adéquate de l'autophagie est nécessaire pour maintenir la chondroprotection ainsi que l'homéostasie du cartilage articulaire, nous avons proposé l’hypothèse suivante : une expression adéquate de ULK1 est requise pour l’induction de l’autophagie dans le cartilage articulaire et une perte de cette expression se traduira par une diminution de la chondroprotection, et une augmentation de la mort des chondrocytes ce qui conduit à la dégénérescence du cartilage articulaire. Le rôle exact de ULK1 dans la pathogénie de l'arthrose est inconnue, j’ai alors créé pour la première fois, des souris KO ULK1spécifiquement dans le cartilage en utilisant la technologie Cre-Lox et j’ai ensuite soumis ces souris à la déstabilisation du ménisque médial (DMM), un modèle de l'arthrose de la souris pour élucider le rôle spécifique in vivo de ULK1 dans pathogenèse de l'arthrose. Mes résultats montrent que ULK1 est essentielle pour le maintien de l'homéostasie du cartilage articulaire. Plus précisément, je montre que la perte de ULK1 dans le cartilage articulaire a causé un phénotype de l’arthrose accéléré, associé à la dégénérescence accélérée du cartilage, l’augmentation de la mort cellulaire des chondrocytes, et l’augmentation de l'expression des facteurs cataboliques. En utilisant des chondrocytes provenant des patients atteints de l’arthrose et qui ont été transfectées avec le plasmide d'expression ULK1, je montre qu’ULK1 est capable de réduire l’expression de la protéine mTOR (principal régulateur négatif de l’autophagie) et de diminuer l’expression des facteurs cataboliques comme MMP-13 et ADAMTS-5 et COX-2. Mes résultats jusqu'à présent indiquent que ULK1 est une cible thérapeutique potentielle pour maintenir l'homéostasie du cartilage articulaire.

Dualité d'action de la galectine-3 dans la pathophysiologie de l'arthrose

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Dualité d'action de la galectine-3 dans la pathophysiologie de l'arthrose

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

The role of chondrocyte senescence in the pathogenesis of canine osteoarthritis

The aims of this study were to (1) evaluate cellular senescence in chondrocytes from osteoarthritic articular cartilage, (2) investigate the hypothesis that oxidative stress is a feature of canine OA chondrocytes and that oxidative stress contributes to cellular senescence in canine chondrocytes, (3) investigate the hypothesis that osteoarthritic chondrocytes alter the gene expression of adjacent normal chondrocytes in OA joints leading to modulation of genes known to play a role in the pathogenesis of OA and (4) evaluate the presentation of dogs undergoing femoral head excision in veterinary referral practice in the UK as a treatment for osteoarthritis of the coxofemoral joint, and to categorise the distribution and severity of associated pathological lesions. Chondrocytes from osteoarthritic and normal cartilage were examined for levels of senescence. Initially chondrocytes were cultured using an alginate bead culture system, thought to mimic the extracellular matrix of articular cartilage. However, these chondrocytes showed almost no growth as compared to monolayer culture where they grew rapidly. OA chondrocytes entered the senescent state after 1.5 to 4.9 population doublings in monolayer culture, while normal chondrocytes underwent 4.8 to 14.6 population doublings before entering the senescent state. Osteoarthritic chondrocytes had increased levels of markers of cellular senescence (senescence associated beta-galactosidase accumulation and p16 protein accumulation) as compared to normal chondrocytes, suggesting that chondrocyte senescence is a feature of canine osteoarthritis. An experimental model for the induction of oxidative stress in chondrocyte cell culture was developed using tert-Butyl hydroperoxide and total cellular glutathione was measured as an indicator of cellular oxidative stress levels. Experimental induction of oxidative stress in both normal and osteoarthritic chondrocytes in cell culture resulted in increased amounts of cellular senescence, shown by an increase in levels of senescence associated beta-galactosidase accumulation and decreased replicative capacity. Experimental induction of oxidative stress also resulted in altered gene expression of three genes important to the degradation of the extracellular matrix; MMP-13, MMP-3 and Col-3A1, measured by RT-PCR, in normal canine chondrocytes in monolayer cell culture. MMP-3 showed the greatest relative expression change, with a fold-change of between 1.43 and 4.78. MMP-13 had a fold change of 1.16 to 1.38. Col-3A1 was down regulated, with a fold-change of between 0.21 and 0.31. These data demonstrate that experimentally induced oxidative stress in chondrocytes in monolayer culture increases levels of cellular senescence and alters the expression of genes relevant to the pathogenesis of canine OA. Coculture of osteoarthritic chondrocytes with normal canine chondrocytes resulted in gene modulation in the normal chondrocytes. Altered gene expression of ten genes known to play a role in the pathogenesis of osteoarthritis was detected in the normal chondrocytes (fold change shown in brackets); TNF-alpha (11.95), MMP-13 (5.93), MMP-3 (5.48), IL-4 (7.03), IL-6 (5.3), IL-8 (4.92), IL-F3 (4.22), COL-3A1 (4.12), ADAMTS-4 (3.78) and ADAMTS-5 (4.27). In total, 594 genes were significantly modulated suggesting that osteoarthritic chondrocytes contribute to the disease propagation by altering the gene expression of adjacent normal chondrocytes, thus recruiting them into the disease process. Gene expression changes were measured by microarray analysis and validated by RT-PCR and Western blot analysis. An epidemiological study of femoral heads collected from dogs undergoing total hip replacement surgery as a treatment for osteoarthritis of the coxofemoral joint secondary to canine hip dysplasia revealed that there was no characteristic pattern of cartilage lesion for canine hip dysplasia. Severe pathology of the femoral head with cartilage erosion occurred in 63.9% of cases and exposure of subchondral bone in 31.3% of cases. The work presented in this thesis has demonstrated that cellular senescence is a feature of chondrocytes from canine osteoarthritic cartilage and suggests that cellular senescence and oxidative stress play an important role in the pathogenesis of osteoarthritis in dogs.

The incidence of thrombotic thrombocytopenic purpura-hemolytic uremic syndrome: all patients, idiopathic patients, and patients with severe ADAMTS-13 deficiency

Summary. Background: Accurate estimates of the incidence of thrombotic thrombocytopenic purpura (TTP) are important to assess the resources required for current treatments as well as to anticipate the need to develop new treatments. Previous estimates have been indirect and have not reported data on patients with ADAMTS-13 deficiency. Objective: To determine the incidence of patients with TTP-hemolytic uremic syndrome (HUS) in three categories: all patients with clinically suspected TTP-HUS, patients with idiopathic TTP-HUS, and patients with severe ADAMTS-13 deficiency. Methods: Incidence rates were estimated from the Oklahoma TTP-HUS Registry, analyzing all 206 consecutive patients from January 1, 1996 to June 30, 2004 who were treated with plasma exchange for their initial episode of clinically suspected TTP-HUS. ADAMTS-13 activity was measured in 186 (90%) of the 206 patients. Results: The age–sex–race standardized annual incidence rates were 11.29 × 106 (95% CI: 9.70–12.88) for all patients with clinically suspected TTP-HUS; 4.46 × 106 (95% CI: 3.43–5.50) for patients with idiopathic TTP-HUS; and 1.74 × 106 (95% CI: 1.06–2.41) for patients with severe ADAMTS-13 deficiency (<5% activity). In all three categories, the incidence rates were greater for women and for blacks. For patients with severe ADAMTS-13 deficiency, the age–sex standardized incidence rate ratio of blacks to non-blacks was 9.29 (95% CI: 4.33–19.93). Conclusions: Accurate incidence rate estimates for all patients with clinically suspected TTP-HUS, idiopathic TTP-HUS, and TTP associated with severe ADAMTS-13 deficiency have been determined. The greater incidence among women and blacks is comparable with their increased risk for other autoimmune disorders.

ADAMTS-13, von Willebrand factor and related parameters in severe sepsis and septic shock

BACKGROUND: Insufficient control of von Willebrand factor (VWF) multimer size as a result of severely deficient ADAMTS-13 activity results in thrombotic thrombocytopenic purpura associated with microvascluar thrombosis and platelet consumption, features not seldom seen in severe sepsis and septic shock. METHODS: ADAMTS-13 activity and VWF parameters of 40 patients with severe sepsis or septic shock were compared with those of 40 healthy controls of the same age and gender and correlated with clinical findings and sepsis outcome. RESULTS: ADAMTS-13 activity was significantly lower in patients than in healthy controls [median 60% (range 27-160%) vs. 110% (range 63-200%); P < 0.001]. VWF parameters behaved reciprocally and both VWF ristocetin cofactor activity (RCo) and VWF antigen (VWF:Ag) were significantly (P < 0.001) higher in patients compared with controls. Neither ADAMTS-13 activity nor VWF parameters correlated with disease severity, organ dysfunction or outcome. However, a contribution of acute endothelial dysfunction to renal impairment in sepsis is suggested by the significantly higher VWF propeptide and soluble thrombomodulin levels in patients with increased creatinine values as well as by their strong positive correlations (creatinine and VWF propeptide r(s) = 0.484, P < 0.001; creatinine and soluble thrombomodulin r(s) = 0.596, P < 0.001). CONCLUSIONS: VWF parameters are reciprocally correlated with ADAMTS-13 activity in severe sepsis and septic shock but have no prognostic value regarding outcome.

Second international collaborative study evaluating performance characteristics of methods measuring the von Willebrand factor cleaving protease (ADAMTS-13)

BACKGROUND: Over the last 4 years ADAMTS-13 measurement underwent dramatic progress with newer and simpler methods. AIMS: Blind evaluation of newer methods for their performance characteristics. DESIGN: The literature was searched for new methods and the authors invited to join the evaluation. Participants were provided with a set of 60 coded frozen plasmas that were prepared centrally by dilutions of one ADAMTS-13-deficient plasma (arbitrarily set at 0%) into one normal-pooled plasma (set at 100%). There were six different test plasmas ranging from 100% to 0%. Each plasma was tested 'blind' 10 times by each method and results expressed as percentage vs. the local and the common standard provided by the organizer. RESULTS: There were eight functional and three antigen assays. Linearity of observed-vs.-expected ADAMTS-13 levels assessed as r2 ranged from 0.931 to 0.998. Between-run reproducibility expressed as the (mean) CV for repeated measurements was below 10% for three methods, 10-15% for five methods and up to 20% for the remaining three. F-values (analysis of variance) calculated to assess the capacity to distinguish between ADAMTS-13 levels (the higher the F-value, the better the capacity) ranged from 3965 to 137. Between-method variability (CV) amounted to 24.8% when calculated vs. the local and to 20.5% when calculated vs. the common standard. Comparative analysis showed that functional assays employing modified von Willebrand factor peptides as substrate for ADAMTS-13 offer the best performance characteristics. CONCLUSIONS: New assays for ADAMTS-13 have the potential to make the investigation/management of patients with thrombotic microangiopathies much easier than in the past.

Neonatal calyceal dilation and renal fibrosis resulting from loss of Adamts-1 in mouse kidney is due to a developmental dysgenesis

Background. A disintegrin and metalloproteinase with thrombospondin motifs 1, Adamts-1, is important for the development and function of the kidney. Mice lacking this protein present with renal lesions comprising enlarged calyces, and reduced cortex and medulla layers. Our current findings are consistent with the defect occurring due to a developmental dysgenesis. Methods. We generated Adamts-1 null mice, and further investigated their kidney phenotype in a time course study ranging from E18.5 to 12 months of age. Immunohistochemistry was used to assess the localization of type IV collagen, TGF-beta and F4/80-positive macrophages in the kidneys of Adcants-1 null mice compared to wild-type control animals. The expression of Adamts-1 mRNA was determined in metanephric kidney explants by in situ hybridization. Results. Adamts-1 null mice have a gross kidney defect. At day 18.5 of gestation, the Adcants-1 null kidney has a normal appearance but at birth when the kidney begins to function, the defect becomes evident. During development of the kidney Adamts-1 expression was specifically detected in the developing loops of Henle, as well as in the proximal and distal convoluted tubules. Expression was not detected in the ureter, ureteric bud or its derivatives as had been previously suggested. At 6 months and I year of age, the Adamts-1 null mice displayed interstitial fibrosis in the cortical and medullary regions of the kidney. At I year of age, the Adamts-1 null mice displayed mild interstitial matrix expansion associated with increased collagen type IV expression, without apparent tubular dilatation, compared to wild-type animals. Immunohistochemical analysis demonstrated TGF-beta protein localized to infiltrating macrophages and glomeruli of Adamts-1 null mice. Conclusions. Adamts-1 is required for the normal development of the kidney. The defect observed in its absence results from a dysgenic malformation affecting the medulla that becomes apparent at birth, once the kidneys start to function.