Tissue engineering approaches to study biomechanical sensing in pseudoachondroplasia

Abstract

Articular cartilage is a dense and avascular tissue present at the ends of diarthrodial joints that protects the underlying bone from shear and compressive forces. Pseudoachondroplasia (PSACH) is a skeletal dysplasia resulting from mutations in cartilage oligomeric matrix protein (COMP), a large glycoprotein found in cartilage. The presence of mutant protein in the cartilage matrix affects tissue stability and mechanosensing, leading to early-onset OA, muscle weakness and tendon abnormalities, thus COMP mutations affecting the C-terminal domain represent a good model of musculoskeletal ageing. Cartilage disease and ageing studies are often hindered by the difficulty in obtaining human material and the use of costly animal models. The aim of this study was to create a model that could recapitulate this disease in a mechanosensing model for the very first time, that could be applied in further ageing and other disease studies. In order to generate a novel mechanosensitive tissue-engineered model of cartilage that would allow the study of the pathomolecular mechanism of COMP PSACH, chondroprogenitor ATDC5 cells were seeded in pellets and 2% agarose constructs, cultured in chondrogenic medium with and without growth factor supplementation, and compared to the established 2D chondrogenesis model. ATDC5 cells transfected with wild type (WT) and mutant COMP constructs were then grown in pellets and 2% agarose cyclically compressed for 2 weeks for 30min/day at 10kPa 0.33Hz to mimic physiological compression of cartilage. Supplementation with both BMP7 and TGF-β3 improved ATDC5 chondrogenesis. Moreover, chondrogenic markers increased in ATDC5 cells upon compression, whilst dedifferentiation markers decreased. The p.T585M COMP ATDC5 models recapitulated the phenotype of the disease, with abnormal ECM deposition, an increase in cell apoptosis and a decrease in cell proliferation also allowed us for the very first time to see its effects in a novel mechanosensitive compressed in vitro model. These data suggest that this novel mechanosensing 3-dimensional 2% agarose and pellet model could be employed to study and discover possible targets to treat rare skeletal diseases and reduce the use of animal sin research in the future.