Modeling early changes associated with cartilage trauma into human-cell-laden hydrogel cartilage models

Abstract BackgroundTraumatic impacts to the articular joint surface are known to lead to degeneration of the cartilage, as in post-traumatic osteoarthritis (PTOA). While animal-based systems have been instrumental in understanding pathogenic progression of PTOA, they have not served to develop effective treatments for the disease. The limited progress in the development of disease-modifying OA drugs (DMOADs) may be due to insufficient mechanistic understanding of human disease onset/progression that can, in part, be attributed to insufficient in vitro models for disease and therapeutic modeling. To overcome this insufficiency, we are testing hydrogel-based models using adult human mesenchymal stromal cells to examine the effects of traumatic impacts on human cell-based engineered cartilage constructs. We hypothesize that cells encapsulated within biomimetic scaffolds will respond to traumatic impacts in a manner congruent with early PTOA pathogenesis in animal models.MethodsEngineered cartilage constructs were fabricated by encapsulating adult human bone marrow-derived mesenchymal stem cells (hBM-MSCs) in a photocrosslinkable, biomimetic hydrogel (15% methacrylated gelatin, GelMA) that were chondrogenically differentiated for 28 days using TGF-b3. Constructs were subjected to traumatic impacts with different strains or 10 ng/ml IL-1b. Cell viability and metabolism, mechanical property, gene expression, matrix protein production and activation of catabolic enzymes were assessed.ResultsLive and dead staining results showed that traumatic impacts of 30% strain caused massive cell death in engineered cartilage constructs. Elastic modulus of engineered cartilage constructs decreased significantly after traumatic impacts. CCK8 assay results also showed significant cell death and metabolism decrease in the constructs. GAG production decreased 1 day after impacts but recovered 7 days after impact, as was also observed in safranin O staining and GAG assay. RT-PCR results and IHC results showed that anabolic activities were depressed and catabolic enzymes (MMP13, ADAMTS4, ADAMTS5) were activated after impact. ConclusionTraumatic impacts delivered to engineered cartilage constructs induced PTOA-like changes in the encapsulated cells. The development of this in vitro PTOA model will contribute to development of DMOADs in the future.