Principle investigator University of Massachusetts Amherst Amherst, Massachusetts, United States
Introduction: Osteoarthritis (OA) is the most common joint disease, characterized by gradual calcification and degradation of the cartilage matrix. While these changes are observed in OA patients, how mineralization initiates and spreads across the cartilage surface remains uncertain. To address this, we developed an in vitro joint tissue model called demineralized cartilage-bone paper (DcBP). This model replicates the multicellular processes within cartilage and bone compartments. DcBP is prepared by sectioning a demineralized bovine femoral head into 20 µm thin sections, preserving the extracellular matrix structure of joint tissue. Histological analyses with Trichrome and Safranin-O staining confirm the presence of proteoglycans and collagen fibers, highlighting its biomaterial relevance. Our studies show that osteoblasts adhere and proliferate on DcBP, with mineral deposition occurring exclusively on the demineralized bone matrix, mimicking a healthy joint. We hypothesized that hyaluronidase treatment, which reduces proteoglycan content in the cartilage matrix, would stimulate OA conditions. This treatment promotes mineralization at the cartilage-bone interface, extending into the cartilage matrix. These findings indicate that DcBP can effectively recapitulate pathological calcification seen in OA, providing a robust biomaterial platform for studying disease progression. To further replicate OA’s cellular environment, we isolated primary mouse ear stem cells (eMSCs) and introduced them to the DcBP for monitoring chondrocyte differentiation. eMSCs cultured on the cartilage side differentiated into chondrocyte-like morphology, while those on the bone side retained their original morphology. This differential response underscores the DcBP's utility in supporting specific cell-matrix interactions, making it an invaluable tool for advancing our understanding of osteoarthritic changes.
Materials and
Methods: The bovine femur head was demineralized with hydrochloric acid under cyclic hydrostatic pressure to dissolve minerals. The demineralized femur heads were then cryosectioned into 20 µm thin sheets of DcBP. The structural and compositional integrity of DcBP was assessed using histological staining with Trichrome and Safranin-O, as well as multiphoton second harmonic and scanning electron microscopy to differentiate collagen structures within each osteochondral layer. Primary osteoblasts were cultured on DcBP, and their morphological changes and mineralization across the osteochondral layers were monitored using fluorescence microscopy. To simulate disease conditions, DcBP was treated with hyaluronidase to degrade cartilage extracellular matrix (ECM) glycoproteins, confirmed by reduced Safranin-O staining. Subsequently, osteoblasts were cultured on the modified DcBP to study the effect of ECM alterations on cell differentiation and mineralization, assessed using light microscopy. Primary ear stem cells (eMSCs) were isolated and introduced onto the DcBP for longitudinal monitoring of chondrocyte differentiation. eMSCs were cultured on DcBP, and chondrocyte differentiation and morphological changes were monitored using light microscopy. Phalloidin actin staining was performed to characterize chondrocyte differentiation.
Results, Conclusions, and Discussions: Results and
Discussion: Our study demonstrated that DcBP retains the ECM structure of joint tissue and effectively replicates osteoarthritic changes at the osteochondral interface. Time-course imaging revealed distinct mineralization, where osteoblasts deposited minerals exclusively on the bone ECM, aligning with healthy joint features. We hypothesized that cartilage ECM glycoproteins significantly inhibit mineral deposition. DcBP was treated with hyaluronidase to degrade cartilage ECM glycoproteins, confirmed by reduced Safranin-O staining, facilitating osteoblastic mineralization at the bone-cartilage interface and into cartilage areas. This change underscores the critical role of ECM components in regulating cellular behaviors and OA progression. Additionally, the differential response of primary mouse ear stem cells (eMSCs) on DcBP highlights its biomaterial relevance. eMSCs on the cartilage side differentiated into chondrocyte-like cells, while those on the bone side retained their original morphology. Together, DcBP, representing both cartilage and bone, supports specific cell-matrix interactions and provides a valuable platform for studying the dynamic regulation of osteoarthritic changes and potential therapeutic interventions.
Conclusions: The development of DcBP has proven effective in mimicking osteoarthritic changes at the osteochondral interface, providing valuable insights into the role of the ECM in osteoarthritis progression. By facilitating targeted ECM modifications and monitoring their effects on cellular behavior, our model identifies potential therapeutic targets. This research paves the way for further studies exploring ECM-related strategies to mitigate osteoarthritis, addressing the disease's underlying mechanisms rather than merely managing symptoms. The DcBP model's ability to support specific cell-matrix interactions makes it an invaluable tool for advancing our understanding of osteoarthritic changes and developing more effective treatments.
