Background: Articular cartilage is a complex tissue with poor healing capacities. Current approaches for cartilage repair based on mesenchymal stromal cells (MSCs) are often disappointing because of the lack of relevant differentiation factors that could drive MSC differentiation towards a stable mature chondrocyte phenotype. Methods: We used a large-scale transcriptomic approach to identify genes that are modulated at early stages of chondrogenic differentiation using the reference cartilage micropellet model. Results: We identified several modulated genes and selected neuromedin B (NMB) as one of the early and transiently modulated genes. We found that the timely regulated increase of NMB was specific for chondrogenesis and not observed during osteogenesis or adipogenesis. Furthermore, NMB expression levels correlated with the differentiation capacity of MSCs and its inhibition resulted in impaired chondrogenic differentiation indicating that NMB is required for chondrogenesis. We further showed that NMB activated the calcineurin activity through a Ca++-dependent signaling pathway. Conclusion: NMB is a newly described chondroinductive bioactive factor that upregulates the key chondrogenic transcription factor Sox9 through the modulation of Ca2+ signaling pathway and calcineurin activity.

Biopolymers are ideal candidates for the development of hydrogels for tissue engineering applications. However, chemical modifications are required to further improve their mechanical properties, in particular to cross-link them for long-lasting applications or biofabrication. Herein, we developed a novel gelatin-based hydrogel precursor, “GelmSi”. Gelatin was chosen as starting material because of its biocompatibility and bioactivity, favouring cell adhesion and migration. Alkoxysilane moieties were introduced in a controlled manner on the lysine side chains of gelatin to obtain a hybrid precursor which reacts in physiological conditions, forming covalent siloxane bonds and allowing the formation of a three-dimensional chemical network. On the contrary to unmodified gelatin, siloxane covalent network dramatically increases the stiffness and the thermal stability of the resulting gelatin-based hydrogel, making it suitable for cell encapsulation and cell culture. The biorthogonality and versatility of the GelmSi hybrid hydrogel unlock a broad range of gelatin-based bioengineering applications.

Background and objectivesSeveral members of the thrombospondin (THBS) family have been shown to play a role in cartilage homeostasis and physiopathology. While mesenchymal stem cells (MSCs) express different THBS members and exert a therapeutic effect in osteoarticular diseases, the role of THBS4 has been poorly investigated. We therefore evaluated the role of THBS4 deficient MSCs in osteoarthritic mice.MethodsMSCs were isolated from the bone marrow of wild type C57BL6 and THBS4 knock-out C57BL6 mice and named wt and THBS4-/- MSC, respectively. Osteoarthritis was induced in C57BL/6 mice by collagenase injections. On day 7, 200,000 MSCs were injected in the joint and on day 42, hind paws were processed for Safranin O-Fast green staining and scored. Tibiae were incubated in 30% of Hexabrix 320 contrast agent and scanned in a microCT scanner (SkyScan). Quantification of cartilage damage was then assessed after scanning the entire articular cartilage of tibiae with a confocal laser scanning microscope (CLSM; SP5 Leica).ResultsHistological analysis showed a significantly lower OA score in the joints of mice injected with wt MSCs as compared to control OA mice or mice that received THBS4-/- MSCs. These results were confirmed by CLSM analysis of tibia plateau cartilages. Both the volume and thickness of articular cartilage were significantly lower in THBS4-/- MSCs treated mice and in control OA mice than in mice treated with wt MSCs. Furthermore after incubation of tibiae with contrast agent, microCT analysis revealed a significant depletion of GAG content in the articular cartilage. Finally, microCT analysis of subchondral bone indicated a significant increase of bone surface degradation (increase of surface/volume ratio) as well as a significant decrease of bone mineral density and subchondral bone thickness in control OA mice and mice injected with THBS4-/- MSCs as compared to wt MSCs treated mice.ConclusionsIn contrast to wt MSCs, THBS4-/- MSCs were defective in their capacity to inhibit cartilage degradation in an osteoarthritic mouse model. Altogether, the data point out the role of the THBS4 pathway in the therapeutic effect of MSCs in osteo-articular diseases.