Molecular Characterization of Secreted Factors and Extracellular Vesicles-Embedded miRNAs from Bone Marrow-Derived Mesenchymal Stromal Cells in Presence of Synovial Fluid from Osteoarthritis Patients

Connexin 43 Modulation in Human Chondrocytes, Osteoblasts and Cartilage Explants: Implications for Inflammatory Joint Disorders

Connexin 43 (Cx43) is crucial for the development and homeostasis of the musculoskeletal system, where it plays multifaceted roles, including intercellular communication, transcriptional regulation and influencing osteogenesis and chondrogenesis. Here, we investigated Cx43 modulation mediated by inflammatory stimuli involved in osteoarthritis, i.e., 10 ng/mL Tumor Necrosis Factor alpha (TNFα) and/or 1 ng/mL Interleukin-1 beta (IL-1β), in primary chondrocytes (CH) and osteoblasts (OB). Additionally, we explored the impact of synovial fluids from osteoarthritis patients in CH and cartilage explants, providing a more physio-pathological context. The effect of TNFα on Cx43 expression in cartilage explants was also assessed. TNFα downregulated Cx43 levels both in CH and OB (-73% and -32%, respectively), while IL-1β showed inconclusive effects. The reduction in Cx43 levels was associated with a significant downregulation of the coding gene GJA1 expression in OB only (-65%). The engagement of proteasome in TNFα-induced effects, already known in CH, was also observed in OB. TNFα treatment significantly decreased Cx43 expression also in cartilage explants. Of note, Cx43 expression was halved by synovial fluid in both CH and cartilage explants. This study unveils the regulation of Cx43 in diverse musculoskeletal cell types under various stimuli and in different contexts, providing insights into its modulation in inflammatory joint disorders.

High efficiency protocol for platelet derived fibrin gel loaded with mesenchymal stromal cells extracellular vesicles

Introduction

Extracellular vesicles from mesenchymal stromal cells (MSC-EVs) are potent stimulators of naïve cartilage and their injection is studied in clinical trials for cartilage lesions, since often cartilage repaired with conventional approaches is incomplete or less performant leading to joint degeneration. The main pitfall of these innovative approaches is the high EVs dispersion into the joint cavity and consequent low concentration at lesion site. Thus, biological scaffolds for concentration of EVs where needed might be a promising option. This work aimed at producing an enhanced platelet-derived fibrin gel loaded with adipose-derived MSCs (ASCs)-EVs.

Methods

EVs' embedment efficiency in platelet gel, their release and incorporation in OA chondrocytes and cartilage explants were monitored by flow cytometry, microfluidic approaches, scansion electron microscopy and real-time quantitative multimodal nonlinear optics imaging. The effect of released EVs was tested in OA chondrocytes by gene expression studies.

Results

A protocol ensuring high incorporation EVs efficiency in platelet gels was defined, relying on a one-step modification of the standard procedure used in current clinical practice. Trapped EVs were released continuously for up to 4 weeks and uptaken in pathologic chondrocytes and cartilage explants. The release of the EVs-loaded platelet gel had stronger and synergic anti-inflammatory/matrix remodelling effects with respect to both EVs per se and unloaded gel released products.

Conclusions

These results suggest the feasibility of producing a platelet gel loaded with MSC-EVs at high efficiency that can be used as an enhanced tool to foster chondrocyte homeostasis, a key requisite for proper cartilage healing.

Inflammatory Treatment Used to Mimic Osteoarthritis and Patients' Synovial Fluid Have Divergent Molecular Impact on Chondrocytes In Vitro

Osteoarthritis (OA) is a chronic disease characterized by joint tissue disruption and inflammation with a paucity of therapeutic options. Chondrocyte in vitro models are commonly used as the first step in evaluating new approaches and rely on the stimulation of an OA-like phenotype with inflammation often the method of choice. Inflammatory priming is frequently based on cytokines used at concentrations very far from the reality in the patients' synovial fluid (SF). The aim of this work was to compare the transcriptional response of chondrocytes to different inflammatory conditions: the high levels of IL1β that are used for standardized inflammation protocols, OA-SF, IL1β, IL6 and IFNγ at SF-like concentrations both individually and simultaneously to mimic a simplified "in vitro" SF. Both high IL1β and OA-SF strongly influenced chondrocytes, while SF-like concentrations of cytokines gave weak (IL1β alone or in combination) or no (IL6 and IFNγ alone) outcomes. Chondrocytes under the two most powerful polarizing conditions had a clearly distinct fingerprint, with only a shared albeit molecularly divergent effect on ECM stability, with IL1β mainly acting on ECM degrading enzymes and OA-SF accounting for a higher turnover in favor of fibrous collagens. Moreover, OA-SF did not induce the inflammatory response observed with IL1β. In conclusion, although partially similar in the endpoint phenotype, this work intends to encourage reflection on the robustness of inflammation-based in vitro OA models for molecular studies on chondrocytes.