Exosome-mediated Bidirectional Signaling between Mesenchymal Stem Cells and Chondrocytes for Enhanced Chondrogenesis

Exosomes of human mesenchymal stem cells (hMSC) are known to effectively increase the proliferation rate of chondrocytes and stimulate cartilage extracellular matrix. However, the therapeutic efficacy of the other signaling direction (i.e., the effect of chondrocyte-derived exosomes on hMSC) has not been extensively investigated. Therefore, the present study was designed to investigate exosome-mediated in vitro bidirectional signalings between progenitor hMSC and mature chondrocytes in cartilage tissues with various culture medial formulations. The exosomes isolated from bovine chondrocytes (BC) and hMSC (50 µg/ mL of exosomes per 3000 cells) were treated to hMSC and BC, respectively. Both cells were cultured in media formulations with 10% FBS, 10% exosome free-FBS, and 0.5% FBS. A variety of cellular responses by exosome treatments including proliferation, chondrogenic differentiation, cartilage extracellular matrix (ECM) deposition were evaluated using WST-1 assay, RT-PCR, and alcian blue staining for glycosaminoglycan (GAG) content. The results demonstrated that bidirectional exosome treatments increased proliferation of both BC and hMSC, and similar bidirectional influences including chondrogenic differentiation, glycosaminoglycan (GAG) ECM deposition were also up-regulated in both cell populations. Moreover, exosome-mediated in vitro activation between two cell populations could be regulated by media formulations. Therefore, exosomes could play important signaling roles in communication between two major cell populations in cartilage tissues.