Therapeutic Potential of Mesenchymal Stem Cell and Tenocyte Secretomes for Tendon Repair: Proteomic Profiling and Functional Characterization In Vitro and In Ovo

Tendon ruptures and tendinopathies represent a major part of musculoskeletal injuries. Due to the hypovascular and hypocellular nature of tendons, the natural healing capacity is slow and limited. Cell-free approaches for tendon injuries are being investigated as the next generation of therapeutic treatments. The aim of this study was to compare the proteomic profiles and biological activities of two different secretomes, obtained from New Zealand white rabbit adipose-tissue-derived mesenchymal stem cells (ADSCs) or a 3:1 mixed culture of ADSCs and rabbit tenocytes. The secretomes were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and their functional properties, such as gene expression, migration and angiogenesis, were investigated in vitro in rabbit tenocytes and in ovo using the chicken chorioallantoic membrane (CAM) assay after stimulation with secretomes or medium control. Both secretomes had a positive effect on angiogenesis and showed similar changes in relative gene expression levels associated with extracellular matrix (ECM) remodeling. Proteomic data showed that the two secretomes were clearly distinguishable, with 182 proteins significantly differentially expressed. The ADSC secretome was more effective in enhancing tenocyte migration under both healthy and inflammatory conditions. In the upregulated protein fraction of the mixed secretome, the tendon-related protein biglycan (BGN) and tenascin C (TNC) were increased. Based on our results, the mixed secretome shows great potential for promoting tendon healing as its composition is more effective in enhancing ECM-related processes and tendon development than the secretome of ADSCs.