Induction of tendon-specific markers in adipose-derived stem cells in serum-free culture

Differentiation of stem cells as a cell-based therapy for repairing, replacing or restoring damaged tissues such as bone, cartilage, and tendon is becoming increasingly attractive within the field of musculoskeletal tissue engineering. Towards this end, there are numerous published and well-defined protocols to differentiate stem cells towards cartilage and bone tissues, but the protocols towards tendon tissue are still emerging and thus less developed. Recent studies focused on the induction of tendon-specific markers in cultured stem cells using different Growth Factors (GFs) including Bone Morphogenetic Proteins (BMPs) and Transforming Growth Factor (TGF) isoforms. However, the inclusion of serum in relatively high concentration across these studies is less favorable, since the components within serum may interfere with the induction of the markers. Alternatively, in vitro studies with low concentration or absence of serum would be ideal. In this study, we assessed the induction effect of BMP-12 and TGF-β1 on tendon-specific markers in Adipose-Derived Stem cells (ADSCs), in serum-free conditions. Specifically, we investigated the temporal and dosing effects of both GFs on several markers. Our results demonstrate that BMP-12 induces late expression of the transcription factors Scleraxis (SCX) and Mohawk (MKX), whereas TGF-β1 induced their earlier expression. Moreover, BMP-12 induced Decorin (DCN) but was inhibited by TGF-β1. Other markers such as Collagen Iα1 (COL1A1) likewise showed this pattern. Importantly, the protein analysis generally supported the gene expression data. Interestingly, differences were observed in the cellular localisation of SCX between BMP-12 and TGF-β1 stimulations. Furthermore, the addition of Ascorbic Acid (AA) with either BMP-12 or TGF-β1 resulted in increased deposition of Collagen I. Our results enhance the existing protocols for the differentiation of ADSCs towards the tenogenic lineage in serum-free conditions and contribute to the understanding and the development of tenogenic induction protocols.