Human bone marrow-derived mesenchymal stem cells: studies on chondrogenic differentiation, chemotaxis and recruitment

Background

We tested the hypothesis that a tissue engineering approach using chemoattractant molecules will allow in situ recruitment of human bone marrow mesenchymal stem cells (MSC) to sites of degenerated articular cartilage.

Objective

The aim of our ongoing study is to characterize molecules that are involved in chondrogenesis and chemotaxis of MSC.

Methods

Human bone marrow aspirates were used to isolate MSC. The culture homogeneity was verified by FACS analysis (CD14^-, CD34^-, CD45^-, CD105⁺, CD166⁺). For differentiation, MSC were centrifuged to form high-density cultures and different TGFs were added. Chondrogenesis was documented by Alcian blue, type II collagen staining and by real-time PCR of marker genes. Chemotaxis was analyzed by chemokine receptor analyses and transwell chamber assays.

Results

The histological staining showed BMP-2 promotes differentiation along the chondrogenic lineage. Matrix formation was comparable to MSC stimulated with TGF-β₃. The results suggest a synergistic stimulation on chondrogenic differentiation with BMP-2 and TGF-β₃. Differentiation was further demonstrated by the induction of type II collagen, aggrecan, SOX-9 and link protein on the gene expression level. Furthermore, for the first time, expression of chemokine receptors of all four chemokine subfamilies was proven by RT-PCR and subsequent sequence analysis, as well as at the protein level using specific antibodies. The chemotactic activity in 24-transwell chemotaxis chambers was demonstrated for, for example, SDF1a.

Conclusion

These findings demonstrate that chondrogenic development of MSC is inducible by different TGF-β₃ superfamily growth factors including BMP-2. Additionally, MSC express chemokine receptors relevant for chemotaxis or in situ recruitment for cartilage regeneration.