Investigation of Integrin Expression in Human Mesenchymal Stem Cells during Chondrogenesis in Different Culture Systems

Cartilage tissue engineering aims to develop a material that can be implanted with cells to repair damage in articular cartilage. The extracellular matrix is known to play a key role in regulating stem cell behaviour via cell-matrix interactions and integrins are major cell adhesion receptors that act as intermediates between cells and their surrounding matrix. Integrin-mediated signalling is known to be important in chondrocytes and to drive chondrogenesis. In our study, we investigated integrin expression during chondrogenic differentiation of human bone marrow-derived mesenchymal stem cells (hMSCs) between three different high density 3D culture methods: pellet culture, micromass culture and collagen type II 3D hydrogels. Integrins are [alpha][beta] heterodimeric transmembrane proteins, so we quantified the mRNA expression of every alpha and beta subunit using quantitative polymerase chain reaction over a period of 21 days. In all culture methods, alpha and beta integrin subunits were down-regulated in hMSCs undergoing chondrogenesis compared to the same cells in growth medium, with the exception for integrin subunits [alpha]11 and [alpha]V which were upregulated in cells undergoing chondrogenesis . Moreover, similar transcript expression was identified irrespective of the culture system for the alpha subunits related to collagen-binding integrins, while the expression of fibronectin- and laminin-binding receptors was greatly variable and dependent on the culture method. In conclusion, this work has led to an increased understanding of the expression of integrins in hMSCs and during chondrogenesis. This knowledge can be used to design materials that present the ligands for these integrins to further improve cartilage tissue engineering.