Human mesenchymal stem cells in contact with their environment: surface characteristics and the integrin system

Abstract

The identification of mesenchymal stem cells (MSCs) in adult human tissues and the disclosure of their self-renew-al and multi-lineage differentiation capabilities have provided exciting prospects for cell-based regeneration and tis-sue engineering. Although a considerable amount of data is available describing MSCs, there is still lack of information regarding the molecular mechanisms that govern their adhesion and migration. In this work, we will review the current state of knowledge on integrins and other adhesion molecules found to be expressed on MSCs. The discussed topics include the characteristics of MSCs and their clinical applications, integrins and their central role in cell-matrix attachment and migration, and comments on mobilization, differentiation and contribution to tumour development. Finally, by understanding the complex and fundamental pathways by which MSCs attach and migrate, it might be possible to fine-tune the strategies for effective and safe use of MSCs in regenerative therapies.

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An example of some accepted criteria that define mesenchymal stem cells. (A) Phase-contrast photomicrograph of human MSCs (supplier: Cambrex, USA) showing their fibroblastoid adherent phenotype. (B) Detection of CD105 antigen in hMSCs. Primary anti-CD105 antibody (Cat. no. P3D1, DSHB, USA), secondary antibody conjugated to Texas Red (in red), (Cat. no. 715-075-151, Dianova, Germany) and DAPI nuclear stain (in blue), (Cat. no. D1306, Molecular Probes, Germany) were used. (C and D) hMSCs were induced to differentiate into osteoblasts and the deposition of a mineralized matrix visualized by von Kossa stain is shown in (C). The non-induced control is shown in (D). (E and F) Under adipogenic conditions, hMSCs accumulated lipid vacuoles, which are positively stained by Oil Red O assay (E), whereas in control media no such vacuoles were observed (F). (G and H) Chondrogenesis was indicated by collagen type II staining. A strong signal was detected in stimulated hMSC pellet-cultures (G). Control hMSC pellets clearly

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A schematic model depicting the structure of focal adhesion and paxillin staining. (A and B) Fluorescent photomicrograph of human MSC showing the immuno-histological detection of paxillin, a multi-domain adaptor that recruits both structural and signalling molecules to focal adhesions (see gray outline in B). Primary anti-paxillin antibody (Cat. no. 1500-1, Epitomics, USA) was combined with secondary Alexa Fluor 488 antibody (in green), (Cat. no. A11034, Molecular Probes, Germany). Actin fibres and nucleus were stained respectively with Phalloidin (in red), (Cat. no. H-22284, Molecular Probes, Germany) and DAPI (in blue), (Cat. no. D1306, Molecular Probes, Germany). Bars: 50 μm (C) Focal adhesions are sites, where the heterodimeric (and) integrin receptors (depicted by the red and blue larger forms) engage with an extracellular matrix (ECM) protein (the shape in pink) and a cascade of integrin-, membrane-, actin- and signalling-associated molecules (represented as multi-colour dots). Besides having central roles in cell motility and cytoskeletal dynamics, focal adhesions convey information across the cell membrane to regulate cell proliferation, differentiation, gene expression and survival.