Adhesion of mesenchymal stem cells to polymer scaffolds occurs via distinct ECM ligands and controls their osteogenic differentiation

Abstract

The osteogenic potential of mesenchymal stem cells (MSCs) cultured on poly(lactide-co-glycolide) (PLGA) or poly(caprolactone) (PCL), two widely used polymeric biomaterials that have been reported to differentially support osteogenic differentiation, was compared in these studies. Here we report that MSCs cultured in 3-D PLGA scaffolds for up to 5 weeks significantly upregulate osteocalcin gene expression levels. By contrast, osteocalcin expression was markedly downregulated in 3-D PCL-based constructs over the same time course. We hypothesized that differential adsorption of extracellular matrix (ECM) proteins present in serum-containing culture medium and subsequent differences in integrin-mediated adhesion are responsible for these differences, and tested this hypothesis using thin (2-D) polymeric films. Supporting this hypothesis, significant amounts of fibronectin and vitronectin deposited onto both materials in serum-containing osteogenic media, with type-I collagen present in lower amounts. Adhesion-blocking studies revealed that MSCs adhere to PCL primarily via vitronectin, while type-I collagen mediates their attachment to PLGA. These adhesive mechanisms correlated with higher levels of alkaline phosphatase (ALP) activity after 2 weeks of monolayer culture on PLGA versus PCL. These data suggest that the initial adhesion of MSCs to PLGA via type-I collagen fosters osteogenesis while adhesion to PCL via vitronectin does not, and stress the need for an improved molecular understanding of cell-ECM interactions in stem cell-based therapies.

Extracellular Matrix Remodeling, Integrin Expression, and Downstream Signaling Pathways Influence the Osteogenic Differentiation of Mesenchymal Stem Cells on Poly(Lactide-Co-Glycolide) Substrates

“…2 After coating, slides were placed in a fume hood to permit residual organic solvents to evaporate, washed extensively, and subsequently sterilized using ultraviolet light before seeding with cells. Cells were seeded in standard growth medium at a pre-defined density (2.5Â10 4 cells=cm 2 ) onto these PLGA-coated slides and cultured overnight to permit attachment and spreading.…”

“…The prototypical scaffolds in this paradigm are often composed of biodegradable polymers, which can be tailored to degrade at a rate coincident with new tissue development 1 and readily support cell attachment. However, the mechanism of cell adhesion to most synthetic polymers is indirect and relies on the passive deposition of extracellular matrix (ECM) proteins, 2,3 a process that is difficult to control and predict. As a result, such traditional polymeric scaffolds may lack the specificity of protein-resistant substrates covalently modified with specific ECM ligands 4 and therefore may fail to provide important instructive signals in a stable fashion.…”

“…2 A subsequent study showed that MSCs on VN-or Col I-coated substrates differentially activated the mitogenactivated protein kinase (MAPK) and phosphatidylinositol-3 kinase (PI3K) signal transduction pathways. 29 However, the synthesis and secretion of new ECM proteins by the cells accompanies prolonged culture of MSCs on polymer scaffolds, and it is unclear what effect this may have on stem cell fate.…”

Quantifying fibronectin adhesion with nanoscale spatial resolution on glycosaminoglycan doped polypyrrole using Atomic Force Microscopy

“…Their initial adsorption, adherence and subsequent conformation are critical to the cell interactions and as such the effect of different surface chemistries and materials on ECM protein interactions has significantly featured in many studies 2,3,4 . While the importance of ECM protein interactions is well recognized, this has been emphasized in recent times by the role they play in regulating stem cell niches 5 .…”

Differentiation of human adipose-derived stem cells towards cardiomyocytes is facilitated by laminin

“…Homing, growth and differentiation of stem cells after MI is known to depend on the environment in the heart, and especially on the adhesion factors at the site of injury, all of which change dramatically after MI (Lu et al 2004;Malek et al 2006;Wang and Sjoquist 2006;Chastain et al 2006;Salasznyk et al 2004). Therefore, stem cell therapy has to be applied at the moment after infarction when the environment is most favourable for stem cell adhesion and cardiomyocyte formation.…”