Mesenchymal stem cell responses to bone-mimetic electrospun matrices composed of polycaprolactone, collagen I and nanoparticulate hydroxyapatite.

The performance of biomaterials designed for bone repair depends, in part, on the ability of the material to support the adhesion and survival of mesenchymal stem cells (MSCs). In this study, a nanofibrous bone-mimicking scaffold was electrospun from a mixture of polycaprolactone (PCL), collagen I, and hydroxyapatite (HA) nanoparticles with a dry weight ratio of 50/30/20 respectively (PCL/col/HA). The cytocompatibility of this tri-component scaffold was compared with three other scaffold formulations: 100% PCL (PCL), 100% collagen I (col), and a bi-component scaffold containing 80% PCL/20% HA (PCL/HA).

The effect of collagen I mimetic peptides on mesenchymal stem cell adhesion and differentiation, and on bone formation at hydroxyapatite surfaces.

Integrin-binding peptides increase cell adhesion to naive hydroxyapatite (HA), however, in the body, HA becomes rapidly modified by protein adsorption. Previously we reported that, when combined with an adsorbed protein layer, RGD peptides interfered with cell adhesion to HA. In the current study we evaluated mesenchymal stem cell (MSC) interactions with HA disks coated with the collagen-mimetic peptides, DGEA, P15 and GFOGER.

Tumor cell migration and invasion are regulated by expression of variant integrin glycoforms.

The ST6Gal-I glycosyltransferase, which adds alpha2-6-linked sialic acids to glycoproteins, is overexpressed in colon adenocarcinoma, and enzyme activity is correlated with tumor cell invasiveness. Previously we reported that forced expression of oncogenic ras in HD3 colonocytes causes upregulation of ST6Gal-I, leading to increased alpha2-6 sialylation of beta1 integrins. To determine whether ras-induced sialylation is involved in promoting the tumor cell phenotype, we used shRNA to downregulate ST6Gal-I in ras-expressors, and then monitored integrin-dependent responses.

Comparison of mesenchymal stem cell and osteosarcoma cell adhesion to hydroxyapatite.

Immortalized cells are often used to model the behavior of osteogenic cells on orthopaedic and dental biomaterials. In the current study we compared the adhesive behavior of two osteosarcoma cell lines, MG-63 and Saos-2, with that of mesenchymal stem cells (MSCs) on hydroxyapatite (HA). It was found that osteosarcoma cells demonstrated maximal binding to fibronectin-coated HA, while MSCs alternately preferred HA coated with collagen-I.

Mesenchymal stem cell interaction with ultra-smooth nanostructured diamond for wear-resistant orthopaedic implants.

Ultra-smooth nanostructured diamond (USND) can be applied to greatly increase the wear resistance of orthopaedic implants over conventional designs. Herein we describe surface modification techniques and cytocompatibility studies performed on this new material. We report that hydrogen (H)-terminated USND surfaces supported robust mesenchymal stem cell (MSC) adhesion and survival, while oxygen- (O) and fluorine (F)-terminated surfaces resisted cell adhesion, indicating that USND can be modified to either promote or prevent cell/biomaterial interactions.

The effect of RGD peptides on osseointegration of hydroxyapatite biomaterials.

Given that hydroxyapatite (HA) biomaterials are highly efficient at adsorbing proadhesive proteins, we questioned whether functionalizing HA with RGD peptides would have any benefit. In this study, we implanted uncoated or RGD-coated HA disks into rat tibiae for 30 min to allow endogenous protein adsorption, and then evaluated mesenchymal stem cell (MSC) interactions with the retrieved disks. These experiments revealed that RGD, when presented in combination with adsorbed tibial proteins (including fibronectin, vitronectin and fibrinogen), has a markedly detrimental effect on MSC adhesion and survival.

The effect of adsorbed serum proteins, RGD and proteoglycan-binding peptides on the adhesion of mesenchymal stem cells to hydroxyapatite.

Prior studies from our laboratory have shown that RGD peptides increase the attachment of mesenchymal stem cells (MSCs) to hydroxyapatite (HA), however, RGD does not induce cell spreading when coupled to this type of biomaterial. In an effort to improve MSC spreading, and possibly cell attachment, proteoglycan-binding peptides (KRSR or FHRRIKA) were combined with RGD in the current study. It was found that the peptide combinations did not enhance MSC attachment relative to RGD alone, although a slight amount of spreading was elicited by both KRSR and FHRRIKA.

A protein kinase C/Ras/ERK signaling pathway activates myeloid fibronectin receptors by altering beta1 integrin sialylation.

Here we report that myeloid cells differentiating along the monocyte/macrophage lineage down-regulate the ST6Gal-I sialyltransferase via a protein kinase C/Ras/ERK signaling cascade. In consequence, the beta1 integrin subunit becomes hyposialylated, which stimulates the ligand binding activity of alpha5beta1 fibronectin receptors. Pharmacologic inhibitors of protein kinase C, Ras, and MEK, but not phosphoinositide 3-kinase, block ST6Gal-I down-regulation, integrin hyposialylation, and fibronectin binding.