Induction of intermembrane adhesion by incorporation of synthetic adhesive molecules into cell membranes.

Modulation of cell adhesion by synthetic materials is useful for a wide range of biomedical applications. Here, we characterized cell adhesion mediated by a semisynthetic molecule, cholesteryl-modified gelatin (chol-gelatin). We found that this hybrid molecule facilitated cell adhesion by connecting two apposed membranes via multiple cholesterol moieties on the gelatin molecules, whereas unmodified gelatin did not bind to cell membranes. Analyses revealed that the rate of the formation of cell adhesions was increased by displaying more cholesterol moieties on the cell membrane. In contrast, the area of the cell adhesion site was unchanged by increasing the number of cholesterol molecules, suggesting that chol-gelatin may suppress cell spreading. Such restriction was not observed in cell adhesion mediated by the mutant of physiological adhesion protein CD2, which lacked its cytoplasmic domain and was unable to connect to cytoplasmic actin filaments, but had a similar affinity for its ligand compared with the chol-gelatin-cell membrane interaction. Further analysis suggested the restriction of cell spreading by chol-gelatin was largely independent of the modulation of the surface force, and thus we hypothesize that the restriction could be in part due to the modulation of cell membrane mechanics by membrane-incorporated chol-gelatin. Our study dissected the two roles of the hybrid molecule in cell adhesion, namely the formation of a molecular connection and the restriction of spreading, and may be useful for designing other novel synthetic agents to modulate various types of cell adhesions.

Effect of risedronate on osteoblast differentiation, expression of receptor activator of NF-κB ligand and apoptosis in mesenchymal stem cells.

Nitrogen-containing bisphosphonates (BPs) are antiresorptive drugs used for the treatment of metabolic bone diseases. Bone marrow stromal cells such as mesenchymal stem cells (MSCs) and MSC-derived osteoblasts that originate from MSCs are known to regulate osteoclast differentiation and activation via the expression of receptor activator of NF-κB ligand (RANKL). Although the effects of nitrogen-containing BPs on osteoclasts and osteoblasts have been well investigated, their effects in MSCs have not been clarified. In this study, we investigated the effects of risedronate (RIS), a nitrogen-containing BP, on osteoblast differentiation, RANKL expression and apoptosis in human and rat MSCs. RIS suppressed the formation of mineralized nodules and mRNA expression of differentiation marker genes such as bone sialoprotein and osteocalcin in MSC-derived osteoblasts. The RANKL expression induced by 1,25-(OH)(2) vitamin D(3) was not affected by RIS in human MSC-derived osteoblasts. In addition, treatment with high-concentration RIS induced chromatin condensation, an apoptosis feature, in MSCs. RIS-induced chromatin condensation was suppressed by a pan-caspase inhibitor zVAD-FMK and a cell-permeable isoprenoid analogue geranylgeraniol. These results indicate that RIS suppressed osteoblast differentiation and induced caspase- and isoprenoid depletion-dependent apoptosis and suggest that the antiresorptive effect of RIS is not mediated by a decrease in the RANKL expression in MSC-derived osteoblasts.