Nanoscale Adhesion Ligand Organization Regulates Osteoblast Proliferation and Differentiation

Abstract

It was hypothesized that nanoscale adhesion ligand spacing regulates cell adhesion, proliferation, and differentiation, and that this control can be decoupled from the overall ligand density. Alginate was chemically modified with a peptide containing the cell adhesion sequence arginineglycine-aspartic acid (RGD), and the nanoscale spacing of RGD ligands in alginate gels was varied. A decrease in the RGD island spacing from 78 to 36 nm upregulated the proliferation rates of MC3T3-E1 cells from 0.59 ± 0.08 to 0.73 ± 0.03 day −1 and resulted in 4-fold increase of the osteocalcin secretion rate. This finding was independent of the bulk ligand density of gels. These results indicate that nanoscale ligand organization may provide an important variable to regulate cell functions in many biomedical applications, including tissue engineering.

FRET measurements of cell-traction forces and nano-scale clustering of adhesion ligands varied by substrate stiffness

“…The average distance between peptides containing dif-ferent fluorophores was calculated assuming an idealized distribution of peptides in close packed, cubic polymer chains. The results of such idealized calculations were previously validated by using a Monte Carlo model that reflected the random nature of polymer chain packing, as described (29). The peptide spacing was experimentally found to be greater than the critical distance known to be required for energy transfer (Ϸ10 nm), in support of the calculations.…”

Regenerative medicine in orthopaedic surgery

“…The density of adhesion ligands, similar to past work with intact ECM molecules, regulates the adhesion, proliferation, and differentiation of cell populations of interest in tissue engineering and regeneration. [48][49][50] However, the nanoscale organization of these ligands appears to modulate the cell response as well, 51 and may be as important as the overall density of ligands presented to cells. Further, the mechanical properties of the synthetic ECM presenting the ligands is equally important, and can significantly alter the response of cells to a specific ligand presentation (type of ligand, density, and nanoscale organization).…”

“…52 The large variable space inherent to adhesion ligand presentation would require massive experimentation to explore in full, but the development of models that can predict the specific range of the relevant variables likely to alter cell receptor binding and clustering promises to focus experiments on the relevant variable ranges. 51,53 While a large number of studies indicate that cell adhesion and phenotype can be regulated in vitro by peptide presentation, the importance of these manipulations to in vivo tissue formation or regeneration is only recently becoming clear. Appropriate adhesion peptide presentation has been shown to regulate bone and cartilage formation by transplanted cells, 48,54 and matching of the degradation rate of the synthetic ECM to the rate of tissue formation in these systems greatly increases the extent and rate of tissue formation.…”

Microenvironmental regulation of biomacromolecular therapies

“…Although, so far, it has not been systematically examined, the mechanical properties of the ECM and the microscale and nanoscale organization of cell-adhesion molecules and their total numbers in the ECM are also likely to be critical. All of these variables regulate cell proliferation, viability and differentiation [65][66][67] . The role of the micropattern and nanopattern of adhesion molecules can be readily probed using model cell-adhesion proteins consisting of synthetic cell-adhesion oligopeptides that are chemically coupled to non-adherent materials 67 .…”