In this new project we are collaborating with NU Professor William Miller to develop biomimetic culture surfaces for expansion of adult stem cells. Specifically, we are interested in expansion of hematoietic stem cells (HSCs), which reside in the bone marrow and give rise to a number of blood cell lineages. In the marrow, HSCs exist in a complex microenvironment consisting of extracellular matrix proteins, other marrow cells, and soluble factors. Mimicry of this complex environment in an in-vitro cell culture system would greatly facilitate studies of cell expansion and differentiation. One goal of this project is to synthesize peptide-lipid conjugates for incorporation into supported lipid monolayers and bilayers. These supported lipopeptide films will form a cell culture surface containing a combination of ligands for stem cell specific cell surface receptors.

Supported lipid monolayer/bilayer systems have previously been developed that allow for presentation of cell adhesion molecule (CAM) ligands for cell interaction, however these systems have employed peptide loadings much higher than those used in polyethylene glycol (PEG)-based immobilization systems. We recently reported the development of synthetic methods that can be used for the efficient and versatile creation of many linear and cyclic lipid-linked peptide moieties. Using RGD-based peptides for the α5β1 integrin as a model system, we have demonstrated that these lipopeptides support efficient cell binding and spreading at CAM ligand loadings as low as 0.1 mol%, which is well below that previously reported for supported lipid systems. Both spreading (human umbilical vein endothelial cells, HUVECs) and non-spreading (hematopoietic progenitor cell line KG-1a) cells are being investigated. Experiments with primary human HSCs are currently underway. Engineered lipopeptide-based surfaces offer unique presentation options not possible with other immobilization systems, and the high activity at low loadings we have shown here may be extremely useful in presenting multiple CAM ligands for studying cell growth, differentiation, and signaling.