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 α
1 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.