Gene expression profiling of CD34+ hematopoietic cells expanded in a collagen I matrix

CD34+ hematopoietic stem/progenitor cells (HSC) reside in the bone marrow in close vicinity to the endosteal bone surface, surrounded by osteoblasts, stromal cells and various extracellular matrix molecules. We utilized a bioartificial matrix containing fibrillar collagen I, the major matrix component of bone, as scaffold for ex vivo expansion of HSCs. CD34+ HSCs were isolated from umbilical cord blood and cultivated within reconstituted collagen I fibrils in presence of FLT3-ligand, SCF and IL-3. After seven days of culture cell number, colony-forming units and gene expression profile of the cultured cells were assessed. Although the total expansion factor of CD34+ cells was slightly lower when cells were cultivated in the collagen I gel, the frequency of colony-forming units (CFU-C) increased compared to control suspension cultures. Gene expression analysis with microarray chip technology revealed the upregulation of more than 50 genes in presence of collagen I. Among them, genes for several growth factors, cytokines and chemokines (e.g. interleukin 8, MIP1-α) could be confirmed by quantitative PCR. Furthermore, increased expression of the negative cell-cycle regulator BTG2/TIS21 and an inhibitor of MAP kinase pathway, DUSP2, underline the regulatory role of the extracellular matrix. Together, these data show that the expansion of CD34+ cord blood cells in a culture system containing a three-dimensional collagen I matrix induces a qualitative change in the gene expression profile of cultivated HSCs. Keywords: hematopoietic stem/progenitor cells, collagen I, gene expression Gene expression profiling of CD34+ hematopoietic cells expanded in a collagen I matrix