167 ISOLATION AND COMPARATIVE PROFILING OF HUMAN ADIPOSE-DERIVED ADULT STEM CELLS

Abstract

The stromal compartment of mesenchymal tissues is thought to harbor stem cells that display extensive proliferative capacity and multilineage potential. However, despite their potential impact in the field of regenerative medicine, little is known about the biology of stromal stem cells prior to culture. After removing adipocytes and erythrocytes from collagenase digested human adipose tissue, we identified two cell populations using flow cytometry which shared expression of stem cell markers SH2 and CD34, but lacked the phenotypic characteristics of leukocytes (CD45−). However, they were found to be discernible based on CD31 expression, a marker for endothelial cells. Using CD31 conjugated magnetic beads, we separated these cells (CD45-CD31− and CD45-CD31+) from three patients and compared global gene expression profiles using an Affymetrix platform. The prominant feature of CD45-CD31+ cells was the up-regulation of genes associated with endothelial cells. By contrast, CD45-CD31− cells were found to overexpress transcripts involved in cell cycle quiescence and cell signaling elements including those of the WNT pathway thought to be important for maintaining the stem cell state. Upon culture in DMEM/F12 with 20% FCS, only CD45-CD31− cells were capable of adhering to plastic and forming colonies. These cells with fibroblastic morphology met the key criterion of stem cells, the ability to proliferate while retaining the capacity to differentiate into mature tissues. Under appropriate inductive conditions, they were found to exclusively form bone, cartilage, adipose and neuronal-like tissues in vitro. Clonal cell lines generated from individually cultured CD45-CD31− cells displayed multilineage and proliferative capacity, validating our conclusion that they are true stem cells and not simply committed progenitors. We then undertook extensive comparative profiling of CD45-CD31− cells with their cultured counterparts to examine changes that stromal stem cells undergo during culture. Except for the disappearance of CD34, flow cytometry analysis using 52 antibodies revealed little change in cell surface phenotype as a result of culture. However, comparative global gene profiling revealed extensive down-regulation of many genes during culture. These included cell cycle arresting genes, as expected, and genes encoding elements involved in cell signaling including those belonging to the tumor necrosis factor, interleukin, transforming growth factor and chemokine families. The consequences of these changes remain unknown, but ultimately may affect the potential use of adipose tissue stem cells in regenerative medicine.