Investigation of growth factors and cytokines that suppress adult stem cell asymmetric cell kinetics

Abstract

Adult stem cells are potentially useful in many biomedical applications that can save lives and increase the quality of a patient's life, such as tissue engineering, cell replacement, and gene therapy. However, these applications are limited because of the difficulty in isolating and expanding pure populations of adult stem cells (ASCs). A major barrier to ASC expansion in vitro is their property of asymmetric cell kinetics. Our lab has developed a method, Suppression of Asymmetric Cell Kinetics (SACK), to expand ASCs in vitro by shifting their cell kinetics program from asymmetric to symmetric. We have found that guanine nucleotide precursors can be used to convert the kinetics of adult stem cells from asymmetric to symmetric, which promotes their exponential expansion. Previously, we have used the SACK method to derive hepatic and cholangiocyte stem cell strains from adult rat livers in vitro. These cell strains provide an assay to evaluate whether growth factors and cytokines previously implicated in proliferation of progenitor cells act by converting the kinetics of the stem cells in the population from asymmetric to symmetric, and thus identify new SACK agents. We are evaluating three agents, Wnt, IGF- 1, and Sonic hedgehog (Shh).

(cont.) Wnt has been found to cause self-renewal and proliferation of hematopoietic stem cells (HSCs) in vitro. IGF- 1 also plays a role in hematopoietic progenitor self-renewal in vivo as well as in tissue maturation. Shh has been implicated in the proliferation of primitive neural cells as well as in cellular proliferation during invertebrate development. Thus far, we have found that Wnt peptide shifts the cell kinetics from asymmetric to symmetric and may reduce the generation time, whereas IGF-1 appears only to affect generation time. Studies involving Shh are currently underway. We are also currently investigating whether Wnt acts additively or synergistically with guanine nucleotide precursors to shift cell kinetic symmetry. Discovering new SACK agents will allow us to obtain purer populations of ASCs that can be used to study properties unique to stem cells. Furthermore, the observation that Wnt shifts the kinetics of adult rat hepatic stem cells from asymmetric to symmetric implicates the involvement of similar cell kinetics symmetry mechanisms in the proliferation effect of Wnt on murine and human HSCs.