Glycogen synthase kinase-3β inhibition preserves hematopoietic stem cell activity and inhibits leukemic cell growth

Ex vivo expansion of cord blood cells generally results in reduced stem cell activity in vivo. Glycogen synthase kinase-3 beta (GSK-3 beta) regulates the degradation of beta-catenin, a critical regulator of hematopoietic stem cells (HSCs). Here we show that GSK-3 beta inhibition activates beta-catenin in cord blood CD34(+) cells and upregulates beta-catenin transcriptional targets c-myc and HoxB4, both known to regulate HSC self-renewal. GSK-3 beta inhibition resulted in delayed ex vivo expansion of CD34(+) cells, yet enhanced the preservation of stem cell activity as tested in long-term culture with bone marrow stroma. Delayed cell cycling, reduced apoptosis, and increased adherence of hematopoietic progenitor cells to bone marrow stroma were observed in these long-term cultures treated with GSK-3 beta inhibitor. This improved adherence to stroma was mediated via upregulation of CXCR4. In addition, GSK-3 beta inhibition preserved severe combined immunodeficiency (SCID) repopulating cells as tested in the nonobese diabetic/SCID mouse model. Our data suggest the involvement of GSK-3 beta inhibition in the preservation of HSC and their interaction with the bone marrow environment. Methods for the inhibition of GSK-3 beta may be developed for clinical ex vivo expansion of HSC for transplantation. In addition, GSK-3 beta inhibition suppressed leukemic cell growth via the induction of apoptosis mediated by the downregulation of survivin. Modulators of GSK-3 beta may increase the range of novel drugs that specifically kill, leukemic cells while sparing normal stem cells.