Dr. Saul Sharkis
Bone Marrow and Stem Cell Transplantation
Professor of Oncology
Ph.D., New York University (Physiology)
Post-doctoral Fellow, National Naval Medical Center
Research Associate, Johns Hopkins University School of Medicince
Our research goals continue to be to characterize the biology of the most primitive hematopoietic stem cells (HSC), which includes their potential for proliferation, differentiation, survival and plasticity. We are currently particularly interested in the mechanisms that are responsible for conversion of HSC into other tissue types, such as epithelial tissues that include lung, liver, pancreas, kidney, mammary gland and intestine. These tissues are targets for cancer. Cancer represents an injury and conversion of HSC and has been demonstrated to occur in response to injury signals from the damaged tissue. Thus, we are studying HSC conversion into epithelial tissues with the hope that these cells may eventually be used as cellular therapy to repair malignant tissue. The purpose of this study was to investigate cell fates and long-term repopulating potential of a primitive HSC population in vitro. HSC were isolated by elutriation and cell-sorting and cultured with a combination of cytokines for seven days. Utilizing the membrane dye PKH-26, cultured cells were separated into two subsets based on their proliferation rates and assayed for progenitors and HSC.
We found that fresh HSC were mostly quiescent. However, some of this population entered cell cycle after cytokine exposure, reaching a peak four to five days after culture. Two subsets of cultured cells were isolated: cells that had divided several times (PKH dull cells) and cells that remained undivided or divided only once or twice (PKH bright cells). The PKH (dull) cells accounted for 94 percent of total viable cells in culture after five days. The PKH (dull) subset contained all the multipotential in vivo progenitors (CFU-S) and 10 times more committed progenitors (CFU-C). Quantitative analysis of HSC engraftment from the PKH (bright) subset demonstrated stem cell maintenance. For the PKH (dull) subset, on day five, HSC numbers increased. By day seven, increased differentiation in the PKH (dull) population supports expanding differentiation divisions. Our primitive HSC population underwent different types of cell divisions stimulated by cytokines, resulting in subsets with different self-renewal and differentiation potentials. This in vitro/in vivo model provides a useful tool for studies of early events during HSC self-renewal and differentiation.
Palapattu, G.S.; Meeker, A.; Harris, T.; Collector, M.I.; Sharkis, S.J.; DeMarzo, A.M.; Warlick, C.; Drake, C.G.; Nelson, W.G. Epithelial architectural destruction is necessary for bone marrow derived cell contribution to regenerating prostate epithelium. J Urol. 2006 Aug;176(2):813-818.
Xiao, L.; Yuan, X.; Sharkis, S.J. Activin A maintains self-renewal and regulates fibroblast growth factor, Wnt, and bone morphogenic protein pathways in human embryonic stem cells. Stem Cells. 2006 Jun;24(6):1476-1486.
Baldwin, B.R.; Li, L.; Tse, K.F.; Small, S.; Collector, M.; Whartenby, K.A.; Sharkis, S.J.; Racke, F.; Huso, D.; Small, D. Transgenic mice expressing Tel-FLT3, a constitutively activated form of FLT3, develop myeloproliferative disease. Leukemia. 2007 Apr;21(4):764-771.
Biankin, S.A.; Collector, M.I.; Biankin, A.V.; Brown, L.J.; Kleeberger, W.; Devereux, W.L.; Zahnow, C.A.; Baylin, S.B.; Watkins, D.N.; Sharkis, S.J.; Leach, S.D. A histological survey of green fluorescent protein expression in 'green' mice: implications for stem cell research. Pathology. 2007 Apr;39(2):247-251.
Jang, Y.Y.; Sharkis, S.J. Fetal to adult stem cell transition: knocking Sox17 off. Cell. 2007 Aug 10;130(3):403-404.
Jang, Y.Y.; Sharkis, S.J. A low level of reactive oxygen species selects for primitive hematopoietic stem cells that may reside in the low-oxygenic niche. Blood. 2007 Oct 15;110(8):3056-3063.
Juopperi, T.A.; Schuler, W.; Yuan, X.; Collector, M.I.; Dang, C.V.; Sharkis, S.J. Isolation of bone marrow-derived stem cells using density-gradient separation. Exp Hematol. 2007 Feb;35(2):335-341.
Juopperi, T.A.; Sharkis, S.J. Isolation of quiescent murine hematopoietic stem cells by homing properties. Methods Mol Biol. 2008;430:21-30.
Hu, R.; Mukhina, G.L.; Lee, S.H.; Jones, R.J.; Englund, P.T.; Brown, P.; Sharkis, S.J.; Buckley, J.T.; Brodsky, R.A. Silencing of genes required for glycosylphosphatidylinositol anchor biosynthesis in Burkitt lymphoma. Exp Hematol. 2009 Apr;37(4):423-434 e422.
Angelini, D.J.; Su, Q.; Kolosova, I.A.; Fan, C.; Skinner, J.T.; Yamaji-Kegan, K.; Collector, M.; Sharkis, S.J.; Johns, R.A. Hypoxia-induced mitogenic factor (HIMF/FIZZ1/RELM alpha) recruits bone marrow-derived cells to the murine pulmonary vasculature. PLoS One. 2010;5(6):e11251.
Liu, H.; Ye, Z.; Kim, Y.; Sharkis, S.; Jang, Y.Y. Generation of endoderm-derived human induced pluripotent stem cells from primary hepatocytes. Hepatology. 2010 May;51(5):1810-1819.