title: The low viability of human CD34+ cells under acidic conditions is improved by exposure to thrombopoietin, stem cell factor, interleukin-3, or increased cyclic adenosine monophosphate levels.
abstract: BACKGROUND
  Transplanted hematopoietic progenitor cells (CD34+) have shown great promise in regenerative medicine. However, the therapeutic potential of transplanted cells is limited by their poor viability. It is well known that the microenvironment in which progenitors reside substantially affects their behavior. Because extracellular acidosis is a common feature of injured tissues or the tumor microenvironment and is a critical regulator of cell survival and activation, we evaluated the impact of acidosis on CD34+ cell biology.
  
  
  METHODS
  Apoptosis was evaluated by fluorescence microscopy and binding of annexin V, hypodiploid cells, Bcl-xL expression, active caspase-3, and mitochondrial membrane potential was determined by flow cytometry. Colony-forming units were studied by clonogenic assays, and cell cycle was evaluated by flow cytometry.
  
  
  RESULTS
  Exposure of CD34+ cells to low pH (7.0-6.5) caused intracellular acidification, decreased cell proliferation, and triggered apoptosis via the mitochondrial pathway. Whereas exposure to thrombopoietin (TPO), stem cell factor (SCF), interleukin (IL)-3 or increases in cyclic adenosine monophosphate (cAMP) levels prevented CD34+ cell death induced by acidic conditions, granulocyte-macrophage-colony-stimulating factor, FMS-like tyrosine kinase 3-ligand, erythropoietin, and vascular endothelial growth factor had no effect. Despite their cytoprotective effect, CD34+ cell expansion triggered by TPO, SCF, or IL-3 was significantly impaired at low pH. However, a cocktail of these three cytokines synergistically supported proliferation, cell cycle progression, and colony formation.
  
  
  CONCLUSIONS
  Our findings indicate that an acidic milieu is deleterious for CD34+ cells and that a combination of certain cytokines and cAMP donors may improve cell viability and function. These data may be useful to develop new therapeutic strategies or to optimize protocols for regenerative medicine.
authors.affiliation: Thrombosis I Laboratory, Hematological Research Institute Mariano R. Castex, National Academy of Medicine, CONICET, Buenos Aires, Argentina.
authors.forename: Lina Paola
authors.initials: LP
authors.lastname: D'Atri
authors.forename: Julia
authors.initials: J
authors.lastname: Etulain
authors.forename: María Albertina
authors.initials: MA
authors.lastname: Romaniuk
authors.forename: Oscar
authors.initials: O
authors.lastname: Torres
authors.forename: Soledad
authors.initials: S
authors.lastname: Negrotto
authors.forename: Mirta
authors.initials: M
authors.lastname: Schattner
mesh_terms: D000143:Acids / Q000494:pharmacology*; D018952:Antigens, CD34 / Q000378:metabolism*; D017209:Apoptosis / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000494:pharmacology*; D004357:Drug Synergism; D005312:Fetal Blood / Q000166:cytology / Q000378:metabolism; D006412:Hematopoietic Stem Cells / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007377:Interleukin-3 / Q000494:pharmacology*; D019089:Stem Cell Factor / Q000494:pharmacology*; D013926:Thrombopoietin / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D000143:Acids; D018952:Antigens, CD34; D007377:Interleukin-3; D019089:Stem Cell Factor; D013926:Thrombopoietin; D000242:Cyclic AMP