title: Semaphorin 7A inhibits platelet production from CD34+ progenitor cells.
abstract: BACKGROUND
  The multifunctional protein semaphorin 7A (Sema7A) may have regulatory effects on blood cell differentiation via its receptors β1-integrin and plexin C1. As thrombocytopenia can be treated with transfusion of ex vivo CD34(+) cell-derived megakaryocytes, we investigated the effect of Sema7A on differentiation of CD34(+) progenitor cells into megakaryocytes and platelets.
  
  
  METHODS
  Megakaryocytes and platelets were differentiated with a specific cytokine cocktail (CC) from CD34(+) progenitor cells in the presence or absence of Sema7A. Expression of cell markers CD41, CD42a and CD61 or detection of the activation of the signal mediator focal adhesion kinase (FAK) was performed by flow cytometry, cytokine secretion by Luminex technology, and megakaryocyte cell density and morphology by microscopic studies. Sema7A levels in vivo were assessed by real-time PCR and ELISA in hematological patients undergoing chemotherapy.
  
  
  RESULTS
  CD34(+) progenitor cells expressed the receptors for Sema7A. Expression of CD41, CD42a and CD61 was markedly reduced in the presence of Sema7A, after CC-dependent platelet production from CD34(+) progenitor cells. As revealed by microscopic analysis, megakaryocyte cell density was significantly lower in the presence of Sema7A as compared with controls. Blocking of CD29 abrogated the Sema7A-mediated inhibition. Sema7A activated FAK in CD34(+) progenitor cells and significantly increased secretion of the proinflammatory cytokines IL-6, IL-8 and GM-CSF. Finally, Sema7A levels were up-regulated in 50% of patients after chemotherapy.
  
  
  CONCLUSIONS
  Sema7A markedly reduces the production rates of megakaryocytes and platelets from CD34(+) progenitor cells. Hence, up-regulation of Sema7A may be a major risk factor for a reduced platelet repopulation after hematopoietic stem cell transplantation.
authors.affiliation: Institute for Transfusion Medicine, Hanover Medical School, Hanover, Germany.
authors.forename: Y
authors.initials: Y
authors.lastname: Jaimes
authors.forename: C
authors.initials: C
authors.lastname: Gras
authors.forename: L
authors.initials: L
authors.lastname: Goudeva
authors.forename: S
authors.initials: S
authors.lastname: Buchholz
authors.forename: B
authors.initials: B
authors.lastname: Eiz-Vesper
authors.forename: A
authors.initials: A
authors.lastname: Seltsam
authors.forename: S
authors.initials: S
authors.lastname: Immenschuh
authors.forename: R
authors.initials: R
authors.lastname: Blasczyk
authors.forename: C
authors.initials: C
authors.lastname: Figueiredo
mesh_terms: D000906:Antibodies; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism*; D018952:Antigens, CD34 / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000494:pharmacology; D015415:Biomarkers / Q000378:metabolism; D001792:Blood Platelets / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects; D002469:Cell Separation / Q000379:methods; D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism; D004789:Enzyme Activation; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D051417:Focal Adhesion Kinase 1 / Q000378:metabolism; D058851:GPI-Linked Proteins / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D018836:Inflammation Mediators / Q000378:metabolism; D019012:Integrin beta1 / Q000276:immunology / Q000378:metabolism; D039661:Integrin beta3 / Q000378:metabolism; D055016:Megakaryocyte Progenitor Cells / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D008533:Megakaryocytes / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D010766:Phosphorylation; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000378:metabolism; D040201:Platelet Membrane Glycoprotein IIb / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D039961:Semaphorins / Q000235:genetics / Q000378:metabolism*
chemical_list: D000906:Antibodies; D015703:Antigens, CD; D018952:Antigens, CD34; D000970:Antineoplastic Agents; D015415:Biomarkers; D016207:Cytokines; D058851:GPI-Linked Proteins; C061248:ITGB3 protein, human; D018836:Inflammation Mediators; D019012:Integrin beta1; D039661:Integrin beta3; D019038:Platelet Glycoprotein GPIb-IX Complex; D040201:Platelet Membrane Glycoprotein IIb; D012333:RNA, Messenger; C118753:SEMA7A protein, human; D039961:Semaphorins; D051417:Focal Adhesion Kinase 1; C496050:PTK2 protein, human