title: Mesodermal progenitor cells (MPCs) differentiate into mesenchymal stromal cells (MSCs) by activation of Wnt5/calmodulin signalling pathway.
abstract: BACKGROUND
  Mesenchymal Stromal Cells (MSCs) remain poorly characterized because of the absence of manifest physical, phenotypic, and functional properties in cultured cell populations. Despite considerable research on MSCs and their clinical application, the biology of these cells is not fully clarified and data on signalling activation during mesenchymal differentiation and proliferation are controversial. The role of Wnt pathways is still debated, partly due to culture heterogeneity and methodological inconsistencies. Recently, we described a new bone marrow cell population isolated from MSC cultures that we named Mesodermal Progenitor Cells (MPCs) for their mesenchymal and endothelial differentiation potential. An optimized culture method allowed the isolation from human adult bone marrow of a highly pure population of MPCs (more than 97%), that showed the distinctive SSEA-4+CD105+CD90(neg) phenotype and not expressing MSCA-1 antigen. Under these selective culture conditions the percentage of MSCs (SSEA-4(neg)CD105+CD90(bright) and MSCA-1+), in the primary cultures, resulted lower than 2%.
  
  
  RESULTS
  We demonstrate that MPCs differentiate to MSCs through an SSEA-4+CD105+CD90(bright) early intermediate precursor. Differentiation paralleled the activation of Wnt5/Calmodulin signalling by autocrine/paracrine intense secretion of Wnt5a and Wnt5b (p<0.05 vs uncondictioned media), which was later silenced in late MSCs (SSEA-4(neg)). We found the inhibition of this pathway by calmidazolium chloride specifically blocked mesenchymal induction (ID₅₀ =  0.5 µM, p<0.01), while endothelial differentiation was unaffected.
  
  
  CONCLUSIONS
  The present study describes two different putative progenitors (early and late MSCs) that, together with already described MPCs, could be co-isolated and expanded in different percentages depending on the culture conditions. These results suggest that some modifications to the widely accepted MSC nomenclature are required.
authors: Hematology Division, Department of Oncology, Transplants and New Advances in Medicine, University of Pisa, Pisa, Italy.
authors: Rita
authors: R
authors: Fazzi
authors: Simone
authors: S
authors: Pacini
authors: Vittoria
authors: V
authors: Carnicelli
authors: Luisa
authors: L
authors: Trombi
authors: Marina
authors: M
authors: Montali
authors: Edoardo
authors: E
authors: Lazzarini
authors: Mario
authors: M
authors: Petrini
mesh_terms: D000328:Adult; D000368:Aged; D002147:Calmodulin / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects; D042783:Endothelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D008297:Male; D059630:Mesenchymal Stem Cells / Q000166:cytology*; D008648:Mesoderm / Q000166:cytology*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D055746:Stage-Specific Embryonic Antigens / Q000378:metabolism; D013234:Stem Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism*; D000071818:Wnt-5a Protein
chemical_list: D002147:Calmodulin; D007093:Imidazoles; D011518:Proto-Oncogene Proteins; D055746:Stage-Specific Embryonic Antigens; C085389:WNT5A protein, human; C435831:WNT5B protein, human; D051153:Wnt Proteins; D000071818:Wnt-5a Protein; C066584:stage-specific embryonic antigen-4; C031938:calmidazolium