30 Nevertheless, there is no consensus regarding the MSC phenotype, because of the broad variety of potential tissue sources and the differences in cell isolation and cell culture procedures used. The four minimal defining criteria for MSCs are: i) adherence to plastic under standard tissue culture conditions ii) expression of CD105, CD73, CD90 iii) lack of expression of CD45, CD34, CD14/CD11b, CD79/CD19 and HLA-DR surface markers and iv) differentiation into adipocytes, osteoblasts and chondroblasts in vitro. In an attempt to standardize the definition of an MSC, the International Society for Cellular Therapy (ISCT) proposed the concept of essential minimal criteria for MSCs in culture. 26 Despite their shared markers and perivascular location in vivo, more evidence is required to prove that MSC-like cells in every tissue are derived from or indeed function as pericytes. An extensive study by Crisan and colleagues has established further links between MSCs and pericytes by validating the phenotype of pericytes as CD146 +, NG2 +, PDGFR +, ALP +, CD34 -, CD45 -, vWF - and CD144 - throughout human fetal and adult organs. 27-29 Pericytes may represent a subpopulation of the total pool of assayable MSCs at least within the bone marrow. 25 Pericytes and adventitial cells also natively express mesenchymal markers and share similar gene expression profiles as well as developmental and differentiation potential with mesenchymal cells. 19-26 Pericytes are thought to stabilize blood vessels, contribute to tissue homeostasis under physiological conditions, and play an active role in response to focal tissue injury through the release of bioactive molecules with trophic and immunomodulatory properties. 10-18 Accumulating evidence indicates a perivascular location for these MSC-like cells in all tissues, implying that all MSCs are pericytes 19 that closely encircle endothelial cells in capillaries and microvessels in multiple organs. Isolation, Marker Specificity and Functional Properties of MSCsĪlthough MSCs are traditionally isolated from bone marrow, cells with MSC-like characteristics have been isolated from a variety of fetal, neonatal and adult tissues, including cord blood, peripheral blood, fetal liver and lung, adipose tissue, compact bone, dental pulp, dermis, human islet, adult brain, skeletal muscle, amniotic fluid, synovium, and the circulatory system. 1 CFU-F initiating cells in vivo have been shown to be quiescent, existing at a low frequency in human bone marrow. in the 1970s then revealed its importance in regulating the proliferation, differentiation and survival of HSCs. 7,8 Functional in vitro characterization of the stromal compartment by Dexter et al. 6 The CFU-F assay is now widely used as a functional method to quantify stromal progenitors. These colony-forming unitfibroblasts (CFU-Fs) were capable of osteogenic differentiation and provided the first evidence of a clonogenic precursor for cells of the bone lineage. 2-5 In the late 1960s, Friedenstein and colleagues established that single cell suspensions of BM stroma could generate colonies of adherent fibroblast-like cells in vitro. MSCs, also termed multipotent marrow stromal cells or mesenchymal stromal cells, are a heterogeneous population of plastic-adherent, fibroblast-like cells, which can self-renew and differentiate into bone, adipose and cartilage tissue in culture. 1 Later evidence demonstrated, however, that at least two distinct stem cell populations reside in the bone marrow of many mammalian species: hematopoietic stem cells (HSCs) and mesenchymal stromal cells (also known as mesenchymal stem cells MSCs), with the latter responsible for the maintenance of the non-hematopoietic bone marrow cells. The bone marrow (BM) stroma contains a heterogeneous population of cells, including endothelial cells, fibroblasts, adipocytes and osteogenic cells, and it was initially thought to function primarily as a structural framework upon which hematopoiesis occurs. Tissue and Cell Culture Dissociation Reagents.Work at STEMCELL View Current Opportunities >
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