Identification of the hemangioblast in postnatal life

Abstract

Postnatal CD34 ؉ cells expressing vascular endothelial growth factor receptor 2 (KDR) generate hematopoietic or endothelial progeny in different in vitro and in vivo assays. Hypothetically, CD34 ؉ KDR ؉ cells may comprise hemangioblasts bipotent for both lineages. This hypothesis is consistent with 2 series of experiments. In the first series, in clonogenic culture permissive for hematopoietic and endothelial cell growth, CD34 ؉ KDR ؉ cells generate large hematoendothelial (Hem-End) colonies (5% of seeded cells), whereas CD34 ؉ KDR ؊ cells do not. Limiting-dilution analysis indicates that Hem-End colonies are clonally generated by single hemangioblasts. Sibling cells generated by a hemangioblast, replated in unicellular culture, produce either hematopoietic or Hem-End colonies, depending on the specific culture conditions. Identification of endothelial cells was based on the expression of VE-cadherin and endothelial markers and with lack of CD45 and hematopoietic molecules, as evaluated by immunofluorescence, immunocytochemistry, and reverse transcription-polymerase chain reaction. Furthermore, endothelial cells were functionally identified using low-density lipoprotein (LDL) uptake and tube-formation assays. In the second series, to evaluate the self-renewal capacity of hemangioblasts, single CD34 ؉ KDR ؉ cells were grown in 3-month extended long-term culture (ELTC) through 3 serial culture rounds-that is, blast cells generated in unicellular ELTC were reseeded for a subsequent round of unicellular ELTC. After 9 months, 10% blasts from tertiary ELTC functioned as hemangioblasts and generated macroscopic HemEnd colonies in clonogenic culture. These studies identified postnatal hemangioblasts in a CD34 ؉ KDR ؉ cell subset, endowed with long-term proliferative potential and bilineage differentiation capacity. Although exceedingly rare, hemangioblasts may represent the lifetime source/reservoir for primitive hematopoietic and endothelial progenitors. (Blood. 2002;100:3203-3208)

Angiogenic endothelium-specific nestin expression is enhanced by the first intron of the nestin gene

“…This region appears to consist of hemangioblast-like cells because CD34 and KDR were also positive in addition to nestin (Figure 2b and c). 13 We examined the cell proliferative features of this region using two proliferation markers; PCNA and Ki-67. PCNA-positive nuclei were distributed in numerous cells in this microcapillary region ( Figure 2e), whereas Ki-67-positive cells were few and limited mostly to the microcapillary endothelia (Figure 2f).…”

“…12 Hemangioblasts are characterized by the hematopoietic marker proteins CD34, and VEGF receptor type 2 (also called Flt-1, or KDR). 12,13 In tumor angiogenesis, bone marrow-derived endothelial progenitor cells contribute much to newly forming angiogenic vessels. 12,14 Thus, in the angiogenic endothelium of tumors, a significant number of hemangioblast-like hematopoietic precursor cells may be integrated in the endothelial cell population.…”

In vitro and in vivo arterial differentiation of human multipotent adult progenitor cells

“…5,13,21,23,24 Many different stem cell populations, including bone marrow (BM) mononuclear cells, AC133 ϩ endothelial progenitor cells, and embryonic stem cells have the potential to differentiate in vitro and in vivo into mature and functional ECs. 4,[25][26][27][28] We have recently described another stem cell population, multipotent adult progenitor cells (MAPCs), that differentiates into most somatic cell types, including functional ECs, in vitro and in vivo. [29][30][31][32][33] The question of whether and how these stem cells can be coaxed into arterial or venous ECs has thus far not been addressed.…”

Enforced expression of KDR receptor promotes proliferation, survival and megakaryocytic differentiation of TF1 progenitor cell line

“…17 Furthermore, postnatal CD34 þ KDR þ cells comprise hemangioblasts, endowed with bipotent hematopoietic and endothelial differentiation capacity. 19 In line with these findings, adult murine VEGF (À/À) cells show a sharp depletion of the HSC pool: importantly, treatment with VEGF mutants revealed that activation of KDR is sufficient to rescue the HSC activity. 20 Specifically, KDR favors self-renewal and survival of primitive hematopoietic cells.…”