Biomedical Engineering Reference
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Fetal endothelial progenitors can then participate in maternal angiogenesis during
pregnancy [
1169
]. After birth, angiogenesis participates in organ growth. During
adulthood, angiogenesis in a healthy subject mainly occurs in the cycling ovary
and the placenta during pregnancy. Otherwise, angiogenesis appears in trauma sites,
wound healing, and developing tumors.
3
Among subsets of mesenchymal stem cells, circulating endothelial progenitors
contribute to angiogenesis, even during steady-state conditions in adult humans.
Circulating angiogenic cells participate in tissue repair.
The sequential recruitment of mesenchymal stem cells begins by their mobi-
lization from the bone marrow through rupture of the CXCL12-CXCR4 com-
plex [
1170
]. Their migration to injury sites results from chemotaxis, not only via
the CXCL12-CXCR4 complex, but also via CCL7 chemokine that targets CCR1,
CCR2, and CCR3 receptors [
1170
].
4
Chemotaxis of hematopoietic progenitor cells
and circulating angiogenic cells is also triggered by the CCL19-CCR7 complex,
but the cell migration is weaker than that stimulated by CCL7 chemokine. In
addition, activated macrophages produce interleukin-6 that regulates the migration
of endothelial progenitor cells via interleukin-6 receptor-
chain. Chemokine
CX3CL1 can also be involved, as its CX3CR1 receptor resides on endothelial
progenitor cells.
Bone marrow-derived endothelial progenitors are recruited to tumoral growing
vessels using transcriptional Class-B basic helix-loop-helix protein bHLHb24
factor. Attracted endothelial progenitors help in the progression of dormant mi-
crometastases to lethal metastases [
1171
].
Recruitment of myelomonocytic cells from the bone marrow to tissues can
serve as a source of pro-angiogenic cytokines after ischemia. The coexistence
of myeloid lineage progenitors capable of endothelial differentiation and pro-
angiogenic myeloid accessory cells then leads to 2 complementary mechanisms of
angiogenesis. Vascular endothelial cells can differentiate from common myeloid
progenitors and more mature granulocyte-macrophage progenitors [
1172
]. Bone
marrow-derived progenitors of endothelial cells express PECAM1, von Willebrand
factor, and TIE2, but not PTPRc, and pericyte marker desmin and smooth muscle
actin.
α
3
Tumors are hypoxic at some stage because of high oxygen consumption and inadequate blood
supply. In response to hypoxia, tumor cells secrete angiogenic factors. Angiogenesis promotes
tumor progression and metastasis.
4
In addition to mesenchymal stem cells, basophils, eosinophils, neutrophils, T lymphocytes,
NK cells, and monocytes use CCL7 chemoattractant.
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