Question:

The acute phase protein α₂-macroglobulin (α2M) is elevated during tissue damage, e.g. cardiac infarction and may be involved in the initiation of repair processes. In the present study the effects of α2M on vasculogenesis of mouse embryonic (ES) cells were investigated.

Results:

In undifferentiated ES cells the α2M receptor LRP-1 was strongly expressed and upregulated during differentiation, whereas the GRP78 receptor was constantly expressed. α2M dose-dependent increased vasculogenesis of ES cells as evaluated by assessing CD31-positive cell structures, and increased expression of the early cardiovascular markers isl-1, Nkx-2.5 and flk-1 as well as numbers of VE-cadherin and flk-1 positive cells. Furthermore α2M treatment of differentiating ES cells augmented the expression of the pro-angiogenic growth factors fibroblast growth factor-2 (FGF-2), vascular endothelial growth factor (VEGF) as well as platelet-derived growth factor BB (PDGF-BB). Enhancement of vasculogenesis/angiogenesis by a₂M was abolished by the LRP-1 antagonist receptor associated protein (RAP) and LRP-1 blocking antibody as well as by the VEGF-R2 (flk-1) antagonist SU5614 and the PDGF-BB receptor antagonist AG1296. Furthermore the upregulation of FGF-2, VEGF and PDGF-BB by α2M was abolished upon inhibition of LRP-1 by RAP. α2M treatment of differentiating ES cells resulted in activation of PI3K, AKT, AMPK and ERK1/2, suggesting involvement of distinct signaling pathways downstream of LRP-1.

Conclusions:

α2M stimulates vasculogenesis of ES cells via upregulation of the well-known pro-angiogenic factors FGF-2, VEGF and PDGF-BB.