Amyloid-β 25–35,an Amyloid-β 1–42 Surrogate,and Proinflammatory Cytokines Stimulate VEGF-A Secretion by Cultured,Early Passage,Normoxic Adult Human Cerebral Astrocytes

Abstract

Cerebrovascular angiopathy affects late-onset Alzheimer's disease (LOAD) brains by possibly increasing vascular endothelial growth factor (VEGF). A expression, thereby stimulating endothelial cell proliferation and migration. Indeed, VEGF-A gene upregulation, with increased VEGF-A protein content of reactive astrocytes and microglia, occurs in LOAD brains, and neovascularization was observed one week after injecting amyloid-β (Aβ)_1–42 into rat hippocampus. We have now found, with cultured 'normoxic' normal adult human astrocytes (NAHAs), that fibrillar Aβ_25–35 (an active Aβ_1–42 fragment) or a cytokine mixture (the (CM)-trio (interleukin [IL]-1β+interferon [IFN]-γ+tumor necrosis factor [TNF]-α), or pair (IFN-γ+TNF-α) like those produced in LOAD brains) stimulates the nuclear translocation of stabilized hypoxia-inducible factor (HIF)-1α protein and its binding to VEGF-A hypoxia-response elements; the mRNA synthesis for three VEGF-A splice variants (121, 165, 189); and the secretion of VEGF-A₁₆₅. The CM-trio was the most powerful stimulus, IFN-γ+TNF-α was less potent, and other cytokine pairs or single cytokines or Aβ_35–25 were ineffective. While Aβ_25–35 did not change HIF-1β protein levels, the CM-trio increased both HIF-1α and HIF-1β protein levels, thereby giving an earlier and stronger stimulus to VEGF-A secretion by NAHAs. Thus, increased VEGF-A secretion from astrocytes stimulated by Aβ_1–42 and by microglia-released cytokines might restore angiogenesis and Aβ_1–42 vascular clearance.