LACK OF OXYGEN AND/OR GLUCOSE DIFFERENTIALLY POTENTIATES Aβ40 _EQ22 - AND Aβ42-INDUCED CEREBRAL ENDOTHELIAL CELL DEATH, BARRIER DYFUNCTION AND ANGIOGENESIS IMPAIRMENT

Background

Disrupted brain hemodynamics and cerebrovascular damage resulting in cerebral hypoperfusion occur early within Alzheimer’s Disease (AD) pathogenesis. Cerebral hypoperfusion is also an extremely common consequence of cardiovascular risk factors and diseases (CVRFs/CVDs), which usually manifest in midlife, when AD pathology initiates, and actively contribute to AD onset and progression. Previously our lab has demonstrated that the vasculotropic Dutch mutant, AβQ22, and Aβ42 promote endothelial cells (ECs) apoptosis, barrier permeability, and angiogenic impairments. Prior research has indicated that hypoperfusion promotes analogous EC dysfunction. Aβ deposition occurs within a hypoperfused environment in AD, but whether exposure of cerebral ECs to Aβ under hypoperfusion results in potentiated cerebral EC dysfunction through activation of common molecular mechanisms remained unknown.

Methods

Human cerebral ECs were treated with Aβ40-Q22 or Aβ42, glucose deprivation (GD), or a combination of both, under normoxia or hypoxia conditions. Cell death mechanisms (apoptosis/necrosis), endothelial barrier dysfunction/permeability (TEER/barrier-regulating proteins/proinflammatory activation), and angiogenesis impairment (vessel branching/VEGF signaling) were evaluated.

Results

Reduction of glucose and/or oxygen potentiates Aβ-induced cerebral EC death, barrier instability, junction protein dysregulation, inflammatory activation, and angiogenesis/wound healing failure. In particular, hypoperfusion exacerbates AβQ22-mediated cerebral EC apoptosis, TEER/ZO1 decreases, ICAM1, IL6, and IL8 upregulation, monocyte migration, and wound healing impairments. Differentially, when in combination with Aβ42, hypoperfusion more strongly potentiates cerebral EC necrosis as well as increases in MMP2, phosphorylated claudin-5, IFNγ, and IL12p70 expression. Additionally, this study identified that GD exerts stronger effects on promoting increases in cerebral EC caspase-3 activation, apoptosis, and MMP2/ICAM1 expression, while hypoxia particularly increases necrosis, ZO1 expression, and pro-angiogenic protein expression.

Conclusions

This study reveals specific and selective mechanisms through which hypoxia, low glucose and amyloidosis mutually operate to produce brain EC dysfunction and death, highlighting new potential molecular targets against vascular pathology in AD/CAA comorbid with hypoperfusion conditions.

Highlights

• Depriving cerebral endothelial cells of glucose and/or oxygen potentiates Aβ-induced endothelial dysfunction, differentially promoting increased cell death, barrier instability and dysregulation of blood brain barrier proteins, inflammatory activation, and angiogenesis and wound healing failure, in relation to the specific peptide and low glucose or oxygen conditions.

• Under hypoperfusion conditions, AβQ22 more strongly exacerbates increases in apoptosis, ICAM1, IL6, and IL8 expression, and monocyte migration and decreases in TEER, ZO1 expression, and wound healing, revealing that the vasculotropic AβQ22 produces even stronger vascular effects when in combination with hypoperfusion.

• Under hypoperfusion conditions, Aβ42 more strongly potentiates increases in necrosis and MMP2, phosphorylated claudin-5, IFNγ, and IL12p70 expression.

• Glucose deprivation exerts stronger effects on increasing caspase-3 activation, apoptosis, and MMP2 and ICAM1 expression, while hypoxia displays stronger effects on increasing necrosis and ZO1 and pro-angiogenic protein expression.

• We demonstrated that AβQ22 more intensely promotes vascular dysfunction when in combination with hypoperfusion conditions versus Aβ42.

• verall, results from this study point to the importance of monitoring and preventing cerebral hypoperfusion particularly during midlife, when AD pathology begins to develop, to prevent this early pathology from working with Aβ to create a more detrimental dementia trajectory, and highlights new targets for possible therapeutic or preventive strategies.