The contribution of hyperhomocysteinemia and hypoperfusion to amyloid‐beta induced cerebral endothelial cell dysfunction

Abstract

AbstractBackgroundCerebrovascular dysfunction has been implicated as a major contributor to Alzheimer’s Disease (AD) pathology, with particularly endothelial cell (EC) stress promoting the focal ischemia, cerebral blood flow impairments, and blood brain barrier (BBB) permeability that are pathologically characteristic in AD. Recent evidence has emerged suggesting a link between cardiovascular (CV) diseases and AD pathology, particularly showing that CV/cerebrovascular risk factors, including hyperhomocysteinemia (Hhcy) and hypoperfusion (oxygen and glucose deprivation (OGD)), contribute to AD pathology and risk. Despite this, the underlying molecular mechanisms for this interaction remain unclear. Previously our lab has demonstrated that amyloid beta (Aβ), particularly Aβ40‐Q22 (the vasculotropic Dutch mutant), promotes TRAIL death receptor (DR)‐mediated apoptosis, barrier permeability, and angiogenic impairment within human cerebral ECs. We tested the hypothesis that Hhcy and hypoperfusion exacerbate Aβ‐induced cerebral EC TRAIL DR‐mediated apoptosis, barrier dysfunction, and angiogenesis defects.MethodHuman cerebral microvascular ECs were challenged with AβQ22 and/or homocysteine (Hcy) in the presence/absence of hypoperfusion. Apoptotic mediator expression, caspase activation, and DNA fragmentation were measured to assess apoptosis. BBB protein expression and trans‐endothelial‐electrical‐resistance (TEER) were measured to assess EC barrier integrity. Angiogenesis inhibition and activation assays were utilized to measure EC angiogenic capability.ResultAβQ22 and Hcy challenge independently upregulated EC expression of TRAIL DR‐related apoptotic mediators and caspase activity, and, at certain time‐points, resulted in an additive upregulation of apoptotic mediators and caspase activity. AβQ22, Hcy, and hypoperfusion individually increased DNA fragmentation within cerebral ECs. Combination treatments of AβQ22 and Hcy created an additive effect on DNA fragmentation. Hypoperfusion and AβQ22 independently decreased BBB protein expression and TEER, while an additive decrease was observed with the combined challenges. AβQ22 and Hcy independently decreased angiogenesis progression, with some timepoints revealing an additive decrease with the combination treatment.ConclusionThe presence of CV risk factors seems to exacerbate Aβ induced‐EC apoptosis, barrier dysfunction, and angiogenic impairment, revealing several of the specific molecular mechanism through which amyloidosis and CV risk factors may additively act to produce EC dysfunction and death in AD pathology.