Amyloid‐mediated TRAIL DRs activation leads to progressive degeneration of cerebral vascular smooth muscle cells

Abstract

AbstractBackgroundVascular accumulation of amyloid beta (Ab) leads to loss of vascular smooth muscle cells (VSMC) in cerebral arteries via unknown mechanisms, promoting cerebral blood flow alterations and contributing to cognitive impairment. Ab species with different lengths or mutated familial variants may have differential effects on VSMC. Ab1‐42, the main pathogenic form of amyloid in the AD brain with the highest propensity to form aggregates, increased apoptosis in brain vascular cells whereas Ab1‐40 was found to be less toxic. By comparison, the familial Ab variant E22Q, induced the most cell death of all the amyloid variants tested. However, there has been little progress in defining the pathways leading to VSMC degeneration in AD and related disorders. The aim of this study was to identify Ab‐mediated cell death mechanisms in VSMC.MethodHuman cerebral VSMC were treated with pre‐oligomerized variants of Ab for 2‐8hrs (acute treatment) and 24‐72hrs (chronic treatment). Analysis of fragmented nucleosomes and visualization of cytochrome c (Cyt. C) expression by immunocytochemistry were used to measure apoptosis. Activation of intrinsic and extrinsic apoptotic pathways were examined by western blot and caspase‐glo assays. The effects of Ab on mitochondrial function were examined using a Seahorse XF96 Analyzer and TMRM fluorescent dye in live cells.ResultsAcute Ab treatment in VSMC up‐regulated tumor necrosis factor‐related apoptosis‐inducing ligand (TRAIL) death receptors DR4 and DR5 with activation of caspase 8 and transient activation of Nuclear Factor k B (NF‐kB). DR4 and DR5 expression remained high with chronic Ab treatment and lead to caspase activation followed by Cyt. C release and apoptosis. 24hrs of Ab treatment also decreased mitochondrial membrane potential and significantly impaired mitochondrial respiration.ConclusionAcute exposure of VSMC to Ab causes up‐regulation and activation of DR4/DR5, that, over time, results in mitochondrial dysfunction, caspase activation and apoptosis. Our data suggests that an early and transient activation of NF‐kB may also contribute to the toxic effects of Ab, possibly by inducing pro‐inflammatory pathways in the neurovascular unit.