The amyloid-β (Aβ) peptide, which is derived from the amyloid precursor protein (APP), is involved in the pathogenesis of Alzheimer's dementia and impairs endothelium-dependent vasodilation in cerebral vessels. We investigated whether cerebrovascular autoregulation, i.e., the ability of the cerebral circulation to maintain flow in the face of changes in mean arterial pressure (MAP), is impaired in transgenic mice that overexpress APP and Aβ. Neocortical cerebral blood flow (CBF) was monitored by laser-Doppler flowmetry in anesthetized APP(+) and APP(−) mice. MAP was elevated by intravenous infusion of phenylephrine and reduced by controlled exsanguination. In APP(−) mice, autoregulation was preserved. However, in APP(+) mice, autoregulation was markedly disrupted. The magnitude of the disruption was linearly related to brain Aβ concentration. The failure of autoregulation was paralleled by impairment of the CBF response to endothelium-dependent vasodilators. Thus Aβ disrupts a critical homeostatic mechanism of the cerebral circulation and renders CBF highly dependent on MAP. The resulting alterations in cerebral perfusion may play a role in the brain dysfunction and periventricular white-matter changes associated with Alzheimer's dementia.
Aβ1–40-related reduction in functional hyperemia in mouse neocortex during somatosensory activation
Proceedings of the National Academy of Sciences | July 26, 2002 | Volume: 97 | Issue: 17 | Pages: 9735-9740
Peptides derived from proteolytic processing of the β-amyloid precursor protein (APP), including the amyloid-β peptide (Aβ), play a critical role in the pathogenesis of Alzheimer's dementia. We report that transgenic mice overexpressing APP and Aβ have a profound attenuation in the increase in neocortical blood flow elicited by somatosensory activation. The impairment is highly correlated with brain Aβ concentration and is reproduced in normal mice by topical neocortical application of exogenous Aβ1–40 but not Aβ1–42. Overexpression of M146L mutant presenilin-1 in APP mice enhances the production of Aβ1–42 severalfold, but it does not produce a commensurate attenuation of the hyperemic response. APP and Aβ overexpression do not diminish the intensity of neural activation, as reflected by the increase in somatosensory cortex glucose usage. Thus, Aβ-induced alterations in functional hyperemia produce a potentially deleterious mismatch between substrate delivery and energy demands imposed by neural activity.