Proinflammatory and Vasoactive Effects of Aβ in the Cerebrovasculature

Abstract

Aβ peptides are thought to be critical molecules in the pathophysiology of Alzheimer's disease (AD) and are the major protein constituents of senile plaques. In most AD cases, Aβ peptides also form some deposits in the cerebrovasculature, leading to cerebral amyloid angiopathy and hemorrhagic stroke. Regional cerebral hypoperfusion is one of the earlier clinical manifestations in both the sporadic and familial forms of AD. In addition, a variety of vascular risk factors of different etiologies (for instance, diabetes, hypertension, high cholesterol level, atherosclerosis, and smoking) constitute risk factors for AD as well, suggesting that functional vascular abnormalities may contribute to AD pathology. We studied the effect of Aβ on constrictor responses elicited by endothelin-1 in isolated human cerebral arteries collected following rapid autopsies. We report that freshly solubilized Aβ potentiates endothelin-1-induced vasoconstriction in isolated human middle cerebral and basilar arteries. The vasoconstriction elicited by Aβ in these large human cerebral arteries appears to be completely antagonized by NS-398, a selective cyclooxygenase-2 inhibitor, or by SB202190, a specific p38 mitogen-activated protein kinase inhibitor, suggesting that Aβ vasoactivity is mediated via the stimulation of a proinflammatory pathway. In addition, a similar proinflammatory response appears to be mediated by Aβ in isolated human brain microvessels, resulting in an increased production of prostaglandin E₂ and F_2α. Using a scanner laser Doppler imager, we show a progressive decline with aging in cortical perfusion level in transgenic APPsw mice (line 2576) compared with age-matched control littermates. The relation between the acute proinflammatory and vasoactive properties of Aβ and the chronic progressive hypoperfusion seen in AD (and transgenic models thereof) is yet to be elucidated.