amyloid-beta-peptides and Hyperemia

Overproduction of the amyloid beta (Abeta) peptide is a key factor in the pathogenesis of Alzheimer's disease (AD), but the mechanisms of its pathogenic effects have not been defined. Patients with AD have cerebrovascular alterations attributable to the deleterious effects of Abeta on cerebral blood vessels. We report here that NADPH oxidase, the major source of free radicals in blood vessels, is responsible for the cerebrovascular dysregulation induced by Abeta. Thus, the free-radical production and the associated alterations in vasoregulation induced by Abeta are abrogated by the NADPH oxidase peptide inhibitor gp91ds-tat and are not observed in mice lacking the catalytic subunit of NADPH oxidase (gp91phox). Furthermore, oxidative stress and cerebrovascular dysfunction do not occur in transgenic mice overexpressing the amyloid precursor protein but lacking gp91phox. The mechanisms by which NADPH oxidase-derived radicals mediate the cerebrovascular dysfunction involve reduced bioavailability of nitric oxide. Thus, a gp91phox-containing NADPH oxidase is the critical link between Abeta and cerebrovascular dysfunction, which may underlie the alteration in cerebral blood flow regulation observed in AD patients.

Topics: Acetylcholine; Adenosine; Alzheimer Disease; Amino Acid Sequence; Amyloid beta-Peptides; Amyloid beta-Protein Precursor; Animals; Bradykinin; Calcimycin; Cerebrovascular Circulation; Female; Glycoproteins; Humans; Hyperemia; Laser-Doppler Flowmetry; Male; Membrane Glycoproteins; Mice; Mice, Inbred C57BL; Mice, Transgenic; Molecular Sequence Data; NADPH Oxidase 2; NADPH Oxidases; Nerve Tissue Proteins; Nitric Oxide Donors; Oxidative Stress; Peptide Fragments; Phenanthridines; Reactive Oxygen Species; S-Nitroso-N-Acetylpenicillamine; Vibrissae; X Chromosome

Peptides derived from proteolytic processing of the beta-amyloid precursor protein (APP), including the amyloid-beta peptide (Abeta), play a critical role in the pathogenesis of Alzheimer's dementia. We report that transgenic mice overexpressing APP and Abeta have a profound attenuation in the increase in neocortical blood flow elicited by somatosensory activation. The impairment is highly correlated with brain Abeta concentration and is reproduced in normal mice by topical neocortical application of exogenous Abeta1-40 but not Abeta1-42. Overexpression of M146L mutant presenilin-1 in APP mice enhances the production of Abeta1-42 severalfold, but it does not produce a commensurate attenuation of the hyperemic response. APP and Abeta overexpression do not diminish the intensity of neural activation, as reflected by the increase in somatosensory cortex glucose usage. Thus, Abeta-induced alterations in functional hyperemia produce a potentially deleterious mismatch between substrate delivery and energy demands imposed by neural activity.

Topics: Amyloid beta-Peptides; Amyloid beta-Protein Precursor; Animals; Cerebrovascular Circulation; Female; Glucose; Humans; Hypercapnia; Hyperemia; Laser-Doppler Flowmetry; Male; Membrane Proteins; Mice; Mice, Inbred C57BL; Mice, Transgenic; Mutation; Peptide Fragments; Physical Stimulation; Presenilin-1; Somatosensory Cortex; Touch; Vibrissae