Evidence for seeding of beta -amyloid by intracerebral infusion of Alzheimer brain extracts in beta -amyloid precursor protein-transgenic mice

Abstract

Many neurodegenerative diseases are associated with the abnormal sequestration of disease-specific proteins in the brain, but the events that initiate this process remain unclear. To determine whether the deposition of the beta-amyloid peptide (Abeta), a key pathological feature of Alzheimer's disease (AD), can be induced in vivo, we infused dilute supernatants of autopsy-derived neocortical homogenates from Alzheimer's patients unilaterally into the hippocampus and neocortex of 3-month-old beta-amyloid precursor protein (betaAPP)-transgenic mice. Up to 4 weeks after the infusion there was no Abeta-deposition in the brain; however, after 5 months, the AD-tissue-injected hemisphere of the transgenic mice had developed profuse Abeta-immunoreactive senile plaques and vascular deposits, some of which were birefringent with Congo Red. There was limited deposition of diffuse Abeta also in the brains of betaAPP-transgenic mice infused with tissue from an age-matched, non-AD brain with mild beta-amyloidosis, but none in mice receiving extract from a young control case. Abeta deposits also were not found in either vehicle-injected or uninjected transgenic mice or in any nontransgenic mice. The results show that cerebral beta-amyloid can be seeded in vivo by a single inoculation of dilute AD brain extract, demonstrating a key pathogenic commonality between beta-amyloidosis and other neurodegenerative diseases involving abnormal protein polymerization. The paradigm can be used to clarify the conditions that initiate in vivo beta-amyloidogenesis in the brain and may yield a more authentic animal model of Alzheimer's disease and other neurodegenerative disorders.

Fig. 1.

Eight-month-old Tg2576 (a) and nontransgenic (b) mice that had received equivalent intracerebral injections of dilute AD brain extract (case 1) 5 months earlier. a, Aβ immunoreactivity in the hippocampus of a transgenic mouse injected with AD brain extract. Note especially the profuse Aβ deposition along the hippocampal fissure.b, Absence of Aβ immunoreactivity in a nontransgenic, littermate control mouse injected with AD brain extract. Antibody 4G8. Scale bar, 500 μm.

Fig. 2.

Photomontage of a coronal section through the dorsal forebrain of a transgenic mouse that had been infused unilaterally (left side) with AD brain extract (AD case 3). A limited amount of Aβ is deposited in and around the corpus callosum and also in the medial aspect of the contralateral hemisphere.Arrows mark the hippocampal fissure in each hemisphere. Antibody R165 to Aβ42. Scale bar, 200 μm.

Fig. 3.

Antibody–antigen adsorption control.a, Aβ immunoreactivity in the hippocampus of a Tg2576 mouse that had been injected with AD brain extract (AD case 1; antibody 6E10). b, Adjacent control section in which antibody 6E10 was preadsorbed with Aβ1–28 peptide. Thearrowheads denote the same blood vessel that has been transversely sectioned in a and b. Scale bar, 100 μm.

Fig. 4.

Aβ immunostaining of the hippocampus in two Tg2576 mice injected with AD brain extract (a, b) and in two transgenic mice injected with control brain extracts (c, d). e shows the amount of hippocampal Aβ deposition in Tg2576 mice in the four long-term experimental groups. a, Tg2576 mouse injected with extract from AD case 1. b, Tg2576 mouse injected with extract from AD case 2. c, Tg2576 mouse injected with extract from an aged, non-AD case. d, Tg2576 mouse injected with extract from a young control case. Antibody 6E10. Scale bar, 100 μm. e, Mean (± SEM) hippocampal plaque area occupied by Aβ-immunoreactive deposits in all AD-tissue-injected Tg2576 mice compared to untreated control transgenic mice (sham and unoperated), as well as mice infused intracerebrally with young control and aged control brain extracts. The treatment effect was statistically significant (F_(3,27) = 6.02; p < 0.01). Antibody 4G8 (antibody 6E10 yielded similar results).

Fig. 5.

Comparative immunostaining of Aβ42 (a) and Aβ40 (b) in a Tg2576 mouse infused with extract from AD case 3. Aβ40 deposits were infrequent in AD tissue-infused animals at 8 months of age, and when they occurred they were usually small, compact parenchymal lesions (arrowheads) or cerebrovascular deposits. Scale bar, 200 μm.

Fig. 6.

Congo Red-stained amyloid plaque in the hippocampus of a Tg2576 mouse infused with extract from AD case 1. Crossed polarizing filters. Scale bar, 10 μm.