Yvonne S. Eisele

Peripherally Applied Aβ-Containing Inoculates Induce Cerebral β-Amyloidosis

Infectious Amyloid? Patients with Alzheimers disease have characteristic lesions in the brains associated with masses of polymerized protein called β-amyloid. Recently, evidence from mouse models of Alzheimers disease shows that brain extracts containing β-amyloid can “infect” otherwise healthy animals when injected directly into their brains. Eisele et al. (p. 980, published online 21 October; see the Perspective by Kim and Holtzman) extend these findings to show that when mice are injected in other parts of their bodies with similar brain extracts after several months, they also develop amyloidosis within their brains. Amyloid-containing brain extracts can “infect” susceptible Alzheimer’s disease model animals. The intracerebral injection of β-amyloid–containing brain extracts can induce cerebral β-amyloidosis and associated pathologies in susceptible hosts. We found that intraperitoneal inoculation with β-amyloid–rich extracts induced β-amyloidosis in the brains of β-amyloid precursor protein transgenic mice after prolonged incubation times.

Peripherally applied Abeta-containing inoculates induce cerebral beta-amyloidosis.

Infectious Amyloid? Patients with Alzheimers disease have characteristic lesions in the brains associated with masses of polymerized protein called β-amyloid. Recently, evidence from mouse models of Alzheimers disease shows that brain extracts containing β-amyloid can “infect” otherwise healthy animals when injected directly into their brains. Eisele et al. (p. 980, published online 21 October; see the Perspective by Kim and Holtzman) extend these findings to show that when mice are injected in other parts of their bodies with similar brain extracts after several months, they also develop amyloidosis within their brains. Amyloid-containing brain extracts can “infect” susceptible Alzheimer’s disease model animals. The intracerebral injection of β-amyloid–containing brain extracts can induce cerebral β-amyloidosis and associated pathologies in susceptible hosts. We found that intraperitoneal inoculation with β-amyloid–rich extracts induced β-amyloidosis in the brains of β-amyloid precursor protein transgenic mice after prolonged incubation times.

Soluble Aβ Seeds Are Potent Inducers of Cerebral β-Amyloid Deposition

Cerebral β-amyloidosis and associated pathologies can be exogenously induced by the intracerebral injection of small amounts of pathogenic Aβ-containing brain extract into young β-amyloid precursor protein (APP) transgenic mice. The probable β-amyloid-inducing factor in the brain extract has been identified as a species of aggregated Aβ that is generated in its most effective conformation or composition in vivo. Here we report that Aβ in the brain extract is more proteinase K (PK) resistant than is synthetic fibrillar Aβ, and that this PK-resistant fraction of the brain extract retains the capacity to induce β-amyloid deposition upon intracerebral injection in young, pre-depositing APP23 transgenic mice. After ultracentrifugation of the brain extract, <0.05% of the Aβ remained in the supernatant fraction, and these soluble Aβ species were largely PK sensitive. However, upon intracerebral injection, this soluble fraction accounted for up to 30% of the β-amyloid induction observed with the unfractionated extract. Fragmentation of the Aβ seeds by extended sonication increased the seeding capacity of the brain extract. In summary, these results suggest that multiple Aβ assemblies, with various PK sensitivities, are capable of inducing β-amyloid aggregation in vivo. The finding that small and soluble Aβ seeds are potent inducers of cerebral β-amyloidosis raises the possibility that such seeds may mediate the spread of β-amyloidosis in the brain. If they can be identified in vivo, soluble Aβ seeds in bodily fluids also could serve as early biomarkers for cerebral β-amyloidogenesis and eventually Alzheimers disease.

Induction of cerebral beta-amyloidosis: intracerebral versus systemic Abeta inoculation.

Despite the importance of the aberrant polymerization of Aβ in the early pathogenic cascade of Alzheimers disease, little is known about the induction of Aβ aggregation in vivo. Here we show that induction of cerebral β-amyloidosis can be achieved in many different brain areas of APP23 transgenic mice through the injection of dilute Aβ-containing brain extracts. Once the amyloidogenic process has been exogenously induced, the nature of the induced Aβ-deposition is determined by the brain region of the host. Because these observations are reminiscent of a prion-like mechanism, we then investigated whether cerebral β-amyloidosis also can be induced by peripheral and systemic inoculations or by the intracerebral implantation of stainless steel wires previously coated with minute amounts of Aβ-containing brain extract. Results reveal that oral, intravenous, intraocular, and intranasal inoculations yielded no detectable induction of cerebral β-amyloidosis in APP23 transgenic mice. In contrast, transmission of cerebral β-amyloidosis through the Aβ-contaminated steel wires was demonstrated. Notably, plasma sterilization, but not boiling of the wires before implantation, prevented the induction of β-amyloidosis. Our results suggest that minute amounts of Aβ-containing brain material in direct contact with the CNS can induce cerebral β-amyloidosis, but that systemic cellular mechanisms of prion uptake and transport to the CNS may not apply to Aβ.

Seeded strain-like transmission of β-amyloid morphotypes in APP transgenic mice.

The polymorphic β‐amyloid lesions present in individuals with Alzheimers disease are collectively known as cerebral β‐amyloidosis. Amyloid precursor protein (APP) transgenic mouse models similarly develop β‐amyloid depositions that differ in morphology, binding of amyloid conformation‐sensitive dyes, and Aβ40/Aβ42 peptide ratio. To determine the nature of such β‐amyloid morphotypes, β‐amyloid‐containing brain extracts from either aged APP23 brains or aged APPPS1 brains were intracerebrally injected into the hippocampus of young APP23 or APPPS1 transgenic mice. APPPS1 brain extract injected into young APP23 mice induced β‐amyloid deposition with the morphological, conformational, and Aβ40/Aβ42 ratio characteristics of β‐amyloid deposits in aged APPPS1 mice, whereas APP23 brain extract injected into young APP23 mice induced β‐amyloid deposits with the characteristics of β‐amyloid deposits in aged APP23 mice. Injecting the two extracts into the APPPS1 host revealed a similar difference between the induced β‐amyloid deposits, although less prominent, and the induced deposits were similar to the β‐amyloid deposits found in aged APPPS1 hosts. These results indicate that the molecular composition and conformation of aggregated Aβ in APP transgenic mice can be maintained by seeded conversion.

Induction of cerebral β-amyloidosis: Intracerebral versus systemic Aβ inoculation

Despite the importance of the aberrant polymerization of Aβ in the early pathogenic cascade of Alzheimers disease, little is known about the induction of Aβ aggregation in vivo. Here we show that induction of cerebral β-amyloidosis can be achieved in many different brain areas of APP23 transgenic mice through the injection of dilute Aβ-containing brain extracts. Once the amyloidogenic process has been exogenously induced, the nature of the induced Aβ-deposition is determined by the brain region of the host. Because these observations are reminiscent of a prion-like mechanism, we then investigated whether cerebral β-amyloidosis also can be induced by peripheral and systemic inoculations or by the intracerebral implantation of stainless steel wires previously coated with minute amounts of Aβ-containing brain extract. Results reveal that oral, intravenous, intraocular, and intranasal inoculations yielded no detectable induction of cerebral β-amyloidosis in APP23 transgenic mice. In contrast, transmission of cerebral β-amyloidosis through the Aβ-contaminated steel wires was demonstrated. Notably, plasma sterilization, but not boiling of the wires before implantation, prevented the induction of β-amyloidosis. Our results suggest that minute amounts of Aβ-containing brain material in direct contact with the CNS can induce cerebral β-amyloidosis, but that systemic cellular mechanisms of prion uptake and transport to the CNS may not apply to Aβ.

Multiple factors contribute to the peripheral induction of cerebral beta-amyloidosis

Deposition of aggregated amyloid-β (Aβ) peptide in brain is an early event and hallmark pathology of Alzheimers disease and cerebral Aβ angiopathy. Experimental evidence supports the concept that Aβ multimers can act as seeds and structurally corrupt other Aβ peptides by a self-propagating mechanism. Here we compare the induction of cerebral β-amyloidosis by intraperitoneal applications of Aβ-containing brain extracts in three Aβ-precursor protein (APP) transgenic mouse lines that differ in levels of transgene expression in brain and periphery (APP23 mice, APP23 mice lacking murine APP, and R1.40 mice). Results revealed that beta-amyloidosis induction, which could be blocked with an anti-Aβ antibody, was dependent on the amount of inoculated brain extract and on the level of APP/Aβ expression in the brain but not in the periphery. The induced Aβ deposits in brain occurred in a characteristic pattern consistent with the entry of Aβ seeds at multiple brain locations. Intraperitoneally injected Aβ could be detected in blood monocytes and some peripheral tissues (liver, spleen) up to 30 d after the injection but escaped histological and biochemical detection thereafter. These results suggest that intraperitoneally inoculated Aβ seeds are transported from the periphery to the brain in which corruptive templating of host Aβ occurs at multiple sites, most efficiently in regions with high availability of soluble Aβ.

Peripherally Applied A -Containing Inoculates Induce Cerebral -Amyloidosis

Infectious Amyloid? Patients with Alzheimers disease have characteristic lesions in the brains associated with masses of polymerized protein called β-amyloid. Recently, evidence from mouse models of Alzheimers disease shows that brain extracts containing β-amyloid can “infect” otherwise healthy animals when injected directly into their brains. Eisele et al. (p. 980, published online 21 October; see the Perspective by Kim and Holtzman) extend these findings to show that when mice are injected in other parts of their bodies with similar brain extracts after several months, they also develop amyloidosis within their brains. Amyloid-containing brain extracts can “infect” susceptible Alzheimer’s disease model animals. The intracerebral injection of β-amyloid–containing brain extracts can induce cerebral β-amyloidosis and associated pathologies in susceptible hosts. We found that intraperitoneal inoculation with β-amyloid–rich extracts induced β-amyloidosis in the brains of β-amyloid precursor protein transgenic mice after prolonged incubation times.

Induction of cerebral -amyloidosis: Intracerebral versus systemic A inoculation

Despite the importance of the aberrant polymerization of Aβ in the early pathogenic cascade of Alzheimers disease, little is known about the induction of Aβ aggregation in vivo. Here we show that induction of cerebral β-amyloidosis can be achieved in many different brain areas of APP23 transgenic mice through the injection of dilute Aβ-containing brain extracts. Once the amyloidogenic process has been exogenously induced, the nature of the induced Aβ-deposition is determined by the brain region of the host. Because these observations are reminiscent of a prion-like mechanism, we then investigated whether cerebral β-amyloidosis also can be induced by peripheral and systemic inoculations or by the intracerebral implantation of stainless steel wires previously coated with minute amounts of Aβ-containing brain extract. Results reveal that oral, intravenous, intraocular, and intranasal inoculations yielded no detectable induction of cerebral β-amyloidosis in APP23 transgenic mice. In contrast, transmission of cerebral β-amyloidosis through the Aβ-contaminated steel wires was demonstrated. Notably, plasma sterilization, but not boiling of the wires before implantation, prevented the induction of β-amyloidosis. Our results suggest that minute amounts of Aβ-containing brain material in direct contact with the CNS can induce cerebral β-amyloidosis, but that systemic cellular mechanisms of prion uptake and transport to the CNS may not apply to Aβ.

Persistence of Aβ seeds in APP null mouse brain.

Cerebral β-amyloidosis is induced by inoculation of Aβ seeds into APP transgenic mice, but not into App−/− (APP null) mice. We found that brain extracts from APP null mice that had been inoculated with Aβ seeds up to 6 months previously still induced β-amyloidosis in APP transgenic hosts following secondary transmission. Thus, Aβ seeds can persist in the brain for months, and they regain propagative and pathogenic activity in the presence of host Aβ.