Janaky Coomaraswamy

Aβ42‐driven cerebral amyloidosis in transgenic mice reveals early and robust pathology

We have generated a novel transgenic mouse model on a C57BL/6J genetic background that coexpresses KM670/671NL mutated amyloid precursor protein and L166P mutated presenilin 1 under the control of a neuron‐specific Thy1 promoter element (APPPS1 mice). Cerebral amyloidosis starts at 6–8 weeks and the ratio of human amyloid (A)β42 to Aβ40 is 1.5 and 5 in pre‐depositing and amyloid‐depositing mice, respectively. Consistent with this ratio, extensive congophilic parenchymal amyloid but minimal amyloid angiopathy is observed. Amyloid‐associated pathologies include dystrophic synaptic boutons, hyperphosphorylated tau‐positive neuritic structures and robust gliosis, with neocortical microglia number increasing threefold from 1 to 8 months of age. Global neocortical neuron loss is not apparent up to 8 months of age, but local neuron loss in the dentate gyrus is observed. Because of the early onset of amyloid lesions, the defined genetic background of the model and the facile breeding characteristics, APPPS1 mice are well suited for studying therapeutic strategies and the pathomechanism of amyloidosis by cross‐breeding to other genetically engineered mouse models.

In vivo reduction of amyloid-β by a mutant copper transporter

Cu ions have been suggested to enhance the assembly and pathogenic potential of the Alzheimers disease amyloid-β (Aβ) peptide. To explore this relationship in vivo, toxic-milk (txJ) mice with a mutant ATPase7b transporter favoring elevated Cu levels were analyzed in combination with the transgenic (Tg) CRND8 amyloid precursor protein mice exhibiting robust Aβ deposition. Unexpectedly, TgCRND8 mice homozygous for the recessive txJ mutation examined at 6 months of age exhibited a reduced number of amyloid plaques and diminished plasma Aβ levels. In addition, homozygosity for txJ increased survival of young TgCRND8 mice and lowered endogenous CNS Aβ at times before detectable increases in Cu in the CNS. These data suggest that the beneficial effect of the txJ mutation on CNS Aβ burden may proceed by a previously undescribed mechanism, likely involving increased clearance of peripheral pools of Aβ peptide.

Invasion of Hematopoietic Cells into the Brain of Amyloid Precursor Protein Transgenic Mice

The significance of the peripheral immune system in Alzheimers disease pathogenesis remains controversial. To study the CNS invasion of hematopoietic cells in the course of cerebral amyloidosis, we used a green fluorescence protein (GFP)-bone marrow chimeric amyloid precursor protein transgenic mouse model (APP23 mice). No difference in the number of GFP-positive invading cells was observed between young APP23 mice and nontransgenic control mice. In contrast, in aged, amyloid-depositing APP23 mice, a significant increase in the number of invading ameboid-like GFP-positive cells was found compared with age-matched nontransgenic control mice. Interestingly, independent of the time after transplantation, only a subpopulation of amyloid deposits was surrounded by invading cells. This suggests that not all amyloid plaques are a target for invading cells or, alternatively, all amyloid plaques attract invading cells but only for a limited time, possibly at an early stage of plaque evolution. Immunological and ultrastructural phenotyping revealed that macrophages and T-cells accounted for a significant portion of these ameboid-like invading cells. Macrophages did not show evidence of amyloid phagocytosis at the electron microscopic level, and no obvious signs for T-cell-mediated inflammation or neurodegeneration were observed. The observation that hematopoietic cells invade the brain in response to cerebral amyloidosis may hold an unrecognized therapeutic potential.

BRI2 Protein Regulates β-Amyloid Degradation by Increasing Levels of Secreted Insulin-degrading Enzyme (IDE)

Background: The British precursor protein (BRI2) influences amyloid precursor protein metabolism. Results: BRI2 lowers β-amyloid peptide levels by increasing levels of secreted insulin-degrading enzyme (IDE) in both cells and mice. Conclusion: BRI2 as a receptor protein regulates IDE levels and in turn promotes β-amyloid degradation. Significance: Targeting the regulation of IDE may lead to new approaches to therapeutically address sporadic Alzheimer disease. The amyloid precursor protein (APP) is one of the major proteins involved in Alzheimer disease (AD). Proteolytic cleavage of APP gives rise to amyloid-β (Aβ) peptides that aggregate and deposit extensively in the brain of AD patients. Although the increase in levels of aberrantly folded Aβ peptide is considered to be important to disease pathogenesis, the regulation of APP processing and Aβ metabolism is not fully understood. Recently, the British precursor protein (BRI2, ITM2B) has been implicated in influencing APP processing in cells and Aβ deposition in vivo. Here, we show that the wild type BRI2 protein reduces plaque load in an AD mouse model, similar to its disease-associated mutant form, ADan precursor protein (ADanPP), and analyze in more detail the mechanism of how BRI2 and ADanPP influence APP processing and Aβ metabolism. We find that overexpression of either BRI2 or ADanPP reduces extracellular Aβ by increasing levels of secreted insulin-degrading enzyme (IDE), a major Aβ-degrading protease. This effect is also observed with BRI2 lacking its C-terminal 23-amino acid peptide sequence. Our results suggest that BRI2 might act as a receptor protein that regulates IDE levels that in turn influences APP metabolism in a previously unrecognized way. Targeting the regulation of IDE may be a promising therapeutic approach to sporadic AD.

P1-072: Transgenic mouse models of familial British and Danish dementias

Background: The identification of the BRI2 gene, due to its relation to Familial British Dementia (FBD) and Familial Danish Dementia (FDD), has provided a new avenue to study the amyloid hypothesis, supporting the notion that the accumulation of amyloid is critical to the pathogenesis of neurodegenerative disease. Mutations of the BRI2 gene, a T-A transversion in FBD and ten nucleotide duplication in FDD, cause continued reading or a frame-shift at the stop codon resulting in BRI2 elongations. The proteolytic C-terminal fragments generated by normal processing of the elongated precursors accumulate in the form of vascular amyloid and hippocampal plaques, coinciding with tangles in both diseases. Objective: Since the identification of mutations in BRI2 causing FBD (1999) and FDD (2000) an animal model for either disease has remained elusive. Thus, it was our objective to create transgenic mice that recapitulate the pathogenesis seen in patients. Methods: Mutations for FBD and FDD were created using point and insertional mutagenesis in cDNA encoding for the wildtype BRI2 protein. Transgenic mice were produced on a C57BL/6J background expressing either transgene under the control of the SHaPrP promoter. Initial analyses have been perfomed on our Danish mice using histological and biochemical methods. Results: Initial results demonstrate that the Danish transgenic mice accumulate amyloid predominantly in the leptomeningeal vessels beginning as early as 2.5 months of age. This amyloid accumulation progresses further in the form of cerebral amyloid angiopathy (CAA) and parenchymal plaques as the mice age. Furthermore, the Danish amyloid deposition observed is immunoreactive with an antibody specific for the C-terminal of the Danish protein as well as thioflavin S positive. Conclusions: This new transgenic mouse model of cerebral amyloidosis provides a new tool in the quest for a better understanding of the role of amyloid, particularly in CAA. This model may be beneficial not only to study mechanistic insights into FBD and FDD but also into the pathophysiology of Alzheimer’s disease and other aggregation proteopathies.