Modified amyloid variants in pathological subgroups of ß-amyloidosis.

OBJECTIVE: Amyloid ß (Aß) depositions in plaques and cerebral amyloid angiopathy (CAA) represent common features of Alzheimer's disease (AD). Sequential deposition of post-translationally modified Aß in plaques characterizes distinct biochemical stages of Aß maturation. However, the molecular composition of vascular Aß deposits in CAA and its relation to plaques remain enigmatic. METHODS: Vascular and parenchymal deposits were immunohistochemically analyzed for pyroglutaminated and phosphorylated Aß in the medial temporal and occipital lobe of 24 controls, 27 pathologically-defined preclinical AD, and 20 symptomatic AD cases. RESULTS: Sequential deposition of Aß in CAA resembled Aß maturation in plaques and enabled the distinction of three biochemical stages of CAA. B-CAA stage 1 was characterized by deposition of Aß in the absence of pyroglutaminated AßN3pE and phosphorylated AßpS8. B-CAA stage 2 showed additional AßN3pE and B-CAA stage 3 additional AßpS8. Based on the Aß maturation staging in CAA and plaques, three case groups for Aß pathology could be distinguished: group 1 with advanced Aß maturation in CAA; group 2 with equal Aß maturation in CAA and plaques; group 3 with advanced Aß maturation in plaques. All symptomatic AD cases presented with end-stage plaque maturation, whereas CAA could exhibit immature Aß deposits. Notably, Aß pathology group 1 was associated with arterial hypertension, and group 2 with the development of dementia. INTERPRETATION: Balance of Aß maturation in CAA and plaques defines distinct pathological subgroups of ß-amyloidosis. The association of CAA-related Aß maturation with cognitive decline, the individual contribution of CAA and plaque pathology to the development of dementia within the defined Aß pathology subgroups, and the subgroup-related association with arterial hypertension should be considered for differential diagnosis and therapeutic intervention.

Neprilysin deficiency alters the neuropathological and behavioral phenotype in the 5XFAD mouse model of Alzheimer's disease.

The deposition of amyloid-ß (Aß) is one of the major neuropathological hallmarks of Alzheimer's disease (AD). In the case of sporadic AD, an imbalance in Aß in production and clearance seems to be the reason for an enhanced Aß accumulation. Besides a systematic clearance through the blood-brain barrier, Aß is cleared from the brain by Aß-degrading enzymes. The metalloprotease neprilysin (NEP) is an important Aß-degrading enzyme as shown by numerous in vitro, in vivo and reverse genetics studies. 5XFAD mice represent an early-onset AD mouse model which develops plaque pathology starting with 2 months of age in addition to robust behavioral deficits at later time points. By crossing 5XFAD mice with homozygous NEP-knock-out mice (NEP-/-), we show that hemizygous NEP deficiency aggravates the behavioral and neuropathological phenotype of 5XFAD mice. We found that 5XFAD mice per se showed strongly decreased NEP expression levels compared to wildtype mice, which was aggravated by NEP reduction. 5XFAD/NEP+/- mice demonstrated impairment in spatial working memory and increased astrocytosis in all studied brain areas, in addition to an overall increased level of soluble Aß42 as well as region-specific increases in extracellular Aß deposition. Surprisingly, in young mice, a more abundant cortical Aß plaque pathology was observed in 5XFAD compared to 5XFAD/NEP+/- mice. Additionally, young 5XFAD/NEP+/- as well as hemi- and homozygous NEP knockout mice showed elevated levels of endothelin-converting enzyme 1 (ECE1), suggesting a mutual regulation of ECE1 and NEP at young ages. The present data indicate that NEP mainly degrades soluble Aß peptides, which confirms previous observations. Increased ECE1 levels correlated well with the strongly reduced extracellular plaque load in young 5XFAD/NEP+/- mice and might suggest a reciprocal effect between ECE and NEP activities in Aß degradation.

The type of Aß-related neuronal degeneration differs between amyloid precursor protein (APP23) and amyloid ß-peptide (APP48) transgenic mice.

BACKGROUND: The deposition of the amyloid ß-peptide (Aß) in the brain is one of the hallmarks of Alzheimer's disease (AD). It is not yet clear whether Aß always leads to similar changes or whether it induces different features of neurodegeneration in relation to its intra- and/or extracellular localization or to its intracellular trafficking routes. To address this question, we have analyzed two transgenic mouse models: APP48 and APP23 mice. The APP48 mouse expresses Aß1-42 with a signal sequence in neurons. These animals produce intracellular Aß independent of amyloid precursor protein (APP) but do not develop extracellular Aß plaques. The APP23 mouse overexpresses human APP with the Swedish mutation (KM670/671NL) in neurons and produces APP-derived extracellular Aß plaques and intracellular Aß aggregates. RESULTS: Tracing of commissural neurons in layer III of the frontocentral cortex with the DiI tracer revealed no morphological signs of dendritic degeneration in APP48 mice compared to littermate controls. In contrast, the dendritic tree of highly ramified commissural frontocentral neurons was altered in 15-month-old APP23 mice. The density of asymmetric synapses in the frontocentral cortex was reduced in 3- and 15-month-old APP23 but not in 3- and 18-month-old APP48 mice. Frontocentral neurons of 18-month-old APP48 mice showed an increased proportion of altered mitochondria in the soma compared to wild type and APP23 mice. Aß was often seen in the membrane of neuronal mitochondria in APP48 mice at the ultrastructural level. CONCLUSIONS: These results indicate that APP-independent intracellular Aß accumulation in APP48 mice is not associated with dendritic and neuritic degeneration but with mitochondrial alterations whereas APP-derived extra- and intracellular Aß pathology in APP23 mice is linked to dendrite degeneration and synapse loss independent of obvious mitochondrial alterations. Thus, Aß aggregates in APP23 and APP48 mice induce neurodegeneration presumably by different mechanisms and APP-related production of Aß may, thereby, play a role for the degeneration of neurites and synapses.

Early intraneuronal accumulation and increased aggregation of phosphorylated Abeta in a mouse model of Alzheimer's disease.

The progressive accumulation of extracellular amyloid plaques in the brain is a common hallmark of Alzheimer's disease (AD). We recently identified a novel species of Aß phosphorylated at serine residue 8 with increased propensity to form toxic aggregates as compared to non-phosphorylated species. The age-dependent analysis of Aß depositions using novel monoclonal phosphorylation-state specific antibodies revealed that phosphorylated Aß variants accumulate first inside of neurons in a mouse model of AD already at 2 month of age. At higher ages, phosphorylated Aß is also abundantly detected in extracellular plaques. Besides a large overlap in the spatiotemporal deposition of phosphorylated and non-phosphorylated Aß species, fractionized extraction of Aß from brains revealed an increased accumulation of phosphorylated Aß in oligomeric assemblies as compared to non-phosphorylated Aß in vivo. Thus, phosphorylated Aß could represent an important species in the formation and stabilization of neurotoxic aggregates, and might be targeted for AD therapy and diagnosis.