RESUMO
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.
RESUMO
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.