Lack of beta-amyloid production in M19 cells deficient in site 2 processing of the sterol regulatory element binding proteins

LR11/SorLA expression is reduced in sporadic Alzheimer disease but not in familial Alzheimer disease

LR11 is an ApoE receptor that is enriched in the brain. We have shown that LR11 is markedly downregulated in patients with sporadic Alzheimer disease (AD). This finding led us to explore whether reduced LR11 expression reflects a primary mechanism of disease or merely a secondary consequence of other AD-associated changes. Therefore, LR11 expression was assessed in a transgenic mouse model of AD and familial AD (FAD) brains. Immunohistochemistry and immunoblotting of LR11 in PS1/APP transgenic and wild-type mice indicated that LR11 levels are not affected by genotype or accumulation of amyloid pathology. LR11 expression was also evaluated based on immunoblotting and LR11 immunostaining intensity in human frontal cortex in controls, sporadic AD, and FAD, including cases with presenilin-1 (PS1) and presenilin-2 (PS2) mutations. Although LR11 was reduced in sporadic AD, there was no difference in protein level or staining intensity between control and FAD cases. The finding that LR11 expression is unaffected in both a mouse model of AD and autosomal-dominant forms of AD suggests that LR11 is not regulated by amyloid accumulation or other AD neuropathologic changes. We hypothesize that LR11 loss may be specific to sporadic AD and influence amyloid pathology through mechanisms independent of substrate-enzyme interactions regulated by FAD mutations.

A model for studying Alzheimer's Abeta42-induced toxicity in Drosophila melanogaster

Alzheimer's disease is a neurological disorder resulting in the degeneration and death of brain neurons controlling memory, cognition and behavior. Although overproduction of Abeta peptides is widely considered a causative event in the disease, the mechanisms by which Abeta peptides cause neurodegeneration and the processes of Abeta clearance and degradation remain unclear. To address these issues, we have expressed the Abeta peptides in Drosophila melanogaster. We show that overexpression of Abeta42 peptides in the nervous system results in phenotypes associated with neuronal degeneration in a dose- and age-dependent manner. We further show that a mutation in a Drosophila neprilysin gene suppresses the Abeta42 phenotypes by lowering the levels of the Abeta42 peptide, supporting the role of neprilysin in the catabolism of Abeta peptides in vivo. We propose that our Drosophila model is suitable for the study and elucidation of Abeta metabolism and toxicity at the genetic level.

Cholesterol in Alzheimer's disease and tauopathy

Cholesterol has been implicated in the pathogenesis of amyloid plaques in Alzheimer's disease (AD) and in the formation of neurofibrillary pathology in Niemann-Pick disease. Several epidemiology studies have implicated high cholesterol as a risk factor for AD and have shown that the use of cholesterol-reducing agents (statins) can be protective against the disease. We and others have shown that cholesterol levels modulate the processing of the amyloid precursor protein (APP) both in vivo and in vitro, affecting the accumulation of A-beta (Abeta) peptides that may directly impact the risk of AD. Mutations in the Niemann-Pick C gene (NPC) result in deficient cholesterol transport/storage. Clinically, Niemann-Pick disease causes a severe childhood lipidosis, with neurodegeneration characterized by the presence of AD-type neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau. Studies of mouse models of NPC show that defects in cellular cholesterol trafficking are associated with enhanced generation of Abeta and the hyperphosphorylation of tau, further implicating the cholesterol homeostasis pathway as a risk factor for amyloidosis.

The functions of the amyloid precursor protein gene

The amyloid precursor protein (APP) gene and its protein products have multiple functions in the central nervous system and fulfil criteria as neuractive peptides: presence, release and identity of action. There is increased understanding of the role of secretases (proteases) in the metabolism of APP and the production of its peptide fragments. The APP gene and its products have physiological roles in synaptic action, development of the brain, and in the response to stress and injury. These functions reveal the strategic importance of APP in the workings of the brain and point to its evolutionary significance.