Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive cognitive decline and neuropathological changes, including the deposition of amyloid ␤ (A␤) in senile plaques. The mechanisms causing the disease and A␤ accumulation are not well understood, but important genetic associations with apolipoprotein E genotype and involvement of lipoprotein receptors have become apparent. LR11 (also known as SorLA), a member of the low-density lipoprotein receptor family, has been identified previously as an altered transcript in microarray analyses of samples from human AD cases. Here, we show neuronal expression of the lipoprotein receptor LR11 in control brain in regions vulnerable to AD neuropathology and marked reduction of LR11 expression in these regions in AD brains before cell death. Overexpression of LR11 drastically reduces levels of extracellular A␤ and also lowers levels of total cellular amyloid precursor protein (APP). LR11 colocalizes with APP and regulates its trafficking in endocytic compartments, which are important intracellular sites for APP processing and A␤ generation. Endogenous LR11 localizes to neuronal multivesicular bodies in both rat and human brain. The robust correlation between reduced LR11 expression and AD neuropathology and its potent effects on extracellular A␤ levels suggest that this neuronal lipoprotein receptor could play an important role in AD pathogenesis.

Apolipoprotein (apo) E4 is the major genetic risk factor for late-onset Alzheimer disease (AD). ApoE4 assumes a pathological conformation through an intramolecular interaction mediated by Arg-61 in the amino-terminal domain and Glu-255 in the carboxyl-terminal domain, referred to as apoE4 domain interaction. Because AD is associated with mitochondrial dysfunction, we examined the effect of apoE4 domain interaction on mitochondrial respiratory function. Steady-state amounts of mitochondrial respiratory complexes were examined in neurons cultured from brain cortices of neuron-specific enolase promoter-driven apoE3 (NSE-apoE3) or apoE4 (NSEapoE4) transgenic mice. All subunits of mitochondrial respiratory complexes assessed were significantly lower in NSEapoE4 neurons compared with NSE-apoE3 neurons. However, no significant differences in levels of mitochondrial complexes were detected between astrocytes expressing different apoE isoforms driven by the glial fibrillary acidic protein promoter, leading to our conclusion that the effect of apoE4 is neuron specific. In neuroblastoma Neuro-2A (N2A) cells, apoE4 expression reduced the levels of mitochondrial respiratory complexes I, IV, and V. Complex IV enzymatic activity was also decreased, lowering mitochondrial respiratory capacity. Mutant apoE4 (apoE4-Thr-61) lacking domain interaction did not induce mitochondrial dysfunction in N2A cells, indicating that the effect is specific to apoE4-expressing cells and dependent on domain interaction. Consistent with this finding, treatment of apoE4-expressing N2A cells with a small molecule that disrupts apoE4 domain interaction restored mitochondrial respiratory complex IV levels. These results suggest that pharmacological intervention with small molecules that disrupt apoE4 domain interaction is a potential therapeutic approach for apoE4-carrying AD subjects. Apolipoprotein (apo)2 E4 is the major genetic risk factor for late-onset Alzheimer disease (AD) (1-6). The protein sequence of apoE4 (299 amino acids) differs from the other two common isoforms (apoE2, apoE3) at residues 112 or 158; apoE3 has a cysteine at residue 112 and an arginine at residue 158, whereas apoE4 has arginines at both positions and apoE2 has cysteines (3, 4). These differences profoundly affect the tertiary protein structure (3-5). ApoE4 displays an intramolecular interaction between its amino-terminal and carboxylterminal domains (7,8), referred to as apoE4 domain interaction. The domain interaction is mediated by Arg-112 in apoE4, which induces a salt bridge between Arg-61 in the amino-terminal domain and Glu-255 in the carboxyl-terminal domain (7,8). This interaction is decreased in apoE2 and apoE3 due to the presence of Cys-112 (8). Substitution of a threonine for Arg-61 in apoE4 disrupts the domain interaction, converting apoE4 to an apoE3-like conformation (7-9).It is postulated that domain interaction is primarily responsible for the pathogenic effects of apoE4 in AD (3-5). Because AD is known to be associated with mitochondrial dysfunction (10 -...

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.

Alzheimer's disease (AD) is the most prevalent form of dementia, resulting in progressive neuronal death and debilitating damage to brain loci that mediate memory and higher cognitive function. While pathogenic genetic mutations have been implicated in ϳ2% of AD cases, the proximal events that underlie the common, sporadic form of the disease are incompletely understood. Converging lines of evidence from human neuropathology, basic biology, and genetics have implicated loss of the multifunctional receptor LR11 (also known as SORLA and SORL1) in AD pathogenesis. Cell-based studies suggest that LR11 reduces the formation of ␤-amyloid (A␤), the molecule believed to be a primary toxic species in AD. Recently, mutant mice deficient in LR11 were shown to upregulate murine A␤ in mouse brain. In the current study, LR11-deficient mice were crossed with transgenic mice expressing autosomal-dominant human AD genes, presenilin-1 (PS1⌬E9) and amyloid precursor protein (APPswe). Here, we show that LR11 deficiency in this AD mouse model significantly increases A␤ levels and exacerbates early amyloid pathology in brain, causing a forward shift in disease onset that is LR11 gene dose-dependent. Loss of LR11 increases the processing of the APP holo-molecule into ␣-, ␤-, and ␥-secretase derived metabolites. We propose that LR11 regulates APP processing and A␤ accumulation in vivo and is of proximal importance to the cascade of pathological amyloidosis. The results of the current study support the hypothesis that control of LR11 expression may exert critical effects on Alzheimer's disease susceptibility in humans.

Changes in synaptic activity alter quantal size, but the relative roles of presynaptic and postsynaptic cells in these changes are only beginning to be understood. We examined the mechanism underlying increased quantal size after block of synaptic activity at the mammalian neuromuscular junction in vivo. We found that changes in neither acetylcholinesterase activity nor acetylcholine receptor density could account for the increase. By elimination, it appears likely that the site of increased quantal size after chronic block of activity is presynaptic and involves increased release of acetylcholine. We used mice with muscle hyperexcitability caused by mutation of the ClC-1 muscle chloride channel to examine the role of postsynaptic activity in controlling quantal size. Surprisingly, quantal size was increased in ClC mice before block of synaptic activity. We examined the mechanism underlying increased quantal size in ClC mice and found that it also appeared to be located presynaptically. When presynaptic activity was completely blocked in both control and ClC mice, quantal size was large in both groups despite the higher level of postsynaptic activity in ClC mice. This suggests that postsynaptic activity does not regulate quantal size at the neuromuscular junction. We propose that presynaptic activity modulates quantal size at the neuromuscular junction by modulating the amount of acetylcholine released from vesicles.