Role of the low-density lipoprotein receptor-related protein in beta-amyloid metabolism and Alzheimer disease

Elevated gonadotropin levels are associated with increased biomarker risk of Alzheimer's disease in midlife women

Introduction

In preclinical studies, menopausal elevations in pituitary gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), trigger Alzheimer's disease (AD) pathology and synaptic loss in female animals. Herein, we took a translational approach to test whether gonadotropin elevations are linked to AD pathophysiology in women.

Methods

We examined 191 women ages 40-65 years, carrying risk factors for late-onset AD, including 45 premenopausal, 67 perimenopausal, and 79 postmenopausal participants with clinical, laboratory, cognitive exams, and volumetric MRI scans. Half of the cohort completed 11C-Pittsburgh Compound B (PiB) amyloid-β (Aβ) PET scans. Associations between serum FSH, LH and biomarkers were examined using voxel-based analysis, overall and stratified by menopause status. Associations with region-of-interest (ROI) hippocampal volume, plasma estradiol levels, APOE-4 status, and cognition were assessed in sensitivity analyses.

Results

FSH levels were positively associated with Aβ load in frontal cortex (multivariable adjusted P≤0.05, corrected for family wise type error, FWE), an effect that was driven by the postmenopausal group (multivariable adjusted PFWE ≤ 0.044). LH levels were also associated with Aβ load in frontal cortex, which did not survive multivariable adjustment. FSH and LH were negatively associated with gray matter volume (GMV) in frontal cortex, overall and in each menopausal group (multivariable adjusted PFWE ≤ 0.040), and FSH was marginally associated with ROI hippocampal volume (multivariable adjusted P = 0.058). Associations were independent of age, clinical confounders, menopause type, hormone therapy status, history of depression, APOE-4 status, and regional effects of estradiol. There were no significant associations with cognitive scores.

Discussion

Increasing serum gonadotropin levels, especially FSH, are associated with higher Aβ load and lower GMV in some AD-vulnerable regions of midlife women at risk for AD. These findings are consistent with preclinical work and provide exploratory hormonal targets for precision medicine strategies for AD risk reduction.

Association between statin compliance and risk of dementia among patients with chronic periodontitis

OBJECTIVES

We investigated the association between statin compliance and the risk of dementia among patients with chronic periodontitis.

METHODS

Chronic periodontitis patients were extracted from the National Health Insurance Service-Health Screening Cohort Database, covering the period from 2002 to 2019. A total of 22,089 subjects were included in the study and divided into three groups based on their compliance with statin administration. The Cox proportional hazard model was utilized to calculate hazard ratios and 95% confidence intervals for analyzing the risk of dementia.

RESULTS

In the restricted cubic spline of the multivariable-adjusted model, the hazard ratio for dementia decreased prominently with a higher medication possession ratio. The hazard ratios and 95% confidence intervals in the multivariable-adjusted model for dementia risk in the middle and high medication possession ratio groups, compared to the low medication possession ratio group, were confirmed as 0.70 (0.57-0.87) and 0.57 (0.45-0.72), respectively. In the subgroup analysis, a significant association between dementia and good statin medication possession ratio was found in both severe periodontitis and mild periodontitis cases.

CONCLUSIONS

Our findings suggest that a group of patients with chronic periodontitis who maintain good statin compliance are associated with a reduced risk of dementia.

Advances in peripheral blood biomarkers of patients with Alzheimer's disease: Moving closer to personalized therapies

Recently, measurable peripheral biomarkers in the plasma of patients with Alzheimer's disease (AD) have gained considerable clinical interest. Several studies have identified one or more blood signatures that may facilitate the development of novel diagnostic and therapeutic strategies. For instance, changes in peripheral amyloid β42 (Aβ42) levels have been largely investigated in patients with AD and correlated with the progression of the pathology, although with controversial results. In addition, tumor necrosis factor α (TNFα) has been identified as an inflammatory biomarker strongly associated with AD, and several studies have consistently suggested the pharmacological targeting of TNFα to reduce systemic inflammation and prevent neurotoxicity in AD. Moreover, alterations in plasma metabolite levels appear to predict the progression of systemic processes relevant to brain functions. In this study, we analyzed the changes in the levels of Aβ42, TNFα, and plasma metabolites in subjects with AD and compared the results with those in healthy elderly (HE) subjects. Differences in plasma metabolites of patients with AD were analyzed with respect to Aβ42, TNFα, and the Mini-Mental State Examination (MMSE) score, searching for plasma signatures that changed simultaneously. In addition, the phosphorylation levels of the Tyr682 residue of the amyloid precursor protein (APP), which we previously proposed as a biomarker of AD, were measured in five HE and five AD patients, in whom the levels of Aβ42, TNFα, and two plasma lipid metabolites increased simultaneously. Overall, this study highlights the potential of combining different plasma signatures to define specific clinical phenotypes of patient subgroups, thus paving the way for the stratification of patients with AD and development of personalized approaches.

Synapse integrity and function: Dependence on protein synthesis and identification of potential failure points

Synaptic integrity and function depend on myriad proteins - labile molecules with finite lifetimes that need to be continually replaced with freshly synthesized copies. Here we describe experiments designed to expose synaptic (and neuronal) properties and functions that are particularly sensitive to disruptions in protein supply, identify proteins lost early upon such disruptions, and uncover potential, yet currently underappreciated failure points. We report here that acute suppressions of protein synthesis are followed within hours by reductions in spontaneous network activity levels, impaired oxidative phosphorylation and mitochondrial function, and, importantly, destabilization and loss of both excitatory and inhibitory postsynaptic specializations. Conversely, gross impairments in presynaptic vesicle recycling occur over longer time scales (days), as does overt cell death. Proteomic analysis identified groups of potentially essential 'early-lost' proteins including regulators of synapse stability, proteins related to bioenergetics, fatty acid and lipid metabolism, and, unexpectedly, numerous proteins involved in Alzheimer's disease pathology and amyloid beta processing. Collectively, these findings point to neuronal excitability, energy supply and synaptic stability as early-occurring failure points under conditions of compromised supply of newly synthesized protein copies.

Hypothyroidism and Diabetes-Related Dementia: Focused on Neuronal Dysfunction, Insulin Resistance, and Dyslipidemia

The incidence of dementia is steadily increasing worldwide. The risk factors for dementia are diverse, and include genetic background, environmental factors, sex differences, and vascular abnormalities. Among the subtypes of dementia, diabetes-related dementia is emerging as a complex type of dementia related to metabolic imbalance, due to the increase in the number of patients with metabolic syndrome and dementia worldwide. Thyroid hormones are considered metabolic regulatory hormones and affect various diseases, such as liver failure, obesity, and dementia. Thyroid dysregulation affects various cellular mechanisms and is linked to multiple disease pathologies. In particular, hypothyroidism is considered a critical cause for various neurological problems-such as metabolic disease, depressive symptoms, and dementia-in the central nervous system. Recent studies have demonstrated the relationship between hypothyroidism and brain insulin resistance and dyslipidemia, leading to diabetes-related dementia. Therefore, we reviewed the relationship between hypothyroidism and diabetes-related dementia, with a focus on major features of diabetes-related dementia such as insulin resistance, neuronal dysfunction, and dyslipidemia.

Circadian control of heparan sulfate levels times phagocytosis of amyloid beta aggregates

Alzheimer's Disease (AD) is a neuroinflammatory disease characterized partly by the inability to clear, and subsequent build-up, of amyloid-beta (Aβ). AD has a bi-directional relationship with circadian disruption (CD) with sleep disturbances starting years before disease onset. However, the molecular mechanism underlying the relationship of CD and AD has not been elucidated. Myeloid-based phagocytosis, a key component in the metabolism of Aβ, is circadianly-regulated, presenting a potential link between CD and AD. In this work, we revealed that the phagocytosis of Aβ42 undergoes a daily circadian oscillation. We found the circadian timing of global heparan sulfate proteoglycan (HSPG) biosynthesis was the molecular timer for the clock-controlled phagocytosis of Aβ and that both HSPG binding and aggregation may play a role in this oscillation. These data highlight that circadian regulation in immune cells may play a role in the intricate relationship between the circadian clock and AD.

Adherence to Statins Use and Risk of Dementia among Patients with Diabetes and Comorbid Hyperlipidemia

The results from previous observational studies and clinical trials about the neuroprotective benefits of statins use for the prevention of dementia are contradictory. It is unclear whether the neuroprotective benefits are experienced in a specific group with a higher risk of dementia, such as patients with concurrent diabetes and hyperlipidemia. We aimed to examine the association between adherence to statins and the risk of dementia among patients with diabetes and comorbid hyperlipidemia. This was a retrospective study with a new user design. We used data from the Taiwan National Health Insurance Research Database to identify patients with diabetes and comorbid hyperlipidemia. The occurrence of dementia was the study outcome. The adherence to statins was the exposure, which was measured by the proportion of days covered (PDC) of statins. The good adherence included patients with ≥80% PDC of statins. Cox proportional hazards regression models were used to evaluate the association between adherence to statins and dementia. Among 18,125 included individuals with diabetes and comorbid hyperlipidemia, 33.5% had good adherence to statins. Compared to poor adherence to statins, good adherence to statins was not significantly associated with a reduced risk of dementia (hazard ratio = 0.94; 95%confidence interval = 0.70–1.24) among patients with diabetes and comorbid hyperlipidemia. Good adherence to statins was not found to be associated with the risk of dementia among patients with diabetes and comorbid hyperlipidemia in Taiwan. Future studies with a more diverse study population are needed to evaluate the neuroprotective effects of statins use on dementia prevention.

Overview the effect of statin therapy on dementia risk, cognitive changes and its pathologic change: a systematic review and meta-analysis

Background

Many studies have reported on the role of statin therapy in dementia, but its efficacy remains controversial. We aimed to search for reliable and meaningful articles to assess the efficacy of statin therapy for dementia risk, cognitive items, and pathologic markers.

Methods

Related literature for this study was published in the period from January 1, 1987 to January 1, 2018. Odds ratio (OR) and 95% confidence interval (95% CI) estimates were pooled in either fixed or random effects models.

Results

A total of 23 relevant studies were included after the application of the search strategy. The pooled results showed that statin therapy would downregulate dementia risk according to an analysis of 1,314,431 dementia patients and 1,836,539 healthy controls (OR: 0.64, 95% CI: 0.50, 0.81). In addition, specific changes in mini-mental state examination (MMSE) score were observed in individuals with dementia with statin therapy (OR: 0.46, 95% CI: 0.17, 0.74). However, the results of this meta-analysis showed that statin therapy did not significantly modify the Alzheimer's Disease Assessment Scale (ADAS-cog) score (OR: -0.26, 95% CI: -1.13, 0.62). No significant association was found between statin therapy and activities of daily living performance (OR: -0.69, 95% CI: -4.12, 2.74). When investigating pathological markers, our results indicated a significant influence of statin therapy on plasma amyloid β₄₀ (Aβ₄₀) (OR: 9.27, 95% CI: 0.71, 17.84), plasma Aβ₄₂ (OR: 2.60, 95% CI: 1.07, 4.13), plasma low-density lipoprotein (LDL) cholesterol (OR: -16.95, 95% CI: -25.54, -8.37), plasma lathosterol (OR: -0.11, 95% CI: -0.14, -0.07), plasma 24s-hydroxycholesterol (OR: -10.41, 95% CI: -15.57, -5.25), and cerebrospinal fluid (CSF) lathosterol (OR: -0.07, 95% CI: -0.12, -0.01).

Conclusions

The available data indicate that statin therapy may reduce dementia risk, altering cognitive items and pathologic markers.

Iron, Copper, and Zinc Concentration in Aβ Plaques in the APP/PS1 Mouse Model of Alzheimer's Disease Correlates with Metal Levels in the Surrounding Neuropil

The metal ions of iron, copper, and zinc have long been associated with the aggregation of β-amyloid (Aβ) plaques in Alzheimer's disease; an interaction that has been suggested to promote increased oxidative stress and neuronal dysfunction. We examined plaque metal load in the hippocampus of APP/PS1 mice using X-ray fluorescence microscopy to assess how the anatomical location of Aβ plaques was influenced by the metal content of surrounding tissue. Immunohistochemical staining of Aβ plaques colocalized with areas of increased X-ray scattering power in unstained tissue sections, allowing direct X-ray based-assessment of plaque metal levels in sections subjected to minimal chemical fixation. We identified and mapped 48 individual plaques in four subregions of the hippocampus from four biological replicates. Iron, Cu, and Zn areal concentrations (ng cm^-2) were increased in plaques compared to the surrounding neuropil. However, this elevation in metal load reflected the local metal makeup of the surrounding neuropil, where different brain regions are enriched for different metal ions. After correcting for tissue density, only Zn levels remained elevated in plaques. This study suggests that the in vivo binding of Zn to plaques is not simply due to increased protein deposition.

The p38 mitogen-activated protein kinase signaling pathway is involved in regulating low-density lipoprotein receptor-related protein 1-mediated β-amyloid protein internalization in mouse brain

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases. Recently, increasing evidence suggests that intracellular β-amyloid protein (Aβ) alone plays a pivotal role in the progression of AD. Therefore, understanding the signaling pathway and proteins that control Aβ internalization may provide new insight for regulating Aβ levels. In the present study, the regulation of Aβ internalization by p38 mitogen-activated protein kinases (MAPK) through low-density lipoprotein receptor-related protein 1 (LRP1) was analyzed in vivo. The data derived from this investigation revealed that Aβ1-42 were internalized by neurons and astrocytes in mouse brain, and were largely deposited in mitochondria and lysosomes, with some also being found in the endoplasmic reticulum. Aβ1-42-LRP1 complex was formed during Aβ1-42 internalization, and the p38 MAPK signaling pathway was activated by Aβ1-42 via LRP1. Aβ1-42 and LRP1 were co- localized in the cells of parietal cortex and hippocampus. Furthermore, the level of LRP1-mRNA and LRP1 protein involved in Aβ1-42 internalization in mouse brain. The results of this investigation demonstrated that Aβ1-42 induced an LRP1-dependent pathway that related to the activation of p38 MAPK resulting in internalization of Aβ1-42. These results provide evidence supporting a key role for the p38 MAPK signaling pathway which is involved in the regulation of Aβ1-42 internalization in the parietal cortex and hippocampus of mouse through LRP1 in vivo.

Gout and the risk of dementia: a nationwide population-based cohort study

Introduction

Uric acid was proposed to have anti-oxidant property and possible neuroprotective effects. We examined the association between gout and dementia with population database.

Methods

The study utilized the claims data from the nationwide representative sample of Taiwan National Health Insurance Research Database (NHIRD). We ascertained patients with gout and dementia covering vascular and non-vascular (including Alzheimer’s) subtypes using International Classification of Diseases Ninth Revision, Clinical Modification (ICD9-CM) codes. A control group matched on sex, age, and index date of gout patients was randomly sampled with a ratio of 1:4 from the same database for comparison.

Results

From 2002 to 2008, 28,769 gout patients who were older than 50 years old were identified, and 114,742 control patients was matched into the study. During follow-up, 7,119 patients developed dementia (1,214 with gout, and 5,905 without gout). After adjusting for age, sex, and relevant comorbidities, a Cox regression analysis showed that gout patients had a lower risk of developing non-vascular dementia (hazard ratio (HR): 0.77; 95% confidence interval (CI): 0.72 - 0.83; p < 0.001) and vascular dementia (HR: 0.76; 95% CI: 0.65 - 0.88; p < 0.001).

Conclusions

Patients with gout have a lower risk of developing dementia. This phenomenon exists for both non-vascular and vascular types of dementia.

Extracellular proteolysis of apolipoprotein E (apoE) by secreted serine neuronal protease

Under normal conditions, brain apolipoprotein E (apoE) is secreted and lipidated by astrocytes, then taken up by neurons via receptor mediated endocytosis. Free apoE is either degraded in intraneuronal lysosomal compartments or released. Here we identified a novel way by which apoE undergoes proteolysis in the extracellular space via a secreted neuronal protease. We show that apoE is cleaved in neuronal conditioned media by a secreted serine protease. This apoE cleavage was inhibited by PMSF and α1-antichymotrypsin, but not neuroserpin-1 or inhibitors of thrombin and cathepsin G, supporting its identity as a chymotrypsin like protease. In addition, apoE incubation with purified chymotrypsin produced a similar pattern of apoE fragments. Analysis of apoE fragments by mass spectrometry showed cleavages occurring at the C-terminal side of apoE tryptophan residues, further supporting our identification of cleavage by chymotrypsin like protease. Hippocampal neurons were more efficient in mediating this apoE cleavage than cortical neurons. Proteolysis of apoE4 generated higher levels of low molecular weight fragments compared to apoE3. Primary glial cultures released an inhibitor of this proteolytic activity. Together, these studies reveal novel mechanism by which apoE can be regulated and therefore could be useful in designing apoE directed AD therapeutic approaches.

Cerebrovascular risk factors in Alzheimer's disease: Brain hemodynamics and pharmacogenomic implications

Recent evidence indicates that different vascular risk factors are present in Alzheimer's disease (AD) and other prevalent dementia types probably contributing to deterioration of cerebrovascular function, thus enhancing neurodegeneration and premature neuronal death due to a reduction in brain perfusion. Brain blood flow shows a reduced velocity and increased pulsatility (PI) and resistance indices (RI) in different types of dementia and in diabetes and hypertension, as well. High levels of diastolic blood pressure correlate with diminished brain blood flow and elevated PI and RI, accompanied by cognitive deterioration. Nitric oxide (NO) levels are found increased in the sera and brain tissue of AD patients. Vascular risk factors (hyperglycemia, LDL-cholesterol, triglycerides, hypertension) and altered brain hemodynamic parameters correlate with APOE genotypes of which APOE-4/4 carriers represent the AD population with the highest cerebrovascular risk. In addition, the genomic profiles of patients with dementia integrating AD-related genes (APOE, PS1, PS2, cFOS) in a mini-tetragenic haplotype significantly differ from controls with an absolute genetic variation of about 50%-60%. Cerebrovascular dysfunction is a factor common to most types of dementia; however, genetic variation among different dementia types might be determinant for the activation of early vascular events inducing or accelerating neurodegeneration. In this regard, cerebrovascular dysfunction should be considered a potential therapeutic target in dementia.

Beneficial effects of novel antagonists of GHRH in different models of Alzheimer's disease

Alzheimer's disease is the most frequent debilitating disorder of the central nervous system. Neuroendocrine mechanisms appear to play an important role in this insidiously developing disease. In the present study, the effects of a recently developed growth hormone-releasing hormone (GHRH) antagonist (MIA-690) were evaluated in vivo observing the behavior of genetically modified "Alzheimer's" 5XFAD mice in a Morris water maze (MWM). The effects of the antagonist were also evaluated in vitro using HCN2 human cortical cell cultures treated with amyloid-β1-42. In vivo, the indices of cognitive performance (latency, cumulative index etc.) were followed up for 6 months. In vitro, the formation of reactive oxygen species, markers of inflammatory and neurohormonal signaling were measured by fluorescent detection, PCR, and ELISA. Accumulation of amyloid-β1-42 rafts and τ filaments in necropsied brain samples was verified with the help of ELISA. In the MWM experiments, MIA-690 decreased escape latency, and, in the brain samples, it inhibited the concentration of amyloid-β1-42 and τ filaments. In cell cultures, the GHRH analog showed anti-oxidative and neuro-protective properties and inhibited the GHRH-growth hormone-insulin like growth factor axis. Our data strongly suggest the merit of further studies with GHRH analogs in models of Alzheimer's disease and in elementary clinical trials.

Apolipoprotein E genotype and LRP1 polymorphisms in patients with different clinical types of metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is a severe, neurodegenerative, metabolic disease which is caused by deficient activity of arylsulfatase A (ARSA). Sulfatides and other substrates of ARSA are stored in central and peripheral nervous systems, and in some other organs. Accumulated sulfatides are especially toxic to oligodendrocytes and Schwann cells leading to progressive demyelination. The kind of apolipoprotein E (apoE) isoform is of essential significance for the modulation of sulfatide quantity in the brain as apoE4 contains more sulfatides than apoE3. Taking into consideration the fact that apoE4 leads to the loss of sulfatides in CSF of Alzheimer's disease patients, we examined if apoE isoforms display any impact on clinical outcome in patients with different forms of MLD in whom sulfatides accumulate. The significant association of age at the onset of MLD symptoms with APOE ε2/ε3/ε4 and LRP1 c.766C>T polymorphisms was shown in multivariate stepwise regression analysis, in which other factors known to affect age at onset of the disease, i.e. clinical type of MLD, family connection of the patient and sex were also analyzed. As expected, the clinical type of MLD explained about 80% of the variance of the dependent variable. The impact of both polymorphisms on age of onset of the disease was considerably lower: 2.0% in the case of APOE polymorphism and 1.0% in the case of LRP1 polymorphism. Thus, the clinical outcome in MLD patients is related principally to the genotype of the ARSA gene, while the polymorphisms in the APOE and LRP1 genes are only slightly modifying factors.

Engulfment adaptor phosphotyrosine-binding-domain-containing 1 (GULP1) is a nucleocytoplasmic shuttling protein and is transactivationally active together with low-density lipoprotein receptor-related protein 1 (LRP1)

APP (amyloid precursor protein) and LRP1 (low-density lipoprotein receptor-related protein 1) have been implicated in the pathogenesis of AD (Alzheimer's disease). They are functionally linked by Fe65, a PTB (phosphotyrosine-binding)-domain-containing adaptor protein that binds to intracellular NPxY-motifs of APP and LRP1, thereby influencing expression levels, cellular trafficking and processing. Additionally, Fe65 has been reported to mediate nuclear signalling in combination with intracellular domains of APP and LRP1. We have previously identified another adaptor protein, GULP1 (engulfment adaptor PTB-domain-containing 1). In the present study we characterize and compare nuclear trafficking and transactivation of GULP1 and Fe65 together with APP and LRP1 and report differential nuclear trafficking of adaptors when APP or LRP1 are co-expressed. The observed effects were additionally supported by a reporter-plasmid-based transactivation assay. The results from the present study indicate that Fe65 might have signalling properties together with APP and LRP1, whereas GULP1 only mediates LRP1 transactivation.

Effect of leuprolide on serum amyloid-β peptide levels and memory in patients with prostate cancer with biochemical recurrence

OBJECTIVE

To investigate whether prostate cancer patients receiving leuprolide demonstrated objective cognitive decline accompanied by a change in plasma levels of amyloid-β.

METHODS

Between November 19, 2003, and July 21, 2008, we prospectively enrolled 50 patients with biochemical recurrence of prostate cancer and measured plasma amyloid-β peptide 40 and amyloid-β peptide 42 levels with sandwich enzyme-linked immunosorbent assay at baseline before the first leuprolide injection and at 2, 4, and 12 months. The Mini-Mental State Examination was used to assess 49 patients at baseline and at subsequent visits, and 24 were also assessed by the California Verbal Learning Test-Short Form.

RESULTS

Patients were a median age of 71 years (range, 59-89 years). Compared with baseline levels, plasma amyloid-β peptide 40 levels were increased at 2 months (P=.04) and 4 months (P=.02). Age was correlated with plasma amyloid-β peptide 40 levels (P=.003) and likely accounted for this relationship. Plasma amyloid-β peptide 42 and performance on cognitive tasks did not differ from baseline, but memory measures improved slightly after baseline, most likely due to a practice effect.

CONCLUSION

Leuprolide therapy was not associated with a decline in cognition or memory function or with elevated plasma amyloid short-term. Larger studies are needed to confirm these findings.

Prenatal lead levels, plasma amyloid β levels, and gene expression in young adulthood

BACKGROUND

Animal studies suggest that early-life lead exposure influences gene expression and production of proteins associated with Alzheimer's disease (AD).

OBJECTIVES

We attempted to assess the relationship between early-life lead exposure and potential biomarkers for AD among young men and women. We also attempted to assess whether early-life lead exposure was associated with changes in expression of AD-related genes.

METHODS

We used sandwich enzyme-linked immunosorbent assays (ELISA) to measure plasma concentrations of amyloid β proteins Aβ40 and Aβ42 among 55 adults who had participated as newborns and young children in a prospective cohort study of the effects of lead exposure on development. We used RNA microarray techniques to analyze gene expression.

RESULTS

Mean plasma Aβ42 concentrations were lower among 13 participants with high umbilical cord blood lead concentrations (≥ 10 μg/dL) than in 42 participants with lower cord blood lead concentrations (p = 0.08). Among 10 participants with high prenatal lead exposure, we found evidence of an inverse relationship between umbilical cord lead concentration and expression of ADAM metallopeptidase domain 9 (ADAM9), reticulon 4 (RTN4), and low-density lipoprotein receptor-related protein associated protein 1 (LRPAP1) genes, whose products are believed to affect Aβ production and deposition. Gene network analysis suggested enrichment in gene sets involved in nerve growth and general cell development.

CONCLUSIONS

Data from our exploratory study suggest that prenatal lead exposure may influence Aβ-related biological pathways that have been implicated in AD onset. Gene network analysis identified further candidates to study the mechanisms of developmental lead neurotoxicity.

Low-density lipoprotein receptor-related protein is decreased in optic neuropathy of Alzheimer disease

BACKGROUND

Alzheimer disease (AD) is associated with optic nerve degeneration, yet the underlying pathophysiology of this disease and the optic nerve disorder remain poorly understood. Low-density lipoprotein receptor-related protein (LRP) is implicated in the pathogenesis of AD by mediating the transport of amyloid-β (Aβ) out of the brain into the systemic circulation. As a key player in the reaction to central nervous system injury, astrocytes associate with LRP in AD. This study investigates the role of LRP and astrocytes in the pathogenesis of AD optic neuropathy.

METHODS

To investigate the role of LRP and astrocytes in the pathogenesis of AD optic neuropathy, we conducted immunohistochemical studies on postmortem optic nerves in AD patients (n = 11) and age-matched controls (n = 10) to examine the presence of LRP. Quantitative analyses using imaging software were used to document the extent of LRP in neural tissues. Axonal integrity was assessed by performing immunohistochemistry on the subjects' optic nerves with an antibody to neurofilament (NF) protein. Double-immunofluorescence labeling was performed to investigate whether LRP colocalized with astrocytes, expressing glial fibrillary acidic protein.

RESULTS

LRP expression was decreased in AD optic nerves compared to that in controls (P < 0.001). LRP immunoreactivity was observed in the microvasculature and perivascularly in close proximity to the astrocytic processes. Colocalization of LRP in the astrocytes of optic nerves was also demonstrated. The presence of optic neuropathy was confirmed in the AD optic nerves by demonstrating greatly reduced immunostaining for NF protein as compared to controls.

CONCLUSIONS

The reduction of LRP in the AD degenerative optic nerves supports the hypothesis that LRP may play a role in the pathophysiology of AD optic neuropathy.

The Basic Biology of BACE1: A Key Therapeutic Target for Alzheimer's Disease

Alzheimer’s disease (AD) is an intractable, neurodegenerative disease that appears to be brought about by both genetic and non-genetic factors. The neuropathology associated with AD is complex, although amyloid plaques composed of the β-amyloid peptide (Aβ) are hallmark neuropathological lesions of AD brain. Indeed, Aβ plays an early and central role in this disease. β-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) is the initiating enzyme in Aβ genesis and BACE1 levels are elevated under a variety of conditions. Given the strong correlation between Aβ and AD, and the elevation of BACE1 in this disease, this enzyme is a prime drug target for inhibiting Aβ production in AD. However, nine years on from the initial identification of BACE1, and despite intense research, a number of key questions regarding BACE1 remain unanswered. Indeed, drug discovery and development for AD continues to be challenging. While current AD therapies temporarily slow cognitive decline, treatments that address the underlying pathologic mechanisms of AD are completely lacking. Here we review the basic biology of BACE1. We pay special attention to recent research that has provided some answers to questions such as those involving the identification of novel BACE1 substrates, the potential causes of BACE1 elevation and the putative function of BACE1 in health and disease. Our increasing understanding of BACE1 biology should aid the development of compounds that interfere with BACE1 expression and activity and may lead to the generation of novel therapeutics for AD.

APP, APOE, complement receptor 1, clusterin and PICALM and their involvement in the herpes simplex life cycle

The major Alzheimer's disease susceptibility genes (APOE, clusterin, complement receptor 1 (CR1) and phosphatidylinositol binding clathrin assembly protein, PICALM) can be implicated directly (APOE, CR1) or indirectly (clusterin and PICALM) in the herpes simplex life cycle. The virus binds to proteoliposomes containing APOE or APOA1 and also to CR1, and both clusterin and PICALM are related to a mannose-6-phosphate receptor used by the virus for cellular entry and intracellular transport. PICALM also binds to a nuclear exportin used by the virus for nuclear egress. Clusterin and complement receptor 1 are both related to the complement pathways and play a general role in pathogen defence. In addition, the amyloid precursor protein APP is involved in herpes viral transport and gamma-secretase cleaves a number of receptors used by the virus for cellular entry. APOE, APOA1 and clusterin, or alpha 2-macroglobulin, insulysin and caspase 3, which also bind to the virus, are involved in beta-amyloid clearance or degradation, as are the viral binding complement components, C3 and CR1. There are multiple ways in which the products of key susceptibility genes might be able to modify the viral life cycle and in turn the virus interacts with key proteins involved in APP and beta-amyloid processing. These interactions support a role for the herpes simplex virus in Alzheimer's disease pathology and suggest that antiviral agents or vaccination might be considered as viable therapeutic strategies in Alzheimer's disease.

Lead-induced accumulation of beta-amyloid in the choroid plexus: role of low density lipoprotein receptor protein-1 and protein kinase C

The choroid plexus (CP), constituting the blood-cerebrospinal fluid barrier, has the capacity to remove beta-amyloid (Abeta) from the cerebrospinal fluid. Our previous work indicates that exposure to lead (Pb) results in Abeta accumulation in the CP by decreasing the expression of low density lipoprotein receptor protein-1 (LRP1), a protein involved in the transport and clearance of Abeta. The current study was designed to explore the relationship between Abeta accumulation, protein kinase C (PKC) activity, and LRP1 status in the CP following Pb exposure. Confocal microscopy revealed that LRP1 was primarily localized in the cytosol of the CP in control rats and migrated distinctly towards the apical surface and the microvilli following acute Pb exposure (27 mg Pb/kg, i.p., 24h). Co-immunostaining revealed a co-localization of both PKC-delta and LRP1 in the cytosol of control rats, with a distinct relocalization of both towards the apical membrane following Pb exposure. Preincubation of the tissues with PKC-delta inhibitor rottlerin (2 microM) prior to Pb exposure in vitro, resulted in abolishing the Pb-induced relocalization of LRP1 to the apical surface. Importantly, a significant elevation in intracellular Abeta levels (p<0.01) was observed in the cytosol of the CP following Pb exposure, which was abolished following preincubation with rottlerin. In addition, rottlerin caused a relocalization of Abeta from the cytosol to the nucleus in both Pb-treated and control CP tissues. Finally, co-immunoprecipitation studies revealed a strong protein-protein interaction between LRP1 and PKC-delta in the CP. These studies suggest that Pb exposure disrupts Abeta homeostasis at the CP, owing partly to a Pb-induced relocalization of LRP1 via PKC-delta.

Linking vascular disorders and Alzheimer's disease: potential involvement of BACE1

The etiology of Alzheimer's disease (AD) remains unknown. However, specific risk factors have been identified, and aging is the strongest AD risk factor. The majority of cardiovascular events occur in older people and a close relationship between vascular disorders and AD exists. Amyloid plaques, composed of the beta amyloid peptide (Abeta), are hallmark lesions in AD and evidence indicates that Abeta plays a central role in AD pathophysiology. The BACE1 enzyme is essential for Abeta generation, and BACE1 levels are elevated in AD brain. The cause(s) of this BACE1 elevation remains undetermined. Here we review the potential contribution of vascular disease to AD pathogenesis. We examine the putative vasoactive properties of Abeta and how the cellular changes associated with vascular disease may elevate BACE1 levels. Despite increasing evidence, the exact role(s) vascular disorders play in AD remains to be determined. However, given that vascular diseases can be addressed by lifestyle and pharmacologic interventions, the potential benefits of these therapies in delaying the clinical appearance and progression of AD may warrant investigation.

Prion protein paralog doppel protein interacts with alpha-2-macroglobulin: a plausible mechanism for doppel-mediated neurodegeneration

Doppel protein (Dpl) is a paralog of the cellular form of the prion protein (PrP^C), together sharing common structural and biochemical properties. Unlike PrP^C, which is abundantly expressed throughout the central nervous system (CNS), Dpl protein expression is not detectable in the CNS. Interestingly, its ectopic expression in the brain elicits neurodegeneration in transgenic mice. Here, by combining native isoelectric focusing plus non-denaturing polyacrylamide gel electrophoresis and mass spectrometry analysis, we identified two Dpl binding partners: rat alpha-1-inhibitor-3 (α₁I₃) and, by sequence homology, alpha-2-macroglobulin (α₂M), two known plasma metalloproteinase inhibitors. Biochemical investigations excluded the direct interaction of PrP^C with either α₁I₃ or α₂M. Nevertheless, enzyme-linked immunosorbent assays and surface plasmon resonance experiments revealed a high affinity binding occurring between PrP^C and Dpl. In light of these findings, we suggest a mechanism for Dpl-induced neurodegeneration in mice expressing Dpl ectopically in the brain, linked to a withdrawal of natural inhibitors of metalloproteinase such as α₂M. Interestingly, α₂M has been proven to be a susceptibility factor in Alzheimer's disease, and as our findings imply, it may also play a relevant role in other neurodegenerative disorders, including prion diseases.

Increased beta-amyloid levels in the choroid plexus following lead exposure and the involvement of low-density lipoprotein receptor protein-1

The choroid plexus, a barrier between the blood and cerebrospinal fluid (CSF), is known to accumulate lead (Pb) and also possibly function to maintain brain's homeostasis of Abeta, an important peptide in the etiology of Alzheimer's disease. This study was designed to investigate if Pb exposure altered Abeta levels at the blood-CSF barrier in the choroid plexus. Rats received ip injection of 27 mg Pb/kg. Twenty-four hours later, a FAM-labeled Abeta (200 pmol) was infused into the lateral ventricle and the plexus tissues were removed to quantify Abeta accumulation. Results revealed a significant increase in intracellular Abeta accumulation in the Pb-exposed animals compared to controls (p<0.001). When choroidal epithelial Z310 cells were treated with 10 microM Pb for 24 h and 48 h, Abeta (2 microM in culture medium) accumulation was significantly increased by 1.5 fold (p<0.05) and 1.8 fold (p<0.05), respectively. To explore the mechanism, we examined the effect of Pb on low-density lipoprotein receptor protein-1 (LRP1), an intracellular Abeta transport protein. Following acute Pb exposure with the aforementioned dose regimen, levels of LRP1 mRNA and proteins in the choroid plexus were decreased by 35% (p<0.05) and 31.8% (p<0.05), respectively, in comparison to those of controls. In Z310 cells exposed to 10 microM Pb for 24 h and 48 h, a 33.1% and 33.4% decrease in the protein expression of LRP1 was observed (p<0.05), respectively. Knocking down LRP1 resulted in even more substantial increases of cellular accumulation of Abeta, from 31% in cells without knockdown to 72% in cells with LRP1 knockdown (p<0.05). Taken together, these results suggest that the acute exposure to Pb results in an increased accumulation of intracellular Abeta in the choroid plexus; the effect appears to be mediated, at least in part, via suppression of LRP1 production following Pb exposure.

What is 'early onset dementia'?

There are two types of dementia with early onset: (i) presenile dementias; and (ii) senile dementias with early onset. Most patients who develop dementia before 65 years of age have Alzheimer's disease (AD). The remainder are likely to have vascular dementia (VaD), frontotemporal dementia, head injury, alcohol intoxication, or metabolic disorder. Presenile dementias, caused by frontotemporal lobar degeneration, progressive supranuclear palsy, and corticobasal degeneration, usually occur in patients of presenile and are rarely seen in patients of senile age. Although the factors responsible for the accelerated onset of the illness are not fully known, genetic abnormalities appear to be important in some types of presenile dementia, such as frontotemporal dementia with parkinsonism linked to chromosome 17. Conversely, senile dementias such as sporadic AD and VaD commonly occur in patients of senile age. These disorders may also occur in patients of presenile age, although less frequently. Alzheimer's disease was originally classified as a 'presenile dementia'. Since the 1980s, 'senile dementia of Alzheimer type' (SDAT) and 'Alzheimer's disease' have been considered to belong to the same pathological entity and both are now known as 'dementia of Alzheimer's type (DAT)' or merely 'Alzheimer's disease'. Rapid progression of cognitive impairment with neuropsychological syndromes and neurological symptoms has been considered a characteristic of early onset AD. However, recently, neurological symptoms such as spastic paraparesis, seizures, and myoclonic convulsions have been reported to occur infrequently in early onset AD, although language problems and visuospatial dysfunctions are common. There are at least three dominant genes that have been identified in cases of familial Alzheimer's disease with early onset, namely the amyloid precursor gene (APP), and the genes encoding presenilin 1 (PSEN1) and presenilin 2 (PSEN2). Therefore, genetic abnormalities are important factors contributing to the earlier onset of the illness. It is also important to investigate the pathophysiological mechanism in relation to genetic abnormalities, environmental factors, physical illnesses, and metabolic disturbances to understand the processes underlying the development of dementia with early onset.

LRP1 and cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA), which causes intracerebral hemorrhage in the elderly population, is a major hallmark of Alzheimer’s disease. In CAA, amyloid-β (Aβ) deposition is mainly detected in the cortex and leptomeningeal arteries along the interstitial fluid drainage pathway. Failure to eliminate Aβ leads to accumulation of Aβ in the perivascular region and CAA. Several clearance routes of Aβ have been described, including elimination along the perivascular interstitial fluid drainage pathway, elimination through the blood–brain barrier and uptake and degradation by glia and neurons. All of these routes express the low-density lipoprotein receptor-related protein (LRP)1, which plays a critical role in Aβ clearance. Consequently, an impairment of Aβ clearance through LRP1 likely contributes to CAA pathogenesis. This review summarizes what is known about LRP1 and CAA as well as providing insights into the possible roles of LRP1 in Aβ clearance.

Mechanism of the metal-mediated endocytosis of the prion protein

The cellular form of the prion protein, PrPc, is critically required for the establishment of prion diseases, such as Creutzfeldt–Jakob disease. Within the N-terminal half of PrPc are four octapeptide repeats that bind Cu2+. Exposure of neuronal cells expressing PrPc to Cu2+ results in the rapid endocytosis of the protein. First, PrPc translocates laterally out of detergent-resistant lipid rafts into detergent-soluble regions of the plasma membrane, then it is internalized through clathrin-coated pits. The extreme N-terminal region of PrPc is critically required for its endocytosis, as is the transmembrane LRP1 (low-density lipoprotein receptor-related protein-1). Incubation of cells with a competitive inhibitor of LRP1 ligands, receptor-associated protein, or down-regulation of LRP1 with siRNA (short interfering RNA) reduces the endocytosis of PrPc. Zn2+ also promotes the endocytosis of PrPc, a phenomenon that is also dependent on the octapeptide repeats and requires LRP1.

Consequence of Abeta immunization on the vasculature of human Alzheimer's disease brain

A major feature of Alzheimer's disease is the accumulation of amyloid-beta peptide (Abeta) in the brain both in the form of plaques in the cerebral cortex and in blood vessel as cerebral amyloid angiopathy (CAA). Experimental models and human clinical trials have shown that accumulation of Abeta plaques can be reversed by immunotherapy. In this study, we hypothesized that Abeta in plaques is solubilized by antibodies generated by immunization and drains via the perivascular pathway, detectable as an increase in cerebrovascular Abeta. We have performed a follow up study of Alzheimer's disease patients immunized against Abeta42. Neuropathological examination was performed on nine patients who died between four months and five years after their first immunization. Immunostaining for Abeta40 and Abeta42 was quantified and compared with that in unimmunized Alzheimer's disease controls (n = 11). Overall, compared with these controls, the group of immunized patients had approximately 14 times as many blood vessels containing Abeta42 in the cerebral cortex (P<0.001) and seven times more in the leptomeninges (P = 0.013); among the affected blood vessels in the immunized cases, most of them had full thickness and full circumference involvement of the vessel wall in the cortex (P = 0.001), and in the leptomeninges (P = 0.015). There was also a significantly higher level of cerebrovascular Abeta40 in the immunized cases than in the unimmunized cases (cortex: P = 0.009 and leptomeninges: P = 0.002). In addition, the immunized patients showed a higher density of cortical microhaemorrhages and microvascular lesions than the unimmunized controls, though none had major CAA-related intracerebral haemorrhages. The changes in cerebral vascular Abeta load did not appear to substantially influence the structural proteins of the blood vessels. Unlike most of the immunized patients, two of the longest survivors, four to five years after first immunization, had virtually complete absence of both plaques and CAA, raising the possibility that, given time, Abeta is eventually cleared from the cerebral vasculature. The findings are consistent with the hypothesis that Abeta immunization results in solubilization of plaque Abeta42 which, at least in part, exits the brain via the perivascular pathway, causing a transient increase in the severity of CAA. The extent to which these vascular alterations following Abeta immunization in Alzheimer's disease are reflected in changes in cognitive function remains to be determined.

[Dementia and diabetes mellitus]

Dementia and Diabetes mellitus (DM) are major health problems nowadays. DM leads to a significant cognitive decline and increases the risk of dementia, mostly Alzheimer's Disease (AD) and vascular dementia (VaD) by 50-100% and 100-150%, respectively. Amyloid beta (Abeta), the main pathogenic factor in AD development, is eliminated by advanced glycation end products (AGEs) and degraded by insulin degrading enzyme (IDE) for which it competes with insulin. Insulin stimulates secretion of Abeta and promotes brain inflammation. DM I and II cause slowing down of mental speed, lowering of mental flexibility and DM II learning and memory disturbances. DM acts both directly by hyperglycaemia and hyperinsulinaemia and by the blood vessel changes. Hyperglycaemia changes synapse plasticity and leads to cognitive decline. AGEs disrupt the neuron function and bonding to Abeta increases its aggregability. Glycation of tau protein promotes production of neurofibrillary tangles (NFT), the main intracellular pathogenic factor in AD. AGE 2 in DM causes pathological angiogenesis and apoptosis of neurons. AGE receptor (RAGE) is also the specific Abeta receptor with which it produces reactive oxygen species that has, as a result, disruption of mitochondrial function and reduction of neuronal energy resources. Insulinoresistance is linked with the dysexecutive syndrome, and hyperinsulinaemia increases the risk of AD especially by enhancing phosphorylation oftau protein and formation of NFT. Application of insulin showed improvement of memory, behaviour and affect in AD patients. Good glycoregulation emerged as an important factor in dementia prevention, and a better insight in relations of DM and brain function will lead to new potential dementia therapies.

Interactions between the products of the Herpes simplex genome and Alzheimer's disease susceptibility genes: relevance to pathological-signalling cascades

The products of the Herpes simplex (HSV-1) genome interact with many Alzheimer's disease susceptibility genes or proteins. These in turn affect those of the virus. For example, HSV-1 binds to heparan sulphate proteoglycans (HSPG2), or alpha-2-macroglobulin (A2M), and enters cells via nectin receptors, which are cleaved by gamma-secretase (APH1B, PSEN1, PSEN2, PEN2, NCSTN). The virus also binds to blood-borne lipoproteins and apolipoprotein E (APOE) is able to modify its infectivity. Viral uptake is cholesterol- and lipid raft-dependent (DHCR24, HMGCR, FDPS, RAFTLIN, SREBF1). The virus is transported to the nucleus via the dynein and kinesin (KNS2) motors associated with the microtubule network (MAPT). Amyloid precursor protein (APP) plays a role in this transport. Nuclear export is mediated via disruption of the nuclear lamina and binding to LMNA. Herpes simplex activates kinases (CDC2 and casein kinase 2) whose substrates include APOE, APP, MAPT, PSEN2, and SREBF1. A viral protein is also able to delete mitochondrial DNA, a situation prevalent in Alzheimer's disease. The virus binds to the host transcription factors transcription factor CP2 (TFCP2) and POU2F1 that control many other genes associated with Alzheimer's disease. Viral latency is controlled by IL6 and IL1B and at different stages of its life cycle the virus can either promote or attenuate apoptosis via Fas and tumor necrosis factor pathways (FAS, TNF, DAPK1, PARP1). Viral evasion strategies include inhibition of the antigen processor TAP2, the production of an Fc immunoglobulin receptor mimic (FCER1G) and inhibition of the viral-activated kinase EIF2AK2. These and other host/viral interactions, targeted to certain Alzheimer's disease susceptibility genes, support the idea that some form of synergy between the pathogen and genetic factors may play a role in the pathology of late-onset Alzheimer's disease.

The Alzheimer's disease beta-secretase enzyme, BACE1

The pathogenesis of Alzheimer's disease is highly complex. While several pathologies characterize this disease, amyloid plaques, composed of the β-amyloid peptide are hallmark neuropathological lesions in Alzheimer's disease brain. Indeed, a wealth of evidence suggests that β-amyloid is central to the pathophysiology of AD and is likely to play an early role in this intractable neurodegenerative disorder. The BACE1 enzyme is essential for the generation of β-amyloid. BACE1 knockout mice do not produce β-amyloid and are free from Alzheimer's associated pathologies including neuronal loss and certain memory deficits. The fact that BACE1 initiates the formation of β-amyloid, and the observation that BACE1 levels are elevated in this disease provide direct and compelling reasons to develop therapies directed at BACE1 inhibition thus reducing β-amyloid and its associated toxicities. However, new data indicates that complete abolishment of BACE1 may be associated with specific behavioral and physiological alterations. Recently a number of non-APP BACE1 substrates have been identified. It is plausible that failure to process certain BACE1 substrates may underlie some of the reported abnormalities in the BACE1-deficient mice. Here we review BACE1 biology, covering aspects ranging from the initial identification and characterization of this enzyme to recent data detailing the apparent dysregulation of BACE1 in Alzheimer's disease. We pay special attention to the putative function of BACE1 during healthy conditions and discuss in detail the relationship that exists between key risk factors for AD, such as vascular disease (and downstream cellular consequences), and the pathogenic alterations in BACE1 that are observed in the diseased state.

Statins and dementia

The incidence and prevalence of dementia are increasing. Dementia is a major cause of disability. Alzheimer's disease (AD) is the most common type of dementia. There are no good prevention or treatment options. Experimental animal and laboratory studies have suggested that cholesterol metabolism in the brain is important in the causal pathway for dementia, possibly by modifying amyloid metabolism. A few studies have showed a possible relationship between mid-life blood cholesterol levels and risk of dementia, including AD. Case-control studies report that patients with AD were less likely to use lipid-lowering drugs, especially statins. Longitudinal epidemiology studies have not demonstrated a decreased risk of AD among statin users versus nonusers. Two clinical trials of statin therapy to reduce cardiovascular disease have not shown any reduction in risk of cognitive decline or dementia. The results of two secondary prevention trials will be reported shortly. In spite of negative studies, the possibility remains that statin therapy may reduce risk of dementia and AD. Primary prevention trials are difficult and expensive and will likely not be done in the United States.

Prevention and treatment of dementia or Alzheimer's disease by statins: a meta-analysis

BACKGROUND/AIM

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) are thought to reduce the amount of Abeta peptides by reducing cholesterol from blood and/or cerebrospinal fluid. We performed this meta-analysis to evaluate the preventive and treatment effects of statins on dementia and Alzheimer disease onset.

METHODS

Relevant studies were systematically identified, and data were abstracted according to predefined criteria. We used a fixed-effects model and a random-effects model to compute pooled relative risks and to assess statistical heterogeneity.

RESULTS

The pooled crude odds ratios in statin users as compared with nonusers were 0.67 (95% confidence interval CI 0.54-0.82) in the dementia group and 0.81 (95% CI 0.64-1.02) in the Alzheimer group. The pooled adjusted relative risks calculated by random-effects model were 0.77 (95% CI 0.45-1.30) in the dementia group and 0.81 (95% CI 0.56-1.16) in the Alzheimer group.

CONCLUSIONS

Statin use did not show a beneficial effect on the risk of dementia or Alzheimer's disease. Further study and independent confirmation of the association between statin use and dementia and Alzheimer's disease in larger clinical trials are warranted.

The low-density lipoprotein receptor-related protein 1 (LRP1) mediates the endocytosis of the cellular prion protein

PrP(C) (cellular prion protein) is located at the surface of neuronal cells in detergent-insoluble lipid rafts, yet is internalized by clathrin-dependent endocytosis. As PrP(C) is glycosyl-phosphatidylinositol-anchored, it requires a transmembrane adaptor protein to connect it to the clathrin endocytosis machinery. Using receptor-associated protein and small interfering RNA against particular LDL (low-density lipoprotein) family members, in combination with immunofluorescence microscopy and surface biotinylation assays, we show that the transmembrane LRP1 (LDL receptor-related protein 1) is required for the Cu(2+)-mediated endocytosis of PrP(C) in neuronal cells. We show also that another LRP1 ligand that can cause neurodegenerative disease, the Alzheimer's amyloid precursor protein, does not modulate the endocytosis of PrP(C).

Dementia epidemiology research: it is time to modify the focus of research

The incidence and prevalence of dementia are increasing. There is an urgent need to develop a preventive strategy. The identification of modifiable risk factors must therefore be a high priority. Newer imaging techniques provide an opportunity to identify subclinical manifestations of "dementias" that can be limited to the risk factors and subsequent clinical disease. The contribution of vascular disease to dementia and Alzheimer's disease (AD) should be a high priority as it offers a potential preventive strategy. Study designs need to be modified, including a greater emphasis on geographic variations in AD and dementia based on imaging studies, longitudinal studies of successful aging without cardiovascular disease (CVD) or AD, gene-environment interactions, and studies of unique populations that may be at lower risk because of specific lifestyles. Primary prevention trials for vascular disease should include a dementia component. Most, if not all, studies should include newer imaging studies.

Pathogenesis of Alzheimer disease

<zakljucak> Alchajmerova bolest javlja se kod 50-60% svih dementnih osoba i predstavlja znacajan zdravstveni i socijalni problem. Upoznavanje patogeneze AB je neophodno u nalazenju terapija koje bi ublazile i modifikovale bolest. Najvise dokaza ima za hipotezu o amiloidnoj kaskadi. Osnovna patohistoloska promena u mozgu obolelih su nakupine amiloida beta (A beta), senilni ili amiloidni pakovi. Ukupni efekat je gubitak sinapsi i neurona. Amiloid se nakuplja i u zidovima krvnih sudova remeteci mozdanu cirkulaciju. Usled navedenih promena nastaje poremecaj neurotransmisije, narocito acetilholina i glutamata i smetnje pamcenja i drugih neuroloskih funkcija. Patogenetski zasnovana terapija se usmerava na aktivaciju alfa sekretaze, inhibiciji beta i gama sekretaza, pojacano uklanjanje A beta, suzbijanje oksidativnog stresa i inflamacije, imunoterapiju upravljenu protiv Abeta i druge mehanizme. U upotrebi su inhibitori ACh-esteraze i antagonista glutamatnih receptora. U prevenciji su dokazani efekti ogranicenog unosa kalorija, Mediteranske dijete i redovne umerene fizicke aktivnosti.

Functional role of the low-density lipoprotein receptor-related protein in Alzheimer's disease

Alzheimer's disease (AD) is the most common age-related neurodegenerative disorder, characterized by neuronal loss, neurofibrillary tangle formation and the extracellular deposition of amyloid-beta (Abeta) plaques. The amyloid precursor protein (APP) and the enzymes responsible for Abeta generation seem to be the base elements triggering the destructive processes. Initially, the low-density lipoprotein receptor-related protein (LRP) was genetically linked to AD and later it emerged to impact on many fundamental events related to this disease. LRP is not only involved in Abeta clearance but is also the major receptor of several AD-associated ligands, e.g. apolipoprotein E and alpha2-macroglobulin. APP processing is mediated by LRP on many levels. Enhanced APP internalization through LRP decreases cell surface APP levels and thereby reduces APP shedding. As a consequence of increased APP internalization LRP enhances Abeta secretion. These effects could be attributed to the cytoplasmic tails of LRP and APP. The receptors bind via their NPXY motifs to the two PID domains of FE65 and form a tripartite complex. However, it appears that the second NPVY motif of LRP is the one responsible for the observed influence over APP metabolism. A more in-depth knowledge of the mechanisms regulating APP cleavage may offer additional targets for therapeutic intervention.

Lipoprotein receptors in Alzheimer's disease

Lipoprotein receptors have important roles in pathological processes that lead to Alzheimer's disease (AD). Previously, they were believed to act mainly by modulating the neuronal metabolism of cholesterol and apolipoprotein E, major risk factors for spontaneous AD. However, recent findings point towards an unexpected new function for lipoprotein receptors in regulation of intracellular transport and processing of the amyloid precursor protein (APP) to give amyloid-beta peptide, the principal component of senile plaques. Here, we will discuss how lipoprotein receptors might modulate distinct steps in neuronal trafficking of APP, and how an intricate balance between opposing receptor activities might be a crucial determinant of APP processing, and of onset and progression of neurodegeneration.

Effects of apoE on neuronal signaling and APP processing in rodent brain

We previously reported that primary neuronal cells treated with apolipoprotein E (apoE) or an apoE-derived peptide (EP) increased ERK activation and decreased JNK activation via apoE receptors. Here, we examined if the effects observed in vitro were observed in vivo. Similar to our observations in primary neurons, in vivo we found that injections of 2muM EP into the rat hippocampus increased the levels of ERK activation and decreased JNK activation. However, the time course of these effects was slower in vivo. Immunohistochemical analysis of the tissue showed prominently increased ERK phosphorylation and decreased JNK phosphorylation in neuronal cells throughout the hippocampus, particularly in the CA3 regions. To determine if apoE was endocytosed by neurons, we conjugated fluorescent microspheres with the EP and injected them into the rat hippocampus. After 7 days, the microspheres were present in neurons. We also examined the in vivo effects of apoE on ApoEr2 and APP processing. EP and full-length apoE3 and apoE4 increased C-terminal fragments of ApoEr2 and APP after a single injection, multiple injections, and chronic infusion paradigms. ApoE3 produced higher levels of ApoEr2 and APP C-terminal fragments than apoE4. These results demonstrate that apoE alters ApoEr2 and APP processing in vivo. The increase in ERK activation is consistent with a role for apoE in a neuronal response to stress, and the decrease in JNK activation suggests that apoE may have anti-apoptotic effects, over several days.

α2-Macroglobulin, lipoprotein receptor-related protein and lipoprotein receptor-associated protein and the genetic risk for developing Alzheimer's disease

Alpha2-macroglobulin (alpha2M) as well as its receptor, the low-density lipoprotein receptor-related (LRP) and the receptor-associated protein (RAP) are involved in the clearance of cerebral A beta. Current evidence suggests that polymorphisms in the genes of alpha2M, LRP and RAP may have functional effects on the proteins. Two independent association samples of 271 AD patients and 280 representative controls were investigated whether the risk for developing AD is altered in carriers of polymorphisms in the alpha2M-gene (Va1000Ile), in the LRP-gene (Ala216Val) and in the RAP-gene (Val311Met). Genotypes were determined by standard PCR and restriction fragment length polymorphism. The results were adjusted for age, gender and apolipoprotein E-epsilon4 (APOE) polymorphism. Inheritance of alpha2M conferred a small increased risk for sporadic AD with an estimated Mantel-Haenszel odds ratio of 1.47. There was no age- or gender-dependent increase in alpha2M Val1000Ile allele frequencies in AD patients compared to controls. There was no significant difference in the allele frequencies among control and AD subjects for the LRP and RAP polymorphisms. We found no evidence of an interaction between the alpha2M and RAP or LRP with regard to conferred risk. Our data suggest that the alpha2M Val1000Ile polymorphism is weakly associated with AD. Although LRP as well as RAP seem to play an essential role in the metabolism of alpha2M and APOE, there is no increase in the genetic risk for AD in patients carrying the investigated polymorphisms.

Energy inhibition elevates beta-secretase levels and activity and is potentially amyloidogenic in APP transgenic mice: possible early events in Alzheimer's disease pathogenesis

Beta-secretase [beta-site amyloid precursor protein-cleaving enzyme 1 (BACE1)] is the key rate-limiting enzyme for the production of the beta-amyloid (Abeta) peptide involved in the pathogenesis of Alzheimer's disease (AD). BACE1 levels and activity are increased in AD brain and are likely to drive Abeta overproduction, but the cause of BACE1 elevation in AD is unknown. Interestingly, cerebral glucose metabolism and blood flow are both reduced in preclinical AD, suggesting that impaired energy production may be an early pathologic event in AD. To determine whether reduced energy metabolism would cause BACE1 elevation, we used pharmacological agents (insulin, 2-deoxyglucose, 3-nitropropionic acid, and kainic acid) to induce acute energy inhibition in C57/B6 wild-type and amyloid precursor protein (APP) transgenic (Tg2576) mice. Four hours after treatment, we observed that reduced energy production caused a approximately 150% increase of cerebral BACE1 levels compared with control. Although this was a modest increase, the effect was long-lasting, because levels of the BACE1 enzyme remained elevated for at least 7 d after a single dose of energy inhibitor. In Tg2576 mice, levels of the BACE1-cleaved APP ectodomain APPsbeta were also elevated and paralleled the BACE1 increase in both relative amount and duration. Importantly, cerebral Abeta40 levels in Tg2576 were increased to approximately 200% of control at 7 d after injection, demonstrating that energy inhibition was potentially amyloidogenic. These results support the hypothesis that impaired energy production in the brain may drive AD pathogenesis by elevating BACE1 levels and activity, which, in turn, lead to Abeta overproduction. This process may represent one of the earliest pathogenic events in AD.

Statin therapy in the treatment of Alzheimer disease: what is the rationale?

Alzheimer disease (AD) is a chronic neurodegenerative disorder that is manifested by cognitive decline, neuropsychiatric symptoms, and diffuse structural abnormalities in the brain. Its prevalence is predicted to rise 4-fold in the next 50 years. AD is characterized pathologically by deposition of extracellular beta-amyloid and accumulation of neurofibrillary tangles. Neuronal death and specific neurotransmitter deficits also are part of the pathologic picture. Strategies to delay symptom progression have focused on addressing the neurotransmitter deficits. Strategies to delay the onset or biologic progression of AD largely have targeted the plaques formed by the deposition of beta-amyloid. AD and cardiovascular disease share common risk factors, notably hypercholesterolemia, and occur together more often than expected by chance. Therapy with the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) is the first-line treatment option for hypercholesterolemia, and observational studies have suggested that the risk of AD is reduced in patients who receive statin therapy in midlife. This reduction in risk of AD observed with statin therapy may be due to statins reducing beta-amyloid formation and deposition or to their known anti-inflammatory effects. Two randomized double-blind statin trials in patients with AD to assess the potential for statins to slow disease progression are currently under way. If successful, statin AD primary prevention trials may be developed.

Fluorescence resonance energy transfer analysis of apolipoprotein E C-terminal domain and amyloid β peptide (1-42) interaction

The potential neurotoxicity of soluble forms of amyloid beta peptide (Abeta) as a key factor in early pathogenesis of Alzheimer's disease is being recognized. In addition, there is growing evidence of the essential role of apolipoprotein E (apoE) in amyloid formation, although molecular details of apoE/Abeta interaction are poorly understood. We employed apoE C-terminal (CT) domain comprising residues 201-299 to identify binding location of Abeta(1-42) by fluorescence resonance energy transfer (FRET) and quenching analyses. Native tryptophan (Trp) residues in the apoE CT domain served as FRET donor, whereas N-(iodoacetyl)-N'-(5-sulfo-1-naphthyl)ethylenediamine (AEDANS) covalently attached to a unique cysteine residue substituted at position 4 of Abeta(1-42) (AEDANS-F4C-Abeta(1-42)) served as FRET acceptor. Fluorescence analysis verified that the oligomerization behavior of AEDANS-F4C-Abeta(1-42) was not abrogated by covalent attachment of AEDANS and that apoE CT domain/AEDANS-F4C-Abeta(1-42) association results in formation of a soluble complex. A large decrease in Trp fluorescence emission was noted in mixtures containing apoE CT domain and AEDANS-F4C-Abeta(1-42), accompanied by appearance of sensitized fluorescence emission of AEDANS as a result of intermolecular FRET. An average distance of separation of 22.6 Angstroms between donors and acceptor was calculated. Fluorescence quenching by potassium iodide (KI) did not reveal significant differences in apoE CT domain Trp microenvironment in the absence or the presence of Abeta(1-42). A twofold increase in quenching constant was noted for KI quenching of AEDANS fluorescence emission in the presence of apoE CT domain, indicative of alterations in Abeta conformation upon interaction with apoE CT domain. We propose intermolecular FRET analysis as a discriminating approach to examine apoE/Abeta interaction, a potentially critical factor in early events involved in amyloid formation.