A familial case of Alzheimer's disease without tau pathology may be linked with chromosome 3 markers

Prickle promotes the formation and maintenance of glutamatergic synapses by stabilizing the intercellular planar cell polarity complex

Whether there exists a common signaling mechanism that assembles all glutamatergic synapses is unknown. We show here that knocking out Prickle1 and Prickle2 reduced the formation of the PSD-95–positive glutamatergic synapses in the hippocampus and medial prefrontal cortex in postnatal development by 70–80%. Prickle1 and Prickle2 double knockout in adulthood lead to the disassembly of 70 to 80% of the postsynaptic-density(PSD)-95–positive glutamatergic synapses. PSD-95–positive glutamatergic synapses in the hippocampus of Prickle2E8Q/E8Q mice were reduced by 50% at postnatal day 14. Prickle2 promotes synapse formation by antagonizing Vangl2 and stabilizing the intercellular complex of the planar cell polarity (PCP) components, whereas Prickle2 E8Q fails to do so. Coculture experiments show that the asymmetric PCP complexes can determine the presynaptic and postsynaptic polarity. In summary, the PCP components regulate the assembly and maintenance of a large number of glutamatergic synapses and specify the direction of synaptic transmission.

Genome-wide linkage analyses of non-Hispanic white families identify novel loci for familial late-onset Alzheimer's disease

INTRODUCTION

Few high penetrance variants that explain risk in late-onset Alzheimer's disease (LOAD) families have been found.

METHODS

We performed genome-wide linkage and identity-by-descent (IBD) analyses on 41 non-Hispanic white families exhibiting likely dominant inheritance of LOAD, and having no mutations at known familial Alzheimer's disease (AD) loci, and a low burden of APOE ε4 alleles.

RESULTS

Two-point parametric linkage analysis identified 14 significantly linked regions, including three novel linkage regions for LOAD (5q32, 11q12.2-11q14.1, and 14q13.3), one of which replicates a genome-wide association LOAD locus, the MS4A6A-MS4A4E gene cluster at 11q12.2. Five of the 14 regions (3q25.31, 4q34.1, 8q22.3, 11q12.2-14.1, and 19q13.41) are supported by strong multipoint results (logarithm of odds [LOD*] ≥1.5). Nonparametric multipoint analyses produced an additional significant locus at 14q32.2 (LOD* = 4.18). The 1-LOD confidence interval for this region contains one gene, C14orf177, and the microRNA Mir_320, whereas IBD analyses implicates an additional gene BCL11B, a regulator of brain-derived neurotrophic signaling, a pathway associated with pathogenesis of several neurodegenerative diseases.

DISCUSSION

Examination of these regions after whole-genome sequencing may identify highly penetrant variants for familial LOAD.

Neprilysin Confers Genetic Susceptibility to Alzheimer's Disease in Han Chinese

Alzheimer's disease (AD) is a progressive neurodegenerative disease, with increasing incidence all over the world. Amyloid-β (Aβ) was considered to be the original cause to AD, and many reported pathogenic or risk genes for AD were located in the Aβ generation and degradation pathways. Neprilysin (NEP), insulin-degrading enzyme (IDE), and matrix metalloprotease-9 (MMP-9) are the most important Aβ-degrading proteases. Accumulating genetic evidence suggested that single nucleotide polymorphisms (SNPs) of these genes confer susceptibility to AD in Caucasian populations. In this study, we screened eight SNPs within these three Aβ-degrading protease genes in 1475 individuals of two independent Han Chinese case-control cohorts. SNP rs1816558 of NEP was found to be significantly associated with AD after adjustment for ε4 allele of the apolipoprotein E gene (APOEε4) and the Bonferroni correction. The remaining variants were not associated with risk of AD in Han Chinese sample set. Further data mining revealed that messenger RNA (mRNA) level of NEP substantially increased during the development of AD and was positively correlated with APP expression. The combined results indicated that NEP confers genetic susceptibility to AD in Han Chinese populations.

A genomewide screen for late-onset Alzheimer disease in a genetically isolated Dutch population

Alzheimer disease (AD) is the most common cause of dementia. We conducted a genome screen of 103 patients with late-onset AD who were ascertained as part of the Genetic Research in Isolated Populations (GRIP) program that is conducted in a recently isolated population from the southwestern area of The Netherlands. All patients and their 170 closely related relatives were genotyped using 402 microsatellite markers. Extensive genealogy information was collected, which resulted in an extremely large and complex pedigree of 4,645 members. The pedigree was split into 35 subpedigrees, to reduce the computational burden of linkage analysis. Simulations aiming to evaluate the effect of pedigree splitting on false-positive probabilities showed that a LOD score of 3.64 corresponds to 5% genomewide type I error. Multipoint analysis revealed four significant and one suggestive linkage peaks. The strongest evidence of linkage was found for chromosome 1q21 (heterogeneity LOD [HLOD]=5.20 at marker D1S498). Approximately 30 cM upstream of this locus, we found another peak at 1q25 (HLOD=4.0 at marker D1S218). These two loci are in a previously established linkage region. We also confirmed the AD locus at 10q22-24 (HLOD=4.15 at marker D10S185). There was significant evidence of linkage of AD to chromosome 3q22-24 (HLOD=4.44 at marker D3S1569). For chromosome 11q24-25, there was suggestive evidence of linkage (HLOD=3.29 at marker D11S1320). We next tested for association between cognitive function and 4,173 single-nucleotide polymorphisms in the linked regions in an independent sample consisting of 197 individuals from the GRIP region. After adjusting for multiple testing, we were able to detect significant associations for cognitive function in four of five AD-linked regions, including the new region on chromosome 3q22-24 and regions 1q25, 10q22-24, and 11q25. With use of cognitive function as an endophenotype of AD, our study indicates the that the RGSL2, RALGPS2, and C1orf49 genes are the potential disease-causing genes at 1q25. Our analysis of chromosome 10q22-24 points to the HTR7, MPHOSPH1, and CYP2C cluster. This is the first genomewide screen that showed significant linkage to chromosome 3q23 markers. For this region, our analysis identified the NMNAT3 and CLSTN2 genes. Our findings confirm linkage to chromosome 11q25. We were unable to confirm SORL1; instead, our analysis points to the OPCML and HNT genes.

Retinoid receptors, transporters, and metabolizers as therapeutic targets in late onset Alzheimer disease

Vitamin A (retinoid) is required in the adult brain to enable cognition, learning, and memory. While brain levels of retinoid diminish over the course of normal ageing, retinoid deficit is greater in late onset Alzheimer disease (LOAD) brains than in normal-aged controls. This paper reviews recent evidence supporting these statements and further suggests that genes necessary for the synthesis, transport and function of retinoid to and within the ageing brain are appropriate targets for treatment of LOAD. These genes tend to be clustered with genes that have been proposed as candidates in LOAD, are found at chromosomal regions linked to LOAD, and suggest the possibility of an overall coordinated regulation. This phenomenon is termed Chromeron and is analogous to the operon mechanism observed in prokaryotes. Suggested treatment targets are the retinoic-acid inactivating enzymes (CYP26)s, the retinol binding and transport proteins, retinol-binding protein (RBP)4 and transthyretin (TTR), and the retinoid receptors. TTR as a LOAD target is the subject of active investigation. The retinoid receptors and the retinoid-inactivating enzymes have previously been proposed as targets. This is the first report to suggest that RBP4 is an amenable treatment target in LOAD. RBP4 is elevated in type-2 diabetes and obesity, conditions associated with increased risk for LOAD. Fenretinide, a novel synthetic retinoic acid (RA) analog lowers RBP4 in glucose intolerant obese mice. The feasibility of using fenretinide either as an adjunct to present LOAD therapies, or on its own as an early prevention strategy should be determined.

Evidence for defective retinoid transport and function in late onset Alzheimer's disease

The hypothesis of this article is that late onset Alzheimer's disease (AD) is influenced by the availability in brain of retinoic acid (RA), the final product of the vitamin A (retinoid) metabolic cascade. Genetic, metabolic, and environmental/dietary evidence is cited supporting this hypothesis. Significant genetic linkages to AD are demonstrated for markers close to four of the six RA receptors, RA receptor G at 12q13, retinoid X receptor B at 6p21.3, retinoid X receptor G at 1q21, and RA receptor A at 17q21. Three of the four retinol-binding proteins at 3q23 and 10q23 and the RA-degrading cytochrome P450 enzymes at 10q23 and 2p13 map to AD linkages. Synthesis of the evidence supports retinoid hypofunction and impaired transport as contributing factors. These findings suggest testable experiments to determine whether increasing the availability of retinoid in brain, possibly through pharmacologic targeting of the RA receptors and the cytochrome P450 RA-inactivating enzymes, can prevent or decrease amyloid plaque formation.

Alzheimer's disease beta-amyloid peptide is increased in mice deficient in endothelin-converting enzyme

The abnormal accumulation of beta-amyloid (Abeta) in the brain is an early and invariant feature in Alzheimer's disease (AD) and is believed to play a pivotal role in the etiology and pathogenesis of the disease. As such, a major focus of AD research has been the elucidation of the mechanisms responsible for the generation of Abeta. As with any peptide, however, the degree of Abeta accumulation is dependent not only on its production but also on its removal. In cell-based and in vitro models we have previously characterized endothelin-converting enzyme-1 (ECE-1) as an Abeta-degrading enzyme that appears to act intracellularly, thus limiting the amount of Abeta available for secretion. To determine the physiological significance of this activity, we analyzed Abeta levels in the brains of mice deficient for ECE-1 and a closely related enzyme, ECE-2. Significant increases in the levels of both Abeta40 and Abeta42 were found in the brains of these animals when compared with age-matched littermate controls. The increase in Abeta levels in the ECE-deficient mice provides the first direct evidence for a physiological role for both ECE-1 and ECE-2 in limiting Abeta accumulation in the brain and also provides further insight into the factors involved in Abeta clearance in vivo.

A new locus on chromosome 19 linked with late-onset Alzheimer's disease

Alzheimer's disease (AD) is a complex neurodegenerative disorder, characterized by cognitive decline and distinctive neuropathology. APOE 4 and APOCI A on chromosome 19 are risk factors for late-onset disease. Using large extended families with multiple siblings affected, we have identified several microsatellite markers which are also linked with late- onset Alzheimer's disease. These microsatellites are distal from the apolipoprotein cluster on chromosome 19. It is likely that multiple genes will be involved with late-onset disease, either as risk factors or as causative agents.

Metabolic regulation of brain Abeta by neprilysin

Amyloid beta peptide (Abeta), the pathogenic agent of Alzheimer's disease (AD), is a physiological metabolite in the brain. We examined the role of neprilysin, a candidate Abeta-degrading peptidase, in the metabolism using neprilysin gene-disrupted mice. Neprilysin deficiency resulted in defects both in the degradation of exogenously administered Abeta and in the metabolic suppression of the endogenous Abeta levels in a gene dose-dependent manner. The regional levels of Abeta in the neprilysin-deficient mouse brain were in the distinct order of hippocampus, cortex, thalamus/striatum, and cerebellum, where hippocampus has the highest level and cerebellum the lowest, correlating with the vulnerability to Abeta deposition in brains of humans with AD. Our observations suggest that even partial down-regulation of neprilysin activity, which could be caused by aging, can contribute to AD development by promoting Abeta accumulation.

Frontotemporal dementia with ubiquitinated inclusions: A case study of the regional distribution of hippocampal pathology

In motor neuron disease (MND) cases associated with dementia, neurons often contain ubiquitin-positive, taunegative cytoplasmic inclusions that are numerous in the granule cell neurons of the hippocampal complex. Dot or threadlike ubiquitinated neurites are also observed in the surrounding neuropil and in other frontotemporal regions. Cases of frontotemporal dementia (FTD) with identical appearing ubiquitinated deposits have been described in FTD cases lacking signs of MND. The underlying pathobiology of these cases remains obscure. We describe a case from a familial FTD kindred and use immunohistochemistry to evaluate the hippocampal ubiquitin-positive cytoplasmic granule cell inclusions in relationship to the threads and dots that surround them. Ubiquitin-positive threads were more numerous in the overlying molecular layer of the dentate gyrus (DG) compared with the underlying polymorphic layer, suggesting that threads are formed primarily in the dendrites of the affected granule cells. In contrast, dot-like inclusions were uniformly distributed. Using antibodies to synapticterminal specific proteins, we observed loss of perforant pathway synapses in the outer molecular layer of the DG. The numbers of thread-and dot-like inclusions were no greater in the region of synaptic loss than in the layer that lacked detectable synaptic loss. Similarly, ubiquitinated aggregates were more numerous in rostral sections, and they tended to cluster, whereas synapse loss was uniform. These findings expand upon previous data by suggesting that formation of these ubiquitinated aggregates relate to an inherent susceptibility in the granule cell neuron, rather than solely to a deafferentation effect. This study contributes to our understanding of what might be a common pathological process underlying FTD and MND cases with ubiquitinated inclusions.