Recent rodent models for Alzheimer’s disease: clinical implications and basic research

Alzheimer’s disease (AD) is the most common origin of dementia in the elderly. Although the cause of AD remains unknown, several factors have been identified that appear to play a critical role in the development of this debilitating disorder. In particular, amyloid precursor protein (APP), tau hyperphosphorylation, and the secretase enzymes, have become the focal point of recent research. Over the last two decades, several transgenic and non-transgenic animal models have been developed to elucidate the mechanistic aspects of AD and to validate potential therapeutic targets. Transgenic rodent models over-expressing human β-amyloid precursor protein (β-APP) and mutant forms of tau have become precious tools to study and understand the pathogenesis of AD at the molecular, cellular and behavioural levels, and to test new therapeutic agents. Nevertheless, none of the transgenic models of AD recapitulate fully all of the pathological features of the disease. Octodon degu, a South American rodent has been recently found to spontaneously develop neuropathological signs of AD in old age. This review aims to address the limitations and clinical relevance of transgenic rodent models in AD, and to highlight the potential for O. degu as a natural model for the study of AD neuropathology.     

On the organization of the retino-tecto-thalamo-telencephalic pathways in a Chilean rodent; theOctodon degus

After performing eye enucleations or restricted lesions in the superior colliculus or the pulvinar nucleus, the degeneration patterns provoked by these procedures were analyzed by means of the Nissl and the Fink-Heimer methods in 30 specimens ofOctodon degus. The pulvinar or lateroposterior nucleus can be subdivided into 3 regions (rostrolateral, rostromedial and caudal), on the basis of cytoarchitecture, tectofugal afferent and efferent connections to the cerebral cortex. In addition, this nucleus projects to the ipsilateral tail of the caudate nucleus and to the nucleus lateralis dorsalis of the thalamus, which has been shown to project over the cingulate cortex in this animal. These findings support the possibility that the pulvinar may have an important role in visuo-limbic interactions, by way of its connections with the nucleus lateralis dorsalis. Another highly interesting finding from the phylogenetic point of view is that the organization of the pulvinar in theOctodon degus is remarkably similar to that organization of the retino-tecto-thalamo-cortical pathways described in the grey squirrel and in the tree shrew is strikingly similar to those found in theOctodon degus, a semi-fossorial South American rodent that has evolved in isolation from the two former species for about 40 million years, makes it impossible to explain the organization of this pathway by advocating convergent evolution, due to environmental pressures determined by arboreal life, as postulated by Kaas et al.³⁹.     

Octodon degus. A useful animal model for social-affective neuroscience research: basic description of separation distress, social attachments and play

A challenge for social-affective neuroscience programs is to identify simple and yet valid animal models for studying the expression of basic social emotions and their role during different developmental windows, from infancy to adulthood. For example, although laboratory rats are useful for studying juvenile social interactions, they are not ideal for studying infant attachment bonds. Here, we evaluate current understanding of the social behavior of Octodon degus, a diurnal precocial rodent, to elucidate the value of this species as a model for social-affective neuroscience research. After a synopsis of species-specific characteristics and brain susceptibility to changes of social environment, our behavioral findings on degu social proclivities are summarized. We then discuss why this pre-clinical model provides a valuable addition to the commonly available animal models for the study of human psychopathology.     

Visuo-limbic interactions: Evidence for a pathway from the pulvinar to the cingulate cortex

Synaptic-terminal degeneration was analyzed in 18 specimens of Octodon degus after stereotaxic lesions in the pulvinar nucleus. Aside from the cortical targets of the pulvinar (Kuljis et al. 1979), a conspicuous projection towards the nucleus lateralis dorsalis of the thalamus (LD) was observed. The LD is known to receive fibers from the fornix (Valenstein and Nauta 1959), and to project heavily over the cingulate cortex (Locke et al. 1964; Ajmone Marsan 1965; Graybiel 1974); we have confirmed the latter projection in 3 operated specimens of Octodon degus. The possibility is discussed, in the light of these findings, that the pulvino-LD pathway may be important for the purposes of visuo-limbic interactions.     

The GABAergic system in the retina of neonate and adult Octodon degus,studied by immunohistochemistry and electroretinography

In the vertebrate retina, gamma‐aminobutyric acid (GABA) mediates inhibitory processes that shape the visual response and is also thought to have neurotrophic functions during retinal development. To investigate the role of GABAergic signaling at the beginning of visual experience, we used immunohistochemistry to compare the distribution of GABA, the two isoforms of glutamic acid decarboxylase GAD65/67, and the GABA receptor types A, B, and C, in neonate versus adult Octodon degus, a native South American rodent with diurnal‐crepuscular activity and a high cone‐to‐rod ratio. In parallel, we used electroretinography to evaluate retinal functionality and to test the contribution of fast GABAergic transmission to light responses at both developmental stages. Neonate O. degus opened their eyes on postnatal day (P)0 and displayed an adult‐like retinal morphology at this time. GABA, its biosynthetic sources, and receptors had a similar cellular distribution in neonates and adults, but labeling of the outer plexiform layer and of certain amacrine and ganglion cells was more conspicuous at P0. In neonates, retinal sensitivity was 10 times lower than in adults, responses to ultraviolet light could not be detected, and oscillatory potentials were reduced or absent. Blockade of GABA_A/C receptors by bicuculline and TPMPA had no noticeable effect in neonates, while it significantly altered the electroretinogram response in adults. Conclusion: In spite of modest differences regarding retinal morphology and GABAergic expression, overall light response properties and GABAergic signaling are undeveloped in neonate O. degus compared to adults, suggesting that full retinal functionality requires a period of neural refinement under visual experience. J. Comp. Neurol. 514:459–472, 2009. © 2009 Wiley‐Liss, Inc.     

Increased dopaminergic cells and protein aggregates in the olfactory bulb of patients with neurodegenerative disorders

Olfactory dysfunction is a frequent and early feature of patients with neurodegenerative disorders such as Alzheimer’s disease (AD) and Parkinson’s disease (PD) and is very uncommon in patients with frontotemporal dementia (FTD). Mechanisms underlying this clinical manifestation are poorly understood but the premature deposition of protein aggregates in the olfactory bulb (OB) of these patients might impair its synaptic organization, thus accounting for the smell deficits. Tau, β-amyloid and alpha-synuclein deposits were studied in 41 human OBs with histological diagnosis of AD (n = 24), PD (n = 6), FTD (n = 11) and compared with the OB of 15 control subjects. Tau pathology was present in the OB of all patients, irrespective of the histological diagnosis, while β-amyloid and alpha-synuclein protein deposit were frequently observed in AD and PD, respectively. Using stereological techniques we found an increased number of dopaminergic periglomerular neurons in the OB of AD, PD and FTD patients when compared with age-matched controls. Moreover, volumetric measurements of OBs showed a significant decrease only in AD patients, while the OB volume was similar to control in PD or FTD cases. The increased dopaminergic tone created in the OBs of these patients could reflect a compensatory mechanism created by the early degeneration of other neurotransmitter systems and might contribute to the olfactory dysfunction exhibited by patients with neurodegenerative disorders.     

Association between polymorphism in the promoter region of <Emphasis Type="Italic">Interleukin 6</Emphasis> (-174 G/C) and risk of Alzheimer’s disease: a meta-analysis

Studies of the relationship between Alzheimer’s disease (AD) and polymorphism in the promoter region of Interleukin 6 (IL-6) -174 G/C have reported inconsistent results. To assess the association between IL-6 -174 G/C promoter polymorphism and AD risk, a meta-analysis containing 3,101 AD cases and 3,860 controls from 18 case–control studies was performed. There were 16 studies involving Europeans and 2 studies involving non-Europeans. The combined results showed significant differences in recessive model [CC versus GC + GG, odds ratio (OR) = 0.70, 95% confidence interval (CI) = 0.54–0.90] and heterozygote comparison (CC versus GC, OR = 0.76, 95% CI = 0.60–0.96) on the basis of all studies. On subgroup analysis by ethnicity, similarly significant differences in recessive model (CC versus GC + GG) were found in both Europeans and non-Europeans, but significant difference in heterozygote comparison (CC versus GC) was found only in non-Europeans. In conclusion, there were statistically significant differences in genotype distribution of IL-6 -174 G/C between AD cases and controls in recessive model (CC versus GC + GG). Genotype CC of IL-6 -174 G/C could decrease the risk of AD. Further studies with large sample size, especially in subgroup analysis, should be done.     

Association of rs2062323 in the TREM1 gene with Alzheimer's disease and cerebrospinal fluid-soluble TREM2

Introduction and aims

Genetic variations play a significant role in determining an individual's AD susceptibility. Research on the connection between AD and TREM1 gene polymorphisms (SNPs) remained lacking. We sought to examine the associations between TREM1 SNPs and AD.

Methods

Based on the 1000 Genomes Project data, linkage disequilibrium (LD) analyses were utilized to screen for candidate SNPs in the TREM1 gene. AD cases (1081) and healthy control subjects (870) were collected and genotyped, and the associations between candidate SNPs and AD risk were analyzed. We explored the associations between target SNP and AD biomarkers. Moreover, 842 individuals from ADNI were selected to verify these results. Linear mixed models were used to estimate associations between the target SNP and longitudinal cognitive changes.

Results

The rs2062323 was identified to be associated with AD risk in the Han population, and rs2062323T carriers had a lower AD risk (co-dominant model: OR, 0.67, 95% CI, 0.51–0.88, p = 0.0037; additive model: OR, 0.82, 95% CI, 0.72–0.94, p = 0.0032). Cerebrospinal fluid (CSF) sTREM2 levels were significantly increased in middle-aged rs2062323T carriers (additive model: β = 0.18, p = 0.0348). We also found significantly elevated levels of CSF sTREM2 in the ADNI. The rate of cognitive decline slowed down in rs2062323T carriers.

Conclusions

This study is the first to identify significant associations between TREM1 rs2062323 and AD risk. The rs2062323T may be involved in AD by regulating the expression of TREM1, TREML1, TREM2, and sTREM2. The TREM family is expected to be a potential therapeutic target for AD.     

A high incidence of apolipoprotein E ε4 allele in middle-aged non-demented subjects with cerebral amyloid β protein deposits

We examined the apolipoprotein E (ApoE) genotypes of 19 middle-aged non-demented subjects with cerebral amyloid β protein (Aβ) deposits, and compared the results with those of 16 patients with sporadic Alzheimer’s disease (AD) and those of 34 age-matched controls. The frequency of the ApoE ɛ4 allele was higher (P = 0.0256) in these 19 subjects (0.211) than in controls (0.059), and was close to that in AD patients (0.281). This result suggests that middle-aged non-demented subjects with cerebral Aβ deposits are at high risk of developing AD, and that the diffuse Aβ deposits in these cases represent an early stage of AD pathology. We speculate that in the majority of late-onset sporadic AD patients, cerebral Aβ deposition commences when these patients are in their forties or fifties, and that the pathological process progresses gradually, taking 20 to 30 years for clinical manifestation of dementia. Received: 16 March 1998 / Revised, accepted: 29 June 1998     

Increased Cerebrospinal Fluid F<Subscript>2</Subscript>-Isoprostanes are Associated with Aging and Latent Alzheimer’s Disease as Identified by Biomarkers

Alzheimer’s disease (AD) is a common age-related chronic illness with latent, prodrome, and fully symptomatic dementia stages. Increased free radical injury to regions of brain is one feature of prodrome and dementia stages of AD; however, it also is associated with advancing age. This raises the possibility that age-related free radical injury to brain might be caused in part or in full by latent AD. We quantified free radical injury in the central nervous system with cerebrospinal fluid (CSF) F₂-isoprostanes (IsoPs) in 421 clinically normal individuals and observed a significant increase over the adult human lifespan (P < 0.001). Using CSF amyloid (A) β₄₂ and tau, we defined normality using results from 28 clinically normal individuals <50 years old, and then stratified 74 clinically normal subjects ≥60 years into those with CSF that had normal CSF Aβ₄₂ and tau (n = 37); abnormal CSF Aβ₄₂ and tau, the biomarker signature of AD (n = 24); decreased Aβ₄₂ only (n = 4); or increased tau only (n = 9). Increased CSF F₂-IsoPs were present in clinically normal subjects with the biomarker signature of AD (P < 0.05) and those subjects with increased CSF tau (P < 0.001). Finally, we analyzed the relationship between age and CSF F₂-IsoPs for those clinically normal adults with normal CSF (n = 37) and those with abnormal CSF Aβ₄₂ and/or tau (n = 37); only those with normal CSF demonstrated a significant increase with age (P < 0.01). These results show that CSF F₂-IsoPs increased across the human lifespan and that this age-related increase in free radical injury to brain persisted after culling those with laboratory evidence of latent AD.     

Ganglionar nervous cells and telocytes in the pancreas of Octodon degus: Extra and intrapancreatic ganglionar cells and telocytes in the degus

This study shows for the first time the presence of intra and extrapancreatic ganglionar neurons and telocytes in Octodon degus such as those described in human and guinea pig pancreas. Pancreatic ganglionar neurons were identified by their histological characteristics as well as their positive immunostaining with mouse anti-human neuron specific enolase (NSE) antibody. Somatostatin secreting delta cells (D cells) in the islets of Langerhans were identified by positive immunostaining with rabbit antihuman polyclonal somatostatin antibody. Electron microscopy evidenced the presence of some unmyelinated axons in the interlobular spaces or septa, usually located adjacent to blood vessels and the exocrine epithelial ducts. The presence of telocytes with at least 2 telopodes was observed in the interlobular space, frequently in close spatial relationship with blood vessels and nerve endings. Telocytes were often observed in the vicinity or even in close proximity with both secretory acini and exocrine epithelial ducts and regulatory nerves and blood vessel apparatuses. A possible framework has been put forward within which such structures might contribute to elicit physiological responses in the pancreas. Further studies of synaptic interactions within and between pancreatic neuron cells are needed to help clarify the morphological results reported here. A broad overview of the field of neurogastroenterology with focus on the pancreas of O. degus related to the enteric nervous system (ENS) is provided in order to help design future studies on the connections of specific neurons forming pancreatic pathways, their neurotransmission processes and how disruption of these pathways may contribute to pancreatic disease.     

Removal of the olfactory bulbs delays photic reentrainment of circadian activity rhythms and modifies the reproductive axis in male Octodon degus

The diurnal rodent, Octodon degus, exhibits robust sex differences in several circadian measures, including circadian period (τ) and reentrainment rates to photic and nonphotic (social) zeitgebers. The neural substrates underlying such physiological differences remain unknown. In female degus, olfactory bulbectomies (BX) inhibit socially-facilitated reentrainment, but do not alter photic reentrainment, entrained measures, or τ in constant darkness (DD). This experiment investigated the effects of BX in male degus on (i) photic reentrainment rates of circadian rhythms following a 6-h phase advance of the light–dark (LD) cycle; (ii) photic entrainment; (iii) τ of free-running activity rhythms in DD; and (iv) body weight, paired testis weight, and the reproductive hormones, testosterone, androstenedione and follicle stimulating hormone (FSH). BX significantly delayed photic reentrainment rates. They did not, however, modify τ, the phase of activity onset or offset, amplitude or duration (α) of the activity rhythm, mean daily locomotor activity levels, or body weight. FSH, testosterone and androstenedione were unaffected by BX, whereas paired testis weights were significantly greater in BX degus compared with shams. Thus, the olfactory bulbs influence photic reentrainment of circadian rhythms and modestly affect the reproductive axis in male degus. Our results suggest that the olfactory bulbs may be a neural source of observed sex differences in photic reentrainment in degus, and highlight interspecies variation in the olfactory bulbs' effects on entrained and free-running circadian rhythms and on reproduction.     

Association analysis of CβS 844ins68 and MTHFD1 G1958A polymorphisms with Alzheimer’s disease in Chinese

Folate deficiency and elevated plasma homocysteine play important roles in pathogenesis of Alzheimer’s disease (AD). The aim of this study was to test the association of folate metabolism-related genes, cystathionine beta-synthase gene (CβS) and 5, 10-methylenetetrahydrofolate dehydrogenase gene (MTHFD1), with sporadic AD. The CβS 844ins68 polymorphism was determined by PCR and the MTHFD1 G1958A single nucleotide polymorphism (rs2236225) by PCR-RFLP. No significant difference of allele and genotype contributions of the CβS polymorphism between AD cases and controls was detected, before and after stratification by APOE ε4-carrying status, age/age at onset and genders. No significant difference of allele and genotype contributions of the MTHFD1 polymorphism between AD cases and controls was detected in total samples. When stratified by age/at onset age, we found that A allele and AA genotype frequencies in cases were higher than in controls and the differences were close to significant [A vs. G, P = 0.032, Odds ratio (OR) 1.642, 95% CI 1.040–2.591; AA + GA vs. GG, P = 0.068, OR 1.665, 95% CI 0.961–2.885; AA vs. GG, P = 0.059, OR 3.458, 95% CI 0.894–13.369] in <65 years groups, which suggested that the MTHFD1 G1958A A allele might be a weak risk factor for early onset AD although it needs further confirmation.     

Oxidative stress damage and oxidative stress responses in the choroid plexus in Alzheimer’s disease

Choroid plexus homogenates from 27 cases with Alzheimer disease-related pathology (AD), stages I/0 (n = 5), III–IV/0-B (n = 15) and V–VI/B-C (n = 7) and 3 age-matched controls (no clinical symptoms, no neuropathological lesions) were processed for gel electrophoresis and western blotting for oxidation markers carboxymethyl-lysine (CML) and N-carboxyethyl-lysine (CEL). Increased CEL and CML expression was seen in AD cases stages IVB, and V–VI/B-C when compared to controls and cases with AD-related pathology classified as I/0 and III/0. Variable stress damage was seen in stage III/B. Although lower stages of AD did not show β-amyloid deposition in the choroid plexus, the amount of β-amyloid was very variable at stages V/VI as revealed by western blotting, suggesting that other factors in addition to local fibrillar β-amyloid were associated with oxidative damage in the choroid plexus. Two-dimensional gel electrophoresis and western blotting to CEL and CML in combination with mass spectrometry disclosed increased intensity of variable spots in AD cases leading to the identification of tyrosine 3/tryptophan 5-monooxygenase activation protein, zeta polypeptide, tropomyosin 3 isoform, and apolipoprotein A-II (ApoA-II) as targets of increased oxidative damage in AD. Oxidation of these proteins may result in impaired protein interactions, protein folding and protein kinase activity; abnormal function of endothelial and vascular smooth muscle cells; and impaired HDL-cholesterol metabolism in the choroid plexus in advanced stages of AD.     

Alternation between short‐ and long photoperiod reveals hypothalamic gene regulation linked to seasonal body weight changes in Djungarian hamsters (Phodopus sungorus)

Djungarian hamsters are able to reduce their body weight by more than 30% in anticipation of the winter season. This particular adaptation to extreme environmental conditions is primarily driven by a natural reduction in day length and conserved under laboratory conditions. We used this animal model to investigate hypothalamic gene expression linked to body weight regulation behind this physiological phenomenon. After an initial collective short photoperiod (SP) adaptation for 14 weeks from a preceding long photoperiod (LP), hamsters were re‐exposed to LP for either 6 or 14 weeks, followed by a second re‐exposure to SP for 8 weeks. Our data showed that re‐exposure to LP led to an increase in body weight. In the hypothalamus Dio2, Vimentin, Crbp1 and Grp50 expression increased, whereas expression of Dio3, Mct8 and Srif decreased. The changes in body weight and gene expression were reversible in most hamsters after a further re‐exposure to SP following 6 or 14 weeks in LP. Interestingly, after 14 weeks in LP, body weight loss was pronounced in six hamsters re‐exposed to SP, but five hamsters did not respond. In nonresponding hamsters, a different gene expression pattern was manifested, with the exception of Dio2, which was reduced not only in SP re‐exposed hamsters, but also in hamsters maintained in LP. Taken together, these data suggest that body weight regulation appears to be tightly linked to a co‐ordinated regulation of several genes in the hypothalamus, including those involved in thyroid hormone metabolism.     

No Association of <Emphasis Type="Italic">LOXL1</Emphasis> Gene Polymorphisms with Alzheimer’s Disease

Aggregation of amyloid-beta is one of the major characteristics in brains of patients with Alzheimer’s disease (AD). Although several mechanisms behind the formation of such aggregates have been suggested the regulatory factors are still unknown. The present study aimed at investigating the association of lysyl oxidase-like 1 (LOXL1) polymorphisms with AD diagnosis and cerebrospinal fluid biomarkers (CSF) for the disease. Proteins of the lysyl oxidase (LOX) family are involved in cross-linking extracellular matrix proteins to insoluble fibers and have been associated with neurodegenerative diseases including AD. Genetic polymorphisms in LOXL1 (rs1048661, rs3825942, and rs2165241) have been linked to exfoliation syndrome and exfoliation glaucoma, conditions that have shown association with AD. The polymorphisms were genotyped by Taqman allelic discrimination in a study sample including AD patients (n = 318) and controls (n = 575). In a subgroup of the population, the polymorphisms were analyzed in relation to APOE ε4 genotype and to CSF (T-tau, P-tau, and Aβ_1–42). No evidence for associations of these polymorphisms with risk for AD or any of the studied CSF biomarkers measured was found. These results do not support LOXL1 as being a major risk gene for AD.     

Decreasing hazards of Alzheimer's disease with the use of antidepressants: mitigating the risk of depression and apolipoprotein E

Objective

Alzheimer's disease (AD) is a neurodegenerative disease, manifesting in clinically observable deficits in memory, thinking, and behavior that disproportionately affects older adults. Susceptibility genes, such as apolipoprotein ε4, have long been associated with an increased risk of AD diagnosis. Studies have shown associations between depression and increased risk of AD development. Furthermore, findings from previous investigations suggest mixed effects in the use of psychotropic medication in older adults. The hypothesis for this study is that antidepressant use modifies the increased hazard of depression or such that a non‐significant hazard will result with respect to eventual AD development.

Methods

Utilizing data from the National Alzheimer's Coordinating Center, we examined evaluations of 11,443 cognitively intact participants. Survival analysis was used to explore relationships between depression, apolipoprotein E, AD diagnosis, and antidepressant use.

Results

An analytical sample of 8732 participants with normal cognition was examined. Among users of antidepressant medication, the hazard, in most cases, was no longer statistically significant. One generic medication showed protective benefits for users (p < 0.001). In addition, there was a statistically significant relationship between recent depression (n = 2083; p < 0.001), lifetime depression (n = 2068; p < 0.05), and ε4 carrier status (n = 2470; p < 0.001) and AD development.

Conclusions

The findings suggest that a mechanism related to antidepressant use may reduce the hazard of eventual AD. Furthermore, the findings reinforce the association between depression, apolipoprotein E (APOE) ε4, and AD diagnosis. This study contributes to the emerging literature exploring interventions aimed at decreasing the risk of AD by targeting potentially modifiable psychosocial risk factors such as depression. Copyright © 2017 John Wiley & Sons, Ltd.     

Polymorphisms in PDLIM5 gene are associated with alcohol dependence,type 2 diabetes,and hypertension

The PDZ and LIM domain 5 (PDLIM5) gene may play a role in alcohol dependence (AD), bipolar disorder, and major depressive disorder; however, no study has identified shared genetic variants within PDLIM5 gene among AD, type 2 diabetes (T2D), and hypertension. This study investigated the association of 72 single nucleotide polymorphism (SNPs) with AD (1066 AD cases and 1278 controls) in the Study of Addiction - Genetics and Environment (SAGE) sample and 47 SNPs with T2D (878 cases and 2686 non-diabetic) and hypertension (825 cases and 2739 non-hypertensive) in the Marshfield sample. Multiple logistic regression models in PLINK software were used to examine the associations of genetic variants with AD, T2D, and hypertension and SNP x alcohol consumption interactions for T2D and hypertension. Twenty-five SNPs were associated with AD in the SAGE sample (p < 0.05); rs1048627 showed the strongest association with AD (p = 5.53 × 10⁻⁴). Of the 25 SNPs, 5 SNPs showed associations with both AD in the SAGE sample and T2D in the Marshfield sample (top SNP rs11097432 with p = 0.00107 for T2D and p = 0.0483 for AD) while 6 SNPs showed associations with both AD in the SAGE sample and hypertension in the Marshfield sample (top SNP rs12500426 with p = 0.0119 for hypertension and p = 1.51 × 10⁻³ for AD). SNP (rs6532496) showed significant interaction with alcohol consumption for hypertension. Our results showed that several genetic variants in PDLIM5 gene influence AD, T2D and hypertension. These findings offer the potential for new insights into the pathogenesis of AD, T2D, and hypertension.     

A 14 bp indel variation in the <Emphasis Type="Italic">NCX1</Emphasis> gene modulates the age at onset in late-onset Alzheimer’s disease

Calcium homeostasis is critical to amyloid beta precursor protein (APP) processing. Na⁺/Ca²⁺ exchanger (NCX) proteins play an important role in maintaining intracellular Na⁺ and Ca²⁺ homeostasis in the brain under physiological and pathological conditions. We sequenced a hyper-variable region in intron 2 of the Na⁺/Ca²⁺ exchanger 1 gene (NCX1), and investigated whether insertion/deletion variations in this region are associated with the occurrence for Alzheimer’s disease (AD). Examining 413 AD patients and 361 healthy controls, we identified 3 insertion/deletion polymorphisms. No significant differences of the allele and genotype frequencies were observed between the AD cases and the controls for any of the three polymorphisms. However, among the AD patients whose age at onset (AAO) was 65 years or older (n = 299), carriers of a 14 bp insertion showed a lower average AAO (ins/ins and ins/del vs. del/del, 72.49 ± 5.17 vs. 74.28 ± 5.79, p = 0.016). It suggested that this 14 bp insertion/deletion polymorphism might modulate AAO in late-onset AD patients.     

BACE1 Polymorphisms Do Not Influence Platelet Membrane β-secretase Activity or Genetic Susceptibility for Alzheimer’s Disease in the Northern Irish Population

β-Site amyloid precursor protein (APP)-cleaving enzyme 1 (BACE1) is a biological and positional candidate gene for Alzheimer’s disease (AD). BACE1 is a protease that catalyses APP cleavage at the β-secretase site. We evaluated all common and putatively functional polymorphisms in the genomic region encompassing BACE1 for an association with AD, and for functional effects on platelet β-secretase activity. Tag SNPs (n = 10) derived from phase II of the International HapMap Project, and a nonsynonymous variant, were successfully genotyped in 901 Caucasian individuals from Northern Ireland using Sequenom iPLEX and TaqMan technologies. APOE genotyping was performed by PCR-RFLP. Platelet membrane β-secretase activity was assayed in a subset of individuals (n = 311). Hardy–Weinberg equilibrium was observed for all variants. Evidence for an association with AD was observed with multi-marker haplotype analyses (P = 0.01), and with rs676134 when stratified for APOE genotype (P = 0.02), however adjusting for multiple testing negated the evidence for association of this variant with AD. χ² analysis of genotype and allele frequencies in cases versus controls for individual SNPs revealed no evidence for association (5% level). No genetic factors were observed that significantly influenced platelet membrane β-secretase activity. We have selected an appropriate subset of variants suitable for comprehensive genetic investigation of the BACE1 gene. Our results suggest that common BACE1 polymorphisms and putatively functional variants have no significant influence on genetic susceptibility to AD, or platelet β-secretase activity, in this Caucasian Northern Irish population.