Current Alzheimer Research - Volume 12, Issue 10, 2015

Aims: Hypertension, a risk factor for Alzheimer’s disease (AD), is a treatable condition, which offers possibilities for prevention of AD. Elevated angiotensin II (AngII) is an important cause of essential hypertension. AngII has deleterious effects on endothelial function and cerebral blood flow (CBF), which may contribute to AD. AngII blocking agents can thus provide potential candidates to reduce AD risk factors in hypertensive patients. Methods: We studied the effect of 2 months induced hypertension (AngII-infusion via osmotic micropumps) on systolic blood pressure (SBP) and CBF in 10 months-old wild-type (WT) C57bl/6j and AβPPswe/PS1ΔE9 (AβPP/PS1) mice, and treatment with two different antihypertensives, 1) eprosartan mesylate (EM, 0.35mg/kg) or 2) hydrochlorotiazide (HCT, 7.5mg/kg), after 1 month of induced-hypertension. SBP was monitored twice each month via tail cuff plethysmography. CBF was measured with MR by flow-sensitive alternating inversion recovery. Results: Chronic AngII-infusion induced an increase in SBP in both AβPP/PS1 and WT mice accompanied by a decrease in hippocampal and thalamic CBF only in the AβPP/PS1 mice. An additional difference between the AβPP/PS1 mice and WT mice was that SBP was much higher in AβPP/PS1 mice in both hypertensive and normotensive conditions. Moreover, both antihypertensives were less effective in reducing AngII-induced hypertension to normal levels in AβPP/PS1 mice, while being effective in WT mice. Conclusions: It can be concluded that AngII-induced elevated SBP results in impaired CBF and a decreased response to blood pressure lowering treatment in a transgenic model of AD. Our findings suggest a relation between midlife hypertension and decreased CBF in an AD mouse model, similar to the relation which has been found in AD patients. This translational mouse model could be used to investigate possible prevention and treatment strategies for AD.

Transgenic APPswe/PS1dE9 mice modeling Alzheimer’s disease demonstrate ongoing accumulation of β-amyloid fragments resulting in formation of amyloid plaques that starts at the age of 4-5 months. Buildup of β-amyloid fragments is accompanied by impairment of muscarinic transmission that becomes detectable at this age, well before the appearance of cognitive deficits that manifest around the age of 12 months. We have recently demonstrated that long-term feeding of trangenic mice with specific isocaloric fish oil-based diets improves specific behavioral parameters. Now we report on the influence of short-term feeding (3 weeks) of three isocaloric diets supplemented with Fortasyn (containing fish oil and ingredients supporting membrane renewal), the plant sterol stigmasterol together with fish oil, and stigmasterol alone on markers of cholinergic neurotransmission in the hippocampus of 5-month-old transgenic mice and their wild-type littermates. Transgenic mice fed normal diet demostrated increase in ChAT activity and attenuation of carbachol-stimulated GTP-γ35S binding compared to wild-type mice. None of the tested diets compared to control diet influenced the activities of ChAT, AChE, BuChE, muscarinic receptor density or carbachol-stimulated GTP-γ35S binding in wild-type mice. In contrast, all experimental diets increased the potency of carbachol in stimulating GTP-γ35S binding in trangenic mice to the level found in wild-type animals. Only the Fortasyn diet increased markers of cholinergic synapses in transgenic mice. Our data demonstrate that even short-term feeding of transgenic mice with chow containing specific lipid-based dietary supplements can influence markers of cholinergic synapses and rectify impaired muscarinic signal transduction that develops in transgenic mice.

During adult life, hippocampus is an important brain region involved in neurogenesis. The generation and cell death of newly generated neuronal cells in this region have critical roles in brain maintenance and alterations in these processes are seen in Alzheimer’s disease (AD). For the purpose of carrying out a neuroregenerative strategy, we propose a novel approach based on the encapsulation of vascular endothelial growth factor (VEGF) in poly (lactic co-glycolic acid) (PLGA) biodegradable nanospheres (NS) administered by craniotomy to stimulate the proliferation of neuronal precursors in a transgenic mouse model of AD. VEGF loaded nanospheres were prepared by double emulsion solvent evaporation technique, obtaining 200 nm nanospheres with a biphasic release profile. After demonstrating their efficacy in the proliferation and differentiation of neuronal cell cultures, in vivo studies were carried out. 3 months after VEGF-NS were implanted directly into the cerebral cortex of APP/Ps1 mice, the determination of BrdU+ cells in the whole hippocampal region and specifically in the dentate gyrus, demonstrated a significantly enhanced cellular proliferation in VEGF-NS treated group. These results were also confirmed showing an increased number of DCX+ and NeuN+ cells. Hence, PLGA-VEGF nanospheres may be a potential strategy to modulate proliferative neuronal progenitors in the hippocampal region, and therefore, provide new insight for future therapeutic approaches in AD.

The corpus callosum is the largest commissural fiber connecting left and right hemisphere of the brain. Emerging evidence suggests that a variety of abnormalities detected in the microstructure of this white matter fiber can be an early event in Alzheimer's disease (AD) pathology. However, little is known about tissue characteristics of these abnormalities and how these abnormalities evolve during AD progression. In this study, we measured in vivo magnetic resonance transverse relaxation times (T2) to longitudinally monitor changes in tissue integrity and abnormalities related to myelination and demyelination processes in corpus callosum of AD mouse models. The most striking finding of our study was a significant elongation of T2 values in the corpus callosum at 10, 14, 16 and 18 months of age compared to age-matched wild-type mice. In contrast, the gray matter regions surrounding the corpus callosum, such as the cortex and hippocampus, showed a significant T2 decrease compared to wild-type mice. Histological analyses clearly revealed demyelination, gliosis and amyloid-plaque deposition in the corpus callosum. Our results suggest that demyelinating and inflammatory pathology may result in prolonged relaxation time during AD progression. To our knowledge, this is the first in vivo T2 study assessing the microstructural changes with age in the corpus callosum of the Tg2576 mouse model and it demonstrates the application of T2 measurement to noninvasively detect tissue integrity of the corpus callosum, which can be an early event in disease progression.

Both the hippocampus and amygdala are early vulnerable brain regions in the development of Alzheimer’s disease (AD). However, previous studies mainly focused on characterizing the hippocampus in the pathophysiology of AD, leaving the amygdala less explored. Here, we characterized the structures and functions of neurons in the hippocampus and amygdala of young (2, 3 and 4 months of age) APP/PS1 double transgenic (Tg) mice, a widely used AD mouse model. Compared to wild-type littermates (Wt ), Tg mice performed worse in amygdala-dominant memory at all three ages, while hippocampus-dominant memory remained intact until 4-month-old. Likewise, the dendritic arbors of neurons in the basolateral amygdala were reduced in Tg mice as early as 2-months-old, while the dendritic arbors of neurons in the hippocampal CA1 and CA3 regions were relatively intact. BDNF signaling pathways (e.g. AKT and PKC) were reduced in the amygdala, but not in the hippocampus, of young Tg mice. Furthermore, reduction of 5-HT and elevation of Aβ levels also occurred earlier in the amygdala and were more pronounced than those in the hippocampus. Negative correlations between the levels of 5-HT and Aβ were evident in the amygdala, but not in the hippocampus. Taken together, these results suggest that neurodegeneration occurs earlier in the amygdala than in the hippocampus. We suggest that amygdala function should be incorporated into the cognitive screening tool for the diagnosis of mild cognitive impairment due to AD.

Alzheimer's disease (AD) is a neurodegenerative disorder that gradually induces cognitive deficit. Working memory deficits have been previously reported in AD and Amyloid-β peptide (Aβ) is regarded as a causative factor for the impairments. Accumulating evidence has identified that neuronal ensemble activity as well as functional connectivity among neurons encode and process information in normal brain. How Aβ contributes to the abnormal neuronal ensemble activity and corresponding functional connectivity which, in turn, leads to the cognitive deficits? To address the issue, we simultaneously recorded neuronal activity from medial prefrontal cortex of rats (control and Aβ injected group) when the rats performed a Y-maze working memory task, to investigate the properties of neuronal ensemble activity and functional connectivity. In the control group, a group of neurons were collectively activated and the connectivity among the neurons strengthened during the working memory task. However, in the Aβ group, the neuronal activity and connectivity never experience significant change. Our results indicate that the dysfunction of neuronal activity and connectivity may provide insight for the Aβ-induced working memory deficits.

Cortical hubs that link functionally specialized neural systems are crucial for cognition. Evidence suggests that the location and organization of hubs are related to Alzheimer’s disease (AD). However, two issues remain unclear: (i) where and how hubs change in AD, and (ii) whether hubs could be a potential pre-diagnosis biomarker for mild cognitive impairment (MCI) - a prodromal phase of AD. Accordingly, we examined the functional connectivity density (FCD) in two cohorts of resting-state functional magnetic resonance imaging (fMRI) scans (26 AD, 27 controls; 33 AD, 21 controls) and revealed consistently vulnerable FCD hub regions in AD compared with controls: within the default mode network, short-range FCD decreases in the posterior cingulate cortex and increases in the medial prefrontal cortex; within the frontal lobe, long-range FCD increases in the medial prefrontal cortex, superior frontal gyrus and middle frontal gyrus. Furthermore, FCD correlates with cognitive score and could distinguish MCI from controls with high accuracy (71.08% in dataset 1, 81% in dataset 2). By reflecting a robust and reproducible global shift in brain functions, FCD provides an fMRI biomarker for the underlying mechanism in AD.

Changes in rRNA and rDNA expression have been associated with cellular and organism aging and have been linked to Alzheimer’s disease (AD) pathogenesis. In this study, we investigated the mRNA expression of ribosomal genes (28S/18S) and β-amyloid precursor protein (APP) in different post mortem brain tissue regions (the entorhinal and auditory cortices and the hippocampus) of AD patients and elderly control subjects and also evaluated the extent of expression in peripheral blood from young, healthy, elderly, and Alzheimer’s disease patients in order to investigate whether these individuals experienced the effects of aging. The comparative threshold cycle (CT) method via Real Time Polymerase Chain Reaction and the Polymerase Chain Reaction- Restriction Fragment Length Polymorphism (PCR-RFLP) were used to analyze gene expression and the Apolipoprotein E (APOE) genotype, respectively. When the brain areas were analyzed collectively, we observed a significant decrease in APP expression and a significant increase in levels of mRNA of 18S and 28S in Alzheimer’s disease patients compared to healthy elderly individuals. Furthermore, there was a significant upregulation of 28SrRNA in the entorhinal cortex and hippocampus, but not in the auditory cortex of patients with AD. On the other hand, tests of blood samples verified a decreased expression of 28S rRNA in patients with AD. These results support the hypothesis that changes in rRNA are present in AD patients, are tissue-specific, and seem to occur independently and differently in each tissue. However, the next challenge is to discover the mechanisms responsible for the differences in expression observed in the blood and the brain in both healthy elderly individuals and Alzheimer’s disease patients, as well as the impact of these genes on AD pathogenesis.

Chromosomal alterations as a sign of genetic instability are a feature of Alzheimer’s disease (AD). Assessment of the genetic instability of non-neuronal cells of AD patients may provide a method to diagnose or monitor prognosis of the disease. Considering the importance of X chromosome alterations in the possible etiology of AD females, we used fluorescent in situ hybridization (FISH) for the centromere region of the X chromosome to determine aneuploidy, for a possible correlation with premature centromere division (PCD, X) in lymphocytes of AD females and age-matched controls. In AD patients, our results showed a marked and significant increase in the frequency of the X chromosome aneuploidy comparing with age matched controls (p<0.001). Also, a significant difference was detected in the PCD, X frequency between AD females when compared with age matched controls (p<0.001). In addition, a strong (R2=0.97, n=20) and significant (p<0.001) correlation was found between the frequency of aneuploidy and PCD, X in the AD group. Our results support the view that AD is a generalized systematic disease where PCD is to be considered as a stable sign of disease leading to aneuploidy.

In the central nervous system Hsp70s seems to have a protective role in repair and removal of cellular proteins damaged by stress conditions. A protective role of Hsp70 was also shown in Alzheimer Disease. The HSP70-1 +190 G/C polymorphism is located in the gene 5’UTR region and it is implicated in alteration of the transcription binding factor; HSP70-2 +1267 A/G causes a silent mutation in the coding region and it seems to influence the mechanism of mRNA translation; HSP70-hom +2437 A/G causes a substitution Met → The (M493T) in the coding region and it seems to influence the bond with the substrate and therefore on the chaperone activity of hsp70. The aim of our study will be to investigate Alzheimer susceptibility to Hsp70 polymorphisms, taking into account our previous findings on HLA class III region, and to hypothesize a role of HLA class III haplotype configuration based on the variants of three genes: RAGE, HSP70 and TNF. We studied these polymorphisms with PCR-RFLP and PCR-TSP. We investigated 173 AD patients and 211 control subjects. Our results have shown a statistically significant decrease of the C allele frequency of the HSP70-1 +190 G/C polymorphism in AD patients vs controls (P value = 0,018), as well as the G allele of HSP70-2 +1267 G/A (p value = 0,02). We focalized our attention on haplotype reconstruction. We have observed a significant statistically decrease of GGT haplotype frequency (empirical p-value=0.0133 ); GAT haplotype was statistically significant increase in AD patients compared with control (empirical p-value=0.007). The total HLA class III haplotype are reconstructed. The causative haplotypes are the following ones: TTGATGGG ( p value =0,005; empirical p =0,0042); TTGATAGG (p value =0,45; empirical p =0,034). Patients with these haplotypes may show an earlier onset of the disease than patients with TTGGTGGG (p value=0,0138; empirical p =0,0102); TTCGTGGG (p value=0,021; empirical p =0,017); TTCGTGGA (p value =0,058; empirical p =0,043) haplotypes. The overall variation of the haplotypes formed by the RAGE and TNF and HSP70 variants influenced the presence of the AD phenotype (omnibus association LR test p-value 0.00185), HSP701 and HSP702 showed independent effect on AD risk after adjusting for the effect of the entire haplotype (conditional LR test p-value=0.0114 and p-value=0.0044 respectively). These data confirm the involvement of HLA class III in AD.

Background: It has been reported that periodontitis is associated with Alzheimer’s disease. However, the association between paranasal sinusitis and Alzheimer’s disease has not been studied, although olfactory dysfunction frequently precedes the progress of dementia or Alzheimer’s disease. Methods: We studied 783 patients (283 men, 500 women; mean age 77.0 ± 7.9 years) who visited the Center for Comprehensive Care and Research on Memory Disorders, National Center for Geriatrics and Gerontology, and 2139 control subjects who participated in a population-based study conducted by the National Institute for Longevity Sciences – Longitudinal Study of Aging (NILS–LSA) in Japan. Sinusitis was evaluated using magnetic resonance imaging (MRI) according to the Lund–Mackay scoring system. A sinusitis score of ≥ 4 was classified as positive and a score of ≤ 3 was classified as negative. Results: The prevalence of positive sinusitis was 6.3% in patients with a mini-mental state examination (MMSE) score of < 24 (n = 507), and 5.7% in patients with Alzheimer’s disease (n = 280). The rate of positive sinusitis was7.2% in the control group. The prevalence of sinusitis was not significantly different between normal controls and patients with dementia or Alzheimer’s disease after adjustments for age and sex. The rate of positive sinusitis was higher in male than in female subjects in both groups. Conclusion: The prevalence of sinusitis in patients with Alzheimer’s disease or dementia was not higher than in the general population.