Promotion of β-amyloid production by C-reactive protein and its implications in the early pathogenesis of Alzheimer's disease

C-reactive protein (CRP) and β-amyloid protein (Aβ) are involved in the development of Alzheimer's disease (AD). However, the relationship between CRP and Aβ production is unclear. In vitro and in vivo experiments were performed to investigate the association of CRP with Aβ production. Using the rat adrenal pheochromocytoma cell line (PC12 cells) to mimic neurons, cytotoxicity was evaluated by cell viability and supernatant lactate dehydrogenase (LDH) activity. The levels of amyloid precursor protein (APP), beta-site APP cleaving enzyme (BACE-1), and presenilins (PS-1 and PS-2) were investigated using real-time polymerase chain reaction and Western blotting analysis. Aβ1-42 was measured by enzyme-linked immunosorbent assay. The relevance of CRP and Aβ as well as potential mechanisms were studied using APP/PS1 transgenic (Tg) mice. Treatment with 0.5-4.0 μM CRP for 48 h decreased cell viability and increased LDH leakage in PC12 cells. Incubation with CRP at a sub-toxic concentration of 0.2 μM increased the mRNA levels of APP, BACE-1, PS-1, and PS-2, as well as Aβ1-42 production. CRP inhibitor reversed the CRP-induced upregulations of the mRNA levels of APP, BACE-1, PS-1, and PS-2, and the protein levels of APP, BACE-1, PS-1, and Aβ1-42, but did not reversed Aβ1-42 cytotoxicity. The cerebral levels of CRP and Aβ1-42 in APP/PS1 Tg mice were positively correlated, accompanied with the elevated mRNA expressions of serum amyloid P component (SAP), complement component 1q (C1q), and tumor necrosis factor-α (TNF-α). These results suggest that CRP cytotoxicity is associated with Aβ formation and Aβ-related markers expressions; CRP and Aβ were relevant in early-stage AD; CRP may be an important trigger in AD pathogenesis.     

Tau protein is involved in morphological plasticity in hippocampal neurons in response to BDNF

Tau protein, a microtubule-associated protein involved in a number of neurological disorders such as Alzheimer's disease (AD), may undergo modifications under both physiological and pathological conditions. However, the signaling pathways that couple tau protein to neuronal physiology such as synaptic plasticity have not yet been elucidated. Here we report that tau protein is involved in morphological plasticity in response to brain derived neurotrophic factor (BDNF). Stimulation of the cultured rat hippocampal neurons with BDNF resulted in increased tau protein expression, as detected by Western blotting. Furthermore, tau protein accumulated in the distal region of the neurite when treated with taxol or taxol plus BDNF. The increased tau protein also protected neurons against nocodazole-induced dendrite loss. Moreover, BDNF promoted spine growth as well as tau protein over-expression. Knockdown of tau protein using specific short-hairpin RNA (shRNA) significantly decreased the spine density. And BDNF could not increase the spine density of tau-knockdown neurons. These results highlight a possible role for tau protein in the dynamic rearrangement of cytoskeletal fibers vital for BDNF-induced synaptic plasticity.     

Renin inhibitor aliskiren exerts neuroprotection against amyloid beta-peptide toxicity in rat cortical neurons

Accumulation of amyloid β-peptide (Aβ) in senile plaques, a pathological hallmark of Alzheimer's disease (AD), has been implicated in neuronal degeneration. Renin-angiotensin system (RAS) blockers, including the renin inhibitor aliskiren, are a group of clinically relevant anti-hypertensive agents. The present study was initiated to investigate whether aliskiren may modulate Aβ neurotoxicity as an additional function aside from its established property of lowering blood pressure. We found aliskiren conferred neuronal resistance to Aβ toxicity in primary rat cortical cultures. Moreover, both Aβ25-35 and Aβ1-42 induced renin expression in cortical neurons; in parallel, a heightened expression of renin was detected in the cerebral cortices of 9-month-old AD transgenic mice. Notably, aliskiren blocked Aβ-mediated neuronal induction of renin. We therefore concluded that aliskiren may carry neuroprotective action against Aβ toxicity. Furthermore, the aliskiren effects may involve downregulation of renin expression induced by Aβ.     

SORL1 and SIRT1 mRNA expression and promoter methylation levels in aging and Alzheimer’s Disease

Alzheimer’s Disease (AD) is a neurodegenerative disorder and the most common cause of dementia among the elderly. Efforts have been made to understand the genetic and epigenetic mechanisms involved in the development of this disease. As SORL1 (sortilin-related receptor) and SIRT1 (sirtuin 1) genes have been linked to AD pathogenesis, we aimed to investigate their mRNA expression and promoter DNA methylation in post mortem brain tissues (entorhinal and auditory cortices and hippocampus) from healthy elderly subjects and AD patients. We also evaluated these levels in peripheral blood leukocytes from young, healthy elderly and AD patients, investigating whether there was an effect of age on these profiles. The comparative CT method by Real Time PCR and MALDI-TOF mass spectrometry were used to analyze gene expression and DNA methylation, respectively. SORL1 gene was differently expressed in the peripheral blood leukocytes and might act as a marker of aging in this tissue. Furthermore, we found that SORL1 promoter DNA methylation might act as one of the mechanisms responsible for the differences in expression observed between blood and brain for both healthy elderly and AD patients groups. The impact of these studied genes on AD pathogenesis remains to be better clarified.     

In vivo hippocampal microdialysis reveals impairment of NMDA receptor–cGMP signaling in APPSW and APPSW/PS1L166P Alzheimer’s transgenic mice

Transgenic (Tg) mice overexpressing human amyloid precursor protein (APP) mutants reproduce features of early Alzheimer’s disease (AD) including memory deficit, presence of β-amyloid (Aβ) oligomers, and age-associated formation of amyloid deposits. In this study we used hippocampal microdialysis to characterize the signaling of N-methyl-d-aspartic acid receptors (NMDA-Rs) in awake and behaving AD Tg mice. The NMDA-R signaling is central to hippocampal synaptic plasticity underlying memory formation and several lines of evidence implicate the role of Aβ oligomers in effecting NMDA-R dysfunction. CA1 NMDA-Rs were stimulated by NMDA infused through reverse microdialysis while changes in the cyclic guanosine monophosphate (cGMP) concentration in the brain interstitial fluid (ISF) were used to determine NMDA-Rs responsiveness. While 4 months old wild type C57BL/6 mice mounted robust cGMP response to the NMDA challenge, the same stimulus failed to significantly change the cGMP level in 4 and 15 months old APP_SW and 4 months old APP_SW/PS1_L166P Tg mice, which were all on C57BL/6 background. Lack of response to NMDA in AD Tg mice occurred in the absence of changes in expression levels of several synaptic proteins including synaptophysin, NR1 NMDA-R subunit and postsynaptic density protein 95, which indicates lack of profound synaptic degeneration. Aβ oligomers were detected in all three AD Tg mice groups and their concentration in the hippocampus ranged from 40.5 ± 3.6 ng/g in 4 months old APP_SW mice to 60.8 ± 15.9 ng/g in 4 months old APP_SW/PS1_L166P mice. Four months old APP_SW mice had no Aβ amyloid plaques, while the other two AD Tg mice groups showed evidence of incipient Aβ amyloid plaque formation. Our studies describes a novel approach useful to study the function of NMDA-Rs in awake and behaving AD Tg mice and demonstrate impairment of NMDA-R response in the presence of endogenously formed Aβ oligomers but predating onset of Aβ amyloidosis.     

Analysis of the formation of flower shapes in wild species and cultivars of tree peony using the MADS-box subfamily gene

Tree peony (Paeonia suffricotisa) cultivars have a unique character compared with wild species; the stamen petalody results in increased whorls of petals and generates different flower forms, which are one of the most important traits for cultivar classification. In order to investigate how petaloid stamens are formed, we obtained the coding sequence (666 bp) and genomic DNA sequence of the PsTM6 genes (belongs to B subfamily of MADS-box gene family) from 23 tree peony samples, Five introns and six exons consisted of the genomic DNA sequence. The analysis of cis-acting regulatory elements in the third and fourth intron indicated that they were highly conserved in all samples. Partial putative amino acids were analyzed and the results suggested that functional differentiation of PsTM6 paralogs apparently affected stamen petalody and flower shape formation due to due to amino acid substitution caused by differences in polarity and electronic charge. Sliding window analysis indicated that the different regions of PsTM6 were subjected to different selection forces, especially in the K domain. This is the first attempt to investigate genetic control of the stamen petalody based on the PsTM6 sequence. This will provide a basis for understanding the evolution of PsTM6 and its the function of in determining stamen morphology of tree peony.     

The use of PIB-PET as a dual pathological and functional biomarker in AD

Amyloid imaging with positron emission tomography (PET) is presently used in Alzheimer's disease (AD) research. In this study we investigated the possibility to use early frames (ePIB) of the PIB scans as a rough index of CBF by comparing normalised early PIB values with cerebral glucose metabolism (rCMRglc). PIB-PET and FDG-PET were performed in 37 AD patients, 21 subjects with mild cognitive impairment (MCI) and 6 healthy controls (HC). The patients were divided based on their PIB retention (amyloid load) as either PIB positive (PIB+) or PIB negative (PIB−). Data of the unidirectional influx K₁ from a subset of the subjects including 7 AD patients and 3 HC was used for correlative analysis. Data was analysed using regions of interest (ROI) analysis. A strong, positive correlation was observed across brain regions between K₁ and ePIB (r = 0.70; p ≤ 0.001). The ePIB values were significantly lower in the posterior cingulate (p ≤ 0.001) and the parietal cortices (p = 0.002) in PIB+ subjects compared to PIB−, although the group difference were stronger for rCMRglc in cortical areas (p ≤ 0.001). Strong positive correlations between ePIB and rCMRglc were observed in all cortical regions analysed, especially in the posterior cingulate and parietal cortices (p ≤ 0.001). A single dynamic PIB-PET scan may provide information about pathological and functional changes (amyloidosis and impaired blood flow). This might be important for diagnosis of AD, enrichment of patients in clinical trials and evaluation of treatment effects. This article is part of a Special Issue entitled: Imaging Brain Aging and Neurodegenerative disease.     

Strength of density feedback in census data increases from slow to fast life histories

Life-history theory predicts an increasing rate of population growth among species arranged along a continuum from slow to fast life histories. We examine the effects of this continuum on density-feedback strength estimated using long-term census data from >700 vertebrates, invertebrates, and plants. Four life-history traits (Age at first reproduction, Body size, Fertility, Longevity) were related statistically to Gompertz strength of density feedback using generalized linear mixed-effects models and multi-model inference. Life-history traits alone explained 10 to 30% of the variation in strength across species (after controlling for time-series length and phylogenetic nonindependence). Effect sizes were largest for body size in mammals and longevity in birds, and density feedback was consistently stronger for smaller-bodied and shorter-lived species. Overcompensatory density feedback (strength <-1) occurred in 20% of species, predominantly at the fast end of the life-history continuum, implying relatively high population variability. These results support the idea that life history leaves an evolutionary signal in long-term population trends as inferred from census data. Where there is a lack of detailed demographic data, broad life-history information can inform management and conservation decisions about rebound capacity from low numbers, and propensity to fluctuate, of arrays of species in areas planned for development, harvesting, protection, and population recovery.     

Effects of changes in the shape of the intracellular action potential on the peak-to-peak ratio of single muscle fibre potentials

In situ recording of the intracellular action potential (IAP) of human muscle fibres is not yet feasible, and consequently, knowledge about certain IAP characteristics of these IAPs is still limited. The ratio between the amplitudes of the second and first phases (the so-called peak-to-peak ratio, PPR) of a single fibre action potential (SFAP) is known to be closely related to the IAP profile. The PPR of experimentally recorded SFAPs has been found to be largely independent of changes in the fibre-to-electrode (radial) distance. The main goal of this paper is to analyze the effect of changes in different aspects of the IAP spike on the relationship between PPR and radial distance. Based on this analysis, we hypothesize about the characteristics of IAPs obtained experimentally. It was found that the sensitivity of the SFAP PPR to changes in radial distance is essentially governed by the duration of the IAP spike. Assuming that, for mammals, the duration of the IAP rising phase lies within the range 0.2-0.4 ms, we tentatively suggest that the duration of the IAP spike should be over approximately 0.75 ms, with the shape of the spike strongly asymmetric. These IAP characteristics broadly coincide with those observed in mammal IAPs.