Several common and debilitating neurodegenerative disorders are characterized by the intracellular accumulation of neurofibrillary tangles (NFTs), which are composed of hyperphosphorylated tau ...protein. In Alzheimer’s disease (AD), NFTs are accompanied by extracellular amyloid-beta (Aβ), but primary tauopathy disorders are marked by the accumulation of tau protein alone, including forms of frontotemporal dementia (FTD), corticobasal degeneration (CBD), and progressive supranuclear palsy (PSP), among others. 18F-THK5351 has been reported to bind pathological tau as well as associated reactive astrogliosis. The goal of this study was to validate the ability of the PET tracer 18F-THK5351 to detect early changes in tau-related pathology and its relation to other pathological hallmarks. We demonstrated elevated in vivo 18F-THK5351 PET signaling over time in transgenic P301S tau mice from 8 months that had a positive correlation with histological and biochemical tau changes, as well as motor, memory, and learning impairment. This study indicates that 18F-THK5351 may help fill a critical need to develop PET imaging tracers that detect aberrant tau aggregation and related neuropathology in order to diagnose the onset of tauopathies, gain insights into their underlying pathophysiologies, and to have a reliable biomarker to follow during treatment trials.
Aims
Here, we tested the hypothesis that glial responses via the production of cytokines such as transforming growth factor‐beta 1 (TGFβ1) and tumour necrosis factor alpha (TNFα), which play ...important roles in neurodegenerative diseases, are correlated with the severity of congenital hydrocephalus in the hyh mouse model. We also searched for evidence of this association in human cases of primary hydrocephalus.
Methods
Hyh mice, which exhibit either severe or compensated long‐lasting forms of hydrocephalus, were examined and compared with wild‐type mice. TGFβ1, TNFα and TNFαR1 mRNA levels were quantified using real‐time PCR. TNFα and TNFαR1 were immunolocalized in the brain tissues of hyh mice and four hydrocephalic human foetuses relative to astroglial and microglial reactions.
Results
The TGFβ1 mRNA levels were not significantly different between hyh mice exhibiting severe or compensated hydrocephalus and normal mice. In contrast, severely hydrocephalic mice exhibited four‐ and two‐fold increases in the mean levels of TNFα and TNFαR1, respectively, compared with normal mice. In the hyh mouse, TNFα and TNFαR1 immunoreactivity was preferentially detected in astrocytes that form a particular periventricular reaction characteristic of hydrocephalus. However, these proteins were rarely detected in microglia, which did not appear to be activated. TNFα immunoreactivity was also detected in the glial reaction in the small group of human foetuses exhibiting hydrocephalus that were examined.
Conclusions
In the hyh mouse model of congenital hydrocephalus, TNFα and TNFαR1 appear to be associated with the severity of the disease, probably mediating the astrocyte reaction, neurodegenerative processes and ischaemia.
Abstract
Background
The apolipoprotein E (
APOE
) gene exists in three isoforms in humans:
APOE2, APOE3
and
APOE4
.
APOE4
causes structural and functional alterations in normal brains, and is the ...strongest genetic risk factor of the sporadic form of Alzheimer’s disease (LOAD). Research on
APOE4
has mainly focused on the neuronal damage caused by defective cholesterol transport and exacerbated amyloid-β and Tau pathology. The impact of
APOE4
on non-neuronal cell functions has been overlooked. Astrocytes, the main producers of ApoE in the healthy brain, are building blocks of neural circuits, and Ca
2+
signaling is the basis of their excitability. Because
APOE4
modifies membrane-lipid composition, and lipids regulate Ca
2+
channels, we determined whether
APOE4
dysregulates Ca
2+
signaling in astrocytes.
Methods
Ca
2+
signals were recorded in astrocytes in hippocampal slices from
APOE3
and
APOE4
gene targeted replacement male and female mice using Ca
2+
imaging. Mechanistic analyses were performed in immortalized astrocytes. Ca
2+
fluxes were examined with pharmacological tools and Ca
2+
probes.
APOE3
and
APOE4
expression was manipulated with GFP-
APOE
vectors and
APOE
siRNA. Lipidomics of lysosomal and whole-membranes were also performed.
Results
We found potentiation of ATP-elicited Ca
2+
responses in
APOE4
versus
APOE3
astrocytes in male, but not female, mice. The immortalized astrocytes modeled the male response, and showed that Ca
2+
hyperactivity associated with
APOE4
is caused by dysregulation of Ca
2+
handling in lysosomal-enriched acidic stores, and is reversed by the expression of
APOE3
, but not of
APOE4
, pointing to loss of function due to
APOE4
malfunction. Moreover, immortalized
APOE4
astrocytes are refractory to control of Ca
2+
fluxes by extracellular lipids, and present distinct lipid composition in lysosomal and plasma membranes.
Conclusions
Immortalized
APOE4
versus
APOE3
astrocytes present: increased Ca
2+
excitability due to lysosome dysregulation, altered membrane lipidomes and intracellular cholesterol distribution, and impaired modulation of Ca
2+
responses upon changes in extracellular lipids. Ca
2+
hyperactivity associated with
APOE4
is found in astrocytes from male, but not female, targeted replacement mice. The study suggests that, independently of Aβ and Tau pathologies, altered astrocyte excitability might contribute to neural-circuit hyperactivity depending on
APOE
allele, sex and lipids, and supports lysosome-targeted therapies to rescue
APOE4
phenotypes in LOAD.
Insulin-like growth factor-I (IGF-I) plays a key role in the modulation of synaptic plasticity and is an essential factor in learning and memory processes. However, during aging, IGF-I levels are ...decreased, and the effect of this decrease in the induction of synaptic plasticity remains unknown. Here we show that the induction of N-methyl-D-aspartate receptor (NMDAR)-dependent long-term potentiation (LTP) at layer 2/3 pyramidal neurons (PNs) of the mouse barrel cortex is favored or prevented by IGF-I (10 nM) or IGF-I (7 nM), respectively, when IGF-I is applied 1 h before the induction of Hebbian LTP. Analyzing the cellular basis of this bidirectional control of synaptic plasticity, we observed that while 10 nM IGF-I generates LTP (LTP IGF-I ) of the post-synaptic potentials (PSPs) by inducing long-term depression (LTD) of the inhibitory post-synaptic currents (IPSCs), 7 nM IGF-I generates LTD of the PSPs (LTD IGF-I ) by inducing LTD of the excitatory post-synaptic currents (EPSCs). This bidirectional effect of IGF-I is supported by the observation of IGF-IR immunoreactivity at both excitatory and inhibitory synapses. Therefore, IGF-I controls the induction of Hebbian NMDAR-dependent plasticity depending on its concentration, revealing novel cellular mechanisms of IGF-I on synaptic plasticity and in the learning and memory machinery of the brain.
As a result of alternative splicing, the D2 gene of the dopamine receptor family exists in two isoforms. The D2 long is characterized by the insertion of 29 amino acids in the third cytoplasmic loop, ...which is absent in the short isoform. We have produced subtype-specific antibodies against both the D2 short and D2 long isoforms and found a unique compartmentalization between these two isoforms in the primate brain. The D2 short predominates in the cell bodies and projection axons of the dopaminergic cell groups of the mesencephalon and hypothalamus, whereas the D2 long is more strongly expressed by neurons in the striatum and nucleus accumbens, structures targeted by dopaminergic fibers. These results show that the splice variants of the dopamine D2 receptor are differentially distributed and possess distinct functions. The strategic localization of the D2 short isoform in dopaminergic cell bodies and axons strongly suggests that this isoform is the likely dopamine autoreceptor, whereas the D2 long isoform is primarily a postsynaptic receptor.
Aging is associated with chronic systemic inflammation, which contributes to the development of many age-related diseases, including vascular disease. The world's population is aging, leading to an ...increasing prevalence of both stroke and vascular dementia. The inflammatory response to ischemic stroke is critical to both stroke pathophysiology and recovery. Age is a predictor of poor outcomes after stroke. The immune response to stroke is altered in aged individuals, which contributes to the disparate outcomes between young and aged patients. In this review, we describe the current knowledge of the effects of aging on the immune system and the cerebral vasculature and how these changes alter the immune response to stroke and vascular dementia in animal and human studies. Potential implications of these age-related immune alterations on chronic inflammation in vascular disease outcome are highlighted.
Inhibition of β-site amyloid–β-protein precursor cleaving enzyme 1 (BACE1) represents a promising approach for the treatment of Alzheimer's disease (AD). However, the development of a selective BACE1 ...inhibitor is difficult due to its highly flexible catalytic site and homology to other aspartic proteases, including BACE2 and Cathepsin D (CTSD). Aiming to better understand the structural factors responsible for selective BACE1 inhibition, we performed alignment studies, molecular dynamics (MD) simulations and docking studies to explore the recognition of four selective BACE1 inhibitors by aspartyl proteases. The results show that selective BACE1 inhibition may be due to the formation of strong electrostatic interactions with Asp32 and Asp228 and a large number of hydrogen bonds, π-π and Van der Waals interactions with the amino acid residues located inside the catalytic cavity, which has different volume and shape compared to BACE2 and CTSD. Hindrance effects avoid the accommodation of ligands in the small catalytic site of BACE2, resulting in a lower affinity and the high cavity of CTSD results in the formation of a small number of interactions with the ligands, although they show a similar binding mode with BACE1. These results might help to rationalize the design of selective BACE1 inhibitors.
•In silico studies showed structural differences between BACE1, BACE2 and CTSD.•The principal structural differences on the catalytic cavity is the volume.•Ligand recognition of four selective BACE1 inhibitors were studied.•The BACE1 selectivity is explained by strong electrostatic with Asp32 and Asp228.
Neuroinflammation and protein accumulation are characteristic hallmarks of both normal aging and age-related neurodegenerative diseases. However, the relationship between these factors in ...neurodegenerative processes is poorly understood. We have previously shown that proteasome inhibition produced higher neurodegeneration in aged than in young rats, suggesting that other additional age-related events could be involved in neurodegeneration. We evaluated the role of lipopolysaccharide (LPS)-induced neuroinflammation as a potential synergic risk factor for hippocampal neurodegeneration induced by proteasome inhibition.
Young male Wistar rats were injected with 1 μL of saline or LPS (5 mg/mL) into the hippocampus to evaluate the effect of LPS-induced neuroinflammation on protein homeostasis. The synergic effect of LPS and proteasome inhibition was analyzed in young rats that first received 1 μL of LPS and 24 h later 1 μL (5 mg/mL) of the proteasome inhibitor lactacystin. Animals were sacrificed at different times post-injection and hippocampi isolated and processed for gene expression analysis by real-time polymerase chain reaction; protein expression analysis by western blots; proteasome activity by fluorescence spectroscopy; immunofluorescence analysis by confocal microscopy; and degeneration assay by Fluoro-Jade B staining.
LPS injection produced the accumulation of ubiquitinated proteins in hippocampal neurons, increased expression of the E2 ubiquitin-conjugating enzyme UB2L6, decreased proteasome activity and increased immunoproteasome content. However, LPS injection was not sufficient to produce neurodegeneration. The combination of neuroinflammation and proteasome inhibition leads to higher neuronal accumulation of ubiquitinated proteins, predominant expression of pro-apoptotic markers and increased neurodegeneration, when compared with LPS or lactacystin (LT) injection alone.
Our results identify neuroinflammation as a risk factor that increases susceptibility to neurodegeneration induced by proteasome inhibition. These results highlight the modulation of neuroinflammation as a mechanism for neuronal protection that could be relevant in situations where both factors are present, such as aging and neurodegenerative diseases.
Background
Current treatments for Alzheimer´s disease (AD) only ameliorate the symptoms, but none of them delays or halts disease progression. In recent years, stem cells have received growing ...attention as a potential therapy for brain disorders. Patients’ self‐derive stem cells offer the possibility to avoid rejection and a more personalized treatment. However, there is an urgent need to replace the conventional intracerebral stem cell therapy for a less invasive method to avoid some of the technical challenges. Our recently published results indicate that peripheral treatment with neural precursors (NPs) ameliorates clinical symptoms by reducing the disease‐associated neuroinflammation in a mouse model of Parkinson’s disease. Therefore, we hypothesize that intravenous administration of NPs could be considered as a non‐invasive therapy to ameliorate memory impairment in mouse models of AD.
Method
NPs derived from mesenchymal stem cells and induced pluripotent stem cells were intravenously injected into APP/PS1 and P301S mice before and after brain pathology is stablished. At the age of 7 months old, experimental and control animals were subjected learning and memory tasks and brain analyzed.
Result
NP‐treated mice demonstrated a significant decreased of cognitive impairment compared to PBS‐injected animals as well as improved motor coordination in P301S mice. Histological analysis showed that although amyloidogenic deposits were slightly reduced, microglial activation decreased after the treatment.
Conclusion
The preclinical analysis of NPs peripheral inoculation suggests that these cells could be considered as a potential treatment to reduce AD‐related pathology.
PDF
