A comparison of mtDNA deletion mutant proliferation mechanisms

In this paper we use simulation methods to investigate the proliferation of deletion mutations of mitochondrial DNA in neurons. We simulate three mtDNA proliferation mechanisms, namely, random drift, replicative advantage and vicious cycle. For each mechanism, we investigated the effect mutation rates have on neuron loss within a human host. We also compare heteroplasmy of each mechanism at mutation rates that yield the levels neuron loss that would be associated with dementia. Both random drift and vicious cycle predicted high levels of heteroplasmy, while replicative advantage showed a small number of dominant clones with a low background of heteroplasmy.

Inhibiting SRC activity attenuates kainic-acid induced mouse epilepsy via reducing NR2B phosphorylation and full-length NR2B expression

OBJECTIVE

To explore the effect of SRC activation on spontaneously recurrent seizures and to investigate the underlying mechanisms of NR2B phosphorylation.

METHODS

C57BL/6 mice were injected intrahippocampally with kainic acid (KA, 0.4 μg/25 g) to induce status epilepticus (SE). Saracatinib(STB) was used as an SRC inhibitor. Spontaneously recurrent seizures were monitored from day 7 to day 14 after the KA injection. Nissl's stain and NeuN were used to detect neuron loss and Timm stain was used to evaluate mossy fibre sprouting 14 days after KA injection. We also investigated the effect of SRC on full-length expression of NR2B. MDL28170 was used to inhibit calpain activity. Western blotting and qPCR were performed to verify phosphorylation levels and expression of SRC and NR2B 24 h after KA injection.

RESULTS

The duration of status epileptics in the SRC inhibitor group decreased significantly compared to the KA group 24 h after the injection of KA (P < 0.05). The application of the SRC inhibitor significantly reduced the degree of contralateral mossy fibre sprouting (P < 0.05) and improved the degree of neuron loss (P < 0.01) compared to the epilepsy group. Full-length NR2B levels in the ipsilateral hippocampus decreased in the epilepsy group (P < 0.01) compared to the sham group, and it further decreased in the STB inhibitor group (P < 0.01). The effect of the STB inhibitor was counteracted by simultaneous inhibition of SRC activity and calpain activation, while the level of full-length NR2B increased compared to the KA+STB group(P < 0.01). Reduction of NR2B cleavage by MDL28170 significantly increased the duration of epileptic status compared to the KA group (P < 0.05).

SIGNIFICANCE

Our data indicated that the early application of SRC inhibitors exerted protective effects on seizure severity, loss of neurons, and sprouting of mossy fibres in KA-induced mouse epilepsy. Seizure severity attenuation due to SRC inhibition was associated with the decrease of NR2B in both the phosphorylation and full-length forms.

High frequency repetitive transcranial magnetic stimulation alleviates cognitive deficits in 3xTg-AD mice by modulating the PI3K/Akt/GLT-1 Axis

Objective

Glutamate mediated excitotoxicity, such as oxidative stress, neuroinflammation, synaptic loss and neuronal death, is ubiquitous in Alzheimer's disease (AD). Our previous study found that 15 Hz repetitive transcranial magnetic stimulation (rTMS) could reduce cortical excitability. The purpose of this study was to explore the therapeutic effect of higher frequency rTMS on 3xTg-AD model mice and further explore the mechanisms of rTMS.

Methods

First, WT and 3xTg-AD model mice received 25 Hz rTMS treatment for 21 days. The Morris water maze test was used to evaluate the cognitive function. The levels of Aβ and neuroinflammation were assessed by ELISA and immunofluorescence. Oxidative stress was quantified by biochemical assay kits. Brain glucose metabolism was assessed by ¹⁸F-FDG PET. Apoptosis was assessed by western blot and TUNEL staining. Synaptic plasticity and PI3K/Akt/GLT-1 pathway related protein expression were assessed by western blot. Next, to explore the activity of PI3K/Akt in the therapeutic effect of rTMS, 3xTg-AD model mice were given LY294002 intervention and rTMS treatment for 21 days, the experimental method was the same as before.

Results

We found that 25 Hz rTMS could improve cognitive function of 3xTg-AD model mice, reduce hippocampal Aβ1-42 levels, ameliorate oxidative stress and improve glucose metabolism. rTMS alleviated neuroinflammatory response, enhanced synaptic plasticity and reduced neuronal loss and cell apoptosis, accompanied by activation of PI3K/Akt/GLT-1 pathway. After administration of PI3K/Akt inhibitor LY294002, 25 Hz rTMS could not improve the cognitive function and reduce neuron damage of 3xTg-AD model mice, nor could it upregulate the expression of GLT-1, indicating that its therapeutic and protective effects required the involvement of PI3K/Akt/GLT-1 pathway.

Conclusion

rTMS exerts protective role for AD through regulating multiple pathological processes. Meanwhile, this study revealed the key role of PI3K/Akt/GLT-1 pathway in the treatment of AD by rTMS, which might be a new target.

Chronic Memantine Treatment Ameliorates Behavioral Deficits, Neuron Loss, and Impaired Neurogenesis in a Model of Alzheimer's Disease

Memantine, a non-competitive NMDA receptor antagonist possessing neuroprotective properties, belongs to the small group of drugs which have been approved for the treatment of Alzheimer's disease (AD). While several preclinical studies employing different transgenic AD mouse models have described beneficial effects with regard to rescued behavioral deficits or reduced amyloid plaque pathology, it is largely unknown whether memantine might have beneficial effects on neurodegeneration. In the current study, we assessed whether memantine treatment has an impact on hippocampal neuron loss and associated behavioral deficits in the Tg4-42 mouse model of AD. We demonstrate that a chronic oral memantine treatment for 4 months diminishes hippocampal CA1 neuron loss and rescues learning and memory performance in different behavioral paradigms, such as Morris water maze or a novel object recognition task. Cognitive benefits of chronic memantine treatment were accompanied by an amelioration of impaired adult hippocampal neurogenesis. Taken together, our results demonstrate that memantine successfully counteracts pathological alterations in a preclinical mouse model of AD.

Texture Features of Magnetic Resonance Images: an Early Marker of Post-stroke Cognitive Impairment

Stroke is frequently associated with delayed, long-term cognitive impairment (CI) and dementia. Recent research has focused on identifying early predictive markers of CI occurrence. We carried out a texture analysis of magnetic resonance (MR) images to identify predictive markers of CI occurrence based on a combination of preclinical and clinical data. Seventy-two-hour post-stroke T1W MR images of 160 consecutive patients were examined, including 75 patients with confirmed CI at the 6-month post-stroke neuropsychological examination. Texture features were measured in the hippocampus and entorhinal cortex and compared between patients with CI and those without. A correlation study determined their association with MoCA and MMSE clinical scores. Significant features were then combined with the classical prognostic factors, age and gender, to build a machine learning algorithm as a predictive model for CI occurrence. A middle cerebral artery transient occlusion model was used. Texture features were compared in the hippocampus of sham and lesioned rats and were correlated with histologically assessed neural loss. In clinical studies, two texture features, kurtosis and inverse difference moment, differed significantly between patients with and without CI and were significantly correlated with MoCA and MMSE scores. The prediction model had an accuracy of 88 ± 3%. The preclinical model revealed a significant correlation between texture features and neural density in the hippocampus contralateral to the ischemic area. These preliminary results suggest that texture features of MR images are representative of neural alteration and could be a part of a screening strategy for the early prediction of post-stroke CI.

LW-AFC, a new formula derived from Liuwei Dihuang decoction, ameliorates behavioral and pathological deterioration via modulating the neuroendocrine-immune system in PrP-hAβPPswe/PS1ΔE9 transgenic mice

BACKGROUND

Accumulating evidence implicates the neuroendocrine immunomodulation (NIM) network in the physiopathological mechanism of Alzheimer's disease (AD). Notably, we previously revealed that the NIM network is dysregulated in the PrP-hAβPPswe/PS1ΔE9 (APP/PS1) transgenic mouse model of AD.

METHODS

After treatment with a novel Liuwei Dihuang formula (LW-AFC), mice were cognitively evaluated in behavioral experiments. Neuron loss, amyloid-β (Aβ) deposition, and Aβ level were analyzed using Nissl staining, immunofluorescence, and an AlphaLISA assay, respectively. Multiplex bead analysis, a radioimmunoassay, immunochemiluminometry, and an enzyme-linked immunosorbent assay (ELISA) were used to measure cytokine and hormone levels. Lymphocyte subsets were detected using flow cytometry. Data between two groups were compared using a Student's t test. Comparison of the data from multiple groups against one group was performed using a one-way analysis of variance (ANOVA) followed by a Dunnett's post hoc test or a two-way repeated-measures analysis of variance with a Tukey multiple comparisons test.

RESULTS

LW-AFC ameliorated the cognitive impairment observed in APP/PS1 mice, including the impairment of object recognition memory, spatial learning and memory, and active and passive avoidance. In addition, LW-AFC alleviated the neuron loss in the hippocampus, suppressed Aβ deposition in the brain, and reduced the concentration of Aβ1-42 in the hippocampus and plasma of APP/PS1 mice. LW-AFC treatment also significantly decreased the secretion of corticotropin-releasing hormone and gonadotropin-releasing hormone in the hypothalamus, and adrenocorticotropic hormone, luteinizing hormone, and follicle-stimulating hormone in the pituitary. Moreover, LW-AFC increased CD8+CD28+ T cells, and reduced CD4+CD25+Foxp3+ T cells in the spleen lymphocytes, downregulated interleukin (IL)-1β, IL-2, IL-6, IL-23, granulocyte-macrophage colony stimulating factor, and tumor necrosis factor-α and -β, and upregulated IL-4 and granulocyte colony stimulating factor in the plasma of APP/PS1 mice.

CONCLUSIONS

LW-AFC ameliorated the behavioral and pathological deterioration of APP/PS1 transgenic mice via the restoration of the NIM network to a greater extent than either memantine or donepezil, which supports the use of LW-AFC as a potential agent for AD therapy.

Dync1h1 Mutation Causes Proprioceptive Sensory Neuron Loss and Impaired Retrograde Axonal Transport of Dorsal Root Ganglion Neurons

BACKGROUND AND PURPOSE

Sprawling (Swl) is a radiation-induced mutation which has been identified to have a nine base pair deletion in dynein heavy chain 1 (DYNC1H1: encoded by a single gene Dync1h1). This study is to investigate the phenotype and the underlying mechanism of the Dync1h1 mutant.

METHODS AND RESULTS

To display the phenotype of Swl mutant mice, we examined the embryos of homozygous (Swl/Swl) and heterozygous (Swl/+) mice and their postnatal dorsal root ganglion (DRG) of surviving Swl/+ mice. The Swl/+ mice could survive for a normal life span, while Swl/Swl could only survive till embryonic (E) 8.5 days. Excessive apoptosis of Swl/+ DRG neurons was revealed during E11.5-E15.5 days, and the peak rate was at E13.5 days. In vitro study of mutated DRG neurons showed impaired retrograde transport of dynein-driven nerve growth factor (NGF). Mitochondria, another dynein-driven cargo, demonstrated much slower retrograde transport velocity in Swl/+ neurons than in wild-type (WT) neurons. Nevertheless, the Swl, Loa, and Cra mutations did not affect homodimerization of DYNC1H1.

CONCLUSION

The Swl/Swl mutation of Dync1h1 gene led to embryonic mal-development and lethality, whereas the Swl/+ DRG neurons demonstrated deficient retrograde transport in dynein-driven cargos and excessive apoptosis during mid- to late-developmental stages. The underlying mechanism of the mutation may not be due to impaired homodimerization of DYNC1H1.

Aging in the canine and feline brain

Aging dogs and cats show neurodegenerative features that are similar to human aging and Alzheimer disease. Neuropathologic changes with age may be linked to signs of cognitive dysfunction both in the laboratory and in a clinic setting. Less is known about cat brain aging and cognition and this represents an area for further study. Neurodegenerative diseases such as lysosomal storage diseases in dogs and cats also show similar features of human aging, suggesting some common underlying pathogenic mechanisms and also suggesting pathways that can be modified to promote healthy brain aging.

Relation between clinical findings and progression of cerebral cortical pathology in MM1-type sporadic Creutzfeldt-Jakob disease: proposed staging of cerebral cortical pathology

In our pathologic observation of the cerebral cortex including the neocortex, hippocampus, and limbic cortex in 43 Japanese patients with MM1-type sporadic Creutzfeldt-Jakob disease, the earliest pathologic finding was spongiform change and next was gliosis. Subsequently, neuropil rarefaction appeared, followed by neuron loss. On the basis of these observations, we propose the following cortical pathologic staging: Stage I, spongiform change; Stage II, hypertrophic astrocytosis; Stage III, neuropil rarefaction; Stage IV, neuron loss; Stage V, status spongiosus; and Stage VI, large cavity formation. We also suggest a more simple staging classification: Stages I and II, mild; Stages III and IV, moderate; and Stages V and VI, severe involvement. Based on statistical analysis of the cases, strong correlation coefficients were obtained between the neocortical and limbic pathologic stage and both total disease duration and brain weight. We estimated that the first observation times of cortical hyperintensity on diffusion-weighted images of magnetic resonance imaging, myoclonus, and periodic sharp wave complexes on the electroencephalogram approximately correspond to the early phase of Stage II of the neocortex. The time to reach the akinetic mutism state approximately corresponds to the middle phase of Stage II of the neocortex. Therefore, we think that approximate clinical manifestations at death, total disease duration, and brain weight can be estimated according to the pathologic stage of the neocortex or limbic cortex. Panencephalopathic-type pathology appeared approximately 12 months after disease onset, and this time approximately corresponds to the middle phase of Stage III of the neocortex.

REGION-SPECIFIC NEURON AND SYNAPSE LOSS IN THE HIPPOCAMPUS OF APPSL/PS1 KNOCK-IN MICE

Transgenic mouse models with knock-in (KI) expression of human mutant amyloid precursor protein (APP) and/or human presenilin 1 (PS1) may be helpful to elucidate the cellular consequences of APP and PS1 misprocessing in the aging brain. Age-related alterations in total numbers of neurons and in numbers of synaptophysin-immunoreactive presynaptic boutons (SIPB), as well as the amyloid plaque load were analyzed in the hippocampal dentate gyrus (DG), CA3, and CA1-2 of 2- and 10-month-old APPSL/PS1 homozygous KI, APPSL (expressing human mutant APP751 carrying the Swedish [K670N/M671L] and London [V717I] mutations under Thy-1 promoter), and PS1 homozygous KI mice (expressing human PS1 mutations [M233T and L235P]). APPSL/PS1 homozygous KI mice, but neither APPSL mice nor PS1 homozygous KI mice, showed substantial age-related loss of neurons (-47.2%) and SIPB (-22.6%), specifically in CA1-2. PS1 homozygous KI mice showed an age-related increase in hippocampal granule cell numbers (+37.9%). Loss of neurons and SIPB greatly exceeded the amount of local extracellular Aβ aggregation and astrocytes, whereas region-specific accumulation of intraneuronal Aβ preceded neuron and synapse loss. An age-related increase in the ratio of SIPB to neuron numbers in CA1-2 of APPSL/PS1 homozygous KI mice was suggestive of compensatory synaptic plasticity. These findings indicate a region-selectivity in intra- and extraneuronal Aβ accumulation in connection with neuron and synapse loss in the hippocampus of APPSL/PS1 homozygous KI mice.