Neurodegenerative Effects Research Articles

Differences in amyloid-β and tau/p-tau deposition in blood-injected mouse brains using micro-syringe to mimic traumatic brain microhemorrhages

BackgroundCerebral microbleeds (CMBs) due to traumatic brain injuries (TBI) have been shown to lead to cognitive decline and impairment. CMBs caused by TBI may be associated with pathophysiological mechanisms involving inflammation and the accumulation of amyloid-β (Aβ), tau, and phosphorylated tau (p-tau), contributing to cognitive abnormalities. However, their relationships remain unclear. ObjectivesTo test our hypothesis that Aβ, tau, and p-tau are accumulated and regulated separately in mice with injuries imitating CMBs from TBI, we studied. MethodsSeven-week-old C57BL/6 male mice were injected with 15 μL of heparinized autologous blood or saline by micro-syringe into the front lobe. Expression profiles and regulation of Aβ, tau, and p-tau were assessed immunohistochemically over time. ResultsOn day 7 after blood injection, Iba-1+ and S100B+ cells in damaged cortex adjacent to the injection site were higher than saline injection group and non-injected sham. On days 3–14, Aβ deposition were gradually increased but normalized by day 28. In contrast, tau/p-tau deposition gradually increased during days 14–28 and dispersed along the corticomedullary junction adjacent to hem deposits, indicating different expression profiles from Aβ. Deposits of Aβ, but not tau/p-tau, were phagocytosed by CD163+ macrophages increased by Gc-protein macrophage-activating factor during days 7–28, suggesting different mechanisms of deposition and regulation between Aβ and tau/p-tau. ConclusionDeposition and regulation differ between Aβ and tau/p-tau in mice with injuries mimicking CMBs from TBI. Further clarification of relationships between the pathologies of cognitive impairment and their neurodegenerative consequences is needed.

Tissue stretching is a confounding factor for the evaluation of neurodegeneration in the fast-ageing killifish.

The fast-ageing killifish has gained increasing attention as a promising gerontology model to study age-related processes and neurodegeneration. Interestingly, it is the first vertebrate model organism that shows physiological neuron loss at old age in its central nervous system (CNS), including its brain and retina. However, the fact that the killifish brain and retina are ever-growing tissues complicates studying neurodegenerative events in aged fish. Indeed, recent studies showed that the method of tissue sampling, either using sections or whole-organs, has a large effect on the observed cell densities in the fast-expanding CNS. Here, we elaborated on how these two sampling methods affect neuronal counts in the senescent retina and how this tissue grows upon ageing. Analysis of the different retinal layers in cryosections revealed age-dependent reduction in cellular density but evaluation of whole-mount retinas did not detect any neuron loss, as a result of an extremely fast retinal expansion with age. Using BrdU pulse-chase experiments, we showed that the young adult killifish retina mainly grows by cell addition. However, with increasing age, the neurogenic potency of the retina declines while the tissue keeps on growing. Further histological analyses revealed tissue stretching, including cell size increase, as the main driver of retinal growth at old age. Indeed, both cell size and inter-neuronal distance augment with ageing, thereby decreasing neuronal density. All in all, our findings urge the 'ageing science' community to consider cell quantification bias and employ tissue-wide counting methods to reliably quantify neuronal numbers in this unique gerontology model.

Intracellular DAMPs in Neurodegeneration and Their Role in Clinical Therapeutics.

Neuroinflammation is the major implication of neurodegeneration. This is a complex process which initiates from the cellular injury triggering the innate immune system which gives rise to damage-associated molecular patterns (DAMPs) which are also recognized as endogenous danger indicators. These originate from various compartments of the cell under pathological stimulus. These are very popular candidates having their origin in the intracellular compartments and organelles of the cell and may have their site of action itself in the intracellular or at the extracellular spaces. Under the influence of the pathological stimuli, they interact with the pattern-recognition receptor to initiate their pro-inflammatory cascade followed by the cytokine release. This provides a good opportunity for diagnostic and therapeutic interventions creating better conditions for repair and reversal. Since the major contributors arise from the intracellular compartment, in this review, we have attempted to focus on the DAMP molecules arising from the intracellular compartments and their specific roles in the neurodegenerative events explaining their downstream mediators and signaling. Moreover, we have tried to cover the latest interventions in terms of DAMPs as clinical biomarkers which can assist in detecting the disease and also target it to reduce the innate-immune activation response which can help in reducing the sterile neuroinflammation having an integral role in the neurodegenerative processes.

Correlative Cellular Mass Spectrometry Imaging and Amperometry Show Dose Dependent Changes in Lipid Composition and Exocytosis.

Aberrant functioning of the proteasome has been associated with crucial pathologic conditions including neurodegeneration. Yet, the complex underlying causes at the cellular level remain unclear and there are conflicting reports of neuroprotective to neurodegenerative effects of proteasomal inhibitors such as lactacystin that are utilised as models for neurodegenerative diseases. The conflicting results may be associated with different dose regimes of lactacystin and hence we have performed a dose dependent study of the effects of lactacystin to identify concurrent changes in the cell membrane lipid profile and the dynamics of exocytosis using a combination of surface sensitive mass spectrometry and single cell amperometry. Significant changes of negatively charged lipids were associated with different lactacystin doses that showed a weak correlation with exocytosis while changes in PE and PE-O lipids showed dose dependent changes correlated with initial pore formation and total release of vesicle content respectively.

Correlative Cellular Mass Spectrometry Imaging and Amperometry Show Dose Dependent Changes in Lipid Composition and Exocytosis

AbstractAberrant functioning of the proteasome has been associated with crucial pathologic conditions including neurodegeneration. Yet, the complex underlying causes at the cellular level remain unclear and there are conflicting reports of neuroprotective to neurodegenerative effects of proteasomal inhibitors such as lactacystin that are utilised as models for neurodegenerative diseases. The conflicting results may be associated with different dose regimes of lactacystin and hence we have performed a dose dependent study of the effects of lactacystin to identify concurrent changes in the cell membrane lipid profile and the dynamics of exocytosis using a combination of surface sensitive mass spectrometry and single cell amperometry. Significant changes of negatively charged lipids were associated with different lactacystin doses that showed a weak correlation with exocytosis while changes in PE and PE−O lipids showed dose dependent changes correlated with initial pore formation and total release of vesicle content respectively.

No signs of neurodegenerative effects in 15q11.2 BP1-BP2 copy number variant carriers in the UK Biobank

The 15q11.2 BP1-BP2 copy number variant (CNV) is associated with altered brain morphology and risk for atypical development, including increased risk for schizophrenia and learning difficulties for the deletion. However, it is still unclear whether differences in brain morphology are associated with neurodevelopmental or neurodegenerative processes. This study derived morphological brain MRI measures in 15q11.2 BP1-BP2 deletion (n = 124) and duplication carriers (n = 142), and matched deletion-controls (n = 496) and duplication-controls (n = 568) from the UK Biobank study to investigate the association with brain morphology and estimates of brain ageing. Further, we examined the ageing trajectory of age-affected measures (i.e., cortical thickness, surface area, subcortical volume, reaction time, hand grip strength, lung function, and blood pressure) in 15q11.2 BP1-BP2 CNV carriers compared to non-carriers. In this ageing population, the results from the machine learning models showed that the estimated brain age gaps did not differ between the 15q11.2 BP1-BP2 CNV carriers and non-carriers, despite deletion carriers displaying thicker cortex and lower subcortical volume compared to the deletion-controls and duplication carriers, and lower surface area compared to the deletion-controls. Likewise, the 15q11.2 BP1-BP2 CNV carriers did not deviate from the ageing trajectory on any of the age-affected measures examined compared to non-carriers. Despite altered brain morphology in 15q11.2 BP1-BP2 CNV carriers, the results did not show any clear signs of apparent altered ageing in brain structure, nor in motor, lung or heart function. The results do not indicate neurodegenerative effects in 15q11.2 BP1-BP2 CNV carriers.

Reconsidering the role of blood-brain barrier in Alzheimer's disease: From delivery to target.

The existence of a selective blood-brain barrier (BBB) and neurovascular coupling are two unique central nervous system vasculature features that result in an intimate relationship between neurons, glia, and blood vessels. This leads to a significant pathophysiological overlap between neurodegenerative and cerebrovascular diseases. Alzheimer's disease (AD) is the most prevalent neurodegenerative disease whose pathogenesis is still to be unveiled but has mostly been explored under the light of the amyloid-cascade hypothesis. Either as a trigger, bystander, or consequence of neurodegeneration, vascular dysfunction is an early component of the pathological conundrum of AD. The anatomical and functional substrate of this neurovascular degeneration is the BBB, a dynamic and semi-permeable interface between blood and the central nervous system that has consistently been shown to be defective. Several molecular and genetic changes have been demonstrated to mediate vascular dysfunction and BBB disruption in AD. The isoform ε4 of Apolipoprotein E is at the same time the strongest genetic risk factor for AD and a known promoter of BBB dysfunction. Low-density lipoprotein receptor-related protein 1 (LRP-1), P-glycoprotein, and receptor for advanced glycation end products (RAGE) are examples of BBB transporters implicated in its pathogenesis due to their role in the trafficking of amyloid-β. This disease is currently devoid of strategies that change the natural course of this burdening illness. This unsuccess may partly be explained by our misunderstanding of the disease pathogenesis and our inability to develop drugs that are effectively delivered to the brain. BBB may represent a therapeutic opportunity as a target itself or as a therapeutic vehicle. In this review, we aim to explore the role of BBB in the pathogenesis of AD including the genetic background and detail how it can be targeted in future therapeutic research.

A Medicinal Chemistry Perspective on Excitatory Amino Acid Transporter 2 Dysfunction in Neurodegenerative Diseases.

The excitatory amino acid transporter 2 (EAAT2) plays a key role in the clearance and recycling of glutamate - the major excitatory neurotransmitter in the mammalian brain. EAAT2 loss/dysfunction triggers a cascade of neurodegenerative events, comprising glutamatergic excitotoxicity and neuronal death. Nevertheless, our current knowledge regarding EAAT2 in neurodegenerative diseases, such as amyotrophic lateral sclerosis (ALS) and Alzheimer's disease (AD), is restricted to post-mortem analysis of brain tissue and experimental models. Thus, detecting EAAT2 in the living human brain might be crucial to improve diagnosis/therapy for ALS and AD. This perspective article describes the role of EAAT2 in physio/pathological processes and provides a structure-activity relationship of EAAT2-binders, bringing two perspectives: therapy (activators) and diagnosis (molecular imaging tools).

Investigating the Neuroprotective and Neuroregenerative Effect of Trazodone Regarding Behavioral Recovery in a BL6C57 Mice Stroke Model.

Stroke is a major cause of death and disability worldwide. Between 1990 and 2010, its global burden increased notably with reference to the absolute number of incident events, number of deaths, and disability-adjusted life-years lost. Trazodone is a triazolopyridine derivative that was approved for more than 40 years as monotherapy or in combination with other antidepressant drugs for the treatment of major depressive disorder in adult patients. The aim was investigated if trazodone can improve behavioural outcome after stroke in a mice model of middle cerebral artery occlusion (MCAo) due to the potential neuroprotective and neurodegenerative effects by using three behavioural tests: adhesive tape test, beam test and hole board test. Trazodone administration show modest improvements regarding the motor-sensorial function after stroke especially in the acute post-stroke phase in aged and young animals. The antidepressant effect of the drug was observed in the post-stroke period in aged animals and to a lesser extent in young animals. Future research is needed to evaluate the effects of trazodone at the cellular level to be sure that it has no benefit in stroke patients who do not suffer from depression.

Perfluorooctanoic acid exposure and its neurodegenerative consequences in C57BL6/J mice.

Perfluorooctanoic acid (PFOA) is a member of Per- and polyfluoroalkyl substances (PFASs), an industrial pollutant that has been produced for decades and widely used in various industries. Accumulation of this compound in the environment and body of organisms led to increased concerns about this compound. The toxic effects of PFOA on the nervous system are unknown yet. We aimed to assess the myelination and neurogenesis in brain tissue. In this study, PFOA at doses of 1, 5, 10, and 20mg/kg were injected intraperitoneally into C57BL/6J mice for 14days, and the myelin content, CD4 + and CD8 + cell infiltration to brain regions were evaluated. Also, bromodeoxyuridine (BrdU) labeling was performed to compare neurogenesis among the groups. Luxol Fast Blue (LFB) staining revealed a significant decrease in myelin content in both sex at high concentrations (p < 0.001). The BrdU incorporation changes were observed in both sexes especially females which was highly related to the dose of PFOA and region of the brain. The infiltration rates of CD4 + and CD8 + cells to the brain were shown to be decreased; meanwhile the lymphocyte count was not significantly changed among groups over time and vice versa for the monocyte and neutrophils. Our results showed that PFOA had a negative impact on neurogenesis and the myelination process through the specific region of the brain depending on the dose and sex. Also, PFOA could disturb the number of CD4 + and CD8 + cells infiltrating the brain, which plays a crucial role in neurogenesis, leading to toxicity and neurological abnormalities. It seems that more research is needed to determine the exact mechanisms of PFOA neurotoxicity and its long-term behavioral consequences.

Tracking the Neurodegeneration and Behavioral Changes in Mice Model of Prodromal Phase Alpha-Synucleinopathy

&#x0D; &#x0D; &#x0D; Background:&#x0D; The aggregation of misfolded alpha-synuclein (αSyn) has been shown to cause neurodegeneration in a mouse model and lead to behavioral changes. While others have examined end-stage (after neurodegeneration has set in) behavioral changes in mice after αSyn preformed fibrils (PFF) seeding, the precise timeline of circuit changes and associated behavioral deficits during the prodromal phase of synucleinopathic spread is poorly understood. We set out to measure and characterize the extent to which behavior is affected by primary motor cortex (M1) PFF seeding in mice.&#x0D; Experimental Design:&#x0D; We quantified the neuronal cell body density at M1 layers 2/3 and 5 using immunohistochemistry cell assays to determine if there were neurodegenerative effects under the PFF seeding strategy. Furthermore, using Bonsai, a visual reactive programming language, we tracked the behavior of the PFF seeded mice for exploratory motives, decreases in which can be used to show cognitive decline. To further ascertain the effect of αSyn on vulnerable excitatory pathways in the cortex, we performed prodromal injections of αSyn PFF into the M1 of ChATCre mice along with projection tracing in the basal forebrain.&#x0D; Results:&#x0D; During the first 3 months following PFF seeding, the density of neuronal cell bodies in M1 layers 2/3 and 5 remains unchanged in PFF seeded mice compared to control mice. The exploratory index of PFF seeded mice was comparable to that of control mice. These results suggest insignificant neurodegeneration and behavioral change in the first 3 months following PFF seeding.&#x0D; Conclusion:&#x0D; Work done previously in this lab tracking the spread of PFF in M1 shows significant spread of αSyn for 3 months following prodromal injection. The results from this work show that there is little neurodegeneration or behavioral change in that timeframe despite the significant spread of αSyn. Future work hinges on further probing this phenomenon.&#x0D; &#x0D; &#x0D;

Glial Cultures Differentiated from iPSCs of Patients with PARK2-Associated Parkinson's Disease Demonstrate a Pro-Inflammatory Shift and Reduced Response to TNFα Stimulation.

Parkinson's disease (PD) is the second most common neurodegenerative diseases characterized by progressive loss of midbrain dopaminergic neurons in the substantia nigra. Mutations in the PARK2 gene are a frequent cause of familial forms of PD. Sustained chronic neuroinflammation in the central nervous system makes a significant contribution to neurodegeneration events. In response to inflammatory factors produced by activated microglia, astrocytes change their transcriptional programs and secretion profiles, thus acting as immunocompetent cells. Here, we investigated iPSC-derived glial cell cultures obtained from healthy donors (HD) and from PD patients with PARK2 mutations in resting state and upon stimulation by TNFα. The non-stimulated glia of PD patients demonstrated higher IL1B and IL6 expression levels and increased IL6 protein synthesis, while BDNF and GDNF expression was down-regulated when compared to that of the glial cells of HDs. In the presence of TNFα, all of the glial cultures displayed a multiplied expression of genes encoding inflammatory cytokines: TNFA, IL1B, and IL6, as well as IL6 protein synthesis, although PD glia responded to TNFα stimulation less strongly than HD glia. Our results demonstrated a pro-inflammatory shift, a suppression of the neuroprotective gene program, and some depletion of reactivity to TNFα in PARK2-deficient glia compared to glial cells of HDs.

Evaluation of anti-Alzheimer activity of Echinacea purpurea extracts in aluminum chloride-induced neurotoxicity in rat model

Alzheimer's disease (AD) is one of the neurodegenerative illnesses that impair individual life & increase the demand for caregivers with no available curative medication right now. Therefore, there is a growing concern about employing herbal medicine to limit AD progression & improve patients' life quality, thus potentiating its add-on therapy. In addition, herbs are cost-effective & accessible with nearly no side effects. In the same vein, our study aimed to investigate the potency of Echinacea purpurea (EP) flower extracts to ameliorate the neurodegenerative effect of Aluminum chloride (AlCl3) in a rat model. Moreover, mechanistic studies, including impact on the cholinesterase activity, redox status, inflammatory mediators, behavior performance, glucose level & histopathology, were carried on. Our results showed that 250 mg/kg of Aqueous (AQ) & Alcoholic (AL) extracts of EP inhibited cholinesterase, restored oxidative balance, down-regulated IL-6 & TNF-α cytokines & improved behavior performance in vivo that was reflected in the brain picture by decreasing neuronal degeneration & amyloid plaques in cerebral cortex & hippocampus. The potency of both extracts was compared to reference drugs & AlCl3 positive control group. The AQ extract showed greater potency against COX-1, COX-2 & α-amylase in vitro, while the AL extract was more potent against cholinesterase in vitro, inflammatory cytokines, behavior & pathological improvement in vivo. Conclusively EP overcame AlCl3-induced neurobehavioral toxicity in the rat model via different pathways, which support its regular administration to postpone progressive neural damage in AD patients.

A Genetic Validation of the Neurodegeneration Biomarkers Tau-A and Tau-C - A Mendelian Randomization Study.

Disease modifying treatments for dementia are only just surfacing, and their development is still significantly hindered by the lack of validated tools for identification of subjects with subclinical disease. Much interest has been taken in developing accessible non-invasive serum biomarkers of neurodegeneration. Recent studies have identified caspase-3-cleaved tau (Tau-C), and ADAM-10 cleaved tau (Tau-A) as possible markers of preclinical neurodegenerative disease. To explore if serum levels of Tau-A and Tau-C change as a consequence of neurodegeneration. Cohort study with measurement of biomarkers and genome sequencing at baseline with follow-up after an average of 14 years. Postmenopausal Danish women from the Prospective Epidemiological Risk Factor (PERF) cohort (n=4968) Methods: Genotyping data was used to perform a Mendelian randomization analysis of serum levels of Tau-A and Tau-C in relation to a diagnosis of dementia at follow-up. A dementia diagnosis was defined as a composite of an all-cause dementia diagnosis derived from the Danish National Health registries, a self-reported diagnosis of dementia and/or cognitive test scores suggestive of dementia. Serum levels of Tau-A and Tau-C were measured blinded in samples from baseline in a CAP certified lab. The association with dementia was assessed using bi-directional one- and two- sample Mendelian randomization. A lead single nucleotide polymorphism (SNP) was identified for Tau-A (rs10414043) and Tau-C (rs429358), respectively were identified. Both were located in the APOE/C1 cluster on chromosome 19. APOE and EPOC1 variants were associated with lower levels of Tau-A and Tau-C levels - effect size -0.13, 95%CI [-0.17 - -0.09] log2 (ng/mL), p=7.05e-11 for rs10414043 association with Tau-A and effect size -0.12, 95%CI [-0.15 - -0.08] log2 (ng/mL), p=2e-11 for rs429358 association with Tau-C. When incorporating genetic data from a larger genetic study we found that Alzheimer's disease was marginally associated with a decreased Tau-A and Tau-C levels (Odds Ratio 0.97, 95%CI [0.93 - 1.00]. No association was found in the forward Mendelian randomization analysis. By combining genotype data with serum measurements of the novel biomarkers Tau-A and Tau-C, we conclude that Tau-A and Tau-C levels change because of neurodegeneration. We also conclude that lower serum-values of the biomarkers are associated with the presence of genetic variants commonly found in individuals suffering from late-onset Alzheimer's Dementia. These findings add to the growing data pointing towards Tau-A and Tau-C as valuable biomarkers for neurodegeneration.

Evolutionary and genomic perspectives of brain aging and neurodegenerative diseases.

This chapter utilizes genomic concepts and evolutionary perspectives to further understand the possible links between typical brain aging and neurodegenerative diseases, focusing on the two most prevalent of these: Alzheimer's disease and Parkinson's disease. Aging is the major risk factor for these neurodegenerative diseases. Researching the evolutionary and molecular underpinnings of aging helps to reveal elements of the typical aging process that leave individuals more vulnerable to neurodegenerative pathologies. Very little is known about the prevalence and susceptibility of neurodegenerative diseases in nonhuman species, as only a few individuals have been observed with these neuropathologies. However, several studies have investigated the evolution of lifespan, which is closely connected with brain size in mammals, and insights can be drawn from these to enrich our understanding of neurodegeneration. This chapter explores the relationship between the typical aging process and the events in neurodegeneration. First, we examined how age-related processes can increase susceptibility to neurodegenerative diseases. Second, we assessed to what extent neurodegeneration is an accelerated form of aging. We found that while at the phenotypic level both neurodegenerative diseases and the typical aging process share some characteristics, at the molecular level they show some distinctions in their profiles, such as variation in genes and gene expression. Furthermore, neurodegeneration of the brain is associated with an earlier onset of cellular, molecular, and structural age-related changes. In conclusion, a more integrative view of the aging process, both from a molecular and an evolutionary perspective, may increase our understanding of neurodegenerative diseases.

Downregulation of the Astroglial Connexin Expression and Neurodegeneration after Pilocarpine-Induced Status Epilepticus

Astrocytic networks and gap junctional communication mediated by connexins (Cxs) have been repeatedly implicated in seizures, epileptogenesis, and epilepsy. However, the effect of seizures on Cx expression is controversial. The present study focused on the response of Cxs to status epilepticus (SE), which is in turn an epileptogenic insult. The expression of neuronal Cx36 and astrocytic Cx30 and Cx43 mRNAs was investigated in the brain of rats in the first day after pilocarpine-induced SE. In situ hybridization revealed a progressive decrease in Cx43 and Cx30 mRNA levels, significantly marked 24 h after SE onset in neocortical areas and the hippocampus, and in most thalamic domains, whereas Cx36 mRNA did not exhibit obvious changes. Regional evaluation with quantitative real-time-RT-PCR confirmed Cx43 and Cx30 mRNA downregulation 24 h after SE, when ongoing neuronal cell death was found in the same brain regions. Immunolabeling showed at the same time point marked a decrease in Cx43, microglia activation, and interleukin-1β induction in some microglial cells. The data showed a transient downregulation of astroglial Cxs in the cortical and thalamic areas in which SE triggers neurodegenerative events in concomitance with microglia activation and cytokine expression. This could potentially represent a protective response of neuroglial networks to SE-induced acute damage.

Impact of Clinical Association Between Gout and Dementia: A Nationwide Population-Based Cohort Study in Korea.

Hyperuricemia might have neuroprotective or neurodegenerative effects on dementia via oxidative stress or inflammatory response regulation. Few studies have explored the association of hyperuricemia or gout with dementia. This retrospective cohort study aimed to investigate the association between gout and dementia in Korea. Altogether, 5,052 gout patients and 25,260 age- and sex-matched controls were selected from the National Health Insurance Service (NHIS)-National Sample Cohort database. The incidence and risk of dementia were evaluated by reviewing the NHIS record. We also performed a subgroup analysis according to age group (age <65 or ≥65 years) using the standard age of 65 years for elderly and nonelderly groups and sex. During follow-up, 81 and 558 participants in the gout and control cohorts developed dementia, respectively. The mean follow-up duration was 4.38 years in gout patients and 4.94 years in controls. Gout patients had a hazard ratio (HR) of 0.79 for overall dementia (95% confidence interval [95% CI] 0.62-1.00) and significantly lower Alzheimer's disease risk (HR 0.73 [95% CI 0.54-0.98]) after adjusting for age, sex, household income, and comorbidities. In subgroup analysis stratified by age and sex, the inverse association between gout and the risk of overall dementia (HR 0.71 [95% CI 0.52-0.97]) and Alzheimer's disease (HR 0.67 [95% CI 0.46-0.97]) were observed in the elderly male group. On the other hand, age- and sex-adjusted analysis showed that the HR for vascular dementia of gout patients was 2.31 (95% CI 1.02-5.25) in the nonelderly male group. Gout decreased the risk of incident Alzheimer's disease-type dementia, especially in elderly patients. The association between gout and dementia risk may differ according to age and disease duration.

White matter associated microglia in Alzheimer’s disease

AbstractBackgroundWhite matter is composed of mostly myelinated axons that connect neurons from different brain regions into functional circuits. Aging results in both grey and white matter degeneration, but the specific microglial responses to the damage is unknown. Strikingly, in Alzheimer’s disease white matter alterations occur early in the disease course. Here, we analyzed microglia responses in the white matter in aging rodents and models of Alzheimer’s disease.MethodWe dissociated grey and white matter tracts and isolated microglia from young and aged mice and performed single cell RNA sequencing. To compare aging and neurodegeneration effects on microglia, we isolated microglia from a transgenic Alzheimer’s disease mouse model, and to study signaling pathways we included aged Trem2 and Apoe knockout mice into the analysis. Validation and characterization of the phenotypes occurred by in situ hybridization, immunohistochemistry, correlated light and electron microscopy.ResultsUsing single‐cell RNA sequencing from white and grey matter separately, we identified white matter associated microglia, which shared distinct parts of the disease‐associated microglia (DAM) gene signature. Within the white matter, microglia frequently cluster in nodules, where they are engaged in clearing degenerated myelin, depending on Trem2 signaling. In the aged brain, white matter associated microglia form independently of ApoE, which is in contrast to mouse models of Alzheimer’s disease, in which microglia with white matter associated microglia gene signature are generated prematurely and in an ApoE‐dependent pathway similar to DAM.ConclusionWe propose that white matter associated microglia represent a protective metabolic response, required to clear the increasing amounts of myelin debris that accumulate during aging and AD. We speculate that premature formation of white matter associated microglia in AD may contribute to the development of neurodegenerative disease, possibly by attrition of microglia function leading to accumulation of toxic protein or lipid species within the brain.

Reaction of retinal macroglia to inflammatory damage

AbstractSepsis is a multi‐organ dysfunction caused by the host uncontrolled inflammatory response to an infection, mediated by proinflammatory cytokines and oxygen free radicals. LPS is unable to trespass the Blood–Brain‐Barrier (BBB), but it can act on the TLR4 (Toll‐Like Receptor 4) receptor, found in the endothelium, causing the secretion of cytokines and chemokines that lead to the activation of glial cells. On the other hand, cisplatin (CISP), also called Cis‐dichlorodiammineplatinum [II], is a heavy metal antineoplastic agent widely employed in the treatment of different forms of cancer. Neurotoxicity has been reported as some of the adverse effects resulting from CISP administration. CISP alters intracellular signal transduction pathways that, in the end, provoke apoptosis through different mechanisms such as the generation of reactive oxygen species, DNA alterations, mitochondrial and/or endoplasmic reticulum dysfunction, and the production of proinflammatory cytokines and chemokines. Both sepsis and CISP cause a systemic damage that can result in brain impairments affecting different areas of the Central Nervous System (CNS), but to our knowledge, the effects of the systemic damage over the retinal cell populations, and specially on macroglial cells, have not been studied in detail. We employed two animal models using male Wistar rats: (1) a model of sepsis based on the systemic administration of bacterial lipopolysaccharide (LPS, 10 mg/kg, i.p.), or its vehicle; to induce a systemic inflammatory response; (2) a model of cisplatin based on the administration of a daily single dose of cisplatin (CISP, 5 mg/kg, i.p.) or its vehicle for 5 consecutive days until sacrifice in order to induce neurotoxicity. Animals were transcardiacally perfused, eyes were extracted, and retinal sections were used for immunohistochemical assays, where Brn3a and GFAP were employed to stain retinal ganglion cells and macroglial cells respectively. LPS induced a reduction in the number of Brn3a+ cells in the whole retina, neurodegenerative effects being more critical in the nasal inferior retina; and provoked a generalized increase in GFAP expression, specially in the nasal and central regions of the retina. Preliminary results indicate that the CISP administration leads to a reduction in the total number of Brn3a+ cells in the retina; and CISP may induce a generalized reduction of GFAP+ cells mainly within the nasal and temporal inferior retina. Taken together, we have provided evidence of retinal damage following the systemic inflammatory processes caused by LPS and CISP administration, which affects macroglial cells, with an increased or decreased GFAP expression depending on the activation pathway of the neuroinflammatory response. This dysregulation of the macroglial response could lead to a significant diminishment of the retinal ganglion cells of the retina, causing an irreversible loss of vision.Supported by Complutense University of Madrid, UCM Research Group: 951579.Keywords: LPS‐induced sepsis, cisplatin, ganglionar and macroglial retinal cells, inflammation.

Genetically Proxied Angiotensin‐Converting‐Enzyme Inhibition is Potentially Causal for Alzheimer Disease: A Mendelian Randomization Study

AbstractBackgroundAngiotensin‐converting enzyme (ACE) has been implicated in the pathogenesis of Alzheimer disease (AD), in which ACE plays a role in metabolizing Amyloid Beta (AB). Genetic variants in the ACE locus have also been associated with AD. The effect of ACE inhibitors on AD risk remains unclear. We sought to investigate the potential causal relationship between ACE inhibition and AD and other neurodegenerative disorders using a mendelian randomization (MR) approach.MethodA genetic proxy for ACE inhibition (MR exposure) was generated using 17 single nucleotide polymorphisms (SNPs) in the ACE gene that were previously associated with lower ACE blood levels in a candidate gene study (n = 4,147; adjusted‐P &lt; 0.05). Summary genome‐wide association study (GWAS) statistics for AD (111,326 cases, 677,663 controls), Frontotemporal dementia (FTD) (3526 cases, 9402 controls) and Lewy body dementia (LBD) (cases 2591, controls 4027) were used as proxies for the MR outcomes. Inverse weighted variance MR was performed to test the potentially causal relationship between the exposure and outcomes. Sensitivity analyses were completed to test the robustness of the results.ResultACE inhibition was significantly associated with increased risk of AD (OR = 1.07, P = 0.0000005); with robust and consistent effects in all sensitivity analyses. Using leave one out method; rs4343 (A allele) showed the strongest effect. rs4343 is in mild linkage disequilibrium with the SNP associated at genome wide significant level with AD rs4277405 (R2 0.35). Rerunning the MR analysis on the AD cohort after removing rs4343 continued to show significant results (OR = 1.04, P = 0.02). ACE inhibition was also associated with increased risk for FTD (OR = 1.16, P = 0.009), but the findings were not robust in some sensitivity analyses, possibly due to lower sample size of FTD cohort. ACE inhibition was not associated with LBD.ConclusionThis is the first study to provide robust genetic evidence for the potentially causal relationship between ACE inhibition in the blood and the diagnosis of AD. These results should encourage further investigation of the potential neurodegenerative side effects of ACE inhibition; and further suggest ACE related pathways as pharmacological targets for treatment and/or prevention of AD.