BACE1 and SCD1 are associated with neurodegeneration

Introduction

Proteolytic processing of amyloid protein precursor by β-site secretase enzyme (BACE1) is dependent on the cellular lipid composition and is affected by endomembrane trafficking in dementia and Alzheimer's disease (AD). Stearoyl-CoA desaturase 1 (SCD1) is responsible for the synthesis of fatty acid monounsaturation (MUFAs), whose accumulation is strongly associated with cognitive dysfunction.

Methods

In this study, we analyzed the relationship between BACE1 and SCD1 in vivo and in vitro neurodegenerative models and their association in familial AD (FAD), sporadic AD (SAD), and cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) using microscopy, biochemical, and mass SPECT approach.

Results

Our findings showed that BACE1 and SCD1 immunoreactivities were increased and colocalized in astrocytes of the hippocampus in a rat model of global cerebral ischemia (2-VO). A synergistic effect of double BACE1/SCD1 silencing on the recovery of motor and cognitive functions was obtained. This neuroprotective regulation involved the segregation of phospholipids (PLs) associated with polyunsaturated fatty acids in the hippocampus, cerebrospinal fluid, and serum. The double silencing in the sham and ischemic groups was stronger in the serum, inducing an inverse ratio between total phosphatydilcholine (PC) and lysophosphatidylcholine (LPC), represented mainly by the reduction of PC 38:4 and PC 36:4 and an increase in LPC 16:0 and LPC 18:0. Furthermore, PC 38:4 and PC:36:4 levels augmented in pathological conditions in in vitro AD models. BACE1 and SCD1 increases were confirmed in the hippocampus of FAD, SAD, and CADASIL.

Conclusion

Therefore, the findings suggest a novel convergence of BACE-1 and SCD1 in neurodegeneration, related to pro-inflammatory phospholipids.

Alzheimer's Disease: An Updated Overview of Its Genetics

Alzheimer's disease (AD) is the most common neurodegenerative disease in the world. It is classified as familial and sporadic. The dominant familial or autosomal presentation represents 1-5% of the total number of cases. It is categorized as early onset (EOAD; <65 years of age) and presents genetic mutations in presenilin 1 (PSEN1), presenilin 2 (PSEN2), or the Amyloid precursor protein (APP). Sporadic AD represents 95% of the cases and is categorized as late-onset (LOAD), occurring in patients older than 65 years of age. Several risk factors have been identified in sporadic AD; aging is the main one. Nonetheless, multiple genes have been associated with the different neuropathological events involved in LOAD, such as the pathological processing of Amyloid beta (Aβ) peptide and Tau protein, as well as synaptic and mitochondrial dysfunctions, neurovascular alterations, oxidative stress, and neuroinflammation, among others. Interestingly, using genome-wide association study (GWAS) technology, many polymorphisms associated with LOAD have been identified. This review aims to analyze the new genetic findings that are closely related to the pathophysiology of AD. Likewise, it analyzes the multiple mutations identified to date through GWAS that are associated with a high or low risk of developing this neurodegeneration. Understanding genetic variability will allow for the identification of early biomarkers and opportune therapeutic targets for AD.

Autophagy: A Key Regulator of Homeostasis and Disease: An Overview of Molecular Mechanisms and Modulators

Autophagy is a highly conserved lysosomal degradation pathway active at basal levels in all cells. However, under stress conditions, such as a lack of nutrients or trophic factors, it works as a survival mechanism that allows the generation of metabolic precursors for the proper functioning of the cells until the nutrients are available. Neurons, as post-mitotic cells, depend largely on autophagy to maintain cell homeostasis to get rid of damaged and/or old organelles and misfolded or aggregated proteins. Therefore, the dysfunction of this process contributes to the pathologies of many human diseases. Furthermore, autophagy is highly active during differentiation and development. In this review, we describe the current knowledge of the different pathways, molecular mechanisms, factors that induce it, and the regulation of mammalian autophagy. We also discuss its relevant role in development and disease. Finally, here we summarize several investigations demonstrating that autophagic abnormalities have been considered the underlying reasons for many human diseases, including liver disease, cardiovascular, cerebrovascular diseases, neurodegenerative diseases, neoplastic diseases, cancers, and, more recently, infectious diseases, such as SARS-CoV-2 caused COVID-19 disease.

Neurovascular dysfunction and vascular amyloid accumulation as early events in Alzheimer's disease

Alzheimer's disease (AD) is clinically characterized by a progressive loss of cognitive functions and short-term memory. AD patients present two distinctive neuropathological lesions: neuritic plaques and neurofibrillary tangles (NFTs), constituted of beta-amyloid peptide (Aβ) and phosphorylated and truncated tau proteins. Aβ deposits around cerebral blood vessels (cerebral amyloid angiopathy, CAA) is a major contributor to vascular dysfunction in AD. Vascular amyloid deposits could be early events in AD due to dysfunction in the neurovascular unit (NVU) and the blood-brain barrier (BBB), deterioration of the gliovascular unit, and/or decrease of cerebral blood flow (CBF). These pathological events can lead to decreased Aβ clearance, facilitate a neuroinflammatory environment as well as synaptic dysfunction and, finally, lead to neurodegeneration. Here, we review the histopathological AD hallmarks and discuss the two-hit vascular hypothesis of AD, emphasizing the role of neurovascular dysfunction as an early factor that favors vascular Aβ aggregation and neurodegeneration. Addtionally, we emphasize that pericyte degeneration is a key and early element in AD that can trigger amyloid vascular accumulation and NVU/BBB dysfunction. Further research is required to better understand the early pathophysiological mechanisms associated with NVU alteration and CAA to generate early biomarkers and timely treatments for AD.

Hispano-American Brain Bank on Neurodevelopmental Disorders: An initiative to promote brain banking, research, education, and outreach in the field of neurodevelopmental disorders

Neurodevelopmental disorders (NDDs) are conditions that present with brain dysfunction due to alterations in the processes of brain development. They present with neuropsychiatric, cognitive, and motor symptoms. Autism spectrum disorder (ASD) and Fragile X syndrome (FXS) are two of the most common NDDs. Human brain tissue is a scarce resource that is obtained from postmortem donations. In the case of NDDs, specifically autism, the reduced donation rate of brains prevents researchers to investigate its pathology and fine anatomy. The Hispano-American Brain Bank of Neurodevelopmental Disorders (Banco Hispanoamericano de CErebros de trastornos del NEurodesarrollo) or CENE is a large-scale brain bank for neurodevelopmental disorders in Hispano-America and the US. CENE's objectives are to collect and distribute brains of patients with NDDS, with a focus on ASD and FXS, to perform research, promote education of future scientists, and enhance public awareness about the importance of human tissue availability for scientific research on brain function and disease. CENE has thus far established a bilingual system of nodes and teams in several American countries including California-US, Pennsylvania-US, México, Puerto Rico, Colombia, and Dominican Republic. CENE ensures that postmortem NDD samples used in research better match the world's genetic and ethnic diversity. CENE enables and expands NDD brain research worldwide, particularly with respect to ASD and FXS.

Tau Protein Phosphorylated at Threonine-231 is Expressed Abundantly in the Cerebellum in Prion Encephalopathies

Background:

Transmissible spongiform encephalopathies (TSEs) are rare neurodegenerative disorders that affect animals and humans. Bovine spongiform encephalopathy (BSE) in cattle, and Creutzfeld-Jakob Disease (CJD) in humans belong to this group. The causative agent of TSEs is called “prion”, which corresponds to a pathological form (PrP^Sc) of a normal cellular protein (PrP^C) expressed in nerve cells. PrP^Sc is resistant to degradation and can induce abnormal folding of PrP^C, and TSEs are characterized by extensive spongiosis and gliosis and the presence of PrP^Sc amyloid plaques. CJD presents initially with clinical symptoms similar to Alzheimer’s disease (AD). In AD, tau aggregates and amyloid-β protein plaques are associated with memory loss and cognitive impairment in patients.

Objective:

In this work, we study the role of tau and its relationship with PrP^Sc plaques in CJD.

Methods:

Multiple immunostainings with specific antibodies were carried out and analyzed by confocal microscopy.

Results:

We found increased expression of the glial fibrillary acidic protein (GFAP) and matrix metalloproteinase (MMP-9), and an exacerbated apoptosis in the granular layer in cases with prion disease. In these cases, tau protein phosphorylated at Thr-231 was overexpressed in the axons and dendrites of Purkinje cells and the extensions of parallel fibers in the cerebellum.

Conclusion:

We conclude that phosphorylation of tau may be a response to a toxic and inflammatory environment generated by the pathological form of prion.

National Dementia BioBank: A Strategy for the Diagnosis and Study of Neurodegenerative Diseases in México

We recently developed the National Dementia Biobank in México (BioBanco Nacional de Demencias, BND) as a unit for diagnosis, research, and tissue transfer for research purposes. BND is associated with the Facultad de Estudios Superiores Cuautitlán, Universidad Nacional Autónoma de Mexico (UNAM), Mexico. The donation of fluids, brain, and other organs of deceased donors is crucial for understanding the underlying mechanisms of neurodegenerative diseases and for the development of successful treatment. Our laboratory research focuses on 1) analysis of the molecular processing of the proteins involved in those neurodegenerative diseases termed tauopathies and 2) the search for biomarkers for the non-invasive and early diagnosis of Alzheimer's disease.

Analysis of the Relationship Between Metalloprotease-9 and Tau Protein in Alzheimer's Disease

BACKGROUND

Neurofibrillary tangles (NFTs) and amyloid plaques are the neuropathological hallmarks in brains with Alzheimer's disease (AD). Post-translational modifications of tau, such as phosphorylation and truncation, have been proposed as initiators in the assembly of the abnormal paired helical filaments that constitute the NFTs. Neurons and NFTs are sites of matrix metalloproteinases (MMPs).

OBJECTIVE

The aim of this study was to analyze the relationship of MMP-9 and tau protein in brain samples with AD.

METHODS

This study was performed on brain tissue samples from patients with early, moderate, and late AD. MMPs and tau levels were analyzed by western blot and gelatin-substrate zymography. Immunofluorescence techniques and confocal microscopy were used to analyze the presence of both proteins in NFTs. Further, molecular dynamics simulations (MDS) and protein-protein docking were conducted to predict interaction between MMP-9 and tau protein.

RESULTS

MMP-9 expression was greatest in moderate and late AD, whereas MMP-2 expression was only increased in late-stage AD. Interestingly, confocal microscopy revealed NFTs in which there was co-localization of MMP-9 and tau protein. MDS and protein-protein docking predictions indicate that a high-affinity complex can be formed between MMP-9 and full-length tau protein.

CONCLUSION

These observations provide preliminary evidence of an interaction between these two proteins. Post-translational modifications of tau protein, such as C-terminal truncation or phosphorylation of amino acid residues in the MMP-9 recognition site and conformational changes in the protein, such as folding of the N-terminal sequence over the three-repeat domain, could preclude the interaction between MMP-9 and tau protein during stages of NFT development.

Elucidating the Neuropathologic Mechanisms of SARS-CoV-2 Infection

The current pandemic caused by the new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become a public health emergency. To date, March 1, 2021, coronavirus disease 2019 (COVID-19) has caused about 114 million accumulated cases and 2.53 million deaths worldwide. Previous pieces of evidence suggest that SARS-CoV-2 may affect the central nervous system (CNS) and cause neurological symptoms in COVID-19 patients. It is also known that angiotensin-converting enzyme-2 (ACE2), the primary receptor for SARS-CoV-2 infection, is expressed in different brain areas and cell types. Thus, it is hypothesized that infection by this virus could generate or exacerbate neuropathological alterations. However, the molecular mechanisms that link COVID-19 disease and nerve damage are unclear. In this review, we describe the routes of SARS-CoV-2 invasion into the central nervous system. We also analyze the neuropathologic mechanisms underlying this viral infection, and their potential relationship with the neurological manifestations described in patients with COVID-19, and the appearance or exacerbation of some neurodegenerative diseases.

Acceptability and adoption of clinical practice guidelines and treatment protocols on preeclampsia/eclampsia in the Dominican Republic

Objective

Estimate the acceptability and adoption by health care workers of clinical practice guidelines and treatment protocols for women with preeclampsia/eclampsia and identify the facilitating factors and barriers to their implementation.

Methods

A qualitative study was conducted, using semi-structured interviews and focus groups in five maternity hospitals. Interviews were compiled for analysis, and barriers and facilitators were characterized.

Results

Seventy health professionals (52 female and 18 male) participated, representing different levels of the health system. The majority of workers and managers were aware of the existence and content of clinical practice guidelines (CPGs) for preeclampsia/eclampsia, especially the participants with more time in the health service. With respect to facilitating factors, both medical and nursing staff were positive about continued development and implementation of high-quality CPGs. There was consensus that limitations exist, especially with respect to a lack of the necessary medicines, supplies, and equipment to meet and implement the established recommendations.

Discussion

The results of the study show the need to strengthen strategies that help close the gap between research and public policy. Studies suggest that research should focus on users, policymakers, and decisionmakers in the health system. The actors in the Dominican health system recognize the GRADE methodology as an appropriate instrument for the development and implementation of CPGs. Implementation barriers require systemic and comprehensive approaches.

Human Dental Pulp Stem Cells Display a Potential for Modeling Alzheimer Disease-Related Tau Modifications

We present here the first description of tau in human dental pulp stem cells (DPSCs) evidenced by RT-PCR data on expression of the gene MAPT and by immunocytochemical detection of epitopes by 12 anti-tau antibodies. The tau specificity of eight of these antibodies was confirmed by their affinity to neurofibrillary tangles (NFTs) in Alzheimer's disease (AD) postmortem brain samples. We therefore used DPSCs and AD brain samples as a test system for determining the probability of the involvement of tau epitopes in the mechanisms converting tau into NFT in AD. Three antibodies to non-phosphorylated and seven antibodies to phosphorylated epitopes bound tau in both DPSCs and AD NFTs, thus suggesting that their function was not influenced by inducers of formation of NFTs in the AD brain. In contrast, AT100, which recognizes a hyperphosphorylated epitope, did not detect it in the cytoplasm of DPSCs but detected it in AD brain NFTs, demonstrating its AD diagnostic potential. This indicated that the phosphorylation/conformational events required for the creation of this epitope do not occur in normal cytoplasm and are a part of the mechanism (s) leading to NFT in AD brain. TG3 bound tau in the cytoplasm and in mitotic chromosomes but did not find it in nuclei. Collectively, these observations characterize DPSCs as a novel tau-harboring neuronal lineage long-term propagable in vitro cellular system for the normal conformational state of tau sites, detectable by antibodies, with their state in AD NFTs revealing those involved in the pathological processes converting tau into NFTs in the course of AD. With this information, one can model the interaction of tau with inducers and inhibitors of hyperphosphorylation toward NFT-like aggregates to search for drug candidates. Additionally, the clonogenicity of DPSCs provides the option for generation of cell lineages with CRISPR-mutagenized genes of familial AD modeling.

Current Status and Challenges of Stem Cell Treatment for Alzheimer's Disease

Neurodegenerative diseases called tauopathies, such as Alzheimer's disease (AD), frontotemporal dementia, progressive supranuclear palsy, and Parkinson's disease, among others, are characterized by the pathological processing and accumulation of tau protein. AD is the most prevalent neurodegenerative disease and is characterized by two lesions: neurofibrillary tangles (NFTs) and neuritic plaques. The presence of NFTs in the hippocampus and neocortex in early and advanced stages, respectively, correlates with the patient's cognitive deterioration. So far, no drugs can prevent, decrease, or limit neuronal death due to abnormal pathological tau accumulation. Among potential non-pharmacological treatments, physical exercise has been shown to stimulate the development of stem cells (SCs) and may be useful in early stages. However, this does not prevent neuronal death from the massive accumulation of NFTs. In recent years, SCs therapies have emerged as a promising tool to repopulate areas involved in cognition in neurodegenerative diseases. Unfortunately, protocols for SCs therapy are still being developed and the mechanism of action of such therapy remains unclear. In this review, we show the advances and limitations of SCs therapy. Finally, we provide a critical analysis of its clinical use for AD.

Molecular Processing of Tau Protein in Progressive Supranuclear Palsy: Neuronal and Glial Degeneration

BACKGROUND

Alzheimer's disease (AD) and progressive supranuclear palsy (PSP) are examples of neurodegenerative diseases, characterized by abnormal tau inclusions, that are called tauopathies. AD is characterized by highly insoluble paired helical filaments (PHFs) composed of tau with abnormal post-translational modifications. PSP is a neurodegenerative disease with pathological and clinical heterogeneity. There are six tau isoforms expressed in the adult human brain, with repeated microtubule-binding domains of three (3R) or four (4R) repeats. In AD, the 4R:3R ratio is 1:1. In PSP, the 4R isoform predominates. The lesions in PSP brains contain phosphorylated tau aggregates in both neurons and glial cells.

OBJECTIVE

Our objective was to evaluate and compare the processing of pathological tau in PSP and AD.

METHODS

Double and triple immunofluorescent labeling with antibodies to specific post-translational tau modifications (phosphorylation, truncation, and conformational changes) and thiazin red (TR) staining were carried out and analyzed by confocal microscopy.

RESULTS

Our results showed that PSP was characterized by phosphorylated tau in neurofibrillary tangles (NFTs) and glial cells. Tau truncated at either Glu391 or Asp421 was not observed. Extracellular NFTs (eNFTs) and glial cells in PSP exhibited a strong affinity for TR in the absence of intact or phosphorylated tau.

CONCLUSION

Phosphorylated tau was as abundant in PSP as in AD. The development of eNFTs from both glial cells and neuronal bodies suggests that truncated tau species, different from those observed in AD, could be present in PSP. Additional studies on truncated tau within PSP lesions could improve our understanding of the pathological processing of tau and help identify a discriminatory biomarker for AD and PSP.

[Acceptability and adoption of clinical practice guidelines and treatment protocols on preeclampsia/eclampsia in the Dominican RepublicAceitabilidade e adoção de diretrizes de prática clínica e protocolos de atenção para pré-eclâmpsia e eclâmpsia na República Dominicana]

Objetivo.

Estimar la aceptabilidad y adopción de las guías de prática clínica (GPC) y protocolos de atención a la mujer con preeclampsia-eclampsia por parte del personal prestador de los servicios de salud, e identificar los factores facilitadores y las barreras para su implementación.

Métodos.

Se desarrolló un estudio cualitativo por medio de entrevistas semiestructuradas y grupos focales en cinco maternidades. Se recopilaron las entrevistas para su análisis y se caracterizaron las barreras y facilitadores.

Resultados.

Participaron 70 profesionales de la salud (52 de sexo femenino y 18 de sexo masculino) que se desempeñan en distintos niveles del sistema de salud, participaron. La mayoría de los prestadores y gerentes conocen la existencia de las GPC de eclampsia-preeclampsia y su contenido, sobre todo los participantes con más tiempo en el servicio. Para los facilitadores, se estableció una valoración positiva entre el personal médico y de enfermería ante el proceso de continuar con la elaboración e implementación de GPC de alta calidad. Hubo consenso en cuanto a la existencia de limitaciones, sobre todo, por la falta de medicamentos, insumos y equipos requeridos, para cumplir y aplicar las recomendaciones formuladas.

Discusión.

Los resultados del estudio exponen la necesidad de fortalecer estrategias que ayuden a cerrar la brecha entre la investigación y la política pública. Estudios fundamentan la investigación en priorizar la atención a los usuarios, y los encargados de formular políticas y los tomadores de decisiones en el sistema de salud. Los actores del sistema de salud dominicano reconocen la metodología GRADE como un instrumento apropiado para la formulación e implementación de GPC. Las barreras de implementación requieren de abordajes sistémicos e integrales.

PHF-Core Tau as the Potential Initiating Event for Tau Pathology in Alzheimer's Disease

Worldwide, around 50 million people have dementia. Alzheimer's disease (AD) is the most common type of dementia and one of the major causes of disability and dependency among the elderly worldwide. Clinically, AD is characterized by impaired memory accompanied by other deficiencies in the cognitive domain. Neuritic plaques (NPs) and neurofibrillary tangles (NFTs) are histopathological lesions that define brains with AD. NFTs consist of abundant intracellular paired helical filaments (PHFs) whose main constituent is tau protein. Tau undergoes posttranslational changes including hyperphosphorylation and truncation, both of which favor conformational changes in the protein. The sequential pathological processing of tau is illustrated with the following specific markers: pT231, TG3, AT8, AT100, and Alz50. Two proteolysis sites for tau have been described-truncation at glutamate 391 and at aspartate 421-and which can be demonstrated by reactivity with the antibodies 423 and TauC-3, respectively. In this review, we describe the molecular changes in tau protein as pre-NFTs progress to extracellular NFTs and during which the formation of a minimal nucleus of the filament, as the PHF core, occurs. We also analyzed the PHF core as the initiator of PHFs and tau phosphorylation as a protective neuronal mechanism against the assembly of the PHF core.

Toxicity evaluation of barium ferrite nanoparticles in bacteria, yeast and nematode

Barium ferrite nanoparticles (BaFeNPs) are a permanent magnetic nanomaterial widely used in electrical energy storage, recording media or in the improvement of the magnetic properties of other nanoparticles (NPs). However, the information about the toxicity of BaFeNPs is almost non-existent. Thus, in the present work, the antimicrobial effect of BaFeNPs was evaluated for the first time in gram-negative and gram-positive bacteria and yeast showing neither antibacterial nor antifungal activity at moderate concentrations. On the other hand, in order to assess the in vivo toxicity of BaFeNPs the model organism Caenorhabditis elegans was used and ingestion, survival, reproduction and ROS production were evaluated in worms treated with different concentrations of BaFeNPs. Our results show that worms ingest these NPs through the digestive system affecting survival, reproduction and ROS production.

Early intervention with ABA prevents neuroinflammation and memory impairment in a triple transgenic mice model of Alzheimer´s disease

Neuroinflammation and insulin resistance in the brain are intimately linked to neurodegenerative disorders, including Alzheimer's disease. Even though traditionally Alzheimer´s disease has been associated to Aβ deposits and hyperphosphorylated Tau intracellular tangles, several studies show that neuroinflammation may be the initial cause that triggers degeneration. Accordingly, a number of natural supplements that improves brain insulin sensitivity and reduce neuroinflammation have been proposed as good choices in the therapeutic prevention of cognitive decline. Further supporting this evidence, we show that phytohormone Abscisic Acid, can prevent memory impairment and neuroinflammation markers in a triple transgenic mouse model, where no peripheral inflammatory changes have occurred. Moreover, our data strongly suggests that early intervention is critical for good prognosis, and that cognitive improvement requires longer treatment than recovering neuroinflammation markers.

Increased Aβ production prompts the onset of glucose intolerance and insulin resistance

Type 2 diabetes (T2D) mellitus and Alzheimer's disease (AD) are two prevalent diseases with comparable pathophysiological features and genetic predisposition. Patients with AD are more susceptible to develop T2D. However, the molecular mechanism linking AD and T2D remains elusive. In this study, we have generated a new mouse model to test the hypothesis that AD would prompt the onset of T2D in mice. To test our hypothesis, we crossed Alzheimer APPswe/PS1dE9 (APP/PS1) transgenic mice with mice partially deficient in leptin signaling (db/+). Body weight, plasma glucose, and insulin levels were monitored. Phenotypic characterization of glucose metabolism was performed using glucose and insulin tolerance tests. β-Cell mass, islet volume, and islet number were analyzed by histomorphometry. APP/PS1 coexpression in mice with intact leptin receptor signaling did not show any metabolic perturbations in glucose metabolism or insulin sensitivity. In contrast, APP/PS1 coexpression in db/+ mice resulted in nonfasting hyperglycemia, hyperinsulinemia, and hypercholesterolemia without changes in body weight. Conversely, fasting blood glucose and cholesterol levels remained unchanged. Coinciding with altered glucose metabolism, APP/PS1 coexpression in db/+ mice resulted in glucose intolerance, insulin resistance, and impaired insulin signaling. In addition, histomorphometric analysis of pancreata revealed augmented β-cell mass. Taken together, these findings provide experimental evidence to support the notion that aberrant Aβ production might be a mechanistic link underlying the pathology of insulin resistance and T2D in AD.