Caspase-mediated cleavage of glial fibrillary acidic protein within degenerating astrocytes of the Alzheimer's disease brain

A cross-tissue transcriptome-wide association study identified susceptibility genes for age-related macular degeneration

Age-related macular degeneration (AMD) is a complex multifactorial disease with a significant genetic component. Despite extensive research efforts, the underlying molecular mechanisms remain elusive, necessitating innovative approaches to identify specific genes involved in the pathogenesis of AMD and to elucidate their functional mechanisms. A transcriptome-wide association study (TWAS) was conducted by integrating eQTL data from 49 tissues of the Genotype-Tissue Expression Project (GTEx) v8 and AMD data from FinnGen R10. The Unified Test for Molecular Signatures (UTMOST) and Functional Summary-based Imputation (FUSION) were used to evaluate gene associations with AMD across tissues and within individual tissues, respectively. Multi-marker Analysis of Genomic Annotation (MAGMA) was employed to validate results and identify reliable susceptibility genes, followed by summary data-based Mendelian randomization (SMR) and colocalization analyses to explore causal associations. The cross-tissue and single-tissue TWAS analyses identified 12 reliable AMD-associated genes. MAGMA analysis confirmed 6 of these as reliable susceptibility genes. SMR analysis provided further validation of these genes, although colocalization results were not significant. This study identified six susceptibility genes associated with the risk of AMD through a cross-tissue TWAS, providing new insights into the potential systemic regulatory mechanisms underlying AMD.

Research progress on astrocyte-derived extracellular vesicles in the pathogenesis and treatment of neurodegenerative diseases

Neurodegenerative disorders, including Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD), pose significant global health risks and represent a substantial public health concern in the contemporary era. A primary factor in the pathophysiology of these disorders is aberrant accumulation and aggregation of pathogenic proteins within the brain and spinal cord. Recent investigations have identified extracellular vesicles (EVs) in the central nervous system (CNS) as potential carriers for intercellular transport of misfolded proteins associated with neurodegenerative diseases. EVs are involved in pathological processes that contribute to various brain disorders including neurodegenerative disorders. Proteins linked to neurodegenerative disorders are secreted and distributed from cell to cell via EVs, serving as a mechanism for direct intercellular communication through the transfer of biomolecules. Astrocytes, as active participants in CNS intercellular communication, release astrocyte-derived extracellular vesicles (ADEVs) that are capable of interacting with diverse target cells. This review primarily focuses on the involvement of ADEVs in the development of neurological disorders and explores their potential dual roles - both advantageous and disadvantageous in the context of neurological disorders. Furthermore, this review examines the current studies investigating ADEVs as potential biomarkers for the diagnosis and treatment of neurodegenerative diseases. The prospects and challenges associated with the application of ADEVs in clinical settings were also comprehensively reviewed.

Changes in the levels of serum glial fibrillary acidic protein and the correlation with outcomes in severe traumatic brain injury patients

Purpose

Glial fibrillary acidic protein serves as a biomarker indicative of astroglial injury, particularly following instances of severe traumatic brain injury. This study aims to evaluate variations in serum glial fibrillary acidic protein levels within the first 3 days and their correlation with outcomes in patients with severe traumatic brain injury.

Subjects and methods

Thirty-nine patients with severe traumatic brain injury were enrolled in the study. Their blood samples were collected at six distinct time points: T0 (upon admission), T1, T2, T3, T4, and T5 (6-, 12-, 24-, 48-, and 72-h post-admission, respectively). The blood samples were run for the quantification of serum glial fibrillary acidic protein levels and other biochemical tests. All patients were closely watched and the outcomes at discharge were evaluated.

Results

Glial fibrillary acidic protein levels tend to increase gradually from the time of admission to 48 h post-admission and then decrease at 72 h post-admission. Glial fibrillary acidic protein T2 is correlated with Acute Physiology and Chronic Health Evaluation II score, lactate, Simplified Acute Physiology Score II score and outcome. Glial fibrillary acidic protein max correlated with lactate, Acute Physiology and Chronic Health Evaluation II score, Simplified Acute Physiology Score II score, and outcome. Glasgow Coma Score at admission and glial fibrillary acidic protein T2 (OR = 1.034; p = 0.025), T3 (OR = 1.029; p = 0.046), T4 (OR = 1.006; p = 0.032), T5 (OR = 1.012; p = 0.048) and glial fibrillary acidic protein max (OR = 1.005; p = 0.010) were independent factors that have significant prognostic value in mortality in patients with severe traumatic brain injury. The predictive model in predicting mortality had the highest area under the curve based on glial fibrillary acidic protein T2 and Glasgow Coma Score T0 with an area under the curve of 0.904 and p < 0.001. In the multivariable regression model, glial fibrillary acidic protein max was associated with Glasgow score (p < 0.001; VIF = 1.585), lactate T0 (p = 0.024; VIF = 1.163), Acute Physiology and Chronic Health Evaluation II score (p = 0.037; VIF = 1.360), and Rotterdam score (p = 0.044; VIF = 1.713).

Conclusion

Glial fibrillary acidic protein levels tend to increase gradually from the time of admission to 48 h post-admission then decreases at 72 h post-admission. Glial fibrillary acidic protein T2, T3, T4, T5, and glial fibrillary acidic protein max were independent factors with significant prognostic mortality values in patients with severe traumatic brain injury.

GFAP as Astrocyte-Derived Extracellular Vesicle Cargo in Acute Ischemic Stroke Patients-A Pilot Study

The utility of serum glial fibrillary acidic protein (GFAP) in acute ischemic stroke (AIS) has been extensively studied in recent years. Here, we aimed to assess its potential role as a cargo protein of extracellular vesicles (EVs) secreted by astrocytes (ADEVs) in response to brain ischemia. Plasma samples from eighteen AIS patients at 24 h (D1), 7 days (D7), and one month (M1) post-symptoms onset, and nine age, sex, and cardiovascular risk factor-matched healthy controls were obtained to isolate EVs using the Exoquick ULTRA EV kit. Subsets of presumed ADEVs were identified further by the expression of the glutamate aspartate transporter (GLAST) as a specific marker of astrocytes with the Basic Exo-Flow Capture kit. Western blotting has tested the presence of GFAP in ADEV cargo. Post-stroke ADEV GFAP levels were elevated at D1 and D7 but not M1 compared to controls (p = 0.007, p = 0.019, and p = 0.344, respectively). Significant differences were highlighted in ADEV GFAP content at the three time points studied (n = 12, p = 0.027) and between D1 and M1 (z = 2.65, p = 0.023). A positive correlation was observed between the modified Rankin Scale (mRS) at D7 and ADEV GFAP at D1 (r = 0.58, p = 0.010) and D7 (r = 0.57, p = 0.013), respectively. ADEV GFAP may dynamically reflect changes during the first month post-ischemia. Profiling ADEVs from peripheral blood could provide a new way to assess the central nervous system pathology.

Panaxcerol D from Panax ginseng ameliorates the memory impairment induced by cholinergic blockade or Aβ25-35 peptide in mice

Background

Alzheimer's disease (AD) has memory impairment associated with aggregation of amyloid plaques and neurofibrillary tangles in the brain. Although anti-amyloid β (Aβ) protein antibody and chemical drugs can be prescribed in the clinic, they show adverse effects or low effectiveness. Therefore, the development of a new drug is necessarily needed. We focused on the cognitive function of Panax ginseng and tried to find active ingredient(s). We isolated panaxcerol D, a kind of glycosyl glyceride, from the non-saponin fraction of P. ginseng extract.

Methods

We explored effects of acute or sub-chronic administration of panaxcerol D on cognitive function in scopolamine- or Aβ25-35 peptide-treated mice measured by several behavioral tests. After behavioral tests, we tried to unveil the underlying mechanism of panaxcerol D on its cognitive function by Western blotting.

Results

We found that pananxcerol D reversed short-term, long-term and object recognition memory impairments. The decreased extracellular signal-regulated kinases (ERK) or Ca2+/calmodulin-dependent protein kinase II (CaMKII) in scopolamine-treated mice was normalized by acute administration of panaxcerol D. Glial fibrillary acidic protein (GFAP), caspase 3, NF-kB p65, synaptophysin and brain-derived neurotrophic factor (BDNF) expression levels in Aβ25-35 peptide-treated mice were modulated by sub-chronic administration of panaxcerol D.

Conclusion

Pananxcerol D could improve memory impairments caused by cholinergic blockade or Aβ accumulation through increased phosphorylation level of ERK or its anti-inflammatory effect. Thus, panaxcerol D as one of non-saponin compounds could be used as an active ingredient of P. ginseng for improving cognitive function.

GFAP as a Potential Biomarker for Alzheimer's Disease: A Systematic Review and Meta-Analysis

Blood biomarkers have been considered tools for the diagnosis, prognosis, and monitoring of Alzheimer's disease (AD). Although amyloid-β peptide (Aβ) and tau are primarily blood biomarkers, recent studies have identified other reliable candidates that can serve as measurable indicators of pathological conditions. One such candidate is the glial fibrillary acidic protein (GFAP), an astrocytic cytoskeletal protein that can be detected in blood samples. Increasing evidence suggests that blood GFAP levels can be used to detect early-stage AD. In this systematic review and meta-analysis, we aimed to evaluate GFAP in peripheral blood as a biomarker for AD and provide an overview of the evidence regarding its utility. Our analysis revealed that the GFAP level in the blood was higher in the Aβ-positive group than in the negative groups, and in individuals with AD or mild cognitive impairment (MCI) compared to the healthy controls. Therefore, we believe that the clinical use of blood GFAP measurements has the potential to accelerate the diagnosis and improve the prognosis of AD.

Astrocyte adaptation in Alzheimer's disease: a focus on astrocytic P2X7R

Astrocytes are key homeostatic and defensive cells of the central nervous system (CNS). They undertake numerous functions during development and in adulthood to support and protect the brain through finely regulated communication with other cellular elements of the nervous tissue. In Alzheimer's disease (AD), astrocytes undergo heterogeneous morphological, molecular and functional alterations represented by reactive remodelling, asthenia and loss of function. Reactive astrocytes closely associate with amyloid β (Aβ) plaques and neurofibrillary tangles in advanced AD. The specific contribution of astrocytes to AD could potentially evolve along the disease process and includes alterations in their signalling, interactions with pathological protein aggregates, metabolic and synaptic impairments. In this review, we focus on the purinergic receptor, P2X7R, and discuss the evidence that P2X7R activation contributes to altered astrocyte functions in AD. Expression of P2X7R is increased in AD brain relative to non-demented controls, and animal studies have shown that P2X7R antagonism improves cognitive and synaptic impairments in models of amyloidosis and tauopathy. While P2X7R activation can induce inflammatory signalling pathways, particularly in microglia, we focus here specifically on the contributions of astrocytic P2X7R to synaptic changes and protein aggregate clearance in AD, highlighting cell-specific roles of this purinoceptor activation that could be targeted to slow disease progression.

Neurovascular injury associated non-apoptotic endothelial caspase-9 and astroglial caspase-9 mediate inflammation and contrast sensitivity decline

Retinal neurovascular injuries are a leading cause of vision loss in young adults presenting unmet therapeutic needs. Neurovascular injuries damage homeostatic communication between endothelial, pericyte, glial, and neuronal cells through signaling pathways that remain to be established. To understand the mechanisms that contribute to neuronal death, we use a mouse model of retinal vein occlusion (RVO). Using this model, we previously discovered that after vascular damage, there was non-apoptotic activation of endothelial caspase-9 (EC Casp9); knock-out of EC Casp9 led to a decrease in retinal edema, capillary ischemia, and neuronal death. In this study, we aimed to explore the role of EC Casp9 in vision loss and inflammation. We found that EC Casp9 is implicated in contrast sensitivity decline, induction of inflammatory cytokines, and glial reactivity. One of the noted glial changes was increased levels of astroglial cl-caspase-6, which we found to be activated cell intrinsically by astroglial caspase-9 (Astro Casp9). Lastly, we discovered that Astro Casp9 contributes to capillary ischemia and contrast sensitivity decline after RVO (P-RVO). These findings reveal specific endothelial and astroglial non-apoptotic caspase-9 roles in inflammation and neurovascular injury respectively; and concomitant relevancy to contrast sensitivity decline.

Characterization of Calpain and Caspase-6-Generated Glial Fibrillary Acidic Protein Breakdown Products Following Traumatic Brain Injury and Astroglial Cell Injury

Glial fibrillary acidic protein (GFAP) is the major intermediate filament III protein of astroglia cells which is upregulated in traumatic brain injury (TBI). Here we reported that GFAP is truncated at both the C- and N-terminals by cytosolic protease calpain to GFAP breakdown products (GBDP) of 46-40K then 38K following pro-necrotic (A23187) and pro-apoptotic (staurosporine) challenges to primary cultured astroglia or neuron-glia mixed cells. In addition, with another pro-apoptotic challenge (EDTA) where caspases are activated but not calpain, GFAP was fragmented internally, generating a C-terminal GBDP of 20 kDa. Following controlled cortical impact in mice, GBDP of 46-40K and 38K were formed from day 3 to 28 post-injury. Purified GFAP protein treated with calpain-1 and -2 generates (i) major N-terminal cleavage sites at A-56*A-61 and (ii) major C-terminal cleavage sites at T-383*Q-388, producing a limit fragment of 38K. Caspase-6 treated GFAP was cleaved at D-78/R-79 and D-225/A-226, where GFAP was relatively resistant to caspase-3. We also derived a GBDP-38K N-terminal-specific antibody which only labels injured astroglia cell body in both cultured astroglia and mouse cortex and hippocampus after TBI. As a clinical translation, we observed that CSF samples collected from severe human TBI have elevated levels of GBDP-38K as well as two C-terminally released GFAP peptides (DGEVIKES and DGEVIKE). Thus, in addition to intact GFAP, both the GBDP-38K as well as unique GFAP released C-terminal proteolytic peptides species might have the potential in tracking brain injury progression.

Impact of different processing methods on the phenolics and neuroprotective activity of Fragaria ananassa Duch. extracts in a D-galactose and aluminum chloride-induced rat model of aging

Age-related diseases, including dementia, are a major health concern affecting daily human life. Strawberry (Fragaria ananassa Duch.) is the most eaten fruit worldwide due to its exceptional aroma and flavor. However, it's rapid softening and decay limit its shelf-life. Freezing and boiling represent the well-known conservation methods to extend its shelf-life. Therefore, we aimed to discover the phytochemical content differences of fresh and processed strawberries associated with investigating and comparing their neuroprotective effects in a rat model of aging. Female Wistar rats were orally pretreated with fresh, boiled, and frozen F. ananassa methanolic extracts (250 mg kg-1) for 2 weeks, and then these extracts were concomitantly exposed to D-galactose [65 mg kg-1, subcutaneously (S/C)] and AlCl3 (200 mg kg-1, orally) for 6 weeks to develop aging-like symptoms. The results of UPLC/ESI-MS phytochemical profiling revealed 36 secondary metabolites, including phenolics, flavonoids, and their glycoside derivatives. Compared with boiled and frozen extracts, the fresh extract ameliorated the behavioral deficits including anxiety and cognitive dysfunction, upregulated brain HO-1 and Nrf2 levels, and markedly reduced caspase-3 and PPAR-γ levels. Moreover, LDH and miRNA-9, 124 and 132 protein expressions were reduced. The histological architecture of the brain hippocampus was restored and glial fibrillary acidic protein (GFAP) immunoexpression was downregulated. In conclusion, the fresh extract has neuroprotective activity that could have a promising role in ameliorating age-related neurodegeneration.

The AIM2 inflammasome is activated in astrocytes during the late phase of EAE

Inflammasomes are a class of innate immune signaling platforms that activate in response to an array of cellular damage and pathogens. Inflammasomes promote inflammation under many circumstances to enhance immunity against pathogens and inflammatory responses through their effector cytokines, IL-1β and IL-18. Multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE), are autoimmune conditions influenced by inflammasomes. Despite work investigating inflammasomes during EAE, little remains known concerning the role of inflammasomes in the central nervous system (CNS) during the disease. Here, we used multiple genetically modified mouse models to monitor activated inflammasomes in situ based on oligomerization of apoptosis-associated speck-like protein containing a CARD (ASC) in the spinal cord. Using inflammasome reporter mice, we found heightened inflammasome activation in astrocytes after the disease peak. In contrast, microglia and CNS-infiltrated myeloid cells had few activated inflammasomes in the CNS during EAE. Astrocyte inflammasome activation during EAE was dependent on absent in melanoma 2 (AIM2), but low IL-1β release and no significant signs of cell death were found. Thus, the AIM2 inflammasome activation in astrocytes may have a distinct role from traditional inflammasome-mediated inflammation.

Alexander disease: models, mechanisms, and medicine

Alexander disease is a primary disorder of astrocytes caused by gain-of-function mutations in the gene for glial fibrillary acidic protein (GFAP), which lead to protein aggregation and a reactive astrocyte response, with devastating effects on the central nervous system. Over the past two decades since the discovery of GFAP as the culprit, several cellular and animal models have been generated, and much has been learned about underlying mechanisms contributing to the disease. Despite these efforts, many aspects of Alexander disease have remained enigmatic, particularly the initiating events in GFAP accumulation and astrocyte pathology, the relation between astrocyte dysfunction and myelin deficits, and the variability in age of onset and disease severity. More recent work in both old and new models has begun to address these complex questions and identify new therapeutics that finally offer the promise of effective treatment.

Salivary GFAP as a potential biomarker for diagnosis of mild cognitive impairment and Alzheimer's disease and its correlation with neuroinflammation and apoptosis

Glial fibrillary acidic protein (GFAP) is the main constituent of the astrocytic cytoskeleton, overexpressed during reactive astrogliosis-a hallmark of Alzheimer's Disease (AD). GFAP and established biomarkers of neurodegeneration, inflammation, and apoptosis have been determined in the saliva of amnestic-single-domain Mild Cognitive Impairment (MCI) (Ν = 20), AD (Ν = 20) patients, and cognitively healthy Controls (Ν = 20). Salivary GFAP levels were found significantly decreased in MCI and AD patients and were proven an excellent biomarker for discriminating Controls from MCI or AD patients. GFAP levels correlate with studied biomarkers and Aβ₄₂, IL-1β, and caspase-8 are its main predictors.

Neurovascular Unit Alterations in the Growth-Restricted Newborn Are Improved Following Ibuprofen Treatment

The developing brain is particularly vulnerable to foetal growth restriction (FGR) and abnormal neurodevelopment is common in the FGR infant ranging from behavioural and learning disorders to cerebral palsy. No treatment exists to protect the FGR newborn brain. Recent evidence suggests inflammation may play a key role in the mechanism responsible for the progression of brain impairment in the FGR newborn, including disruption to the neurovascular unit (NVU). We explored whether ibuprofen, an anti-inflammatory drug, could reduce NVU disruption and brain impairment in the FGR newborn. Using a preclinical FGR piglet model, ibuprofen was orally administered for 3 days from birth. FGR brains demonstrated a proinflammatory state, with changes to glial morphology (astrocytes and microglia), and blood-brain barrier disruption, assessed by IgG and albumin leakage into the brain parenchyma and a decrease in blood vessel density. Loss of interaction between astrocytic end-feet and blood vessels was evident where plasma protein leakage was present, suggestive of structural deficits to the NVU. T-cell infiltration was also evident in the parenchyma of FGR piglet brains. Ibuprofen treatment reduced the pro-inflammatory response in FGR piglets, reducing the number of activated microglia and enhancing astrocyte interaction with blood vessels. Ibuprofen also attenuated plasma protein leakage, regained astrocytic end-feet interaction around vessels, and decreased T-cell infiltration into the FGR brain. These findings suggest postnatal administration of ibuprofen modulates the inflammatory state, allowing for stronger interaction between vasculature and astrocytic end-feet to restore NVU integrity. Modulation of the NVU improves the FGR brain microenvironment and may be key to neuroprotection.

GFAP at 50

Fifty years have passed since the discovery of glial fibrillary acidic protein (GFAP) by Lawrence Eng and colleagues. Now recognized as a member of the intermediate filament family of proteins, it has become a subject for study in fields as diverse as structural biology, cell biology, gene expression, basic neuroscience, clinical genetics and gene therapy. This review covers each of these areas, presenting an overview of current understanding and controversies regarding GFAP with the goal of stimulating continued study of this fascinating protein.

Systematic review of human post-mortem immunohistochemical studies and bioinformatics analyses unveil the complexity of astrocyte reaction in Alzheimer's disease

AIMS

Reactive astrocytes in Alzheimer's disease (AD) have traditionally been demonstrated by increased glial fibrillary acidic protein (GFAP) immunoreactivity; however, astrocyte reaction is a complex and heterogeneous phenomenon involving multiple astrocyte functions beyond cytoskeletal remodelling. To better understand astrocyte reaction in AD, we conducted a systematic review of astrocyte immunohistochemical studies in post-mortem AD brains followed by bioinformatics analyses on the extracted reactive astrocyte markers.

METHODS

NCBI PubMed, APA PsycInfo and WoS-SCIE databases were interrogated for original English research articles with the search terms 'Alzheimer's disease' AND 'astrocytes.' Bioinformatics analyses included protein-protein interaction network analysis, pathway enrichment, and transcription factor enrichment, as well as comparison with public human -omics datasets.

RESULTS

A total of 306 articles meeting eligibility criteria rendered 196 proteins, most of which were reported to be upregulated in AD vs control brains. Besides cytoskeletal remodelling (e.g., GFAP), bioinformatics analyses revealed a wide range of functional alterations including neuroinflammation (e.g., IL6, MAPK1/3/8 and TNF), oxidative stress and antioxidant defence (e.g., MT1A/2A, NFE2L2, NOS1/2/3, PRDX6 and SOD1/2), lipid metabolism (e.g., APOE, CLU and LRP1), proteostasis (e.g., cathepsins, CRYAB and HSPB1/2/6/8), extracellular matrix organisation (e.g., CD44, MMP1/3 and SERPINA3), and neurotransmission (e.g., CHRNA7, GABA, GLUL, GRM5, MAOB and SLC1A2), among others. CTCF and ESR1 emerged as potential transcription factors driving these changes. Comparison with published -omics datasets validated our results, demonstrating a significant overlap with reported transcriptomic and proteomic changes in AD brains and/or CSF.

CONCLUSIONS

Our systematic review of the neuropathological literature reveals the complexity of AD reactive astrogliosis. We have shared these findings as an online resource available at www.astrocyteatlas.org.

Elevated GFAP isoform expression promotes protein aggregation and compromises astrocyte function

Alexander disease (AxD) caused by mutations in the coding region of GFAP is a neurodegenerative disease characterized by astrocyte dysfunction, GFAP aggregation, and Rosenthal fiber accumulation. Although how GFAP mutations cause disease is not fully understood, Rosenthal fibers could be induced by forced overexpression of human GFAP and this could be lethal in mice implicate that an increase in GFAP levels is central to AxD pathogenesis. Our recent studies demonstrated that intronic GFAP mutations cause disease by altering GFAP splicing, suggesting that an increase in GFAP isoform expression could lead to protein aggregation and astrocyte dysfunction that typify AxD. Here we test this hypothesis by establishing primary astrocyte cultures from transgenic mice overexpressing human GFAP. We found that GFAP-δ and GFAP-κ were disproportionately increased in transgenic astrocytes and both were enriched in Rosenthal fibers of human AxD brains. In vitro assembly studies showed that while the major isoform GFAP-α self-assembled into typical 10-nm filaments, minor isoforms including GFAP-δ, -κ, and -λ were assembly-compromised and aggregation prone. Lentiviral transduction showed that expression of these minor GFAP isoforms decreased filament solubility and increased GFAP stability, leading to the formation of Rosenthal fibers-like aggregates that also disrupted the endogenous intermediate filament networks. The aggregate-bearing astrocytes lost their normal morphology and glutamate buffering capacity, which had a toxic effect on neighboring neurons. In conclusion, our findings provide evidence that links elevated GFAP isoform expression with GFAP aggregation and impaired glutamate transport, and suggest a potential non-cell-autonomous mechanism underlying neurodegeneration through astrocyte dysfunction.

Neuronal tau species transfer to astrocytes and induce their loss according to tau aggregation state

Deposits of different abnormal forms of tau in neurons and astrocytes represent key anatomo-pathological features of tauopathies. Although tau protein is highly enriched in neurons and poorly expressed by astrocytes, the origin of astrocytic tau is still elusive. Here, we used innovative gene transfer tools to model tauopathies in adult mouse brains and to investigate the origin of astrocytic tau. We showed in our adeno-associated virus (AAV)-based models and in Thy-Tau22 transgenic mice that astrocytic tau pathology can emerge secondarily to neuronal pathology. By designing an in vivo reporter system, we further demonstrated bidirectional exchanges of tau species between neurons and astrocytes. We then determined the consequences of tau accumulation in astrocytes on their survival in models displaying various status of tau aggregation. Using stereological counting of astrocytes, we report that, as for neurons, soluble tau species are highly toxic to some subpopulations of astrocytes in the hippocampus, whereas the accumulation of tau aggregates does not affect their survival. Thus, astrocytes are not mere bystanders of neuronal pathology. Our results strongly suggest that tau pathology in astrocytes may significantly contribute to clinical symptoms.

Thorough overview of ubiquitin C-terminal hydrolase-L1 and glial fibrillary acidic protein as tandem biomarkers recently cleared by US Food and Drug Administration for the evaluation of intracranial injuries among patients with traumatic brain injury

Traumatic brain injury (TBI) is a major cause of mortality and morbidity affecting all ages. It remains to be a diagnostic and therapeutic challenge, in which, to date, there is no Food and Drug Administration‐approved drug for treating patients suffering from TBI. The heterogeneity of the disease and the associated complex pathophysiology make it difficult to assess the level of the trauma and to predict the clinical outcome. Current injury severity assessment relies primarily on the Glasgow Coma Scale score or through neuroimaging, including magnetic resonance imaging and computed tomography scans. Nevertheless, such approaches have certain limitations when it comes to accuracy and cost efficiency, as well as exposing patients to unnecessary radiation. Consequently, extensive research work has been carried out to improve the diagnostic accuracy of TBI, especially in mild injuries, because they are often difficult to diagnose. The need for accurate and objective diagnostic measures led to the discovery of biomarkers significantly associated with TBI. Among the most well‐characterized biomarkers are ubiquitin C‐terminal hydrolase‐L1 and glial fibrillary acidic protein. The current review presents an overview regarding the structure and function of these distinctive protein biomarkers, along with their clinical significance that led to their approval by the US Food and Drug Administration to evaluate mild TBI in patients.

Glia-Driven Neuroinflammation and Systemic Inflammation in Alzheimer's Disease

The neuroinflammatory hypothesis of Alzheimer's disease (AD) was proposed more than 30 years ago. The involvement of the two main types of glial cells microglia and astrocytes, in neuroinflammation, was suggested early on. In this review, we highlight that the exact contributions of reactive glia to AD pathogenesis remain difficult to define, likely due to the heterogeneity of glia populations and alterations in their activation states through the stages of AD progression. In the case of microglia, it is becoming apparent that both beneficially and adversely activated cell populations can be identified at various stages of AD, which could be selectively targeted to either limit their damaging actions or enhance beneficial functions. In the case of astrocytes, less information is available about potential subpopulations of reactive cells; it also remains elusive whether astrocytes contribute to the neuropathology of AD by mainly gaining neurotoxic functions or losing their ability to support neurons due to astrocyte damage. We identify L-type calcium channel blocker, nimodipine, as a candidate drug for AD, which potentially targets both astrocytes and microglia. It has already shown consistent beneficial effects in basic experimental and clinical studies. We also highlight the recent evidence linking peripheral inflammation and neuroinflammation. Several chronic systemic inflammatory diseases, such as obesity, type 2 diabetes mellitus, and periodontitis, can cause immune priming or adverse activation of glia, thus exacerbating neuroinflammation and increasing risk or facilitating the progression of AD. Therefore, reducing peripheral inflammation is a potentially effective strategy for lowering AD prevalence.

Serum Glial Fibrillary Acidic Protein: A Surrogate Marker of the Activity of Multiple Sclerosis

Objective

Multiple sclerosis (MS) is a neurodegenerative disorder with various clinical types. Glial fibrillary acidic protein (GFAP) is significantly elevated in the cerebrospinal fluid (CSF) of MS patients compared with that of healthy controls. The aim of this study is to evaluate serum levels of GFAP in relation to disease activity in relapsing-remitting MS patients and to compare them with those of healthy controls.

Method

This study involved 58 MS patients of relapsing-remitting MS (RRMS) type, 22 in an active stage of the disease and 36 in remission, and 50 healthy individuals as age- and sex-matched controls. Blood samples were taken from the patients at the MS Clinic of the Baghdad Teaching Hospital, and the serum levels of GFAP were determined using the enzyme-linked immunosorbent assay (ELISA) technique.

Results

Mean GFAP serum levels in 22 patients presenting in the active state of the disease (6.47±3.39 ng/ml) and 36 cases in remission were (5.33±2.82 ng/ml) (p=0.074) were determined as indicated. When RRMS patients (n=58) were compared with the healthy controls (n=50, 1.89±1.21), the difference in serum levels of GFAP was statistically significant (p<0.001). The area under the curve of the serum measures of GFAP obtained through the receiver operating characteristics was 0.903, which was also statistically significant (p<0.001).

Conclusion

GFAP biomarker is an indicator of disease activity in RRMS patients, and its serum level may correlate with the state of remission or exacerbation.

Amyloid-ß peptides inhibit the expression of AQP4 and glutamate transporter EAAC1 in insulin-treated C6 glioma cells

Astrocytic aquaporin 4 (AQP4) facilitates glutamate clearance via regulation of the glutamate transporter function, involved in the modulation of brain plasticity and cognitive function to prevent neurodegenerative disorders such as Alzheimer's disease (AD). In in vitro studies, the C6 rat glioma cell line is a widely applied aging model system to investigate changes in glial cells associated with aging or AD. However, the neurotoxicity mechanism whether AQP4 mediate glutamate uptake in Aβ-stimulated C6 cell remain uncertain. In this study, we examined the effects of Aβ on the expression of AQP4, Glu transporters, Glu uptake, and cell viability in insulin-treated C6 cells. Our results showed that the expression of AQP4 mRNA and protein was significantly enhanced by insulin in older cultures (passage 45), and the expression was inhibited by Aβ at 10 μM. In addition, the cell viability and glutamate uptake in Aβ-treated C6 cells were decreased in dose-dependent manners. GFAP showed similar changes in gene and protein expression patterns as AQP4, but no significant alterations were seen in GLAST expression. In C6 cells, the glutamate transport was found to be EAAC1, not GLT-1. EAAC1 expression was decreased by the treatment of Aβ. Taken together, our findings suggest that C6 cells may have astrocytic characteristics, and the astrocytic cytotoxicity induced by Aβ was mediated by reduction of glutamate uptake through AQP4/EAAC1 pathway in C6 cells. This indicates that C6 glioma cells could be used to study the roles of AQP4 on astrocyte function in AD.

Antioxidant Effects of Walnut (Juglans regia L.) Kernel and Walnut Septum Extract in a D-Galactose-Induced Aging Model and in Naturally Aged Rats

Antioxidant dietary intervention is considered a potential strategy in delaying age-related dysfunctions. In this study of 56 days, we assessed the antioxidant effects of walnut kernel (WK) and walnut septum extract (WSE) in a D-galactose (D-gal)-induced aging model and in a naturally aged rat model. Young Wistar rats, treated with D-gal (1200 mg/week), and old rats received daily WK or WSE added to the feed. After 8 weeks, blood, liver, and brain samples were collected and hematological, biochemical, oxidative stress biomarkers, histological, and immunohistochemical analyses were performed. Moreover, acetylcholinesterase activity was investigated in brain homogenates. The outcomes demonstrated significant improvement in cellular antioxidant activity and/or decrease of reactive oxygen species, advanced glycation end products, nitric oxide, malondialdehyde, or increase of glutathione after WK or WSE intake in both models. Additionally, WSE showed hypoglycemic effect, and both WK and WSE lowered acetylcholinesterase activity. Both diets could protect neurons against the induced senescence and could reverse the pathological conditions in the physiological aged brain. Thus, dietary supplementation with WK or WSE can maintain the liver and brain health and reduce the risk of age-related diseases, as well as delaying the onset of aging processes.

An Overview of the Intrinsic Role of Citrullination in Autoimmune Disorders

A protein undergoes many types of posttranslation modification. Citrullination is one of these modifications, where an arginine amino acid is converted to a citrulline amino acid. This process depends on catalytic enzymes such as peptidylarginine deiminase enzymes (PADs). This modification leads to a charge shift, which affects the protein structure, protein-protein interactions, and hydrogen bond formation, and it may cause protein denaturation. The irreversible citrullination reaction is not limited to a specific protein, cell, or tissue. It can target a wide range of proteins in the cell membrane, cytoplasm, nucleus, and mitochondria. Citrullination is a normal reaction during cell death. Apoptosis is normally accompanied with a clearance process via scavenger cells. A defect in the clearance system either in terms of efficiency or capacity may occur due to massive cell death, which may result in the accumulation and leakage of PAD enzymes and the citrullinated peptide from the necrotized cell which could be recognized by the immune system, where the immunological tolerance will be avoided and the autoimmune disorders will be subsequently triggered. The induction of autoimmune responses, autoantibody production, and cytokines involved in the major autoimmune diseases will be discussed.

A caspase-6-cleaved fragment of Glial Fibrillary Acidic Protein as a potential serological biomarker of CNS injury after cardiac arrest

Blood levels of Glial Fibrillary Acidic protein (GFAP) reflect processes associated with different types of CNS injury. Evidence suggests that GFAP is cleaved by caspases during CNS injury, hence positioning GFAP fragments as potential biomarkers of injury-associated processes. We set out to develop an assay detecting the neo-epitope generated by caspase-6 cleavage of GFAP (GFAP-C6), and to assess the ability of GFAP-C6 to reflect pathological processes in patients suffering a cardiac arrest and subsequent global cerebral ischemia. Anti-GFAP-C6 antibodies recognized their specific target sequence, and dilution and spike recoveries in serum were within limits of ±20% reflecting high precision and accuracy of measurements. Intra- and inter-assay CVs were below limits of 10% and 15%, respectively. Serological levels of GFAP-C6 were significantly elevated 72 hours after CA (Mean±SD) (20.39±10.59 ng/mL) compared to time of admission (17.79±10.77 ng/mL, p<0.0001), 24 hours (17.40±7.99 ng/mL, p<0.0001) and 48 hours (17.87±8.56 ng/mL, p<0.0001) after CA, but were not related to neurological outcome at day 180. GFAP-C6 levels at admission, 24, 48, and 72 hours after cardiac arrest correlated with two proteolytic fragments of tau, tau-A (r = 0.30, r = 0.40, r = 0.50, r = 0.53, p < 0.0001) and tau-C (r = 54, r = 0.48, r = 0.55, r = 0.54, p < 0.0001), respectively. GFAP-C6 levels did not correlate with other markers of CNS damage; total tau, NSE and S100B. In conclusion, we developed the first assay detecting a caspase-6 cleaved fragment of GFAP in blood. Increased levels at 72 hours after cardiac arrest as well as moderate correlations between GFAP-C6 and two other blood biomarkers of neurodegeneration suggest the ability of GFAP-C6 to reflect pathological processes of the injured brain. Investigations into the potential of GFAP-C6 in other types of CNS injury are warranted.

Gut epithelial and vascular barrier abnormalities in patients with chronic intestinal pseudo-obstruction

BACKGROUND

Chronic intestinal pseudo-obstruction (CIPO) is a rare condition due to severe impairment of gut motility responsible for recurrent subocclusive episodes. Although neuromuscular-glial-ICC abnormalities represent the main pathogenetic mechanism, the pathophysiology of CIPO remains poorly understood. Intestinal epithelial and vascular endothelial barrier (IEVB) abnormalities can contribute to neuroepithelial changes by allowing passage of harmful substances.

METHODS

To test retrospectively whether IEVB defects occur in patients with CIPO, we measured the jejunal protein expression of the major tight junction (TJ) components. CIPO patients were subdivided according to gut neuromuscular histopathology: apparently normal (AN); with inflammation (INF); or with degenerative alterations (DEG). The presence of occludin/claudin oligomers (index of TJ assembly), the amount of occludin, claudin-4, and zonula occludens-1 (ZO-1), and the expression of vasoactive intestinal polypeptide (VIP) and glial fibrillary acidic protein (GFAP) immunoreactivities were evaluated on jejunal full-thickness biopsies using Western blot.

KEY RESULTS

Oligomers were absent in the 73% of CIPO. Total occludin decreased in CIPO with AN and INF changes. Claudin-4 was upregulated in CIPO with INF and DEG features. ZO-1 and VIP expression decreased selectively in DEG group. GFAP increased in CIPO regardless the histopathological phenotype.

CONCLUSIONS & INFERENCES

The absence of oligomers demonstrated in our study suggests that IEBV is altered in CIPO. The mechanism leading to oligomerization is occludin-dependent in AN and INF, whereas is ZO-1-dependent in DEG. Our study provides support to IEVB abnormalities contributing to CIPO clinical and histopathological features.

NRGN, S100B and GFAP levels are significantly increased in patients with structural lesions resulting from mild traumatic brain injuries

OBJECTIVE

To determine whether serum neurogranin (NRGN), glial fibrillary acidic protein (GFAP), and calcium-binding protein S100 beta (S100B) levels are associated with traumatic intracranial lesions compared to computed tomography (CT) findings of patients with mild traumatic brain injury (mTBI).

PATIENTS AND METHODS

The cross-sectional study cohort included 48 patients who were admitted to the Emergency Department with a complaint of mTBI, a Glasgow Coma Scale score of 14-15, and at least one symptom of head trauma (i.e., post-traumatic amnesia, nausea or vomiting, post-traumatic seizures, persistent headache, and transient loss of consciousness). Blood samples and CT scans were obtained for all patients within 4 h of injury. Age-matched patients without intracranial traumatic pathology (CT-) were recruited as a control group. Blood samples were measured for NRGN, GFAP, and S100B levels.

RESULTS

Of 48 patients, 24 were CT + and had significantly higher serum NRGN (5.79 vs. 2.95 ng/mL), GFAP (0.59 vs.0.36 ng/mL), and S100B (1.72 vs.0.73 μg/L) levels than those who were CT- (p = 0.001, p = 0.026, and p < 0.001, respectively). ROC curves showed that NRGN, GFAP, and S100B levels were sufficient to distinguish traumatic brain injury in patients with mTBI. At the cut-off value for NRGN of 1.87 ng/mL, sensivity was 83.3%, and specificity was 58.3%. At the cut-off value for GFAP of 0.23 ng/mL, sensivity was 75% and specificity was 62.5%. The optimal cut-off value for S100B was 0.47 μg/L (95.8% sensitivity and 62.5% specificity).

CONCLUSION

This is the first study to evaluate NRGN in human serum after mTBI. We confirmed that NRGN levels were significantly higher in CT + patients than CT- patients in the mTBI patient population. Future studies of larger populations and different age groups (especially pediatric) can help reduce the number of CT scans as a reliable and noninvasive diagnostic tool for evaluating NRGN protein levels in mTBI patients with a low probability of intracranial lesions.

Exosomes in Pathogenesis, Diagnosis, and Treatment of Alzheimer's Disease

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by the accumulation of β-amyloid peptide 1-42 and phosphorylation of tau protein in the brain. Thus far, the transfer mechanism of these cytotoxic proteins between nerve cells remains unclear. Recent studies have shown that nanoscale extracellular vesicles (exosomes) originating from cells may play important roles in this transfer process. In addition, several genetic materials and proteins are also involved in intercellular communication by the secretion of the exosomes. That proposes novel avenues for early diagnosis and biological treatment in AD, based on exosome detection and intervention. In this review, exosome-related pathways of cytotoxic protein intercellular transfer in AD, and the effect of membrane proteins on exosomes targeting cells are first introduced. The advances in exosome-related biomarker detection in AD are summarized. Finally, the advantages and challenges of reducing cytotoxic protein accumulation via exosomal intervention for AD treatment are discussed. It is envisaged that future research in exosomes may well provide new insights into the pathogenesis, diagnosis, and treatment of AD.

Helper CD4 T cells expressing granzyme B cause glial fibrillary acidic protein fragmentation in astrocytes in an MHCII-independent manner

During inflammatory processes of the central nervous system, helper T cells have the capacity to cross the blood-brain barrier and injure or kill neural cells through cytotoxic mechanisms. Glial fibrillary acidic protein (GFAP) is an intermediate filament protein that is part of the astrocyte cytoskeleton that can become fragmented in neuroinflammatory conditions. The mechanism of action by which helper T cells with cytotoxic properties injure astrocytes is not completely understood. Primary human astrocytes were obtained from fetal brain tissue. Human helper (CD4⁺ ) T cells were isolated from peripheral blood mononuclear cells and activated with the superantigen staphylococcal enterotoxin E (SEE). Granzyme B was detected by enzyme linked immunosorbent assay and intracellular flow cytometry. GFAP fragmentation was monitored by western blotting. Cell death was monitored by lactic acid dehydrogenase release and terminal biotin-dUTP nick labeling (TUNEL). Astrocyte migration was monitored by scratch assay. Adult human oligodendrocytes were cultured with sublethally injured astrocytes to determine support function. Helper T cells activated with SEE expressed granzyme B but not perforin. Helper T cells released granzyme B upon contact with astrocytes and caused GFAP fragmentation in a caspase-dependent, MHCII-independent manner. Sublethally injured astrocytes were not apoptotic; however, their processes were thin and elongated, their migration was attenuated, and their ability to support oligodendrocytes was reduced in vitro. Helper T cells can release granzyme B causing sublethal injury to astrocytes, which compromises the supportive functions of astrocytes. Blocking these pathways may lead to improved resolution of neuroinflammatory lesions.

Serum GFAP level: A novel adjunctive diagnostic test in differentiate epileptic seizures from psychogenic attacks

PURPOSE

There has been increasing interest in the use of different biomarkers to help distinguish psychogenic from epileptic seizures, in patients presenting acutely with seizure-like events. In the present study, we measured serum glial fibrillary astrocytic protein (GFAP) levels in patients presenting with such events who were subsequently diagnosed as epileptic seizures (ESs) or psychogenic non-epileptic seizures (PNESs) and compared GFAP levels obtained with those found in healthy subjects.

METHODS

Sixty-three patients with seizures (43 with ES and 20 with PNES), and 19 healthy subjects participated in the study. Venous blood samples were obtained within the first 6 h after seizures and serum GFAP levels were measured by protein quantification (ELIZA kit) with an electrochemical luminescence immunoassay.

RESULTS

Serum GFAP levels were significantly higher in patients with ES compared to PNES or healthy controls. A cut-off point of 2.71 ng/ml was found optimally to differentiate ES from PNES (sensitivity 72%, specificity 59%).

CONCLUSION

Our study suggests that post-seizure serum GFAP levels could be used in future studies better to understand the underlying mechanism of seizures and may offer as an adjunctive diagnostic test in differentiating ES from PNES.

Synergistic Toxicity of the Neurometabolites Quinolinic Acid and Homocysteine in Cortical Neurons and Astrocytes: Implications in Alzheimer's Disease

The brain of patients affected by Alzheimer's disease (AD) develops progressive neurodegeneration linked to the formation of proteins aggregates. However, their single actions cannot explain the extent of brain damage observed in this disorder, and the characterization of co-adjuvant involved in the early toxic processes evoked in AD is essential. In this line, quinolinic acid (QUIN) and homocysteine (Hcy) appear to be involved in the AD neuropathogenesis. Herein, we investigate the effects of QUIN and Hcy on early toxic events in cortical neurons and astrocytes. Exposure of primary cortical cultures to these neurometabolites for 24 h induced concentration-dependent neurotoxicity. In addition, QUIN (25 μM) and Hcy (30 μM) triggered ROS production, lipid peroxidation, diminished of Na⁺,K⁺-ATPase activity, and morphologic alterations, culminating in reduced neuronal viability by necrotic cell death. In astrocytes, QUIN (100 μM) and Hcy (30 μM) induced caspase-3-dependent apoptosis and morphologic alterations through oxidative status imbalance. To establish specific mechanisms, we preincubated cell cultures with different protective agents. The combined toxicity of QUIN and Hcy was attenuated by melatonin and Trolox in neurons and by NMDA antagonists and glutathione in astrocytes. Cellular death and morphologic alterations were prevented when co-culture was treated with metabolites, suggesting the activation of protector mechanisms dependent on soluble factors and astrocyte and neuron communication through gap junctions. These findings suggest that early damaging events involved in AD can be magnified by synergistic toxicity of the QUIN and Hcy. Therefore, this study opens new possibilities to elucidate the molecular mechanisms of neuron-astrocyte interactions and their role in neuroprotection against QUIN and Hcy.

CSF tau is associated with impaired cortical plasticity, cognitive decline and astrocyte survival only in APOE4-positive Alzheimer's disease

In Alzheimer’s disease (AD) patients, apopoliprotein (APOE) polymorphism is the main genetic factor associated with more aggressive clinical course. However, the interaction between cerebrospinal fluid (CSF) tau protein levels and APOE genotype has been scarcely investigated. A possible key mechanism invokes the dysfunction of synaptic plasticity. We investigated how CSF tau interacts with APOE genotype in AD patients. We firstly explored whether CSF tau levels and APOE genotype influence disease progression and long-term potentiation (LTP)-like cortical plasticity as measured by transcranial magnetic stimulation (TMS) in AD patients. Then, we incubated normal human astrocytes (NHAs) with CSF collected from sub-groups of AD patients to determine whether APOE genotype and CSF biomarkers influence astrocytes survival. LTP-like cortical plasticity differed between AD patients with apolipoprotein E4 (APOE4) and apolipoprotein E3 (APOE3) genotype. Higher CSF tau levels were associated with more impaired LTP-like cortical plasticity and faster disease progression in AD patients with APOE4 but not APOE3 genotype. Apoptotic activity was higher when cells were incubated with CSF from AD patients with APOE4 and high tau levels. CSF tau is detrimental on cortical plasticity, disease progression and astrocyte survival only when associated with APOE4 genotype. This is relevant for new therapeutic approaches targeting tau.

New astroglial injury-defined biomarkers for neurotrauma assessment

Traumatic brain injury (TBI) is an expanding public health epidemic with pathophysiology that is difficult to diagnose and thus treat. TBI biomarkers should assess patients across severities and reveal pathophysiology, but currently, their kinetics and specificity are unclear. No single ideal TBI biomarker exists. We identified new candidates from a TBI CSF proteome by selecting trauma-released, astrocyte-enriched proteins including aldolase C (ALDOC), its 38kD breakdown product (BDP), brain lipid binding protein (BLBP), astrocytic phosphoprotein (PEA15), glutamine synthetase (GS) and new 18-25kD-GFAP-BDPs. Their levels increased over four orders of magnitude in severe TBI CSF. First post-injury week, ALDOC levels were markedly high and stable. Short-lived BLBP and PEA15 related to injury progression. ALDOC, BLBP and PEA15 appeared hyper-acutely and were similarly robust in severe and mild TBI blood; 25kD-GFAP-BDP appeared overnight after TBI and was rarely present after mild TBI. Using a human culture trauma model, we investigated biomarker kinetics. Wounded (mechanoporated) astrocytes released ALDOC, BLBP and PEA15 acutely. Delayed cell death corresponded with GFAP release and proteolysis into small GFAP-BDPs. Associating biomarkers with cellular injury stages produced astroglial injury-defined (AID) biomarkers that facilitate TBI assessment, as neurological deficits are rooted not only in death of CNS cells, but also in their functional compromise.

Distinct Mechanisms Underlying Resveratrol-Mediated Protection from Types of Cellular Stress in C6 Glioma Cells

The polyphenolic phytostilbene, trans-resveratrol, is found in high amounts in several types and tissues of plants, including grapes, and has been proposed to have beneficial effects in the central nervous system due to its activity as an antioxidant. The objective of the present study was to identify the mechanisms underlying the protective effects of resveratrol under conditions of oxidative stress or DNA damage, induced by the extracellularly applied oxidant, tert-butyl hydrogen peroxide, or UV-irradiation, respectively. In C6 glioma cells, a model system for glial cell biology and pharmacology, resveratrol was protective against both types of insult. Prevention of tau protein cleavage and of the formation of neurofibrillary tangles were identified as mechanisms of action of resveratrol-mediated protection in both paradigms of cellular damage. However, depending on the type of insult, resveratrol exerted its protective activity differentially: under conditions of chemically induced oxidative stress, inhibition of caspase activity, while with DNA damage, resveratrol regulated tau phosphorylation at Ser⁴²². Results advance our understanding of resveratrol’s complex impact on cellular signaling pathway and contribute to the notion of resveratrol’s role as a pleiotropic therapeutic agent.

Characterization of a panel of monoclonal antibodies recognizing specific epitopes on GFAP

Alexander disease (AxD) is a neurodegenerative disease caused by heterozygous mutations in the GFAP gene, which encodes the major intermediate filament protein of astrocytes. This disease is characterized by the accumulation of cytoplasmic protein aggregates, known as Rosenthal fibers. Antibodies specific to GFAP could provide invaluable tools to facilitate studies of the normal biology of GFAP and to elucidate the pathologic role of this IF protein in disease. While a large number of antibodies to GFAP are available, few if any of them have defined epitopes. Here we described the characterization of a panel of commonly used anti-GFAP antibodies, which recognized epitopes at regions extending across the rod domain of GFAP. We show that all of the antibodies are useful for immunoblotting and immunostaining, and identify a subset that preferentially recognized human GFAP. Using these antibodies, we demonstrate the presence of biochemically modified forms of GFAP in brains of human AxD patients and mouse AxD models. These data suggest that this panel of anti-GFAP antibodies will be useful for studies of animal and cell-based models of AxD and related diseases in which cytoskeletal defects associated with GFAP modifications occur.

Acute death of astrocytes in blast-exposed rat organotypic hippocampal slice cultures

Blast traumatic brain injury (bTBI) affects civilians, soldiers, and veterans worldwide and presents significant health concerns. The mechanisms of neurodegeneration following bTBI remain elusive and current therapies are largely ineffective. It is important to better characterize blast-evoked cellular changes and underlying mechanisms in order to develop more effective therapies. In the present study, our group utilized rat organotypic hippocampal slice cultures (OHCs) as an in vitro system to model bTBI. OHCs were exposed to either 138 ± 22 kPa (low) or 273 ± 23 kPa (high) overpressures using an open-ended helium-driven shock tube, or were assigned to sham control group. At 2 hours (h) following injury, we have characterized the astrocytic response to a blast overpressure. Immunostaining against the astrocytic marker glial fibrillary acidic protein (GFAP) revealed acute shearing and morphological changes in astrocytes, including clasmatodendrosis. Moreover, overlap of GFAP immunostaining and propidium iodide (PI) indicated astrocytic death. Quantification of the number of dead astrocytes per counting area in the hippocampal cornu Ammonis 1 region (CA1), demonstrated a significant increase in dead astrocytes in the low- and high-blast, compared to sham control OHCs. However only a small number of GFAP-expressing astrocytes were co-labeled with the apoptotic marker Annexin V, suggesting necrosis as the primary type of cell death in the acute phase following blast exposure. Moreover, western blot analyses revealed calpain mediated breakdown of GFAP. The dextran exclusion additionally indicated membrane disruption as a potential mechanism of acute astrocytic death. Furthermore, although blast exposure did not evoke significant changes in glutamate transporter 1 (GLT-1) expression, loss of GLT-1-expressing astrocytes suggests dysregulation of glutamate uptake following injury. Our data illustrate the profound effect of blast overpressure on astrocytes in OHCs at 2 h following injury and suggest increased calpain activity and membrane disruption as potential underlying mechanisms.

PrPC expression and calpain activity independently mediate the effects of closed head injury in mice

The normal cellular prion protein (PrP^C) is a sialoglycoprotein with a glycophosphatidylinositol anchor and expressed in highest levels within the CNS particularly at neuronal synapses. This membrane-bound protein is involved with many cell functions including cell signaling and neuroprotection. Calpains are calcium-activated cysteine proteases that typically undergo controlled activation. PrP^C is a calpain substrate and is neurotoxic if it undergoes aberrant processing with cytosol accumulation. Following traumatic brain injury (TBI), there is an abnormal influx of Ca⁺² and overactivation of calpains resulting in neuronal dysfunction and cell death. We investigated whether PrP^C expression and calpain activity have an effect on, or are affected by, TBI. PrP^C expression in the hippocampus, cortex and cerebellum of WT and Tga20 (PrP^C overexpression) mice were unchanged after closed head injury (CHI). Further, PrP^C in WT and Tga20 mice was resistant to TBI-induced calpain proteolysis. CHI-induced calpain activation resulted in breakdown products (BDPs) of αII-spectrin (SBDPs) and GFAP (GBDP-44K) in all brain regions and mouse lines. CHI caused significant increases in SBDP145, GFAP and GBDP-44K when compared to sham. With few exceptions, the calpain inhibitor, SNJ-1945, reduced SBDP145 and GBDP-44K levels. Behavioral studies suggested that PrP^C and calpain independently affect learning and memory. Overall, we conclude that: (i) there is SNJ-1945-sensitive calpain activation in both neuron and glial cells following CHI, (ii) closed head trauma is not affected by, nor does it have an influence on, PrP^C expression, and (iii) PrP^C expression plays a minor role, if any, in CHI-induced calpain activation in vivo.

Astrogliosis: An integral player in the pathogenesis of Alzheimer's disease

Alzheimer's disease is the main cause of dementia in the elderly and begins with a subtle decline in episodic memory followed by a more general decline in overall cognitive abilities. Though the exact trigger for this cascade of events remains unknown the presence of the misfolded amyloid-beta protein triggers reactive gliosis, a prominent neuropathological feature in the brains of Alzheimer's patients. The cytoskeletal and morphological changes of astrogliosis are its evident features, while changes in oxidative stress defense, cholesterol metabolism, and gene transcription programs are less manifest. However, these latter molecular changes may underlie a disruption in homeostatic regulation that keeps the brain environment balanced. Astrocytes in Alzheimer's disease show changes in glutamate and GABA signaling and recycling, potassium buffering, and in cholinergic, purinergic, and calcium signaling. Ultimately the dysregulation of homeostasis maintained by astrocytes can have grave consequences for the stability of microcircuits within key brain regions. Specifically, altered inhibition influenced by astrocytes can lead to local circuit imbalance with farther reaching consequences for the functioning of larger neuronal networks. Healthy astrocytes have a role in maintaining and modulating normal neuronal communication, synaptic physiology and energy metabolism, astrogliosis interferes with these functions. This review considers the molecular and functional changes occurring during astrogliosis in Alzheimer's disease, and proposes that astrocytes are key players in the development of dementia.

Glial fibrillary acidic protein as a biomarker in severe traumatic brain injury patients: a prospective cohort study

Introduction

Glial fibrillary acidic protein (GFAP) may serve as a serum marker of traumatic brain injury (TBI) that can be used to monitor biochemical changes in patients and gauge the response to treatment. However, the temporal profile of serum GFAP in the acute period of brain injury and the associated utility for outcome prediction has not been elucidated.

Methods

We conducted a prospective longitudinal cohort study of consecutive severe TBI patients in a local tertiary neurotrauma center in Shanghai, China, between March 2011 and September 2014. All patients were monitored and managed with a standardized protocol with inclusion of hypothermia and other intensive care treatments. Serum specimens were collected on admission and then daily for the first 5 days. GFAP levels were measured using enzyme-linked immunosorbent assay techniques. Patient outcome was assessed at 6 months post injury with the Glasgow Outcome Scale and further grouped into death versus survival and unfavorable versus favorable.

Results

A total of 67 patients were enrolled in the study. The mean time from injury to admission was 2.6 hours, and the median admission Glasgow Coma Scale score was 6. Compared with healthy subjects, patients with severe TBI had increased GFAP levels on admission and over the subsequent 5 days post injury. Serum GFAP levels showed a gradual reduction from admission to day 3, and then rebounded on day 4 when hypothermia was discontinued with slow rewarming. GFAP levels were significantly higher in patients who died or had an unfavorable outcome across all time points than in those who were alive or had a favorable outcome. Results of receiver operating characteristic curve analysis indicated that serum GFAP at each time point could predict neurological outcome at 6 months. The areas under the curve for GFAP on admission were 0.761 for death and 0.823 for unfavorable outcome, which were higher than those for clinical variables such as age, Glasgow Coma Scale score, and pupil reactions.

Conclusions

Serum GFAP levels on admission and during the first 5 days of injury were increased in patients with severe TBI and were predictive of neurological outcome at 6 months.

Glial fibrillary acidic protein: from intermediate filament assembly and gliosis to neurobiomarker

Glial fibrillary acidic protein (GFAP) is an intermediate filament (IF) III protein uniquely found in astrocytes in the central nervous system (CNS), non-myelinating Schwann cells in the peripheral nervous system (PNS), and enteric glial cells. GFAP mRNA expression is regulated by several nuclear-receptor hormones, growth factors, and lipopolysaccharides (LPSs). GFAP is also subject to numerous post-translational modifications (PTMs), while GFAP mutations result in protein deposits known as Rosenthal fibers in Alexander disease. GFAP gene activation and protein induction appear to play a critical role in astroglial cell activation (astrogliosis) following CNS injuries and neurodegeneration. Emerging evidence also suggests that, following traumatic brain and spinal cord injuries and stroke, GFAP and its breakdown products are rapidly released into biofluids, making them strong candidate biomarkers for such neurological disorders.

The potential of pathological protein fragmentation in blood-based biomarker development for dementia - with emphasis on Alzheimer's disease

The diagnosis of dementia is challenging and early stages are rarely detected limiting the possibilities for early intervention. Another challenge is the overlap in the clinical features across the different dementia types leading to difficulties in the differential diagnosis. Identifying biomarkers that can detect the pre-dementia stage and allow differential diagnosis could provide an opportunity for timely and optimal intervention strategies. Also, such biomarkers could help in selection and inclusion of the right patients in clinical trials of both Alzheimer’s disease and other dementia treatment candidates. The cerebrospinal fluid (CSF) has been the most investigated source of biomarkers and several candidate proteins have been identified. However, looking solely at protein levels is too simplistic to provide enough detailed information to differentiate between dementias, as there is a significant crossover between the proteins involved in the different types of dementia. Additionally, CSF sampling makes these biomarkers challenging for presymptomatic identification. We need to focus on disease-specific protein fragmentation to find a fragment pattern unique for each separate dementia type – a form of protein fragmentology. Targeting protein fragments generated by disease-specific combinations of proteins and proteases opposed to detecting the intact protein could reduce the overlap between diagnostic groups as the extent of processing as well as which proteins and proteases constitute the major hallmark of each dementia type differ. In addition, the fragments could be detectable in blood as they may be able to cross the blood–brain barrier due to their smaller size. In this review, the potential of the fragment-based biomarker discovery for dementia diagnosis and prognosis is discussed, especially highlighting how the knowledge from CSF protein biomarkers can be used to guide blood-based biomarker development.

Increased levels and activity of cathepsins B and D in kainate-induced toxicity

Administration of kainic acid induces acute seizures that result in the loss of neurons, gliosis and reorganization of mossy fiber pathways in the hippocampus resembling those observed in human temporal lobe epilepsy. Although these structural changes have been well characterized, the mechanisms underlying the degeneration of neurons following administration of kainic acid remain unclear. Since the lysosomal enzymes, cathepsins B and D, are known to be involved in the loss of neurons and clearance of degenerative materials in a variety of experimental conditions, we evaluated their potential roles in kainic acid-treated rats. In parallel, we also measured the levels and expression of insulin-like growth factor-II/mannose 6-phosphate (IGF-II/M6P) receptors, which mediate the intracellular trafficking of these enzymes, in kainic acid-treated rats. Our results showed that systemic administration of kainic acid evoked severe loss of neurons along with hypertrophy of astrocytes and microglia in the hippocampus of the adult rat brain. The levels and activity of cathepsins B and D increased with time in the hippocampus of kainic acid-treated rats compared to the saline-injected control animals. The expression of both cathepsins B and D, as evident by immunolabeling studies, was also markedly increased in activated astrocytes and microglia of the kainic acid-treated rats. Additionally, cytosolic levels of the cathepsins were enhanced along with cytochrome c and to some extent Bax in the hippocampus in kainic acid-treated rats. These changes were accompanied by appearance of cleaved caspase-3-positive neurons in the hippocampus of kainic acid-treated animals. The levels of IGF-II/M6P receptors, on the other hand, were not significantly altered, but these receptors were found to be present in a subset of reactive astrocytes following administration of kainic acid. These results, taken together, suggest that enhanced levels/expression and activity of lysosomal enzymes may have a role in the loss of neurons and/or clearance of degenerative materials observed in kainic acid-treated rats.

Combined suppression of CASP2 and CASP6 protects retinal ganglion cells from apoptosis and promotes axon regeneration through CNTF-mediated JAK/STAT signalling

We have previously shown that crushing the optic nerve induces death of retinal ganglion cells by apoptosis, but suppression of CASP2, which is predominantly activated in retinal ganglion cells, using a stably modified short interfering RNA CASP2, inhibits retinal ganglion cell apoptosis. Here, we report that combined delivery of short interfering CASP2 and inhibition of CASP6 using a dominant negative CASP6 mutant activates astrocytes and Müller cells, increases CNTF levels in the retina and leads to enhanced retinal ganglion cell axon regeneration. In dissociated adult rat mixed retinal cultures, dominant negative CASP6 mutant + short interfering CASP2 treatment also significantly increases GFAP+ glial activation, increases the expression of CNTF in culture, and subsequently increases the number of retinal ganglion cells with neurites and the mean retinal ganglion cell neurite length. These effects are abrogated by the addition of MAB228 (a monoclonal antibody targeted to the gp130 component of the CNTF receptor) and AG490 (an inhibitor of the JAK/STAT pathway downstream of CNTF signalling). Similarly, in the optic nerve crush injury model, MAB228 and AG490 neutralizes dominant negative CASP6 mutant + short interfering CASP2-mediated retinal ganglion cell axon regeneration, Müller cell activation and CNTF production in the retina without affecting retinal ganglion cell survival. We therefore conclude that axon regeneration promoted by suppression of CASP2 and CASP6 is CNTF-dependent and mediated through the JAK/STAT signalling pathway. This study offers insights for the development of effective therapeutics for promoting retinal ganglion cell survival and axon regeneration.