Astrocyte Biomarker Research Articles

Glial Fibrillary Acidic Protein's Usefulness as an Astrocyte Biomarker Using the Fully Automated LUMIPULSE® System.

Glial fibrillary acidic protein (GFAP) is an important biomarker for neuroinflammatory conditions. Recently, advancements in the treatment of neurological diseases have highlighted the increasing importance of biomarkers, creating a demand for accurate and simple measurement systems for GFAP levels, which are essential for both research and clinical applications. This study presents the development and validation of a novel fully automated immunoassay for the quantitative determination of GFAP levels in biological samples. We examined the analytical performance of the GFAP assay on the LUMIPULSE platform. The assay's parameters, including antibody concentrations, incubation times, and detection methods, were optimized to enhance sensitivity and specificity. GFAP levels were measured in 396 serum or plasma samples, comprising both healthy controls and patients with neurodegenerative diseases. In the analytical performance studies, intra- and inter-assay coefficients of variation (CV) were below 5%, indicating high reproducibility. Additionally, the assay demonstrated good linearity over the measurement range. The limit of quantification (LoQ) for this assay was 6.0 pg/mL, which is sufficient for measuring specimens from healthy controls. In clinical validation studies, GFAP levels were significantly elevated in patients with neurodegenerative diseases compared to healthy controls. This automated GFAP assay provides a robust and reliable tool for GFAP measurement, facilitating further research into GFAP's role in neurological disorders and potentially aiding in the diagnosis and monitoring of these conditions.

Oneyear longitudinal study on biomarkers of blood–brain barrier permeability in COVID-19 patients

The pathophysiology behind neurological and cognitive sequelae of COVID-19 may be related to dysfunction of the blood-brain barrier (BBB) and previous research indicate transient neuronal injury and glial activation. The aim of this study was to investigate if COVID-19 is related to increased BBB permeability by analyzing leakage of biomarkers such as astrocyte-derived extracellular vesicles (EVs) and S100B. We also investigated whether levels of these biomarkers correlated with self-reported symptoms that persisted > 2 months. The samples in this 1-year follow-up study came from an ongoing longitudinal study of unvaccinated patients hospitalized for COVID-19 at Danderyd University Hospital, Stockholm, Sweden, between April and June 2020. Blood samples were collected at baseline and 4, 8, and 12 months after hospitalization. Information on self-reported clinical symptoms was collected at follow-up visits. A total of 102 patients were enrolled, and 47 completed all follow-up measurements. Peak levels of both biomarkers were observed at 4 months in the subset of 55 patients who were measured at this timepoint. At 12 months, the biomarkers had returned to baseline levels. The biomarkers were not correlated with any of the long-term self-reported symptoms. COVID-19 is associated with transient increased BBB permeability, shown by elevated levels of astrocyte biomarkers in plasma. However, these levels return to baseline 12 months post-infection and do not correlate with long-term symptoms. Further research is needed to unravel the underlying mechanisms causing long-term symptoms in COVID-19 patients.

Quercetin ameliorates neuroinflammatory and neurodegenerative biomarkers in the brain and improves neurobehavioral parameters in a repeated intranasal amyloid-beta exposed model of Alzheimer's disease.

Objectives: The aim of the present study was to study the potential therapeutic effects of quercetin in protection against repeated intranasal exposure of an amyloid-beta-induced mouse model. Methods: Mice received intranasal Aβ1-42 (5 μg/10 μL) exposure once daily for seven consecutive days. Quercetin was orally administered to them at 30 mg kg-1 and 100 mg kg-1 doses for one week starting from day five following Aβ1-42 peptide administration. Following this, the animals were evaluated for neurobehavioral parameters using a Morris water maze test and a novel object recognition test. Further to this, the biomarkers for neuroinflammation and neurodegeneration were evaluated in the hippocampus and cortex regions of the brain in these animals. Results: Multiple exposures to intranasal Aβ led to a significant decline in the learning and cognitive memory of the animals, whereas oral treatment with quercetin at dosages of 30 and 100 mg kg-1 alleviated Aβ-induced effects. Quercetin treatment significantly reduced Aβ accumulation, oxidative stress and proinflammatory cytokine biomarkers in the brain. In addition, it also alleviated the activation of astrocytic biomarkers, amyloid precursor protein and phosphorylated-tau proteins in the brain. Conclusion: Quercetin was found to be a potent antioxidant, anti-inflammatory compound with protection against neurodegenerative damage and improved learning and cognitive memory in a repeated Aβ-exposure model of AD.

Blood Astrocyte Biomarkers in Alzheimer Disease: A Systematic Review and Meta-Analysis.

Neuroinflammation, particularly early astrocyte reactivity, is a significant driver of Alzheimer disease (AD) pathogenesis. It is unclear how the levels of astrocyte biomarkers change in patients across the AD continuum and which best reflect AD-related change. We performed a systematic review and meta-analysis of 3 blood astrocyte biomarkers (glial fibrillary acidic protein [GFAP], chitinase-3-like protein 1 [YKL-40], and S100B) in patients clinically diagnosed with AD. MEDLINE and Web of Science were searched on March 23, 2023, without restrictions on language, time, or study design, for studies reporting blood levels of the astrocyte biomarkers GFAP, YKL-40, or S100B in patients on the AD continuum (including those with mild cognitive impairment [MCI] and dementia) and a cognitively unimpaired (CU) control population. AD diagnosis was based on established diagnostic criteria and/or comprehensive multidisciplinary clinical consensus. Studies reporting indirect biomarker measures (e.g., levels of biomarker autoantibodies) were excluded. Risk of bias assessment was performed using the revised Quality Assessment of Diagnostic Accuracy Studies tool. Pooled effect sizes were determined using the Hedge g method with a random-effects model. The review was prospectively registered on PROSPERO (registration number CRD42023458305). The search identified 1,186 studies; 36 met inclusion criteria (AD continuum n = 3,366, CU n = 4,115). No study was assessed to have a high risk of bias. Compared with CU individuals, patients on the AD continuum had higher GFAP and YKL-40 levels (GFAP effect size 1.15, 95% CI 0.94-1.36, p < 0.0001; YKL-40 effect size 0.38, 95% CI 0.28-0.49, p < 0.0001). Both biomarkers were elevated in more advanced clinical stages of the disease (i.e., in AD dementia compared with MCI due to AD: GFAP effect size 0.48, 95% CI 0.19-0.76, p = 0.0009; YKL-40 effect size 0.34, 95% CI 0.10-0.57, p = 0.0048). No significant differences in blood S100B levels were identified. We demonstrated significant elevations in blood GFAP and YKL-40 levels in patients on the AD continuum compared with CU individuals. Furthermore, within the AD clinical spectrum, significant elevation correlated with more advanced disease stage. Our findings suggest that both biomarkers reflect AD-related pathology. Our findings are limited by the lack of cultural and linguistic diversity in the study populations meta-analyzed. Future meta-analyses using a biomarker-defined AD population are warranted.

Associations between Microglia and Astrocytic Proteins and Tau Biomarkers across the Continuum of Alzheimer's Disease.

Recent investigations implicate neuroinflammatory changes, including astrocyte and microglia activation, as crucial in the progression of Alzheimer's disease (AD) Thus, we compared selected proteins reflecting neuroinflammatory processes to establish their connection to AD pathologies. Our study, encompassing 80 subjects with (n = 42) AD, (n = 18) mild cognitive impairment (MCI) and (n = 20) non-demented controls compares the clinical potential of tested molecules. Using antibody-based methods, we assessed concentrations of NGAL, CXCL-11, sTREM1, and sTREM2 in cerebrospinal fluid (CSF). Proinflammatory proteins, NGAL, and CXCL-11 reached a peak in the early stage of the disease and allowed for the identification of patients with MCI. Furthermore, the concentration of the anti-inflammatory molecule sTREM2 was highest in the more advanced stage of the disease and permitted differentiation between AD and non-demented controls. Additionally, sTREM2 was biochemically linked to tau and pTau in the AD group. Notably, NGAL demonstrated superior diagnostic performance compared to classical AD biomarkers in discriminating MCI patients from controls. These findings suggest that proteins secreted mainly through microglia dysfunction might play not only a detrimental but also a protective role in the development of AD pathology.

In Vivo Assessment of Astrocyte Reactivity in Patients with Progressive Supranuclear Palsy.

Although astrocytic pathology is a pathological hallmark of progressive supranuclear palsy (PSP), its pathophysiological role remains unclear. This study aimed to assess astrocyte reactivity in vivo in patients with PSP. Furthermore, we investigated alterations in brain lactate levels and their relationship with astrocyte reactivity. We included 30 patients with PSP-Richardson syndrome and 30 healthy controls; in patients, tau deposition was confirmed through 18F-florzolotau positron emission tomography. Myo-inositol, an astroglial marker, and lactate were quantified in the anterior cingulate cortex through magnetic resonance spectroscopy. We measured plasma biomarkers, including glial fibrillary acidic protein as another astrocytic marker. The anterior cingulate cortex was histologically assessed in postmortem samples of another 3 patients with PSP with comparable disease durations. The levels of myo-inositol and plasma glial fibrillary acidic protein were significantly higher in patients than those in healthy controls (p < 0.05); these increases were significantly associated with PSP rating scale and cognitive function scores (p < 0.05). The lactate level was high in patients, and correlated significantly with high myo-inositol levels. Histological analysis of the anterior cingulate cortex in patients revealed reactive astrocytes, despite mild tau deposition, and no marked synaptic loss. We discovered high levels of astrocyte biomarkers in patients with PSP, suggesting astrocyte reactivity. The association between myo-inositol and lactate levels suggests a link between reactive astrocytes and brain energy metabolism changes. Our results indicate that astrocyte reactivity in the anterior cingulate cortex precedes pronounced tau pathology and neurodegenerative processes in that region, and affects brain function in PSP. ANN NEUROL 2024;96:247-261.

TREM2 AD risk variants impact pTau and microglia and astrocyte related biomarkers in cognitively unimpaired subjects

AbstractBackgroundIn the central nervous system, Triggering Receptor Expressed on Myeloid Cells 2 (TREM2) is expressed primarily in microglia. TREM2 receptors are important for microglial functions including phagocytosis, lipid metabolism and inflammatory responses. TREM2 coding variants (e.g. R47H rs75932628 and R62H rs143332484) increase the risk of late onset Alzheimer’s Diseases (AD). However, the impact of TREM2 risk variants on microglial cell functions in humans remains to be elucidated.MethodCSF and plasma samples were collected from AD patients (n = 120) and cognitively unimpaired control subjects (n = 53) with subjective complaints who do not meet biomarker‐based criteria for AD diagnosis. TREM2 AD risk variant carriers (n = 52) were screened from over 6000 samples of the Amsterdam dementia cohort using a combination of genotype array and exome sequencing. We performed extensive biomarker analysis of CSF and plasma samples with multidisciplinary approaches. We compared the effect of TREM2 mutations on AD disease and microglial and astrocytic biomarkers in AD patients and in cognitively unimpaired control subjects, respectively. A linear model was used with age and gender adjusted for the data analysis.ResultWe found higher levels of pTau181 and pTau231 in CSF and plasma in cognitively unimpaired TREM2 mutation carriers compared to non‐carriers, while no difference was observed between TREM2 genotype among the AD patients. Microglia and astrocyte biomarkers including sTREM2, FABP3, OLR1, YKL40 and GFAP were higher in the CSF from cognitively unimpaired TREM2 mutation carriers compared to non‐carriers, but no difference was detected between TREM2 genotype among the AD patients. We also found different levels of lipid metabolites in CSF and plasma samples from the TREM2 mutation carriers compared to non‐carriers in both AD patients and cognitively unimpaired control subjects.ConclusionTREM2 AD risk variants in cognitively unimpaired subjects increase pTau biomarkers and microglial and astrocytic related biomarkers. In AD patients, the biomarker differences between TREM2 genotype are diminished likely due to the extensive microglial responses to AD pathology. Moreover, our data indicates TREM2 AD risk variants may impact lipid‐metabolic processes in microglial cells. These data provide the biomarker insights on how TREM2 mutations may increase the risk of AD.

Association between glial and synaptic fluid biomarkers and brain [18F]FDG‐PET signal

AbstractBackgroundBeyond the hypometabolic signature, indexed by [18F]FDG‐PET imaging, seen in the brain of Alzheimer’s disease (AD) patients, a transient brain glucose hypermetabolism has been recently identified in the early stages of AD. The cellular source of this dual metabolic response remains controversial, with glial cells gaining a lot of attention. In light of this, whether glial and synaptic fluid biomarkers are associated with [18F]FDG‐PET signal in the early stages of AD remains debatable. Thus, we evaluated the association of astrocyte, microglial and synaptic fluid biomarkers with [18F]FDG‐PET signal in an AD rat model.Method[18F]FDG‐PET imaging was conducted in ten‐month‐old (early amyloid stage) APP/PS1 (TgF344‐AD, n = 8‐17) and wild‐type (WT, n = 8‐15) rats. Glial (GFAP and sTREM2), synaptic (neurogranin), and amyloid biomarkers (Aß1‐40 and Aß1‐42) were quantified in the cerebrospinal fluid (CSF) and plasma through a multiplex immunoassay. T‐statistical maps of brain [18F]FDG‐PET and those fluid biomarkers were conducted at the voxel level using RMINC. Differences were considered statistically significant at p&lt;0.05 (t&gt;2).ResultA large hypermetabolic cluster was identified in ten‐month‐old TgF344‐AD (Fig. 1AB, local maxima, t(13) = 4.28). We found positive correlations between CSF TREM2 and brain [18F]FDG‐PET signal (Fig. 2AC, local maxima, t(13) = 4.12). In addition, we identified a positive correlation between plasma GFAP and brain [18F]FDG‐PET signal (Fig. 2BC, local maxima, t(13) = 10.62). Plasma TREM2, CSF GFAP, and plasma neurogranin did not associate with brain glucose metabolism.ConclusionOur findings suggest that CSF TREM2 and plasma GFAP are associated with brain metabolism before amyloid load reaches a plateau. Stronger association of plasma GFAP, rather than CSF GFAP, with brain pathology corroborates cross‐sectional human studies. One could argue that [18F]FDG‐PET hypermetabolism identified is likely a response to astrocyte and microglial changes.

Temporal evaluation of imaging and biofluid biomarkers, spatial neuropathology and glial function in the TgF344‐AD rat model

AbstractBackgroundThe development and characterization of Alzheimer’s disease (AD) animal models is particularly important for the investigation of pathophysiological mechanisms and drug development. The TgF344‐AD rat is a model harboring human APP/PS1 mutations with comprehensive presentation, including age‐dependent development of amyloid‐β (Aβ) plaques, neuronal loss and tau deposits, but not yet fully characterized. In light of this, we evaluated imaging and biofluid biomarkers, spatial neuropathology and glial function in these animals across multiple key ages.MethodsTgF344‐AD rats and wild‐type littermates were longitudinally evaluated at 3, 6, 9, 12 and 16‐18 months of age. Rats underwent [18F]FDG‐microPET scans and CSF samplings. CSF glial and immune markers (GFAP, S100B, TREM2, IL‐6, TNF‐α, IL‐10) were measured by multiplex immunoassay. A cross‐sectional cohort was used to measure cortical glutamate uptake (ex‐vivo slices) and follow the spatial distribution of Aβ plaques (6E10 antibody) at the same time points.ResultsAt 3, 6, 12 and 16‐18mo, no changes in [18F]FDG metabolism were observed. At 9mo, we identified a significant cortical hypermetabolism in the TgF344‐AD rats. CSF GFAP levels were elevated at 6 and 9 months of age, while CSF S100B was decreased at 9mo. The CSF inflammatory markers IL‐6, TNF‐α and IL‐10 were elevated at 16‐18mo. Additionally, the glutamate uptake was increased in the cortex at 9mo and 12mo, and in the hippocampus at 12mo. TREM2 was not altered in any of the ages evaluated. The (Aβ) plaques deposition starts at 6mo in the posterior temporal cortices and hippocampus and spreads slowly to frontal brain regions, reaching a plateau around 16mo.ConclusionThis work shows that the TgF344‐AD rat model recapitulates the early and transient glucose hypermetabolism seen in AD patients. Our results also indicate an associated early astrocyte response in these animals, with changes in relevant astrocyte biomarkers and function (glutamate uptake). Due to the critical role of astrocytes in brain glucose handling, these findings suggest that astrocyte reactivity could be driving glucose hypermetabolism. In contrast, the neuroinflammatory biomarkers changes identified suggest a strong neuroinflammatory response only at later stages in this rat model, however, further investigations are necessary to better elucidate these findings.

Astrocyte biomarkers GFAP and YKL-40 mediate early Alzheimer's disease progression.

We studied how biomarkers of reactive astrogliosis mediate the pathogenic cascade in the earliest Alzheimer's disease (AD) stages. We performed path analysis on data from 384 cognitively unimpaired individuals from the ALzheimer and FAmilies (ALFA)+ study using structural equation modeling to quantify the relationships between biomarkers of reactive astrogliosis and the AD pathological cascade. Cerebrospinal fluid (CSF) amyloid beta (Aβ)42/40 was associated with Aβ aggregation on positron emission tomography (PET) and with CSF p-tau181 , which was in turn directly associated with CSF neurofilament light (NfL). Plasma glial fibrillary acidic protein (GFAP) mediated the relationship between CSF Aβ42/40 and Aβ-PET, and CSF YKL-40 partly explained the association between Aβ-PET, p-tau181 , and NfL. Our results suggest that reactive astrogliosis, as indicated by different fluid biomarkers, influences the pathogenic cascade during the preclinical stage of AD. While plasma GFAP mediates the early association between soluble and insoluble Aβ, CSF YKL-40 mediates the latter association between Aβ and downstream Aβ-induced tau pathology and tau-induced neuronal injury. Lower CSF Aβ42/40 was directly linked to higher plasma GFAP concentrations. Plasma GFAP partially explained the relationship between soluble Aβ and insoluble Aβ. CSF YKL-40 mediated Aβ-induced tau phosphorylation and tau-induced neuronal injury.

Plasma β-synuclein, GFAP, and neurofilaments in patients with malignant gliomas undergoing surgical and adjuvant therapy.

We analyzed the longitudinal concentrations and prognostic roles of plasma β-synuclein (β-syn), glial fibrillary acidic protein (GFAP), and neurofilament proteins (NfL and NfH) in 33 patients with malignant gliomas, who underwent surgical and adjuvant therapy. GFAP and NfL levels were increased in patients with glioblastoma compared to cases with other tumors. β-syn, NfL and NfH increased after surgery, whereas GFAP decreased at long-term follow-up. β-syn andneurofilament concentrations were influenced by surgery and/or radiotherapy regimens. GFAP and neurofilament levels were significantly associated with survival. Plasma neuronal and astrocytic biomarkers are differentially altered in malignant glioma types and displayed distinct trajectories after surgical and adjuvant therapy.

Remedy Efficiency through Paclitaxel on Rat (Rattus norvegicus) Brain Injury and Risk Premium of N- Diethyl nitrosamine (DEN) Injection

Abstract The current study deals with the effect of N-Diethylnitrosamine (DEN) induced traumatic brain injury on male albino rats, as well as the outcome results of treatment with paclitaxel nanoparticles for a period of 8 weeks with two-week intervals is the concern of the present study. Mean body weight, as well as brain weight, was considered as the main parameters whereas a detailed immunohistochemical study on rat brain sections was performed. Astrocytic biomarkers for the diagnosis of astrocytes by fibrillary glial acidic protein (GFAP). Neuronal GFAP staining used for various broke sections were forwarded. Comparison and Contrast of all these parameters in all steps of the experiment had been discussed. The efficiency of the treatment was found to be evident. The effect on body weight was significant whereas brain weight results showed insignificant differences. A longer duration of treatment may well reflect more significant results.

The role of astrocytic α7 nicotinic acetylcholine receptors in Alzheimer disease.

The ongoing search for therapeutic interventions in Alzheimer disease (AD) has highlighted the complexity of this condition and the need for additional biomarkers, beyond amyloid-β (Aβ) and tau, to improve clinical assessment. Astrocytes are brain cells that control metabolic and redox homeostasis, among other functions, and are emerging as an important focus of AD research owing to their swift response to brain pathology in the initial stages of the disease. Reactive astrogliosis - the morphological, molecular and functional transformation of astrocytes during disease - has been implicated in AD progression, and the definition of new astrocytic biomarkers could help to deepen our understanding of reactive astrogliosis along the AD continuum. As we highlight in this Review, one promising biomarker candidate is the astrocytic α7 nicotinic acetylcholine receptor (α7nAChR), upregulation of which correlates with Aβ pathology in the brain of individuals with AD. We revisit the past two decades of research into astrocytic α7nAChRs to shed light on their roles in the context of AD pathology and biomarkers. We discuss the involvement of astrocytic α7nAChRs in the instigation and potentiation of early Aβ pathology and explore their potential as a target for future reactive astrocyte-based therapeutics and imaging biomarkers in AD.

Hippocampal GFAP-positive astrocyte responses to amyloid and tau pathologies

IntroductionIn Alzheimer’s disease clinical research, glial fibrillary acidic protein (GFAP) released/leaked into the cerebrospinal fluid and blood is widely measured and perceived as a biomarker of reactive astrogliosis. However, it was demonstrated that GFAP levels differ in individuals presenting with amyloid-β (Aβ) or tau pathologies. The molecular underpinnings behind this specificity are little explored. Here we investigated biomarker and transcriptomic associations of hippocampal GFAP-positive astrocytes with Aβ and tau pathologies in humans and mouse models. MethodsWe studied 90 individuals with plasma GFAP, Aβ- and Tau-PET to investigate the association between biomarkers. Then, transcriptomic analysis in hippocampal GFAP-positive astrocytes isolated from mouse models presenting Aβ (PS2APP) or tau (P301S) pathologies was conducted to explore differentially expressed genes (DEGs), Gene Ontology terms, and protein–protein interaction networks associated with each phenotype. ResultsIn humans, we found that plasma GFAP associates with Aβ but not tau pathology. Unveiling the unique nature of hippocampal GFAP-positive astrocytic responses to Aβ or tau pathologies, mouse transcriptomics showed scarce overlap of DEGs between the Aβ. and tau mouse models. While Aβ GFAP-positive astrocytes were overrepresented with DEGs associated with proteostasis and exocytosis-related processes, tau hippocampal GFAP-positive astrocytes presented greater abnormalities in functions related to DNA/RNA processing and cytoskeleton dynamics. ConclusionOur results offer insights into Aβ- and tau-driven specific signatures in hippocampal GFAP-positive astrocytes. Characterizing how different underlying pathologies distinctly influence astrocyte responses is critical for the biological interpretation of astrocyte biomarkers and suggests the need to develop context-specific astrocyte targets to study AD. FundingThis study was supported by Instituto Serrapilheira, Alzheimer’s Association, CAPES, CNPq and FAPERGS.

Transient Changes in the Plasma of Astrocytic and Neuronal Injury Biomarkers in COVID-19 Patients without Neurological Syndromes.

The levels of several glial and neuronal plasma biomarkers have been found to increase during the acute phase in COVID-19 patients with neurological symptoms. However, replications in patients with minor or non-neurological symptoms are needed to understand their potential as indicators of CNS injury or vulnerability. Plasma levels of glial fibrillary acidic protein (GFAP), neurofilament light chain protein (NfL), and total Tau (T-tau) were determined by Single molecule array (Simoa) immunoassays in 45 samples from COVID-19 patients in the acute phase of infection [moderate (n = 35), or severe (n = 10)] with minor or non-neurological symptoms; in 26 samples from fully recovered patients after ~2 months of clinical follow-up [moderate (n = 23), or severe (n = 3)]; and in 14 non-infected controls. Plasma levels of the SARS-CoV-2 receptor, angiotensin-converting enzyme 2 (ACE2), were also determined by Western blot. Patients with COVID-19 without substantial neurological symptoms had significantly higher plasma concentrations of GFAP, a marker of astrocytic activation/injury, and of NfL and T-tau, markers of axonal damage and neuronal degeneration, compared with controls. All these biomarkers were correlated in COVID-19 patients at the acute phase. Plasma GFAP, NfL and T-tau levels were all normalized after recovery. Recovery was also observed in the return to normal values of the quotient between the ACE2 fragment and circulating full-length species, following the change noticed in the acute phase of infection. None of these biomarkers displayed differences in plasma samples at the acute phase or recovery when the COVID-19 subjects were sub-grouped according to occurrence of minor symptoms at re-evaluation 3 months after the acute episode (so called post-COVID or "long COVID"), such as asthenia, myalgia/arthralgia, anosmia/ageusia, vision impairment, headache or memory loss. Our study demonstrated altered plasma GFAP, NfL and T-tau levels in COVID-19 patients without substantial neurological manifestation at the acute phase of the disease, providing a suitable indication of CNS vulnerability; but these biomarkers fail to predict the occurrence of delayed minor neurological symptoms.

NEURONAL AND ASTROCYTIC TETRAPLOIDY IS INCREASED IN DRUG-RESISTANT EPILEPSY.

Epilepsy is one of the most prevalent neurological diseases. A third of patients with epilepsy remain drug-resistant. The exact aetiology of drug-resistant epilepsy (DRE) is still unknown. Neuronal tetraploidy has been associated with neuropathology. The aim of this study was to assess the presence of tetraploid neurons and astrocytes in DRE. For that purpose, cortex, hippocampus and amygdala samples were obtained from patients subjected to surgical resection of the epileptogenic zone. Post-mortem brain tissue of subjects without previous records of neurological, neurodegenerative, or psychiatric diseases was used as control. The percentage of tetraploid cells was measured by immunostaining of neurons (NeuN) or astrocytes (S100β) followed by flow cytometry analysis. The results were confirmed by image cytometry (ImageStream X Amnis System Cytometer) and with an alternative astrocyte biomarker (NDRG2). Statistical comparison was performed using univariate tests. A total of 22 patients and 10 controls were included. Tetraploid neurons and astrocytes were found both in healthy individuals and DRE patients in the three brain areas analysed: cortex, hippocampus and amygdala. DRE patients presented a higher number of tetraploid neurons (p=0.020) and astrocytes (p=0.002) in the hippocampus than controls. These results were validated by image cytometry CONCLUSIONS: We demonstrated the presence of both tetraploid neurons and astrocytes in healthy subjects as well as increased levels of both cell populations in DRE patients. Herein, we describe for the first time the presence of tetraploid astrocytes in healthy subjects. Furthermore, these results provide new insights into epilepsy, opening new avenues for future treatment.

Arundic acid (ONO-2506) downregulates neuroinflammation and astrocyte dysfunction after status epilepticus in young rats induced by Li-pilocarpine

Astrocytes, the most abundant glial cells, have several metabolic functions, including ionic, neurotransmitter and energetic homeostasis for neuronal activity. Reactive astrocytes and their dysfunction have been associated with several brain disorders, including the epileptogenic process. Glial Fibrillary Acidic Protein (GFAP) and S100 calcium-binding protein B (S100B) are astrocyte biomarkers associated with brain injury. We hypothesize that arundic acid (ONO-2506), which is known as an inhibitor of S100B synthesis and secretion, protects the hippocampal tissue from neuroinflammation and astrocyte dysfunction after status epileptics (SE) induction by Li-pilocarpine in young rats. Herein, we investigated the effects of arundic acid treatment, at time points of 6 or 24 h after the induction of SE by Li-pilocarpine, in young rats. In SE animals, arundic acid was able to prevent the damage induced by Li-pilocarpine in the hippocampus, decreasing neuroinflammatory signaling (reducing IL-1β, COX2, TLR4 and RAGE contents), astrogliosis (decreasing GFAP and S100B) and astrocytic dysfunction (recovering levels of GSH, glutamine synthetase and connexin-43). Furthermore, arundic acid improved glucose metabolism and reduced the glutamate excitotoxicity found in epilepsy. Our data reinforce the role of astrocytes in epileptogenesis development and the neuroprotective role of arundic acid, which modulates astrocyte function and neuroinflammation in SE animals.

Serum levels of glial fibrillary acidic protein in patients with amyotrophic lateral sclerosis.

To compare serum levels of the astrocyte biomarker glial fibrillary acidic protein (GFAP) in patients with amyotrophic lateral sclerosis (ALS) and neurologically healthy controls and to analyze the relations between serum GFAP (sGFAP) and phenotype in ALS. We studied 114 ALS patients and 38 controls. sGFAP was quantified with single molecule array (Simoa) technology. In both ALS patients and controls, sGFAP moderately correlated with age. ALS patients had higher sGFAP levels compared to controls, but this yielded a weak discriminative performance (AUC=0.6198). In ALS, sGFAP was not associated with most of the motor phenotypic features, including site of onset, functional status, disease progression rate, disease stage, and indices of upper (UMN) and lower motor neuron (LMN) impairment. However, sGFAP negatively correlated with cognitive scores regarding ALS-nonspecific functions, particularly memory (r=-0.2082) and tended to be higher in ALS patients with eye movement abnormalities (p=0.0628). sGFAP also correlated with polysomnographic indices of oxygen desaturation (ODI; r=0.2639) and apnea-hypopnea (AHI; r=0.2858). In a multivariate analysis, sGFAP was negatively associated with survival (HR=1.005). Relevantly, we found a negative correlation between sGFAP and estimated glomerular filtration rate (eGFR; r=-0.3500). Our work provides neurochemical evidence of astrocyte involvement in ALS pathophysiology and particularly in the development of extra-motor manifestations (namely, cognitive - memory - impairment) and respiratory dysfunction. The negative correlation between sGFAP and eGFR has practical relevance and should not be disregarded in future investigations.

Longitudinal changes in brain glucose metabolism, astrocyte biomarkers and behavior in an APP/PS1 rat model

AbstractBackgroundImaging and fluid biomarkers have helped to reconceptualize Alzheimer’s Disease (AD) as a continuum. However, the biological interpretation of each AD biomarker remains under investigation. In this context, animal models that mimic the AD dynamic biomarkers cascade model present high translational value and can be used to refine our interpretation of biomarker findings. In light of this, we longitudinally evaluated [18F]FDG‐PET imaging, cerebrospinal fluid (CSF) glial and immune biomarkers, and behavior in the TgF344‐AD rat, a model harboring human APP/PS1 mutations.MethodsTgF344‐AD rats and wild‐type littermates were longitudinally evaluated at 3, 6, 9, and 12 months of age. Rats underwent [18F]FDG‐microPET scans, behavioral tasks (Y‐maze and novel objective recognition) and CSF samplings. The [18F]FDG SUVr was calculated with pons as the reference region. CSF glial and immune markers were measured by multiplex ELISA. A cross‐sectional cohort was used to measure cortical glutamate uptake (ex‐vivo slices) at the same time points. Further examination of astrocyte proteins immunocontent was conducted at 9 months of age.ResultsAt 3, 6 and 12 months, no changes in [18F]FDG metabolism were found. At 9 months of age, we identified a significant cortical hypermetabolism in the TgF344‐AD and a decline in alternance during the Y‐maze task. CSF GFAP levels were elevated at 6 and 9 months of age, while CSF S100B was decreased at 9 months of age. Additionally, the cortical and hippocampal glutamate uptake and GFAP cortical immunocontent were increased at 9 and 12 months of age. The recognition memory and CSF inflammatory markers (sTREM2, IL‐6, TNF‐α, IL‐10) were not altered in any of the ages evaluated.ConclusionOur results suggest that the TgF344‐AD rat model is suitable for studying astrocytic adaptations during early stages of amyloidosis in the rat brain. These adaptations include cortical glucose hypermetabolism, fluid biomarker evidence of reactive astrogliosis, and spatial memory impairment with concurrent abnormalities in astrocyte glutamate uptake in the cortex and hippocampus. Due to the critical role of astrocytes in brain glucose handling, our findings suggest that astrocyte reactivity could be driving glucose hypermetabolism and memory impairment early in the disease course.

Comparison of plasma amyloid, tau, and astrocyte biomarkers to identify AD pathophysiology

AbstractBackgroundAlthough it has been alredy demonstrated that plasma amyloid‐β (Aβ), phosphorylated tau (p‐tau), and glial fibrillar protein (GFAP) can predict with high accuracy Alzheimer's disease (AD) pathophysiology, no previous study has compared their performance in the same set of individuals. Here, we compare the performance of plasma Aβ42/40, p‐tau, GFAP, and NfL against Aβ and tau PET across the AD spectrum.MethodWe used the ROC curve to test the predictive performance of Simoa plasma Aβ42/40, p‐tau (at threonine 181 and 231), NfL, and GFAP to identify Aβ and Pau PET positivity in 138 cognitive unimpaired (CU) and 87 cognitive impaired (CI) from the McGill TRIAD cohort. Pearson correlation and linear regression tested the association between markers.ResultWe showed that plasma p‐tau231, p‐tau181, GFAP, and NfL correlated with each other (Figure 1), while Aβ42/40 did not. In CU, voxel‐wise linear regressions (Figure 2A) showed that p‐tau231, p‐tau181, and GFAP concentrations were significantly associated with Aβ‐PET (Figure 2A). While for Tau‐PET (Figure 2B), there was a significant association only with p‐tau231 and p‐tau181 (Figure 2B). P‐tau231 outperformed the other plasma biomarkers to identify both Aβ‐ and Tau‐PET positivity (AUC 0.877 and 0.796, respectively) in CU individuals. In CI, Aβ‐ and Tau‐PET were significantly associated with p‐tau231, p‐tau181, and GFAP, whereas NfL was only associated with Tau‐PET. The discriminative accuracy of GFAP in identifying both Aβ‐PET and Tau positivity (AUC 0.936 and 0.944, respectively) outperformed the other plasma biomarkers in CI individuals (Figure 3, Table 1).ConclusionWe showed that plasma p‐tau231, a novel biomarker of early AD, best depicted AD pathophysiology in CU individuals. Interestingly, GFAP, an astrocyte reactivity marker, was better associated with brain Aβ and tau pathologies than plasma p‐tau and Aβ markers in CI individuals. Our results highlight that the performance of the novel plasma biomarkers of amyloid, tau and neuroinflammation to detect brain AD pathophysiology is disease stage specific.