Background/Objectives: Acute liver failure (ALF) rapidly induces hepatic encephalopathy (HE), a severe neurological syndrome associated with astrocytic dysfunction and glutamatergic dysregulation. Guanosine (GUO), an endogenous guanine-based nucleoside, has neuroprotective properties, but its effects on astrocyte-associated glutamate regulation in ALF-induced HE remain incompletely understood. This study tested whether GUO attenuates neurological deterioration and glutamatergic dysfunction in an experimental model of ALF-induced HE. Methods: Male Wistar rats underwent 92% subtotal hepatectomy and received intraperitoneal GUO (7.5 mg/kg) or saline at prespecified time points after surgery. Neurological severity and survival were monitored for 72 h. Astrocytic morphology was assessed by GFAP immunofluorescence. Cerebrospinal fluid (CSF) albumin, glutamate, and glutamine levels, cortical Na+-dependent glutamate uptake, GLAST immunocontent, and the 67 kDa GLT-1 monomer immunocontent were evaluated. Results: Subtotal hepatectomy induced progressive neurological impairment, high mortality, GFAP-associated astrocytic remodeling, increased CSF albumin, glutamate, and glutamine levels, and reduced cortical glutamate uptake. GUO attenuated neurological deterioration and increased 72 h survival from 10.5% to 39.0% (log-rank p = 0.03). GUO also reduced CSF albumin, glutamate, and glutamine concentrations and improved cortical Na+-dependent glutamate uptake without altering GLAST or GLT-1 monomer immunocontent. Conclusions: GUO attenuated astrocyte-associated glutamatergic dysregulation and improved survival in ALF-induced HE. These findings support further mechanistic and translational investigation of GUO as an experimental modulator of astrocyte-associated glutamate handling in ALF-induced HE.

Quantifying tau aggregates in the human brain can be achieved using Positron Emission Tomography (PET) techniques, which can potentially be affected by binding competition due to medication use. Patients with dementia often have high rates of comorbidities and polypharmacy. Therefore, this study aims to investigate the potential influence of multiple medications on the uptake of the tau tracers MK6240 (MK) and Flortaucipir (FTP). Five classes of medications were evaluated: Anti-Hypertensives, Statins, Anti-Diabetics, Psychoactive drugs, and NSAIDs (Table 1). We included 292 individuals [170 cognitively unimpaired (CU) Aβ-negative and 122 cognitively impaired (CI) Aβ-positive] from the HEAD study (Table 2). We compared MK and FTP SUVR in the Medial Temporal Lobe (MTL) and Neotemporal Cortex (NTC) in individuals on and off medications. The linear regressions that tested associations were corrected for confounding factors, including age, sex, education, and MoCA score. Correction for multiple comparisons was applied using the Bonferroni method (adjusted p -value at 0.00125). Among CI Aβ-positive individuals, Anti-Diabetics were associated with lower SUVR in the NTC for both FTP and MK. However, these associations did not remain significant after correction for multiple comparisons. (Table 3). Our findings indicate that there are no significant associations between the use of the medications studied and MK or FTP uptake when accounting for covariates and applying multiple comparison corrections.

Glutamatergic neurotransmission system dysregulation may play an important role in the pathophysiology of Alzheimer’s disease (AD). However, reported results on glutamatergic components across brain regions are contradictory. Here, we conducted a systematic review with meta-analysis to examine whether there are consistent glutamatergic abnormalities in the human AD brain. We searched PubMed and Web of Science(database origin-October 2023) reports evaluating glutamate, glutamine, glutaminase, glutamine synthetase, glutamate reuptake, aspartate, excitatory amino acid transporters, vesicular glutamate transporters, glycine, D-serine, metabotropic and ionotropic glutamate receptors in the AD human brain. The studies were synthesized by outcome and brain region. We included cortical regions, the whole brain(cortical and subcortical regions combined), the entorhinal cortex and the hippocampus. Pooled effect sizes were determined with standardized mean differences (SMD), random effects adjusted by false discovery rate, and heterogeneity was examined by I 2 statistics. The search retrieved 6 936 articles,63 meeting the inclusion criteria(N = 709CN/786AD;mean age 75/79). We showed that the brain of AD individuals presents decreased glutamate (SMD = -0.82;P<0.001) and aspartate levels (SMD = -0.64; I 2 = 89.71%; P = 0.006), and reuptake (SMD = -0.75;P<0.001). We also found reduced AMPAR-GluA2/3 levels(SMD = -0.63;P = 0.046), hypofunctional NMDAR (SMD = -0.60;P<0.001) and selective reduction of NMDAR-GluN2B subunit levels(SMD = -1.07;P<0.001). Regional differences include lower glutamate levels in cortical areas and aspartate levels in cortical areas and in the hippocampus, reduced glutamate reuptake, reduced AMPAR-GluA2/3 in the entorhinal cortex, hypofunction of NMDAR in cortical areas, and a decrease in NMDAR-GluN2B subunit levels in the entorhinal cortex and hippocampus. Other parameters studied were not altered. Our findings show depletion of the glutamatergic system and emphasize the importance of understanding glutamate-mediated neurotoxicity in AD. This study has implications for the development of therapies and biomarkers in AD.

Alzheimer's disease (AD) biomarker research has largely concentrated on populations from the Global North. The emergence of blood-based biomarkers presents an opportunity to reduce this disparity. In this perspective presentation, I will present data on the performance of blood-based biomarkers in a real-world, memory clinic-based cohort from Brazil, a population characterized by lower educational attainment compared to those typically studied in the Global North. Specifically, I will examine the performance of plasma biomarkers-Aβ40, Aβ42, p-tau217, NfL, and GFAP-in differentiating AD from cognitively unimpaired (CU) individuals and vascular dementia (VaD) in a Brazilian cohort (n = 59). Preliminary findings indicate that p-tau217 exhibits the highest accuracy in distinguishing AD from CU (AUC 0.96). However, the performance of all plasma biomarkers in differentiating AD from VaD is lower (AUC 0.52 to 0.79) than expected based on studies conducted in the Global North. Finally, I will share initial findings from the Brazilian Initiative of Blood Biomarkers in Neurodegenerative Disorders, a program funded by the Ministry of Health. Additionally, I will discuss the role of blood biomarkers in shaping state and national dementia plans in Brazil.

Imaging biomarkers have helped to reconceptualize Alzheimer's disease pathophysiology. More specifically, positron emission tomography (PET) radiopharmaceuticals for non-invasively assessing amyloid-beta (Aβ) plaques, glucose metabolism, and glial reactivity allow for tracking disease progression in a temporally ordered manner. However, whether transgenic models recapitulate biomarker-related changes remains elusive. Here, we longitudinally evaluated Aβ, glucose metabolism, and glial reactivity using PET in a transgenic amyloid rat model. TGF344-AD (APP/PS1) and wild-type rats were scanned at 6, 9, and 12 months with [ 18 F]FDG, [ 11 C]PK11195 and [ 11 C]PIB. Images were manually co-registered in a rat magnetic resonance template. Standardized uptake values (SUV) were calculated for [ 18 F]FDG and [ 11 C]PK11195, and SUV ratio (SUVR) was calculated for [ 11 C]PIB using the pons as the reference region. The results were normalized using Z-Score and statistical significance was determined at Z>2 (p < 0.05). At 6 months, no differences between groups were observed. At 9 months, however, we detected significant amyloid load, glucose hypermetabolism, and increased glial reactivity. At 12 months, animals presented increased Aβ load while still presenting signs of brain glucose hypermetabolism. By contrast, glial reactivity did not present alterations compared to 9-month-old rats. Our findings indicate that in the early phases of detectable Aβ deposition, there is a joint increase in brain glucose metabolism and glial reactivity. These findings suggest that amyloid deposition triggers early neuroinflammatory response. We and others have provided evidence that early FDG-PET hypermetabolism is an indicator of glial reactivity.

Alzheimer's disease (AD) biomarker research has largely concentrated on populations from the Global North. The emergence of blood-based biomarkers presents an opportunity to reduce this disparity. In this perspective presentation, I will present data on the performance of blood-based biomarkers in a real-world, memory clinic-based cohort from Brazil, a population characterized by lower educational attainment compared to those typically studied in the Global North. Specifically, I will examine the performance of plasma biomarkers—Aβ40, Aβ42, p -tau217, NfL, and GFAP—in differentiating AD from cognitively unimpaired (CU) individuals and vascular dementia (VaD) in a Brazilian cohort ( n  = 59). Preliminary findings indicate that p -tau217 exhibits the highest accuracy in distinguishing AD from CU (AUC 0.96). However, the performance of all plasma biomarkers in differentiating AD from VaD is lower (AUC 0.52 to 0.79) than expected based on studies conducted in the Global North. Finally, I will share initial findings from the Brazilian Initiative of Blood Biomarkers in Neurodegenerative Disorders, a program funded by the Ministry of Health. Additionally, I will discuss the role of blood biomarkers in shaping state and national dementia plans in Brazil.

One of the hallmarks of Alzheimer's disease (AD) is the progressive spread of tau pathology. However, heterogeneity in the spatial patterns of tau deposition at the individual level may contribute to distinct clinical presentations. Here, we investigated the different patterns of tau deposition across disease progression and the different cognitive profiles linked to these patterns. We investigated 106 tau PET positive individuals (16% cognitively unimpaired, 84% amnestic cognitively impaired) from the HEAD study using head-to-head Flortaucipir and MK6240 tau PET. For each tracer, we extracted the SUVR values from seven major brain networks: Limbic, Visual (Vis), Default Mode (Default), Dorsal Attention (DorsAttn), Frontoparietal, Somatomotor (SomMot) and Salience Ventral Attention (SalVentAttn) as well as the Entorhinal cortex. Pathways were identified by ranking regions from highest to lowest SUVR, with the region displaying the highest SUVR value being defined as the peak region. Individuals in late stages of tau deposition displaying distinct pathways were compared. Image averages and voxel-wise group comparisons using tau negative individuals as the reference were generated for each pathway and tau PET tracer. Cognitive differences were assessed using ANOVA for MoCA score and domain-specific composite scores for Memory, Attention and Visuospatial skills. In all individuals and tracers, tau in the Entorhinal cortex progressed to the Limbic network, supporting a common starting point for tau propagation. Beyond these initial stages, tau propagation followed three main distinct pathways following either the Vis, Default or DorsAttn networks (Figure 1). Voxel-wise comparison between individuals across these three pathways captured clear and similar differences in tau PET uptake as measured with Flortaucipir and MK6240. (Figure 2). While MoCA and Memory scores did not differ between groups, individuals following the Vis network exhibited significantly lower Attention scores compared to those in the Default and DorsAttn networks. Additionally, individuals following the Vis network exhibited lower Visuospatial scores compared to the Default network group (Figure 3). Our results indicate a model in which, although tau progresses hierarchically, its deposition peaks mainly follow specific networks, which drive tau deposition and, consequently, the clinical manifestations of AD.

Vascular cognitive impairment/dementia (VD) is the second most prevalent cause of dementia following Alzheimer’s disease (AD). VD is characterized by the progression of white matter hyperintensity burden (WMH) and associated neurodegeneration. GFAP, a biomarker for reactive astrogliosis, is associated with Aβ pathology and mediates tau-pathology in preclinical AD. However, the association of GFAP levels with the markers associated with VD is poorly understood. We assessed 796 participants from a research cohort (TRIAD: 355) and a memory clinic cohort (BICWALZ: 441) that were divided into four groups according to their Aβ (Aβ+/Aβ-) and WMH status (WMH+/WMH-). WMH values were corrected by intracranial volume, and cutoffs were determined based on the highest WMH value within 50% of the individuals with the lowest WMH rate in the CU Aβ- group. Biomarker mean level differences between groups were estimated via Ancova Tukey’s test, and linear regressions accounting for age, sex, and cognitive status were used to estimate the association. For TRIAD, WMH+/Aβ+ individuals exhibit higher levels of plasma GFAP when compared to all groups except WMH-/Aβ+, with no differences in NfL levels and hippocampal volume between groups ( Fig. 1A ). In BICWALZ, only hippocampal volume differs between groups with lower levels observed in both WMH-/Aβ- and WMH-/Aβ+ ( Fig. 1B’’ ). The association of GFAP and NfL was observed in all groups ( Fig. 2A, 2B’ ). On the other hand, hippocampal degeneration was associated with higher GFAP levels in individuals with abnormal WMH and absence of Aβ burden in both cohorts ( Fig. 3A : TRIAD: β = -0.3036; p = 0.0195; Fig. 3B’ : BICWALZ: β = -0.1791; p = 0.0125). Our findings suggest that astrocyte reactivity, as indicated by plasma GFAP levels, plays a significant role in the hippocampal atrophy observed in patients with vascular disease. These results suggest that therapies targeting astrocyte reactivity could potentially alleviate progressive cognitive deficits commonly found in patients with chronic vasculopathy.

The deposition of β-amyloid (Aβ) plaques is a classical neuropathological feature of Alzheimer’s disease (AD). Currently, it is believed that intermediate products of the Aβ fibrillogenesis process, like the β-amyloid oligomers (AβOs), are the most toxic forms, and are involved in neurodegenerative processes in AD. The evaluation of cerebral glucose metabolism in patients with β-amyloid plaque deposition using [ 18 F]FDG-PET has been used as a marker of neurodegeneration in AD. However, little is understood about AβOs' impact on glucose metabolism prior to Aβ plaques formation. The aim of this study was to evaluate the impact of the intracerebroventricular infusion of AβOs on in vivo glucose metabolism via [ 18 F]FDG-PET. Male Swiss mice (3-month-old, n = 20 per group) were divided into three groups: Vehicle, AβOs 10pmol, and AβOs 100pmol. Vehicle/AβOs were infused into mice’ right ventricle using the freehand technique after brief isoflurane anesthesia. [ 18 F]FDG-PET scans were performed 24h after AβOs infusion. The same animals underwent the Novel Object Recognition (NOR) task 24h after scanning. The images were processed and analyzed using MINC tools. Metabolic networks were built by computing Pearson correlation coefficients based on 2,000 bootstrap samples and FDR corrected (P<0.05). See Fig. 1a, for a experimental design illustration. AβOs induced dose-dependent brain glucose hypometabolism ( Fig. 1b ) and metabolic network disturbances. Voxel-wise percentage change analysis revealed moderate reductions in glucose brain metabolism (5% to 15%) following infusion of 10pmol AβOs, whereas 100 pmol AβOs led to widespread and substantial reductions of up to 25% ( Fig. 1c ). T-statistical voxel-wise analysis indicated statistically significant brain glucose hypometabolism only in the 100pmol group ( Fig. 1d ). The low-dose AβOs (10pmol) induced brain inter-region metabolic hyperconnectivity, while the 100 pmol dose caused hypoconnectivity ( Fig. 1e ). Furthermore, both AβOs infusion groups exhibited impaired recognition memory in the NOR task ( Fig. 1f ). Our results are the first demonstration of AβOs causing in vivo glucose hypometabolism and metabolic network disturbances in the absence of plaques. These findings point to an early impact of AβOs on glucose metabolism, independent of β-amyloid plaque formation. While the molecular pathways underlying this effect require further investigation, they may represent important AD pathophysiological mechanisms and potential targets for therapeutic intervention.

Alzheimer's disease (AD) has been known for more than a century, but its complex pathophysiology remains unclear. Previous studies have been suggesting a potential role of neuroinflammation and cerebral vascular changes in AD progression. Part of the immune response relies on the role of Vascular Cell Adhesion Molecule (VCAM) in cell transit through the endothelium. However, there is little information about the impact of VCAM in AD-related impairment. Here, we investigated the association of plasma VCAM levels with biological and clinical AD markers. We assessed 357 individuals from the Alzheimer's Disease Neuroimaging Initiative cohort with plasma VCAM and medical data available. Statistical analyses were performed using R Studio. Association with diagnosis was evaluated by a linear regression between VCAM and clinical diagnosis, with adjustments for age, sex, APOEε4 status and years of education. Regressions analysis was also used to assess the association of VCAM with Clinical Dementia Rating Scale - Sum of Boxes (CDR-SB), adjusting for age, sex, APOEε4 status and years of education, as well as cerebrospinal fluid Aβ42 and p-Tau181. The group of individuals with dementia had higher blood VCAM levels (p=0.005) than both CN and MCI (p=0.003) groups, but there was no statistical significance between CN and MCI (Figure 1). VCAM showed a positive association (p = 0.018, Figure 2) with greater impairment as measured by CDR-SB when adjustments for Aβ42 and p-Tau181 were included. Our results suggest differential effects of vascular factors in biological and clinical AD. Further studies are needed to assess whether these relations include causality and whether targeting VCAM can lead to improvements in neuroinflammatory or vascular-related changes.

Blood-based biomarkers (BBMs) have emerged as promising tools to enhance Alzheimer's disease (AD) diagnosis. Despite two-thirds of dementia cases occurring in the Global South, research on BBMs has predominantly focused on populations from the Global North. This geographical disparity hinders our understanding of BBM performance in diverse populations. To address this, we evaluated the diagnostic properties of AD BBMs in a real-world memory clinic from Brazil, one of the largest countries in the Global South. We measured blood and cerebrospinal fluid (CSF) biomarkers - amyloid-β (Aβ)40, Aβ42, phosphorylated tau (p-tau) 217, neurofilament light (NfL) chain, and glial fibrillary acidic protein (GFAP) - in 59 individuals. Sample comprised 20 cognitively unimpaired (CU) individuals, 22 with AD dementia, and 17 with vascular dementia (VaD). We compared BBM levels across diagnostic groups and assessed their discriminative ability for AD. Notably, individuals with VaD and AD had lower educational levels (6.8±3.0) compared to CU individuals (61.4±6.6). Among the BBMs tested, plasma p-tau217 demonstrated the best performance, exhibiting high accuracy in differentiating CU from AD (AUC 0.96) and Aβ pathology (AUC 0.98). However, the ability of AD BBMs to distinguish between AD and VaD was lower than expected (AUC from 0.52 to 0.79), particularly when compared to studies from the Global North. Our findings highlight the potential utility of BBMs for AD diagnosis in real-world settings within the Global South. However, they also underscore the need for proper implementation and validation of these biomarkers within these populations to ensure accurate and reliable results.

Recent studies have suggested a transient glucose hypermetabolism in early phases of Alzheimer’s Disease (AD), which is followed by a characteristic glucose hypometabolism in dementia stages. This phenomenon desveres further investigation and it is suggested to be associated to glial/inflammatory or compensatory neuronal responses. Here, we aimed to longitudinally investigate brain glucose metabolism in an AD animal model and explore associated cellular and inflammatory changes. Longitudinal assessments, including cerebral glucose metabolism ( 18 F]FDG-PET), behavioral tasks and cerebrospinal fluid (CSF) sample collection were performed at 3, 6, 9, and 12 months of age (mo) in wild type (WT) and TgF344-AD rats (Tg). Glial and inflammatory markers were evaluated in the CSF via ELISA multiplex. A cross-sectional cohort was used to follow the spatial distribution of Aβ plaques (IHC), to assess the brain content of glial and neuronal proteins (western blot), and to analyze the cortical glutamate uptake (ex-vivo slices) at the same time points. At 9mo, three months after the initial appearance of Aβ plaque deposits, Tg animals exhibited cortical glucose hypermetabolism ( Figure 1A-C ). At the same age, astrocytic glutamate uptake was increased in the cortex and hippocampus ( Figure 2 ). Declines in performance on the Y-maze and Novel Object Recognition tasks were observed at 9 and 12mo ( Figure 1D ). CSF analysis revealed elevated GFAP levels at 6, 9 and 12mo, and reduced S100B at 9mo ( Figure 1E e F ). Tissue GFAP immunocontent increased in the temporoparietal cortex at 6 and 9mo, in the hippocampus at 9mo, and was reduced in the frontal and temporoparietal cortices at 12mo ( Figure 3 ). Our findings suggest the presence of an early, transient phase of brain glucose hypermetabolism in TgF344-AD rats, consistent with observations in recent animal and human studies. This phenomenon seems to be closely linked to the astrocyte response, reflected in variations of crucial astrocyte proteins such as GFAP and S100B, along with an increase in the glutamate uptake by these cells. In contrast, neuronal, microglial and inflammatory markers did not exhibit changes during this timeframe.

Our objective was to evaluate the in vitro binding properties of [18F]flortaucipir, 6-(fluoro-18F)-3-(1H-pyrrolo[2,3-c]pyridin-1-yl)isoquinolin-5-amine ([18F]MK6240), and 2-(2-([18F]fluoro)pyridin-4-yl)-9H-pyrrolo[2,3-b:4,5c']dipyridine ([18F]PI2620) head-to-head in postmortem human brain tissue. Methods: Autoradiography was used to assess uptake of [18F]flortaucipir, [18F]MK6240, and [18F]PI2620 in control and Alzheimer disease (AD) autopsy-confirmed brain tissues. The study focused on the analysis of the prefrontal cortex, hippocampus, and cerebellum sections in 12 controls and 12 AD cases, as well as whole-brain hemisphere in 1 control and 1 AD sample, for each radiotracer. The binding values of [18F]flortaucipir, [18F]MK6240, and [18F]PI2620 were calculated from regions of interest manually drawn in the prefrontal, hippocampal, and cerebellar cortices. Results: For all 3 radioligands investigated, we observed significant tracer binding differences between control and AD tissues in the whole-brain hemisphere, prefrontal cortex, and hippocampus but not in the cerebellar cortex. [18F]MK6240 and [18F]PI2620 had higher effect sizes to differentiate control and AD cases than did [18F]flortaucipir. Bland-Altman analyses revealed strong correlations between [18F]MK6240, [18F]PI2620, and [18F]flortaucipir, with the highest agreement found for [18F]MK6240 versus [18F]PI2620. Conclusion: The 3 radioligands showed comparable diagnostic properties to assess tau aggregates in vitro. Binding to AD brain tissues was higher for [18F]MK6240 and [18F]PI2620 than for [18F]flortaucipir. Additionally, [18F]MK6240 and [18F]PI2620 had greater selectivity, displaying decreased uptake in control brain tissue compared with [18F]flortaucipir. These results might provide insights on ongoing initiatives to create a universal scale for tau imaging studies.

Multiple studies in the past years have supported the idea that microglial cells play a crucial role in the pathophysiology of Alzheimer’s disease (AD) and that their response might be quite heterogeneous. However, whether these cells react differently to Amyloid-β (Aβ) and Tau pathology, as well as, the molecular mechanisms and distinct pathways underlying these responses remains elusive. In this work, we aimed to investigate the response of microglia to Aβ and Tau fibrils, which are being recognized as one of their most toxic forms. We hypothesize that microglia will present a unique response for Aβ and Tau fibrils. Transcriptomic analysis of mice primary microglial cultures exposed to Aβ or Tau fibrils (5µM, 12-24hs) was performed. Differentially expressed genes (DEGs) between control and Aβ or Tau fibrils were identified using the DESeq2 method. Functional enrichment (FEA), semantic similarities and protein-protein interaction networks were conducted. Differences were statistically significant with FDR-adjusted p-value < 0.05 and logFC > 1. Compared to controls, microglia exposed to Aβ fibrils presented 917 DEGs, while the ones exposed to Tau fibrils presented 672 DEGs, of which, only 275 were shared. In contrast, the FEA indicated that more than 69% (736 BP, 50 MF and 32 CC) of the enriched terms were shared between Aβ and Tau. Among the not shared terms, the semantic similarities analysis identified 16 clusters specific for each treatment: Aβ clusters included “regulation of lipids, carbohydrate and ATP metabolic process”, “response to starvation” and “autophagy”, while Tau clusters included “regulation of transmembrane transport of ions”, “gliogenesis” and “neural cells proliferation”. This work corroborates the idea that microglia react differently to Aβ or Tau pathology but reveals that this response might not be unique as we hypothesized. Although different at the gene level, a big portion of the microglial response to Aβ and Tau converged to the same mechanisms. Despite that, there is still a smaller quantity of adaptations that are specific, such as substrates handling for Aβ and ions transport for Tau. Further validation of these unique phenotypes is being conducted in additional Aβ and Tau pathology models.

Cerebrospinal fluid (CSF) and Positron emission tomography (PET) amyloid-β biomarkers are commonly used interchangeably to measure amyloid-β deposition, an early event in the development of Alzheimer’s disease (AD). However, it is not uncommon to find individuals with discordant measurements of amyloid-β CSF and PET. It has been hypothesized that this discordance may be an intermediate step between the CSF and brain amyloid deposition, and that discordant individuals might be in different disease stages or have different disease phenotypes. Here, we applied blood transcriptomic analysis to evaluate differences in amyloid-β CSF and PET discordant and concordant individuals. We analyzed the blood transcriptome of 200 individuals from the ADNI cohort who had measurements of both CSF amyloid-β42 and [18F]Florbetapir PET at baseline and at 2-year follow-up. The demographic characteristics of the sample are presented in table 1. Our analysis yielded four groups: CSF+/PET- (n = 18), CSF-/PET+ (n = 19), CSF+/PET+ (n = 76), and CSF-/PET- (n = 87). The latter was the control group for all analyses. Differentially expressed genes (DEGs, uncorrected p-value < 0.01) were used for gene set enrichment analysis (GSEA) to identify group-specific altered biological pathways. CSF+/PET-, CSF-/PET+ and CSF+/PET+ individuals showed a great proportion of unshared DEGs (Figure 1). The CSF+/PET- group, which is thought to represent a very early stage in the disease, presented the highest number of unshared DEGs (273) with upregulated GO terms involved mainly in metabolic processes. The CSF-/PET+ group possessed 113 unique DEGs, while the CSF+/PET+ possessed 47. Interestingly, these groups presented similar alterations in biological processes, representing mainly alterations in immune response and inflammation. Our results highlight the differences in the blood transcriptomic phenotype between CSF and PET amyloid-β concordant and discordant individuals. Importantly, individuals very early in the AD continuum (CSF+/PET-) presented the most distinct phenotype. Our results suggest that blood transcriptomics are able to capture subtle changes in brain amyloid-β and might help identify individuals in different stages of AD.

The brain is an energetically demanding organ that mostly relies on glucose oxidation to sustain its sophisticated networks. Transcriptomic studies suggest metabolic-related genes are downregulated in the aging brain but inflammation-related genes are highly upregulated. Astrocytes are key mediators of brain inflammation and metabolism. Yet, the relationship between inflammatory signals and energy substrates consumption in the aging brain remains unclear. To address this question, we investigated the response of the young and aged rat brain metabolism to a nonsteroidal anti-inflammatory (NSAID) drug. Five young adults (4 mo), and five aged (24 mo) male Wistar rats were scanned using positron emission microtomography with 18 F-fluorodeoxyglucose ([ 18 F]FDG-PET). Scans were done under basal conditions or after three-day treatment with 5mg/kg ketoprofen (i.p.), an NSAID known to cross the blood-brain barrier. Standard uptake values ratios (SUVr, pons as reference) were calculated for the main brain regions. Synaptosome and total mitochondria preparations from the cortex had their oxygen consumption rates measured in an Oroboros Instrument, using a SUIT protocol. Results were analyzed by t-test, with statistical significance P < 0.05. Under basal conditions, glucose uptake showed no differences between young and aged rats. After ketoprofen treatment, clusters of glucose hypermetabolism appeared in the cortex and hippocampus of the adult but not the aged brain. Synaptosomal and mitochondrial preparations did not present differences in ATP-linked, maximal, or leak respiration between groups under basal conditions. However, aged synaptosomes (t = 3.417, p = 0.0112) and total mitochondria (t = 3.131, p = 0.0166) presented higher respiratory coupling ratios. We previously showed that [ 18 F]FDG-PET signal highly depends on astrocyte function. The lack of response to ketoprofen in aged rats may be related to astrocyte dysfunction in aging. As a counter-response to the aging process, the brain mitochondria are highly coupled, keeping the system as efficient as necessary. Our findings indicate that brain metabolism might not be coupled to inflammation in the aged rat brain. Still, we identified a remarkable plasticity of the mitochondria, which can sustain physiological responses despite the aging process.

Neuroinflammation is thought to play an important role in the pathogenesis of Alzheimer’s disease (AD). It has recently been demonstrated that [ 18 F]FDG positron emission tomography (PET) signal is sensitive to central inflammatory changes in AD. However, it is unknown whether blood cytokines, which are important signaling molecules that regulate the peripheral inflammatory process, are associated with the cerebral [ 18 F]FDG-PET signal. In this work, we aimed to investigate whether plasma cytokines are associated with brain glucose metabolism in a transgenic amyloid rat model. Brain metabolism of 4- and 10-month-old wild-type (WT) and APP/PS1 rats (TgF344-AD) were assessed with [ 18 F]FDG-PET imaging. Plasma inflammatory markers (IFN-γ, IL-1α, IL-1β, IL-6, IL-10 and TNF-α) were measured by multiplex immunoassay. [ 18 F]FDG-SUVr was calculated with pons as the reference region. Correlation between inflammatory markers and [ 18 F]FDG-PET signal was conducted at the voxel level (RMINC; p<0.05 and t>2). At 4 months, IL-10 levels significantly associate with [ 18 F]FDG-PET signal in the frontal and temporoparietal cortices (FCx and TPCx) and hippocampus (Fig1A), whereas other biomarkers present only small clusters associated with [ 18 F]FDG-PET signal (Fig1A). At 10 months, a positive association with [ 18 F]FDG-PET was found between IL-1α and IL-1β at FCx and TPCx, while IL-10 showed a positive correlation at the TPCx (Fig1B). Additionality, IFN-γ and TNF-α presented small correlation clusters at the TPCx, and IL-6 at the TPCx and CxF (Fig1B). At the pre-amyloid plaque stage, only an anti-inflammatory cytokine, IL-10, presented positive associations with brain glucose metabolism. However, multiple pro-inflammatory cytokines correlated with brain glucose metabolism at the amyloid plaque stage. These findings suggest a dual peripheral inflammatory response impacting brain metabolism, which can be associated with amyloid species and deposition.

Introduction In Alzheimer’s disease clinical research, glial fibrillary acidic protein (GFAP) released 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 pathology. The molecular underpinnings behind this specificity are unexplored. Here we investigated biomarker and transcriptomic associations of GFAP-positive astrocytes with Aβ and tau pathologies in humans and mouse models. Methods We 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 applied to explore differentially expressed genes (DEGs), Gene Ontology processes, and protein-protein interaction networks associated with each phenotype. Results In humans, we found that plasma GFAP associates with Aβ but not tau pathology. Unveiling the unique nature of GFAP-positive astrocytic responses to Aβ or tau pathology, mouse transcriptomics showed scarce overlap of DEGs between the Aβ and tau mouse models, While Aβ GFAP-positive astrocytes were overrepresented with genes 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. Conclusion Our results offer insights into Aβ- and tau-driven specific signatures in GFAP-positive astrocytes. Characterizing how different underlying pathologies distinctly influence astrocyte responses is critical for the biological interpretation of astrocyte-related biomarker and suggests the need to develop context-specific astrocyte targets to study AD. Funding This study was supported by Instituto Serrapilheira, Alzheimer’s Association, CAPES, CNPq and FAPERGS.

Sepsis-associated encephalopathy (SAS) is a neurological complication of a severe systemic inflammatory episode that compromises brain function. This neurological impairment can lead to cognitive dysfunction that appears to precede neurodegenerative disorders such as Alzheimer’s disease. However, the events by which systemic inflammation causes such significant damage to the brain are not yet fully established. With that in mind, this study sought to investigate persistent brain changes after a severe systemic inflammatory episode. Male Wistar rats (90 days old) were divided into two experimental groups: sham (n = 33) and sepsis (n = 37). For the induction of severe systemic inflammation, the animals underwent cecal ligation and perforation (CLP). Animals were followed for 30, 60 and 120 days. In all time-points, we performed the object recognition task to evaluate declarative memory and Western Blotting to assess astrocyte-related proteins (GFAP, GLT-1 and Mao-B). At 30 and 120 days, we evaluated the ΒBB integrity [cerebrospinal fluid (CSF) albumin levels and cellularity by HCLP] and brain glucose metabolism (FDG-PET imaging). Our results show that CLP model compromised long-term memory at 60 and 120 days. Furthermore, we found higher levels of albumin in the CSF in CLP animals compared to sham at 30 (p = 0.023) and 120 days post-sepsis (p = 0.002). In addition, we also observed an increase in CSF cellularity in CLP animals after 30 days after sepsis induction. We also found persistent glucose whole brain hypometabolism at 30 (local maxima, t (12) = -3.7) and 120 days (local maxima, t (9) = -8.45), suggesting persistent metabolic abnormalities. Finally, we observed changes in astrocyte-related proteins. At 30 days, hippocampal GLT-1 (p<0.001) and cortical GFAP (p < 0.0001) immunocontents were reduced in CLP rats compared to sham. At 60 days, we observed decreased hippocampal GFAP (p < 0,05) and MAO-B (p < 0.01) immunocontents. At 120 days, we found decreased MAO-B in the hippocampus (p<0.05). We found that a severe systemic inflammation episode causes persistent changes in brain glucose metabolism and BBB integrity, which seems associated with long-term memory impairment. In addition, astrocytes seem to be reacting by changing their protein expression, a typical feature of reactive astrocytes.