Pathologic and clinical correlates of region-specific brain GFAP in Alzheimer’s disease

The accumulation of the intermediate filament protein, glial fibrillary acidic protein (GFAP), in astrocytes of Alexander disease (AxD) impairs proteasome function in astrocytes. We have explored the molecular mechanism that underlies the proteasome inhibition. We find that both assembled and unassembled wild type (wt) and R239C mutant GFAP protein interacts with the 20 S proteasome complex and that the R239C AxD mutation does not interfere with this interaction. However, the R239C GFAP accumulates to higher levels and forms more protein aggregates than wt protein. These aggregates bind components of the ubiquitin-proteasome system and, thus, may deplete the cytosolic stores of these proteins. We also find that the R239C GFAP has a greater inhibitory effect on proteasome system than wt GFAP. Using a ubiquitin-independent degradation assay in vitro, we observed that the proteasome cannot efficiently degrade unassembled R239C GFAP, and the interaction of R239C GFAP with proteasomes actually inhibits proteasomal protease activity. The small heat shock protein, alphaB-crystallin, which accumulates massively in AxD astrocytes, reverses the inhibitory effects of R239C GFAP on proteasome activity and promotes degradation of the mutant GFAP, apparently by shifting the size of the mutant protein from larger oligomers to smaller oligomers and monomers. These observations suggest that oligomeric forms of GFAP are particularly effective at inhibiting proteasome activity.

To determine if glial fibrillary acidic protein (GFAP) is associated with brain injury in children with sickle cell disease (SCD), we measured plasma GFAP among cross-sectional groups of unselected children with SCD, subsets of children with SCD and normal brain MRI or MRI evidence of cerebral infarct, healthy pediatric controls, and adults with brain injury. Children with SCD had higher plasma GFAP than healthy pediatric controls (mean concentrations 0.14 ± 0.37 vs. 0.07 ± 0.08 ng/mL; P 5 0.003); also, 16.0% (16/100) of children with SCD and cerebral infarct had GFAP elevations above the 95th percentile of healthy pediatric controls (P 5 0.04). Although not statistically significant, children with SCD and cerebral infarct had more elevated GFAP levels than with SCD and no infarct (16/100, 16.0% vs. 14/168, 8.3%; P 5 0.07). Children with SCD and acute brain ischemia had a higher proportion of elevated GFAP than SCD children with normal MRI (3/6, 50% vs.8.3%; P 5 0.01). GFAP was associated with elevated systolic blood pressure in the preceding year and correlated positively with white blood cell count and negatively with age and performance IQ. Plasma GFAP is elevated among children with SCD and may be associated with subclinical brain injury.

Idiopathic/isolated Rapid Eye Movement (REM) sleep behavior disorder (iRBD) is recognized as a prodromal stage of neurodegenerative diseases, particularly of α-synucleinopathies. The development of blood-based biomarkers enables the in vivo assessment of neuronal, glial, and Alzheimer's disease (AD)-related changes. This study aimed to analyze plasma levels of neurofilament light chain (NfL), glial fibrillary acidic protein (GFAP), and phosphorylated-Tau 181 (pTau181) in iRBD patients compared to healthy controls (HC) and AD patients. In this cross-sectional study, iRBD patients were compared to age- and sex-matched HC and AD patients. All participants underwent cognitive and motor assessments. Plasma NfL, GFAP, and pTau181 levels were quantified using SIMOA (Quanterix, Billerica, MA). Analyses of covariance and Spearman correlation coefficients were used for group comparisons and correlation analyses. The study included 44 iRBD patients (81.8% males, mean age 71.0 ± 6.4years), 55 HC (66.3% males, mean age 69.1 ± 5.5years), and 28AD patients (82.1% males, mean age of 70.4 ± 6.7years). iRBD patients showed significantly higher plasma NfL and GFAP levels and similar pTau181 levels compared to HC. Compared to AD patients, iRBD patients had lower levels of GFAP, NfL, and pTau181. In iRBD, GFAP and NfL levels were significantly correlated, while no correlations were observed between plasma biomarkers and clinical symptoms. High plasma NfL and GFAP levels in iRBD patients reflect a possible ongoing neurodegenerative process. Normal pTau181 plasma levels in iRBD suggest that AD-related neurodegeneration is not present at this stage. Future studies on plasma markers predicting phenoconversion are crucial for setting neuroprotective interventions in iRBD patients. Statement of Significance This study identifies plasma biomarkers that reflect neurodegeneration in idiopathic/isolated REM sleep behavior disorder (iRBD), a prodromal stage of α-synucleinopathies. Higher plasma neurofilament light chain (NfL) and glial fibrillary acidic protein (GFAP) levels in iRBD patients compared to healthy controls suggest early neuronal and glial degeneration, while similar phosphorylated-Tau 181 levels indicate an absence of Alzheimer's disease co-pathology. These findings support the utility of NfL and GFAP as potential blood-based markers for tracking early neurodegenerative changes in iRBD. Further studies focusing on these markers in predicting disease progression could be instrumental in guiding timely neuroprotective interventions.

2095 Background: Magnetic resonance imaging (MRI) of the brain primarily assesses blood brain barrier (BBB) dysfunction which provides indirect information regarding tumor size. The limitations of MRI have become evident with the use of temozolomide (pseudo-progression) and VEGF based therapies (pseudo-response). As a result, a blood-based marker to assess tumor burden is increasingly important. Previous studies suggested that plasma glial fibrillary acidic protein (GFAP) levels are sensitive and specific for glioblastoma (GBM). This pilot study examines the utility of GFAP as a biomarker in pre- and post-operative gliomas. Methods: Plasma samples were collected in patients pre-operatively (N=34) and 24-48 hours post-operatively (N=24) for what was post-operatively confirmed to be newly diagnosed glioma. Plasma GFAP was detected using an electrochemiluminescent immunoassay with a detection threshold of >0.04ng/ml. Presence or absence of contrast enhancement (CE) on the pre-op MRI was compared with the pre-op plasma GFAP level using Fisher’s exact test. Results: The histologic, radiographic, and detection rates and pre- and post-op plasma GFAP levels are presented below. Higher grade tumors more often had CE on MRI than lower grade tumors (p=0.002). Plasma GFAP was detectable in 80% of patients with CE and 21% without CE (p=0.001). Conclusions: Higher grade tumors had more CE and higher plasma GFAP levels pre-operatively. However, post-operative GFAP levels dramatically increased in patients with lower grade gliomas that previously had undetectable levels. These data strongly suggest that GFAP is not a specific biomarker for GBM or an accurate measure of tumor burden. In addition, injury to the brain or BBB from surgery results in striking elevations of plasma GFAP independent of histologic grade or prior contrast enhancement. Histologic findings Contrast enhancement pre-op GFAP detectable pre-op GFAP levels pre-op median (range) GFAP detectable post-op GFAP levels post-op median (range) Grade 4 (n=9) 89% 100% 0.09 (0.07-0.15) 100% 0.07 (0.04-0.32) (N=5) Grade 3 (n=11) 55% 36% 0 (0-0.58) 100% 1.18 (0.11-4.56) (N=8) Grade 2 (n=14) 7% 21% 0 (0-0.22) 91% 0.38 (0.05-9.65) (N=11)

Individuals with Down syndrome (DS) are at high risk of Alzheimer's disease (AD), displaying AD pathology similar to the general population. This study evaluated AD-related blood biomarkers in DS within the AT(N) framework through a systematic review and meta-analysis of studies published between 2017 and October 2024. The meta-analysis focused on plasma amyloid beta (Aβ)42, Aβ40, total tau (t-tau), phosphorylated tau (p-tau)181, neurofilament light chain (NfL), and glial fibrillary acidic protein (GFAP) levels, comparing 2109 DS individuals and 1006 euploid controls. Plasma Aβ42, Aβ40, NfL, and GFAP levels were significantly elevated in DS compared to euploid controls, while the Aβ42/40 ratio was reduced. In DS-AD individuals, Aβ42 and t-tau levels were elevated, with p-tau181, NfL, and GFAP consistently high across clinical subgroups. Notably, Aβ40 and the Aβ42/40 ratio changed significantly in preclinical AD, while t-tau increased in clinical AD. Incorporating inflammation (I) markers highlights neuroinflammation's role in DS-AD progression, supporting the blood-based AT(N)I framework for early AD detection and monitoring in DS. HIGHLIGHTS: We reviewed 58 studies on Down syndrome (DS) blood biomarkers and a meta-analysis of 18 using single molecule array. Plasma amyloid beta (Aβ)42, Aβ40, neurofilament light chain (NfL), and glial fibrillary acidic protein (GFAP) levels were elevated in DS compared to controls. DS-Alzheimer's disease (AD) individuals showed higher Aβ42, total tau (t-tau), phosphorylated tau (p-tau)181, NfL, and GFAP levels. Plasma p-tau181, NfL, and GFAP were elevated across all clinical subgroups. Aβ40 and Aβ42/40 ratio changed in preclinical AD; t-tau rose in clinical AD.

Objective:Blood-based biomarkers represent a scalable and accessible approach for the detection and monitoring of Alzheimer’s disease (AD). Plasma phosphorylated tau (p-tau) and neurofilament light (NfL) are validated biomarkers for the detection of tau and neurodegenerative brain changes in AD, respectively. There is now emphasis to expand beyond these markers to detect and provide insight into the pathophysiological processes of AD. To this end, a reactive astrocytic marker, namely plasma glial fibrillary acidic protein (GFAP), has been of interest. Yet, little is known about the relationship between plasma GFAP and AD. Here, we examined the association between plasma GFAP, diagnostic status, and neuropsychological test performance. Diagnostic accuracy of plasma GFAP was compared with plasma measures of p-tau181 and NfL.Participants and Methods:This sample included 567 participants from the Boston University (BU) Alzheimer’s Disease Research Center (ADRC) Longitudinal Clinical Core Registry, including individuals with normal cognition (n=234), mild cognitive impairment (MCI) (n=180), and AD dementia (n=153). The sample included all participants who had a blood draw. Participants completed a comprehensive neuropsychological battery (sample sizes across tests varied due to missingness). Diagnoses were adjudicated during multidisciplinary diagnostic consensus conferences. Plasma samples were analyzed using the Simoa platform. Binary logistic regression analyses tested the association between GFAP levels and diagnostic status (i.e., cognitively impaired due to AD versus unimpaired), controlling for age, sex, race, education, and APOE e4 status. Area under the curve (AUC) statistics from receiver operating characteristics (ROC) using predicted probabilities from binary logistic regression examined the ability of plasma GFAP to discriminate diagnostic groups compared with plasma p-tau181 and NfL. Linear regression models tested the association between plasma GFAP and neuropsychological test performance, accounting for the above covariates.Results:The mean (SD) age of the sample was 74.34 (7.54), 319 (56.3%) were female, 75 (13.2%) were Black, and 223 (39.3%) were APOE e4 carriers. Higher GFAP concentrations were associated with increased odds for having cognitive impairment (GFAP z-score transformed: OR=2.233, 95% CI [1.609, 3.099], p<0.001; non-z-transformed: OR=1.004, 95% CI [1.002, 1.006], p<0.001). ROC analyses, comprising of GFAP and the above covariates, showed plasma GFAP discriminated the cognitively impaired from unimpaired (AUC=0.75) and was similar, but slightly superior, to plasma p-tau181 (AUC=0.74) and plasma NfL (AUC=0.74). A joint panel of the plasma markers had greatest discrimination accuracy (AUC=0.76). Linear regression analyses showed that higher GFAP levels were associated with worse performance on neuropsychological tests assessing global cognition, attention, executive functioning, episodic memory, and language abilities (ps<0.001) as well as higher CDR Sum of Boxes (p<0.001).Conclusions:Higher plasma GFAP levels differentiated participants with cognitive impairment from those with normal cognition and were associated with worse performance on all neuropsychological tests assessed. GFAP had similar accuracy in detecting those with cognitive impairment compared with p-tau181 and NfL, however, a panel of all three biomarkers was optimal. These results support the utility of plasma GFAP in AD detection and suggest the pathological processes it represents might play an integral role in the pathogenesis of AD.

BackgroundWomen are at greater risk of developing sporadic Alzheimer's disease (AD). While their longer lifespans contribute to AD‐risk, this factor does not fully explain the observed sex differences. Increased glial activation and neuroinflammation associated with female‐sex may play a role. Glial fibrillary acidic protein (GFAP), a marker of astrocyte activation and neuroinflammation, has been linked to AD‐ risk. In preclinical and prodromal AD, higher brain GFAP levels are associated with cognitive decline, Aβ deposition, tau spread, and neurodegeneration associated with AD. Studies have reported that plasma GFAP levels are higher in women compared to men, but few have thoroughly examined this influence. This prompted us to examine sex‐differences in plasma GFAP in cognitively unimpaired older adults and its relationship to cognitive performance and other plasma AD biomarkers, both at baseline and longitudinally.MethodParticipants were enrolled in the Memory Education and Research Initiative (MERI) program and completed a neuropsychological battery, clinical and psychiatric evaluation, and blood draw. Plasma GFAP, Aβ42, Aβ40 concentrations were measured using single‐molecule array (SIMOA) platform. Participants were included if they gave blood (2+ timepoints), MMSE>23 at Baseline, and age 50‐85. Analysis of covariance (ANCOVA) was conducted to assess for sex differences, and longitudinal analyses using linear mixed models were conducted to examine associations with cognition.ResultA total 325 MERI (mean age=72 years; 59% females) were included in the analysis. ANCOVA, controlling for age, showed significantly higher plasma GFAP levels in females compared to males (p = 0.001). Longitudinal analysis of 229 MERI revealed that higher baseline GFAP is associated with lower MMSE scores over time (Figure 1, p = 0.002). When stratified by sex, these associations remained significant in females but not males (p = 0.002). GFAP was also inversely associated with Aβ42/40 over time (Figure 2, p <0.001) in females.ConclusionCognitively unimpaired females had higher levels of plasma GFAP compared to males. Moreover, elevated GFAP levels associated with greater decline in global cognition and lower Aβ42/40 in females but not males. These findings suggest increased astrocytic activation that may lead to cognitive decline in females. More studies are needed to understand how sex‐differences in neuroinflammation may impact future AD‐risk. Potential mechanisms will be discussed.

BackgroundPlasma glial fibrillary acidic protein (GFAP) is associated with amyloid‐β (Aβ) and tau, but their causal relationships remain unclear. We used Mendelian randomization (MR; using genetic causal anchors to avoid reverse causation) to clarify the causal relationship between plasma/brain GFAP, Aβ, and tau.MethodsStudy participants are from two independent datasets: the Harvard Aging Brain Study (HABS) and the Religious Orders Study/the Rush Memory and Aging Project (ROSMAP) (Table 1). From HABS, we used baseline plasma GFAP (MSD platform) and Aβ (PiB PET cortical composite with partial volume correction [PVC]) and longitudinal inferior temporal (IT) tau (FTP PET SUVR with PVC) data. From ROSMAP, we used post‐mortem frontal cortex GFAP expression (RNA‐Seq) and midfrontal Aβ and tau burden (immunohistochemistry). We used linear regressions to assess the relationship between APOE ε4, GFAP, and Aβ. For MR, we performed instrumental variable (IV) analyses using APOE ε4 as the instrument. In HABS, we used linear mixed effect models to assess baseline GFAP ‐ longitudinal IT tau association. In ROSMAP, we assessed the cross‐sectional GFAP ‐ tau association (linear regression). All variables were standardized, and all models were adjusted for age and sex.ResultIn HABS, APOE ε4 carriers had higher baseline plasma GFAP (n=324, β=0.32, p=0.0025), but this association attenuated after adjusting for Aβ (p=0.42). MR suggested the causal effect of Aβ on plasma GFAP (2SLS β=0.40, p=0.0018). Baseline plasma GFAP predicted longitudinal increase in IT tau (n=187, β=0.051, p=1.9×10‐4); this association attenuated after adjusting baseline Aβ and its time‐interaction (p=0.16). We observed consistent results in ROSMAP: APOE ε4 carriers had higher frontal GFAP expression (n=609, β=0.26, p=0.0051), but this association attenuated after adjusting for Aβ (p=0.11). MR supported the causal effect of Aβ on brain GFAP (2SLS β=0.39, p=0.0085). The frontal GFAP– tau association (β=0.10, p=0.012) weakened after controlling for Aβ (p=0.50).ConclusionOur study leveraging APOE ε4 as a genetic causal anchor supports that Aβ is at the causal upstream of increased brain GFAP gene expression and elevated plasma GFAP (Figure 1A). By contrast, the neocortical tau – GFAP association is likely confounded by Aβ (Figure 1B‐C).

ABSTRACTBackgroundRecent advances now allow detection of brain‐specific proteins in blood, including neurofilament light chain (NfL), a marker of axonal pathology, and glial fibrillary acidic protein (GFAP), indicative of astrocytic activation. Given the evidence of astroglial pathology and neuronal dysfunction in bipolar disorder, and ongoing debates on neuroprogression, we investigated plasma NfL and GFAP levels in affected individuals.MethodsThis study analysed plasma NfL and GFAP measured in 216 individuals using Simoa. We used bootstrapped general linear models (GLM) to compare plasma NfL and GFAP levels between people with bipolar depression (n = 120) and healthy controls (n = 96), adjusting for age, sex, and weight. We examined associations between these biomarkers and clinical variables while adjusting for multiple comparisons. For sensitivity analyses, predictors were evaluated using Bayesian model averaging (BMA).ResultsPlasma GFAP (β = 0.21 [0.07, 0.35], p = 0.006) and NfL (β = 0.06 [0.01, 0.10], p = 0.028) were elevated in people with bipolar depression. Illness duration was positively associated with NfL (r = 2.97, p = 0.002), and further supported by BMA analysis (posterior inclusion probability, PIP = 0.85). Age of onset was positively associated with GFAP (r = 0.246 p = 0.041), which was also supported by BMA analysis (PIP = 0.67).ConclusionsThese findings indicate increased plasma NfL and GFAP levels in bipolar disorder. Our findings support the neuroprogression hypothesis, where prolonged illness duration contributes to neuroaxonal damage. Elevated GFAP in those with later onset suggests a role for neuroinflammation, potentially linked to increased cardiovascular and metabolic comorbidities.

Glial fibrillary acidic protein (GFAP) is a marker of reactive astrogliosis that increases in the cerebrospinal fluid (CSF) and blood of individuals with Alzheimer disease (AD). However, it is not known whether there are differences in blood GFAP levels across the entire AD continuum and whether its performance is similar to that of CSF GFAP. To evaluate plasma GFAP levels throughout the entire AD continuum, from preclinical AD to AD dementia, compared with CSF GFAP. This observational, cross-sectional study collected data from July 29, 2014, to January 31, 2020, from 3 centers. The Translational Biomarkers in Aging and Dementia (TRIAD) cohort (Montreal, Canada) included individuals in the entire AD continuum. Results were confirmed in the Alzheimer's and Families (ALFA+) study (Barcelona, Spain), which included individuals with preclinical AD, and the BioCogBank Paris Lariboisière cohort (Paris, France), which included individuals with symptomatic AD. Plasma and CSF GFAP levels measured with a Simoa assay were the main outcome. Other measurements included levels of CSF amyloid-β 42/40 (Aβ42/40), phosphorylated tau181 (p-tau181), neurofilament light (NfL), Chitinase-3-like protein 1 (YKL40), and soluble triggering receptor expressed on myeloid cells 2 (sTREM2) and levels of plasma p-tau181 and NfL. Results of amyloid positron emission tomography (PET) were available in TRIAD and ALFA+, and results of tau PET were available in TRIAD. A total of 300 TRIAD participants (177 women [59.0%]; mean [SD] age, 64.6 [17.6] years), 384 ALFA+ participants (234 women [60.9%]; mean [SD] age, 61.1 [4.7] years), and 187 BioCogBank Paris Lariboisière participants (116 women [62.0%]; mean [SD] age, 69.9 [9.2] years) were included. Plasma GFAP levels were significantly higher in individuals with preclinical AD in comparison with cognitively unimpaired (CU) Aβ-negative individuals (TRIAD: Aβ-negative mean [SD], 185.1 [93.5] pg/mL, Aβ-positive mean [SD], 285.0 [142.6] pg/mL; ALFA+: Aβ-negative mean [SD], 121.9 [42.4] pg/mL, Aβ-positive mean [SD], 169.9 [78.5] pg/mL). Plasma GFAP levels were also higher among individuals in symptomatic stages of the AD continuum (TRIAD: CU Aβ-positive mean [SD], 285.0 [142.6] pg/mL, mild cognitive impairment [MCI] Aβ-positive mean [SD], 332.5 [153.6] pg/mL; AD mean [SD], 388.1 [152.8] pg/mL vs CU Aβ-negative mean [SD], 185.1 [93.5] pg/mL; Paris: MCI Aβ-positive, mean [SD], 368.6 [158.5] pg/mL; AD dementia, mean [SD], 376.4 [179.6] pg/mL vs CU Aβ-negative mean [SD], 161.2 [67.1] pg/mL). Plasma GFAP magnitude changes were consistently higher than those of CSF GFAP. Plasma GFAP more accurately discriminated Aβ-positive from Aβ-negative individuals than CSF GFAP (area under the curve for plasma GFAP, 0.69-0.86; area under the curve for CSF GFAP, 0.59-0.76). Moreover, plasma GFAP levels were positively associated with tau pathology only among individuals with concomitant Aβ pathology. This study suggests that plasma GFAP is a sensitive biomarker for detecting and tracking reactive astrogliosis and Aβ pathology even among individuals in the early stages of AD.

Aspirin-induced blockade of NF-kB activity restrains up-regulation of glial fibrillary acidic protein in human astroglial cells

Glial fibrillary acidic protein (GFAP) is a promising candidate blood-based biomarker for Alzheimer's disease (AD) diagnosis and prognostication. The timing of its disease-associated changes, its clinical correlates, and biofluid-type dependency will influence its clinical utility. We evaluated plasma, serum, and cerebrospinal fluid (CSF) GFAP in families with autosomal dominant AD (ADAD), leveraging the predictable age at symptom onset to determine changes by stage of disease. Plasma GFAP elevations appear a decade before expected symptom onset, after amyloid beta (Aβ) accumulation and prior to neurodegeneration and cognitive decline. Plasma GFAP distinguished Aβ-positive from Aβ-negative ADAD participants and showed a stronger relationship with Aβ load in asymptomatic than symptomatic ADAD. Higher plasma GFAP was associated with the degree and rate of neurodegeneration and cognitive impairment. Serum GFAP showed similar relationships, but these were less pronounced for CSF GFAP. Our findings support a role for plasma GFAP as a clinical biomarker of Aβ-related astrocyte reactivity that is associated with cognitive decline and neurodegeneration. Plasma glial fibrillary acidic protein (GFAP) elevations appear a decade before expected symptom onset in autosomal dominant Alzheimer's disease (ADAD). Plasma GFAP was associated to amyloid positivity in asymptomatic ADAD. Plasma GFAP increased with clinical severity and predicted disease progression. Plasma and serum GFAP carried similar information in ADAD, while cerebrospinal fluid GFAP did not.

Aspirin-induced blockade of NF-κB activity restrains up-regulation of glial fibrillary acidic protein in human astroglial cells

BackgroundPlasma levels of amyloid‐β1‐42/1‐40, and glial fibrillary acidic protein (GFAP) have demonstrated predictive potential for amyloid pathology in the early stages of Alzheimer’s disease (AD) development. Utilizing baseline and up to 6‐year follow‐up plasma, positron emission tomography (PET) and cognitive data from cognitively unimpaired individuals, we here aim to test whether early changes in plasma biomarker levels associate with change in amyloid status and cognitive decline.MethodsFrom the EMIF‐AD PreclinAD study we selected individuals with normal cognition and longitudinal plasma, PET and cognitive data available (nbaseline=200, table 1). Amyloid‐status was determined using visual assessment of dynamic [18F]flutemetamol‐PET scans. Plasma levels of amyloid‐β1‐40, amyloid‐β1‐42, neurofilament light (NfL), and GFAP were measured using the neurology 4‐plex E Simoa assay (Quanterix). Linear mixed models were applied to examine longitudinal changes in plasma biomarker levels, and their association with longitudinal changes in amyloid‐status and cognition.ResultsAt baseline 13.3%, and at 4‐year follow‐up 25.9% of participants were amyloid‐positive. Twenty‐one participants converted from a negative to positive amyloid‐status. At baseline, GFAP levels were higher and amyloid‐β1‐42/1‐40 lower in amyloid‐positive compared to negative individuals (β(SE)=0.43(0.14), β(SE)=‐0.75(0.21), p&lt;0.005, respectively). In the total cohort, plasma levels of GFAP and NfL increased over time, whereas amyloid‐β1‐42/1‐40 remained stable (Figure 1). Although overall stable, plasma amyloid‐β1‐42/1‐40 decreased in participants that converted from a negative to positive amyloid‐status over time (β(SE)=‐0.04(0.02), p=0.02). Alongside, an increase in GFAP levels was observed in participants that converted from a negative to positive amyloid‐status compared to stable negative participants (Figure 1). No group differences were observed for NfL. A longitudinal increase in GFAP levels was associated with memory decline in stable amyloid positive individuals (GFAP*time*amyloid‐group status: β(SE)=‐0.09(0.02), p&lt;0.001, Figure 2).ConclusionsEarly changes in plasma GFAP and amyloid‐β1‐42/1‐40 are associated with changes in amyloid‐status in cognitively unimpaired individuals. Further, increases in plasma GFAP levels over time are predictive of future memory decline in amyloid‐positive individuals. These results support the potential of plasma GFAP and, to a lesser extent, amyloid‐β1‐42/1‐40 as diagnostic and prognostic markers for AD in early stages of disease development.

AxD (Alexander disease) is a rare disorder caused by heterozygous mutations in GFAP (glial fibrillary acidic protein) resulting in accumulation of the GFAP protein and elevation of Gfap mRNA. To test whether GFAP itself can serve as a biomarker of disease status or progression, we investigated two independent measures of GFAP expression in AxD mouse models, one using a genetic reporter of promoter activity and the other quantifying GFAP protein directly in a manner that could also be employed in human studies. Using a transgenic reporter line that expresses firefly luciferase under the control of the murine Gfap promoter (Gfap-luc), we found that luciferase activity reflected the regional CNS (central nervous system) variability of Gfap mRNA in Gfap+/+ mice, and increased in mice containing a point mutation in Gfap that mimics a common human mutation in AxD (R239H in the human sequence, and R236H in the murine sequence). In a second set of studies, we quantified GFAP protein in CSF (cerebrospinal fluid) taken from three different AxD mouse models and littermate controls. GFAP levels in CSF were increased in all three AxD models, in a manner corresponding to the concentrations of GFAP in brain. These studies demonstrate that transactivation of the Gfap promoter is an early and sustained indicator of the disease process in the mouse. Furthermore, GFAP in CSF serves as a potential biomarker that is comparable between mouse models and human patients.