Growth-associated Protein Research Articles

P53-induced GAP-43 Upregulation in Primary Cortical Neurons of Rats.

In this study, we employed an in vitro culturing technique to investigate the impact of p53 on the modulation of growth-associated protein-43 (GAP-43) within the primary cortical neurons of rat specimens. (1) Within the first 24 hours after birth, the bilateral cortex was extracted from newborn Wistar rats and primary cortical neurons were cultured and identified. (2) The changes in the mRNA and protein expressions of GAP-43 induced by p53 in rat primary cortical neurons cultured in vitro were identified utilizing real-time polymerase chain reaction and western blot techniques. (1) Lentiviral transfection of p53 within primary cortical neurons of rats elicited elevated levels of both mRNA and protein expressions of GAP-43, consequently culminating in a noteworthy augmentation of p53 expression. (2) The introduction of a p53 inhibitor in rat primary cortical neurons resulted in a reduction in both mRNA and protein expressions of GAP-43. Within primary rat cortical neurons, p53 has the potential to prompt an augmentation in both the transcriptional and protein expression levels of the GAP-43 protein.

Fermented Protaetia brevitarsis Larvae Improves Neurotoxicity in Chronic Ethanol-Induced-Dementia Mice via Suppressing AKT and NF-κB Signaling Pathway.

This study was investigated to examine the neuroprotective effect of fermented Protaetia brevitarsis larvae (FPB) in ethanol-induced-dementia mice. Consumption of FPB by mice resulted in improved memory dysfunction in the Y-maze, passive avoidance, and Morris water maze tests. FPB significantly decreased oxidative stress by regulating levels of malondialdehyde (MDA), superoxide dismutase (SOD), and reduced glutathione (GSH) in brain tissues. In addition, FPB restored cerebral mitochondrial dysfunction by modulating levels of reactive oxygen species (ROS), mitochondrial membrane potential (MMP), and ATP. In addition, FPB enhanced the cholinergic system via the regulation of acetylcholine (ACh) content, acetylcholinesterase (AChE) activity, and expressions of AChE and choline acetyltransferase (ChAT) in brain tissues. FPB ameliorated neuronal apoptosis through modulation of the protein kinase B (AKT)/B-cell lymphoma (BCL)-2 signaling pathway. Also, FPB improved inflammation response by down-regulating the toll-like receptor (TLR)-4/nuclear factor (NF)-κB pathway. Additionally, FPB ameliorated synaptic plasticity via the increase of the expressions of synaptophysin (SYP), postsynaptic density protein (PSD)-95, and growth-associated protein (GAP)-43. Treatment with FPB also reinforced the blood-brain barrier by increasing tight junctions including zonula occludens (ZO)-1, occludin, and claudin-1. In conclusion, these results show that FPB can improve cognitive impairment via AKT/NF-κB pathways in ethanol-induced-dementia mice.

Microglial Reactivity Correlates with Presynaptic Loss Independent of β-Amyloid and Tau.

Triggering receptor expressed on myeloid cells-2 (TREM2) and progranulin (PGRN) are critical regulators of microglia activation and can be detected in cerebrospinal fluid (CSF). However, whether microglial reactivity is detrimental or neuroprotective for Alzheimer disease (AD) is still debatable. We identified 663 participants with baseline β-amyloid (Aβ) positron emission tomography (PET) and CSF biomarker data, including phosphorylated tau181 (p-Tau181), soluble TREM2 (sTREM2), PGRN, and growth-associated protein-43 (GAP-43). Among them, 254 participants had concurrent longitudinal CSF biomarkers. We used multivariate regression analysis to study the associations of CSF microglial biomarkers with Aβ PET, CSF p-Tau181, and CSF GAP-43 cross-sectionally and longitudinally. A Chinese aging cohort's independent CSF samples (n = 65) were analyzed as a validation. Higher baseline levels of CSF microglial biomarkers were related to faster rates of CSF sTREM2 increase and CSF PGRN decrease. Elevated CSF p-Tau181 was associated with higher levels of CSF microglial biomarkers and faster rates of CSF sTREM2 increase and CSF PGRN decrease. In both cohorts, higher Aβ burden was associated with attenuated CSF p-Tau181 effects on CSF microglial biomarker increases. Independent of Aβ PET and CSF p-Tau181 pathologies, higher levels of CSF sTREM2 but not CSF PGRN were related to elevated CSF GAP-43 levels and faster rates of CSF GAP-43 increase. These findings suggest that higher Aβ burden may attenuate the p-Tau-associated microglial responses, and TREM2-related microglial reactivity may independently correlate with GAP-43-related presynaptic loss. This study highlights the two-edged role of microglial reactivity in AD and other neurodegenerative diseases. ANN NEUROL 2024;95:917-928.

Associations of Growth-Associated Protein 43 with Cerebral Microbleeds: A Longitudinal Study.

Cerebral microbleeds (CMB) play an important role in neurodegenerative pathology. The present study aims to test whether cerebrospinal fluid (CSF) growth-associated protein 43 (GAP-43) level is linked to CMBs in elderly people. A total of 750 participants from the Alzheimer's Disease Neuroimaging Initiative (ADNI) who had measurements of GAP-43 and CMBs were included in the study. According to the presence and extent of CMBs, participants were stratified into different groups. Regression analyses were used to assess cross-sectional and longitudinal associations between GAP-43 and CMBs. Participants with CMB were slightly older and had higher concentrations of CSF GAP43. In multivariable adjusted analyses for age, gender, APOEɛ4 status, and cognitive diagnoses, higher CSF GAP-43 concentrations were modestly associated with CMB presence (OR = 1.169, 95% CI = 1.001-1.365) and number (β= 0.020, SE = 0.009, p = 0.027). Similarly, higher CSF GAP43 concentrations were accrual of CMB lesions, associated with higher CMB progression (OR = 1.231, 95% CI = 1.044-1.448) and number (β= 0.017, SE = 0.005, p = 0.001) in the follow up scan. In stratified analyses, slightly stronger associations were noted in male participants, those 65 years and older, carriers of APOEɛ4 alleles, and with more advanced cognitive disorders. CSF GAP-43 was cross-sectionally associated with the presence and extent of CMBs. GAP-43 might be used as a biomarker to track the dynamic changes of CMBs in elderly persons.

Restraint stress-induced effects on learning, memory, cognition, and expression of transcripts in different brain regions of mice.

Stress is one of the prevalent factors influencing cognition. Several studies examined the effect of mild or chronic stress on cognition. However, most of these studies are limited to a few behavioral tests or the expression of selected RNA/proteins markers in a selected brain region. This study examined the effect of restraint stress on learning, memory, cognition, and expression of transcripts in key learning centers. Male mice were divided into three groups (n = 6/group)-control group, stress group (adult stressed group; S), and F1 group (parental stressed group). Stress group mice were subjected to physical restraint stress for 2h before light offset for 2weeks. The F1 group comprised adult male mice born of stressed parents. All animals were subjected to different tests and were sacrificed at the end. Transcription levels of Brain-Derived Neurotrophic Factor (Bdnf), Tyrosine kinase (TrkB), Growth Associated Protein 43 (Gap-43), Neurogranin (Ng), cAMP Response Element-Binding Protein (Creb), Glycogen synthase kinase-3β (Gsk3β), Interleukine-1 (IL-1) and Tumour necrosis factor-α (Tnf-α) were studied. Results show that both adult and parental stress negatively affect learning, memory and cognition, as reflected by taking longer time to achieve the task or showing reduced exploratory behavior. Expression of Bdnf, TrkB, Gsk3β and Ng was downregulated, while IL-1 and Tnf-α were upregulated in the brain's cortex, thalamus, and hippocampus region of stressed mice. These effects seem to be relatively less severe in the offspring of stressed parents. The findings suggest that physical restraint stress can alter learning, memory, cognition, and expression of transcripts in key learning centers of brain.

Advancements in the study of synaptic plasticity and mitochondrial autophagy relationship.

Synapses serve as the points of communication between neurons, consisting primarily of three components: the presynaptic membrane, synaptic cleft, and postsynaptic membrane. They transmit signals through the release and reception of neurotransmitters. Synaptic plasticity, the ability of synapses to undergo structural and functional changes, is influenced by proteins such as growth-associated proteins, synaptic vesicle proteins, postsynaptic density proteins, and neurotrophic growth factors. Furthermore, maintaining synaptic plasticity consumes more than half of the brain's energy, with a significant portion of this energy originating from ATP generated through mitochondrial energy metabolism. Consequently, the quantity, distribution, transport, and function of mitochondria impact the stability of brain energy metabolism, thereby participating in the regulation of fundamental processes in synaptic plasticity, including neuronal differentiation, neurite outgrowth, synapse formation, and neurotransmitter release. This article provides a comprehensive overview of the proteins associated with presynaptic plasticity, postsynaptic plasticity, and common factors between the two, as well as the relationship between mitochondrial energy metabolism and synaptic plasticity.

Chronic Expression of Interleukin-10 Transgene Modulates Cardiac Sympathetic Ganglion Resulting in Reduced Ventricular Arrhythmia.

The cardiac autonomic nervous system (CANS) is intimately connected to the regulation of electrophysiology and arrhythmogenesis in cardiac systems. This work aimed at investigating whether interleukin-10 (IL-10) could effectively modulate CANS and suppress ischemia-induced ventricular arrhythmia (VA) through chronically acting on the cardiac sympathetic ganglion (CSG). Using an adeno-associated virus (AAV), we achieved local chronic overproduction of IL-10 in the CSG, left stellate ganglion (LSG). As a result, in the IL-10 group, we observed a decreased number of tyrosine hydroxylase-positive (TH+) cells in the LSG. IL-10 markedly downregulated the nerve growth factor, synaptophysin, as well as growth-associated protein 43 expression. In vivo, results from ambulatory electrocardiography showed that IL-10 overexpression significantly inhibited the cardiac sympathetic nervous system activity and improved heart rate variability. Meanwhile, we observed decreased LSG function as well as prolonged ventricular effective refractory period and suppressed VA after myocardial infarction (MI) in the IL-10 group. In addition, IL-10 overexpression attenuated inflammation and decreased norepinephrine levels in the myocardium after acute MI. In conclusion, our data suggest that chronic IL-10 overexpression modulates cardiac sympathetic nerve remodeling and suppresses VA induced by MI. Neuromodulation through AAV-mediated IL-10 overexpression may have the characteristics of and advantages as a potential neuroimmunotherapy for preventing MI-induced VAs.

DDT and titanium dioxide nanoparticle coexposure induced neurobehavioral deficits in zebrafish

Both dichlorodiphenyltrichloroethane (DDT) and titanium dioxide nanoparticle (TiO2 NP) have worldwide-scale commercial applications, resulting in their co-pollution in the ecosystems and posing combined health risks. However, there is a lack of toxicity studies for the interactions of DDT and TiO2 NP in the environmental relevant concentrations. In this study, we characterized the coexposures using a zebrafish waterborne exposure approach and evaluated the neurotoxicity response of the treated embryos or adults. Our results showed that DDT/TiO2 NP coexposure enhanced the DDT accumulation in vivo and increased the larval locomotor. The chronic DDT/TiO2 NP coexposure did not affect the overall survival rate, sex ratio and growth. However, DDT/TiO2 NP coexposure severely affected the adult locomotor activity, social contact, shoaling and aggressive behaviors compared to single treatment groups or controls. These adult behavioral deficits were accompanied by changes in neurotransmitter acetylcholine (ACH) level in the brain and muscle tissues, as well as neural development genes expression activation of growth-associated protein 43 (gap43) and synaptic vesicle glycoprotein 2 (sv2) in the brain. The significantly increased ACH level and the activated neural genes expression in the DDT/TiO2 NP co-exposed fish may account for the observed hyperactivity and social deficits.

Insights into early pathogenesis of sporadic Alzheimer's disease: role of oxidative stress and loss of synaptic proteins.

Oxidative stress, induced by impaired insulin signaling in the brain contributes to cognitive loss in sporadic Alzheimer's disease (sAD). This study evaluated early hippocampal oxidative stress, pre- and post-synaptic proteins in intraperitoneal (IP) and intracerebroventricular (ICV) streptozotocin (STZ) models of impaired insulin signaling. Adult male Wistar rats were injected with STZ, IP, or ICV, and sacrificed 1-, 3-, or 6-weeks post injection. Rat's cognitive behavior was assessed using Morris water maze (MWM) tests at weeks 3 and 6. Hippocampal synaptosomal fractions were examined for oxidative stress markers and presynaptic [synapsin I, synaptophysin, growth-associated protein-43 (GAP-43), synaptosomal-associated protein-25 (SNAP-25)] and postsynaptic [drebrin, synapse-associated protein-97 (SAP-97), postsynaptic density protein-95 (PSD-95)] proteins. IP-STZ and ICV-STZ treatment impaired rat's cognition, decreased the levels of reduced glutathione (GSH) and increased the levels of thiobarbituric acid reactive species (TBARS) in a time dependent manner. In addition, it reduced the expression of pre- and post-synaptic proteins in the hippocampus. The decline in cognition is significantly correlated with the reduction in synaptic proteins in the hippocampus. In conclusion, impaired insulin signaling in the brain is deleterious in causing early synaptosomal oxidative damage and synaptic loss that exacerbates with time and correlates with cognitive impairments. Our data implicates oxidative stress and synaptic protein loss as an early feature of sAD and provides insights into early biochemical and behavioral changes during disease progression.

Elevated CSF GAP-43 is associated with accelerated tau accumulation and spread in Alzheimer’s disease

In Alzheimer’s disease, amyloid-beta (Aβ) triggers the trans-synaptic spread of tau pathology, and aberrant synaptic activity has been shown to promote tau spreading. Aβ induces aberrant synaptic activity, manifesting in increases in the presynaptic growth-associated protein 43 (GAP-43), which is closely involved in synaptic activity and plasticity. We therefore tested whether Aβ-related GAP-43 increases, as a marker of synaptic changes, drive tau spreading in 93 patients across the aging and Alzheimer’s spectrum with available CSF GAP-43, amyloid-PET and longitudinal tau-PET assessments. We found that (1) higher GAP-43 was associated with faster Aβ-related tau accumulation, specifically in brain regions connected closest to subject-specific tau epicenters and (2) that higher GAP-43 strengthened the association between Aβ and connectivity-associated tau spread. This suggests that GAP-43-related synaptic changes are linked to faster Aβ-related tau spread across connected regions and that synapses could be key targets for preventing tau spreading in Alzheimer’s disease.

A highly bioavailable curcumin formulation ameliorates inflammation cytokines and neurotrophic factors in mice with traumatic brain injury.

A novel curcumin formulation increases relative absorption by 46 times (CurcuWIN®) of the total curcuminoids over the unformulated standard curcumin form. However, the exact mechanisms by which curcumin demonstrates its neuroprotective effects are not fully understood. This study aimed to investigate the impact of a novel formulation of curcumin on the expression of brain-derived neurotrophic factor (BDNF), glial fibrillary acidic protein (GFAP), a main component of the glial scar and growth-associated protein-43 (GAP-43), a signaling molecule in traumatic brain injury (TBI). Mice (adult, male, C57BL/6j) were randomly divided into three groups as follows: TBI group (TBI-induced mice); TBI + CUR group (TBI mice were injected i.p. curcumin just after TBI); TBI+ CurcuWIN® group (TBI mice were injected i.p. CurcuWIN® just after TBI). Brain injury was induced using a cold injury model. Injured brain tissue was stained with Cresyl violet to evaluate infarct volume and brain swelling, analyzed, and measured using ImageJ by Bethesda (MD, USA). Western blot analysis was performed to determine the protein levels related to injury. While standard curcumin significantly reduced brain injury, CurcuWIN® showed an even greater reduction associated with reductions in glial activation, NF-κB, and the inflammatory cytokines IL-1β and IL-6. Additionally, both standard curcumin and CurcuWIN® led to increased BDNF, GAP-43, ICAM-1, and Nrf2 expression. Notably, CurcuWIN® enhanced their expression more than standard curcumin. This data suggests that highly bioavailable curcumin formulation has a beneficial effect on the traumatic brain in mice.

Grape seed-derived procyanidins decreases neuropathic pain and nerve regeneration by suppression of toll-like receptor 4-myeloid differentiation factor-88 signaling.

Background: Recent studies have shown that peripheral nerve regeneration process is closely related to neuropathic pain. Toll-like receptor 4 (TLR4) signaling was involved in different types of pain and nerve regeneration. TLR4 induced the recruitment of myeloid differentiation factor-88 adaptor protein (MyD88) and NF-κB-depended transcriptional process in sensory neurons and glial cells, which produced multiple cytokines and promoted the induction and persistence of pain. Our study aimed to investigate procyanidins's effect on pain and nerve regeneration via TLR4-Myd88 signaling. Methods: Spinal nerve ligation (SNL) model was established to measure the analgesic effect of procyanidins. Anatomical measurement of peripheral nerve regeneration was measured by microscopy and growth associated protein 43 (GAP43) staining. Western blotting and/or immunofluorescent staining were utilized to detect TLR4, myeloid differentiation factor-88 adaptor protein (MyD88), ionized calcium-binding adapter molecule 1 (IBA1) and nuclear factor kappa-B-p65 (NF-κB-p65) expression, as well as the activation of astrocyte and microglia. The antagonist of TLR4 (LPS-RS-Ultra, LRU) were intrathecally administrated to assess the behavioral effects of blocking TLR4 signaling on pain and nerve regeneration. Result: Procyanidins reduced mechanical allodynia, thermal hyperalgesia and significantly suppressed the number of nerve fibers regenerated and the degree of myelination in SNL model. Compared with sham group, TLR4, MyD88, IBA1 and phosphorylation of NF-κB-p65 were upregulated in SNL rats which were reversed by procyanidins administration. Additionally, procyanidins also suppressed activation of spinal astrocytes and glial cells. Conclusion: Suppression of TLR4-MyD88 signaling contributes to the alleviation of neuropathic pain and reduction of nerve regeneration by procyanidins.

Preparation of a minocycline polymer micelle thermosensitive gel and its application in spinal cord injury.

Neuroprotection is an important approach for the treatment of spinal cord injury (SCI). Minocycline (MC), a known neuroprotective agent, has been utilized for SCI treatment, but its therapeutic effect is limited by instability and low bioavailability. Herein, we developed an innovative micellar thermosensitive hydrogel (MCPP-M-gel) that encapsulates MC in polyethylene glycol (PEG)-poly(lactide-co-glycolic acid) (PLGA) micelles to enhance its therapeutic efficacy in a rat model of SCI. The micelles were synthesized via the thin-film hydration method and characterized for encapsulation efficiency, particle size, zeta potential, and polydispersity index (PDI). MCPP-M-gel demonstrated favorable physico-mechanical properties and extended MC release over 72 hours in vitro without cytotoxic effects on neural crest-derived ectoderm mesenchymal stem cells (EMSCs). Thereafter, MC, MCPP-M, MCPP-M-gel and a blank micellar thermosensitive gel were injected into the injured site of SCI rats. Histopathological evaluation demonstrated that MCPP-M-gel could promote neuronal regeneration at the injured site of the SC after 28 days. Immunofluorescence techniques revealed that MCPP-M-gel increased the expression of neuronal class III β-tubulin (Tuj1), myelin basic protein (MBP), growth-associated protein 43 (GAP43), neurofilament protein-200 (NF-200) and nestin as well as reduced glial-fibrillary acidic protein (GFAP) expression in damaged areas of the SC. In conclusion, this study innovatively developed MCPP-M-gel based on a PEG-PLGA copolymer as a biomaterial, laying a solid foundation for further research and application of MCPP-M-gel in SCI models or other neurodegenerative diseases.

Increased CSF GAP‐43 is associated with accelerated tau accumulation and spread in Alzheimer’s disease

AbstractBackgroundAnimal and in vitro studies of Alzheimer’s disease (AD) found that tau spreads trans‐synaptically in an activity‐dependent manner, suggesting that synapses are key routes for tau spread. Importantly, amyloid‐beta (Ab) induces synaptic remodeling and aberrant synaptic activity, which may accelerate trans‐synaptic tau spread. In AD patients, we found previously that PET‐assessed tau spreads from circumscribed epicenters across functionally connected brain regions. Yet, it remains unclear whether connectivity‐associated spread of tau in AD is accelerated by Ab‐related synaptic changes. The presynaptic growth‐associated protein 43 (GAP‐43) is implicated in synaptic plasticity and is consistently increased in cerebrospinal fluid (CSF) in AD, suggesting that GAP‐43 captures deviations in synaptic integrity such as aberrant synaptic activity. We therefore tested whether higher GAP‐43 is associated with faster Ab‐related tau spread.MethodsWe included longitudinal [18F]Flortaucipir tau‐PET (follow‐up∼3.21±1.48yrs), baseline [18F]Florbetapir amyloid‐PET and CSF GAP‐43 from 93 subjects (i.e., cognitively normal [CN] controls Ab‐, n = 54; CN/Mild Cognitive Impairment Ab+, n = 33/21). To model connectivity‐associated tau spread, we determined a connectivity template across 200 cortical regions (i.e., Schaefer atlas) using 3T multi‐band resting‐state fMRI in 42 age‐ and sex‐matched Ab‐/tau‐ controls. All statistical models were controlled for age, sex and diagnosis.ResultsUsing linear regression, we found that higher CSF GAP‐43 levels were associated with faster Ab‐related tau‐PET increase in pre‐defined ROIs (centiloid x GAP‐43 interaction, global/temporal‐meta‐ROI: b = 0.0019/0.0028; p = 0.009/0.007, Fig.1) as well as in the personalized Q1 ROI (b = 0.0024; p = 0.004) that summarizes regions most closely connected to subject‐specific tau epicenters with highest baseline tau‐PET (Fig.2A). Importantly, this centiloid x GAP‐43 interaction decreased across regions less strongly connected to tau epicenters (Q2/Q3/Q4: b = 0.0017/0.0008/0.0002; p = 0.009/0.080/0.344, Fig.2B‐D, 3A). Further, we quantified subject‐specific connectivity‐associated tau spread (i.e., the regression‐derived association between epicenter connectivity and tau‐PET increase in remaining brain regions). Here, higher CSF GAP‐43 was associated with a stronger association between Ab and connectivity‐associated tau spread (centiloid x GAP‐43 interaction, b = ‐0.0031; p = 0.037, Fig.3B).ConclusionsHigher CSF GAP‐43 is associated with faster Ab‐related tau spread across interconnected brain regions in AD, suggesting that AD‐related synaptic abnormalities are associated with accelerated tau spread rendering synaptic changes a potential treatment target to attenuate tau spreading.

Synapse dysfunction and astrocyte reactivity are associated independently of amyloid‐β and tau pathologies

AbstractBackgroundBiomarkers of astrocyte reactivity have the potential to improve diagnostic precision, disease monitoring, and treatment efficacy. Glial fibrillary acidic protein (GFAP) protein is expressed in astrocytes, which is important to synaptic plasticity, cell communication, and reactive gliosis.MethodCerebrospinal fluid (CSF) biomarkers were measured in participants of the McGill TRIAD cohort. 75 individuals (>50 years old, 44 cognitively unimpaired (CU), and 31 with cognitive impairment (CI)), had available Aβ and tau‐PET. We measured CSF GFAP and synaptic markers (growth‐associated protein 43 (GAP‐43), neurogranin (Ng), synaptotagmin 1 (SYT1), presynaptic protein synaptosomal‐associated protein 25 (SNAP‐25)). Linear regressions adjusted for age, sex, clinical diagnosis, and Aβ/tau‐PET were used to test the associations between astrocyte reactivity and synaptic function.ResultDemographic information is shown in Table 1. We found an association between CSF GFAP and presynaptic markers (GAP‐43: p<0.0001, β = 0.1076; SYT1: p<0.0001, β = 0.0024; SNAP‐25 long: p<0.0001, β = 0.0008) as well as postsynaptic markers (Ng: p<0.05, β = 0.0066) independently of Aβ and tau burden (Figure 1).ConclusionOur biomarker results support experimental literature suggesting that astrocyte reactivity plays a role in downstream synaptic dysfunction independent of the brain levels of Aβ and tau tangles pathologies. This supports in vitro literature suggesting that therapeutic interventions targeting astrocyte reactivity can contribute to halting AD progression.

Synapse dysfunction and astrocyte reactivity are associated independently of amyloid‐β and tau pathologies

AbstractBackgroundBiomarkers of astrocyte reactivity have the potential to improve diagnostic precision, disease monitoring, and treatment efficacy. Glial fibrillary acidic protein (GFAP) protein is expressed in astrocytes, which is important to synaptic plasticity, cell communication, and reactive gliosis.MethodCerebrospinal fluid (CSF) biomarkers were measured in participants of the McGill TRIAD cohort. 75 individuals (>50 years old, 44 cognitively unimpaired (CU), and 31 with cognitive impairment (CI)), had available Aß and tau‐PET. We measured CSF GFAP and synaptic markers (growth‐associated protein 43 (GAP‐43), neurogranin (Ng), synaptotagmin 1 (SYT1), presynaptic protein synaptosomal‐associated protein 25 (SNAP‐25)). Linear regressions adjusted for age, sex, clinical diagnosis, and Aß/tau‐PET were used to test the associations between astrocyte reactivity and synaptic function.ResultDemographic information is shown in Table 1. We found an association between CSF GFAP and presynaptic markers (GAP‐43: p<0.0001, ß = 0.1076; SYT1: p<0.0001, ß = 0.0024; SNAP‐25 long: p<0.0001, ß = 0.0008) as well as postsynaptic markers (Ng: p<0.05, ß = 0.0066) independently of Aß and tau burden (Figure 1).ConclusionOur biomarker results support experimental literature suggesting that astrocyte reactivity plays a role in downstream synaptic dysfunction independent of the brain levels of Aß and tau tangles pathologies. This supports in vitro literature suggesting that therapeutic interventions targeting astrocyte reactivity can contribute to halting AD progression.

Astrocyte reactivity is associated with synaptic dysfunction across the aging and Alzheimer’s disease spectrum, whereas microglial reactivity is specifically associated with synaptic dysfunction related to cognitive impairment

AbstractBackgroundHealthy synapses are the key to proper brain function, ensuring communication between neurons. Recent studies have associated synaptic dysfunction with Alzheimer’s disease (AD) proteins, however, little is known about the role of glial reactivity, another pathology closely linked to AD, in brain synaptic dysfunction (Figure 1).MethodWe evaluated 123 individuals (67 cognitively unimpaired (CU) and 56 cognitively impaired (CI)) who had available Aβ‐ and Tau‐PET as well as cerebrospinal fluid measures of glial fibrillary acidic protein (GFAP), chitinase‐3‐like protein 1 (YKL‐40), soluble triggering receptor expressed on myeloid cells 2 (sTREM2), synaptic markers (growth‐associated protein 43 (GAP‐43), neurogranin (Ng), synaptotagmin 1 (SYT1), and presynaptic protein synaptosomal‐associated protein 25 (SNAP‐25)). ANCOVA adjusted for clinical diagnosis, age, and sex was used to compare levels of CSF biomarkers; whereas linear regressions adjusted for age, sex, clinical diagnosis, and Aβ/tau‐PET were used to test the associations between glial reactivity and synaptic markers.ResultDemographic information is shown in Table 1. Increased levels of GAP‐43, SNAP‐25, and Ng were observed in CI compared to CU individuals. CSF GFAP was highly associated with both presynaptic and postsynaptic biomarkers in CU and CI groups. CSF YKL‐40 was associated only with presynaptic biomarkers in both clinical groups. On the other hand, CSF sTREM2 showed an association with all synaptic markers but only in the CI group (Figure 2).ConclusionWe found a heterogeneous association between synaptic markers and glial activation. The presence of GFAP+ astrocytes was associated with dysfunction of presynaptic/postsynaptic markers, whereas YKL‐40+ astrocytes specifically reflected presynaptic dysfunction across aging and AD spectrums. On the other hand, microglial activation reflected synaptic dysfunction associated with dementia symptoms. Our results support recent experimental observations suggesting that clarifying the heterogeneity of different glial cell phenotypes is crucial to advancing our understanding of the role of immune cells in cognitive decline.

Astrocyte reactivity is associated with synaptic dysfunction across the aging and Alzheimer’s disease spectrum, whereas microglial reactivity is specifically associated with synaptic dysfunction related to cognitive impairment

AbstractBackgroundHealthy synapses are the key to proper brain function, ensuring communication between neurons. Recent studies have associated synaptic dysfunction with Alzheimer’s disease (AD) proteins, however, little is known about the role of glial reactivity, another pathology closely linked to AD, in brain synaptic dysfunction (Figure 1).MethodWe evaluated 123 individuals (67 cognitively unimpaired (CU) and 56 cognitively impaired (CI)) who had available Aß‐ and Tau‐PET as well as cerebrospinal fluid measures of glial fibrillary acidic protein (GFAP), chitinase‐3‐like protein 1 (YKL‐40), soluble triggering receptor expressed on myeloid cells 2 (sTREM2), synaptic markers (growth‐associated protein 43 (GAP‐43), neurogranin (Ng), synaptotagmin 1 (SYT1), and presynaptic protein synaptosomal‐associated protein 25 (SNAP‐25)). ANCOVA adjusted for clinical diagnosis, age, and sex was used to compare levels of CSF biomarkers; whereas linear regressions adjusted for age, sex, clinical diagnosis, and Aß/tau‐PET were used to test the associations between glial reactivity and synaptic markers.ResultDemographic information is shown in Table 1. Increased levels of GAP‐43, SNAP‐25, and Ng were observed in CI compared to CU individuals. CSF GFAP was highly associated with both presynaptic and postsynaptic biomarkers in CU and CI groups. CSF YKL‐40 was associated only with presynaptic biomarkers in both clinical groups. On the other hand, CSF sTREM2 showed an association with all synaptic markers but only in the CI group (Figure 2).ConclusionWe found a heterogeneous association between synaptic markers and glial activation. The presence of GFAP+ astrocytes was associated with dysfunction of presynaptic/postsynaptic markers, whereas YKL‐40+ astrocytes specifically reflected presynaptic dysfunction across aging and AD spectrums. On the other hand, microglial activation reflected synaptic dysfunction associated with dementia symptoms. Our results support recent experimental observations suggesting that clarifying the heterogeneity of different glial cell phenotypes is crucial to advancing our understanding of the role of immune cells in cognitive decline.

Association of microglial activation with Alzheimer’s pathologies, presynaptic loss, hippocampal atrophy, and cognitive decline

AbstractBackgroundLoss of function of triggering receptor expressed on myeloid cells 2 (TREM2) and progranulin (PGRN), predominantly expressed by microglia in the brain, contribute to the development of Alzheimer’s disease (AD). Although animal studies suggest that the expressions of TREM2 and PGRN increase in activated microglia, their associations with AD‐related pathologies and subsequent outcomes are not well characterized. This study aimed to explore how cerebrospinal fluid (CSF) soluble TREM2 (sTREM2) and PGRN relate to β‐amyloid (Aβ), tau, synaptic loss, neurodegeneration, and cognitive decline.MethodWe identified 610 ADNI participants with Aβ PET and CSF biomarkers measurements at baseline and 250 individuals with longitudinal CSF biomarkers measurements. All participants had concurrent longitudinal structure MRI and Preclinical Alzheimer’s Cognitive Composite (PACC) assessments. Using generalized linear models, we investigated the associations of CSF microglial biomarkers with Aβ PET, CSF p‐Tau181, CSF presynaptic biomarker growth‐associated protein‐43 (GAP‐43), hippocampal atrophy, and cognitive decline.ResultCSF p‐Tau181 levels rather than Aβ PET were positively associated with CSF microglial biomarkers, whereas higher Aβ PET SUVRs were related to attenuated effects of CSF p‐Tau181 on changes in CSF sTREM2 and CSF PGRN (Figure. 1). Mediation analyses further showed that Aβ PET and CSF p‐Tau181 had opposing effects on CSF microglial biomarkers (Figure. 2). In addition, CSF sTREM2 rather than CSF PGRN were positively associated with CSF GAP‐43 cross‐sectionally and longitudinally, independent of Aβ PET and CSF p‐Tau181 (Figure. 3). Furthermore, augmented microglial activation was associated with slower rates of hippocampal atrophy (sTREM2: standard β (βstd) = 0.11, p = 0.007; PGRN: βstd = 0.11, p = 0.003), but only CSF sTREM2 was related to reduced rates of cognitive decline (βstd = 0.11, p = 0.003).ConclusionThis study provides novel insights into the opposing microglial immune response to Aβ and tau pathologies, where elevated CSF p‐Tau181 rather than Aβ plaque is associated with microglial activation. TREM2‐dependent signaling may contribute to the microglia‐related presynaptic loss beyond Aβ and tau pathologies, and microglial activation is protective against hippocampal atrophy and cognitive decline. These findings are critical for understanding the roles of neuroinflammation in AD or other neurodegenerative diseases.

Biomarkers of synaptic and neuronal dysfunction in relation to mild behavioral impairment: a study of dementia‐free older adults

AbstractBackgroundMild behavioral impairment (MBI) represents a high‐risk state for incident cognitive decline and dementia, capturing later‐life emergent and persistent neuropsychiatric symptoms in five domains: 1) decreased motivation; 2) affective dysregulation 3) impulse dyscontrol; 4) social inappropriateness; and 5) psychosis. We examined cross‐sectional associations between MBI and cerebrospinal fluid levels of markers of synaptic/neuronal dysfunction including 1) alpha‐synuclein (α‐syn); 2) growth‐associated protein 43 (GAP‐43); 3) neurogranin (NGRN); 4) synaptosomal‐associated protein 25 (SNAP‐25); 5) visinin‐like protein 1 (VILIP‐1); and 6) chitinase‐3‐like protein 1 (YKL‐40). Longitudinally, we determined associations between these biomarkers and incident MBI or dementia.MethodAlzheimer’s Disease Neuroimaging Initiative participants with normal cognition and mild cognitive impairment were included (n = 853). MBI scores were derived from the Neuropsychiatric Inventory using a published algorithm. Participants were classified as MBI+ if MBI symptoms were present at ≥2 consecutive visits.Cross‐sectional associations between MBI total score and each log‐transformed biomarker were modelled using multivariable‐adjusted linear regression. Biomarkers with cross‐sectional associations meeting a pre‐defined p‐value threshold (p<0.1) were then incorporated as exposures into adjusted longitudinal Cox proportional hazard regression models (n = 111) of 1) MBI and 2) dementia as the outcomes, the latter of which also included interactions between MBI status and biomarker levels.ResultDemographics are summarized in Table 1. Cross‐sectionally, only MBI associations with VILIP‐1 (beta = 3.3%, 95%CI:+0.2% to +6.5%, p = 0.04) and SNAP‐25 (beta = 2.0%, 95%CI:‐0.4% to 6.3%, p = 0.09) met the pre‐defined p‐value for inclusion in Cox models. Longitudinally, higher VILIP‐1 levels were associated with a 3.02‐fold greater rate of incident MBI (95%CI:1.43‐6.40, p = 0.004) and a 3.83‐fold greater rate of incident dementia (95%CI:1.22‐12.03, p = 0.021). The relationship between VILIP‐1 and dementia did not depend on participants having MBI. MBI status predicted incident dementia with an HR = 4.75 (95%CI:2.36‐9.55, p<0.001) and HR = 4.06 (95%CI:2.01‐8.21, p<0.001) after adjusting for VILIP‐1.ConclusionElevated VILIP‐1 levels are associated with greater incidence of MBI and greater incidence of dementia, suggesting that synaptic dysfunction traditionally related to cognitive decline and dementia may also contribute to behavioral changes. Treatments aimed to mitigate MBI symptoms and dementia may explore VILIP‐1—a neuronal calcium‐sensor protein—as a therapeutic target, though more research is needed.