The pre-synaptic vesicle protein synaptotagmin is a novel biomarker for Alzheimer's disease

Cerebrospinal fluid in the differential diagnosis of Alzheimer's disease: an update of the literature

INTRODUCTION

The importance of cerebrospinal fluid (CSF) biomarkers in Alzheimer's disease (AD) diagnosis is rapidly increasing, and there is a growing interest in the use of CSF biomarkers in monitoring the response to therapy, especially in the light of newly available approaches to the therapy of neurodegenerative diseases.

AREAS COVERED

In this review we discuss the most relevant measures of neurodegeneration that are being used to distinguish patients with AD from healthy controls and individuals with mild cognitive impairment, in order to provide an overview of the latest information available in the scientific literature. We focus on markers related to amyloid processing, markers associated with neurofibrillary tangles, neuroinflammation, neuroaxonal injury and degeneration, synaptic loss and dysfunction, and markers of α-synuclein pathology.

EXPERT OPINION

In addition to neuropsychological evaluation, core CSF biomarkers (Aβ42, t-tau, and p-tau181) have been recommended for improvement of timely, accurate and differential diagnosis of AD, as well as to assess the risk and rate of disease progression. In addition to the core CSF biomarkers, various other markers related to synaptic dysfunction, neuroinflammation, and glial activation (neurogranin, SNAP-25, Nfl, YKL-40, TREM2) are now investigated and have yet to be validated for future potential clinical use in AD diagnosis.

A Map of Transcriptomic Signatures of Different Brain Areas in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder that progressively involves brain regions with an often-predictable pattern. Damage to the brain appears to spread and worsen with time, but the molecular mechanisms underlying the region-specific distribution of AD pathology at different stages of the disease are still under-investigated. In this study, a whole-transcriptome analysis was carried out on brain samples from the hippocampus (HI), temporal and parietal cortices (TC and PC, respectively), cingulate cortex (CG), and substantia nigra (SN) of six subjects with a definite AD diagnosis and three healthy age-matched controls in duplicate. The transcriptomic results showed a greater number of differentially expressed genes (DEGs) in the TC (1571) and CG (1210) and a smaller number of DEGs in the HI (206), PC (109), and SN (60). Furthermore, the GSEA showed a difference between the group of brain areas affected early (HI and TC) and the group of areas that were subsequently involved (PC, CG, and SN). Notably, in the HI and TC, there was a significant downregulation of shared DEGs primarily involved in synaptic transmission, while in the PC, CG, and SN, there was a significant downregulation of genes primarily involved in protein folding and trafficking. The course of AD could follow a definite time- and severity-related pattern that arises from protein misfolding, as observed in the PC, CG, and SN, and leads to synaptic impairment, as observed in the HI and TC. Therefore, a map of the molecular and biological processes involved in AD pathogenesis may be traced. This could aid in the discovery of novel biological targets in order to develop effective and well-timed therapeutic approaches.

Biological mechanisms of resilience to tau pathology in Alzheimer's disease

BACKGROUND

In Alzheimer's disease (AD), the associations between tau pathology and brain atrophy and cognitive decline are well established, but imperfect. We investigate whether cerebrospinal fluid (CSF) biomarkers of biological processes (vascular, synaptic, and axonal integrity, neuroinflammation, neurotrophic factors) explain the disconnection between tau pathology and brain atrophy (brain resilience), and tau pathology and cognitive decline (cognitive resilience).

METHODS

We included 428 amyloid positive participants (134 cognitively unimpaired (CU), 128 with mild cognitive impairment (MCI), 166 with AD dementia) from the BioFINDER-2 study. At baseline, participants underwent tau positron emission tomography (tau-PET), magnetic resonance imaging (MRI), cognitive testing, and lumbar puncture. Longitudinal data were available for MRI (mean (standard deviation) follow-up 26.4 (10.7) months) and cognition (25.2 (11.4) months). We analysed 18 pre-selected CSF proteins, reflecting vascular, synaptic, and axonal integrity, neuroinflammation, and neurotrophic factors. Stratifying by cognitive status, we performed linear mixed-effects models with cortical thickness (brain resilience) and global cognition (cognitive resilience) as dependent variables to assess whether the CSF biomarkers interacted with tau-PET levels in its effect on cortical atrophy and cognitive decline.

RESULTS

Regarding brain resilience, interaction effects were observed in AD dementia, with vascular integrity biomarkers (VEGF-A (βinteraction = -0.009, pFDR = 0.047) and VEGF-B (βinteraction = -0.010, pFDR = 0.037)) negatively moderating the association between tau-PET signal and atrophy. In MCI, higher NfL levels were associated with more longitudinal cortical atrophy (β = -0.109, pFDR = 0.033) and lower baseline cortical thickness (β = -0.708, pFDR = 0.033) controlling for tau-PET signal. Cognitive resilience analyses in CU revealed interactions with tau-PET signal for inflammatory (GFAP, IL-15; βinteraction -0.073--0.069, pFDR 0.001-0.045), vascular (VEGF-A, VEGF-D, PGF; βinteraction -0.099--0.063, pFDR < 0.001-0.046), synaptic (14-3-3ζ/δ; βinteraction = -0.092, pFDR = 0.041), axonal (NfL; βinteraction = -0.079, pFDR < 0.001), and neurotrophic (NGF; βinteraction = 0.091, pFDR < 0.001) biomarkers. In MCI higher NfL levels (βmain = -0.690, pFDR = 0.025) were associated with faster cognitive decline independent of tau-PET signal.

CONCLUSIONS

Biomarkers of co-existing pathological processes, in particular vascular pathology and axonal degeneration, interact with levels of tau pathology on its association with the downstream effects of AD pathology (i.e. brain atrophy and cognitive decline). This indicates that vascular pathology and axonal degeneration could impact brain and cognitive resilience.

Analysis of Brain Protein Stability Changes in a Mouse Model of Alzheimer's Disease

The stability of proteins from rates of oxidation (SPROX), thermal proteome profiling (TPP), and limited proteolysis (LiP) techniques were used to profile the stability of ∼2500 proteins in hippocampus tissue cell lysates from 2- and 8-months-old wild-type (C57BL/6J; n = 7) and transgenic (5XFAD; n = 7) mice with five Alzheimer's disease (AD)-linked mutations. Approximately 200-500 protein hits with AD-related stability changes were detected by each technique at each age point. The hit overlap from technique to technique was low, and all of the techniques generated protein hits that were more numerous and largely different from those identified in protein expression level analyses, which were also performed here. The hit proteins identified by each technique were enriched in a number of the same pathways and biological processes, many with known connections to AD. The protein stability hits included 25 high-value conformation biomarkers with AD-related stability changes detected using at least 2 techniques at both age points. Also discovered were subunit- and age-specific AD-related stability changes in the proteasome, which had reduced function at both age points. The different folding stability profiles of the proteasome at the two age points are consistent with a different mechanism for proteasome dysfunction at the early and late stages of AD.

Navigating the intersection: Diabetes and Alzheimer's intertwined relationship

Alzheimer's disease (AD) and Diabetes mellitus (DM) exhibit comparable pathophysiological pathways. Genetic abnormalities in APP, PS-1, and PS-2 are linked to AD, with diagnostic aid from CSF and blood biomarkers. Insulin dysfunction, termed "type 3 diabetes mellitus" in AD, involves altered insulin signalling and neuronal shrinkage. Insulin influences beta-amyloid metabolism, exacerbating neurotoxicity in AD and amyloid production in DM. Both disorders display impaired glucose transporter expression, hastening cognitive decline. Mitochondrial dysfunction and Toll-like receptor 4-mediated inflammation worsen neurodegeneration in both diseases. ApoE4 raises disease risk, especially when coupled with dyslipidemia common in DM. Targeting shared pathways like insulin-degrading enzyme activation and HSP60 holds promise for therapeutic intervention. Recognizing these interconnected mechanisms underscores the imperative for developing tailored treatments addressing the overlapping pathophysiology of AD and DM, offering potential avenues for more effective management of both conditions.

Synaptotagmin 13 Could Drive the Progression of Esophageal Squamous Cell Carcinoma Through Upregulating ACRV1

SYT13 is one of the atypical members of the synaptotagmin (SYT) family whose function has attracted considerable attention in recent years. Although SYT13 has been studied in several types of human cancers, such as lung cancer, its role in esophageal squamous cell carcinoma (ESCC) is still unclear. It was demonstrated that SYT13 is significantly upregulated in ESCC tissues compared with normal ones and correlated with higher degree of malignancy. Knockdown of SYT13 could inhibit ESCC cell proliferation and migration, while promoting cell apoptosis. Meanwhile, ESCC cells with relatively lower SYT13 expression grew slower in vivo and finally formed smaller xenografts. Furthermore, acrosomal vesicular protein 1 was identified as a potential downstream target of SYT13, which regulates cell phenotypes of ESCC cells in cooperation with SYT13. All the in vitro and in vivo results in this study identified that SYT13 silencing could be an effective strategy to inhibit the development of ESCC, which could be considered as a promising therapeutic target in the treatment of ESCC.

Photosensitive Nanoprobes for Rapid Isolation and Size-Specific Enrichment of Synthetic and Extracellular Vesicle Subpopulations

The biggest challenge in current isolation methods for lipid bilayer-encapsulated vesicles, such as exosomes, secretory, and synthetic vesicles, lies in the absence of a unified approach that seamlessly delivers high purity, yield, and scalability for large-scale applications. To address this gap, we have developed an innovative method that utilizes photosensitive lipid nanoprobes specifically designed for efficient isolation of vesicles and sorting them into subpopulations based on size. The photosensitive component in the probe undergoes cleavage upon exposure to light, facilitating the release of vesicles in their near-native form. We demonstrate that our method provides superior capability in isolating extracellular vesicles from complex biological media and separating them into size-based subpopulations within 1 hour, achieving more efficiency and purity than ultracentrifugation. Furthermore, this method's cost-effectiveness and rapid enrichment of the vesicles align with demands for large-scale isolation and downstream analyses of nucleic acids and proteins. Our method opens new avenues in exploring, analyzing, and utilizing synthetic and extracellular vesicle subpopulations in various biomedical applications, including diagnostics, therapeutic delivery, and biomarker discovery.

Protective effect of melatonin against metabolic disorders and neuropsychiatric injuries in type 2 diabetes mellitus mice

BACKGROUND

Type 2 diabetes mellitus (T2DM) is a metabolic disease characterized by hyperglycemia and progressive cognitive dysfunction, and our clinical investigation revealed that the plasma concentration of melatonin (Mlt) decreased and was closely related to cognition in T2DM patients. However, although many studies have suggested that Mlt has a certain protective effect on glucose and lipid metabolism disorders and neuropsychiatric injury, the underlying mechanism of Mlt against T2DM-related metabolic and cognitive impairments remains unclear.

PURPOSE

The aim of the present study was to investigate the therapeutic effect of Mlt on metabolic disorders and Alzheimer's disease (AD)-like neuropsychiatric injuries in T2DM mice and to explore the possible underlying molecular mechanism involved.

METHODS

A T2DM mouse model was established by a combination of a high-fat diet (HFD) and streptozotocin (STZ, 100 mg/kg, i.p.), and Mlt (5, 10 or 20 mg/kg) was intragastrically administered for six consecutive weeks. The serum levels of glycolipid metabolism indicators were measured, behavioral performance was tested, and the protein expression of key molecules involved in the regulation of synaptic plasticity, circadian rhythms, and neuroinflammation in the hippocampus was detected. Moreover, the fluorescence intensities of glial fibrillary acidic protein (GFAP), ionized calcium binding adapter molecule 1 (IBA-1), amyloid β-protein (Aβ) and phosphorylated Tau (p-Tau) in the hippocampus were also observed.

RESULTS

Treatment with Mlt not only improved T2DM-related metabolic disorders, as indicated by increased serum concentrations of fasting blood glucose (FBG), glycosylated hemoglobin (HbAlc), insulin (INS), total cholesterol (TC) and triglyceride (TG), improved glucose tolerance and liver and pancreas function but also alleviated AD-like neuropsychiatric injuries in a HFD/STZ-induced mouse model, as indicated by decreased immobility time in the tail suspension test (TST) and forced swimming test (FST), increased preference indices of novel objects or novel arms in the novel object recognition test (NOR) and Y-maze test (Y-maze), and improved platform positioning capability in the Morris water maze (MWM) test. Moreover, treatment with Mlt also improved the hyperactivation of astrocytes and microglia in the hippocampus of mice, accompanied by reduced expression of interleukin 1β (IL-1β), interleukin 6 (IL-6), tumor necrosis factor (TNF-α), Aβ, and p-Tau and increased expression of brain-derived neurotrophic factor (BDNF), Synapsin I, Synaptotagmin I, melatonin receptor 1B (MT1B), brain muscle arnt-like protein 1 (Bmal1), circadian locomotor output cycles kaput (Clock), period 2 (Per2), and cryptochrome 2 (Cry2).

CONCLUSION

Mlt alleviated T2DM-related metabolic disorders and AD-like neuropsychiatric injuries in a HFD/STZ-induced mouse model, possibly through a mechanism involving the regulation of glial activation and associated neuroinflammation and the balancing of synaptic plasticity and circadian rhythms in the hippocampus.

A guide to selecting high-performing antibodies for Synaptotagmin-1 (Uniprot ID P21579) for use in western blot, immunoprecipitation, immunofluorescence and flow cytometry

Synaptotagmin-1 is a synaptic vesicle transmembrane protein that senses calcium influx via its tandem C2-domains, triggering synchronous neurotransmitter release. Disruption to SYT1 is associated with neurodevelopmental disorders, highlighting the importance of identifying high-quality research reagents to enhance understanding of Synaptotagmin-1 in health and disease. Here we have characterized thirteen Synaptotagmin-1 commercial antibodies for western blot, immunoprecipitation, immunofluorescence and flow cytometry using a standardized experimental protocol based on comparing read-outs in knockout cell lines and isogenic parental controls. These studies are part of a larger, collaborative initiative seeking to address antibody reproducibility issues by characterizing commercially available antibodies for human proteins and publishing the results openly as a resource for the scientific community. While use of antibodies and protocols vary between laboratories, we encourage readers to use this report as a guide to select the most appropriate antibodies for their specific needs.

Cerebrospinal fluid biomarker panel for synaptic dysfunction in a broad spectrum of neurodegenerative diseases

Synaptic dysfunction and degeneration is likely the key pathophysiology for the progression of cognitive decline in various dementia disorders. Synaptic status can be monitored by measuring synaptic proteins in CSF. In this study, both known and new synaptic proteins were investigated and compared as potential biomarkers of synaptic dysfunction, particularly in the context of Alzheimer's disease (AD). Seventeen synaptic proteins were quantified in CSF using two different targeted mass spectrometry assays in the prospective Swedish BioFINDER-2 study. The study included 958 individuals, characterized as having mild cognitive impairment (MCI, n = 205), AD dementia (n = 149) and a spectrum of other neurodegenerative diseases (n = 171), in addition to cognitively unimpaired individuals (CU, n = 443). Synaptic protein levels were compared between diagnostic groups and their associations with cognitive decline and key neuroimaging measures (amyloid-β-PET, tau-PET and cortical thickness) were assessed. Among the 17 synaptic proteins examined, 14 were specifically elevated in the AD continuum. SNAP-25, 14-3-3 zeta/delta, β-synuclein, and neurogranin exhibited the highest discriminatory accuracy in differentiating AD dementia from controls (areas under the curve = 0.81-0.93). SNAP-25 and 14-3-3 zeta/delta also had the strongest associations with tau-PET, amyloid-β-PET and cortical thickness at baseline and were associated with longitudinal changes in these imaging biomarkers [β(standard error, SE) = -0.056(0.0006) to 0.058(0.005), P < 0.0001]. SNAP-25 was the strongest predictor of progression to AD dementia in non-demented individuals (hazard ratio = 2.11). In contrast, neuronal pentraxins were decreased in all neurodegenerative diseases (except for Parkinson's disease), and NPTX2 showed the strongest associations with subsequent cognitive decline [longitudinal Mini-Mental State Examination: β(SE) = 0.57(0.1), P ≤ 0.0001; and mPACC: β(SE) = 0.095(0.024), P ≤ 0.001] across the AD continuum. Interestingly, utilizing a ratio of the proteins that displayed higher levels in AD, such as SNAP-25 or 14-3-3 zeta/delta, over NPTX2 improved the biomarkers' associations with cognitive decline and brain atrophy. We found 14-3-3 zeta/delta and SNAP-25 to be especially promising as synaptic biomarkers of pathophysiological changes in AD. Neuronal pentraxins were identified as general indicators of neurodegeneration and associated with cognitive decline across various neurodegenerative dementias. Cognitive decline and brain atrophy were best predicted by ratios of SNAP-25/NPTX2 and 14-3-3 zeta/delta/NPTX2.

PTPRS is a novel marker for early Tau pathology and synaptic integrity in Alzheimer's disease

We examined the role of protein tyrosine phosphatase receptor sigma (PTPRS) in the context of Alzheimer's disease and synaptic integrity. Publicly available datasets (BRAINEAC, ROSMAP, ADC1) and a cohort of asymptomatic but "at risk" individuals (PREVENT-AD) were used to explore the relationship between PTPRS and various Alzheimer's disease biomarkers. We identified that PTPRS rs10415488 variant C shows features of neuroprotection against early Tau pathology and synaptic degeneration in Alzheimer's disease. This single nucleotide polymorphism correlated with higher PTPRS transcript abundance and lower p(181)Tau and GAP-43 levels in the CSF. In the brain, PTPRS protein abundance was significantly correlated with the quantity of two markers of synaptic integrity: SNAP25 and SYT-1. We also found the presence of sexual dimorphism for PTPRS, with higher CSF concentrations in males than females. Male carriers for variant C were found to have a 10-month delay in the onset of AD. We thus conclude that PTPRS acts as a neuroprotective receptor in Alzheimer's disease. Its protective effect is most important in males, in whom it postpones the age of onset of the disease.

Systematic Analysis of Biological Processes Reveals Gene Co-expression Modules Driving Pathway Dysregulation in Alzheimer's Disease

Alzheimer's disease (AD) manifests as a complex systems pathology with intricate interplay among various genes and biological processes. Traditional differential gene expression (DEG) analysis, while commonly employed to characterize AD-driven perturbations, does not sufficiently capture the full spectrum of underlying biological processes. Utilizing single-nucleus RNA-sequencing data from postmortem brain samples across key regions-middle temporal gyrus, superior frontal gyrus, and entorhinal cortex-we provide a comprehensive systematic analysis of disrupted processes in AD. We go beyond the DEG-centric analysis by integrating pathway activity analysis with weighted gene co-expression patterns to comprehensively map gene interconnectivity, identifying region- and cell-type-specific drivers of biological processes associated with AD. Our analysis reveals profound modular heterogeneity in neurons and glia as well as extensive AD-related functional disruptions. Co-expression networks highlighted the extended involvement of astrocytes and microglia in biological processes beyond neuroinflammation, such as calcium homeostasis, glutamate regulation, lipid metabolism, vesicle-mediated transport, and TOR signaling. We find limited representation of DEGs within dysregulated pathways across neurons and glial cells, suggesting that differential gene expression alone may not adequately represent the disease complexity. Further dissection of inferred gene modules revealed distinct dynamics of hub DEGs in neurons versus glia, suggesting that DEGs exert more impact on neurons compared to glial cells in driving modular dysregulations underlying perturbed biological processes. Interestingly, we observe an overall downregulation of astrocyte and microglia modules across all brain regions in AD, indicating a prevailing trend of functional repression in glial cells across these regions. Notable genes from the CALM and HSP90 families emerged as hub genes across neuronal modules in all brain regions, suggesting conserved roles as drivers of synaptic dysfunction in AD. Our findings demonstrate the importance of an integrated, systems-oriented approach combining pathway and network analysis to comprehensively understand the cell-type-specific roles of genes in AD-related biological processes.

p75 neurotrophin receptor modulation in mild to moderate Alzheimer disease: a randomized, placebo-controlled phase 2a trial

p75 neurotrophin receptor (p75NTR) signaling pathways substantially overlap with degenerative networks active in Alzheimer disease (AD). Modulation of p75NTR with the first-in-class small molecule LM11A-31 mitigates amyloid-induced and pathological tau-induced synaptic loss in preclinical models. Here we conducted a 26-week randomized, placebo-controlled, double-blinded phase 2a safety and exploratory endpoint trial of LM11A-31 in 242 participants with mild to moderate AD with three arms: placebo, 200 mg LM11A-31 and 400 mg LM11A-31, administered twice daily by oral capsules. This trial met its primary endpoint of safety and tolerability. Within the prespecified secondary and exploratory outcome domains (structural magnetic resonance imaging, fluorodeoxyglucose positron-emission tomography and cerebrospinal fluid biomarkers), significant drug-placebo differences were found, consistent with the hypothesis that LM11A-31 slows progression of pathophysiological features of AD; no significant effect of active treatment was observed on cognitive tests. Together, these results suggest that targeting p75NTR with LM11A-31 warrants further investigation in larger-scale clinical trials of longer duration. EU Clinical Trials registration: 2015-005263-16 ; ClinicalTrials.gov registration: NCT03069014 .

Which neuroimaging and fluid biomarkers method is better in theranostic of Alzheimer's disease? An umbrella review

Biomarkers are measured to evaluate physiological and pathological processes as well as responses to a therapeutic intervention. Biomarkers can be classified as diagnostic, prognostic, predictor, clinical, and therapeutic. In Alzheimer's disease (AD), multiple biomarkers have been reported so far. Nevertheless, finding a specific biomarker in AD remains a major challenge. Three databases, including PubMed, Web of Science, and Scopus were selected with the keywords of Alzheimer's disease, neuroimaging, biomarker, and blood. The results were finalized with 49 potential CSF/blood and 35 neuroimaging biomarkers. To distinguish normal from AD patients, amyloid-beta42 (Aβ42), plasma glial fibrillary acidic protein (GFAP), and neurofilament light (NFL) as potential biomarkers in cerebrospinal fluid (CSF) as well as the serum could be detected. Nevertheless, most of the biomarkers fairly change in the CSF during AD, listed as kallikrein 6, virus-like particles (VLP-1), galectin-3 (Gal-3), and synaptotagmin-1 (Syt-1). From the neuroimaging aspect, atrophy is an accepted biomarker for the neuropathologic progression of AD. In addition, Magnetic resonance spectroscopy (MRS), diffusion weighted imaging (DWI), diffusion tensor imaging (DTI), tractography (DTT), positron emission tomography (PET), and functional magnetic resonance imaging (fMRI), can be used to detect AD. Using neuroimaging and CSF/blood biomarkers, in combination with artificial intelligence, it is possible to obtain information on prognosis and follow-up on the different stages of AD. Hence physicians could select the suitable therapy to attenuate disease symptoms and follow up on the efficiency of the prescribed drug.

Lysosomal and synaptic dysfunction markers in longitudinal cerebrospinal fluid of de novo Parkinson's disease

Lysosomal and synaptic dysfunctions are hallmarks in neurodegeneration and potentially relevant as biomarkers, but data on early Parkinson's disease (PD) is lacking. We performed targeted mass spectrometry with an established protein panel, assessing autophagy and synaptic function in cerebrospinal fluid (CSF) of drug-naïve de novo PD, and sex-/age-matched healthy controls (HC) cross-sectionally (88 PD, 46 HC) and longitudinally (104 PD, 58 HC) over 10 years. Multiple markers of autophagy, synaptic plasticity, and secretory pathways were reduced in PD. We added samples from prodromal subjects (9 cross-sectional, 12 longitudinal) with isolated REM sleep behavior disorder, revealing secretogranin-2 already decreased compared to controls. Machine learning identified neuronal pentraxin receptor and neurosecretory protein VGF as most relevant for discriminating between groups. CSF levels of LAMP2, neuronal pentraxins, and syntaxins in PD correlated with clinical progression, showing predictive potential for motor- and non-motor symptoms as a valid basis for future drug trials.

PTPRS is a novel marker for early tau pathology and synaptic integrity in Alzheimer's disease

We examined the role of protein tyrosine phosphatase receptor sigma (PTPRS) in the context of Alzheimer's disease and synaptic integrity. Publicly available datasets (BRAINEAC, ROSMAP, ADC1) and a cohort of asymptomatic but "at risk" individuals (PREVENT-AD) were used to explore the relationship between PTPRS and various Alzheimer's disease biomarkers. We identified that PTPRS rs10415488 variant C shows features of neuroprotection against early tau pathology and synaptic degeneration in Alzheimer's disease. This single nucleotide polymorphism correlated with higher PTPRS transcript abundance and lower P-tau181 and GAP-43 levels in the CSF. In the brain, PTPRS protein abundance was significantly correlated with the quantity of two markers of synaptic integrity: SNAP25 and SYT-1. We also found the presence of sexual dimorphism for PTPRS, with higher CSF concentrations in males than females. Male carriers for variant C were found to have a 10-month delay in the onset of AD. We thus conclude that PTPRS acts as a neuroprotective receptor in Alzheimer's disease. Its protective effect is most important in males, in whom it postpones the age of onset of the disease.

Insulin-like growth factor binding protein-2 in at-risk adults and autopsy-confirmed Alzheimer brains

Insulin, insulin-like growth factors (IGF) and their receptors are highly expressed in the adult hippocampus. Thus, disturbances in the insulin-IGF signalling pathway may account for the selective vulnerability of the hippocampus to nascent Alzheimer's disease (AD) pathology. In the present study, we examined the predominant IGF-binding protein in the CSF, IGFBP2. CSF was collected from 109 asymptomatic members of the parental history-positive PREVENT-AD cohort. CSF levels of IGFBP2, core AD and synaptic biomarkers were measured using proximity extension assay, ELISA and mass spectrometry. Cortical amyloid-beta (Aβ) and tau deposition were examined using 18F-NAV4694 and flortaucipir. Cognitive assessments were performed during up to 8 years of follow-up, using the Repeatable Battery for the Assessment of Neuropsychological Status. T1-weighted structural MRI scans were acquired, and neuroimaging analyses were performed on pre-specified temporal and parietal brain regions. Next, in an independent cohort, we allocated 241 dementia-free ADNI-1 participants into four stages of AD progression based on the biomarkers CSF Aβ42 and total-tau (t-tau). In this analysis, differences in CSF and plasma IGFBP2 levels were examined across the pathological stages. Finally, IGFBP2 mRNA and protein levels were examined in the frontal cortex of 55 autopsy-confirmed AD and 31 control brains from the Quebec Founder Population (QFP) cohort, a unique population isolated from Eastern Canada. CSF IGFBP2 progressively increased over 5 years in asymptomatic PREVENT-AD participants. Baseline CSF IGFBP2 was positively correlated with CSF AD biomarkers and synaptic biomarkers, and negatively correlated with longitudinal changes in delayed memory (P = 0.024) and visuospatial abilities (P = 0.019). CSF IGFBP2 was negatively correlated at a trend-level with entorhinal cortex volume (P = 0.082) and cortical thickness in the piriform (P = 0.039), inferior temporal (P = 0.008), middle temporal (P = 0.014) and precuneus (P = 0.033) regions. In ADNI-1, CSF (P = 0.009) and plasma (P = 0.001) IGFBP2 were significantly elevated in Stage 2 [CSF Aβ(+)/t-tau(+)]. In survival analyses in ADNI-1, elevated plasma IGFBP2 was associated with a greater rate of AD conversion (hazard ratio = 1.62, P = 0.021). In the QFP cohort, IGFBP2 mRNA was reduced (P = 0.049); however, IGFBP2 protein levels did not differ in the frontal cortex of autopsy-confirmed AD brains (P = 0.462). Nascent AD pathology may induce an upregulation in IGFBP2 in asymptomatic individuals. CSF and plasma IGFBP2 may be valuable markers for identifying CSF Aβ(+)/t-tau(+) individuals and those with a greater risk of AD conversion.

Biofluid biomarkers for Alzheimer's disease

Alzheimer's disease (AD) is a multifactorial neurodegenerative disease, with a complex pathogenesis and an irreversible course. Therefore, the early diagnosis of AD is particularly important for the intervention, prevention, and treatment of the disease. Based on the different pathophysiological mechanisms of AD, the research progress of biofluid biomarkers are classified and reviewed. In the end, the challenges and perspectives of future research are proposed.

Systematic Analysis of Biological Processes Reveals Gene Co-expression Modules Driving Pathway Dysregulation in Alzheimer's Disease

Alzheimer's disease (AD) manifests as a complex systems pathology with intricate interplay among various genes and biological processes. Traditional differential gene expression (DEG) analysis, while commonly employed to characterize AD-driven perturbations, does not sufficiently capture the full spectrum of underlying biological processes. Utilizing single-nucleus RNA-sequencing data from postmortem brain samples across key regions-middle temporal gyrus, superior frontal gyrus, and entorhinal cortex-we provide a comprehensive systematic analysis of disrupted processes in AD. We go beyond the DEG-centric analysis by integrating pathway activity analysis with weighted gene co-expression patterns to comprehensively map gene interconnectivity, identifying region- and cell-type-specific drivers of biological processes associated with AD. Our analysis reveals profound modular heterogeneity in neurons and glia as well as extensive AD-related functional disruptions. Co-expression networks highlighted the extended involvement of astrocytes and microglia in biological processes beyond neuroinflammation, such as calcium homeostasis, glutamate regulation, lipid metabolism, vesicle-mediated transport, and TOR signaling. We find limited representation of DEGs within dysregulated pathways across neurons and glial cells, indicating that differential gene expression alone may not adequately represent the disease complexity. Further dissection of inferred gene modules revealed distinct dynamics of hub DEGs in neurons versus glia, highlighting the differential impact of DEGs on neurons compared to glial cells in driving modular dysregulations underlying perturbed biological processes. Interestingly, we note an overall downregulation of both astrocyte and microglia modules in AD across all brain regions, suggesting a prevailing trend of functional repression in glial cells across these regions. Notable genes, including those of the CALM and HSP90 family genes emerged as hub genes across neuronal modules in all brain regions, indicating conserved roles as drivers of synaptic dysfunction in AD. Our findings demonstrate the importance of an integrated, systems-oriented approach combining pathway and network analysis for a comprehensive understanding of the cell-type-specific roles of genes in AD-related biological processes.

Identification of key regulatory molecules in the early development stage of Alzheimer's disease

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases, the incidence of which increases with age, and the pathological changes in the brain are irreversible. Recent studies have highlighted the essential role of long noncoding RNAs (lncRNAs) in AD by acting as competing endogenous RNAs (ceRNAs). Our aim was to construct lncRNA-associated ceRNA regulatory networks composed of potential biomarkers for the early stage of AD. AD related datasets come from AlzData and GEO databases. The R package 'Limma' identifies differentially expressed genes (DEGs), Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) databases for functional enrichment analysis. Protein-protein interactions (PPIs) in DEGs were constructed in the STRING database, and Cytoscape software identified DEGs. Convergent functional genomics (CFG) analysis of differentially expressed hub genes (referred to as early-DEGs) in the brain before the development of AD pathology. The AlzData database analyses the expression levels of early-DEGs in different nerve cells. The lncRNA-miRNA-mRNA regulatory network was established according to the ceRNA hypothesis. We identified four lncRNAs (XIST, NEAT1, KCNQ1OT1 and HCG18) and four miRNAs (hsa-let-7c-5p, hsa-miR-107, hsa-miR-129-2-3p and hsa-miR-214-3p) were preliminarily identified as potential biomarkers for early AD, competitively regulating Atp6v0b, Atp6v1e1 Atp6v1f and Syt1. This study indicates that NEAT1, XIST, HCG18 and KCNQ1OT1 act as ceRNAs in competitive binding with miRNAs to regulate the expression of Atp6v0b, Atp6v1e1, Atp6v1f and Syt1 before the occurrence of pathological changes in AD.

Monitoring synaptic pathology in Alzheimer's disease through fluid and PET imaging biomarkers: a comprehensive review and future perspectives

Alzheimer's disease (AD) is currently constrained by limited clinical treatment options. The initial pathophysiological event, which can be traced back to decades before the clinical symptoms become apparent, involves the excessive accumulation of amyloid-beta (Aβ), a peptide comprised of 40-42 amino acids, in extraneuronal plaques within the brain. Biochemical and histological studies have shown that overaccumulation of Aβ instigates an aberrant escalation in the phosphorylation and secretion of tau, a microtubule-binding axonal protein. The accumulation of hyperphosphorylated tau into intraneuronal neurofibrillary tangles is in turn correlated with microglial dysfunction and reactive astrocytosis, culminating in synaptic dysfunction and neurodegeneration. As neurodegeneration progresses, it gives rise to mild clinical symptoms of AD, which may eventually evolve into overt dementia. Synaptic loss in AD may develop even before tau alteration and in response to possible elevations in soluble oligomeric forms of Aβ associated with early AD. These findings largely rely on post-mortem autopsy examinations, which typically involve a limited number of patients. Over the past decade, a range of fluid biomarkers such as neurogranin, α-synuclein, visinin-like protein 1 (VILIP-1), neuronal pentraxin 2, and β-synuclein, along with positron emission tomography (PET) markers like synaptic vesicle glycoprotein 2A, have been developed. These advancements have facilitated the exploration of how synaptic markers in AD patients correlate with cognitive impairment. However, fluid biomarkers indicating synaptic loss have only been validated in cerebrospinal fluid (CSF), not in plasma, with the exception of VILIP-1. The most promising PET radiotracer, [11C]UCB-J, currently faces significant challenges hindering its widespread clinical use, primarily due to the necessity of a cyclotron. As such, additional research geared toward the exploration of synaptic pathology biomarkers is crucial. This will not only enable their extensive clinical application, but also refine the optimization process of AD pharmacological trials.

Alzheimer's Disease Biomarker Analysis Using Targeted Mass Spectrometry

Alzheimer's disease (AD) is characterized by several neuropathological changes, mainly extracellular amyloid aggregates (plaques), intraneuronal inclusions of phosphorylated tau (tangles), as well as neuronal and synaptic degeneration, accompanied by tissue reactions to these processes (astrocytosis and microglial activation) that precede neuronal network disturbances in the symptomatic phase of the disease. A number of biomarkers for these brain tissue changes have been developed, mainly using immunoassays. In this review, we discuss how targeted mass spectrometry (TMS) can be used to validate and further characterize classes of biomarkers reflecting different AD pathologies, such as tau- and amyloid-beta pathologies, synaptic dysfunction, lysosomal dysregulation, and axonal damage, and the prospect of using TMS to measure these proteins in clinical research and diagnosis. TMS advantages and disadvantages in relation to immunoassays are discussed, and complementary aspects of the technologies are discussed.

Neuroprotective effect of plasmalogens on AlCl3-induced Alzheimer's disease zebrafish via acting on the regulatory network of ferroptosis, apoptosis and synaptic neurotransmission release with oxidative stress as the center

Plasmalogens (Pls) are considered to play a potential role in the treatment of neurodegenerative diseases. In the present study, an Alzheimer's disease (AD) model of zebrafish induced by AlCl3 was established to investigate whether the marine-derived Pls could alleviate cognitive impairments of AD zebrafish. Behavioral tests were carried out to assess the athletic ability. The transcriptional profiles of zebrafish in the control, AD model and AD_PLS group were compared and analyzed to determine the potential mechanisms of dietary Pls on AD. The study found that Pls could reverse athletic impairment in the AD zebrafish model, and the expression levels of genes related to ferroptosis, synaptic dysfunction and apoptosis were significantly altered between experimental groups. Further analysis showed that all of these genes were associated with oxidative stress (OS). These data suggest that healthy protective role of marine-derived Pls on AD zebrafish may result from inhibition of ferroptosis and neuronal apoptosis, restoring synaptic neurotransmission release, and reducing neuroinflammation. Among them, Oxidative stress is acted as the center to connect different regulation pathways. This study provides evidence to support the essential roles of OS in pathogenesis of AD, and the application of Pls in relieving AD.

Serial Cerebrospinal Fluid Sampling Reveals Trajectories of Potential Synaptic Biomarkers in Early Stages of Alzheimer's Disease

Background

Synaptic dysfunction is closely associated with cognitive function in Alzheimer's disease (AD), and is present already in an early stage of the disease.

Objective

Using serial cerebrospinal fluid (CSF) sampling, we aimed to investigate slopes of CSF synaptic proteins, and their relation with cognition along the AD continuum.

Methods

We included subjects with subjective cognitive decline (SCD) or mild cognitive impairment (MCI) (n = 50 amyloid-β+ [A +], n = 50 A-) and 50 patients with AD dementia from the Amsterdam dementia cohort, with CSF at two time points (median[IQR] 2.1[1.4-2.7] years). We analyzed 17 synaptic proteins and neurofilament light (NfL). Using linear mixed models we assessed trajectories of protein levels, and associations with cognitive decline (repeated Mini-Mental State Examination). We used Cox regression models to assess predictive value of protein levels for progression to AD dementia.

Results

At baseline most proteins showed increased levels in AD dementia compared to the other groups. In contrast NPTX2 levels were lower in AD dementia. Higher baseline levels of SNAP25, β-syn, and 14-3-3 proteins were associated with faster cognitive decline (St.B[SE] -0.27[0.12] to -0.61[0.12]). Longitudinal analyses showed that SYT1 and NPTX levels decreased over time in AD dementia (st.B[SE] -0.10[0.04] to -0.15[0.05]) and SCD/MCI-A+ (St.B[SE] -0.07[0.03] to -0.12[0.03]), but not in SCD/MCI-A- (pinteraction < 0.05). Increase over time in NfL levels was associated with faster cognitive decline in AD dementia (St.B[SE] -1.75[0.58]), but not in the other groups (pinteraction < 0.05).

Conclusions

CSF synaptic proteins showed different slopes over time, suggesting complex synaptic dynamics. High levels of especially SNAP-25 may have value for prediction of cognitive decline in early AD stages, while increase in NfL over time correlates better with cognitive decline in later stages.

Mapping the human brain proteome: opportunities, challenges, and clinical potential

INTRODUCTION

Due to the segmented functions and complexity of the human brain, the characterization of molecular profiles within specific areas such as brain structures and biofluids is essential to unveil the molecular basis for structure specialization as well as the molecular imbalance associated with neurodegenerative and psychiatric diseases.

AREAS COVERED

Much of our knowledge about brain functionality derives from neurophysiological, anatomical, and transcriptomic approaches. More recently, laser capture and imaging proteomics, technological and computational developments in LC-MS/MS, as well as antibody/aptamer-based platforms have allowed the generation of novel cellular, spatial, and posttranslational dimensions as well as innovative facets in biomarker validation and druggable target identification.

EXPERT OPINION

Proteomics is a powerful toolbox to functionally characterize, quantify, and localize the extensive protein catalog of the human brain across physiological and pathological states. Brain function depends on multi-dimensional protein homeostasis, and its elucidation will help us to characterize biological pathways that are essential to properly maintain cognitive functions. In addition, comprehensive human brain pathological proteomes may be the basis in computational drug-repositioning methods as a strategy for unveiling potential new therapies in neurodegenerative and psychiatric disorders.

Evaluation of cerebrospinal fluid levels of synaptic vesicle protein, VAMP-2, across the sporadic Alzheimer's disease continuum

BACKGROUND

Synapse loss is an early event that precedes neuronal death and symptom onset and is considered the best neuropathological correlate of cognitive decline in Alzheimer's disease (AD). Vesicle-associated membrane protein 2 (VAMP-2) has emerged as a promising biomarker of AD-related synapse degeneration in cerebrospinal fluid (CSF). The aim of this study was to explore the CSF profile of VAMP-2 across the AD continuum in relation to core AD biomarkers, other synaptic proteins, neurogranin (Ng) and synaptosomal-associated Protein-25 kDa (SNAP-25) and cognitive performance.

METHODS

We developed a digital immunoassay on the Single Molecule Array platform to quantify VAMP-2 in CSF and used existing immunoassays to quantify Ng, SNAP-25 and core CSF AD biomarkers. The clinical study included 62 cognitively unimpaired AD biomarker-negative subjects and 152 participants across the AD continuum from the SPIN cohort (Sant Pau Initiative on Neurodegeneration). Cognitive measures of episodic, semantic, executive and visuospatial domains and global cognition were included. Statistical methods included χ2 tests, spearman correlation, and ANCOVA analyses.

RESULTS

The VAMP-2 assay had a good analytical performance (repeatability 8.9%, intermediate precision 10.3%). Assay antibodies detected native VAMP-2 protein in human brain homogenates. CSF concentrations of VAMP-2, neurogranin and SNAP-25 were lower in preclinical AD stage 1 compared to controls and higher at later AD stages compared to AD stage 1 and were associated with core AD biomarkers, particularly total tau (adj. r2 = 0.62 to 0.78, p < 0.001). All three synaptic proteins were associated with all cognitive domains in individuals on the AD continuum (adj. r2 = 0.04 to 0.19, p < 0.05).

CONCLUSIONS

Our novel digital immunoassay accurately measures VAMP-2 changes in CSF, which reflect AD biomarkers and cognitive performance across multiple domains.

Emerging Alzheimer's disease therapeutics: promising insights from lipid metabolism and microglia-focused interventions

More than 55 million people suffer from dementia, with this number projected to double every 20 years. In the United States, 1 in 3 aged individuals dies from Alzheimer's disease (AD) or another type of dementia and AD kills more individuals than breast cancer and prostate cancer combined. AD is a complex and multifactorial disease involving amyloid plaque and neurofibrillary tangle formation, glial cell dysfunction, and lipid droplet accumulation (among other pathologies), ultimately leading to neurodegeneration and neuronal death. Unfortunately, the current FDA-approved therapeutics do not reverse nor halt AD. While recently approved amyloid-targeting antibodies can slow AD progression to improve outcomes for some patients, they are associated with adverse side effects, may have a narrow therapeutic window, and are expensive. In this review, we evaluate current and emerging AD therapeutics in preclinical and clinical development and provide insight into emerging strategies that target brain lipid metabolism and microglial function - an approach that may synergistically target multiple mechanisms that drive AD neuropathogenesis. Overall, we evaluate whether these disease-modifying emerging therapeutics hold promise as interventions that may be able to reverse or halt AD progression.

Gene expression analysis reveals GRIN1, SYT1, and SYN2 as significant therapeutic targets and drug repurposing reveals lorazepam and lorediplon as potent inhibitors to manage Alzheimer's disease

Alzheimer's disease (AD) is a slowly progressive neurodegenerative disease and a leading cause of dementia. We aim to identify key genes for the development of therapeutic targets and biomarkers for potential treatments for AD. Meta-analysis was performed on six microarray datasets and identified the differentially expressed genes between healthy and Alzheimer's disease samples. Thereafter, we filtered out the common genes which were present in at least four microarray datasets for downstream analysis. We have constructed a gene-gene network for the common genes and identified six hub genes. Furthermore, we investigated the regulatory mechanisms of these hub genes by analysing their interaction with miRNAs and transcription factors. The gene ontology analysis results highlighted the enriched terms significantly associated with hub genes. Through an extensive literature survey, we found that three of the hub genes including GRIN1, SYN2, and SYT1 were critically involved in disease development. To leverage existing drugs for potential repurposing, we predicted drug-gene interaction using the drug-gene interaction database, and performed molecular docking studies. The docking results revealed that the drug compounds had strong interactions and favorable binding with selected hub genes. Lorazepam exhibits a binding energy of -7.3 kcal/mol with GRIN1, Lorediplon exhibits binding energies of -7.7 kcal/mol and -6.3 kcal/mol with the SYT1, and SYN2 respectively. In addition, 100 ns molecular dynamics simulations were carried out for the top complexes and apo protein as well. Furthermore, the MM-PBSA free energy calculations also revealed that these complexes are stable and had favorable energies. According to our study, the identified hub gene could serve as a biomarker as well as a therapeutic target for AD, and the proposed repurposed drug molecules appear to have promising efficacy in treating the disease.Communicated by Ramaswamy H. Sarma.

Alzheimer's disease biomarker profiling in a memory clinic cohort without common comorbidities

Alzheimer's disease is a multifactorial disorder with large heterogeneity. Comorbidities such as hypertension, hypercholesterolaemia and diabetes are known contributors to disease progression. However, less is known about their mechanistic contribution to Alzheimer's pathology and neurodegeneration. The aim of this study was to investigate the relationship of several biomarkers related to risk mechanisms in Alzheimer's disease with the well-established Alzheimer's disease markers in a memory clinic population without common comorbidities. We investigated 13 molecular markers representing key mechanisms underlying Alzheimer's disease pathogenesis in CSF from memory clinic patients without diagnosed hypertension, hypercholesterolaemia or diabetes nor other neurodegenerative disorders. An analysis of covariance was used to compare biomarker levels between clinical groups. Associations were analysed by linear regression. Two-step cluster analysis was used to determine patient clusters. Two key markers were analysed by immunofluorescence staining in the hippocampus of non-demented control and Alzheimer's disease individuals. CSF samples from a total of 90 participants were included in this study: 30 from patients with subjective cognitive decline (age 62.4 ± 4.38, female 60%), 30 with mild cognitive impairment (age 65.6 ± 7.48, female 50%) and 30 with Alzheimer's disease (age 68.2 ± 7.86, female 50%). Angiotensinogen, thioredoxin-1 and interleukin-15 had the most prominent associations with Alzheimer's disease pathology, synaptic and axonal damage markers. Synaptosomal-associated protein 25 kDa and neurofilament light chain were increased in mild cognitive impairment and Alzheimer's disease patients. Grouping biomarkers by biological function showed that inflammatory and survival components were associated with Alzheimer's disease pathology, synaptic dysfunction and axonal damage. Moreover, a vascular/metabolic component was associated with synaptic dysfunction. In the data-driven analysis, two patient clusters were identified: Cluster 1 had increased CSF markers of oxidative stress, vascular pathology and neuroinflammation and was characterized by elevated synaptic and axonal damage, compared with Cluster 2. Clinical groups were evenly distributed between the clusters. An analysis of post-mortem hippocampal tissue showed that compared with non-demented controls, angiotensinogen staining was higher in Alzheimer's disease and co-localized with phosphorylated-tau. The identification of biomarker-driven endophenotypes in cognitive disorder patients further highlights the biological heterogeneity of Alzheimer's disease and the importance of tailored prevention and treatment strategies.

Heart failure-induced cognitive dysfunction is mediated by intracellular Ca2+ leak through ryanodine receptor type 2

Cognitive dysfunction (CD) in heart failure (HF) adversely affects treatment compliance and quality of life. Although ryanodine receptor type 2 (RyR2) has been linked to cardiac muscle dysfunction, its role in CD in HF remains unclear. Here, we show in hippocampal neurons from individuals and mice with HF that the RyR2/intracellular Ca2+ release channels were subjected to post-translational modification (PTM) and were leaky. RyR2 PTM included protein kinase A phosphorylation, oxidation, nitrosylation and depletion of the stabilizing subunit calstabin2. RyR2 PTM was caused by hyper-adrenergic signaling and activation of the transforming growth factor-beta pathway. HF mice treated with a RyR2 stabilizer drug (S107), beta blocker (propranolol) or transforming growth factor-beta inhibitor (SD-208), or genetically engineered mice resistant to RyR2 Ca2+ leak (RyR2-p.Ser2808Ala), were protected against HF-induced CD. Taken together, we propose that HF is a systemic illness driven by intracellular Ca2+ leak that includes cardiogenic dementia.

Mass Spectrometry as a Quantitative Proteomic Analysis Tool for the Search for Temporal Lobe Epilepsy Biomarkers: A Systematic Review

Temporal lobe epilepsy (TLE) is the most common form of epilepsy in adults. Tissue reorganization at the site of the epileptogenic focus is accompanied by changes in the expression patterns of protein molecules. The study of mRNA and its corresponding proteins is crucial for understanding the pathogenesis of the disease. Protein expression profiles do not always directly correlate with the levels of their transcripts; therefore, it is protein profiling that is no less important for understanding the molecular mechanisms and biological processes of TLE. The study and annotation of proteins that are statistically significantly different in patients with TLE is an approach to search for biomarkers of this disease, various stages of its development, as well as a method for searching for specific targets for the development of a further therapeutic strategy. When writing a systematic review, the following aggregators of scientific journals were used: MDPI, PubMed, ScienceDirect, Springer, and Web of Science. Scientific articles were searched using the following keywords: "proteomic", "mass-spectrometry", "protein expression", "temporal lobe epilepsy", and "biomarkers". Publications from 2003 to the present have been analyzed. Studies of brain tissues, experimental models of epilepsy, as well as biological fluids, were analyzed. For each of the groups, aberrantly expressed proteins found in various studies were isolated. Most of the studies omitted important characteristics of the studied patients, such as: duration of illness, type and response to therapy, gender, etc. Proteins that overlap across different tissue types and different studies have been highlighted: DPYSL, SYT1, STMN1, APOE, NME1, and others. The most common biological processes for them were the positive regulation of neurofibrillary tangle assembly, the regulation of amyloid fibril formation, lipoprotein catabolic process, the positive regulation of vesicle fusion, the positive regulation of oxidative stress-induced intrinsic apoptotic signaling pathway, removal of superoxide radicals, axon extension, and the regulation of actin filament depolymerization. MS-based proteomic profiling for a relevant study must accept a number of limitations, the most important of which is the need to compare different types of neurological and, in particular, epileptic disorders. Such a criterion could increase the specificity of the search work and, in the future, lead to the discovery of biomarkers for a particular disease.

Synaptic proteins in neuron-derived extracellular vesicles as biomarkers for Alzheimer's disease: novel methodology and clinical proof of concept

Aims

Blood biomarkers can improve drug development for Alzheimer's disease (AD) and its treatment. Neuron-derived extracellular vesicles (NDEVs) in plasma offer a minimally invasive platform for developing novel biomarkers that may be used to monitor the diverse pathogenic processes involved in AD. However, NDEVs comprise only a minor fraction of circulating extracellular vesicles (EVs). Most published studies have leveraged the L1 cell adhesion molecule (L1CAM) for NDEV immunocapture. We aimed to develop and optimize an alternative, highly specific immunoaffinity method to enrich blood NDEVs for biomarker development.

Methods

After screening multiple neuronal antigens, we achieved NDEV capture with high affinity and specificity using antibodies against Growth-Associated Protein (GAP) 43 and Neuroligin 3 (NLGN3). The EV identity of the captured material was confirmed by electron microscopy, western blotting, and proteomics. The specificity for neuronal origin was demonstrated by showing enrichment for neuronal markers (proteins, mRNA) and recovery of spiked neuronal EVs. We performed NDEV isolation retrospectively from plasma samples from two cohorts of early AD patients (N = 19 and N = 40) and controls (N = 20 and N = 19) and measured p181-Tau, amyloid-beta (Aβ) 42, brain-derived neurotrophic factor (BDNF), precursor brain-derived neurotrophic factor (proBDNF), glutamate receptor 2 (GluR2), postsynaptic density protein (PSD) 95, GAP43, and syntaxin-1.

Results

p181-Tau, Aβ42, and NRGN were elevated in AD samples, whereas proBDNF, GluR2, PSD95, GAP43, and Syntaxin-1 were reduced. Differences for p181-Tau, proBDNF, and GluR2 survived multiple-comparison correction and were correlated with cognitive scores. A model incorporating biomarkers correctly classified 94.7% of AD participants and 61.5% of control participants. The observed differences in NDEVs-associated biomarkers are consistent with previous findings.

Conclusion

NDEV isolation by GAP43 and NLGN3 immunocapture offers a robust novel platform for biomarker development in AD, suitable for large-scale validation.

Advanced Overview of Biomarkers and Techniques for Early Diagnosis of Alzheimer's Disease

The development of early non-invasive diagnosis methods and identification of novel biomarkers are necessary for managing Alzheimer's disease (AD) and facilitating effective prognosis and treatment. AD has multi-factorial nature and involves complex molecular mechanism, which causes neuronal degeneration. The primary challenges in early AD detection include patient heterogeneity and lack of precise diagnosis at the preclinical stage. Several cerebrospinal fluid (CSF) and blood biomarkers have been proposed to show excellent diagnosis ability by identifying tau pathology and cerebral amyloid beta (Aβ) for AD. Intense research endeavors are being made to develop ultrasensitive detection techniques and find potent biomarkers for early AD diagnosis. To mitigate AD worldwide, understanding various CSF biomarkers, blood biomarkers, and techniques that can be used for early diagnosis is imperative. This review attempts to provide information regarding AD pathophysiology, genetic and non-genetic factors associated with AD, several potential blood and CSF biomarkers, like neurofilament light, neurogranin, Aβ, and tau, along with biomarkers under development for AD detection. Besides, numerous techniques, such as neuroimaging, spectroscopic techniques, biosensors, and neuroproteomics, which are being explored to aid early AD detection, have been discussed. The insights thus gained would help in finding potential biomarkers and suitable techniques for the accurate diagnosis of early AD before cognitive dysfunction.

Role of calcium-sensor proteins in cell membrane repair

Cell membrane repair is a critical process used to maintain cell integrity and survival from potentially lethal chemical, and mechanical membrane injury. Rapid increases in local calcium levels due to a membrane rupture have been widely accepted as a trigger for multiple membrane-resealing models that utilize exocytosis, endocytosis, patching, and shedding mechanisms. Calcium-sensor proteins, such as synaptotagmins (Syt), dysferlin, S100 proteins, and annexins, have all been identified to regulate, or participate in, multiple modes of membrane repair. Dysfunction of membrane repair from inefficiencies or genetic alterations in these proteins contributes to diseases such as muscular dystrophy (MD) and heart disease. The present review covers the role of some of the key calcium-sensor proteins and their involvement in membrane repair.

Evolutionary and genomic perspectives of brain aging and neurodegenerative diseases

This chapter utilizes genomic concepts and evolutionary perspectives to further understand the possible links between typical brain aging and neurodegenerative diseases, focusing on the two most prevalent of these: Alzheimer's disease and Parkinson's disease. Aging is the major risk factor for these neurodegenerative diseases. Researching the evolutionary and molecular underpinnings of aging helps to reveal elements of the typical aging process that leave individuals more vulnerable to neurodegenerative pathologies. Very little is known about the prevalence and susceptibility of neurodegenerative diseases in nonhuman species, as only a few individuals have been observed with these neuropathologies. However, several studies have investigated the evolution of lifespan, which is closely connected with brain size in mammals, and insights can be drawn from these to enrich our understanding of neurodegeneration. This chapter explores the relationship between the typical aging process and the events in neurodegeneration. First, we examined how age-related processes can increase susceptibility to neurodegenerative diseases. Second, we assessed to what extent neurodegeneration is an accelerated form of aging. We found that while at the phenotypic level both neurodegenerative diseases and the typical aging process share some characteristics, at the molecular level they show some distinctions in their profiles, such as variation in genes and gene expression. Furthermore, neurodegeneration of the brain is associated with an earlier onset of cellular, molecular, and structural age-related changes. In conclusion, a more integrative view of the aging process, both from a molecular and an evolutionary perspective, may increase our understanding of neurodegenerative diseases.

Cerebrospinal Fluid Biomarkers of Synaptic Dysfunction are Altered in Parkinson's Disease and Related Disorders

BACKGROUND

Synaptic dysfunction and degeneration are central contributors to the pathogenesis and progression of parkinsonian disorders. Therefore, identification and validation of biomarkers reflecting pathological synaptic alterations are greatly needed and could be used in prognostic assessment and to monitor treatment effects.

OBJECTIVE

To explore candidate biomarkers of synaptic dysfunction in Parkinson's disease (PD) and related disorders.

METHODS

Mass spectrometry was used to quantify 15 synaptic proteins in two clinical cerebrospinal fluid (CSF) cohorts, including PD (n₁  = 51, n₂  = 101), corticobasal degeneration (CBD) (n₁  = 11, n₂  = 3), progressive supranuclear palsy (PSP) (n₁  = 22, n₂  = 21), multiple system atrophy (MSA) (n₁  = 31, n₂  = 26), and healthy control (HC) (n₁  = 48, n₂  = 30) participants, as well as Alzheimer's disease (AD) (n₂  = 23) patients in the second cohort.

RESULTS

Across both cohorts, lower levels of the neuronal pentraxins (NPTX; 1, 2, and receptor) were found in PD, MSA, and PSP, compared with HC. In MSA and PSP, lower neurogranin, AP2B1, and complexin-2 levels compared with HC were observed. In AD, levels of 14-3-3 zeta/delta, beta- and gamma-synuclein were higher compared with the parkinsonian disorders. Lower pentraxin levels in PD correlated with Mini-Mental State Exam scores and specific cognitive deficits (NPTX2; rho = 0.25-0.32, P < 0.05) and reduced dopaminergic pre-synaptic integrity as measured by DaTSCAN (NPTX2; rho = 0.29, P = 0.023). Additionally, lower levels were associated with the progression of postural imbalance and gait difficulty symptoms (All NPTX; β-estimate = -0.025 to -0.038, P < 0.05) and cognitive decline (NPTX2; β-estimate = 0.32, P = 0.021).

CONCLUSIONS

These novel findings show different alterations of synaptic proteins in parkinsonian disorders compared with AD and HC. The neuronal pentraxins may serve as prognostic CSF biomarkers for both cognitive and motor symptom progression in PD. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Novel diagnostic biomarkers related to immune infiltration in Parkinson's disease by bioinformatics analysis

Background

Parkinson's disease (PD) is Pengfei Zhang Liwen Zhao Pengfei Zhang Liwen Zhao a common neurological disorder involving a complex relationship with immune infiltration. Therefore, we aimed to explore PD immune infiltration patterns and identify novel immune-related diagnostic biomarkers.

Materials and methods

Three substantia nigra expression microarray datasets were integrated with elimination of batch effects. Differentially expressed genes (DEGs) were screened using the "limma" package, and functional enrichment was analyzed. Weighted gene co-expression network analysis (WGCNA) was performed to explore the key module most significantly associated with PD; the intersection of DEGs and the key module in WGCNA were considered common genes (CGs). The CG protein-protein interaction (PPI) network was constructed to identify candidate hub genes by cytoscape. Candidate hub genes were verified by another two datasets. Receiver operating characteristic curve analysis was used to evaluate the hub gene diagnostic ability, with further gene set enrichment analysis (GSEA). The immune infiltration level was evaluated by ssGSEA and CIBERSORT methods. Spearman correlation analysis was used to evaluate the hub genes association with immune cells. Finally, a nomogram model and microRNA-TF-mRNA network were constructed based on immune-related biomarkers.

Results

A total of 263 CGs were identified by the intersection of 319 DEGs and 1539 genes in the key turquoise module. Eleven candidate hub genes were screened by the R package "UpSet." We verified the candidate hub genes based on two validation sets and identified six (SYT1, NEFM, NEFL, SNAP25, GAP43, and GRIA1) that distinguish the PD group from healthy controls. Both CIBERSORT and ssGSEA revealed a significantly increased proportion of neutrophils in the PD group. Correlation between immune cells and hub genes showed SYT1, NEFM, GAP43, and GRIA1 to be significantly related to immune cells. Moreover, the microRNA-TFs-mRNA network revealed that the microRNA-92a family targets all four immune-related genes in PD pathogenesis. Finally, a nomogram exhibited a reliable capability of predicting PD based on the four immune-related genes (AUC = 0.905).

Conclusion

By affecting immune infiltration, SYT1, NEFM, GAP43, and GRIA1, which are regulated by the microRNA-92a family, were identified as diagnostic biomarkers of PD. The correlation of these four genes with neutrophils and the microRNA-92a family in PD needs further investigation.

Association of CSF GAP-43 With the Rate of Cognitive Decline and Progression to Dementia in Amyloid-Positive Individuals

BACKGROUND AND OBJECTIVES

To test the associations between the presynaptic growth-associated protein 43 (GAP-43), quantified in CSF, and biomarkers of Alzheimer disease (AD) pathophysiology, cross-sectionally and longitudinally.

METHODS

In this retrospective study, GAP-43 was measured in participants from the AD Neuroimaging Initiative (ADNI) cohort using an in-house ELISA method, and levels were compared between groups, both cross-sectionally and longitudinally. Linear regression models tested the associations between biomarkers of AD (amyloid beta [Aβ] and tau pathologies, neurodegeneration, and cognition) adjusted by age, sex, and diagnosis. Linear mixed-effect models evaluated how baseline GAP-43 predicts brain hypometabolism, atrophy, and cognitive decline over time. Cox proportional hazard regression models tested how GAP-43 levels and Aβ status, at baseline, increased the risk of progression to AD dementia over time.

RESULTS

This study included 786 participants from the ADNI cohort, which were further classified in cognitively unimpaired (CU) Aβ-negative (nCU- = 197); CU Aβ-positive (nCU+ = 55), mild cognitively impaired (MCI) Aβ-negative (nMCI- = 228), MCI Aβ-positive (nMCI+ = 193), and AD dementia Aβ-positive (nAD = 113). CSF GAP-43 levels were increased in Aβ-positive compared with Aβ-negative participants, independent of the cognitive status. In Aβ-positive participants, high baseline GAP-43 levels led to worse brain metabolic decline (p = 0.01), worse brain atrophy (p = 8.8 × 10-27), and worse MMSE scores (p = 0.03) over time, as compared with those with low GAP-43 levels. Similarly, Aβ-positive participants with high baseline GAP-43 had the highest risk to convert to AD dementia (hazard ratio [HR = 8.56, 95% CI 4.94-14.80, p = 1.5 × 10-14]). Despite the significant association with Aβ pathology (η2 Aβ PET = 0.09, P Aβ PET < 0.001), CSF total tau (tTau) and phosphorylated tau (pTau) had a larger effect size on GAP43 than Aβ PET (η2 pTau-181 = 0.53, P pTau-181 < 0.001; η2 tTau = 0.59, P tTau < 0.001).

DISCUSSION

High baseline levels of CSF GAP-43 are associated with progression in Aβ-positive individuals, with a more aggressive neurodegenerative process, faster rate of cognitive decline, and increased risk of converting to dementia.

Biomarkers of Activity-Dependent Plasticity and Persistent Enhancement of Synaptic Transmission in Alzheimer Disease: A Review of the Current Status

Alzheimer disease (AD) is a chronic and heterogeneous neurodegenerative disorder characterized by complex pathological processes involving neuroinflammation, neurodegeneration, and synaptic dysfunction. Understanding the exact neurobiological mechanisms underlying AD pathology may help to provide a biomarker for early diagnosis or at least for assessment of vulnerability to dementia development. Neural plasticity is defined as a capability of the brain to respond to alterations including aging, injury, or learning, with a crucial role of synaptic elements. Long-term potentiation (LTP) and long-term depression (LTD) are important in regulating synaptic connections between neural cells in functional plasticity. Synaptic loss and impairment of the brain's plasticity in AD leads to cognitive impairment, and one of important roles of synaptic biomarkers is monitoring synaptic dysfunction, response to treatment, and predicting future development of AD. Synaptic biomarkers are undoubtedly very promising in developing novel approach to AD treatment and control, especially in the era of aging of societies, which is one of the most common risk factor of AD. Implementing a widespread measurement of synaptic biomarkers of AD will probably be crucial in early diagnosis of AD, early therapeutic intervention, monitoring progression of the disease, or response to treatment. One of the most important challenges is finding a biomarker whose blood concentration correlates with its level in the central nervous system (CNS). This review aims to present the current status of biomarkers of activity-dependent plasticity and persistent enhancement of synaptic transmission in Alzheimer disease.

Sulforaphene, a CDK5 Inhibitor, attenuates cognitive deficits in a transgenic mouse model of Alzheimer's disease via reducing Aβ Deposition, tau hyperphosphorylation and synaptic dysfunction

BACKGROUND

Alzheimer's disease (AD) is the most common form of neurodegenerative disorder characterized by progressive loss of memory and cognitive functions. There are two pathological hallmarks, including accumulation of amyloid plaques composed of β-amyloid peptide (Aβ) and deposits of neurofibrillatory tangles (NFT). Cyclin-dependent kinase 5 (CDK5), a serine/threonine kinase, plays an important role in synaptic plasticity and cognitive behavior. Sulforaphene (SF) has been demonstrated to exert anti-AD activity in AD rat model. In this study, we aimed to evaluate the cognitive deficits improving effects of SF on in TgCRND8 mice and to elucidate the underlying molecular mechanisms.

METHODS

TgCRND8 mice were intragastrically treated with SF (25 and 50 mg/kg) for 4 months from 3-month-old. The cognitive functions were assessed using Morris Water Maze Test. Cultured primary mouse neurons were pre-treated with SF, followed by co-treatment with Aβ1-42 oligomers. CDK5 inhibitor (roscovitine) was used to determine the involvement of CDK5/p25 pathway in the anti-AD effects of SF in primary neurons.

RESULTS

Our results showed that SF treatment significantly ameliorated the cognitive deficits in TgCRND8 mice and protected primary mouse neurons against Aβ1-42 induced neurotoxicity. SF could modulate the expression of Aβ production related markers, and suppress the phosphorylation of tau protein at specific sites in the TgCRND8 mice. In addition, SF enhanced the expressions of synaptic plasticity related markers and CDK5. SF also markedly suppressed the CDK5/p25 activity.

CONCLUSIONS

SF is a potent CDK5 inhibitor and a potential therapeutic agent for treatment and prevention of AD. Moreover, SF inhibited the overexpression of CDK5 in primary neurons of mouse.

Cerebrospinal Fluid Panel of Synaptic Proteins in Cerebral Amyloid Angiopathy and Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) and cerebral amyloid angiopathy (CAA) share pathogenic pathways related to amyloid-β deposition. Whereas AD is known to affect synaptic function, such an association for CAA remains yet unknown.

OBJECTIVE

We therefore aimed to investigate synaptic dysfunction in CAA.

METHODS

Multiple reaction monitoring mass spectrometry was used to quantify cerebrospinal fluid (CSF) concentrations of 15 synaptic proteins in CAA and AD patients, and age- and sex-matched cognitively unimpaired controls.

RESULTS

We included 25 patients with CAA, 49 patients with AD, and 25 controls. Only neuronal pentraxin-2 levels were decreased in the CSF of CAA patients compared with controls (p = 0.04). CSF concentrations of 12 other synaptic proteins were all increased in AD compared with CAA or controls (all p≤0.01) and were unchanged between CAA and controls. Synaptic protein concentrations in the subgroup of CAA patients positive for AD biomarkers (CAA/ATN+; n = 6) were similar to AD patients, while levels in CAA/ATN- (n = 19) were comparable with those in controls. A regression model including all synaptic proteins differentiated CAA from AD at high accuracy levels (area under the curve 0.987).

CONCLUSION

In contrast to AD, synaptic CSF biomarkers were found to be largely unchanged in CAA. Moreover, concomitant AD pathology in CAA is associated with abnormal synaptic protein levels. Impaired synaptic function in AD was confirmed in this independent cohort. Our findings support an apparent differential involvement of synaptic dysfunction in CAA and AD and may reflect distinct pathological mechanisms.

Characterization of the contactin 5 protein and its risk-associated polymorphic variant throughout the Alzheimer's disease spectrum

INTRODUCTION

We investigate the CNTN5 rs1461684 G variant and the contactin 5 protein in sporadic Alzheimer's disease (sAD).

METHODS

Contactin 5, sAD biomarkers, and synaptic markers were measured in the cerebrospinal fluid (CSF). Amyloid and tau deposition were assessed using positron emission tomography. Contactin 5 protein and mRNA levels were measured in brain tissue.

RESULTS

CSF contactin 5 increases progressively in cognitively unimpaired individuals and is decreased in mild cognitive impairment and sAD. CSF contactin 5 correlates with sAD biomarkers and with synaptic markers. The rs1461684 G variant associates with faster disease progression in cognitively unimpaired subjects. Cortical full-length and isoform 3 CNTN5 mRNAs are decreased in the presence of the G allele and as a function of Consortium to Establish a Registry for Alzheimer's Disease stages.

DISCUSSION

The newly identified rs1461684 G variant associates with sAD risk, rate of disease progression, and gene expression. Contactin 5 protein and mRNA are affected particularly in the early stages of the disease.

Multipronged diagnostic and therapeutic strategies for Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and a major contributor to dementia cases worldwide. AD is clinically characterized by learning, memory, and cognitive deficits. The accumulation of extracellular amyloid β (Aβ) plaques and neurofibrillary tangles (NFTs) of tau are the pathological hallmarks of AD and are explored as targets for clinical diagnosis and therapy. AD pathology is poorly understood and there are no fully approved diagnosis and treatments. Notwithstanding the gap, decades of research in understanding disease mechanisms have revealed the multifactorial nature of AD. As a result, multipronged and holistic approaches are pertinent to targeting multiple biomarkers and targets for developing effective diagnosis and therapeutics. In this perspective, recent developments in Aβ and tau targeted diagnostic and therapeutic tools are discussed. Novel indirect, combination, and circulating biomarkers as potential diagnostic targets are highlighted. We underline the importance of multiplexing and multimodal detection of multiple biomarkers to generate biomarker fingerprints as a reliable diagnostic strategy. The classical therapeutics targeting Aβ and tau aggregation pathways are described with bottlenecks in the strategy. Drug discovery efforts targeting multifaceted toxicity involving protein aggregation, metal toxicity, oxidative stress, mitochondrial damage, and neuroinflammation are highlighted. Recent efforts focused on multipronged strategies to rationally design multifunctional modulators targeting multiple pathological factors are presented as future drug development strategies to discover potential therapeutics for AD.

β-Synuclein as a candidate blood biomarker for synaptic degeneration in Alzheimer's disease

Synaptic degeneration is an early event closely associated with the course of Alzheimer's disease (AD). The identification of synaptic blood biomarkers is, therefore, of great interest and clinical relevance. The levels of most synaptic proteins are increased in the cerebrospinal fluid (CSF) of patients with AD, but their detection in blood is hitherto either unavailable or not very informative. This paradigm is related to their low concentration, their peripheral origin, or the presence of highly abundant blood proteins that hinder detection. In recent years, significant progress has been made in detecting the presynaptic protein β-synuclein. This mini-review summarizes the results that highlight the role of β-synuclein as a candidate blood marker for synaptic degeneration in AD.

Visinin-like protein 1 levels in blood and CSF as emerging markers for Alzheimer's and other neurodegenerative diseases

BACKGROUND

Visinin-like protein 1 (VILIP-1) belongs to the group of emerging biomarkers with the potential to support the early diagnosis of Alzheimer's disease (AD). However, studies investigating the differential diagnostic potential in cerebrospinal fluid (CSF) are rare and are not available for blood.

METHODS

We set up a novel, sensitive single molecule array (Simoa) assay for the detection of VILIP-1 in CSF and serum. In total, paired CSF and serum samples from 234 patients were investigated: 73 AD, 18 behavioral variant frontotemporal dementia (bvFTD), 26 parkinsonian syndromes, 20 amyotrophic lateral sclerosis (ALS), 22 Creutzfeldt-Jakob disease (CJD), and 75 non-neurodegenerative control (Con) patients. The differential diagnostic potential of CSF and serum VILIP-1 was assessed using the receiver operating characteristic curve analysis and findings were compared to core AD biomarkers.

RESULTS

CSF and serum VILIP-1 levels correlated weakly (r=0.32 (CI: 0.20-0.43), p<0.0001). VILIP-1 concentrations in CSF and serum were elevated in AD compared to Con (p<0.0001 and p<0.01) and CJD (p<0.0001 for CSF and serum), and an increase in CSF was observed already in early AD stages (p<0.0001). In the discrimination of AD versus Con, we could demonstrate a strong diagnostic potential for CSF VILIP-1 alone (area under the curve (AUC): 0.87), CSF VILIP-1/CSF Abeta 1-42 (AUC: 0.98), and serum VILIP-1/CSF Abeta 1-42 ratio (AUC: 0.89).

CONCLUSIONS

We here report on the successful establishment of a novel Simoa assay for VILIP-1 and illustrate the potential of CSF and serum VILIP-1 in the differential diagnosis of AD with highest levels in CJD.

Combined Effects of Synaptic and Axonal Integrity on Longitudinal Gray Matter Atrophy in Cognitively Unimpaired Adults

BACKGROUND AND OBJECTIVES

Synaptic dysfunction and degeneration is a predominant feature of brain aging, and synaptic preservation buffers against Alzheimer disease (AD) protein-related brain atrophy. We tested whether CSF synaptic protein concentrations similarly moderate the effects of axonal injury, indexed by CSF neurofilament light [NfL]), on brain atrophy in clinically normal adults.

METHODS

Clinically normal older adults enrolled in the observational Hillblom Aging Network study at the UCSF Memory and Aging Center completed baseline lumbar puncture and longitudinal brain MRI (mean scan [follow-up] = 2.6 [3.7 years]). CSF was assayed for synaptic proteins (synaptotagmin-1, synaptosomal-associated protein 25 [SNAP-25], neurogranin, growth-associated protein 43 [GAP-43]), axonal injury (NfL), and core AD biomarkers (ptau181/Aβ42 ratio; reflecting AD proteinopathy). Ten bilateral temporoparietal gray matter region of interest (ROIs) shown to be sensitive to clinical AD were summed to generate a composite temporoparietal ROI. Linear mixed-effects models tested statistical moderation of baseline synaptic proteins on baseline NfL-related temporoparietal trajectories, controlling for ptau181/Aβ42 ratios.

RESULTS

Forty-six clinically normal older adults (mean age = 70 years; 43% female) were included. Synaptic proteins exhibited small to medium correlations with NfL (r range: 0.10-0.36). Higher baseline NfL, but not ptau181/Aβ42 ratios, predicted steeper temporoparietal atrophy (NfL × time: β = -0.08, p < 0.001; ptau181/Aβ42 × time: β = -0.02, p = 0.31). SNAP-25, neurogranin, and GAP-43 significantly moderated NfL-related atrophy trajectories (-0.07 ≤ β's ≥ -0.06, p's < 0.05) such that NfL was associated with temporoparietal atrophy at high (more abnormal) but not low (more normal) synaptic protein concentrations. At high NfL concentrations, atrophy trajectories were 1.5-4.5 times weaker when synaptic protein concentrations were low (β range: -0.21 to -0.07) than high (β range: -0.33 to -0.30).

DISCUSSION

The association between baseline CSF NfL and longitudinal temporoparietal atrophy is accelerated by synaptic dysfunction and buffered by synaptic integrity. Beyond AD proteins, concurrent examination of in vivo axonal and synaptic biomarkers may improve detection of neural alterations that precede overt structural changes in AD-sensitive brain regions.

Fluid biomarkers in Alzheimer's disease

Alzheimer's disease (AD) characterization has progressed from being indexed using clinical symptomatology followed by neuropathological examination at autopsy to in vivo signatures using cerebrospinal fluid (CSF) biomarkers and positron emission tomography. The core AD biomarkers reflect amyloid-β plaques (A), tau pathology (T) and neurodegeneration (N), following the ATN schedule, and are now being introduced into clinical routine practice. This is an important development, as disease-modifying treatments are now emerging. Further, there are now reproducible data on CSF biomarkers which reflect synaptic pathology, neuroinflammation and common co-pathologies. In addition, the development of ultrasensitive techniques has enabled the core CSF biomarkers of AD pathophysiology to be translated to blood (e.g., phosphorylated tau, amyloid-β and neurofilament light). In this chapter, we review where we stand with both core and novel CSF biomarkers, as well as the explosion of data on blood biomarkers. Also, we discuss potential applications in research aiming to better understand the disease, as well as possible use in routine clinical practice and therapeutic trials.

Associations between cerebrospinal fluid markers and cognition in ageing and dementia: A systematic review

A biomarker associated with cognition in neurodegenerative dementias would aid in the early detection of disease progression, complement clinical staging and act as a surrogate endpoint in clinical trials. The current systematic review evaluates the association between cerebrospinal fluid protein markers of synapse loss and neuronal injury and cognition. We performed a systematic search which revealed 67 studies reporting an association between cerebrospinal fluid markers of interest and neuropsychological performance. Despite the substantial heterogeneity between studies, we found some evidence for an association between neurofilament-light and worse cognition in Alzheimer's diseases, frontotemporal dementia and typical cognitive ageing. Moreover, there was an association between cerebrospinal fluid neurogranin and cognition in those with an Alzheimer's-like cerebrospinal fluid biomarker profile. Some evidence was found for cerebrospinal fluid neuronal pentraxin-2 as a correlate of cognition across dementia syndromes. Due to the substantial heterogeneity of the field, no firm conclusions can be drawn from this review. Future research should focus on improving standardization and reporting as well as establishing the importance of novel markers such as neuronal pentraxin-2 and whether such markers can predict longitudinal cognitive decline.

CSF GAP-43 as a biomarker of synaptic dysfunction is associated with tau pathology in Alzheimer's disease

To test whether cerebrospinal fluid (CSF) growth-associated protein 43 (GAP-43) concentration is elevated in Alzheimer's disease (AD) dementia and its associations with other hallmarks of AD, we examined the CSF GAP-43 measurements of 787 participants (245 cognitively normal (CN), 415 individuals with mild cognitive impairment (MCI) and 127 individuals with AD dementia) from the Alzheimer's Disease Neuroimaging Initiative (ADNI) study. Associations were investigated between CSF GAP-43 and clinical diagnosis, Aβ/tau/neurodegeneration (AT(N)) status, CSF and blood biomarkers of AD, cognitive measurements and brain neuroimaging findings. CSF GAP-43 levels were increased in patients with AD dementia (mean, 6331.05 pg/ml) compared with the CN (mean, 5001.05 pg/ml) and MCI (mean, 5118.8 pg/ml) (P < 0.001) groups. CSF GAP-43 correlated with CSF phosphorylated tau 181(p-tau) (r = 0.768, P < 0.001), and had high diagnostic accuracy in differentiating tau positive status vs. tau negative status (area under the receiver operating characteristic curve, 0.8606). CSF GAP-43 was particularly elevated among individuals with tau positive status. High CSF GAP-43 was associated with longitudinal deterioration of cognitive scores and brain neuroimaging findings. CSF GAP-43 was associated with a clinical diagnosis of AD dementia and with an individual's tau status, cognitive measurements and findings from neuroimaging. This study implies that CSF GAP-43 as a biomarker of synaptic dysfunction could predict the disease progression of AD patients.

SYT1-Associated Neurodevelopmental Disorder: A Narrative Review

Synaptic dysregulations often result in damaging effects on the central nervous system, resulting in a wide range of brain and neurodevelopment disorders that are caused by mutations disrupting synaptic proteins. SYT1, an identified synaptotagmin protein, plays an essential role in mediating the release of calcium-triggered neurotransmitters (NT) involved in regular synaptic vesicle exocytosis. Considering the significant role of SYT1 in the physiology of synaptic neurotransmission, dysfunction and degeneration of this protein can result in a severe neurological impairment. Genetic variants lead to a newly discovered rare disorder, known as SYT1-associated neurodevelopment disorder. In this review, we will discuss in depth the function of SYT1 in synapse and the underlying molecular mechanisms. We will highlight the genetic basis of SYT1-associated neurodevelopmental disorder along with known phenotypes, with possible interventions and direction of research.