CSF YKL-40 and pTau181 are related to different cerebral morphometric patterns in early AD

Different inflammatory signatures based on CSF biomarkers relate to preserved or diminished brain structure and cognition

Neuroinflammation is a hallmark of Alzheimer's disease (AD) and both positive and negative associations of individual inflammation-related markers with brain structure and cognitive function have been described. We aimed to identify inflammatory signatures of CSF immune-related markers that relate to changes of brain structure and cognition across the clinical spectrum ranging from normal aging to AD. A panel of 16 inflammatory markers, Aβ42/40 and p-tau181 were measured in CSF at baseline in the DZNE DELCODE cohort (n = 295); a longitudinal observational study focusing on at-risk stages of AD. Volumetric maps of gray and white matter (GM/WM; n = 261) and white matter hyperintensities (WMHs, n = 249) were derived from baseline MRIs. Cognitive decline (n = 204) and the rate of change in GM volume was measured in subjects with at least 3 visits (n = 175). A principal component analysis on the CSF markers revealed four inflammatory components (PCs). Of these, the first component PC1 (highly loading on sTyro3, sAXL, sTREM2, YKL-40, and C1q) was associated with older age and higher p-tau levels, but with less pathological Aβ when controlling for p-tau. PC2 (highly loading on CRP, IL-18, complement factor F/H and C4) was related to male gender, higher body mass index and greater vascular risk. PC1 levels, adjusted for AD markers, were related to higher GM and WM volumes, less WMHs, better baseline memory, and to slower atrophy rates in AD-related areas and less cognitive decline. In contrast, PC2 related to less GM and WM volumes and worse memory at baseline. Similar inflammatory signatures and associations were identified in the independent F.ACE cohort. Our data suggest that there are beneficial and detrimental signatures of inflammatory CSF biomarkers. While higher levels of TAM receptors (sTyro/sAXL) or sTREM2 might reflect a protective glia response to degeneration related to phagocytic clearance, other markers might rather reflect proinflammatory states that have detrimental impact on brain integrity.

The potential of blood neurofilament light as a marker of neurodegeneration for Alzheimer's disease

Over the past several years, there has been a surge in blood biomarker studies examining the value of plasma or serum neurofilament light (NfL) as a biomarker of neurodegeneration for Alzheimer's disease. However, there have been limited efforts to combine existing findings to assess the utility of blood NfL as a biomarker of neurodegeneration for Alzheimer's disease. In addition, we still need better insight into the specific aspects of neurodegeneration that are reflected by the elevated plasma or serum concentration of NfL. In this review, we survey the literature on the cross-sectional and longitudinal relationships between blood-based NfL levels and other, neuroimaging-based, indices of neurodegeneration in individuals on the Alzheimer's continuum. Then, based on the biomarker classification established by the FDA-NIH Biomarker Working group, we determine the utility of blood-based NfL as a marker for monitoring the disease status (i.e. monitoring biomarker) and predicting the severity of neurodegeneration in older adults with and without cognitive decline (i.e. a prognostic or a risk/susceptibility biomarker). The current findings suggest that blood NfL exhibits great promise as a monitoring biomarker because an increased NfL level in plasma or serum appears to reflect the current severity of atrophy, hypometabolism and the decline of white matter integrity, particularly in the brain regions typically affected by Alzheimer's disease. Longitudinal evidence indicates that blood NfL can be useful not only as a prognostic biomarker for predicting the progression of neurodegeneration in patients with Alzheimer's disease but also as a susceptibility/risk biomarker predicting the likelihood of abnormal alterations in brain structure and function in cognitively unimpaired individuals with a higher risk of developing Alzheimer's disease (e.g. those with a higher amyloid-β). There are still limitations to current research, as discussed in this review. Nevertheless, the extant literature strongly suggests that blood NfL can serve as a valuable prognostic and susceptibility biomarker for Alzheimer's disease-related neurodegeneration in clinical settings, as well as in research settings.

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

INTRODUCTION

We studied how biomarkers of reactive astrogliosis mediate the pathogenic cascade in the earliest Alzheimer's disease (AD) stages.

METHODS

We performed path analysis on data from 384 cognitively unimpaired individuals from the ALzheimer and FAmilies (ALFA)+ study using structural equation modeling to quantify the relationships between biomarkers of reactive astrogliosis and the AD pathological cascade.

RESULTS

Cerebrospinal fluid (CSF) amyloid beta (Aβ)42/40 was associated with Aβ aggregation on positron emission tomography (PET) and with CSF p-tau181 , which was in turn directly associated with CSF neurofilament light (NfL). Plasma glial fibrillary acidic protein (GFAP) mediated the relationship between CSF Aβ42/40 and Aβ-PET, and CSF YKL-40 partly explained the association between Aβ-PET, p-tau181 , and NfL.

DISCUSSION

Our results suggest that reactive astrogliosis, as indicated by different fluid biomarkers, influences the pathogenic cascade during the preclinical stage of AD. While plasma GFAP mediates the early association between soluble and insoluble Aβ, CSF YKL-40 mediates the latter association between Aβ and downstream Aβ-induced tau pathology and tau-induced neuronal injury.

HIGHLIGHTS

Lower CSF Aβ42/40 was directly linked to higher plasma GFAP concentrations. Plasma GFAP partially explained the relationship between soluble Aβ and insoluble Aβ. CSF YKL-40 mediated Aβ-induced tau phosphorylation and tau-induced neuronal injury.

Astrocytic Chitinase-3-like protein 1 in neurological diseases: Potential roles and future perspectives

Chitinase-3-like protein 1 (CHI3L1) is a secreted glycoprotein characterized by its ability to regulate multiple biological processes, such as the inflammatory response and gene transcriptional signaling activation. Abnormal CHI3L1 expression has been associated with multiple neurological disorders and serves as a biomarker for the early detection of several neurodegenerative diseases. Aberrant CHI3L1 expression is also reportedly associated with brain tumor migration and metastasis, as well as contributions to immune escape, playing important roles in brain tumor progression. CHI3L1 is synthesized and secreted mainly by reactive astrocytes in the central nervous system. Thus, targeting astrocytic CHI3L1 could be a promising approach for the treatment of neurological diseases, such as traumatic brain injury, ischemic stroke, Alzheimer's disease, Parkinson's disease, multiple sclerosis, amyotrophic lateral sclerosis, and glioma. Based on current knowledge of CHI3L1, we assume that it acts as a molecule mediating several signaling pathways driving the initiation and progression of neurological disorders. This narrative review is the first to introduce the potential roles of astrocytic CHI3L1 in neurological disorders. We also equally explore astrocytic CHI3L1 mRNA expression under physiological and pathological conditions. Inhibiting CHI3L1 and disrupting its interaction with its receptors through multiple mechanisms of action are briefly discussed. These endeavors highlight the pivotal roles of astrocytic CHI3L1 in neurological disorders and could contribute to the development of effective inhibitors based on the strategy of structure-based drug discovery, which could be an attractive therapeutic approach for neurological disease treatment.

Chitinase Signature in the Plasticity of Neurodegenerative Diseases

Several reports have pointed out that Chitinases are expressed and secreted by various cell types of central nervous system (CNS), including activated microglia and astrocytes. These cells play a key role in neuroinflammation and in the pathogenesis of many neurodegenerative disorders. Increased levels of Chitinases, in particular Chitotriosidase (CHIT-1) and chitinase-3-like protein 1 (CHI3L1), have been found increased in several neurodegenerative disorders. Although having important biological roles in inflammation, to date, the molecular mechanisms of Chitinase involvement in the pathogenesis of neurodegenerative disorders is not well-elucidated. Several studies showed that some Chitinases could be assumed as markers for diagnosis, prognosis, activity, and severity of a disease and therefore can be helpful in the choice of treatment. However, some studies showed controversial results. This review will discuss the potential of Chitinases in the pathogenesis of some neurodegenerative disorders, such as Alzheimer’s disease, Parkinson’s disease, amyotrophic lateral sclerosis, and multiple sclerosis, to understand their role as distinctive biomarkers of neuronal cell activity during neuroinflammatory processes. Knowledge of the role of Chitinases in neuronal cell activation could allow for the development of new methodologies for downregulating neuroinflammation and consequently for diminishing negative neurological disease outcomes.

Astrocyte adaptation in Alzheimer's disease: a focus on astrocytic P2X7R

Astrocytes are key homeostatic and defensive cells of the central nervous system (CNS). They undertake numerous functions during development and in adulthood to support and protect the brain through finely regulated communication with other cellular elements of the nervous tissue. In Alzheimer's disease (AD), astrocytes undergo heterogeneous morphological, molecular and functional alterations represented by reactive remodelling, asthenia and loss of function. Reactive astrocytes closely associate with amyloid β (Aβ) plaques and neurofibrillary tangles in advanced AD. The specific contribution of astrocytes to AD could potentially evolve along the disease process and includes alterations in their signalling, interactions with pathological protein aggregates, metabolic and synaptic impairments. In this review, we focus on the purinergic receptor, P2X7R, and discuss the evidence that P2X7R activation contributes to altered astrocyte functions in AD. Expression of P2X7R is increased in AD brain relative to non-demented controls, and animal studies have shown that P2X7R antagonism improves cognitive and synaptic impairments in models of amyloidosis and tauopathy. While P2X7R activation can induce inflammatory signalling pathways, particularly in microglia, we focus here specifically on the contributions of astrocytic P2X7R to synaptic changes and protein aggregate clearance in AD, highlighting cell-specific roles of this purinoceptor activation that could be targeted to slow disease progression.

Genetics behind Cerebral Disease with Ocular Comorbidity: Finding Parallels between the Brain and Eye Molecular Pathology

Cerebral visual impairments (CVIs) is an umbrella term that categorizes miscellaneous visual defects with parallel genetic brain disorders. While the manifestations of CVIs are diverse and ambiguous, molecular diagnostics stand out as a powerful approach for understanding pathomechanisms in CVIs. Nevertheless, the characterization of CVI disease cohorts has been fragmented and lacks integration. By revisiting the genome-wide and phenome-wide association studies (GWAS and PheWAS), we clustered a handful of renowned CVIs into five ontology groups, namely ciliopathies (Joubert syndrome, Bardet-Biedl syndrome, Alstrom syndrome), demyelination diseases (multiple sclerosis, Alexander disease, Pelizaeus-Merzbacher disease), transcriptional deregulation diseases (Mowat-Wilson disease, Pitt-Hopkins disease, Rett syndrome, Cockayne syndrome, X-linked alpha-thalassaemia mental retardation), compromised peroxisome disorders (Zellweger spectrum disorder, Refsum disease), and channelopathies (neuromyelitis optica spectrum disorder), and reviewed several mutation hotspots currently found to be associated with the CVIs. Moreover, we discussed the common manifestations in the brain and the eye, and collated animal study findings to discuss plausible gene editing strategies for future CVI correction.

Brain alterations in the early Alzheimer's continuum with amyloid-β, tau, glial and neurodegeneration CSF markers

Higher grey matter volumes/cortical thickness and fluorodeoxyglucose uptake have been consistently found in cognitively unimpaired individuals with abnormal Alzheimer’s disease biomarkers compared with those with normal biomarkers. It has been hypothesized that such transient increases may be associated with neuroinflammatory mechanisms triggered in response to early Alzheimer’s pathology. Here, we evaluated, in the earliest stages of the Alzheimer’s continuum, associations between grey matter volume and fluorodeoxyglucose uptake with CSF biomarkers of several pathophysiological mechanisms known to be altered in preclinical Alzheimer’s disease stages. We included 319 cognitively unimpaired participants from the ALFA+ cohort with available structural MRI, fluorodeoxyglucose PET and CSF biomarkers of amyloid-β and tau pathology (phosphorylated tau and total tau), synaptic dysfunction (neurogranin), neuronal and axonal injury (neurofilament light), glial activation (soluble triggering receptor on myeloid cells 2, YKL40, GFAP, interleukin-6 and S100b) and α-synuclein using the Roche NeuroToolKit. We first used the amyloid-β/tau framework to investigate differences in the neuroimaging biomarkers between preclinical Alzheimer’s disease stages. Then, we looked for associations between the neuroimaging markers and all the CSF markers. Given the non-negative nature of the concentrations of CSF biomarkers and their high collinearity, we clustered them using non-negative matrix factorization approach (components) and sought associations with the imaging markers. By groups, higher grey matter volumes were found in the amyloid-β-positive tau-negative participants with respect to the reference amyloid-β-negative tau-negative group. Both amyloid-β and tau-positive participants showed higher fluorodeoxyglucose uptake than tau-negative individuals. Using the obtained components, we observed that tau pathology accompanied by YKL-40 (astrocytic marker) was associated with higher grey matter volumes and fluorodeoxyglucose uptake in extensive brain areas. Higher grey matter volumes in key Alzheimer-related regions were also found in association with two other components characterized by a higher expression of amyloid-β in combination with different glial markers: one with higher GFAP and S100b levels (astrocytic markers) and the other one with interleukin-6 (pro-inflammatory). Notably, these components’ expression had different behaviours across amyloid-β/tau stages. Taken together, our results show that CSF amyloid-β and phosphorylated tau, in combination with different aspects of glial response, have distinctive associations with higher grey matter volumes and increased glucose metabolism in key Alzheimer-related regions. These mechanisms combine to produce transient higher grey matter volumes and fluorodeoxyglucose uptake at the earliest stages of the Alzheimer’s continuum, which may revert later on the course of the disease when neurodegeneration drives structural and metabolic cerebral changes.

Biomarkers and Tools for Predicting Alzheimer's Disease in the Preclinical Stage

Alzheimer's disease (AD) is the only leading cause of death for which no disease-modifying therapy is currently available. Over the past decade, a string of disappointing clinical trial results has forced us to shift our focus to the preclinical stage of AD, which represents the most promising therapeutic window. However, the accurate diagnosis of preclinical AD requires the presence of brain β- amyloid deposition determined by cerebrospinal fluid or amyloid-positron emission tomography, significantly limiting routine screening and diagnosis in non-tertiary hospital settings. Thus, an easily accessible marker or tool with high sensitivity and specificity is highly needed. Recently, it has been discovered that individuals in the late stage of preclinical AD may not be truly "asymptomatic" in that they may have already developed subtle or subjective cognitive decline. In addition, advances in bloodderived biomarker studies have also allowed the detection of pathologic changes in preclinical AD. Exosomes, as cell-to-cell communication messengers, can reflect the functional changes of their source cell. Methodological advances have made it possible to extract brain-derived exosomes from peripheral blood, making exosomes an emerging biomarker carrier and liquid biopsy tool for preclinical AD. The eye and its associated structures have rich sensory-motor innervation. In this regard, studies have indicated that they may also provide reliable markers. Here, our report covers the current state of knowledge of neuropsychological and eye tests as screening tools for preclinical AD and assesses the value of blood and brain-derived exosomes as carriers of biomarkers in conjunction with the current diagnostic paradigm.

Pathophysiology of neurodegenerative diseases: An interplay among axonal transport failure, oxidative stress, and inflammation?

Neurodegenerative diseases (NDs) are heterogeneous neurological disorders characterized by a progressive loss of selected neuronal populations. A significant risk factor for most NDs is aging. Considering the constant increase in life expectancy, NDs represent a global public health burden. Axonal transport (AT) is a central cellular process underlying the generation and maintenance of neuronal architecture and connectivity. Deficits in AT appear to be a common thread for most, if not all, NDs. Neuroinflammation has been notoriously difficult to define in relation to NDs. Inflammation is a complex multifactorial process in the CNS, which varies depending on the disease stage. Several lines of evidence suggest that AT defect, axonopathy and neuroinflammation are tightly interlaced. However, whether these impairments play a causative role in NDs or are merely a downstream effect of neuronal degeneration remains unsettled. We still lack reliable information on the temporal relationship between these pathogenic mechanisms, although several findings suggest that they may occur early during ND pathophysiology. This article will review the latest evidence emerging on whether the interplay between AT perturbations and some aspects of CNS inflammation can participate in ND etiology, analyze their potential as therapeutic targets, and the urge to identify early surrogate biomarkers.

Soluble TAM receptors sAXL and sTyro3 predict structural and functional protection in Alzheimer's disease

There is an urgent need to improve the understanding of neuroinflammation in Alzheimer's disease (AD). We analyzed cerebrospinal fluid inflammatory biomarker correlations to brain structural volume and longitudinal cognitive outcomes in the DELCODE study and in a validation cohort of the F.ACE Alzheimer Center Barcelona. We investigated whether respective biomarker changes are evident before onset of cognitive impairment. YKL-40; sTREM2; sAXL; sTyro3; MIF; complement factors C1q, C4, and H; ferritin; and ApoE protein were elevated in pre-dementia subjects with pathological levels of tau or other neurodegeneration markers, demonstrating tight interactions between inflammation and accumulating neurodegeneration even before onset of symptoms. Intriguingly, higher levels of ApoE and soluble TAM receptors sAXL and sTyro3 were related to larger brain structure and stable cognitive outcome at follow-up. Our findings indicate a protective mechanism relevant for intervention strategies aiming to regulate neuroinflammation in subjects with no or subjective symptoms but underlying AD pathology profile.

YKL-40 as a Potential Biomarker for the Differential Diagnosis of Alzheimer's Disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder, associated with extensive neuronal loss, dendritic and synaptic changes resulting in significant cognitive impairment. An increased number of studies have given rise to the neuroinflammatory hypothesis in AD. It is widely accepted that AD brains show chronic inflammation, probably triggered by the presence of insoluble amyloid beta deposits and neurofibrillary tangles (NFT) and is also related to the activation of neuronal death cascade. In the present study we aimed to investigate the role of YKL-40 levels in the cerebrospinal fluid (CSF) in the diagnosis of AD, and to discuss whether there are further potential roles of this protein in the management and treatment of AD. We conducted an online search on PubMed, Web of Science, and the Cochrane library databases from 1990 to 2021. The quantitative analysis showed that the levels of YKL-40 were significantly higher in Alzheimer’s disease compared to controls, to mild cognitive impairment (MCI) AD (MCI-AD) and to stable MCI. They were also increased in MCI-AD compared to stable MCI. The present study shows that the CSF levels of YKL-40 could be potentially used as a biomarker for the prognosis of mild cognitive impairment and the likelihood of progression to AD, as well as for the differential diagnosis between AD and MCI.

Neurodegeneration and Glial Activation Related CSF Biomarker as the Diagnosis of Alzheimer's Disease: A Systematic Review and an Updated Meta-analysis

OBJECTIVE

Recently, neuron specific enolase (NSE), Visinin-like protein-1 (VLP-1), neurogranin (Ng), and YKL-40 have been identified as candidates for neuronal degeneration and glial activation biomarkers. Therefore, we perform a comprehensive meta-analysis to assess the diagnostic value of CSF NSE, VLP-1, Ng and YKL-40 in Alzheimer's disease (AD).

METHODS

We searched Pubmed, MEDLINE, EMBASE databases for research about the levels of CSF NSE, VLP-1, Ng and YKL-40 in AD patients compared with controls or other dementia diseases until Dec 2020.

RESULTS

The present meta-analysis contained a total of 51 studies comprising 6248 patients with dementia disorders and 3861 controls. Among them, there were 3262 patients with AD, 2456 patients with mild cognitive impairment (MCI), 173 patients with vascular dementia (VaD), 221 patients with frontotemporal dementia (FTD), and 136 with Lewy bodies dementia (DLB). Our study demonstrated that CSF NSE, VLP-1, Ng and YKL-40 levels were increased in AD as compared to healthy controls. We also observed that the CSF NSE level was higher in AD than VaD, suggesting CSF NSE might act as a key role in distinguishing between AD and VaD. Interestingly, there was a higher VLP-1 expression in AD, and a lower expression in DLB patients. Moreover, we found the CSF Ng level was increased in AD than MCI, implying CSF Ng might be a biomarker for identifying the progression of AD. Additionally, a significantly higher CSF YKL-40 level was detected not only in AD, but also in FTD, DLB, VaD, signifying YKL-40 was not sensitive in the diagnosis of AD.

CONCLUSION

Our study confirmed that CSF levels of NSE, VLP-1, and Ng could be valuable biomarkers for identifying patients who are more susceptible to AD and distinguishing AD from other neurodegenerative dementia disorders.

YKL-40 and neuron-specific enolase in neurodegeneration and neuroinflammation

Neurodegenerative diseases comprise a large number of disorders with high impact on human health. Neurodegenerative processes are caused by various etiological factors and differ in their clinical presentation. Neuroinflammation is widely discussed as both a cause and a consequence in the manifestation of these disorders. The interplay between the two entities is considered as a major contributor to the ongoing disease progression. An attentive search and implementation of new and reliable markers specific for the processes of inflammation and degeneration is still needed. YKL-40 is a secreted glycoprotein produced by activated glial cells during neuroinflammation. Neuron-specific enolase (NSE), expressed mainly by neuronal cells, is a long-standing marker for neuronal damage. The aim of this review is to summarize, clarify, and evaluate the potential significance and relationship between YKL-40 and NSE as biomarkers in the monitoring and prognosis of a set of neurological diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and multiple sclerosis. YKL-40 appears to be a more reliable biomarker in neurological diseases than NSE. The more prominent expression pattern of YKL-40 could be explained with the more obvious involvement of glial cells in pathological processes accompanying each neurodegenerative disease, whereas reduced NSE levels are likely related to low metabolic activity and increased death of neurons.

Astrocyte Biomarkers in Alzheimer Disease: A Systematic Review and Meta-analysis

OBJECTIVE

To perform a systematic review and meta-analysis to determine whether fluid and imaging astrocyte biomarkers are altered in Alzheimer disease (AD).

METHODS

PubMed and Web of Science databases were searched for articles reporting fluid or imaging astrocyte biomarkers in AD. Pooled effect sizes were determined with standardized mean differences (SMDs) using the Hedge G method with random effects to determine biomarker performance. Adapted questions from the Quality Assessment of Diagnostic Accuracy Studies were applied for quality assessment. A protocol for this study has been previously registered in PROSPERO (registration number: CRD42020192304).

RESULTS

The initial search identified 1,425 articles. After exclusion criteria were applied, 33 articles (a total of 3,204 individuals) measuring levels of glial fibrillary acidic protein (GFAP), S100B, chitinase-3-like protein 1 (YKL-40), and aquaporin 4 in the blood and CSF, as well as monoamine oxidase-B indexed by PET 11C-deuterium-l-deprenyl, were included. GFAP (SMD 0.94, 95% confidence interval [CI] 0.71-1.18) and YKL-40 (SMD 0.76, 95% CI 0.63-0.89) levels in the CSF and S100B levels in the blood (SMD 2.91, 95% CI 1.01-4.8) were found to be significantly increased in patients with AD.

CONCLUSIONS

Despite significant progress, applications of astrocyte biomarkers in AD remain in their early days. This meta-analysis demonstrated that astrocyte biomarkers are consistently altered in AD and supports further investigation for their inclusion in the AD clinical research framework for observational and interventional studies.

Right Frontoinsular Cortex: A Potential Imaging Biomarker to Evaluate T2DM-Induced Cognitive Impairment

Cognitive impairment in type 2 diabetes mellitus (T2DM) is associated with functional and structural abnormalities in the intrinsic brain network. The salience network (SN) is a neurocognitive network that maintains normal cognitive function, but it has received little attention in T2DM. We explored SN changes in patients with T2DM with normal cognitive function (DMCN) and in patients with T2DM with mild cognitive impairment (DMCI). Sixty-five T2DM patients and 31 healthy controls (HCs) underwent a neuropsychological assessment, independent component analysis (ICA), and voxel-based morphometry (VBM) analysis. The ICA extracted the SN for VBM to compare SN functional connectivity (FC) and gray matter (GM) volume (GMV) between groups. A correlation analysis examined the relationship between abnormal FC and GMV and clinical/cognitive variables. Compared with HCs, DMCN patients demonstrated increased FC in the left frontoinsular cortex (FIC), right anterior insula, and putamen, while DMCI patients demonstrated decreased right middle/inferior frontal gyrus FC. Compared with DMCN patients, DMCI patients showed decreased right FIC FC. There was no significant difference in SN GMV in DMCN and DMCI patients compared with HCs. FIC GMV was decreased in the DMCI patients compared with DMCN patients. In addition, right FIC FC and SN GMV positively correlated with Montreal Cognitive Assessment and Mini-Mental State Examination (MMSE) scores. These findings indicate that changes in SN FC, and GMV are complex non-linear processes accompanied by increased cognitive dysfunction in patients with T2DM. The right FIC may be a useful imaging biomarker for supplementary assessment of early cognitive dysfunction in patients with T2DM.

Plasma pTau181 predicts cortical brain atrophy in aging and Alzheimer's disease

BACKGROUND

To investigate the association of plasma pTau181, assessed with a new immunoassay, with neurodegeneration of white matter and gray matter cross-sectionally and longitudinally, in aging and Alzheimer's disease.

METHODS

Observational data was obtained from the Alzheimer's Disease Neuroimaging Initiative, in which participants underwent plasma assessment and magnetic resonance imaging. Based on their clinical diagnosis, participants were classified as cognitively unimpaired and cognitively impaired. Linear regressions and linear mixed-effect models were used to test the cross-sectional and longitudinal associations between baseline plasma pTau181 and neurodegeneration using voxel-based morphometry.

RESULTS

We observed a negative correlation at baseline between plasma pTau181 and gray matter volume in cognitively unimpaired individuals. In cognitively impaired individuals, we observed a negative association between plasma pTau181 and both gray and white matter volume. In longitudinal analyses conducted in the cognitively unimpaired group, plasma pTau181 was negatively correlated with gray matter volume, starting 36 months after baseline assessments. Finally, in cognitively impaired individuals, plasma pTau181 concentrations were negatively correlated with both gray and white matter volume as early as 12 months after baseline, and neurodegeneration increased in an incremental manner until 48 months.

CONCLUSIONS

Higher levels of plasma pTau181 correlate with neurodegeneration and predict further brain atrophy in aging and Alzheimer's disease. Plasma pTau181 may be useful in predicting AD-related neurodegeneration, comparable to positron emission tomography or cerebrospinal fluid assessment with high specificity for AD neurodegeneration.

Fluid Biomarkers in Clinical Trials for Alzheimer's Disease: Current and Future Application

Alzheimer's disease (AD) research is entering a unique moment in which enormous information about the molecular basis of this disease is being translated into therapeutics. However, almost all drug candidates have failed in clinical trials over the past 30 years. These many trial failures have highlighted a need for the incorporation of biomarkers in clinical trials to help improve the trial design. Fluid biomarkers measured in cerebrospinal fluid and circulating blood, which can reflect the pathophysiological process in the brain, are becoming increasingly important in AD clinical trials. In this review, we first succinctly outline a panel of fluid biomarkers for neuropathological changes in AD. Then, we provide a comprehensive overview of current and future application of fluid biomarkers in clinical trials for AD. We also summarize the many challenges that have been encountered in efforts to integrate fluid biomarkers in clinical trials, and the barriers that have begun to be overcome. Ongoing research efforts in the field of fluid biomarkers will be critical to make significant progress in ultimately unveiling disease-modifying therapies in AD.

Clinical Utility of the Pathogenesis-Related Proteins in Alzheimer's Disease

Research on the Aβ cascade and alternations of biomarkers in neuro-inflammation, synaptic dysfunction, and neuronal injury followed by Aβ have progressed. But the question is how to use the biomarkers. Here, we examine the evidence and pathogenic implications of protein interactions and the time order of alternation. After the deposition of Aβ, the change of tau, neurofilament light chain (NFL), and neurogranin (Ng) is the main alternation and connection to others. Neuro-inflammation, synaptic dysfunction, and neuronal injury function is exhibited prior to the structural and metabolic changes in the brain following Aβ deposition. The time order of such biomarkers compared to the tau protein is not clear. Despite the close relationship between biomarkers and plaque Aβ deposition, several factors favor one or the other. There is an interaction between some proteins that can predict the brain amyloid burden. The Aβ cascade hypothesis could be the pathway, but not all subjects suffer from Alzheimer's disease (AD) within a long follow-up, even with very elevated Aβ. The interaction of biomarkers and the time order of change require further research to identify the right subjects and right molecular target for precision medicine therapies.

Chitinase-3 like-protein-1 function and its role in diseases

Non-enzymatic chitinase-3 like-protein-1 (CHI3L1) belongs to glycoside hydrolase family 18. It binds to chitin, heparin, and hyaluronic acid, and is regulated by extracellular matrix changes, cytokines, growth factors, drugs, and stress. CHI3L1 is synthesized and secreted by a multitude of cells including macrophages, neutrophils, synoviocytes, chondrocytes, fibroblast-like cells, smooth muscle cells, and tumor cells. It plays a major role in tissue injury, inflammation, tissue repair, and remodeling responses. CHI3L1 has been strongly associated with diseases including asthma, arthritis, sepsis, diabetes, liver fibrosis, and coronary artery disease. Moreover, following its initial identification in the culture supernatant of the MG63 osteosarcoma cell line, CHI3L1 has been shown to be overexpressed in a wealth of both human cancers and animal tumor models. To date, interleukin-13 receptor subunit alpha-2, transmembrane protein 219, galectin-3, chemo-attractant receptor-homologous 2, and CD44 have been identified as CHI3L1 receptors. CHI3L1 signaling plays a critical role in cancer cell growth, proliferation, invasion, metastasis, angiogenesis, activation of tumor-associated macrophages, and Th2 polarization of CD4⁺ T cells. Interestingly, CHI3L1-based targeted therapy has been increasingly applied to the treatment of tumors including glioma and colon cancer as well as rheumatoid arthritis. This review summarizes the potential roles and mechanisms of CHI3L1 in oncogenesis and disease pathogenesis, then posits investigational strategies for targeted therapies.

Cerebrospinal Fluid YKL-40 and Chitotriosidase Levels in Frontotemporal Dementia Vary by Clinical, Genetic and Pathological Subtype

BACKGROUND

Chronic glial dysfunction may contribute to the pathogenesis of frontotemporal dementia (FTD). Cerebrospinal fluid (CSF) levels of glia-derived proteins YKL-40 and chitotriosidase are increased in Alzheimer's disease (AD) but have not been explored in detail across the spectrum of FTD.

METHODS

We investigated whether CSF YKL-40 and chitotriosidase levels differed between FTD patients and controls, across different clinical and genetic subtypes of FTD, and between individuals with a clinical FTD syndrome due to AD versus non-AD (frontotemporal lobar degeneration, FTLD) pathology (based on CSF neurodegenerative biomarkers). Eighteen healthy controls and 64 people with FTD (behavioural variant FTD, n = 20; primary progressive aphasia [PPA], n = 44: nfvPPA, n = 16, svPPA, n = 11, lvPPA, n = 14, PPA-NOS, n = 3) were included. 10/64 had familial FTD, with mutations in GRN(n = 3), MAPT(n = 4), or C9orf72 (n = 3). 15/64 had neurodegenerative biomarkers consistent with AD pathology. Levels were measured by immunoassay and compared using multiple linear regressions. We also examined relationships of YKL-40 and chitotriosidase with CSF total tau (T-tau), phosphorylated tau 181 (P-tau) and β-amyloid 1-42 (Aβ42), with each other, and with age and disease du-ration.

RESULTS

CSF YKL-40 and chitotriosidase levels were higher in FTD, particularly lvPPA (both) and nfvPPA (YKL-40), compared with controls. GRN mutation carriers had higher levels of both proteins than controls and C9orf72 expansion carriers, and YKL-40 was higher in MAPT mutation carriers than controls. Individuals with underlying AD pathology had higher YKL-40 and chitotriosidase levels than both controls and those with likely FTLD pathology. CSF YKL-40 and chitotriosidase levels were variably associated with levels of T-tau, P-tau and Aβ42, and with each other, depending on clinical syndrome and underlying pathology. CSF YKL-40 but not chitotriosidase was associated with age, but not disease duration.

CONCLUSION

CSF YKL-40 and chitotriosidase levels are increased in individuals with clinical FTD syndromes, particularly due to AD pathology. In a preliminary analysis of genetic groups, levels of both proteins are found to be highly elevated in FTD due to GRN mutations, while YKL-40 is increased in individuals with MAPT mutations. As glia-derived protein levels generally correlate with T-tau and P-tau levels, they may reflect the glial response to neurodegeneration in FTLD.

Association of plasma YKL-40 with brain amyloid-β levels, memory performance, and sex in subjective memory complainers

Neuroinflammation, a key early pathomechanistic alteration of Alzheimer's disease, may represent either a detrimental or a compensatory mechanism or both (according to the disease stage). YKL-40, a glycoprotein highly expressed in differentiated glial cells, is a candidate biomarker for in vivo tracking neuroinflammation in humans. We performed a longitudinal study in a monocentric cohort of cognitively healthy individuals at risk for Alzheimer's disease exploring whether age, sex, and the apolipoprotein E ε4 allele affect plasma YKL-40 concentrations. We investigated whether YKL-40 is associated with brain amyloid-β (Aβ) deposition, neuronal activity, and neurodegeneration as assessed via neuroimaging biomarkers. Finally, we investigated whether YKL-40 may predict cognitive performance. We found an age-associated increase of YKL-40 and observed that men display higher concentrations than women, indicating a potential sexual dimorphism. Moreover, YKL-40 was positively associated with memory performance and negatively associated with brain Aβ deposition (but not with metabolic signal). Consistent with translational studies, our results suggest a potentially protective effect of glia on incipient brain Aβ accumulation and neuronal homeostasis.

Higher CSF sTREM2 and microglia activation are associated with slower rates of beta-amyloid accumulation

Microglia activation is the brain's major immune response to amyloid plaques in Alzheimer's disease (AD). Both cerebrospinal fluid (CSF) levels of soluble TREM2 (sTREM2), a biomarker of microglia activation, and microglia PET are increased in AD; however, whether an increase in these biomarkers is associated with reduced amyloid-beta (Aβ) accumulation remains unclear. To address this question, we pursued a two-pronged translational approach. Firstly, in non-demented and demented individuals, we tested CSF sTREM2 at baseline to predict (i) amyloid PET changes over ∼2 years and (ii) tau PET cross-sectionally assessed in a subset of patients. We found higher CSF sTREM2 associated with attenuated amyloid PET increase and lower tau PET. Secondly, in the App^NL-G-F mouse model of amyloidosis, we studied baseline ¹⁸ F-GE180 microglia PET and longitudinal amyloid PET to test the microglia vs. Aβ association, without any confounding co-pathologies often present in AD patients. Higher microglia PET at age 5 months was associated with a slower amyloid PET increase between ages 5-to-10 months. In conclusion, higher microglia activation as determined by CSF sTREM2 or microglia PET shows protective effects on subsequent amyloid accumulation.

Sleep Disturbances in MCI and AD: Neuroinflammation as a Possible Mediating Pathway

Mild cognitive impairment (MCI) and Alzheimer's disease (AD) affect a high proportion of the elderly population with an increasing prevalence. Sleep disturbances are frequent in those with MCI and AD. This review summarizes existing research on sleep disturbances and neuroinflammation in MCI and AD. Although strong evidence supports various pathways linking sleep and AD pathology, the temporal direction of this central relationship is not yet known. Improved understanding of sleep disturbance and neuroinflammation in MCI and AD may aid in the identification of targets for their prevention.

New fluid biomarkers tracking non-amyloid-β and non-tau pathology in Alzheimer's disease

Cerebrospinal fluid (CSF) biomarkers based on the core pathological proteins associated with Alzheimer’s disease (AD), i.e., amyloid-β (Aβ) and tau protein, are widely regarded as useful diagnostic biomarkers. However, a lack of biomarkers for monitoring the treatment response and indexing clinical severity has proven to be problematic in drug trials targeting Aβ. Therefore, new biomarkers are needed to track non-Aβ and non-tau pathology. Many proteins involved in the pathophysiological progression of AD have shown promise as new biomarkers. Neurodegeneration- and synapse-related biomarkers in CSF (e.g., neurofilament light polypeptide [NFL], neurogranin, and visinin-like protein 1) and blood (e.g., NFL) aid prediction of AD progress, as well as early diagnosis. Neuroinflammation, lipid dysmetabolism, and impaired protein clearance are considered important components of AD pathophysiology. Inflammation-related proteins in the CSF, such as progranulin, intercellular adhesion molecule 1, and chitinase-3-like protein 1 (YKL-40), are useful for the early detection of AD and can represent clinical severity. Several lipid metabolism-associated biomarkers and protein clearance-linked markers have also been suggested as candidate AD biomarkers. Combinations of subsets of new biomarkers enhance their utility in terms of broadly characterizing AD-associated pathological changes, thereby facilitating precise selection of susceptible patients and comprehensive monitoring of the treatment response. This approach could facilitate the development of effective treatments for AD.

Finding new biomarkers for Alzheimer’s disease (AD) may help in tracking disease progression and identifying optimal patient-specific treatments. Although useful markers are available for diagnosis of AD, they are unreliable for tracking disease progression. Looking for better ways to track disease progression, Sun Ah Park at the Ajou University School of Medicine, Suwon, South Korea, and coworkers have reviewed alternative AD markers. They report that several markers for axonal degeneration, synaptic loss, brain inflammation and lipid metabolism show promise for tracking AD. Some of these markers can be obtained from blood samples, which are minimally invasive to collect. Use of combinations of markers is especially promising for estimating a patient’s disease stage. These results will contribute to developing tailored treatments for this common cause of dementia.

GFAP Mutations in Astrocytes Impair Oligodendrocyte Progenitor Proliferation and Myelination in an hiPSC Model of Alexander Disease

Alexander disease (AxD) is a leukodystrophy that primarily affects astrocytes and is caused by mutations in the astrocytic filament gene GFAP. While astrocytes are thought to have important roles in controlling myelination, AxD animal models do not recapitulate critical myelination phenotypes and it is therefore not clear how AxD astrocytes contribute to leukodystrophy. Here, we show that AxD patient iPSC-derived astrocytes recapitulate key features of AxD pathology such as GFAP aggregation. Moreover, AxD astrocytes inhibit proliferation of human iPSC-derived oligodendrocyte progenitor cells (OPCs) in co-culture and reduce their myelination potential. CRISPR/Cas9-based correction of GFAP mutations reversed these phenotypes. Transcriptomic analyses of AxD astrocytes and postmortem brains identified CHI3L1 as a key mediator of AxD astrocyte-induced inhibition of OPC activity. Thus, this iPSC-based model of AxD not only recapitulates patient phenotypes not observed in animal models, but also reveals mechanisms underlying disease pathology and provides a platform for assessing therapeutic interventions.

The Influence of Cerebrospinal Fluid Abnormalities and APOE 4 on PHF-Tau Protein: Evidence From Voxel Analysis and Graph Theory

Mild cognitive impairment (MCI) is a transitional state between the cognitive changes in normal aging and Alzheimer’s disease (AD), which induces abnormalities in specific brain regions. Previous studies showed that paired helical filaments Tau (PHF-Tau) protein is a potential pathogenic protein which may cause abnormal brain function and structure in MCI and AD patients. However, the understanding of the PHF-Tau protein network in MCI patients is limited. In this study, 225 subjects with PHF-Tau Positron Emission Tomography (PET) images were divided into four groups based on whether they carried Apolipoprotein E ε4 (APOE 4) or abnormal cerebrospinal fluid Total-Tau (CSF T-Tau). They are two important pathogenic factors that might cause cognitive function impairment. The four groups were: individuals harboring CSF T-Tau pathology but no APOE 4 (APOE 4−T+); APOE 4 carriers with normal CSF T-Tau (APOE 4+T−); APOE 4 carriers with abnormal CSF T-Tau (APOE 4+T+); and APOE 4 noncarriers with abnormal CSF T-Tau (APOE 4−T−). We explored the topological organization of PHF-Tau networks in these four groups and calculated five kinds of network properties: clustering coefficient, shortest path length, Q value of modularity, nodal centrality and degree. Our findings showed that compared with APOE 4−T− group, the other three groups showed different alterations in the clustering coefficient, shortest path length, Q value of modularity, nodal centrality and degree. Simultaneously, voxel-level analysis was conducted and the results showed that compared with APOE 4−T− group, the other three groups were found increased PHF-Tau distribution in some brain regions. For APOE 4+T+ group, positive correlation was found between the value of PHF-Tau distribution in altered regions and Functional Assessment Questionnaire (FAQ) score. Our results indicated that the effects of APOE 4 and abnormal CSF T-Tau may induce abnormalities of PHF-Tau protein and APOE 4 has a greater impact on PHF-Tau than abnormal CSF T-Tau. Our results may be particularly helpful in uncovering the pathophysiology underlying the cognitive dysfunction in MCI patients.

Cerebrospinal fluid biomarkers for understanding multiple aspects of Alzheimer's disease pathogenesis

Alzheimer's disease (AD) is a multifactorial age-related brain disease. Numerous pathological events run forth in the brain leading to AD. There is an initial long, dormant phase before the clinical symptoms become evident. There is a need to diagnose the disease at the preclinical stage since therapeutic interventions are most likely to be effective if initiated early. Undoubtedly, the core cerebrospinal fluid (CSF) biomarkers have a good diagnostic accuracy and have been used in clinical trials as end point measures. However, looking into the multifactorial nature of AD and the overlapping pathology with other forms of dementia, it is important to integrate the core CSF biomarkers with a broader panel of other biomarkers reflecting different aspects of pathology. The review is focused upon a panel of biomarkers that relate to different aspects of AD pathology, as well as various studies that have evaluated their diagnostic potential. The panel includes markers of neurodegeneration: neurofilament light chain and visinin-like protein (VILIP-1); markers of amyloidogenesis and brain amyloidosis: apolipoproteins; markers of inflammation: YKL-40 and monocyte chemoattractant protein 1; marker of synaptic dysfunction: neurogranin. These markers can highlight on the state and stage-associated changes that occur in AD brain with disease progression. A combination of these biomarkers would not only aid in preclinical diagnosis, but would also help in identifying early brain changes during the onset of disease. Successful treatment strategies can be devised by understanding the contribution of these markers in different aspects of disease pathogenesis.

CSF glial biomarkers YKL40 and sTREM2 are associated with longitudinal volume and diffusivity changes in cognitively unimpaired individuals

Cerebrospinal fluid (CSF) YKL40 and sTREM2 are astroglial and microglial activity biomarkers, respectively. We assessed whether CSF YKL40 and sTREM2 baseline levels are associated with longitudinal brain volume and diffusivity changes in cognitively unimpaired adults. Two brain MRI scans of 36 participants (57 to 78-years old, 12 male) were acquired in a 2-year interval. Aβ42, p-tau, YKL40 and sTREM2 concentrations in CSF were determined at baseline. We calculated gray and white matter volume changes per year maps (ΔGM and ΔWM, respectively) by means of longitudinal pairwise registration, and mean diffusivity variation per year (ΔMD) by subtraction. We checked voxel-wise for associations between ΔGM, ΔWM and ΔMD and baseline CSF level of YKL40 and sTREM2 and verified to what extent these associations were modulated by age (YKL40xAGE and sTREM2xAGE interactions). We found a positive association between ΔGM and YKL40 in the left inferior parietal region and no association between sTREM2 and ΔGM. Negative associations were also observed between ΔGM and YKL40xAGE (bilateral frontal areas, left precuneus and left postcentral and supramarginal gyri) and sTREM2xAGE (bilateral temporal and frontal cortex, putamen and left middle cingulate gyrus). We found negative associations between ΔWM and YKL40xAGE (bilateral superior longitudinal fasciculus) and sTREM2xAGE (bilateral superior longitudinal fasciculus, left superior corona radiata, retrolenticular external capsule and forceps minor, among other regions) but none between ΔWM and neither YKL40 nor sTREM2. ΔMD was positively correlated with YKL40 in right orbital region and negatively with sTREM2 in left lingual gyrus and precuneus. In addition, significant associations were found between ΔMD and YKL40xAGE (tail of left hippocampus and surrounding areas and right anterior cingulate gyrus) and sTREM2xAGE (right superior temporal gyrus). Areas showing statistically significant differences were disjoint in analyses involving YKL40 and sTREM2. These results suggest that glial biomarkers exert a relevant and distinct influence in longitudinal brain macro- and microstructural changes in cognitively unimpaired adults, which appears to be modulated by age. In younger subjects increased glial markers (both YKL40 and sTREM2) predict a better outcome, as indicated by a decrease in ΔGM and ΔWM and an increase in ΔMD, whereas in older subjects this association is inverted and higher levels of glial markers are associated with a poorer neuroimaging outcome.

Glial activation and inflammation along the Alzheimer's disease continuum

Background

Neuronal and glial cell interaction is essential for synaptic homeostasis and may be affected in Alzheimer’s disease (AD). We measured cerebrospinal fluid (CSF) neuronal and glia markers along the AD continuum, to reveal putative protective or harmful stage-dependent patterns of activation.

Methods

We included healthy controls (n = 36) and Aβ-positive (Aβ+) cases (as defined by pathological CSF amyloid beta 1-42 (Aβ42)) with either subjective cognitive decline (SCD, n = 19), mild cognitive impairment (MCI, n = 39), or AD dementia (n = 27). The following CSF markers were measured: a microglial activation marker—soluble triggering receptor expressed on myeloid cells 2 (sTREM2), a marker of microglial inflammatory reaction—monocyte chemoattractant protein-1 (MCP-1), two astroglial activation markers—chitinase-3-like protein 1 (YKL-40) and clusterin, a neuron-microglia communication marker—fractalkine, and the CSF AD biomarkers (Aβ42, phosphorylated tau (P-tau), total tau (T-tau)). Using ANOVA with planned comparisons, or Kruskal-Wallis tests with Dunn’s pairwise comparisons, CSF levels were compared between clinical groups and between stages of biomarker severity using CSF biomarkers for classification based on amyloid pathology (A), tau pathology (T), and neurodegeneration (N) giving rise to the A/T/N score.

Results

Compared to healthy controls, sTREM2 was increased in SCD (p < .01), MCI (p < .05), and AD dementia cases (p < .001) and increased in AD dementia compared to MCI cases (p < .05). MCP-1 was increased in MCI (p < .05) and AD dementia compared to both healthy controls (p < .001) and SCD cases (p < .01). YKL-40 was increased in dementia compared to healthy controls (p < .01) and MCI (p < .05). All of the CSF activation markers were increased in subjects with pathological CSF T-tau (A+T−N+ and A+T+N+), compared to subjects without neurodegeneration (A−T−N− and A+T−N−).

Discussion

Microglial activation as indicated by increased sTREM2 is present already at the preclinical SCD stage; increased MCP-1 and astroglial activation markers (YKL-40 and clusterin) were noted only at the MCI and AD dementia stages, respectively, and in Aβ+ cases (A+) with pathological T-tau (N+). Possible different effects of early and later glial activation need to be explored.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1399-2) contains supplementary material, which is available to authorized users.

YKL40 in sporadic amyotrophic lateral sclerosis: cerebrospinal fluid levels as a prognosis marker of disease progression

Amyotrophic lateral sclerosis (ALS) has variable clinical course and fatal outcome. Since inflammation plays a role in the pathogenesis of ALS, chitinase-3-like protein 1 or YKL40 has been assessed as putative biomarker of disease progression. YKL40 mRNA levels are increased in anterior horn of the spinal cord (P=0.004) in sporadic ALS (sALS) cases when compared with age-matched controls. These correlate with increased mRNA expression of microglial markers AIF1 and CD68 in the spinal cord in sALS (P=0.044 and P=0.000, respectively). YKL40 mRNA and protein expression had a tendency to increase in post-mortem frontal cortex area 8 (P=0.06 and P=0.08, respectively). Yet YKL40 immunoreactivity is restricted to a subpopulation of astrocytes in these regions. YKL40 protein levels, as revealed by enzyme-linked immunosorbent assay (ELISA), are significantly increased in the CSF in sALS (n=86) compared with age-matched controls (n=21) (P=0.045). Higher levels are found in patients with fast progression when compared with patients with slow and normal progression (P=0.008 and P=0.004, respectively), and correlates with ALS-FRS-R slope (P=0.000). Additionally, increased protein levels of neurofilament light chain (NF-L) are also found in sALS (P=0.000); highest values are found in patients with fast progression when compared with cases with slow and normal progression (P=0.005 and P=0.000, respectively), and also correlate with ALS-FRS-R slope (P=0.000). Pearson's correlation test linked positively the increased levels of YKL40 with increased NF-L levels (P=0.013). These data point to YKL40 and NF-L protein levels in the CSF as a good biomarker combination of disease progression in sALS.

Neuroinflammation in Alzheimer's disease: Pleiotropic roles for cytokines and neuronal pentraxins

Neuroinflammation is a potential factor speculated to underlie Alzheimer's disease (AD) etiopathogenesis and progression. The overwhelming focus in this area of research to date has been on the chronic upregulation of pro-inflammatory cytokines to understand how neuroinflammatory mechanisms contribute to neurodegeneration. Yet, it is important to understand the pleiotropic roles of these cytokines in modulating neuroinflammation in which they cannot be labeled as a strictly "good" or "bad" biomarker phenotype. As such, biomarkers with more precise functions are needed to better understand how neuroinflammation impacts the brain in AD. Neuronal pentraxins are a concentration- dependent group of pro- or anti- inflammatory cytokines. There is contradictory evidence of these pentraxins as being both neuroprotective and potentially detrimental in AD. Potential neuroprotective examples include their ability to predict AD-related outcomes such as cognition, memory function and synaptic refinement. This review will briefly outline the basis of AD and subsequently summarize findings for neuropathological mechanisms of neuroinflammation, roles for traditional pro-and anti-inflammatory cytokines, and data found thus far on the neuronal pentraxins.

Longitudinal decreases in multiple cerebrospinal fluid biomarkers of neuronal injury in symptomatic late onset Alzheimer's disease

INTRODUCTION

Individuals in early stages of Alzheimer's disease are a targeted population for secondary prevention trials aimed at preserving normal cognition. Understanding within-person biomarker(s) change over time is critical for trial enrollment and design.

METHODS

Longitudinal cerebrospinal fluid samples from the Alzheimer's Disease Neuroimaging Initiative were assayed for novel markers of neuronal/synaptic injury (visinin-like protein 1, Ng, and SNAP-25) and neuroinflammation (YKL-40) and compared with β amyloid 42, tau, and phospho-tau181. General linear mixed models were used to compare within-person rates of change in three clinical groups (cognitively normal, mild cognitive impairment, and Alzheimer's disease) further defined by β amyloid status.

RESULTS

Levels of injury markers were highly positively correlated. Despite elevated baseline levels as a function of clinical status and amyloid-positivity, within-person decreases in these measures were observed in the early symptomatic, amyloid-positive Alzheimer's disease group.

DISCUSSION

Knowledge of within-person biomarker change will impact interpretation of biomarker outcomes in clinical trials that are dependent on disease stage.

YKL-40 as a Potential Biomarker and a Possible Target in Therapeutic Strategies of Alzheimer's Disease

Background:

Growing body of evidence suggests that the pathogenesis of Alzheimer’s disease (AD), a progressing neurodegenerative condition, is not limited to the neuronal compartment, but also involves various immunological mechanisms. Insoluble Aβ aggregates in the brain can induce the activation of microglia, resulting in the synthesis of proinflammatory mediators, which further can stimulate astrocytic expression of YKL-40. Therefore, the aim of the current review is to present up-to-date data about the role of YKL-40 as a biomarker of AD as well as the possibility of therapeutic strategies targeting neuroinflammation.

Objective/Methods:

We searched PubMed articles for the terms “YKL-40”, “neurodegeneration”, “neuroinflammation” and “Alzheimer’s disease”, and included papers focusing on this review’s scope.

Results:

Recent studies indicate that CSF concentrations of YKL-40 were significantly higher in AD patients than in cognitively normal individuals and correlated with dementia biomarkers, such as tau proteins and amyloid beta. Determination of YKL-40 CSF concentration may be also helpful in differentiation between types of dementia and in the distinction of patients in the stable phase of MCI from those who progressed to dementia. Moreover, significantly increased levels of YKL-40 mRNA were found in AD brains in comparison with non-demented controls. Additionally, it was suggested that anti-inflammatory treatment might relief the symptoms of AD and slow its progression.

Conclusion:

Based on the recent knowledge, YKL-40 might be useful as a possible biomarker in the diagnosis and prognosis of AD. Modulation of risk factors and targeting of immune mechanisms, including systemic inflammation could lead to future preventive or therapeutic strategies for AD.

The Relationship between Markers of Inflammation and Degeneration in the Central Nervous System and the Blood-Brain Barrier Impairment in Alzheimer's Disease

BACKGROUND

It is known that YKL-40- a marker of glial inflammation, and VILIP-1- a marker of neuronal injury, reflect functional and structural changes in AD brains, although there is limited data concerning their potential influence on blood-brain barrier (BBB) homeostasis.

OBJECTIVE

Therefore, the aim of our study was to investigate the relationship between markers of inflammation and degeneration in the central nervous system (CNS) of patients with AD and mild cognitive impairment (MCI) as well as immunological response in CNS and BBB function.

METHODS

Cerebrospinal fluid (CSF) concentrations of proteins tested were determined in 45 AD patients, 18 MCI subjects, and 23 non-demented controls using ELISA method.

RESULTS

CSF concentrations of YKL-40 were significantly higher in MCI and AD patients, whereas CSF levels of VILIP-1 were statistically higher in the AD group as compared to the subjects without cognitive deficits. Elevated concentrations of YKL-40 correlated significantly with increased albumin quotient and decreased Aβ42/40 ratio in AD patients and with IgG quotient in the total study group. We did not find a relationship between VILIP-1 and immunological parameters reflecting BBB dysfunction and humoral immune response.

CONCLUSION

Our findings indicate that YKL-40 may contribute to decreased stability and increased permeability of BBB in AD patients. It is assumed that YKL-40 is implicated in the development of brain barriers, although its precise mechanism of action in the BBB disruption remains unrevealed. Further studies on larger groups of patients are required to confirm our hypothesis.

Transcriptome sequencing of neurologic diseases associated genes in HHV-6A infected human astrocyte

Human Herpesvirus 6 (HHV-6) has been involved in the development of several central nervous system (CNS) diseases, such as Alzheimer's disease, multiple sclerosis and glioma. In order to identify the pathogenic mechanism of HHV-6A infection, we carried out mRNA-seq study of human astrocyte HA1800 cell with HHV-6A GS infection. Using mRNA-seq analysis of HA1800-control cells with HA1800-HHV-6A GS cells, we identified 249 differentially expressed genes. After investigating these candidate genes, we found seven genes associated with two or more CNS diseases: CTSS, PTX3, CHI3L1, Mx1, CXCL16, BIRC3, and BST2. This is the first transcriptome sequencing study which showed the significant association of these genes between HHV-6A infection and neurologic diseases. We believe that our findings can provide a new perspective to understand the pathogenic mechanism of HHV-6A infection and neurologic diseases.

The Rationale Behind the New Alzheimer's Disease Conceptualization: Lessons Learned During the Last Decades

In the last decades, progress in neuroimaging techniques and cerebrospinal fluid assays has enabled the characterization of several Alzheimer's disease (AD) biomarkers. This knowledge has shifted the conceptualization of AD from a clinical-pathological construct, where its diagnosis required the presence of dementia with distinct pathologic features, toward a clinical-biological one that recognizes AD as a pathological continuum with a clinical picture that ranges from normal cognition to a dementia stage. Specifically, AD is now divided into three stages: preclinical (abnormal biomarkers and no or only subtle cognitive impairment), mild cognitive impairment or prodromal AD (abnormal pathophysiological biomarkers and episodic memory impairment), and dementia (abnormal biomarkers and clear cognitive and functional impairment). The possibility of assessing AD pathophysiology in vivo before the onset of clinical symptoms in the preclinical stage provides the unprecedented opportunity to intervene at earlier stages of the continuum in secondary prevention trials. Currently, large cohort studies of cognitively healthy participants are undergoing with the main aim of disentangling the natural history of AD to identify individuals with an increased risk of developing AD in the near future to be recruited in these clinical trials. In this paper, we review how the concept of AD has changed over the years as well as discuss the implications of this conceptual change.

YKL-40 in the brain and cerebrospinal fluid of neurodegenerative dementias

BACKGROUND

YKL-40 (also known as Chitinase 3-like 1) is a glycoprotein produced by inflammatory, cancer and stem cells. Its physiological role is not completely understood but YKL-40 is elevated in the brain and cerebrospinal fluid (CSF) in several neurological and neurodegenerative diseases associated with inflammatory processes. Yet the precise characterization of YKL-40 in dementia cases is missing.

METHODS

In the present study, we comparatively analysed YKL-40 levels in the brain and CSF samples from neurodegenerative dementias of different aetiologies characterized by the presence of cortical pathology and disease-specific neuroinflammatory signatures.

RESULTS

YKL-40 was normally expressed in fibrillar astrocytes in the white matter. Additionally YKL-40 was highly and widely expressed in reactive protoplasmic cortical and perivascular astrocytes, and fibrillar astrocytes in sporadic Creutzfeldt-Jakob disease (sCJD). Elevated YKL-40 levels were also detected in Alzheimer's disease (AD) but not in dementia with Lewy bodies (DLB). In AD, YKL-40-positive astrocytes were commonly found in clusters, often around β-amyloid plaques, and surrounding vessels with β-amyloid angiopathy; they were also distributed randomly in the cerebral cortex and white matter. YKL-40 overexpression appeared as a pre-clinical event as demonstrated in experimental models of prion diseases and AD pathology. CSF YKL-40 levels were measured in a cohort of 288 individuals, including neurological controls (NC) and patients diagnosed with different types of dementia. Compared to NC, increased YKL-40 levels were detected in sCJD (p < 0.001, AUC = 0.92) and AD (p < 0.001, AUC = 0.77) but not in vascular dementia (VaD) (p > 0.05, AUC = 0.71) or in DLB/Parkinson's disease dementia (PDD) (p > 0.05, AUC = 0.70). Further, two independent patient cohorts were used to validate the increased CSF YKL-40 levels in sCJD. Additionally, increased YKL-40 levels were found in genetic prion diseases associated with the PRNP-D178N (Fatal Familial Insomnia) and PRNP-E200K mutations.

CONCLUSIONS

Our results unequivocally demonstrate that in neurodegenerative dementias, YKL-40 is a disease-specific marker of neuroinflammation showing its highest levels in prion diseases. Therefore, YKL-40 quantification might have a potential for application in the evaluation of therapeutic intervention in dementias with a neuroinflammatory component.

Sex differences in the interacting roles of impulsivity and positive alcohol expectancy in problem drinking: A structural brain imaging study

Alcohol expectancy and impulsivity are implicated in alcohol misuse. However, how these two risk factors interact to determine problem drinking and whether men and women differ in these risk processes remain unclear. In 158 social drinkers (86 women) assessed for Alcohol Use Disorder Identification Test (AUDIT), positive alcohol expectancy, and Barratt impulsivity, we examined sex differences in these risk processes. Further, with structural brain imaging, we examined the neural bases underlying the relationship between these risk factors and problem drinking. The results of general linear modeling showed that alcohol expectancy best predicted problem drinking in women, whereas in men as well as in the combined group alcohol expectancy and impulsivity interacted to best predict problem drinking. Alcohol expectancy was associated with decreased gray matter volume (GMV) of the right posterior insula in women and the interaction of alcohol expectancy and impulsivity was associated with decreased GMV of the left thalamus in women and men combined and in men alone, albeit less significantly. These risk factors mediated the correlation between GMV and problem drinking. Conversely, models where GMV resulted from problem drinking were not supported. These new findings reveal distinct psychological factors that dispose men and women to problem drinking. Although mediation analyses did not determine a causal link, GMV reduction in the insula and thalamus may represent neural phenotype of these risk processes rather than the consequence of alcohol consumption in non-dependent social drinkers. The results add to the alcohol imaging literature which has largely focused on dependent individuals and help elucidate alterations in brain structures that may contribute to the transition from social to habitual drinking.

•

Alcohol expectancy (AE) and impulsivity are risk factors for problem drinking.

•

AE mediates the correlation between right insula GMV and problem drinking in women.

•

AE and impulsivity interacts to mediate left thalamus GMV and problem drinking in all.

•

Models where changes in GMV as a result of problem drinking are not supported.

The APOE ε4 genotype modulates CSF YKL-40 levels and their structural brain correlates in the continuum of Alzheimer's disease but not those of sTREM2

INTRODUCTION

Among other metabolic functions, the apolipoprotein E (APOE) plays a crucial role in neuroinflammation. We aimed at assessing whether APOE ε4 modulates levels of glial cerebrospinal fluid (CSF) biomarkers and their structural cerebral correlates along the continuum of Alzheimer's disease (AD).

METHODS

Brain magnetic resonance imaging (MRI) scans were acquired in 110 participants (49 control; 19 preclinical; 27 mild cognitive impairment [MCI] due to AD; 15 mild AD dementia) and CSF concentrations of YKL-40 and sTREM2 were determined. Differences in CSF biomarker concentrations and interactions in their association with gray-matter volume according to APOE ε4 status were sought after.

RESULTS

Preclinical and MCI carriers showed higher YKL-40 levels. There was a significant interaction in the association between YKL-40 levels and gray-matter volume according to ε4 status. No similar effects could be detected for sTREM2 levels.

DISCUSSION

Our findings are indicative of an increased astroglial activation in APOE ε4 carriers while both groups displayed similar levels of CSF AD core biomarkers.

High avidity HSV-1 antibodies correlate with absence of amnestic Mild Cognitive Impairment conversion to Alzheimer's disease

Amnestic Mild Cognitive Impairment (aMCI) is an alteration in cognitive abilities that can progress to Alzheimer's disease (AD), a condition in which herpes simplex type 1 (HSV-1) infection might play a pathogenetic role. Prognostic indexes capable of predicting aMCI conversion to AD are only partially understood. The objective of the present work is to verify whether HSV-1 immune responses is involved in conversion of aMCI to AD and correlate with grey matter brain morphometry. Two homogeneous groups of individuals who did or did not convert to AD over a 24-months period were selected after retrospective analysis of a cohort of patients with a diagnosis of aMCI. The selection of subjects was based on: a) clinical follow-up; b) neurocognitive evaluation at baseline and after 24months; c) availability of serum and DNA samples at baseline. 36 aMCI individuals, 21 of whom did (aMCI-converters) and 15 of whom did not (aMCI-non-converters) convert to AD, were included in the study. HSV-1 antibody (Ab) titers, avidity index and APOE genotyping were performed in all the enrolled individuals at baseline. Brain magnetic resonance imaging (MRI) by 1.5T scanner results at baseline were available as well in most (29/36) of these individuals. HSV-1-specific Ab titers were increased at baseline in aMCI-non-converters, and the avidity of these Ab was significantly higher in aMCI-non-converter compared to aMCI-converter (p=0.0018). Receiver operating characteristics analysis showed that HSV-1 avidity had a predictive value in distinguishing between aMCI-non-converters and aMCI-converters (p<0.0001). Notably, a positive correlation was detected as well between HSV-1 antibody titers and MRI-evaluated cortical volumes in the left hippocampus and amigdala (p_corr<0.05). In conclusion, stronger HSV-1-specific humoral responses associate with protection against AD conversion and better-preserved cortical volumes. These results reinforce the hypothesis for a role for HSV-1 in the pathogenesis of AD.

Cerebrospinal fluid sTREM2 levels are associated with gray matter volume increases and reduced diffusivity in early Alzheimer's disease

INTRODUCTION

TREM2 is involved in the regulation of inflammatory response and phagocytosis. A soluble fragment (sTREM2) is often found abnormally increased in cerebrospinal fluid (CSF) in Alzheimer's disease (AD).

METHODS

One hundred fourteen participants (45 control, 19 preclinical, 27 mild cognitive impairment [MCI], and 23 AD) underwent CSF sTREM2 determination and magnetic resonance imaging (MRI). We studied the association between CSF sTREM2, gray matter volume, and water motion diffusivity and anisotropy across groups.

RESULTS

In MCI patients, a positive correlation between CSF sTREM2 and gray matter volume was found in the bilateral inferior and middle temporal cortices, precuneus, the supramarginal, and angular gyri, after controlling by age, sex, and p-tau. A negative correlation with mean diffusivity was detected in overlapping regions, among others.

DISCUSSION

In early AD, augmented CSF sTREM2 levels correspond with cerebral MRI features typical of brain swelling, supporting a role for TREM2 in the regulation of the neuroinflammatory response to early neurodegeneration.

The roles of inflammation and immune mechanisms in Alzheimer's disease

The Alzheimer's Association's Research roundtable met in April 2015 to explore the role of neuroinflammatory mechanisms in the progression of Alzheimer's disease (AD). The ability of innate immune cells, particularly microglia and astrocytes, to mediate neuroinflammation in AD has been implicated as a significant contributor to disease pathogenesis. Adaptive immunity, which plays an important role in responding to injury and some diseases of the central nervous system, may contribute to neuroinflammation in AD as well. Communication between the central and peripheral immune systems may also be important in AD. An increased understanding of the physiology of the innate immune system may aid the identification of new therapeutic targets or mechanisms. The development of predictive animal models and translatable neuroinflammation biomarkers for AD would also facilitate the advancement of novel treatments for innate immunity. Important challenges impeding the advancement of new therapeutic agents and strategies to overcome them were discussed.