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ObjectiveTo investigate the role of neuroinflammation in asymptomatic and symptomatic amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) mutation carriers.MethodsThe neuroinflammatory markers chitotriosidase 1 (CHIT1), YKL-40 and glial fibrillary acidic protein (GFAP) were measured in cerebrospinal fluid (CSF) and blood samples from asymptomatic and symptomatic ALS/FTD mutation carriers, sporadic cases and controls by ELISA.ResultsCSF levels of CHIT1, YKL-40 and GFAP were unaffected in asymptomatic mutation carriers (n=16). CHIT1 and YKL-40 were increased in gALS (p<0.001, n=65) whereas GFAP was not affected. Patients with ALS carrying a CHIT1 polymorphism had lower CHIT1 concentrations in CSF (−80%) whereas this polymorphism had no influence on disease severity. In gFTD (n=23), increased YKL-40 and GFAP were observed (p<0.05), whereas CHIT1 was nearly not affected. The same profile as in gALS and gFTD was observed in sALS (n=64/70) and sFTD (n=20/26). CSF and blood concentrations correlated moderately (CHIT1, r=0.51) to weak (YKL-40, r=0.30, GFAP, r=0.39). Blood concentrations of these three markers were not significantly altered in any of the groups except CHIT1 in gALS of the Ulm cohort (p<0.05).ConclusionOur data indicate that neuroinflammation is linked to the symptomatic phase of ALS/FTD and shows a similar pattern in sporadic and genetic cases. ALS and FTD are characterised by a different neuroinflammatory profile, which might be one driver of the diverse presentations of the ALS/FTD syndrome.

Disease-modifying treatments are in development for Huntington's disease; crucial to their success is to identify a timepoint in a patient's life when there is a measurable biomarker of early neurodegeneration while clinical function is still intact. We aimed to identify this timepoint in a novel cohort of young adult premanifest Huntington's disease gene carriers (preHD) far from predicted clinical symptom onset. We did the Huntington's disease Young Adult Study (HD-YAS) in the UK. We recruited young adults with preHD and controls matched for age, education, and sex to ensure each group had at least 60 participants with imaging data, accounting for scan fails. Controls either had a family history of Huntington's disease but a negative genetic test, or no known family history of Huntington's disease. All participants underwent detailed neuropsychiatric and cognitive assessments, including tests from the Cambridge Neuropsychological Test Automated Battery and a battery assessing emotion, motivation, impulsivity and social cognition (EMOTICOM). Imaging (done for all participants without contraindications) included volumetric MRI, diffusion imaging, and multiparametric mapping. Biofluid markers of neuronal health were examined using blood and CSF collection. We did a cross-sectional analysis using general least-squares linear models to assess group differences and associations with age and CAG length, relating to predicted years to clinical onset. Results were corrected for multiple comparisons using the false discovery rate (FDR), with FDR <0·05 deemed a significant result. Data were obtained between Aug 2, 2017, and April 25, 2019. We recruited 64 young adults with preHD and 67 controls. Mean ages of participants were 29·0 years (SD 5·6) and 29·1 years (5·7) in the preHD and control groups, respectively. We noted no significant evidence of cognitive or psychiatric impairment in preHD participants 23·6 years (SD 5·8) from predicted onset (FDR 0·22–0·87 for cognitive measures, 0·31–0·91 for neuropsychiatric measures). The preHD cohort had slightly smaller putamen volumes (FDR=0·03), but this did not appear to be closely related to predicted years to onset (FDR=0·54). There were no group differences in other brain imaging measures (FDR >0·16). CSF neurofilament light protein (NfL), plasma NfL, and CSF YKL-40 were elevated in this far-from-onset preHD cohort compared with controls (FDR<0·0001, =0·01, and =0·03, respectively). CSF NfL elevations were more likely in individuals closer to expected clinical onset (FDR <0·0001). We report normal brain function yet a rise in sensitive measures of neurodegeneration in a preHD cohort approximately 24 years from predicted clinical onset. CSF NfL appears to be a more sensitive measure than plasma NfL to monitor disease progression. This preHD cohort is one of the earliest yet studied, and our findings could be used to inform decisions about when to initiate a potential future intervention to delay or prevent further neurodegeneration while function is intact. Wellcome Trust, CHDI Foundation.

INTRODUCTION We examined whether the aging suppressor KLOTHO gene's functionally advantageous KL‐VS variant (KL‐VS heterozygosity [KL‐VSHET]) confers resilience against deleterious effects of aging indexed by cerebrospinal fluid (CSF) biomarkers of neuroinflammation (interleukin‐6 [IL‐6], S100 calcium‐binding protein B [S100B], triggering receptor expressed on myeloid cells [sTREM2], chitinase‐3‐like protein 1 [YKL‐40], glial fibrillary acidic protein [GFAP]), neurodegeneration (total α‐synuclein [α‐Syn], neurofilament light chain protein), and synaptic dysfunction (neurogranin [Ng]). METHODS This Alzheimer disease risk‐enriched cohort consisted of 454 cognitively unimpaired adults (Mage = 61.5 ± 7.75). Covariate‐adjusted multivariate regression examined relationships between age (mean‐split[age ≥ 62]) and CSF biomarkers (Roche/NeuroToolKit), and whether they differed between KL‐VSHET (N = 122) and non‐carriers (KL‐VSNC; N = 332). RESULTS Older age was associated with a poorer biomarker profile across all analytes (Ps ≤ 0.03). In age‐stratified analyses, KL‐VSNC exhibited this same pattern (Ps ≤ 0.05) which was not significant for IL‐6, S100B, Ng, and α‐Syn (Ps ≥ 0.13) in KL‐VSHET. Although age‐related differences in GFAP, sTREM2, and YKL‐40 were evident for both groups (Ps ≤ 0.01), the effect magnitude was markedly stronger for KL‐VSNC. DISCUSSION Higher levels of neuroinflammation, neurodegeneration, and synaptic dysfunction in older adults were attenuated in KL‐VSHET. Highlights Older age was associated with poorer profiles across all cerebrospinal fluid biomarkers of neuroinflammation, neurodegeneration, and synaptic dysfunction. KLOTHO KL‐VS non‐carriers exhibit this same pattern, which is does not significantly differ between younger and older KL‐VS heterozygotes for interleukin‐6, S100 calcium‐binding protein B, neurogranin, and total α‐synuclein. Although age‐related differences in glial fibrillary acidic protein, triggering receptor expressed on myeloid cells, and chitinase‐3‐like protein 1 are evident for both KL‐VS groups, the magnitude of the effect is markedly stronger for KL‐VS non‐carriers. Higher levels of neuroinflammation, neurodegeneration, and synaptic dysfunction in older adults are attenuated in KL‐VS heterozygotes.

ObjectiveTo evaluate the classifier performance, clinical and biochemical correlations of cerebrospinal fluid (CSF) levels of the chitinase proteins Chitotriosidase-1 (CHIT1), Chitinase-3-like protein 1 (CHI3L1) and Chitinase-3-like protein 2 (CHI3L2) in amyotrophic lateral sclerosis (ALS).MethodsCSF levels of CHIT1, CHI3L1, CHI3L2, phosphorylated neurofilament heavy chain (pNFH) and C-reactive protein were measured by ELISA in a longitudinal cohort of patients with ALS (n=82), primary lateral sclerosis (PLS, n=10), ALS-mimic conditions (n=12), healthy controls (n=25) and asymptomatic carriers of ALS-causing genetic mutations (AGC; n=5).ResultsCSF CHIT1, CHI3L1 and CHI3L2 were elevated in patients with ALS compared with healthy controls (p<0.001) and ALS-mimics (CHIT1, p<0.001; CHI3L1, p=0.017; CHI3L2, p<0.001). CHIT1 and CHI3L2 were elevated in ALS compared with PLS (CHIT1, p=0.021; CHI3L1, p=0.417; CHI3L2, p<0.001). Chitinase levels were similar in AGCs and healthy controls. Chitinase proteins distinguished ALS from healthy controls (area under the curve (AUC): CHIT1 0.92; CHI3L1 0.80; CHI3L2 0.90), mimics (AUC: CHIT1 0.84; CHI3L1 0.73; CHI3L2 0.88) and, to a lesser extent, PLS (AUC: CHIT 0.73; CHI3L1 0.51; CHI3L2 0.82) but did not outperform pNFH. CHIT1 and CHI3L2 correlated with disease progression rate (Pearson’s r=0.49, p<0.001; r=0.42, p<0.001, respectively). CHI3L1 correlated with degree of cognitive dysfunction (r=−0.25, p=0.038). All chitinases correlated with pNFH. CHIT1 levels were associated with survival in multivariate models. Chitinase levels were longitudinally stable.ConclusionsCSF chitinase proteins may have limited value as independent diagnostic and stratification biomarkers in ALS, but offer a window into non-autonomous mechanisms of motor neuronal loss in ALS, specifically in assessing response to therapies targeting neuroinflammatory pathways.

Multiple sclerosis (MS) is characterized by heterogeneity in disease course and prediction of long-term outcome remains a major challenge. Here, we investigate five myeloid markers – CHIT1, CHI3L1, sTREM2, GPNMB and CCL18 – in the cerebrospinal fluid (CSF) at diagnostic lumbar puncture in a longitudinal cohort of 192 MS patients. Through mixed-effects and machine learning models, we show that CHIT1 is a robust predictor for faster disability progression. Integrative analysis of 11 CSF and 26 central nervous system (CNS) parenchyma single-cell/nucleus RNA sequencing samples reveals CHIT1 to be predominantly expressed by microglia located in active MS lesions and enriched for lipid metabolism pathways. Furthermore, we find CHIT1 expression to accompany the transition from a homeostatic towards a more activated, MS-associated cell state in microglia. Neuropathological evaluation in post-mortem tissue from 12 MS patients confirms CHIT1 production by lipid-laden phagocytes in actively demyelinating lesions, already in early disease stages. Altogether, we provide a rationale for CHIT1 as an early biomarker for faster disability progression in MS. Here, the authors provide evidence for the potential of CHIT1 concentration in the cerebrospinal fluid at diagnostic lumbar puncture as a biomarker for disability progression in multiple sclerosis (MS) as it reflects early microglial activation in active lesions of MS patients.

INTRODUCTION Semorinemab, an anti‐tau monoclonal antibody, was assessed in two Phase II trials for Alzheimer's disease (AD). Plasma and cerebrospinal fluid (CSF) biomarkers provided insights into the drug's potential mechanism of action. METHODS Qualified assays were used to measure biomarkers of tau, amyloidosis, glial activity, neuroinflammation, synaptic function, and neurodegeneration from participant samples in Tauriel (NCT03289143) and Lauriet (NCT03828747) Phase II trials. RESULTS Plasma phosphorylated Tau 181 (pTau181) and CSF chitinase‐3‐like protein 1 (YKL‐40) increased following semorinemab treatment in both studies. In Lauriet, increasing plasma glial fibrillary protein (GFAP) concentrations stabilized with semorinemab, while this was not observed in Tauriel. Other AD pathophysiology biomarkers showed no consistent response to semorinemab. DISCUSSION Increases in CSF YKL‐40 suggest that semorinemab may stimulate microglia activation in the presence of AD‐associated Tau pathology, but not in healthy controls. Stabilization of plasma GFAP in Lauriet indicates a possible impact on reactive gliosis in mild‐to‐moderate AD. Trial Registration: Tauriel ClinicalTrials.gov Identifier: NCT03289143. Lauriet ClinicalTrials.gov Identifier: NCT03828747. Phase 1 ClinicalTrials.gov Identifier: NCT02820896. Highlights AD pathophysiology biomarkers were measured to assess the mechanism of action. Semorinemab increased CSF YKL‐40 in participants with AD but not in healthy controls. Semorinemab possibly stabilized plasma GFAP in the Lauriet trial. Semorinemab treatment may activate microglia and moderate reactive gliosis.

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.

INTRODUCTION We investigated blood DNA methylation patterns associated with 15 well‐established cerebrospinal fluid (CSF) biomarkers of Alzheimer's disease (AD) pathophysiology, neuroinflammation, and neurodegeneration. METHODS We assessed DNA methylation in 885 blood samples from the European Medical Information Framework for Alzheimer's Disease (EMIF‐AD) study using the EPIC array. RESULTS We identified Bonferroni‐significant differential methylation associated with CSF YKL‐40 (five loci) and neurofilament light chain (NfL; seven loci) levels, with two of the loci associated with CSF YKL‐40 levels correlating with plasma YKL‐40 levels. A co‐localization analysis showed shared genetic variants underlying YKL‐40 DNA methylation and CSF protein levels, with evidence that DNA methylation mediates the association between genotype and protein levels. Weighted gene correlation network analysis identified two modules of co‐methylated loci correlated with several amyloid measures and enriched in pathways associated with lipoproteins and development. DISCUSSION We conducted the most comprehensive epigenome‐wide association study (EWAS) of AD‐relevant CSF biomarkers to date. Future work should explore the relationship between YKL‐40 genotype, DNA methylation, and protein levels in the brain. Highlights Blood DNA methylation was assessed in the EMIF‐AD MBD study. Epigenome‐wide association studies (EWASs) were performed for 15 Alzheimer's disease (AD)–relevant cerebrospinal fluid (CSF) biomarker measures. Five Bonferroni‐significant loci were associated with YKL‐40 levels and seven with neurofilament light chain (NfL). DNA methylation in YKL‐40 co‐localized with previously reported genetic variation. DNA methylation potentially mediates the effect of single‐nucleotide polymorphisms (SNPs) in YKL‐40 on CSF protein levels.

Neurofilament light chain protein (NfL) is currently the most accurate cerebrospinal fluid (CSF) biomarker in amyotrophic lateral sclerosis (ALS) in terms of both diagnostic and prognostic value, but the mechanism underlying its increase is still a matter of debate. Similarly, emerging CSF biomarkers of neurodegeneration and neuroinflammation showed promising results, although further studies are needed to clarify their clinical and pathophysiological roles. In the present study we compared the diagnostic accuracy of CSF NfL, phosphorylated (p)-tau/total (t)-tau ratio, chitinase-3-like protein 1 (YKL-40) and chitotriosidase 1 (CHIT1), in healthy controls ( n  = 43) and subjects with ALS ( n  = 80) or ALS mimics ( n  = 46). In ALS cases, we also investigated the association between biomarker levels and clinical variables, the extent of upper motor neuron (UMN) and lower motor neuron (LMN) degeneration, and denervation activity through electromyography (EMG). ALS patients showed higher levels of CSF NfL, YKL-40, CHIT1, and lower values of p-tau/t-tau ratio compared to both controls and ALS mimics. Among all biomarkers, NfL yielded the highest diagnostic performance (> 90% sensitivity and specificity) and was the best predictor of disease progression rate and survival in ALS. NfL levels showed a significant  correlation with the extent of LMN involvement, whereas YKL-40 levels increased together with the number of areas showing both UMN and LMN damage. EMG denervation activity did not correlate with any CSF biomarker change. These findings confirm the highest value of NfL among currently available CSF biomarkers for the diagnostic and prognostic assessment of ALS and contribute to the understanding of the pathophysiological and electrophysiological correlates of biomarker changes.

INTRODUCTION The role of neuroinflammation in preclinical Alzheimer's disease (AD) remains unclear. METHODS We assessed changes in microglial and astrocytic biomarkers in a well‐characterized cohort of 211 cognitively unimpaired individuals. Structural equation modeling was used to simultaneously assess all relationships among microglial and astrocytic responses and AD pathological events. RESULTS Plasma glial fibrillary acidic protein (GFAP) and cerebrospinal fluid (CSF) soluble triggering receptor expressed on myeloid cells 2 (sTREM2) were increased in preclinical AD. Plasma GFAP showed an inverse bidirectional relationship with CSF amyloid beta (Aβ)42/40. CSF sTREM2 directly influenced CSF phosphorylated tau‐181 (p‐tau181) and neurogranin, and correlated with CSF S100 calcium‐binding protein beta (S100β). CSF chitinase‐3‐like protein 1 (YKL‐40) mediated the association between CSF p‐tau181 and total tau (t‐tau), whereas CSF S100β and neurofilament light showed mutual influence. DISCUSSION Our findings suggest that microglial and astrocyte reactivity, measured through fluid biomarkers, occur early and impact the amyloid cascade on the preclinical Alzheimer´s continuum. Specifically, GFAP influences amyloid accumulation, sTREM2 promotes tau pathology, and YKL‐40 and S100β contribute to the progression of downstream neurodegenerative changes. Highlights Preclinical Alzheimer's disease (AD) showed increased levels of plasma glial fibrillary acidic protein (GFAP) and soluble triggering receptor expressed on myeloid cells 2 (sTREM2) compared to cerebrospinal fluid (CSF) in healthy subjects. Higher plasma GFAP levels was directly associated with lower CSF amyloid beta (Aβ)42/Aβ40. Higher CSF sTREM2 concentrations increased CSF phosphorylated tau‐181. Chitinase‐3‐like protein 1 (YKL‐40) mediated tau‐induced neurodegeneration. S100 calcium‐binding protein beta (S100β) was directly linked to higher neurofilament light (NfL) and showed a mutual relationship with sTREM2.