Cerebrospinal fluid neurofilament light chain mediates age-associated lower learning and memory in healthy adults.

Multiple cognitive domains, including learning, memory, and psychomotor speed, show significant reductions with age. Likewise, several cerebrospinal fluid (CSF) neurodegenerative biomarkers, including total tau (t-tau, a marker of neuronal body injury) and neurofilament light chain (NfL, a marker of axonal injury) show age-related increases in normal aging. In the current study, we aimed to investigate whether the age-effect within different cognitive domains was mediated by age-associated CSF markers for neurodegenerative changes. We fitted 10 mediation models using structural equation modeling to investigate this in a cohort of 137 healthy adults, aged 40-80 years, from the Norwegian Dementia Disease Initiation (DDI) study. Here, t-tau and NfL were defined as mediators between age and different cognitive tests. The models showed that NfL mediated the age-effect for CERAD learning and memory recall (learning: ß = -0.395, p < 0.05; recall: ß = -0.261, p < 0.01). No such effect was found in the other models. Our findings suggest that the age-related lower performance in verbal learning and memory may be linked to NfL-associated neurodegenerative changes in cognitively healthy adults.

Exploring the aging process of cognitively healthy adults by analyzing cerebrospinal fluid metabolomics using liquid chromatography-tandem mass spectrometry.

BACKGROUND: During biological aging, significant metabolic dysregulation in the central nervous system may lead to cognitive decline and neurodegeneration. However, the metabolomics of the aging process in cerebrospinal fluid (CSF) has not been thoroughly explored. METHODS: In this cohort study of CSF metabolomics using liquid chromatography-mass spectrometry (LC-MS), fasting CSF samples collected from 92 cognitively unimpaired adults aged 20-87 years without obesity or diabetes were analyzed. RESULTS: We identified 37 metabolites in these CSF samples with significant positive correlations with aging, including cysteine, pantothenic acid, 5-hydroxyindoleacetic acid (5-HIAA), aspartic acid, and glutamate; and two metabolites with negative correlations, asparagine and glycerophosphocholine. The combined alterations of asparagine, cysteine, glycerophosphocholine, pantothenic acid, sucrose, and 5-HIAA showed a superior correlation with aging (AUC = 0.982). These age-correlated changes in CSF metabolites might reflect blood-brain barrier breakdown, neuroinflammation, and mitochondrial dysfunction in the aging brain. We also found sex differences in CSF metabolites with higher levels of taurine and 5-HIAA in women using propensity-matched comparison. CONCLUSIONS: Our LC-MS metabolomics of the aging process in a Taiwanese population revealed several significantly altered CSF metabolites during aging and between the sexes. These metabolic alterations in CSF might provide clues for healthy brain aging and deserve further exploration.

Importance of CSF-based Aß clearance with age in humans increases with declining efficacy of blood-brain barrier/proteolytic pathways.

The kinetics of amyloid beta turnover within human brain is still poorly understood. We previously found a dramatic decline in the turnover of Aß peptides in normal aging. It was not known if brain interstitial fluid/cerebrospinal fluid (ISF/CSF) fluid exchange, CSF turnover, blood-brain barrier function or proteolysis were affected by aging or the presence of ß amyloid plaques. Here, we describe a non-steady state physiological model developed to decouple CSF fluid transport from other processes. Kinetic parameters were estimated using: (1) MRI-derived brain volumes, (2) stable isotope labeling kinetics (SILK) of amyloid-ß peptide (Aß), and (3) lumbar CSF Aß concentration during SILK. Here we show that changes in blood-brain barrier transport and/or proteolysis were largely responsible for the age-related decline in Aß turnover rates. CSF-based clearance declined modestly in normal aging but became increasingly important due to the slowing of other processes. The magnitude of CSF-based clearance was also lower than that due to blood-brain barrier function plus proteolysis. These results suggest important roles for blood-brain barrier transport and proteolytic degradation of Aß in the development Alzheimer's Disease in humans.

Association of a Total Cholesterol Polygenic Score with Cholesterol Levels and Pathological Biomarkers across the Alzheimer's Disease Spectrum.

Midlife hypercholesterolemia is a well-known risk factor for sporadic Alzheimer's disease (AD), and like AD, it is highly influenced by genetics with heritability estimates of 32-63%. We thus hypothesized that genetics underlying peripheral blood total cholesterol (TC) levels could influence the risk of developing AD. We created a weighted polygenic score (TC-PGS) using summary data from a meta-analysis of TC genome-wide association studies for evaluation in three independent AD-related cohorts spanning pre-clinical, clinical, and pathophysiologically proved AD. APOE-ε4 variant was purposely included in the analysis as it represents an already well-established genetic risk factor for both AD and circulating TC. We could vastly improve the performance of the score when considering p-value thresholds for inclusion in the score, sex, and statin use. This optimized score (p-value threshold of 1 × 10-6 for inclusion in the score) explained 18.2% of the variance in TC levels in statin free females compared to 6.9% in the entire sample and improved prediction of hypercholesterolemia (receiver operator characteristics analysis revealed area under the curve increase from 70.8% to 80.5%). The TC-PGS was further evaluated for association with AD risk and pathology. We found no association between the TC-PGS and either of the AD hallmark pathologies, assessed by cerebrospinal fluid levels of Aß-42, p-Tau, and t-Tau, and 18F-NAV4694 and 18F-AV-1451 positron emission tomography. Similarly, we found no association with the risk of developing amyloid pathology or becoming cognitively impaired in individuals with amyloid pathology.

Evaluation of Age-Dependent Immune Signatures in Patients With Multiple Sclerosis.

BACKGROUND AND OBJECTIVES: In MS, an age-related decline in disease activity and a decreased efficacy of disease-modifying treatment have been linked to immunosenescence, a state of cellular dysfunction associated with chronic inflammation. METHODS: To evaluate age-related immunologic alterations in MS, we compared immune signatures in peripheral blood (PB) and CSF by flow cytometry in patients with relapsing-remitting (RR) (PB n = 38; CSF n = 51) and primary progressive (PP) MS (PB n = 40; CSF n = 36) and respective controls (PB n = 40; CSF n = 85). RESULTS: Analysis revealed significant age-related changes in blood immune cell composition, especially in the CD8 T-cell compartment of healthy donors (HDs) and patients with MS. However, HDs displayed a strong age-dependent decline in the expression of the immunoregulatory molecules KLRG1, LAG3, and CTLA-4 on memory CD8 T cells, whereas this age-dependent reduction was completely abrogated in patients with MS. An age-dependent increase in the expression of the costimulatory molecule CD226 on memory CD8 T cells was absent in patients with MS. CD226 expression correlated with disability in younger (≤50 years) patients with MS. CSF analysis revealed a significant age-dependent decline in various immune cell populations in PPMS but not RRMS, suggesting a differential effect of aging on the intrathecal compartment in PPMS. DISCUSSION: Our data illustrate that aging in MS is associated with a dysbalance between costimulatory and immunoregulatory signals provided by CD8 T cells favoring a proinflammatory phenotype and, more importantly, a pattern of premature immune aging in the CD8 T-cell compartment of young patients with MS with potential implications for disease severity.

Metabolic drift in the aging nervous system is reflected in human cerebrospinal fluid.

Chronic diseases affecting the central nervous system (CNS) like Alzheimer's or Parkinson's disease typically develop with advanced chronological age. Yet, aging at the metabolic level has been explored only sporadically in humans using biofluids in close proximity to the CNS such as the cerebrospinal fluid (CSF). We have used an untargeted liquid chromatography high-resolution mass spectrometry (LC-HRMS) based metabolomics approach to measure the levels of metabolites in the CSF of non-neurological control subjects in the age of 20 up to 74. Using a random forest-based feature selection strategy, we extracted 69 features that were strongly related to age (page < 0.001, rage = 0.762, R2Boruta age = 0.764). Combining an in-house library of known substances with in silico chemical classification and functional semantic annotation we successfully assigned putative annotations to 59 out of the 69 CSF metabolites. We found alterations in metabolites related to the Cytochrome P450 system, perturbations in the tryptophan and kynurenine pathways, metabolites associated with cellular energy (NAD+, ADP), mitochondrial and ribosomal metabolisms, neurological dysfunction, and an increase of adverse microbial metabolites. Taken together our results point at a key role for metabolites found in CSF related to the Cytochrome P450 system as most often associated with metabolic aging.

Association of Aortic Stiffness With Biomarkers of Neuroinflammation, Synaptic Dysfunction, and Neurodegeneration.

OBJECTIVES: To test the hypothesis that increased aortic stiffening is associated with greater CSF evidence of core Alzheimer disease pathology (ß-amyloid [Aß], phosphorylated tau [p-tau]), neurodegeneration (total tau [t-tau]), synaptic dysfunction (neurogranin), neuroaxonal injury (neurofilament light [NFL]), and neuroinflammation (YKL-40, soluble triggering receptor expressed on myeloid cells 2 [sTREM2]), we analyzed pulse wave velocity (PWV) data and CSF data among older adults. METHODS: Participants free of stroke and dementia from the Vanderbilt Memory and Aging Project, an observational community-based study, underwent cardiac magnetic resonance to assess aortic PWV (meters per second) and lumbar puncture to obtain CSF. Linear regressions related aortic PWV to CSF Aß, p-tau, t-tau, neurogranin, NFL, YKL-40, and sTREM2 concentrations after adjustment for age, race/ethnicity, education, apolipoprotein (APOE) ε4 status, Framingham Stroke Risk Profile, and cognitive diagnosis. Models were repeated testing PWV interactions with age, diagnosis, APOE ε4, and hypertension on each biomarker. RESULTS: One hundred forty-six participants were examined (age 72 ± 6 years). Aortic PWV interacted with age on p-tau (ß = 0.31, p = 0.04), t-tau, (ß = 2.67, p = 0.05), neurogranin (ß = 0.94, p = 0.04), and sTREM2 (ß = 20.4, p = 0.05). Among participants >73 years of age, higher aortic PWV related to higher p-tau (ß = 2.4, p = 0.03), t-tau (ß = 19.3, p = 0.05), neurogranin (ß = 8.4, p = 0.01), and YKL-40 concentrations (ß = 7,880, p = 0.005). Aortic PWV had modest interactions with diagnosis on neurogranin (ß = -10.76, p = 0.03) and hypertension status on YKL-40 (ß = 18,020, p < 0.001). CONCLUSIONS: Among our oldest participants, ≥74 years of age, greater aortic stiffening is associated with in vivo biomarker evidence of neuroinflammation, tau phosphorylation, synaptic dysfunction, and neurodegeneration, but not amyloidosis. Central arterial stiffening may lead to cumulative cerebral microcirculatory damage and reduced blood flow delivery to tissue, resulting in neuroinflammation and neurodegeneration in more advanced age.

Spatial correlation maps of the hippocampus with cerebrospinal fluid biomarkers and cognition in Alzheimer's disease: A longitudinal study.

This study is an observational study that takes the existing longitudinal data from Alzheimer's disease Neuroimaging Initiative to examine the spatial correlation map of hippocampal subfield atrophy with CSF biomarkers and cognitive decline in the course of AD. This study included 421 healthy controls (HC), 557 patients of stable mild cognitive impairment (s-MCI), 304 Alzheimer's Disease (AD) patients, and 241 subjects who converted to be AD from MCI (c-MCI), and 6,525 MRI scans in a period from 2004 to 2019. Our findings revealed that all the hippocampal subfields showed their accelerated atrophy rate from cognitively normal aging to stable MCI and AD. The presubiculum, dentate gyrus, and fimbria showed greater atrophy beyond the whole hippocampus in the HC, s-MCI, and AD groups and corresponded to a greater decline of memory and attention in the s-MCI group. Moreover, the higher atrophy rates of the subiculum and CA2/3, CA4 were also associated with a greater decline in attention in the s-MCI group. Interestingly, patients with c-MCI showed that the presubiculum atrophy was associated with CSF tau levels and corresponded to the onset age of AD and a decline in attention in patients with c-MCI. These spatial correlation findings of the hippocampus suggested that the hippocampal subfields may not be equally impacted by normal aging, MCI, and AD, and their atrophy was selectively associated with declines in specific cognitive domains. The presubiculum atrophy was highlighted as a surrogate marker for the AD prognosis along with tau pathology and attention decline.

Age and the association between apolipoprotein E genotype and Alzheimer disease: A cerebrospinal fluid biomarker-based case-control study.

BACKGROUND: The ε4 allele of apolipoprotein E (APOE) gene and increasing age are two of the most important known risk factors for developing Alzheimer disease (AD). The diagnosis of AD based on clinical symptoms alone is known to have poor specificity; recently developed diagnostic criteria based on biomarkers that reflect underlying AD neuropathology allow better assessment of the strength of the associations of risk factors with AD. Accordingly, we examined the global and age-specific association between APOE genotype and AD by using the A/T/N classification, relying on the cerebrospinal fluid (CSF) levels of ß-amyloid peptide (A, ß-amyloid deposition), phosphorylated tau (T, pathologic tau), and total tau (N, neurodegeneration) to identify patients with AD. METHODS AND FINDINGS: This case-control study included 1,593 white AD cases (55.4% women; mean age 72.8 [range = 44-96] years) with abnormal values of CSF biomarkers from nine European memory clinics and the American Alzheimer's Disease Neuroimaging Initiative (ADNI) study. A total of 11,723 dementia-free controls (47.1% women; mean age 65.6 [range = 44-94] years) were drawn from two longitudinal cohort studies (Whitehall II and Three-City), in which incident cases of dementia over the follow-up were excluded from the control population. Odds ratio (OR) and population attributable fraction (PAF) for AD associated with APOE genotypes were determined, overall and by 5-year age categories. In total, 63.4% of patients with AD and 22.6% of population controls carried at least one APOE ε4 allele. Compared with non-ε4 carriers, heterozygous ε4 carriers had a 4.6 (95% confidence interval 4.1-5.2; p < 0.001) and ε4/ε4 homozygotes a 25.4 (20.4-31.2; p < 0.001) higher OR of AD in unadjusted analysis. This association was modified by age (p for interaction < 0.001). The PAF associated with carrying at least one ε4 allele was greatest in the 65-70 age group (69.7%) and weaker before 55 years (14.2%) and after 85 years (22.6%). The protective effect of APOE ε2 allele for AD was unaffected by age. Main study limitations are that analyses were based on white individuals and AD cases were drawn from memory centers, which may not be representative of the general population of patients with AD. CONCLUSIONS: In this study, we found that AD diagnosis based on biomarkers was associated with APOE ε4 carrier status, with a higher OR than previously reported from studies based on only clinical AD criteria. This association differs according to age, with the strongest effect at 65-70 years. These findings highlight the need for early interventions for dementia prevention to mitigate the effect of APOE ε4 at the population level.

Variability in Cerebrospinal Fluid MicroRNAs Through Life.

The development of the human brain starts in the first weeks of embryo differentiation. However, there are many relevant neurodevelopmental processes that take place after birth and during lifespan. Such a fine and changing scenario requires the coordinated expression of thousands of genes to achieve the proper specialization and inter-connectivity. In this context, microRNAs (miRNAs), which can modulate mRNA stability and translation, are gaining recognition for their involvement in both brain development and neurodevelopmental disorders. Therefore, cerebrospinal fluid (CSF) miRNAs should be perfectly differentiated in relevant age periods. In this study, we aimed to highlight the biological variability of miRNA expression in the CSF throughout life, which is also crucial for biomarker discovery in CNS pathologies, especially in children, where they are desperately needed. We analyzed the CSF microRNAome of 14 healthy children (aged 0-7.4 years) by smallRNA-Seq and compared it with previously published data in adults (N = 7) and elders (N = 11). miR-423-5p and miR-22-3p were overexpressed in the < 1 and > 3 years groups, respectively. Additionally, we detected 18 miRNAs that reached their highest peak of expression at different time-points during the lifespan and sets of miRNAs that were exclusively expressed in a specific age group. On the contrary, miR-191-5p showed stable expression in CSF from the first year of life. Our results remark the complex differential miRNA expression profile that can be observed through life, which underlines the need for including appropriate age-matched controls when the expression of CSF miRNAs is analyzed in different pathological contexts. Graphical abstract.

CSF biomarkers in Olmsted County: Evidence of 2 subclasses and associations with demographics.

OBJECTIVE: We studied interrelationships between CSF biomarkers and associations with APOE ε4 genotype, demographic variables, vascular variables, and clinical diagnosis in Olmsted County, Minnesota. METHODS: We included 774 Mayo Clinic Study of Aging participants (693 cognitively unimpaired [CU]; 71 with mild cognitive impairment [MCI]). CSF ß-amyloid 42 (Aß42), total tau (t-tau), and hyperphosphorylated tau (p-tau) were analyzed using Aß42 CSF, t-tau CSF, and p-tau (181P) CSF electrochemiluminescence immunoassays. Bivariate mixture models were used to evaluate latent classes. We used linear regression models to evaluate independent associations of APOE ε4, demographic factors, cardiovascular risk, and diagnosis with CSF biomarker levels. Results were weighted back to the Olmsted County population. RESULTS: Interrelationships between CSF Aß42 and p-tau/t-tau were consistent with 2 latent classes in the general population. In subgroup 1 (n = 547 [71%]), we found a strong positive correlation between Aß42 and p-tau (ρ = 0.81), while the correlation was much smaller in group 2 (ρ = 0.26, n = 227 [29%]). Group 2 was associated with older age, APOE ε4 genotype, a diagnosis of MCI, and elevated amyloid PET. Overall, APOE ε4 genotype and MCI were associated with Aß42, while age was associated with p-tau/t-tau. There were no associations with sex, education, or vascular risk. CONCLUSION: We hypothesize the population without dementia can be subdivided into participants with and without biological Alzheimer disease (AD) based on the combination of CSF Aß42 and p-tau/t-tau (represented also by the p-tau/t-tau/Aß42 ratio). In those without biological AD, common factors such as CSF dynamics may cause a positive correlation between CSF Aß42 and p-tau/t-tau, while AD leads to dissociation of these proteins.

Biomarker profiling beyond amyloid and tau: cerebrospinal fluid markers, hippocampal atrophy, and memory change in cognitively unimpaired older adults.

Brain changes occurring in aging can be indexed by biomarkers. We used cluster analysis to identify subgroups of cognitively unimpaired individuals (n = 99, 64-93 years) with different profiles of the cerebrospinal fluid biomarkers beta amyloid 1-42 (Aß42), phosphorylated tau (P-tau), total tau, chitinase-3-like protein 1 (YKL-40), fatty acid binding protein 3 (FABP3), and neurofilament light (NFL). Hippocampal volume and memory were assessed across multiple follow-up examinations covering up to 6.8 years. Clustering revealed one group (39%) with more pathological concentrations of all biomarkers, which could further be divided into one group (20%) characterized by tauopathy and high FABP3 and one (19%) by brain ß-amyloidosis, high NFL, and slightly higher YKL-40. The clustering approach clearly outperformed classification based on Aß42 and P-tau alone in prediction of memory decline, with the individuals with most tauopathy and FABP3 showing more memory decline, but not more hippocampal volume change. The results demonstrate that older adults can be classified based on biomarkers beyond amyloid and tau, with improved prediction of memory decline.

CSF amyloid is a consistent predictor of white matter hyperintensities across the disease course from aging to Alzheimer's disease.

This study investigated the relationship between white matter hyperintensities (WMH) and cerebrospinal fluid (CSF) Alzheimer's disease (AD) biomarkers. Subjects included 180 controls, 107 individuals with a significant memory concern, 320 individuals with early mild cognitive impairment, 171 individuals with late mild cognitive impairment, and 151 individuals with AD, with 3T MRI and CSF Aß1-42, total tau (t-tau), and phosphorylated tau (p-tau) data. Multiple linear regression models assessed the relationship between WMH and CSF Aß1-42, t-tau, and p-tau. Directionally, a higher WMH burden was associated with lower CSF Aß1-42 within each diagnostic group, with no evidence for a difference in the slope of the association across diagnostic groups (p = 0.4). Pooling all participants, this association was statistically significant after adjustment for t-tau, p-tau, age, diagnostic group, and APOE-ε4 status (p < 0.001). Age was the strongest predictor of WMH (partial R2~16%) compared with CSF Aß1-42 (partial R2~5%). There was no evidence for an association with WMH and either t-tau or p-tau. These data are supportive of a link between amyloid burden and presumed vascular pathology.

CSF Cytokines in Aging, Multiple Sclerosis, and Dementia.

Inflammation is a common process involved in aging, multiple sclerosis (MS), and age-related neurodegenerative disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD), but there is limited evidence for the effects of aging on inflammation in the central nervous system. We collected cerebrospinal fluid (CSF) from 105 healthy control subjects representing a wide age range (23-86), and analyzed levels of cytokines associated innate immunity (TNF-α) and different T-helper subtypes: interferon-gamma induced protein 10 (IP-10) for Th1, interleukin-10 (IL-10) for Th2, and interleukin 8 (IL-8/CXCL8) for Th17. We show that CSF levels of TNF-α, IP-10, and IL-8 all increased linearly with age, but levels of IL-10 demonstrated a U-shaped relationship with age. We further found greater age-related increases in TNF-α, IL-10, and IL-8 relative to increases in IP-10 levels, consistent with a shift from Th1 to other inflammatory phenotypes. Finally, when we analyzed the same four cytokines in people with neurological disorders, we found that MS and AD, but not PD or dementia with Lewy bodies, further accentuated the age-related shift from Th1- to non-Th1-related cytokines. We propose that CSF cytokine levels represent powerful surrogates of brain inflammation and aging, and some, but not all, neurological disorders accelerate the shift away from Th1 phenotypes.

The human central nervous system discharges carbon dioxide and lactic acid into the cerebrospinal fluid.

BACKGROUND: The central nervous system was previously thought to draw oxygen and nutrition from the arteries and discharge carbon dioxide and other metabolic wastes into the venous system. At present, the functional role of cerebrospinal fluid in brain metabolism is not fully known. METHODS: In this prospective observational study, we performed gas analysis on venous blood and cerebrospinal fluid simultaneously acquired from 16 consecutive preoperative patients without any known neurological disorders. RESULTS: The carbon dioxide partial pressure (pCO2) (p < 0.0001) and lactic acid level (p < 0.001) in the cerebrospinal fluid were significantly higher than those in the peripheral venous blood, suggesting that a considerable proportion of metabolic carbon dioxide and lactic acid is discharged from the central nervous system into the cerebrospinal fluid. The oxygen partial pressure (pO2) was much higher in the cerebrospinal fluid than in the venous blood, corroborating the conventional theory of cerebrospinal fluid circulatory dynamics. The pCO2 of the cerebrospinal fluid showed a strong negative correlation with age (R = - 0.65, p = 0.0065), but the other studied variables did not show significant correlation with age. CONCLUSION: Carbon dioxide and lactic acid are discharged into the circulating cerebrospinal fluid, as well as into the venules. The level of carbon dioxide in the cerebrospinal fluid significantly decreased with age.

Association of Cerebrospinal Fluid Neurofilament Light Protein With Risk of Mild Cognitive Impairment Among Individuals Without Cognitive Impairment.

Importance: Accumulating data suggest that elevated cerebrospinal fluid (CSF) neurofilament light (NfL) and neurogranin (Ng) levels are associated with cognitive decline and may be useful markers of neurodegeneration. However, to our knowledge, previous studies have not assessed these CSF markers in the community, evaluated them with regards to risk of mild cognitive impairment (MCI), or compared their prognostic value with CSF total tau (T-tau) or phosphorylated tau (P-tau). Objective: To determine (1) whether CSF NfL and Ng levels were associated with risk of MCI, (2) the effect size of these markers compared with CSF T-tau or P-tau for risk of MCI, and (3) whether CSF amyloid-ß (Aß42) modified these associations. Design, Setting and Participants: The analyses included 648 participants without cognitive impairment who were enrolled into the prospective population-based Mayo Clinic Study of Aging between January 2004 and December 2015 with available CSF data and at least 1 follow-up visit. Participants were followed up for a median of 3.8 years (interquartile range, 2.6-5.4 years). The CSF NfL and Ng levels were measured using an in-house sandwich enzyme-linked immunosorbent assay. The CSF Aß42, T-tau, and P-tau levels were measured with automated electrochemiluminescence immunoassays. Cox proportional hazards models, with age as the timescale, were used to assess the association between CSF NfL, Ng, Aß42, T-tau, or P-tau with risk of MCI after adjusting for sex, education, apolipoprotein E genotype, and the Charlson comorbidity index. To examine CSF Aß42 as an effect modifier, it was categorized into tertiles; the bottom tertile was defined as having elevated brain amyloid. Main Outcomes and Measures: Risk of MCI. Results: At baseline, the median age of the 648 participants without cognitive impairment was 72.3 years (range, 50.7-95.3 years) and 366 (56.5%) were men; 96 (14.8%) developed incident MCI. Compared with the bottom quartile, the top quartile of CSF NfL was associated with a 3.1-fold increased risk of MCI (hazard ratio, 3.13; 95% CI, 1.36-7.18) in multivariate models. Neither CSF T-tau, P-tau, nor Ng was associated with risk of MCI. There was no interaction between Aß42 and CSF NfL for risk of MCI. Conclusions and Relevance: Elevated CSF NfL levels but not CSF T-tau, P-tau or Ng are a risk factor for MCI in a community population and are independent of brain amyloid.

Biomarkers for tau pathology.

The aggregation of fibrils of hyperphosphorylated and C-terminally truncated microtubule-associated tau protein characterizes 80% of all dementia disorders, the most common neurodegenerative disorders. These so-called tauopathies are hitherto not curable and their diagnosis, especially at early disease stages, has traditionally proven difficult. A keystone in the diagnosis of tauopathies was the development of methods to assess levels of tau protein in vivo in cerebrospinal fluid, which has significantly improved our knowledge about these conditions. Tau proteins have also been measured in blood, but the importance of tau-related changes in blood is still unclear. The recent addition of positron emission tomography ligands to visualize, map and quantify tau pathology has further contributed with information about the temporal and spatial characteristics of tau accumulation in the living brain. Together, the measurement of tau with fluid biomarkers and positron emission tomography constitutes the basis for a highly active field of research. This review describes the current state of biomarkers for tau biomarkers derived from neuroimaging and from the analysis of bodily fluids and their roles in the detection, diagnosis and prognosis of tau-associated neurodegenerative disorders, as well as their associations with neuropathological findings, and aims to provide a perspective on how these biomarkers might be employed prospectively in research and clinical settings.

Combined effects of aquaporin-4 and hypoxia produce age-related hydrocephalus.

Aquaporin-4, present in ependymal cells, in glia limiting and abundantly in pericapillary astrocyte foot processes, and aquaporin-1, expressed in choroid plexus epithelial cells, play an important role in cerebrospinal fluid production and may be involved in the pathophysiology of age-dependent hydrocephalus. The finding that brain aquaporins expression is regulated by low oxygen tension led us to investigate how hypoxia and elevated levels of cerebral aquaporins may result in an increase in cerebrospinal fluid production that could be associated with a hydrocephalic condition. Here we have explored, in young and aged mice exposed to hypoxia, whether aquaporin-4 and aquaporin-1 participate in the development of age-related hydrocephalus. Choroid plexus, striatum, cortex and ependymal tissue were analyzed separately both for mRNA and protein levels of aquaporins. Furthermore, parameters such as total ventricular volume, intraventricular pressure, cerebrospinal fluid outflow rate, ventricular compliance and cognitive function were studied in wild type, aquaporin-1 and aquaporin-4 knock-out animals subjected to hypoxia or normoxia. Our data demonstrate that hypoxia is involved in the development of age-related hydrocephalus by a process that depends on aquaporin-4 channels as a main route for cerebrospinal fluid movement. Significant increases in aquaporin-4 expression that occur over the course of animal aging, together with a reduced cerebrospinal fluid outflow rate and ventricular compliance, contribute to produce more severe hydrocephalus related to hypoxic events in aged mice, with a notable impairment in cognitive function. These results indicate that physiological events and/or pathological conditions presenting with cerebral hypoxia/ischemia contribute to the development of chronic adult hydrocephalus.

Functional aspects of meningeal lymphatics in ageing and Alzheimer's disease.

Ageing is a major risk factor for many neurological pathologies, but its mechanisms remain unclear. Unlike other tissues, the parenchyma of the central nervous system (CNS) lacks lymphatic vasculature and waste products are removed partly through a paravascular route. (Re)discovery and characterization of meningeal lymphatic vessels has prompted an assessment of their role in waste clearance from the CNS. Here we show that meningeal lymphatic vessels drain macromolecules from the CNS (cerebrospinal and interstitial fluids) into the cervical lymph nodes in mice. Impairment of meningeal lymphatic function slows paravascular influx of macromolecules into the brain and efflux of macromolecules from the interstitial fluid, and induces cognitive impairment in mice. Treatment of aged mice with vascular endothelial growth factor C enhances meningeal lymphatic drainage of macromolecules from the cerebrospinal fluid, improving brain perfusion and learning and memory performance. Disruption of meningeal lymphatic vessels in transgenic mouse models of Alzheimer's disease promotes amyloid-ß deposition in the meninges, which resembles human meningeal pathology, and aggravates parenchymal amyloid-ß accumulation. Meningeal lymphatic dysfunction may be an aggravating factor in Alzheimer's disease pathology and in age-associated cognitive decline. Thus, augmentation of meningeal lymphatic function might be a promising therapeutic target for preventing or delaying age-associated neurological diseases.