Transmembrane protein 97 is a potential synaptic amyloid beta receptor in human Alzheimer's disease.

Synapse loss correlates with cognitive decline in Alzheimer's disease, and soluble oligomeric amyloid beta (Aß) is implicated in synaptic dysfunction and loss. An important knowledge gap is the lack of understanding of how Aß leads to synapse degeneration. In particular, there has been difficulty in determining whether there is a synaptic receptor that binds Aß and mediates toxicity. While many candidates have been observed in model systems, their relevance to human AD brain remains unknown. This is in part due to methodological limitations preventing visualization of Aß binding at individual synapses. To overcome this limitation, we combined two high resolution microscopy techniques: array tomography and Förster resonance energy transfer (FRET) to image over 1 million individual synaptic terminals in temporal cortex from AD (n = 11) and control cases (n = 9). Within presynapses and post-synaptic densities, oligomeric Aß generates a FRET signal with transmembrane protein 97. Further, Aß generates a FRET signal with cellular prion protein, and post-synaptic density 95 within post synapses. Transmembrane protein 97 is also present in a higher proportion of post synapses in Alzheimer's brain compared to controls. We inhibited Aß/transmembrane protein 97 interaction in a mouse model of amyloidopathy by treating with the allosteric modulator CT1812. CT1812 drug concentration correlated negatively with synaptic FRET signal between transmembrane protein 97 and Aß. In human-induced pluripotent stem cell derived neurons, transmembrane protein 97 is present in synapses and colocalizes with Aß when neurons are challenged with human Alzheimer's brain homogenate. Transcriptional changes are induced by Aß including changes in genes involved in neurodegeneration and neuroinflammation. CT1812 treatment of these neurons caused changes in gene sets involved in synaptic function. These data support a role for transmembrane protein 97 in the synaptic binding of Aß in human Alzheimer's disease brain where it may mediate synaptotoxicity.

Synaptic resilience is associated with maintained cognition during ageing.

INTRODUCTION: It remains unclear why age increases risk of Alzheimer's disease and why some people experience age-related cognitive decline in the absence of dementia. Here we test the hypothesis that resilience to molecular changes in synapses contribute to healthy cognitive ageing. METHODS: We examined post-mortem brain tissue from people in mid-life (n = 15), healthy ageing with either maintained cognition (n = 9) or lifetime cognitive decline (n = 8), and Alzheimer's disease (n = 13). Synapses were examined with high resolution imaging, proteomics, and RNA sequencing. Stem cell-derived neurons were challenged with Alzheimer's brain homogenate. RESULTS: Synaptic pathology increased, and expression of genes involved in synaptic signaling decreased between mid-life, healthy ageing and Alzheimer's. In contrast, brain tissue and neurons from people with maintained cognition during ageing exhibited decreases in synaptic signaling genes compared to people with cognitive decline. DISCUSSION: Efficient synaptic networks without pathological protein accumulation may contribute to maintained cognition during ageing.

Correlation between cerebrospinal fluid and plasma neurofilament light protein in treated HIV infection: results from the COBRA study.

Cerebrospinal fluid (CSF) neurofilament light protein (NfL) is a marker of central nervous system neuro-axonal injury. A novel, ultra-sensitive assay can determine plasma NfL. In untreated people-with-HIV (PWH), CSF and plasma NfL are strongly correlated. We aimed to assess this correlation in PWH on suppressive antiretroviral treatment (ART) and lifestyle-similar HIV-negative individuals enrolled into the COmorBidity in Relation to AIDS (COBRA) study. Differences in paired CSF (sandwich ELISA, UmanDiagnostics) and plasma (Simoa digital immunoassay, Quanterix™) NfL between PWH and HIV-negative participants were tested using Wilcoxon's test; associations were assessed using Pearson's correlation. CSF and plasma NfL, standardised to Z-scores, were included as dependent variables in linear regression models to identify factors independently associated with values in PWH and HIV-negative participants. Overall, 132 PWH (all with plasma HIV RNA < 50 copies/mL) and 79 HIV-negative participants were included. Neither CSF (median 570 vs 568 pg/mL, p = 0.37) nor plasma (median 10.7 vs 9.9 pg/mL, p = 0.15) NfL differed significantly between PWH and HIV-negative participants, respectively. CSF and plasma NfL correlated moderately, with no significant difference by HIV status (PWH: rho = 0.52; HIV-negative participants: rho = 0.47, p (interaction) = 0.63). In multivariable regression analysis, higher CSF NfL Z-score was statistically significantly associated with older age and higher CSF protein, and higher plasma NfL Z-score with older age, higher serum creatinine and lower bodyweight. In conclusion, in PWH on ART, the correlation between CSF and plasma NfL is moderate and similar to that observed in lifestyle-similar HIV-negative individuals. Consideration of renal function and bodyweight may be required when utilising plasma NfL.

Neurofilament light predicts neurological outcome after subarachnoid haemorrhage.

To improve outcome prediction following subarachnoid haemorrhage (SAH), we sought a biomarker integrating early brain injury and multiple secondary pathological processes in a prospective study of 42 non-traumatic SAH patients and 19 control individuals. Neurofilament light (NF-L) was elevated in CSF and serum following SAH. CSF and serum NF-L on Days 1-3 post-SAH strongly predicted modified Rankin score at 6 months, independent of World Federation of Neurosurgical Societies (WFNS) score. NF-L from Day 4 onwards also had a profound impact on outcome. To link NF-L to a SAH-specific pathological process, we investigated NF-L's relationship with extracellular haemoglobin. Most CSF haemoglobin was not complexed with haptoglobin, yet was able to be bound by exogenous haptoglobin i.e. haemoglobin was scavengeable. CSF scavengeable haemoglobin was strongly predictive of subsequent CSF NF-L. Next, we investigated NF-L efflux from the brain after SAH. Serum and CSF NF-L correlated positively. The serum/CSF NF-L ratio was lower in SAH versus control subjects, in keeping with glymphatic efflux dysfunction after SAH. CSF/serum albumin ratio was increased following SAH versus controls. The serum/CSF NF-L ratio correlated negatively with the CSF/serum albumin ratio, indicating that transfer of the two proteins across the blood-brain interface is dissociated. In summary, NF-L is a strong predictive marker for SAH clinical outcome, adding value to the WFNS score, and is a promising surrogate end point in clinical trials.

Familial Alzheimer's disease patient-derived neurons reveal distinct mutation-specific effects on amyloid beta.

Familial Alzheimer's disease (fAD) mutations alter amyloid precursor protein (APP) cleavage by γ-secretase, increasing the proportion of longer amyloidogenic amyloid-ß (Aß) peptides. Using five control induced pluripotent stem cell (iPSC) lines and seven iPSC lines generated from fAD patients, we investigated the effects of mutations on the Aß secretome in human neurons generated in 2D and 3D. We also analysed matched CSF, post-mortem brain tissue, and iPSCs from the same participant with the APP V717I mutation. All fAD mutation lines demonstrated an increased Aß42:40 ratio relative to controls, yet displayed varied signatures for Aß43, Aß38, and short Aß fragments. We propose four qualitatively distinct mechanisms behind raised Aß42:40. (1) APP V717I mutations alter γ-secretase cleavage site preference. Whereas, distinct presenilin 1 (PSEN1) mutations lead to either (2) reduced γ-secretase activity, (3) altered protein stability or (4) reduced PSEN1 maturation, all culminating in reduced γ-secretase carboxypeptidase-like activity. These data support Aß mechanistic tenets in a human physiological model and substantiate iPSC-neurons for modelling fAD.

CSF Beta-amyloid 1-42 Concentration Predicts Delirium Following Elective Arthroplasty Surgery in an Observational Cohort Study.

OBJECTIVE: To test the hypothesis that APOE ε4 status and cerebrospinal fluid (CSF) Aß42, T-tau and P-tau would independently predict the risk of postoperative delirium. BACKGROUND: Delirium following surgery is common and associated with adverse outcomes. Age and cognitive impairment are consistent risk factors for postoperative delirium. METHODS: This observational cohort study recruited 282 participants aged 65 years or older, without a diagnosis of dementia, admitted for primary elective hip or knee arthroplasty. Cognitive tests were undertaken preoperatively, blood and CSF were sampled at the time of spinal anesthesia, and participants were assessed daily postoperatively for delirium. RESULTS: Increasing age (P = 0.04), preoperative comorbidity (P = 0.03), type of surgery (P = 0.05), intravenous opioid usage (P = 0.04), and low CSF Aß42 (P < 0.01) were independent predictors of postoperative delirium. CONCLUSIONS: This study is the first to show an independent association between CSF Aß42 and delirium incidence in an elective surgical population, suggesting that postoperative delirium may indicate incipient Alzheimer disease.

Direct estimates of natural selection in Iberia indicate calcium absorption was not the only driver of lactase persistence in Europe.

Lactase persistence (LP) is a genetically determined trait whereby the enzyme lactase is expressed throughout adult life. Lactase is necessary for the digestion of lactose--the main carbohydrate in milk--and its production is downregulated after the weaning period in most humans and all other mammals studied. Several sources of evidence indicate that LP has evolved independently, in different parts of the world over the last 10,000 years, and has been subject to strong natural selection in dairying populations. In Europeans, LP is strongly associated with, and probably caused by, a single C to T mutation 13,910 bp upstream of the lactase (LCT) gene (-13,910*T). Despite a considerable body of research, the reasons why LP should provide such a strong selective advantage remain poorly understood. In this study, we examine one of the most widely cited hypotheses for selection on LP--that fresh milk consumption supplemented the poor vitamin D and calcium status of northern Europe's early farmers (the calcium assimilation hypothesis). We do this by testing for natural selection on -13,910*T using ancient DNA data from the skeletal remains of eight late Neolithic Iberian individuals, whom we would not expect to have poor vitamin D and calcium status because of relatively high incident UVB light levels. None of the eight samples successfully typed in the study had the derived T-allele. In addition, we reanalyze published data from French Neolithic remains to both test for population continuity and further examine the evolution of LP in the region. Using simulations that accommodate genetic drift, natural selection, uncertainty in calibrated radiocarbon dates, and sampling error, we find that natural selection is still required to explain the observed increase in allele frequency. We conclude that the calcium assimilation hypothesis is insufficient to explain the spread of LP in Europe.

Impact of interrupting antiretroviral therapy started during primary HIV-1 infection on plasma neurofilament light chain protein, a marker of neuronal injury: The SPARTAC trial.

Objective: Antiretroviral therapy (ART)-conferred suppression of HIV replication limits neuronal injury and inflammation. ART interruption tests efficacy in HIV cure trials and viral rebound after ART interruption may induce neuronal injury. We investigated the impact of protocol-defined ART interruption, commenced during primary HIV-1 infection (PHI) on a biomarker of neuro-axonal injury (neurofilament light protein (NfL)), and its associations with inflammation (D-dimer and interleukin-6 (IL-6)) and HIV-1 reservoir size (total HIV-1 DNA). Design: Retrospective study measuring plasma NfL in 83 participants enrolled in SPARTAC randomised to receive 48-weeks ART initiated during PHI, followed by ART interruption. Methods: NfL (Simoa immunoassay, Quanterix™) was measured before ART, after 48 weeks on ART, and 12 weeks after stopping ART. Plasma D-dimer and IL-6, and total HIV-1 DNA in peripheral CD4+ T-cells results were available in a subset of participants. Longitudinal NfL changes were assessed using mixed models, and associations with clinical and laboratory parameters using linear regression. Results: NfL decreased following 48-weeks ART (geometric mean 6.9 to 5.8 pg/mL, p = 0.006) with no further significant change up to 12-weeks post-stopping ART despite viral rebound in the majority of participants (median 1.7 to 3.9 plasma HIV-1 RNA log10 copies/mL). Higher baseline NfL was independently associated with higher plasma HIV-1 RNA (p = 0.020) and older age (p = 0.002). While NfL was positively associated with D-dimer (n = 48; p = 0.002), there was no significant association with IL-6 (n = 48) or total HIV-1 DNA (n = 51). Conclusions: Using plasma NfL as a surrogate marker, a decrease in neuro-axonal injury was observed in a cohort of participants following ART initiation during PHI, with no evidence of neuro-axonal injury rebound following ART interruption for up to 12 weeks, despite viral rebound in the majority of participants.

Identification of an important potential confound in CSF AD studies: aliquot volume.

BACKGROUND: Cerebrospinal fluid (CSF) amyloid ß1-42 (Aß1-42), total tau (T-tau) and phosphorylated tau181 (P-tau) are finding increasing utility as biomarkers of Alzheimer's disease (AD). The purpose of this study was to determine whether measured CSF biomarker concentrations were affected by aliquot storage volume and whether addition of detergent-containing buffer mitigates any observed effects. METHODS: AD and control CSF was distributed into polypropylene tubes in aliquots of different volumes (50-1500 µL). Aß1-42, T-tau and P-tau were measured with and without addition of Tween 20 (0.05%). RESULTS: Measured concentrations of Aß1-42 increased two-fold with aliquot storage volume. A volume increase of 10 µL caused an Aß1-42 increase of 0.95 pg/mL [95% confidence interval (CI) 0.36-1.50, p=0.02] in controls, and 0.60 pg/mL (CI 0.23-0.98 pg/mL, p=0.003) in AD samples. Following addition of Tween 20, the positive relationship between Aß1-42 and aliquot volume disappeared. T-tau and P-tau were not significantly affected. CONCLUSIONS: CSF aliquot storage volume has a significant impact on the measured concentration of Aß1-42. The introduction of a buffer detergent at the initial aliquoting stage may be an effective solution to this problem.