CSF biomarkers of immune activation and Alzheimer's disease for predicting cognitive impairment risk in the elderly.

The immune system substantially influences age-related cognitive decline and Alzheimer's disease (AD) progression, affected by genetic and environmental factors. In a Mayo Clinic Study of Aging cohort, we examined how risk factors like APOE genotype, age, and sex affect inflammatory molecules and AD biomarkers in cerebrospinal fluid (CSF). Among cognitively unimpaired individuals over 65 (N = 298), we measured 365 CSF inflammatory molecules, finding age, sex, and diabetes status predominantly influencing their levels. We observed age-related correlations with AD biomarkers such as total tau, phosphorylated tau-181, neurofilament light chain (NfL), and YKL40. APOE4 was associated with lower Aß42 and higher SNAP25 in CSF. We explored baseline variables predicting cognitive decline risk, finding age, CSF Aß42, NfL, and REG4 to be independently correlated. Subjects with older age, lower Aß42, higher NfL, and higher REG4 at baseline had increased cognitive impairment risk during follow-up. This suggests that assessing CSF inflammatory molecules and AD biomarkers could predict cognitive impairment risk in the elderly.

Timing of Biomarker Changes in Sporadic Alzheimer's Disease in Estimated Years from Symptom Onset.

OBJECTIVE: A clock relating amyloid positron emission tomography (PET) to time was used to estimate the timing of biomarker changes in sporadic Alzheimer disease (AD). METHODS: Research participants were included who underwent cerebrospinal fluid (CSF) collection within 2 years of amyloid PET. The ages at amyloid onset and AD symptom onset were estimated for each individual. The timing of change for plasma, CSF, imaging, and cognitive measures was calculated by comparing restricted cubic splines of cross-sectional data from the amyloid PET positive and negative groups. RESULTS: The amyloid PET positive sub-cohort (n = 118) had an average age of 70.4 ± 7.4 years (mean ± standard deviation) and 16% were cognitively impaired. The amyloid PET negative sub-cohort (n = 277) included individuals with low levels of amyloid plaque burden at all scans who were cognitively unimpaired at the time of the scans. Biomarker changes were detected 15-19 years before estimated symptom onset for CSF Aß42/Aß40, plasma Aß42/Aß40, CSF pT217/T217, and amyloid PET; 12-14 years before estimated symptom onset for plasma pT217/T217, CSF neurogranin, CSF SNAP-25, CSF sTREM2, plasma GFAP, and plasma NfL; and 7-9 years before estimated symptom onset for CSF pT205/T205, CSF YKL-40, hippocampal volumes, and cognitive measures. INTERPRETATION: The use of an amyloid clock enabled visualization and analysis of biomarker changes as a function of estimated years from symptom onset in sporadic AD. This study demonstrates that estimated years from symptom onset based on an amyloid clock can be used as a continuous staging measure for sporadic AD and aligns with findings in autosomal dominant AD. ANN NEUROL 2024;95:951-965.

Alzheimer amyloid-ß- peptide disrupts membrane localization of glucose transporter 1 in astrocytes: implications for glucose levels in brain and blood.

Alzheimer's disease (AD) is associated with disturbances in blood glucose regulation, and type-2 diabetes elevates the risk for dementia. A role for amyloid-ß peptide (Aß) in linking these age-related conditions has been proposed, tested primarily in transgenic mouse lines that overexpress mutated amyloid precursor protein (APP). Because APP has its own impacts on glucose regulation, we examined the BRI-Aß42 line ("Aß42-tg"), which produces extracellular Aß1-42 in the CNS without elevation of APP. We also looked for interactions with diet-induced obesity (DIO) resulting from a high-fat, high-sucrose ("western") diet. Aß42-tg mice were impaired in both spatial memory and glucose tolerance. Although DIO induced insulin resistance, Aß1-42 accumulation did not, and the impacts of DIO and Aß on glucose tolerance were merely additive. Aß42-tg mice exhibited no significant differences from wild-type in insulin production, body weight, lipidemia, appetite, physical activity, respiratory quotient, an-/orexigenic factors, or inflammatory factors. These negative findings suggested that the phenotype in these mice arose from perturbation of glucose excursion in an insulin-independent tissue. To wit, cerebral cortex of Aß42-tg mice had reduced glucose utilization, similar to human patients with AD. This was associated with insufficient trafficking of glucose transporter 1 to the plasma membrane in parenchymal brain cells, a finding also documented in human AD tissue. Together, the lower cerebral metabolic rate of glucose and diminished function of parenchymal glucose transporter 1 indicate that aberrant regulation of blood glucose in AD likely reflects a central phenomenon, resulting from the effects of Aß on cerebral parenchyma, rather than a generalized disruption of hypothalamic or peripheral endocrinology. The involvement of a specific glucose transporter in this deficit provides a new target for the design of AD therapies.

Pimavanserin, a 5HT2A receptor inverse agonist, rapidly suppresses Aß production and related pathology in a mouse model of Alzheimer's disease.

Amyloid-ß (Aß) peptide aggregation into soluble oligomers and insoluble plaques is a precipitating event in the pathogenesis of Alzheimer's disease (AD). Given that synaptic activity can regulate Aß generation, we postulated that 5HT2A -Rs may regulate Aß as well. We treated APP/PS1 transgenic mice with the selective 5HT2A inverse agonists M100907 or Pimavanserin systemically and measured brain interstitial fluid (ISF) Aß levels in real-time using in vivo microdialysis. Both compounds reduced ISF Aß levels by almost 50% within hours, but had no effect on Aß levels in 5HT2A -R knock-out mice. The Aß-lowering effects of Pimavanserin were blocked by extracellular-regulated kinase (ERK) and NMDA receptor inhibitors. Chronic administration of Pimavanserin by subcutaneous osmotic pump to aged APP/PS1 mice significantly reduced CSF Aß levels and Aß pathology and improved cognitive function in these mice. Pimavanserin is FDA-approved to treat Parkinson's disease psychosis, and also has been shown to reduce psychosis in a variety of other dementia subtypes including Alzheimer's disease. These data demonstrate that Pimavanserin may have disease-modifying benefits in addition to its efficacy against neuropsychiatric symptoms of Alzheimer's disease. Read the Editorial Highlight for this article on page 560.

Predictors of Hypophosphatemia and Outcomes during Continuous Renal Replacement Therapy.

INTRODUCTION: Hypophosphatemia occurs in up to 80% of patients undergoing continuous renal replacement therapy (CRRT) and has been associated with poor outcomes. Whether preemptive phosphate supplementation is warranted in select patients has not been adequately explored. This single-center, retrospective cohort study evaluates predictors of hypophosphatemia and characterizes treatment approaches in adult patients undergoing at least 12 h of CRRT. METHODS: Patients were divided into 2 groups based on the presence or absence of hypophosphatemia as defined by serum phosphorus <2.5 mg/dL. Select laboratory values at baseline and during CRRT, medications and nutritional sources affecting phosphorus, and CRRT parameters were compared. Patient outcomes including resolution of acute kidney injury (AKI), freedom from renal replacement therapy at hospital discharge, duration of intensive care unit (ICU) and hospital stay, duration of mechanical ventilation, and ICU mortality were evaluated. RESULTS: Seventy-two patients were included. The group was 43% female and 51% African American. CRRT was ordered for AKI in 83% and for end-stage renal disease in 15%. Hypophosphatemia occurred in 45 patients (63%). Mean time to development of hypophosphatemia was 34 ± 22 h. Patients who developed hypophosphatemia received a longer duration of CRRT (p = 0.001), were more likely to have a diet ordered (p = 0.005), less likely to have received calcium infusions (p = 0.045), and had lower phosphorus (p = 0.017) and potassium levels (p = 0.038) and higher calcium levels at baseline (p = 0.048). Development of hypophosphatemia was associated with an increased duration of ICU stay (p = 0.014) but not with the other patient outcomes evaluated. Twenty-seven of the 45 patients (60%) who developed hypophosphatemia received phosphorus supplementation with near equal use of intravenous, oral, and combination routes. Only 17 patients (38%) achieved resolution of hypophosphatemia while on CRRT. CONCLUSION: Hypophosphatemia is common, difficult to correct, and contributes to longer ICU stays in patients requiring CRRT. A preemptive approach to address hypophosphatemia including aggressive supplementation strategies to correct phosphorus is warranted in patients requiring CRRT.

Functional assessments through novel proteomics approaches: Application to insulin/IGF signaling in neurodegenerative disease'.

BACKGROUND: Events that instigate disease may involve biochemical events distinct from changes in the steady-state levels of proteins. Even chronic degenerative disorders appear to involve changes such as post-translational modifications. NEW METHOD: We have begun a series of proteomics analyses on proteins that have been fractionated by functional status. Because Alzheimer's disease (AD) is associated with metabolic perturbations such as Type-2 diabetes, fractionation hinged on binding to phosphatidylinositol trisphosphate (PIP3), key to insulin/insulin-like growth factor signaling. We compared mice on normal chow to counterparts subjected to diet-induced obesity (DIO) or to mice expressing human Aß1-42 from a transgene. RESULTS: The prevailing phenotypic finding in either experimental group was loss of PIP3 binding. Of the 1228 proteins that showed valid PIP3 binding in any group of mice, 55% exhibited a significant quantitative difference in the number of spectral counts as a function of DIO, 63% as function of the Aß transgene, and 79% as a function of either variable. There was remarkable overlap among the proteins altered in the two experimental groups, and pathway analysis indicated effects on proteostasis, apoptosis, and synaptic vesicles. COMPARISON WITH EXISTING METHODS: Most proteomics approaches only identify differences in the steady-state levels of proteins. Our overlay of a functional distinction permits new levels of discovery that may achieve novel insights into physiology in an unbiased and inclusive manner. CONCLUSIONS: Proteomics analyses have revolutionized the discovery phase of biomedical research but are conventionally limited in scope. The creative use of fractionation prior to proteomic discovery is likely to provide important insights into AD and related disorders.

Ablation of amyloid precursor protein increases insulin-degrading enzyme levels and activity in brain and peripheral tissues.

The amyloid precursor protein (APP) is a type I transmembrane glycoprotein widely studied for its role as the source of ß-amyloid peptide, accumulation of which is causal in at least some cases of Alzheimer's disease (AD). APP is expressed ubiquitously and is involved in diverse biological processes. Growing bodies of evidence indicate connections between AD and somatic metabolic disorders related to type 2 diabetes, and App-/- mice show alterations in glycemic regulation. We find that App-/- mice have higher levels of insulin-degrading enzyme (IDE) mRNA, protein, and activity compared with wild-type controls. This regulation of IDE by APP was widespread across numerous tissues, including liver, skeletal muscle, and brain as well as cell types within neural tissue, including neurons, astrocytes, and microglia. RNA interference-mediated knockdown of APP in the SIM-A9 microglia cell line elevated IDE levels. Fasting levels of blood insulin were lower in App-/- than App+/+ mice, but the former showed a larger increase in response to glucose. These low basal levels may enhance peripheral insulin sensitivity, as App-/- mice failed to develop impairment of glucose tolerance on a high-fat, high-sucrose ("Western") diet. Insulin levels and insulin signaling were also lower in the App-/- brain; synaptosomes prepared from App-/- hippocampus showed diminished insulin receptor phosphorylation compared with App+/+ mice when stimulated ex vivo. These findings represent a new molecular link connecting APP to metabolic homeostasis and demonstrate a novel role for APP as an upstream regulator of IDE in vivo.

Conserved Oligomeric Golgi and Neuronal Vesicular Trafficking.

The conserved oligomeric Golgi (COG) complex is an evolutionary conserved multi-subunit vesicle tethering complex essential for the majority of Golgi apparatus functions: protein and lipid glycosylation and protein sorting. COG is present in neuronal cells, but the repertoire of COG function in different Golgi-like compartments is an enigma. Defects in COG subunits cause alteration of Golgi morphology, protein trafficking, and glycosylation resulting in human congenital disorders of glycosylation (CDG) type II. In this review we summarize and critically analyze recent advances in the function of Golgi and Golgi-like compartments in neuronal cells and functions and dysfunctions of the COG complex and its partner proteins.

FlgM proteins from different bacteria exhibit different structural characteristics.

Intrinsically disordered proteins (IDPs) are a unique class of proteins that do not require a stable structure for function. The importance of IDPs in many biological processes has been established but there remain unanswered questions about their evolution and conservation of their disordered state within a protein family. Our group has been studying the structural similarities among orthologous FlgM proteins, a model class of IDPs. We have previously shown that the FlgM protein from the thermophile Aquifex aeolicus has more structure at A. aeolicus' physiological temperature (85°C) than is observed for the Salmonella typhimurium FlgM, suggesting that the disordered nature of FlgM varies among organisms and is not universally conserved. In this work, we extend these studies to the FlgM proteins from Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis, and Bacillus subtilis. We demonstrate that the B. subtilis, E. coli, and S. typhimurium FlgMs exist in a premolten globule-like conformation, though the B. subtilis FlgM is in a more compacted conformation than the other two. The P. aeruginosa and P. mirabilis FlgM proteins exist in a currently unknown conformation that is not either coil-like or premolten globule-like. The P. aeruginosa FlgM appears to contain more weak intramolecular contacts given its more compacted state than the P. mirabilis FlgM. These results provide experimental evidence that members of the same protein family can exhibit different degrees of disorder, though understanding how different disordered states evolve in the same protein family will require more study.