Mitochondrial Membrane Potential Influences Amyloid-β Protein Precursor Localization and Amyloid-β Secretion

Background: Amyloid-β (Aβ), which derives from the amyloid-β protein precursor (AβPP), forms plaques and serves as a fluid biomarker in Alzheimer’s disease (AD). How Aβ forms from AβPP is known, but questions relating to AβPP and Aβ biology remain unanswered. AD patients show mitochondrial dysfunction, and an Aβ/AβPP mitochondria relationship exists. Objective: We considered how mitochondrial biology may impact AβPP and Aβ biology. Methods: SH-SY5Y cells were transfected AβPP constructs. After treatment with FCCP (uncoupler), Oligomycin (ATP synthase inhibitor), or starvation Aβ levels were measured. β-secretase (BACE1) expression was measured. Mitochondrial localized full-length AβPP was also measured. All parameters listed were measured in ρ0 cells on an SH-SY5Y background. iPSC derived neurons were also used to verify key results. Results: We showed that mitochondrial depolarization routes AβPP to, while hyperpolarization routes AβPP away from, the organelle. Mitochondrial AβPP and cell Aβ secretion inversely correlate, as cells with more mitochondrial AβPP secrete less Aβ, and cells with less mitochondrial AβPP secrete more Aβ. An inverse relationship between secreted/extracellular Aβ and intracellular Aβ was observed. Conclusion: Our findings indicate mitochondrial function alters AβPP localization and suggest enhanced mitochondrial activity promote Aβ secretion while depressed mitochondrial activity minimize Aβ secretion. Our data complement other studies that indicate a mitochondrial, AβPP, and Aβ nexus, and could help explain why cerebrospinal fluid Aβ is lower in those with AD. Our data further suggest Aβ secretion could serve as a biomarker of cell or tissue mitochondrial function.

Inhibiting α1-adrenergic Receptor Signaling Pathway Ameliorates Alzheimer’s Disease Type Pathologies and Behavioral Deficits in an AD Mouse Model

Background The role of α1 adrenergic receptors (α1-ARs) signaling pathway in the pathogenesis of Alzheimer’s disease (AD) has rarely been investigated. Clarifying pathophysiological functions of α1-ARs in the AD brain is helpful for better understanding the pathogenesis and screening novel therapeutic target of AD. Methods This study included 2 arms of in vivo investigations: 1) 6-month-old female APPswe/PS1 mice were intravenously treated with AAV-PHP.eB-shRNA (ARs)-GFP or AAV-PHP.eB-GFP for 3 months. 2) 3-month-old female APPswe/PS1 mice were daily treated with 0.5 mg/kg terazosin or equal saline for 6 months. SH-SY5Y cell lines bearing human Amyloid precurssor protein were treated with terazosin or saline for investigating possible mechanisms. Results α1-ARs knockdown mice exhibited improved behavioral performances than control mice. α1-ARs knockdown mice had significantly lower brain amyloid burden, as reflected by soluble Aβ species, compact and total plaques, than control mice. The α1-ARs inhibitor terazosin substantially reduced Aβ deposition, attenuated downstream pathologies including Tau hyperphosphorylation, glial activation, neuronal loss, synaptic dysfunction, and rescued behavioral deficits of APPswe/PS1 mice. In vitro investigation demonstrated that α1-ARs inhibition down-regulated BACE1 expression, and promoted ser9 phosphorylation of GSK-3β, thus reduced Aβ production. Conclusions This study indicates that inhibition of α1-ARs signaling pathway might represent a promising therapeutic strategy for AD.

Novel Plasma miRNAs as Biomarkers and Therapeutic Targets of Alzheimer’s Disease at the Prodromal Stage

Background: Amnestic mild cognitive impairment (aMCI) is a prodromal stage of Alzheimer’s disease (AD) involving imbalanced beta-site amyloid precursor protein cleaving enzyme 1 (BACE1). MicroRNAs (miRNAs) are associated with AD. Objective: This study aimed to investigated whether plasma miRNAs can predict prodromal AD or are associated with AD pathology. Methods: Participants in the discovery set (n = 10), analysis set (n = 30), and validation set (n = 80) were screened from the China Longitudinal Aging Study. RNA was extracted from the participants’ plasma. Microarray sequencing provided miRNA profiles and differentially expressed miRNAs (DEmiRNAs) in the discovery set included patients with 18F-Flutemetamol positron emission tomography scan-confirmed aMCI. Potential biomarkers were screened in the analysis set. The predict capability of candidate miRNAs was assessed in the validation set. Candidate miRNAs modulation of BACE1 expression was explored in rat and human hippocampal neurons in vitro. Results: We verified 46 significant DEmiRNAs between the aMCI and NC groups (p < 0.05), among which 33 were downregulated. In the analysis set, miR-1185-2-3p, miR-1909-3p, miR-22-5p, and miR-134-3p levels decreased significantly in the aMCI group. These miRNAs and previously identified miR-107 were selected as potential biomarkers. A prediction model comprising these five miRNAs showed outstanding accuracy (81.25%) to discriminate aMCI at cut-off value of 0.174. Except for miR-134-3p, the other four miRNAs significantly suppressed Bace1 expression in rat hippocampal neurons in vitro. BACE1 modulation of miR-1185-2-3p, miR-1909-3p, and miR-134-3p was confirmed in human hippocampal neurons in vitro. Conclusion: A predictive model consisting of five BACE1-related plasma miRNAs could be a novel biomarker for aMCI.

Casein Kinase 2 dependent phosphorylation of eIF4B regulates BACE1 expression in Alzheimer’s disease

Alzheimer’s disease (AD) is the most common age-related neurodegenerative disorder. Increased Aβ production plays a fundamental role in the pathogenesis of the disease and BACE1, the protease that triggers the amyloidogenic processing of APP, is a key protein and a pharmacological target in AD. Changes in neuronal activity have been linked to BACE1 expression and Aβ generation, but the underlying mechanisms are still unclear. We provide clear evidence for the role of Casein Kinase 2 in the control of activity-driven BACE1 expression in cultured primary neurons, organotypic brain slices, and murine AD models. More specifically, we demonstrate that neuronal activity promotes Casein Kinase 2 dependent phosphorylation of the translation initiation factor eIF4B and this, in turn, controls BACE1 expression and APP processing. Finally, we show that eIF4B expression and phosphorylation are increased in the brain of APPPS1 and APP-KI mice, as well as in AD patients. Overall, we provide a definition of a mechanism linking brain activity with amyloid production and deposition, opening new perspectives from the therapeutic standpoint.

Quantitative 3D microscopy reveals a genetic network predicting the local activity of anti-Aβ compounds

Genetic and biochemical evidence suggests a role for amyloid-β (Aβ) in Alzheimer’s disease, yet many anti-Aβ treatments are clinically ineffective. Regional heterogeneity of efficacy may contribute to these disappointing results. Here we compared the regiospecificity of various anti-Aβ treatments by combining focused electrophoretic whole-brain clearing, amyloid labelling and light-sheet imaging with whole-brain analyses of plaque topology in Aβ-overexpressing mice. Aβ plaque numbers progressed from around 1’200’000 to 2’500’000 over a 9-month period. We then assessed the regiospecific plaque clearance in mice subjected to β-secretase inhibition, amyloid intercalation by polythiophenes, and anti-Aβ antibodies. Each treatment showed unique spatiotemporal Aβ clearance signatures, with polythiophenes emerging as potent anti-Aβ compounds with promising pharmacokinetic properties and the anti-Aβ antibody showing only minor effects. By aligning (25 µm)3 voxels that showed drug effectiveness to spatial transcriptomics atlases, we identified genes matching regiospecific Aβ clearance. As expected, Bace1 expression was highly correlated with the regiospecific efficacy of BACE inhibition. In addition, we found that voxels cleared by polythiophenes correlated with transcripts encoding synaptic proteins, whereas voxels cleared by BACE inhibition correlated with oligodendrocyte-specific genes. The differential regional susceptibility of distinct plaque populations to specific treatments may explain the clinical failure of anti-Aβ therapies, and suggests that combinatorial regimens may improve functional outcomes.

Exercise-mediated alteration of hippocampal Dicer mRNA and miRNAs is associated with lower BACE1 gene expression and Aβ1-42 in female 3xTg-AD mice

Previous studies have outlined the beneficial effects of exercise on lowering BACE1 expression and reducing Aβ plaques. This study extends upon the work of others by outlining a new potential mechanism by which exercise elicits beneficial effects on Alzheimer’s disease pathology, specifically through modulation of Dicer and miRNA expression. This is the first study to examine Dicer and miRNA expression in the hippocampus of the 3xTg model within the context of exercise.