E3 ubiquitin ligase Nedd4-2 exerts neuroprotective effects during endoplasmic reticulum stress

Exosomal NEDD4L derived from HG+oxLDL-induced vascular endothelial cells accelerates macrophage M1 polarization and oxLDL uptake by ubiquitinating IκBα and PPARγ

BACKGROUND

Vascular endothelial cell-derived exosomes are thought to mediate disease progression by regulating macrophage polarization. However, its mechanism in diabetes mellitus (DM)-related atherosclerosis (AS) progress is unclear.

METHODS

High-glucose (HG) and oxLDL were used to induce human cardiac microvascular endothelial cells (HCMECs) to mimic DM-related AS model. The conditioned medium (CM) from HG+oxLDL-induced HCMECs was incubated with THP1-M0 monocytes treated with LPS or oxLDL. The mRNA levels of macrophage M1/M2 polarization markers, NEDD4L, IκBα and PPARγ were determined by qRT-PCR. Flow cytometry was used to analyze macrophage marker. Dil-labeled oxLDL and oil red O staining were performed to assess oxLDL uptake by THP1-M0 cells. The levels of inflammatory factors were examined using ELISA. Transmission electron microscope was used for observing foam cell formation and exosome morphology. The protein levels of p-Smad1/Smad1, p-Smad2/Smad2, p-IκBα/IκBα, p-P65/P65, anti-lipid metabolism-related markers, and NEDD4L were tested by western blot. The interaction between NEDD4L and IκBα or PPARγ was assessed by Co-IP assay.

RESULTS

The CM of HG+oxLDL-induced HCMECs could promote macrophage M1 polarization, oxLDL uptake and foam cell formation, and exosome inhibiter GW4869 eliminated these effects. NEDD4L was overexpressed in exosomes from HG+oxLDL-induced HCMECs, which could be taken up by THP1-M0 cells. Exosomal NEDD4L knockdown inhibited macrophage M1 polarization, oxLDL uptake and foam cell formation by reducing the protein levels of p-Smad1/Smad1, p-Smad2/Smad2, p-IκBα/IκBα and p-P65/P65. NEDD4L could reduce IκBα and PPARγ expression through ubiquitination.

CONCLUSION

HG+oxLDL-induced HCMECs-derived exosomal NEDD4L could enhance the ubiquitination of IκBα and PPARγ to facilitate macrophage M1 polarization and oxLDL uptake, thus accelerating DM-related AS.

NEDD4L-mediated RASGRP2 suppresses high-glucose and oxLDL-induced vascular endothelial cell dysfunctions by activating Rap1 and R-Ras

BACKGROUND

Ras guanyl-releasing protein 2 (RASGRP2) is an important regulator mediating endothelial cell function. However, whether RASGRP2 mediates diabetes mellitus (DM)-related atherosclerosis (AS) progression by regulating endothelial cell functions is unknown.

METHODS

Human cardiac microvascular endothelial cells (HCMECs) were treated with high-glucose (HG) and oxidized low-density lipoprotein (oxLDL). The expression of RASGRP2 and neural precursor cell expressed developmentally downregulated 4-like (NEDD4L) was examined by quantitative real-time PCR and western blot (WB). Cell viability, apoptosis, migration, angiogenesis were detected by CCK8 assay, flow cytometry, transwell assay and tube formation assay. ROS production and cell permeability were tested to assess cell function. Rap1 and R-Ras protein levels were examined using WB. The interaction between RASGRP2 and NEDD4L was confirmed by Co-IP assay and ubiquitination assay. Exosomes were isolated from adipose-derived MSC (ADMSC)-transfected RASGRP2 overexpression vector, and then co-cultured with HG + oxLDL-induced HCMECs.

RESULTS

RASGRP2 was lowly expressed in HG + oxLDL-induced HCMECs. RASGRP2 overexpression inhibited HG + oxLDL-induced HCMECs permeability, apoptosis and ROS production, while accelerated cell viability, migration and angiogenesis. NEDD4L could interact with RASGRP2 by ubiquitination, thus inhibiting RASGRP2 protein stability to degrade its expression. Functional experiments showed that NEDD4L knockdown suppressed HG + oxLDL-induced HCMECs dysfunction, while these effects were reversed by RASGRP2 downregulation. ADMSC-Exo overexpressed RASGRP2 could promote cell viability, migration and angiogenesis, while suppress permeability, apoptosis and ROS production in HG + oxLDL-induced HCMECs.

CONCLUSION

Our data showed that targeting NEDD4L/RASGRP2 axis or inducing RASGRP2-modified ADMSC-Exo might be the efficient strategy for alleviating DM-related AS.

Network Pharmacology, Molecular Dynamics and In Vitro Assessments of Indigenous Herbal Formulations for Alzheimer's Therapy

Alzheimer's disease (AD) is an age-associated neurodegenerative condition marked by amyloid plaques, synaptic dysfunction, and neuronal loss. Besides conventional medical care, herbal therapies, both raw and refined, have attracted researchers for their potential therapeutic effects. As a proof-of-concept, our study combined HPLC-DAD analysis of bioactive constituents, network pharmacology, molecular dynamics (MD), molecular docking, post-MD analysis, and experimental verification to investigate the mechanisms of crude drug formulations as a therapeutic strategy for AD. We identified nine bioactive compounds targeting 188 proteins and 1171 AD-associated genes. Using a Venn diagram, we found 47 overlapping targets, forming "herb-compound-target (HCT)" interaction networks and a protein‒protein interaction (PPI) network. Simulations analyzed binding interactions among the three core targets and their compounds. MD assessed the stability of the best-ranked poses and beneficial compounds for each protein. Among the top 22 hub genes, AChE, BChE, and MAO, ranked 10, 14, and 34, respectively, were selected for further analysis. Two tetraherbal formulations, Form A and Form B, showed notable activity against AChE. Form A exhibited significant (p < 0.0001) inhibitory activity (IC50 = 114.842 ± 2.084 µg/mL) compared to Form B (IC50 = 142.829 ± 4.258 µg/mL), though weaker than galantamine (IC50 = 27.950 ± 0.122 µg/mL). Form B had significant inhibitory effects on BChE (IC50 = 655.860 ± 32.812 µg/mL) compared to Form A (IC50 = 679.718 ± 20.656 µg/mL), but lower than galantamine (IC50 = 23.126 ± 0.683 µg/mL). Both forms protected against Fe2+-mediated brain injury by inhibiting MAO. Docking identified quercetin (-10.2 kcal/mol) and myricetin (-10.1 kcal/mol) for AChE; rutin (-10.6 kcal/mol) and quercetin (-9.7 kcal/mol) for BChE; and kaempferol (-9.1 kcal/mol) and quercetin (-8.9 kcal/mol) for MAO. These compounds were thermodynamically stable based on MD analysis. Collectively, the results offer a scientific rationale for the use of these specifically selected medicinal herbs as AD medications.

Hyperfunction of post-synaptic density protein 95 promotes seizure response in early-stage aβ pathology

Accumulation of amyloid-beta (Aβ) can lead to the formation of aggregates that contribute to neurodegeneration in Alzheimer's disease (AD). Despite globally reduced neural activity during AD onset, recent studies have suggested that Aβ induces hyperexcitability and seizure-like activity during the early stages of the disease that ultimately exacerbate cognitive decline. However, the underlying mechanism is unknown. Here, we reveal an Aβ-induced elevation of postsynaptic density protein 95 (PSD-95) in cultured neurons in vitro and in an in vivo AD model using APP/PS1 mice at 8 weeks of age. Elevation of PSD-95 occurs as a result of reduced ubiquitination caused by Akt-dependent phosphorylation of E3 ubiquitin ligase murine-double-minute 2 (Mdm2). The elevation of PSD-95 is consistent with the facilitation of excitatory synapses and the surface expression of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors induced by Aβ. Inhibition of PSD-95 corrects these Aβ-induced synaptic defects and reduces seizure activity in APP/PS1 mice. Our results demonstrate a mechanism underlying elevated seizure activity during early-stage Aβ pathology and suggest that PSD-95 could be an early biomarker and novel therapeutic target for AD.

Preface: Special issue "Brain Proteostasis in Health and Disease"

This preface introduces the Journal of Neurochemistry Special Issue on Brain Proteostasis. Adequate control of protein homeostasis, or proteostasis, has been at the center stage of brain physiology, and its deregulation may contribute to brain diseases, including several neuropsychiatric and neurodegenerative conditions. Therefore, delineating the processes underlying protein synthesis, folding, stability, function, and degradation in brain cells is key to promoting brain function and identifying effective therapeutic options for neurological disorders. This special issue comprises four review articles and four original articles covering the roles of protein homeostasis in several mechanisms that are of relevance to sleep, depression, stroke, dementia, and COVID-19. Thus, these articles highlight different aspects of proteostasis regulation in the brain and present important evidence on this growing and exciting field.

Nedd4-2 Haploinsufficiency in Mice Impairs the Ubiquitination of Rer1 and Increases the Susceptibility to Endoplasmic Reticulum Stress and Seizures

Neural precursor cell expressed developmentally downregulated gene 4-like (NEDD4-2) is an epilepsy-associated gene encoding an E3 ligase that ubiquitinates neuroactive substrates. An involvement of NEDD4-2 in endoplasmic reticulum (ER) stress has been recently found with mechanisms needing further investigations. Herein, Nedd4-2+/− mice were found intolerant to thapsigargin (Tg) to develop ER stress in the brain. Pretreatment of Tg aggravated the pentylenetetrazole (PTZ)-induced seizures. Retention in endoplasmic reticulum 1 (Rer1), an ER retrieval receptor, was upregulated through impaired ubiquitination in Nedd4-2+/− mouse brain. Nedd4-2 interacted with Rer1 more strongly in mice with Tg administration. The negative regulation and NEDD4-2-mediated ubiquitination on RER1 were evaluated in cultured neurocytes and gliacytes by NEDD4-2 knockdown and overexpression. NEDD4-2 interacted with RER1 at higher levels in the cells with Tg treatment. Disruption of the 36STPY39 motif of RER1 attenuated the interaction with NEDD4-2, and the ubiquitinated RER1 underwent proteasomal degradation. Furthermore, the interactome of Rer1 was screened by immunoprecipitation-mass spectrometry in PTZ-induced mouse hippocampus, showing multiple potential ER retrieval cargoes that mediate neuroexcitability. The α1 subunit of the GABAA receptor was validated to interact with Rer1 and retain in ER more heavily in Nedd4-2+/− mouse brain by Endo-H digestion. In conclusion, Nedd4-2 deficiency in mice showed impaired ubiquitination of Rer1 and increased ER stress and seizures. These data indicate a protective effect of NEDD4-2 in ER stress and seizures possibly via RER1. We also provided potential ER retention cargoes of Rer1 awaiting further investigation.

Amyloid beta induces Fmr1 ‐dependent translational suppression and hyposynchrony of neural activity via phosphorylation of eIF2α and eEF2

Alzheimer's disease (AD) is the most common cause of dementia, with the accumulation of amyloid beta peptide (Aβ) being one of the main causes of the disease. Fragile X mental retardation protein (FMRP), encoded by fragile X mental retardation 1 (Fmr1), is an RNA‐binding protein that represses translation of its bound mRNAs or exerts other indirect mechanisms that result in translational suppression. Because the accumulation of Aβ has been shown to cause translational suppression resulting from the elevated cellular stress response, in this study we asked whether and how Fmr1 is involved in Aβ‐induced translational regulation. Our data first showed that the application of synthetic Aβ peptide induces the expression of Fmr1 in cultured primary neurons. We followed by showing that Fmr1 is required for Aβ‐induced translational suppression, hyposynchrony of neuronal firing activity, and loss of excitatory synapses. Mechanistically, we revealed that Fmr1 functions to repress the expression of phosphatases including protein phosphatase 2A (PP2A) and protein phosphatase 1 (PP1), leading to elevated phosphorylation of eukaryotic initiation factor 2‐α (eIF2α) and eukaryotic elongation factor 2 (eEF2), and subsequent translational suppression. Finally, our data suggest that such translational suppression is critical to Aβ‐induced hyposynchrony of firing activity, but not the loss of synapses. Altogether, our study uncovers a novel mechanism by which Aβ triggers translational suppression and we reveal the participation of Fmr1 in altered neural plasticity associated with Aβ pathology. Our study may also provide information for a better understanding of Aβ‐induced cellular stress responses in AD.

Proteomic Analysis of Vero Cells Infected with Pseudorabies Virus

Suid herpesvirus 1 (SuHV-1), known as pseudorabies virus (PRV), is one of the most devastating swine pathogens in China, particularly the sudden occurrence of PRV variants in 2011. The higher pathogenicity and cross-species transmission potential of the newly emerged variants caused not only colossal economic losses, but also threatened public health. To uncover the underlying pathogenesis of PRV variants, Tandem Mass Tag (TMT)-based proteomic analysis was performed to quantitatively screen the differentially expressed cellular proteins in PRV-infected Vero cells. A total of 7072 proteins were identified and 960 proteins were significantly regulated: specifically 89 upregulated and 871 downregulated. To make it more credible, the expression of XRCC5 and XRCC6 was verified by western blot and RT-qPCR, and the results dovetailed with the proteomic data. The differentially expressed proteins were involved in various biological processes and signaling pathways, such as chaperonin-containing T-complex, NIK/NF-κB signaling pathway, DNA damage response, and negative regulation of G2/M transition of mitotic cell cycle. Taken together, our data holistically outline the interactions between PRV and host cells, and our results may shed light on the pathogenesis of PRV variants and provide clues for pseudorabies prevention.