Autophagy deficiency in neurodevelopmental disorders

Autophagy is a cell self-digestion pathway through lysosome and plays a critical role in maintaining cellular homeostasis and cytoprotection. Characterization of autophagy related genes in cell and animal models reveals diverse physiological functions of autophagy in various cell types and tissues. In central nervous system, by recycling injured organelles and misfolded protein complexes or aggregates, autophagy is integrated into synaptic functions of neurons and subjected to distinct regulation in presynaptic and postsynaptic neuronal compartments. A plethora of studies have shown the neuroprotective function of autophagy in major neurodegenerative diseases, such as Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD) and amyotrophic lateral sclerosis (ALS). Recent human genetic and genomic evidence has demonstrated an emerging, significant role of autophagy in human brain development and prevention of spectrum of neurodevelopmental disorders. Here we will review the evidence demonstrating the causal link of autophagy deficiency to congenital brain diseases, the mechanism whereby autophagy functions in neurodevelopment, and therapeutic potential of autophagy.

Neuroglobin in Retinal Neurodegeneration: A Potential Target in Therapeutic Approaches

Retinal neurodegeneration affects an increasing number of people worldwide causing vision impairments and blindness, reducing quality of life, and generating a great economic challenge. Due to the complexity of the tissue, and the diversity of retinal neurodegenerative diseases in terms of etiology and clinical presentation, so far, there are no cures and only a few early pathological markers have been identified. Increasing efforts have been made to identify and potentiate endogenous protective mechanisms or to abolish detrimental stress responses to preserve retinal structure and function. The discovering of the intracellular monomeric globin neuroglobin (NGB), found at high concentration in the retina, has opened new possibilities for the treatment of retinal disease. Indeed, the NGB capability to reversibly bind oxygen and its neuroprotective function against several types of insults including oxidative stress, ischemia, and neurodegenerative conditions have raised the interest in the possible role of the globin as oxygen supplier in the retina and as a target for retinal neurodegeneration. Here, we provide the undercurrent knowledge on NGB distribution in retinal layers and the evidence about the connection between NGB level modulation and the functional outcome in terms of retinal neuroprotection to provide a novel therapeutic/preventive target for visual pathway degenerative disease.

The proSAAS chaperone provides neuroprotection and attenuates transsynaptic α–synuclein spread in rodent models of Parkinson’s disease

ABSTRACTParkinson’s disease is a devastating motor disorder involving the aberrant aggregation of the synaptic protein synuclein (aSyn) and degeneration of the nigrostriatal dopaminergic tract. We previously showed that proSAAS, a small secreted chaperone protein widely expressed in neurons within the brain, is able to block aSyn-induced dopaminergic cytotoxicity in primary nigral neuron cultures. We show here that coinjection of proSAAS-encoding lentivirus profoundly reduced the motor asymmetry caused by unilateral nigral AAV-mediated human aSyn overexpression. This positive functional outcome was accompanied by significant amelioration of the human aSyn-induced loss of both nigral tyrosine hydroxylase-positive cells and striatal tyrosine hydroxylase-positive terminals, demonstrating clear proSAAS-mediated protection of the nigro-striatal tract. ProSAAS overexpression also reduced the content of human aSyn protein in both the nigra and striatum and reduced the loss of tyrosine hydroxylase protein in both regions. Since proSAAS is a secreted protein, we tested the possibility that proSAAS is able to block the transsynaptic spread of aSyn from the periphery to the central nervous system, increasingly recognized as a potentially significant pathological mechanism. The number of human aSyn-positive neurites in the pons and caudal midbrain of mice following administration of human aSyn-encoding AAV into the vagus nerve was considerably reduced in mice coinjected with proSAAS-encoding AAV, supporting proSAAS-mediated blockade of transsynaptic aSyn transmission. We suggest that proSAAS may represent a promising target for therapeutic development in Parkinson’s disease.SignificanceThis paper describes two independent avenues of research that both provide support for the in vivo neuroprotective function of this small chaperone protein. In the first approach, we show that proSAAS overexpression provides remarkably effective protection against dopaminergic neurotoxicity in a rat model of Parkinson’s disease. This conclusion is supported both by three independent assays of motor function as well as by quantitative analysis of surviving dopaminergic neurons in brain areas involved in the control of motor function. In the second line of research, we show that in mice, the spread of human synuclein across synapses can be blunted by proSAAS overexpression.

NPD1 Enhances Autophagy and Reduces Hyperphosphorylated Tau and Amyloid-β42 by Inhibiting GSK3β Activation in N2a/APP695swe Cells

Background: The most prevalent kind of dementia, Alzheimer’s disease (AD), is a neurodegenerative disease. Previous research has shown that glycogen synthase kinase-3β (GSK-3β) is involved in the etiology and progression of AD, including amyloid-β (Aβ), phosphorylated tau, and mitochondrial dysfunction. NPD1 has been shown to serve a neuroprotective function in AD, although the mechanism is unclear. Objective: The effects of NPD1 on Aβ expression levels, tau protein phosphorylation, apoptosis ratio, autophagy activity, and GSK-3β activity in N2a/APP695swe cells (AD cell model) were studied, as well as the mechanism behind such effects. Methods: N2a/APP695swe cells were treated with NPD1, SB216763, or wortmannin as an AD cell model. The associated proteins of hyperphosphorylated tau and autophagy, as well as the activation of GSK3β, were detected using western blot and RT-PCR. Flow cytometry was utilized to analyze apoptosis and ELISA was employed to observe Aβ 42. Images of autophagy in cells are captured using transmission electron microscopy. Results: In N2a/APP695swe cells, NPD1 decreased Aβ 42 and hyperphosphorylated tau while suppressing cell death. NPD1 also promoted autophagy while suppressing GSK-3β activation in N2a/APP695swe cells. The outcome of inhibiting GSK-3β is comparable to that of NPD1 therapy. However, after activating GSK-3β, the opposite experimental results were achieved. Conclusion: NPD1 might minimize cell apoptosis, downregulate Aβ expression, control tau hyperphosphorylation, and enhance autophagy activity in AD cell models to promote neuronal survival. NPD1’s neuroprotective effects may be mediated via decreasing GSK-3β.

Engineered neuron-targeting, placental mesenchymal stromal cell-derived extracellular vesicles for in utero treatment of myelomeningocele

This study investigated the feasibility and efficiency of neuron-targeting hybrid placental mesenchymal stromal cell-derived extracellular vesicles (PMSC-EVs), engineered by membrane fusion with Targeted Axonal Import (TAxI) peptide modified, TrkB agonist 7,8-DHF-loaded liposomes for treatment of myelomeningocele (MMC) via intra-amniotic cavity administration. The prepared TAxI modified liposomes with 7,8-DHF were used to fuse with PMSC-EVs. Different fusion approaches were investigated and freeze-thaw-extrude method was found to be the optimal. The engineered PMSC-EVs had a uniform particle size and efficiently loaded 7,8-DHF. It also had typical markers of native EVs. Freeze-thaw-extrude process did not change the release profile of 7,8-DHF from engineered EVs compared to TAxI modified, 7,8-DHF loaded liposomes. The engineered EVs could elicit TrkB phosphorylation depending on the incorporation of 7,8-DHF while native EVs did not. The engineered EVs increased neurite outgrowth of apoptotic cortical neurons induced by staurosporine, suggesting that they exhibited neuroprotective function. In a rodent model of MMC, neuron-targeting, engineered EVs became an active targeting delivery system to MMC defect sites. Pups treated with engineered EVs had the lowest density of apoptotic cells and displayed a therapeutic outcome. The study suggests the potential use of engineered hybrid, active neuron-targeting EVs for the in utero treatment of MMC.

ZNF598 co-translationally titrates poly(GR) protein implicated in the pathogenesis of C9ORF72-associated ALS/FTD

C9ORF72-derived dipeptide repeat proteins have emerged as the pathogenic cause of neurodegeneration in amyotrophic lateral sclerosis and frontotemporal dementia (C9-ALS/FTD). However, the mechanisms underlying their expression are not fully understood. Here, we demonstrate that ZNF598, the rate-limiting factor for ribosome-associated quality control (RQC), co-translationally titrates the expression of C9ORF72-derived poly(GR) protein. A Drosophila genetic screen identified key RQC factors as potent modifiers of poly(GR)-induced neurodegeneration. ZNF598 overexpression in human neuroblastoma cells inhibited the nuclear accumulation of poly(GR) protein and decreased its cytotoxicity, whereas ZNF598 deletion had opposing effects. Poly(GR)-encoding sequences in the reporter RNAs caused translational stalling and generated ribosome-associated translation products, sharing molecular signatures with canonical RQC substrates. Furthermore, ZNF598 and listerin 1, the RQC E3 ubiquitin-protein ligase, promoted poly(GR) degradation via the ubiquitin-proteasome pathway. An ALS-relevant ZNF598R69C mutant displayed loss-of-function effects on poly(GR) expression, as well as on general RQC. Moreover, RQC function was impaired in C9-ALS patient-derived neurons, whereas lentiviral overexpression of ZNF598 lowered their poly(GR) expression and suppressed proapoptotic caspase-3 activation. Taken together, we propose that an adaptive nature of the RQC-relevant ZNF598 activity allows the co-translational surveillance to cope with the atypical expression of pathogenic poly(GR) protein, thereby acquiring a neuroprotective function in C9-ALS/FTD.

GSK-126 protects CA1 neurons from H3K27me3-mediated apoptosis in cerebral ischemia

Epigenetics, including histone modifications, play a significant role in central nervous system diseases, but the underlying mechanism remains to be elucidated. The aim of this study was to evaluate the role of H3K27me3 in regulating transcriptomic and pathogenic mechanisms following global ischemic stroke. Here, we found that in vivo ischemic/reperfusion (I/R) injury induced marked upregulation of H3K27me3 in the hippocampus. The administration of GSK-126 to rat brains decreased the levels of H3K27me3 in the hippocampus and reduced neuronal apoptosis after experimental stroke. Furthermore, ChIP-seq data demonstrated that the primary role of GSK-126 in the ischemic brain is to reduce H3K27me3 enrichment, mediating negative regulation of the execution phase of apoptosis and the MAPK signaling pathway. Further study suggested that the protective role of GSK-126 in ischemic rats was antagonized by U0126, an inhibitor of ERK1/2. Collectively, we demonstrated the potential of H3K27me3 as a novel stroke therapeutic target, and GSK-126 exerted a neuroprotective function in ischemic brain injury, which might be associated with activation of the MAPK/ERK pathway.

Effect of gold nanoparticles on the structure and neuroprotective function of protein L-isoaspartyl methyltransferase (PIMT)

Fibrillation of peptides and proteins is implicated in various neurodegenerative diseases and is a global concern. Aging leads to the formation of abnormal isoaspartate (isoAsp) residues from isomerization of normal aspartates in proteins, triggering fibril formation that leads to neurodegenerative diseases. Protein L-isoaspartyl methyltransferase (PIMT) is a repair enzyme which recognizes and converts altered isoAsp residues back to normal aspartate. Here we report the effect of gold nanoparticles (AuNPs) of different sizes on the structure and function of PIMT. Spherical AuNPs, viz. AuNS5, AuNS50 and AuNS100 (the number indicating the diameter in nm) stabilize PIMT, with AuNS100 exhibiting the best efficacy, as evident from various biophysical experiments. Isothermal titration calorimetry (ITC) revealed endothermic, but entropy driven mode of binding of PIMT with all the three AuNSs. Methyltransferase activity assay showed enhanced activity of PIMT in presence of all AuNSs, the maximum being with AuNS100. The efficacy of PIMT in presence of AuNS100 was further demonstrated by the reduction of fibrillation of Aβ42, the peptide that is implicated in Alzheimer’s disease. The enhancement of anti-fibrillation activity of PIMT with AuNS100 was confirmed from cell survival assay with PC12 derived neuronal cells against Aβ42 induced neurotoxicity.