Presynaptic terminals are metabolically active and accrue damage through continuous vesicle cycling. How synapses locally regulate protein homeostasis is poorly understood. We show that the ...presynaptic lipid phosphatase synaptojanin is required for macroautophagy, and this role is inhibited by the Parkinson's disease mutation R258Q. Synaptojanin drives synaptic endocytosis by dephosphorylating PI(4,5)P2, but this function appears normal in SynaptojaninRQ knock‐in flies. Instead, R258Q affects the synaptojanin SAC1 domain that dephosphorylates PI(3)P and PI(3,5)P2, two lipids found in autophagosomal membranes. Using advanced imaging, we show that SynaptojaninRQ mutants accumulate the PI(3)P/PI(3,5)P2‐binding protein Atg18a on nascent synaptic autophagosomes, blocking autophagosome maturation at fly synapses and in neurites of human patient induced pluripotent stem cell‐derived neurons. Additionally, we observe neurodegeneration, including dopaminergic neuron loss, in SynaptojaninRQ flies. Thus, synaptojanin is essential for macroautophagy within presynaptic terminals, coupling protein turnover with synaptic vesicle cycling and linking presynaptic‐specific autophagy defects to Parkinson's disease.
Synopsis
Parkinson's disease‐related human synaptojanin 1 (SYNJ1) or Drosophila synaptojanin (Synj) SAC1 function drives autophagosome biogenesis within synapses by dephosphorylating PI(3)P/PI(3,5)P2, releasing WIPI2/Atg18a from immature autophagosomes, independent from Synj function in endocytosis.
Parkinson's disease related synaptojanin RQ SAC1 mutation does not affect synaptic vesicle endocytosis at fly excitatory glutamatergic neurons and photoreceptors.
Synaptojanin is required for autophagosome formation in presynaptic terminals, analogous to synaptic vesicle uncoating by synaptojanin.
The PI(3)P/PI(3,5)P2‐binding protein, WIPI2/Atg18a accumulates in Synj mutant flies and SYNJ1 R258Q patient‐derived human induced neurons.
Synaptojanin regulates Atg18a mobility at autophagosomal membranes.
Synaptojanin RQ knock‐in flies show neurodegeneration.
The Parkinson's disease‐associated lipid phosphatase synaptojanin promotes synaptic autophagosome formation, a function that is impaired by pathogenic mutations.
Severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) infection is associated with a diverse spectrum of neurological complications during the acute and postacute stages. The pathogenesis of ...these complications is complex and dependent on many factors. For accurate and consistent interpretation of experimental data in this fast-growing field of research, it is essential to use terminology consistently. In this article, we outline the distinctions between neuroinvasiveness, neurotropism, and neurovirulence. Additionally, we discuss current knowledge of these distinct features underlying the pathogenesis of SARS-CoV-2-associated neurological complications. Lastly, we briefly discuss the advantages and limitations of different experimental models, and how these approaches can further be leveraged to advance the field.
Severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) infection has been shown to be associated with a range of neurological complications during the acute and postacute phases.The pathogenesis of SARS-CoV-2-associated CNS disease is complex and diverse, and cannot be explained by one sole mechanism.To understand the pathogenesis of SARS-CoV-2-associated CNS disease, it is important to gain deeper insights into the neuroinvasiveness, neurotropism, and neurovirulence of SARS-CoV-2. It is also imperative to consider the kinetics, since a viral infection is not a static event.Relevant in vivo models can be used to study the neuroinvasiveness, neurotropism, and neurovirulence of SARS-CoV-2, and in vitro human pluripotent stem cell (hPSC) models can be used to study the neurotropism of the virus and the associated cellular responses. These models may be further leveraged to study differences among SARS-CoV-2 variants and for the design of therapeutic approaches.
Hepatitis E virus (HEV), as a hepatotropic virus, is supposed to exclusively infect the liver and only cause hepatitis. However, a broad range of extrahepatic manifestations (in particular, ...idiopathic neurological disorders) have been recently reported in association with its infection. In this study, we have demonstrated that various human neural cell lines (embryonic stem cell–derived neural lineage cells) induced pluripotent stem cell–derived human neurons and primary mouse neurons are highly susceptible to HEV infection. Treatment with interferon-α or ribavirin, the off-label antiviral drugs for chronic hepatitis E, exerted potent antiviral activities against HEV infection in neural cells. More importantly, in mice and monkey peripherally inoculated with HEV particles, viral RNA and protein were detected in brain tissues. Finally, patients with HEV-associated neurological disorders shed the virus into cerebrospinal fluid, indicating a direct infection of their nervous system. Thus, HEV is neurotropic in vitro, and in mice, monkeys, and possibly humans. These results challenge the dogma of HEV as a pure hepatotropic virus and suggest that HEV infection should be considered in the differential diagnosis of idiopathic neurological disorders.
Abstract Lack of fragile X mental retardation protein (FMRP) causes Fragile X Syndrome, the most common form of inherited mental retardation. FMRP is an RNA-binding protein and is a component of ...messenger ribonucleoprotein complexes, associated with brain polyribosomes, including dendritic polysomes. FMRP is therefore thought to be involved in translational control of specific mRNAs at synaptic sites. In mice lacking FMRP, protein synthesis-dependent synaptic plasticity is altered and structural malformations of dendritic protrusions occur. One hypothesized cause of the disease mechanism is based on exaggerated group I mGluR receptor activation. In this study, we examined the effect of the mGluR5 antagonist MPEP on Fragile X related behavior in Fmr1 KO mice. Our results demonstrate a clear defect in prepulse inhibition of startle in Fmr1 KO mice, that could be rescued by MPEP. Moreover, we show for the first time a structural rescue of Fragile X related protrusion morphology with two independent mGluR5 antagonists.
Mutations affecting the gene encoding the ubiquitin ligase UBE3A cause Angelman syndrome. Although most studies focus on the synaptic function of UBE3A, we show that UBE3A is highly enriched in the ...nucleus of mouse and human neurons. We found that the two major isoforms of UBE3A exhibit highly distinct nuclear versus cytoplasmic subcellular localization. Both isoforms undergo nuclear import through direct binding to PSMD4 (also known as S5A or RPN10), but the amino terminus of the cytoplasmic isoform prevents nuclear retention. Mice lacking the nuclear UBE3A isoform recapitulate the behavioral and electrophysiological phenotypes of Ube3a
mice, whereas mice harboring a targeted deletion of the cytosolic isoform are unaffected. Finally, we identified Angelman syndrome-associated UBE3A missense mutations that interfere with either nuclear targeting or nuclear retention of UBE3A. Taken together, our findings elucidate the mechanisms underlying the subcellular localization of UBE3A, and indicate that the nuclear UBE3A isoform is the most critical for the pathophysiology of Angelman syndrome.
Abstract Fragile X syndrome, the most common form of inherited intellectual disability, is caused by a lack of FMRP, which is the product of the Fmr1 gene. FMRP is an RNA-binding protein and a ...component of RNA-granules found in the dendrites of neurons. At the synapse, FMRP is involved in regulation of translation of specific target mRNAs upon stimulation of mGluR5 receptors. In this study, we test the effects of a new mGluR5 antagonist (AFQ056) on the prepulse inhibition of startle response in mice. We show that Fmr1 KO mice have a deficit in inhibition of the startle response after a prepulse and that AFQ056 can rescue this phenotype. We also studied the effect of AFQ056 on cultured Fmr1 KO hippocampal neurons; untreated neurons showed elongated spines and treatment resulted in shortened spines. These results suggest that AFQ056 might be a potent mGluR5 antagonist to rescue various aspects of the fragile X phenotype.
Noncoding RNAs have been widely recognized as essential mediators of gene regulation. However, in contrast to protein‐coding genes, much less is known about the influence of noncoding RNAs on human ...diseases. Here we examined the association of genetic variants located in primary microRNA sequences and long noncoding RNAs (lncRNAs) with Alzheimer disease (AD) by leveraging data from the largest genome‐wide association meta‐analysis of late‐onset AD. Variants annotated to 5 miRNAs and 10 lncRNAs (in seven distinct loci) exceeded the Bonferroni‐corrected significance threshold (p < 1.02 × 10−6). Among these, a leading variant (rs2526377:A>G) at the 17q22 locus annotated to two noncoding RNAs (MIR142 and BZRAP1‐AS) was significantly associated with a reduced risk of AD and fulfilled predefined criteria for being a functional variant. Our functional genomic analyses revealed that rs2526377 affects the promoter activity and decreases the expression of miR‐142. Moreover, differential expression analysis by RNA‐Seq in human iPSC‐derived neural progenitor cells and the hippocampus of miR‐142 knockout mice demonstrated multiple target genes of miR‐142 in the brain that are likely to be involved in the inflammatory and neurodegenerative manifestations of AD. These include TGFBR1 and PICALM, of which their derepression in the brain due to reduced expression levels of miR‐142‐3p may reduce the risk of AD.
We examined the association of genetic variants located in primary microRNA sequences and long noncoding RNAs with Alzheimer disease (AD) by leveraging data from the largest genome‐wide association meta‐analysis of late‐onset AD. Five miRNAs and ten lncRNAs in seven distinct loci exceeded the Bonferroni‐corrected significance threshold, including a new susceptibility locus at 17q22. The top SNP annotated to MIR142 and BZRAP1‐AS was significantly associated with a reduced risk of AD and fulfilled predefined criteria for being functional variant. Our functional genomic analyses revealed that rs2526377 affects promoter activity and decreases the expression of miR‐142. Moreover, differential expression analysis by RNA‐Seq in human iPSC‐derived neural progenitor cells and the hippocampus of miR‐142 knockout mice demonstrated multiple miR‐142‐3p target genes (e.g., TGFBR1 and PICALM) in the brain that are likely to be involved in the inflammatory and neurodegenerative manifestations of AD.
► Adult Fmr1 knockout mice show an immature spine phenotype in the hippocampus. ► Immature spine phenotype present in CA1 region but not in CA3 region of hippocampus. ► Spine phenotype in the ...hippocampus of Fmr1 knockout mice is region=specific.
Fragile X syndrome (FXS) is the most common inherited form of mental retardation and is caused by the lack of fragile X mental retardation protein (FMRP). In the brain, spine abnormalities have been reported in both patients with FXS and Fmr1 knockout mice. This altered spine morphology has been linked to disturbed synaptic transmission related to altered signaling in the excitatory metabotropic glutamate receptor 5 (mGluR5) pathway. We investigated hippocampal protrusion morphology in adult Fmr1 knockout mice. Our results show a hippocampal CA1-specific altered protrusion phenotype, which was absent in the CA3 region of the hippocampus. This suggests a subregion-specific function of FMRP in synaptic plasticity in the brain.
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is associated with various neurological complications. Although the mechanism is not fully understood, several studies have ...shown that neuroinflammation occurs in the acute and post-acute phase. As these studies have predominantly been performed with isolates from 2020, it is unknown if there are differences among SARS-CoV-2 variants in their ability to cause neuroinflammation. Here, we compared the neuroinvasiveness, neurotropism and neurovirulence of the SARS-CoV-2 ancestral strain D614G, the Delta (B.1.617.2) and Omicron BA.1 (B.1.1.529) variants using in vitro and in vivo models. The Omicron BA.1 variant showed reduced neurotropism and neurovirulence compared to Delta and D614G in human induced pluripotent stem cell (hiPSC)-derived cortical neurons co-cultured with astrocytes. Similar differences were obtained in Syrian hamsters inoculated with D614G, Delta and the Omicron BA.1 variant 5 days post infection. Replication in the olfactory mucosa was observed in all hamsters, but most prominently in D614G inoculated hamsters. Furthermore, neuroinvasion into the CNS via the olfactory nerve was observed in D614G, but not Delta or Omicron BA.1 inoculated hamsters. Furthermore, neuroinvasion was associated with neuroinflammation in the olfactory bulb of hamsters inoculated with D614G. Altogether, our findings suggest differences in the neuroinvasive, neurotropic and neurovirulent potential between SARS-CoV-2 variants using in vitro hiPSC-derived neural cultures and in vivo in hamsters during the acute phase of the infection.
Loss of function of the FMR1 gene leads to fragile X syndrome (FXS), the most common form of intellectual disability. The loss of FMR1 function is usually caused by epigenetic silencing of the FMR1 ...promoter leading to expansion and subsequent methylation of a CGG repeat in the 5′ untranslated region. Very few coding sequence variations have been experimentally characterized and shown to be causal to the disease. Here, we describe a novel FMR1 mutation and reveal an unexpected nuclear export function for the C‐terminus of FMRP. We screened a cohort of patients with typical FXS symptoms who tested negative for CGG repeat expansion in the FMR1 locus. In one patient, we identified a guanine insertion in FMR1 exon 15. This mutation alters the open reading frame creating a short novel C‐terminal sequence, followed by a stop codon. We find that this novel peptide encodes a functional nuclear localization signal (NLS) targeting the patient FMRP to the nucleolus in human cells. We also reveal an evolutionarily conserved nuclear export function associated with the endogenous C‐terminus of FMRP. In vivo analyses in Drosophila demonstrate that a patient‐mimetic mutation alters the localization and function of Dfmrp in neurons, leading to neomorphic neuronal phenotypes.
Synopsis
A novel point mutation in the FMR1 gene was identified in a typical fragile X syndrome patient, suggesting that undiagnosed FXS patients with single point mutations may exist. Functional analysis shows an unexpected nuclear export role for the prematurely truncated protein.
Sequencing of a patient with typical FXS features reveals a point mutation in the FMR1 gene.
The resulting FMRP protein encodes a frameshifted sequence resulting in a nuclear/nucleolar localization signal and truncation of the C‐terminal region of FMRP.
Mutating the ectopic nucleolar localization signal or restoring the C‐terminus of the human protein results in normal FMRP sub‐cellular localization.
Overexpression of a patient‐mimicking protein in Drosophila neurons in vivo causes nuclear localization and novel axonal growth and guidance phenotypes.
Restoration of the C‐terminus rescues the localization and the normal activity of Drosophila FMRP.
A novel point mutation in the FMR1 gene was identified in a typical fragile X syndrome patient, suggesting that undiagnosed FXS patients with single point mutations may exist. Functional analysis shows an unexpected nuclear export role for the prematurely truncated protein.
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