Implication of Endoplasmic Reticulum Stress in Autism Spectrum Disorder

Altered offspring neurodevelopment in an L-NAME-induced preeclampsia rat model

Introduction

To investigate the mechanism underlying the increased risk of subsequent neurodevelopmental disorders in children born to mothers with preeclampsia, we evaluated the neurodevelopment of offspring of a preeclampsia rat model induced by the administration of N-nitro-L-arginine methyl ester (L-NAME) and identified unique protein signatures in the offspring cerebrospinal fluid.

Methods

Pregnant rats received an intraperitoneal injection of L-NAME (250 mg/kg/day) during gestational days 15-20 to establish a preeclampsia model. Behavioral experiments (negative geotaxis, open-field, rotarod treadmill, and active avoidance tests), immunohistochemistry [anti-neuronal nuclei (NeuN) staining in the hippocampal dentate gyrus and cerebral cortex on postnatal day 70], and proteome analysis of the cerebrospinal fluid on postnatal day 5 were performed on male offspring.

Results

Offspring of the preeclampsia dam exhibited increased growth restriction at birth (52.5%), but showed postnatal catch-up growth on postnatal day 14. Several behavioral abnormalities including motor development and vestibular function (negative geotaxis test: p < 0.01) in the neonatal period; motor coordination and learning skills (rotarod treadmill test: p = 0.01); and memory skills (active avoidance test: p < 0.01) in the juvenile period were observed. NeuN-positive cells in preeclampsia rats were significantly reduced in both the hippocampal dentate gyrus and cerebral cortex (p < 0.01, p < 0.01, respectively). Among the 1270 proteins in the cerebrospinal fluid identified using liquid chromatography-tandem mass spectrometry, 32 were differentially expressed. Principal component analysis showed that most cerebrospinal fluid samples achieved clear separation between preeclampsia and control rats. Pathway analysis revealed that differentially expressed proteins were associated with endoplasmic reticulum translocation, Rab proteins, and ribosomal proteins, which are involved in various nervous system disorders including autism spectrum disorders, schizophrenia, and Alzheimer's disease.

Conclusion

The offspring of the L-NAME-induced preeclampsia model rats exhibited key features of neurodevelopmental abnormalities on behavioral and pathological examinations similar to humans. We found altered cerebrospinal fluid protein profiling in this preeclampsia rat, and the unique protein signatures related to endoplasmic reticulum translocation, Rab proteins, and ribosomal proteins may be associated with subsequent adverse neurodevelopment in the offspring.

Dysregulation of immune and metabolism pathways in maternal immune activation induces an increased risk of autism spectrum disorders

AIMS

Maternal immune activation (MIA) via infection during pregnancy is known to be an environmental risk factor for neurodevelopmental disorders and the development of autism spectrum disorders (ASD) in the offspring, but it still remains elusive that the molecular relevance between infection-induced abnormal neurodevelopmental events and an increased risk for ASD development.

MAIN METHODS

Fully considering the extremely high genetic heterogeneity of ASD and the universality of risk-gene with minimal effect-sizes, the gene and pathway-based association analysis was performed with the transcriptomic and DNA methylation landscapes of temporal human embryonic brain development and ASD, and the time-course transcriptional profiling of MIA. We conducted the transcriptional profiling of mouse abnormal neurodevelopment two days following induced MIA via LPS injection at E10.5.

KEY FINDINGS

A novel evidence was proved that illustrated altering four immune and metabolism-related risk pathways, including starch and sucrose metabolism, ribosome, protein processing in endoplasmic reticulum, and retrograde endocannabinoid signaling pathway, which were prominent involvement in the process of MIA regulating abnormal fetal brain development to induce an increased risk of ASD. Here, we have observed that almost all key genes within these risk pathways are significantly differentially expressed at embryonic days (E) 10.5-12.5, which is considered to be the optimal coincidence window of mouse embryonic brain development to study the intimate association between MIA and ASD using mouse animal models.

SIGNIFICANCE

There search establishes that MIA causes dysregulation of immune and metabolic pathways, which leads to abnormal embryonic neurodevelopment, thus promoting development of ASD symptoms in offspring.

Sel1l May Contributes to the Determinants of Neuronal Lineage and Neuronal Maturation Regardless of Hrd1 via Atf6-Sel1l Signaling

The endoplasmic reticulum (ER) is the primary site of intracellular quality control involved in the recognition and degradation of unfolded proteins. A variety of stresses, including hypoxia and glucose starvation, can lead to accumulation of unfolded proteins triggering the ER-associated degradation (ERAD) pathway. Suppressor Enhancer Lin12/Notch1 Like (Sel1l) acts as a "gate keeper" in the quality control of de novo synthesized proteins and complexes with the ubiquitin ligase Hrd1 in the ER membrane. We previously demonstrated that ER stress-induced aberrant neural stem cell (NSC) differentiation and inhibited neurite outgrowth. Inhibition of neurite outgrowth was associated with increased Hrd1 expression; however, the contribution of Sel1l remained unclear. To investigate whether ER stress is induced during normal neuronal differentiation, we semi-quantitatively evaluated mRNA expression levels of unfolded protein response (UPR)-related genes in P19 embryonic carcinoma cells undergoing neuronal differentiation in vitro. Stimulation with all-trans retinoic acid (ATRA) for 4 days induced the upregulation of Nestin and several UPR-related genes (Atf6, Xbp1, Chop, Hrd1, and Sel1l), whereas Atf4 and Grp78/Bip were unchanged. Small-interfering RNA (siRNA)-mediated knockdown of Sel1l uncovered that mRNA levels of the neural progenitor marker Math1 (also known as Atoh1) and the neuronal marker Math3 (also known as Atoh3 and NeuroD4) were significantly suppressed at 4 days after ATRA stimulation. Consistent with this result, Sel1l silencing significantly reduced protein levels of immature neuronal marker βIII-tubulin (also known as Tuj-1) at 8 days after induction of neuronal differentiation, whereas synaptogenic factors, such as cell adhesion molecule 1 (CADM1) and SH3 and multiple ankyrin repeat domain protein 3 (Shank3) were accumulated in Sel1l silenced cells. These results indicate that neuronal differentiation triggers ER stress and suggest that Sel1l may facilitate neuronal lineage through the regulation of Math1 and Math3 expression.

Chemical chaperones ameliorate neurodegenerative disorders in Derlin-1-deficient mice via improvement of cholesterol biosynthesis

There are no available therapies targeting the underlying molecular mechanisms of neurodegenerative diseases. Although chaperone therapies that alleviate endoplasmic reticulum (ER) stress recently showed promise in the treatment of neurodegenerative diseases, the detailed mechanisms remain unclear. We previously reported that mice with central nervous system-specific deletion of Derlin-1, which encodes an essential component for ER quality control, are useful as models of neurodegenerative diseases such as spinocerebellar degeneration. Cholesterol biosynthesis is essential for brain development, and its disruption inhibits neurite outgrowth, causing brain atrophy. In this study, we report a novel mechanism by which chemical chaperones ameliorate brain atrophy and motor dysfunction. ER stress was induced in the cerebella of Derlin-1 deficiency mice, whereas the administration of a chemical chaperone did not alleviate ER stress. However, chemical chaperone treatment ameliorated cholesterol biosynthesis impairment through SREBP-2 activation and simultaneously relieved brain atrophy and motor dysfunction. Altogether, these findings demonstrate that ER stress may not be the target of action of chaperone therapies and that chemical chaperone-mediated improvement of brain cholesterol biosynthesis is a promising novel therapeutic strategy for neurodegenerative diseases.

Autism-associated mutation in Hevin/Sparcl1 induces endoplasmic reticulum stress through structural instability

Hevin is a secreted extracellular matrix protein that is encoded by the SPARCL1 gene. Recent studies have shown that Hevin plays an important role in regulating synaptogenesis and synaptic plasticity. Mutations in the SPARCL1 gene increase the risk of autism spectrum disorder (ASD). However, the molecular basis of how mutations in SPARCL1 increase the risk of ASD is not been fully understood. In this study, we show that one of the SPARCL1 mutations associated with ASD impairs normal Hevin secretion. We identified Hevin mutants lacking the EF-hand motif through analyzing ASD-related mice with vulnerable spliceosome functions. Hevin deletion mutants accumulate in the endoplasmic reticulum (ER), leading to the activation of unfolded protein responses. We also found that a single amino acid substitution of Trp⁶⁴⁷ with Arg in the EF-hand motif associated with a familial case of ASD causes a similar phenotype in the EF-hand deletion mutant. Importantly, molecular dynamics (MD) simulation revealed that this single amino acid substitution triggers exposure of a hydrophobic amino acid to the surface, increasing the binding of Hevin with molecular chaperons, BIP. Taken together, these data suggest that the integrity of the EF-hand motif in Hevin is crucial for proper folding and that ASD-related mutations impair the export of Hevin from the ER. Our data provide a novel mechanism linking a point mutation in the SPARCL1 gene to the molecular and cellular characteristics involved in ASD.

Autism-associated synaptic vesicle transcripts are differentially expressed in maternal plasma exosomes of physiopathologic pregnancies

BACKGROUND

During intrauterine development, the formation and function of synaptic vesicles (SVs) are thought to be fundamental conditions essential for normal development of the brain. Lacking advanced technology during the intrauterine period, such as longitudinal real-time monitoring of the SV-associated transcripts (SVATs), which include six pairs of lncRNA-mRNA, has limited acquisition of the dynamic gene expression profile (GEP) of SVATs. We previously reported the differential expression of SVATs in the peripheral blood of autistic children. The current study was designed to determine the dynamic profiles of differentially-expressed SVATs in circulating exosomes (EXs) derived from autistic children and pregnant women at different gestational ages.

METHODS

Blood samples were collected from autistic children and women with variant physiopathologic pregnancies. EXs were isolated with an ExoQuick Exosome Precipitation Kit and characterized by transmission electron microscopy (TEM), nanoparticle tracking analysis (NTA), and Western blotting. The expression of lncRNAs and lncRNA-targeted mRNAs were quantified using real-time PCR.

RESULTS

SVAT-associated lncRNAs-mRNAs were detected in autistic children and differentially expressed from the first trimester of pregnancy to the term of delivery. Pathologic pregnancies, including spontaneous preterm birth (sPTB), preeclampsia (PE), and gestational diabetes mellitus (GDM), were compared to normal physiologic pregnancies, and shown to exhibit specific correlations between SVAT-lncRNA and SVAT-mRNA of STX8, SLC18A2, and SYP with sPTB; SVAT-lncRNA and SVAT-mRNA of STX8 with PE; and SVAT-lncRNA and SVAT-mRNA of SV2C as well as SVAT-mRNA of SYP with GDM.

CONCLUSION

Variant complications in pathologic pregnancies may alter the GEP of SVATs, which is likely to affect the intrauterine development of neural circuits and consequently influence fetal brain development.

Interpretable Machine Learning Reveals Dissimilarities Between Subtypes of Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a heterogeneous neuropsychiatric disorder with a complex genetic background. Analysis of altered molecular processes in ASD patients requires linear and nonlinear methods that provide interpretable solutions. Interpretable machine learning provides legible models that allow explaining biological mechanisms and support analysis of clinical subgroups. In this work, we investigated several case-control studies of gene expression measurements of ASD individuals. We constructed a rule-based learning model from three independent datasets that we further visualized as a nonlinear gene-gene co-predictive network. To find dissimilarities between ASD subtypes, we scrutinized a topological structure of the network and estimated a centrality distance. Our analysis revealed that autism is the most severe subtype of ASD, while pervasive developmental disorder-not otherwise specified and Asperger syndrome are closely related and milder ASD subtypes. Furthermore, we analyzed the most important ASD-related features that were described in terms of gene co-predictors. Among others, we found a strong co-predictive mechanism between EMC4 and TMEM30A, which may suggest a co-regulation between these genes. The present study demonstrates the potential of applying interpretable machine learning in bioinformatics analyses. Although the proposed methodology was designed for transcriptomics data, it can be applied to other omics disciplines.

Protein Biomarkers of Autism Spectrum Disorder Identified by Computational and Experimental Methods

Background: Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder that affects millions of people worldwide. However, there are currently no reliable biomarkers for ASD diagnosis. Materials and Methods: The strategy of computational prediction combined with experimental verification was used to identify blood protein biomarkers for ASD. First, brain tissue-based transcriptome data of ASD were collected from Gene Expression Omnibus database and analyzed to find ASD-related genes by bioinformatics method of significance analysis of microarrays. Then, a prediction program of blood-secretory proteins was applied on these genes to predict ASD-related proteins in blood. Furthermore, ELISA was used to verify these proteins in plasma samples of ASD patients. Results: A total of 364 genes were identified differentially expressed in brain tissue of ASD, among which 59 genes were predicted to encode ASD-related blood-secretory proteins. After functional analysis and literature survey, six proteins were chosen for experimental verification and five were successfully validated. Receiver operating characteristic curve analyses showed that the area under the curve of SLC25A12, LIMK1, and RARS was larger than 0.85, indicating that they are more powerful in discriminating ASD cases from controls. Conclusion: SLC25A12, LIMK1, and RARS might serve as new potential blood protein biomarkers for ASD. Our findings provide new insights into the pathogenesis and diagnosis of ASD.

The neuroligins and the synaptic pathway in Autism Spectrum Disorder

The genetics underlying autism spectrum disorder (ASD) is complex and heterogeneous, and de novo variants are found in genes converging in functional biological processes. Neuronal communication, including trans-synaptic signaling involving two families of cell-adhesion proteins, the presynaptic neurexins and the postsynaptic neuroligins, is one of the most recurrently affected pathways in ASD. Given the role of these proteins in determining synaptic function, abnormal synaptic plasticity and failure to establish proper synaptic contacts might represent mechanisms underlying risk of ASD. More than 30 mutations have been found in the neuroligin genes. Most of the resulting residue substitutions map in the extracellular, cholinesterase-like domain of the protein, and impair protein folding and trafficking. Conversely, the stalk and intracellular domains are less affected. Accordingly, several genetic animal models of ASD have been generated, showing behavioral and synaptic alterations. The aim of this review is to discuss the current knowledge on ASD-linked mutations in the neuroligin proteins and their effect on synaptic function, in various brain areas and circuits.

The Emerging Role of Electrophiles as a Key Regulator for Endoplasmic Reticulum (ER) Stress

The unfolded protein response (UPR) is activated by the accumulation of misfolded proteins in the endoplasmic reticulum (ER), which is called ER stress. ER stress sensors PERK, IRE1, and ATF6 play a central role in the initiation and regulation of the UPR; they inhibit novel protein synthesis and upregulate ER chaperones, such as protein disulfide isomerase, to remove unfolded proteins. However, when recovery from ER stress is difficult, the UPR pathway is activated to eliminate unhealthy cells. This signaling transition is the key event of many human diseases. However, the precise mechanisms are largely unknown. Intriguingly, reactive electrophilic species (RES), which exist in the environment or are produced through cellular metabolism, have been identified as a key player of this transition. In this review, we focused on the function of representative RES: nitric oxide (NO) as a gaseous RES, 4-hydroxynonenal (HNE) as a lipid RES, and methylmercury (MeHg) as an environmental organic compound RES, to outline the relationship between ER stress and RES. Modulation by RES might be a target for the development of next-generation therapy for ER stress-associated diseases.

Ubiquitin ligase HMG-CoA reductase degradation 1 (HRD1) prevents cell death in a cellular model of Parkinson's disease

Endoplasmic reticulum (ER) stress may play a role in the etiology of Parkinson's disease (PD). We have previously reported that ubiquitin ligase 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase degradation 1 (HRD1) involved in ER stress degrades unfolded protein that accumulates in the ER due to loss of function of Parkin, which is a causative factor in familial PD. We have also demonstrated that cell death is suppressed by the degradation of unfolded proteins. These findings indicate that HRD1 may serve as a compensatory mechanism for the loss of function of Parkin in familial PD patients. However, the role of HRD1 in sporadic PD has not yet been identified. This study aimed to reveal the roles of HRD1 and associated molecules in a cellular model of PD. We demonstrated that expressions of HRD1 and Suppressor/Enhancer Lin12 1-like (SEL1L: a HRD1 stabilizer) increased in SH-SY5Y human neuroblastoma cells upon exposure to 6-hydroxydopamine (6-OHDA). The 6-OHDA-induced cell death was suppressed in cells overexpressing wt-HRD1, whereas cell death was enhanced in cells with knockdown of HRD1 expression. These results suggest that HRD1 is a key molecule involved in 6-OHDA-induced cell death. By contrast, suppression of SEL1L expression decreased the amount of HRD1 protein. As a result, 6-OHDA-induced cell death was enhanced in cells suppressing SEL1L expression, and this cell death was much more evident than that in cells with suppression of HRD1 expression. These findings strongly indicate that SEL1L is necessary for maintaining and stabilizing the amount of HRD1 protein, and stabilizing the amount of HRD1 protein through SEL1L may serve to protect against 6-OHDA-induced cell death. Furthermore, the expression of Parkin was reinforced when HRD1 mRNA had been suppressed in cells, but was not observed when SEL1L mRNA had been restrained. It is possible that Parkin expression is induced as a compensatory mechanism when HRD1 mRNA decreases. This intracellular transduction may suppress the enhancement of 6-OHDA-induced cell death caused by the loss of HRD1. Taken together with these results, it is suggested that HRD1 and its stabilizer (SEL1L) are key molecules for elucidating the pathogenesis and treatment of PD.