Ngly1 -/- rats develop neurodegenerative phenotypes and pathological abnormalities in their peripheral and central nervous systems

MAGI1 attenuates osteoarthritis by regulating osteoclast fusion in subchondral bone through the RhoA-ROCK1 signaling pathway

Background

Osteoarthritis (OA) is a chronic joint disorder that predominantly affects middle-aged or elderly individuals. Subchondral bone remodeling due to osteoclast hyperactivation is regarded as a major feature of early OA. During osteoclast fusion and multinucleation, the cytoskeleton reorganization leads to the formation of actin belts and ultimately bone resorption. Membrane-associated guanylate kinase with an inverted repeat member 1 (MAGI1) is a scaffolding protein that is crucial for linking the extracellular environment to intracellular signaling pathways and cytoskeleton. However, the role of MAGI1 in subchondral bone osteoclast fusion remains unclear.

Methods

In this study, we collected knee joint samples from OA patients and established the OA mouse model to examine the expression of MAGI1. Furthermore, we established the OA rat model and locally injected rAAV9-mediated shMagi1 into the subchondral bone to knock down MAGI1 expression. Micro-CT, histological staining, and immunofluorescence were employed to assess the effects of MAGI1 knockdown on subchondral bone homeostasis and OA process. We isolated and cultured osteoclasts from femoral and tibial bone marrow. Receptor activator of nuclear factor-κB ligand (RANKL)-stimulated osteoclasts served as an in vitro model for OA and underwent RNA sequencing. We employed gain- and loss-of-function experiments using MAGI1-overexpression plasmids and small interfering RNA to explore the role of MAGI1 in osteoclast differentiation. Further molecular experiments, including RT-qPCR, western blotting, immunofluorescence staining, and LC-MS/MS were performed to investigate underlying mechanisms.

Results

MAGI1 expression was significantly downregulated during RANKL-induced osteoclastogenesis in vitro. Additionally, a progressive decrease in MAGI1 expression was consistently observed in both knee joint samples from OA patients and mouse OA models, correlating with OA progression. Knockdown of MAGI1 in subchondral bone increased osteoclast numbers and worsened subchondral bone microarchitecture and cartilage degeneration; MAGI1 knockdown rats exhibited elevated PDGF-BB, Netrin-1, and CGRP+ sensory innervation. Overexpression and knockdown of MAGI1 suppressed and promoted osteoclast differentiation, respectively. Mechanistically, MAGI1 overexpression decreased the levels of RhoA, ROCK1, and p-p65 in RANKL-treated osteoclasts, which was rescued by the addition of RhoA activator narciclasine.

Conclusion

Our results demonstrate that MAGI1 suppresses osteoclast fusion through the RhoA/ROCK1 signaling pathway, targeting MAGI1 in subchondral bone osteoclasts may be a promising therapeutic strategy mitigate the advancement of OA.

The translational potential of this article

This study reveals that the scaffold protein MAGI1 participates in osteoarthritis progression by regulating osteoclast fusion, providing novel theoretical foundations and potential therapeutic targets for osteoarthritis treatment.

Increased oxidative stress and autophagy in NGLY1 patient iPSC-derived neural stem cells

NGLY1 (N-glycanase) is a de-glycosylating enzyme that promotes clearance of misfolded glycan proteins. NGLY1 deficiency leads to a disease pathology with varied symptoms, including severe neurological defects. There are no therapeutic options currently available for the treatment of this rare disease. With the goal of finding potential therapeutic avenues, we performed comprehensive characterization of aberrant cellular stress pathways in a patient relevant model of NGLY1 deficiency. For a more accurate study of NGLY1 deficiency without other confounding factors, we compared differences between iPSC-derived neural stem cells carrying the commonly occurring nonsense mutation c.1201A > T (p.R401X) and their genetically similar CRISPR-corrected isogenic controls. Our findings demonstrate that NGLY1 deficiency in neural stem cells leads to an upregulation of ER stress, increased autophagic flux and significant signs of oxidative stress. These results provide new insights into the cellular dysfunctions associated with this disorder. Moreover, they point to better establishing reliable high throughput phenotypic assays that can be utilized for drug discovery.

The Therapeutic Future for Congenital Disorders of Glycosylation

The past decade, novel treatment options for congenital disorders of glycosylation (CDG) have advanced rapidly. Innovative therapies, targeting both the root cause, the affected metabolic pathways, and resulting manifestations, have transitioned from the research stage to practical applications. However, with novel therapeutic abilities, novel challenges await, specifically when it concerns the large number of clinical trials that need to be performed in order to treat all 190 genetic defects that cause CDG known to date. The present paper aims to provide an overview of how the CDG field can keep advancing its therapeutic strategies over the coming years with these challenges in mind. We focus on three important pillars that may shape the future of CDG: the use of disease models, clinical trial readiness, and the possibility to make individualized treatments scalable to the entire CDG cohort.

Small-molecule activators of NRF1 transcriptional activity prevent protein aggregation

Intracellular protein aggregation causes proteotoxic stress, underlying highly debilitating neurodegenerative disorders in parallel with decreased proteasome activity. Nevertheless, under such stress conditions, the expression of proteasome subunits is upregulated by Nuclear Factor Erythroid 2-related factor 1 (NRF1), a transcription factor that is encoded by NFE2L1. Activating the NRF1 pathway could accordingly delay the onset of neurodegenerative and other disorders with impaired cell proteostasis. Here, we present a series of small-molecule compounds based on bis(phenylmethylen)cycloalkanones and their heterocyclic analogues, identified via targeted library screening, that can induce NRF1-dependent downstream events, such as proteasome synthesis, heat shock response, and autophagy, in both model cell lines and Caenorhabditis elegans strains. These compounds increase proteasome activity and decrease the size and number of protein aggregates without causing any cellular stress or inhibiting the ubiquitin-proteasome system (UPS). Therefore, our compounds represent a new promising therapeutic approach for various protein conformational diseases, including the most debilitating neurodegenerative diseases.

Advancing ex vivo functional whole-organ prostate gland model for regeneration and drug screening

Model organisms are vital for biomedical research and drug testing but face high costs, complexity, and ethical issues. While newer techniques like organoids and assembloids have shown improvements, they still remain inadequate in addressing all research needs. In this study, we present a new method for maintaining the prostate gland of the earthworm, Eudrilus eugeniae ex vivo and examine its potential for regeneration and drug screening. We successfully maintained the earthworm prostate gland in cell culture media for over 200 days, with observed beating behavior confirming its viability. Apoptotic staining and histological analysis show no significant changes, indicating that the prostate gland remains stable. However, significant overexpression of H3 and H2AX on the 10th and 50th days suggests stem cell proliferation and differentiation. Alkaline phosphatase expression analysis confirmed that the stem cell niche is localized to the anterior region. Remarkably, the posterior region of the prostate gland demonstrated significant regenerative capacity, with complete regeneration occurring within 45 days following amputation. Furthermore, treatment with valproic acid enhanced posterior regeneration, leading to full restoration within 12 days. This study confirms the feasibility of maintaining the prostate gland of earthworms in an ex vivo setting, providing a valuable model for studying regeneration and conducting drug screening.

Ex vivo functional whole organ in biomedical research: a review

Model systems are critical in biomedical and preclinical research. Animal and in vitro models serve an important role in our current understanding of human physiology, disease pathophysiology, and therapy development. However, if the system is between cell culture and animal models, it may be able to overcome the knowledge gap that exists in the current system. Studies employing ex vivo organs as models have not been thoroughly investigated. Though the integration of other organs and systems has an impact on many biological mechanisms and disorders, it can add a new dimension to modeling and aid in the identification of new possible therapeutic targets. Here, we have discussed why the ex vivo organ model is desirable and the importance of the inclusion of organs from diverse species, described its historical aspects, studied organs as models in scientific research, and its ex vivo stability. We also discussed, how an ex vivo organ model might help researchers better understand organ physiology, as well as organ-specific diseases and therapeutic targets. We emphasized how this ex vivo organ dynamics will be more competent than existing models, as well as what tissues or organs would have potentially viable longevity for ex vivo modeling including human tissues, organs, and/or at least biopsies and its possible advantage in clinical medicine including organ transplantation procedure and precision medicine.

A Rare Case of Polymicrogyria in an Elderly Individual With Unique Polygenic Underlining

Polymicrogyria (PMG) is the most common malformation of cortical development (MCD) and presents as an irregularly patterned cortical surface with numerous small gyri and shallow sulci leading to various neurological deficits including developmental delays, intellectual disability, epilepsy, and language and motor issues. The presentation of PMG varies and is often found in conjunction with other congenital anomalies. Histologically, PMG features an abnormal cortical structure and dyslamination, resulting in its classification as a defect of neuronal migration and organization. Due in part to a variety of etiologies, little is known about the molecular mechanism(s) underlining PMG. To address this gap in knowledge, a case study is presented where an elderly individual with a medical history of unspecified PMG was examined postmortem by using a combination of anatomical, magnetic resonance imaging (MRI), histopathological, and genetic techniques. The results of the study allowed the classification of this case as bifrontal PMG. The genetic screening by whole exome sequencing (WES) on the Illumina Next Generation Sequencing (NGS) platform yielded 83 rare (minor allele frequency, MAF ≤ 0.01) pathological/deleterious variants where none of the respective genes has been previously linked to PMG. However, a subsequent analysis of those variants revealed that a significant number of affected genes were associated with most of the biological processes known to be impaired in PMG thereby pointing toward a polygenic nature in the present case. One of the notable features of the WES dataset was the presence of rare pathological/deleterious variants of genes (ADGRA2, PCDHA1, PCDHA12, PTK7, TPGS1, and USP4) involved in the regulation of Wnt signaling potentially highlighting the latter as an important PMG contributor in the present case. Notably, ADGRA2 warrants a closer look as a candidate gene for PMG because it not only regulates cortical patterning but has also been recently linked to two cases of bifrontal PMG with multiple congenital anomalies through its compound heterozygous mutations.

Systemic gene therapy corrects the neurological phenotype in a mouse model of NGLY1 deficiency

The cytoplasmic peptide:N-glycanase (NGLY1) is ubiquitously expressed and functions as a de-N-glycosylating enzyme that degrades misfolded N-glycosylated proteins. NGLY1 deficiency due to biallelic loss-of-function NGLY1 variants is an ultrarare autosomal recessive deglycosylation disorder with multisystemic involvement; the neurological manifestations represent the main disease burden. Currently, there is no treatment for this disease. To develop a gene therapy, we first characterized a tamoxifen-inducible Ngly1-knockout (iNgly1) C57BL/6J mouse model, which exhibited symptoms recapitulating human disease, including elevation of the biomarker GlcNAc-Asn, motor deficits, kyphosis, Purkinje cell loss, and gait abnormalities. We packaged a codon-optimized human NGLY1 transgene cassette into 2 adeno-associated virus (AAV) capsids, AAV9 and AAV.PHPeB. Systemic administration of the AAV.PHPeB vector to symptomatic iNgly1 mice corrected multiple disease features at 8 weeks after treatment. Furthermore, another cohort of AAV.PHPeB-treated iNgly1 mice were monitored over a year and showed near-complete normalization of the neurological aspects of the disease phenotype, demonstrating the durability of gene therapy. Our data suggested that brain-directed NGLY1 gene replacement via systemic delivery is a promising therapeutic strategy for NGLY1 deficiency. Although the superior CNS tropism of AAV.PHPeB vector does not translate to primates, emerging AAV capsids with enhanced primate CNS tropism will enable future translational studies.

Mutations in nucleotide metabolism genes bypass proteasome defects in png-1/NGLY1-deficient Caenorhabditis elegans

The conserved SKN-1A/Nrf1 transcription factor regulates the expression of proteasome subunit genes and is essential for maintenance of adequate proteasome function in animal development, aging, and stress responses. Unusual among transcription factors, SKN-1A/Nrf1 is a glycoprotein synthesized in the endoplasmic reticulum (ER). N-glycosylated SKN-1A/Nrf1 exits the ER and is deglycosylated in the cytosol by the PNG-1/NGLY1 peptide:N-glycanase. Deglycosylation edits the protein sequence of SKN-1A/Nrf1 by converting N-glycosylated asparagine residues to aspartate, which is necessary for SKN-1A/Nrf1 transcriptional activation of proteasome subunit genes. Homozygous loss-of-function mutations in the peptide:N-glycanase (NGLY1) gene cause NGLY1 deficiency, a congenital disorder of deglycosylation. There are no effective treatments for NGLY1 deficiency. Since SKN-1A/Nrf1 is a major client of NGLY1, the resulting proteasome deficit contributes to NGLY1 disease. We sought to identify targets for mitigation of proteasome dysfunction in NGLY1 deficiency that might indicate new avenues for treatment. We isolated mutations that suppress the sensitivity to proteasome inhibitors caused by inactivation of the NGLY1 ortholog PNG-1 in Caenorhabditis elegans. We identified multiple suppressor mutations affecting 3 conserved genes: rsks-1, tald-1, and ent-4. We show that the suppressors act through a SKN-1/Nrf-independent mechanism and confer proteostasis benefits consistent with amelioration of proteasome dysfunction. ent-4 encodes an intestinal nucleoside/nucleotide transporter, and we show that restriction of nucleotide availability is beneficial, whereas a nucleotide-rich diet exacerbates proteasome dysfunction in PNG-1/NGLY1-deficient C. elegans. Our findings suggest that dietary or pharmacological interventions altering nucleotide availability have the potential to mitigate proteasome insufficiency in NGLY1 deficiency and other diseases associated with proteasome dysfunction.

Intranasal oxytocin suppresses seizure-like behaviors in a mouse model of NGLY1 deficiency

NGLY1 deficiency is a genetic disease caused by biallelic mutations of the Ngly1 gene. Although epileptic seizure is one of the most severe symptoms in patients with NGLY1 deficiency, preclinical studies have not been conducted due to the lack of animal models for epileptic seizures in NGLY1 deficiency. Here, we observed the behaviors of male and female Ngly1-/- mice by video monitoring and found that these mice exhibit spontaneous seizure-like behaviors. Gene expression analyses and enzyme immunoassay revealed significant decreases in oxytocin, a well-known neuropeptide, in the hypothalamus of Ngly1-/- mice. Seizure-like behaviors in Ngly1-/- mice were transiently suppressed by a single intranasal administration of oxytocin. These findings suggest the therapeutic potential of oxytocin for epileptic seizure in patients with NGLY1 deficiency and contribute to the clarification of the disease mechanism.

Development of a fluorescence and quencher-based FRET assay for detection of endogenous peptide:N-glycanase/NGLY1 activity

Cytosolic peptide:N-glycanase (PNGase/NGLY1 in mammals) catalyzes deglycosylation of N-glycans on glycoproteins. A genetic disorder caused by mutations in the NGLY1 gene leads to NGLY1 deficiency with symptoms including motor deficits and neurological problems. Effective therapies have not been established, though, a recent study used the administration of an adeno-associated viral vector expressing human NGLY1 to dramatically rescue motor functions in young Ngly1-/- rats. Thus, early therapeutic intervention may improve symptoms arising from central nervous system dysfunction, and assay methods for measuring NGLY1 activity in biological samples are critical for early diagnostics. In this study, we established an assay system for plate-based detection of endogenous NGLY1 activity using a FRET-based probe. Using this method, we revealed significant changes in NGLY1 activity in rat brains during aging. This novel assay offers reliable disease diagnostics and provides valuable insights into the regulation of PNGase/NGLY1 activity in diverse organisms under different stress conditions.

A commentary on 'Patient-derived gene and protein expression signatures of NGLY1 deficiency'

The cytosolic peptide:N-glycanase (PNGase; NGLY1 in human and PNG1 in budding yeast) is a deglycosylating enzyme widely conserved in eukaryotes. Initially, functional importance of this enzyme remained unknown as the png1Δ mutant in yeast did not exhibit any significant phenotypes. However, the discovery of NGLY1 deficiency, a rare genetic disorder with biallelic mutations in NGLY1 gene, prompted an intensification of research that has resulted in uncovering the significance of NGLY1 as well as the proteins under its influence that are involved in numerous cellular processes. A recent report by Rauscher et al. (Patient-derived gene and protein expression signatures of NGLY1 deficiency. J. Biochem. 2022; 171: 187-199) presented a comprehensive summary of transcriptome/proteome analyses of various cell types derived from NGLY1-deficient patients. The authors also provide a web application called 'NGLY1 browser', which will allow researchers to have access to a wealth of information on gene and protein expression signature for patients with NGLY1 deficiency.

NGLY1: A fascinating, multifunctional molecule

NGLY1, a cytoplasmic de-N-glycosylating enzyme is well conserved among eukaryotes. This enzyme has attracted considerable attention after mutations on the NGLY1 gene were found to cause a rare genetic disorder called NGLY1 deficiency. Recent explosive progress in NGLY1 research has revealed multi-functional aspects of this protein.

NGLY1 mutations cause protein aggregation in human neurons

Biallelic mutations in the gene that encodes the enzyme N-glycanase 1 (NGLY1) cause a rare disease with multi-symptomatic features including developmental delay, intellectual disability, neuropathy, and seizures. NGLY1's activity in human neural cells is currently not well understood. To understand how NGLY1 gene loss leads to the specific phenotypes of NGLY1 deficiency, we employed direct conversion of NGLY1 patient-derived induced pluripotent stem cells (iPSCs) to functional cortical neurons. Transcriptomic, proteomic, and functional studies of iPSC-derived neurons lacking NGLY1 function revealed several major cellular processes that were altered, including protein aggregate-clearing functionality, mitochondrial homeostasis, and synaptic dysfunctions. These phenotypes were rescued by introduction of a functional NGLY1 gene and were observed in iPSC-derived mature neurons but not astrocytes. Finally, laser capture microscopy followed by mass spectrometry provided detailed characterization of the composition of protein aggregates specific to NGLY1-deficient neurons. Future studies will harness this knowledge for therapeutic development.

A Natural Compound Containing a Disaccharide Structure of Glucose and Rhamnose Identified as Potential N-Glycanase 1 (NGLY1) Inhibitors

N-glycanase 1 (NGLY1) is an essential enzyme involved in the deglycosylation of misfolded glycoproteins through the endoplasmic reticulum (ER)-associated degradation (ERAD) pathway, which could hydrolyze N-glycan from N-glycoprotein or N-glycopeptide in the cytosol. Recent studies indicated that NGLY1 inhibition is a potential novel drug target for antiviral therapy. In this study, structure-based virtual analysis was applied to screen candidate NGLY1 inhibitors from 2960 natural compounds. Three natural compounds, Poliumoside, Soyasaponin Bb, and Saikosaponin B2 showed significantly inhibitory activity of NGLY1, isolated from traditional heat-clearing and detoxifying Chinese herbs. Furthermore, the core structural motif of the three NGLY1 inhibitors was a disaccharide structure with glucose and rhamnose, which might exert its action by binding to important active sites of NGLY1, such as Lys238 and Trp244. In traditional Chinese medicine, many compounds containing this disaccharide structure probably targeted NGLY1. This study unveiled the leading compound of NGLY1 inhibitors with its core structure, which could guide future drug development.

Genetic disruption of mammalian endoplasmic reticulum-associated protein degradation: Human phenotypes and animal and cellular disease models

Endoplasmic reticulum-associated protein degradation (ERAD) is a stringent quality control mechanism through which misfolded, unassembled and some native proteins are targeted for degradation to maintain appropriate cellular and organelle homeostasis. Several in vitro and in vivo ERAD-related studies have provided mechanistic insights into ERAD pathway activation and its consequent events; however, a majority of these have investigated the effect of ERAD substrates and their consequent diseases affecting the degradation process. In this review, we present all reported human single-gene disorders caused by genetic variation in genes that encode ERAD components rather than their substrates. Additionally, after extensive literature survey, we present various genetically manipulated higher cellular and mammalian animal models that lack specific components involved in various stages of the ERAD pathway.

Regulation and Functions of the ER-Associated Nrf1 Transcription Factor

Nrf1 is a member of the nuclear erythroid 2-like family of transcription factors that regulate stress-responsive gene expression in animals. Newly synthesized Nrf1 is targeted to the endoplasmic reticulum (ER) where it is N-glycosylated. N-glycosylated Nrf1 is trafficked to the cytosol by the ER-associated degradation (ERAD) machinery and is subject to rapid proteasomal degradation. When proteasome function is impaired, Nrf1 escapes degradation and undergoes proteolytic cleavage and deglycosylation. Deglycosylation results in deamidation of N-glycosylated asparagine residues to edit the protein sequence encoded by the genome. This truncated and "sequence-edited" form of Nrf1 enters the nucleus where it induces up-regulation of proteasome subunit genes. Thus, Nrf1 drives compensatory proteasome biogenesis in cells exposed to proteasome inhibitor drugs and other proteotoxic insults. In addition to its role in proteasome homeostasis, Nrf1 is implicated in responses to oxidative stress, and maintaining lipid and cholesterol homeostasis. Here, we describe the conserved and complex mechanism by which Nrf1 is regulated and highlight emerging evidence linking this unusual transcription factor to development, aging, and disease.

Generation and characterization of NGLY1 patient-derived midbrain organoids

NGLY1 deficiency is an ultra-rare, autosomal recessive genetic disease caused by mutations in the NGLY1 gene encoding N-glycanase one that removes N-linked glycan. Patients with pathogenic mutations in NGLY1 have complex clinical symptoms including global developmental delay, motor disorder and liver dysfunction. To better understand the disease pathogenesis and the neurological symptoms of the NGLY1 deficiency we generated and characterized midbrain organoids using patient-derived iPSCs from two patients with distinct disease-causing mutations-one homozygous for p. Q208X, the other compound heterozygous for p. L318P and p. R390P and CRISPR generated NGLY1 knockout iPSCs. We demonstrate that NGLY1 deficient midbrain organoids show altered neuronal development compared to one wild type (WT) organoid. Both neuronal (TUJ1) and astrocytic glial fibrillary acid protein markers were reduced in NGLY1 patient-derived midbrain organoids along with neurotransmitter GABA. Interestingly, staining for dopaminergic neuronal marker, tyrosine hydroxylase, revealed a significant reduction in patient iPSC derived organoids. These results provide a relevant NGLY1 disease model to investigate disease mechanisms and evaluate therapeutics for treatments of NGLY1 deficiency.

N-glycoproteomics reveals distinct glycosylation alterations in NGLY1-deficient patient-derived dermal fibroblasts

Congenital disorders of glycosylation are genetic disorders that occur due to defects in protein and lipid glycosylation pathways. A deficiency of N-glycanase 1, encoded by the NGLY1 gene, results in a congenital disorder of deglycosylation. The NGLY1 enzyme is mainly involved in cleaving N-glycans from misfolded, retro-translocated glycoproteins in the cytosol from the endoplasmic reticulum before their proteasomal degradation or activation. Despite the essential role of NGLY1 in deglycosylation pathways, the exact consequences of NGLY1 deficiency on global cellular protein glycosylation have not yet been investigated. We undertook a multiplexed tandem mass tags-labeling-based quantitative glycoproteomics and proteomics analysis of fibroblasts from NGLY1-deficient individuals carrying different biallelic pathogenic variants in NGLY1. This quantitative mass spectrometric analysis detected 8041 proteins and defined a proteomic signature of differential expression across affected individuals and controls. Proteins that showed significant differential expression included phospholipid phosphatase 3, stromal cell-derived factor 1, collagen alpha-1 (IV) chain, hyaluronan and proteoglycan link protein 1, and thrombospondin-1. We further detected a total of 3255 N-glycopeptides derived from 550 glycosylation sites of 407 glycoproteins by multiplexed N-glycoproteomics. Several extracellular matrix glycoproteins and adhesion molecules showed altered abundance of N-glycopeptides. Overall, we observed distinct alterations in specific glycoproteins, but our data revealed no global accumulation of glycopeptides in the patient-derived fibroblasts, despite the genetic defect in NGLY1. Our findings highlight new molecular and system-level insights for understanding NGLY1-CDDG.

An induced pluripotent stem cell-derived NMJ platform for study of the NGLY1-Congenital Disorder of Deglycosylation

There are many neurological rare diseases where animal models have proven inadequate or do not currently exist. NGLY1 Deficiency, a congenital disorder of deglycosylation, is a rare disease that predominantly affects motor control, especially control of neuromuscular action. In this study, NGLY1-deficient, patient-derived induced pluripotent stem cells (iPSCs) were differentiated into motoneurons (MNs) to identify disease phenotypes analogous to clinical disease pathology with significant deficits apparent in the NGLY1-deficient lines compared to the control. A neuromuscular junction (NMJ) model was developed using patient and wild type (WT) MNs to study functional differences between healthy and diseased NMJs. Reduced axon length, increased and shortened axon branches, MN action potential (AP) bursting and decreased AP firing rate and amplitude were observed in the NGLY1-deficient MNs in monoculture. When transitioned to the NMJ-coculture system, deficits in NMJ number, stability, failure rate, and synchronicity with indirect skeletal muscle (SkM) stimulation were observed. This project establishes a phenotypic NGLY1 model for investigation of possible therapeutics and investigations into mechanistic deficits in the system.

AAV9-NGLY1 gene replacement therapy improves phenotypic and biomarker endpoints in a rat model of NGLY1 Deficiency

N-glycanase 1 (NGLY1) Deficiency is a progressive, ultra-rare, autosomal recessive disorder with no approved therapy and five core clinical features: severe global developmental delay, hyperkinetic movement disorder, elevated liver transaminases, alacrima, and peripheral neuropathy. Here, we confirmed and characterized the Ngly1 ^{-/- /} rat as a relevant disease model. GS-100, a gene therapy candidate, is a recombinant, single-stranded adeno-associated virus (AAV) 9 vector designed to deliver a functional copy of the human NGLY1 gene. Using the Ngly1 ^-/- rat, we tested different administration routes for GS-100: intracerebroventricular (ICV), intravenous (IV), or the dual route (IV + ICV). ICV and IV + ICV administration resulted in widespread biodistribution of human NGLY1 DNA and corresponding mRNA and protein expression in CNS tissues. GS-100 delivered by ICV or IV + ICV significantly reduced levels of the substrate biomarker N-acetylglucosamine-asparagine (GlcNAc-Asn or GNA) in CSF and brain tissue compared with untreated Ngly1^-/- rats. ICV and IV + ICV administration of GS-100 resulted in behavioral improvements in rotarod and rearing tests, whereas IV-only administration did not. IV + ICV did not provide additional benefit compared with ICV administration alone. These data provide evidence that GS-100 could be an effective therapy for NGLY1 Deficiency using the ICV route of administration.

Identification of endoplasmic reticulum stress-associated genes and subtypes for prediction of Alzheimer’s disease based on interpretable machine learning

Introduction: Alzheimer’s disease (AD) is a severe dementia with clinical and pathological heterogeneity. Our study was aim to explore the roles of endoplasmic reticulum (ER) stress-related genes in AD patients based on interpretable machine learning.

Methods: Microarray datasets were obtained from the Gene Expression Omnibus (GEO) database. We performed nine machine learning algorithms including AdaBoost, Logistic Regression, Light Gradient Boosting (LightGBM), Decision Tree (DT), eXtreme Gradient Boosting (XGBoost), Random Forest, K-nearest neighbors (KNN), Naïve Bayes, and support vector machines (SVM) to screen ER stress-related feature genes and estimate their efficiency of these genes for early diagnosis of AD. ROC curves were performed to evaluate model performance. Shapley additive explanation (SHAP) was applied for interpreting the results of these models. AD patients were classified using a consensus clustering algorithm. Immune infiltration and functional enrichment analysis were performed via CIBERSORT and GSVA, respectively. CMap analysis was utilized to identify subtype-specific small-molecule compounds.

Results: Higher levels of immune infiltration were found in AD individuals and were markedly linked to deregulated ER stress-related genes. The SVM model exhibited the highest AUC (0.879), accuracy (0.808), recall (0.773), and precision (0.809). Six characteristic genes (RNF5, UBAC2, DNAJC10, RNF103, DDX3X, and NGLY1) were determined, which enable to precisely predict AD progression. The SHAP plots illustrated how a feature gene influence the output of the SVM prediction model. Patients with AD could obtain clinical benefits from the feature gene-based nomogram. Two ER stress-related subtypes were defined in AD, subtype2 exhibited elevated immune infiltration levels and immune score, as well as higher expression of immune checkpoint. We finally identified several subtype-specific small-molecule compounds.

Conclusion: Our study provides new insights into the role of ER stress in AD heterogeneity and the development of novel targets for individualized treatment in patients with AD.

Hypolacrimia and Alacrimia as Diagnostic Features for Genetic or Congenital Conditions

As part of the lacrimal apparatus, the lacrimal gland participates in the maintenance of a healthy eye surface by producing the aqueous part of the tear film. Alacrimia and hypolacrimia, which are relatively rare during childhood or young adulthood, have their origin in a number of mechanisms which include agenesia, aplasia, hypoplasia, or incorrect maturation of the gland. Moreover, impaired innervation of the gland and/or the cornea and alterations of protein secretion pathways can lead to a defective tear film. In most conditions leading to alacrimia or hypolacrimia, however, the altered tear film is only one of numerous defects that arise and therefore is commonly disregarded. Here, we have systematically reviewed all of those genetic conditions or congenital disorders that have alacrimia or hypolacrimia as a feature. Where it is known, we describe the mechanism of the defect in question. It has been possible to clearly establish the physiopathology of only a minority of these conditions. As hypolacrimia and alacrimia are rare features, this review could be used as a tool in clinical genetics to perform a quick diagnosis, necessary for appropriate care and counseling.

NGLY1 Deficiency Zebrafish Model Manifests Abnormalities of the Nervous and Musculoskeletal Systems

Background: NGLY1 is an enigmatic enzyme with multiple functions across a wide range of species. In humans, pathogenic genetic variants in NGLY1 are linked to a variable phenotype of global neurological dysfunction, abnormal tear production, and liver disease presenting the rare autosomal recessive disorder N-glycanase deficiency. We have ascertained four NGLY1 deficiency patients who were found to carry a homozygous nonsense variant (c.1294G > T, p.Glu432*) in NGLY1.

Methods: We created an ngly1 deficiency zebrafish model and studied the nervous and musculoskeletal (MSK) systems to further characterize the phenotypes and pathophysiology of the disease.

Results: Nervous system morphology analysis has shown significant loss of axon fibers in the peripheral nervous system. In addition, we found muscle structure abnormality of the mutant fish. Locomotion behavior analysis has shown hypersensitivity of the larval ngly1^(−/−) fish during stress conditions.

Conclusion: This first reported NGLY1 deficiency zebrafish model might add to our understanding of NGLY1 role in the development of the nervous and MSK systems. Moreover, it might elucidate the natural history of the disease and be used as a platform for the development of novel therapies.

An in vivo drug repurposing screen and transcriptional analyses reveals the serotonin pathway and GSK3 as major therapeutic targets for NGLY1 deficiency

NGLY1 deficiency, a rare disease with no effective treatment, is caused by autosomal recessive, loss-of-function mutations in the N-glycanase 1 (NGLY1) gene and is characterized by global developmental delay, hypotonia, alacrima, and seizures. We used a Drosophila model of NGLY1 deficiency to conduct an in vivo, unbiased, small molecule, repurposing screen of FDA-approved drugs to identify therapeutic compounds. Seventeen molecules partially rescued lethality in a patient-specific NGLY1 deficiency model, including multiple serotonin and dopamine modulators. Exclusive dNGLY1 expression in serotonin and dopamine neurons, in an otherwise dNGLY1 deficient fly, was sufficient to partially rescue lethality. Further, genetic modifier and transcriptomic data supports the importance of serotonin signaling in NGLY1 deficiency. Connectivity Map analysis identified glycogen synthase kinase 3 (GSK3) inhibition as a potential therapeutic mechanism for NGLY1 deficiency, which we experimentally validated with TWS119, lithium, and GSK3 knockdown. Strikingly, GSK3 inhibitors and a serotonin modulator rescued size defects in dNGLY1 deficient larvae upon proteasome inhibition, suggesting that these compounds act through NRF1, a transcription factor that is regulated by NGLY1 and regulates proteasome expression. This study reveals the importance of the serotonin pathway in NGLY1 deficiency, and serotonin modulators or GSK3 inhibitors may be effective therapeutics for this rare disease.

NGLY1 deficiency is a rare disease with no effective treatment. We conducted a drug repurposing screen and used the Connectivity Map, a transcriptional-based computational approach, to identify compounds that may serve as therapeutics for NGLY1 deficient individuals. The drug repurposing screen identified FDA-approved compounds acting through the serotonin and dopamine pathway that partially rescued lethality in an NGLY1 deficiency fly model. We also found that expressing dNGLY1 (the Drosophila ortholog of NGLY1) exclusively in serotonin neurons, in an otherwise dNGLY1 deficient fly, partially rescued lethality. These data indicate the importance of the serotonin and dopamine systems in NGLY1 deficiency. The Connectivity Map analyses found GSK3 inhibitors as potential therapeutic compounds, which were validated in vivo in the fly. Furthermore, knockdown of sgg (the Drosophila ortholog of GSK3) partially rescued lethality in dNGLY1 deficient flies, suggesting GSK3 as a therapeutic target for NGLY1 deficiency. Taken together, this work identifies therapeutic strategies for NGLY1 deficiency.

Comprehensive Analysis of the Structure and Function of Peptide:N-Glycanase 1 and Relationship with Congenital Disorder of Deglycosylation

The cytosolic PNGase (peptide:N-glycanase), also known as peptide-N4-(N-acetyl-β-glucosaminyl)-asparagine amidase, is a well-conserved deglycosylation enzyme (EC 3.5.1.52) which catalyzes the non-lysosomal hydrolysis of an N(4)-(acetyl-β-d-glucosaminyl) asparagine residue (Asn, N) into a N-acetyl-β-d-glucosaminyl-amine and a peptide containing an aspartate residue (Asp, D). This enzyme (NGLY1) plays an essential role in the clearance of misfolded or unassembled glycoproteins through a process named ER-associated degradation (ERAD). Accumulating evidence also points out that NGLY1 deficiency can cause an autosomal recessive (AR) human genetic disorder associated with abnormal development and congenital disorder of deglycosylation. In addition, the loss of NGLY1 can affect multiple cellular pathways, including but not limited to NFE2L1 pathway, Creb1/Atf1-AQP pathway, BMP pathway, AMPK pathway, and SLC12A2 ion transporter, which might be the underlying reasons for a constellation of clinical phenotypes of NGLY1 deficiency. The current comprehensive review uncovers the NGLY1’ssdetailed structure and its important roles for participation in ERAD, involvement in CDDG and potential treatment for NGLY1 deficiency.

NGLY1 Deficiency, a Congenital Disorder of Deglycosylation: From Disease Gene Function to Pathophysiology

N-Glycanase 1 (NGLY1) is a cytosolic enzyme involved in removing N-linked glycans of misfolded N-glycoproteins and is considered to be a component of endoplasmic reticulum-associated degradation (ERAD). The 2012 identification of recessive NGLY1 mutations in a rare multisystem disorder has led to intense research efforts on the roles of NGLY1 in animal development and physiology, as well as the pathophysiology of NGLY1 deficiency. Here, we present a review of the NGLY1-deficient patient phenotypes, along with insights into the function of this gene from studies in rodent and invertebrate animal models, as well as cell culture and biochemical experiments. We will discuss critical processes affected by the loss of NGLY1, including proteasome bounce-back response, mitochondrial function and homeostasis, and bone morphogenetic protein (BMP) signaling. We will also cover the biologically relevant targets of NGLY1 and the genetic modifiers of NGLY1 deficiency phenotypes in animal models. Together, these discoveries and disease models have provided a number of avenues for preclinical testing of potential therapeutic approaches for this disease.

Spatial Transcriptomic Analysis Using R-Based Computational Machine Learning Reveals the Genetic Profile of Yang or Yin Deficiency Syndrome in Chinese Medicine Theory

OBJECTIVES

Yang and Yin are two main concepts responsible for harmonious balance reflecting health conditions based on Chinese medicine theory. Of note, deficiency of either Yang or Yin is associated with disease susceptibility. In this study, we aim to clarify the molecular feature of Yang and Yin deficiency by reanalyzing a transcriptomic data set retrieved from the GEO database using R-based machine learning analyses, which lays a foundation for medical diagnosis, prevention, and treatment of unbalanced Yang or Yin.

METHODS

Besides conventional methods for target mining, we took the advantage of spatial transcriptomic analysis using R-based machine learning approaches to elucidate molecular profiles of Yin and Yang deficiency by reanalyzing an RNA-Seq data set (GSE87474) in the GEO focusing on peripheral blood mononuclear cells (PBMCs). The add-on functions in R including GEOquery, DESeq2, WGCNA (target identification with a scale-free topological assumption), Scatterplot3d, Tidyverse, and UpsetR were used. For information in the selected GEO data set, PBMCs representing 20,740 expressed genes were collected from subjects with Yang or Yin deficiency (n = 12 each), based on Chinese medicine-related diagnostic criteria.

RESULTS

The symptomatic gene targets for Yang deficiency (KAT2B, NFKB2, CREBBP, GTF2H3) or Yin deficiency (JUNB, JUND, NGLY1, TNF, RAF1, PPP1R15A) were potentially discovered. CREBBP was identified as a shared key contributive gene regulating either the Yang or Yin deficiency group. The intrinsic molecular characteristics of these specific genes could link with clinical observations of Yang/Yin deficiency, in which Yang deficiency is associated with immune dysfunction tendency and energy deregulation, while Yin deficiency mainly contains oxidative stress, dysfunction of the immune system, and abnormal lipid/protein metabolism.

CONCLUSION

Our study provides representative gene targets and modules for supporting clinical traits of Yang or Yin deficiency in Chinese medicine theory, which is beneficial for promoting the modernization of Chinese medicine theory. Besides, R-based machine learning approaches adopted in this study might be further applied for investigating the underlying genetic polymorphisms related to Chinese medicine theory.

Deficiency of N-glycanase 1 perturbs neurogenesis and cerebral development modeled by human organoids

Mutations in N-glycanase 1 (NGLY1), which deglycosylates misfolded glycoproteins for degradation, can cause NGLY1 deficiency in patients and their abnormal fetal development in multiple organs, including microcephaly and other neurological disorders. Using cerebral organoids (COs) developed from human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs), we investigate how NGLY1 dysfunction disturbs early brain development. While NGLY1 loss had limited impact on the undifferentiated cells, COs developed from NGLY1-deficient hESCs showed defective formation of SATB2-positive upper-layer neurons, and attenuation of STAT3 and HES1 signaling critical for sustaining radial glia. Bulk and single-cell transcriptomic analysis revealed premature neuronal differentiation accompanied by downregulation of secreted and transcription factors, including TTR, IGFBP2, and ID4 in NGLY1-deficient COs. NGLY1 malfunction also dysregulated ID4 and enhanced neuronal differentiation in CO transplants developed in vivo. NGLY1-deficient CO cells were more vulnerable to multiple stressors; treating the deficient cells with recombinant TTR reduced their susceptibility to stress from proteasome inactivation, likely through LRP2-mediated activation of MAPK signaling. Expressing NGLY1 led to IGFBP2 and ID4 upregulation in CO cells developed from NGLY1-deficiency patient’s hiPSCs. In addition, treatment with recombinant IGFBP2 enhanced ID4 expression, STAT3 signaling, and proliferation of NGLY1-deficient CO cells. Overall, our discoveries suggest that dysregulation of stress responses and neural precursor differentiation underlies the brain abnormalities observed in NGLY1-deficient individuals.

Patient-derived gene and protein expression signatures of NGLY1 deficiency

N-Glycanase 1 (NGLY1) deficiency is a rare and complex genetic disorder. Although recent studies have shed light on the molecular underpinnings of NGLY1 deficiency, a systematic characterization of gene and protein expression changes in patient-derived cells has been lacking. Here, we performed RNA-sequencing and mass spectrometry to determine the transcriptomes and proteomes of 66 cell lines representing 4 different cell types derived from 14 NGLY1 deficient patients and 17 controls. Although NGLY1 protein levels were up to 9.5-fold downregulated in patients compared to parents, residual and likely non-functional NGLY1 protein was detectable in all patient-derived lymphoblastoid cell lines. Consistent with the role of NGLY1 as a regulator of the transcription factor Nrf1, we observed a cell type-independent downregulation of proteasomal genes in NGLY1 deficient cells. In contrast, genes involved in ribosome biogenesis and mRNA processing were upregulated in multiple cell types. In addition, we observed cell type-specific effects. For example, genes and proteins involved in glutathione synthesis, such as the glutamate-cysteine ligase subunits GCLC and GCLM, were downregulated specifically in lymphoblastoid cells. We provide a web application that enables access to all results generated in this study at https://apps.embl.de/ngly1browser. This resource will guide future studies of NGLY1 deficiency in directions that are most relevant to patients.

Assay for the peptide:N-glycanase/NGLY1 and disease-specific biomarkers for diagnosing NGLY1 deficiency

Cytosolic peptide:N-glycanase (NGLY1 in mammals), a highly conserved enzyme in eukaryotes, catalyzes the deglycosylation of N-glycans that are attached to glycopeptide/glycoproteins. In 2012, an autosomal recessive disorder related to the NGLY1 gene, which was referred to as NGLY1 deficiency, was reported. Since then, more than 100 patients have been identified. Patients with this disease exhibit various symptoms, including various motor deficits and other neurological problems. Effective therapeutic treatments for this disease, however, have not been established. Most recently, it was demonstrated that the intracerebroventricular administration of an adeno-associated virus 9 vector expressing human NGLY1 during the weaning period allowed some motor functions to be recovered in Ngly1-/- rats. This observation led us to hypothesize that a therapeutic intervention for improving these motor deficits or other neurological symptoms found in the patients might be possible. To achieve this, it is critical to establish robust and facile methods for assaying NGLY1 activity in biological samples, for the early diagnosis and evaluation of the therapeutic efficacy for the treatment of NGLY1 deficiency. In this mini-review, we summarize progress made in the development of various assay methods for NGLY1 activity, as well as a recent progress in the identification of NGLY1 deficiency-specific biomarkers.

NGLY1: Insights from C. elegans

Peptide:N-glycanase is an evolutionarily conserved deglycosylating enzyme that catalyzes the removal of N-linked glycans from cytosolic glycoproteins. Recessive mutations that inactivate this enzyme cause NGLY1 deficiency, a multisystemic disorder with symptoms including developmental delay and defects in cognition and motor control. Developing treatments for NGLY1 deficiency will require an understanding of how failure to deglycosylate NGLY1 substrates perturbs cellular and organismal function. In this review, I highlight insights into peptide:N-glycanase biology gained by studies in the highly tractable genetic model animal C. elegans. I focus on the recent discovery of SKN-1A/Nrf1, an N-glycosylated transcription factor, as a peptide:N-glycanase substrate critical for regulation of the proteasome. I describe the elaborate post-translational mechanism that culminates in activation of SKN-1A/Nrf1 via NGLY1-dependent 'sequence editing' and discuss the implications of these findings for our understanding of NGLY1 deficiency.

GlcNAc-Asn (GNA) is a biomarker for NGLY1 deficiency

Substrate-derived biomarkers are necessary in slowly progressing monogenetic diseases caused by single-enzyme deficiencies to identify affected patients and serve as surrogate markers for therapy response. N-glycanase 1 (NGLY1) deficiency is an ultra-rare autosomal recessive disorder characterized by developmental delay, peripheral neuropathy, elevated liver transaminases, hyperkinetic movement disorder and (hypo)-alacrima. We demonstrate that N-acetylglucosamine-asparagine (GlcNAc-Asn; GNA), is the analyte most closely associated with NGLY1 deficiency, showing consistent separation in levels between patients and controls. GNA accumulation is directly linked to the absence of functional NGLY1, presenting strong potential for its use as a biomarker. In agreement, a quantitative liquid chromatography with tandem mass spectrometry assay, developed to assess GNA from 3 to 3000 ng/ml, showed that it is conserved as a marker for loss of NGLY1 function in NGLY1-deficient cell lines, rodents (urine, cerebrospinal fluid, plasma and tissues) and patients (plasma and urine). Elevated GNA levels differentiate patients from controls, are stable over time and correlate with changes in NGLY1 activity. GNA as a biomarker has the potential to identify and validate patients with NGLY1 deficiency, act as a direct pharmacodynamic marker and serve as a potential surrogate endpoint in clinical trials.

Physiological importance of NGLY1, as revealed by rodent model analyses

Cytosolic peptide:N-glycanase (NGLY1) is an enzyme that cleaves N-glycans from glycoproteins that has been retrotranslocated from the endoplasmic reticulum (ER) lumen into the cytosol. It is known that NGLY1 is involved in the degradation of cytosolic glycans (non-lysosomal glycan degradation) as well as ER-associated degradation (ERAD), a quality control system for newly synthesized glycoproteins. The discovery of NGLY1 deficiency, which is caused by mutations in the human NGLY1 gene and results in multisystemic symptoms, has attracted interest in the physiological functions of NGLY1 in mammals. Studies using various animal models led to the identification of possible factors that contribute to the pathogenesis of NGLY1 deficiency. In this review, we summarize phenotypic consequences that have been reported for various Ngly1-deficient rodent models, and discuss future perspectives to provide more insights into the physiological functions of NGLY1.

Tracing the NGLY1 footprints: Insights from Drosophila

Recessive mutations in human N-glycanase 1 (NGLY1) cause a multisystem disorder with various phenotypes including global developmental delay. One of the models utilized to understand the biology of NGLY1 and the pathophysiology of NGLY1 deficiency is Drosophila melanogaster, a well-established, genetically tractable organism broadly used to study various biological processes and human diseases. Loss of the Drosophila NGLY1 homolog (Pngl) causes a host of phenotypes including developmental delay and lethality. Phenotypic, transcriptomic and genome-wide association analyses on Drosophila have revealed links between NGLY1 and several critical developmental and cellular pathways/processes. Further, repurposing screens of FDA-approved drugs have identified potential candidates to ameliorate some of the Pngl mutant phenotypes. Here, we will summarize the insights gained into the functions of NGLY1 from Drosophila studies. We hope that the current review article will encourage additional studies in Drosophila and other model systems towards establishing a therapeutic strategy for NGLY1 deficiency patients.

Loss of peptide:N-glycanase causes proteasome dysfunction mediated by a sugar-recognizing ubiquitin ligase

Mutations in the human peptide:N-glycanase gene (NGLY1), which encodes a cytosolic de-N-glycosylating enzyme, cause a congenital autosomal recessive disorder. In rodents, the loss of Ngly1 results in severe developmental delay or lethality, but the underlying mechanism remains unknown. In this study, we found that deletion of Fbxo6 (also known as Fbs2), which encodes a ubiquitin ligase subunit that recognizes glycoproteins, rescued the lethality-related defects in Ngly1-KO mice. In NGLY1-KO cells, FBS2 overexpression resulted in the substantial inhibition of proteasome activity, causing cytotoxicity. Nuclear factor, erythroid 2-like 1 (NFE2L1, also known as NRF1), an endoplasmic reticulum-associated transcriptional factor involved in expression of proteasome subunits, was also abnormally ubiquitinated by SCFFBS2 in NGLY1-KO cells, resulting in its retention in the cytosol. However, the cytotoxicity caused by FBS2 was restored by the overexpression of "glycan-less" NRF1 mutants, regardless of their transcriptional activity, or by the deletion of NRF1 in NGLY1-KO cells. We conclude that the proteasome dysfunction caused by the accumulation of N-glycoproteins, primarily NRF1, ubiquitinated by SCFFBS2 accounts for the pathogenesis resulting from NGLY1 deficiency.

Reversibility of motor dysfunction in the rat model of NGLY1 deficiency

N-glycanase 1 (NGLY1) deficiency is a rare inherited disorder characterized by developmental delay, hypolacrima or alacrima, seizure, intellectual disability, motor deficits, and other neurological symptoms. The underlying mechanisms of the NGLY1 phenotype are poorly understood, and no effective therapy is currently available. Similar to human patients, the rat model of NGLY1 deficiency, Ngly1-/-, shows developmental delay, movement disorder, somatosensory impairment, scoliosis, and learning disability. Here we show that single intracerebroventricular administration of AAV9 expressing human NGLY1 cDNA (AAV9-hNGLY1) to Ngly1-/- rats during the weaning period restored NGLY1 expression in the brain and spinal cord, concomitant with increased enzymatic activity of NGLY1 in the brain. hNGLY1 protein expressed by AAV9 was found predominantly in mature neurons, but not in glial cells, of Ngly1-/- rats. Strikingly, intracerebroventricular administration of AAV9-hNGLY1 normalized the motor phenotypes of Ngly1-/- rats assessed by the rota-rod test and gait analysis. The reversibility of motor deficits in Ngly1-/- rats by central nervous system (CNS)-restricted gene delivery suggests that the CNS is the primary therapeutic target organs for NGLY1 deficiency, and that the Ngly1-/- rat model may be useful for evaluating therapeutic treatments in pre-clinical studies.

JF1/B6F1 Ngly1-/- mouse as an isogenic animal model of NGLY1 deficiency

N-Glycanase 1 (NGLY1) deficiency is a congenital disorder caused by mutations in the NGLY1 gene. Because systemic Ngly1-/- mice with a C57BL/6 (B6) background are embryonically lethal, studies on the mechanism of NGLY1 deficiency using mice have been problematic. In this study, B6-Ngly1-/+ mice were crossed with Japanese wild mice-originated Japanese fancy mouse 1 (JF1) mice to produce viable F2 Ngly1-/- mice from (JF1×B6)F1 Ngly1-/+ mice. Systemic Ngly1-/- mice with a JF1 mouse background were also embryonically lethal. Hybrid F1 Ngly1-/- (JF1/B6F1) mice, however, showed developmental delay and motor dysfunction, similar to that in human patients. JF1/B6F1 Ngly1-/- mice showed increased levels of plasma and urinary aspartylglycosamine, a potential biomarker for NGLY1 deficiency. JF1/B6F1 Ngly1-/- mice are a useful isogenic animal model for the preclinical testing of therapeutic options and understanding the precise pathogenic mechanisms responsible for NGLY1 deficiency.

A Drosophila screen identifies NKCC1 as a modifier of NGLY1 deficiency

N-Glycanase 1 (NGLY1) is a cytoplasmic deglycosylating enzyme. Loss-of-function mutations in the NGLY1 gene cause NGLY1 deficiency, which is characterized by developmental delay, seizures, and a lack of sweat and tears. To model the phenotypic variability observed among patients, we crossed a Drosophila model of NGLY1 deficiency onto a panel of genetically diverse strains. The resulting progeny showed a phenotypic spectrum from 0 to 100% lethality. Association analysis on the lethality phenotype, as well as an evolutionary rate covariation analysis, generated lists of modifying genes, providing insight into NGLY1 function and disease. The top association hit was Ncc69 (human NKCC1/2), a conserved ion transporter. Analyses in NGLY1-/- mouse cells demonstrated that NKCC1 has an altered average molecular weight and reduced function. The misregulation of this ion transporter may explain the observed defects in secretory epithelium function in NGLY1 deficiency patients.

Cytosolic N-GlcNAc proteins are formed by the action of endo-β-N-acetylglucosaminidase

NGLY1 is a widely conserved eukaryotic cytosolic deglycosylating enzyme involved in the endoplasmic reticulum-associated degradation (ERAD) process, which eliminates misfolded proteins through retrograde translocation and proteasomal degradation. A human genetic disorder called NGLY1-deficiency has been reported, indicating the functional importance of NGLY1 in humans. Evidence suggests that Ngly1-KO is embryonic lethal in mice, while additional deletion of the Engase gene, encoding another cytosolic deglycosylating enzyme (endo-β-N-acetylglucosaminidase; ENGase), partially rescued lethality. Upon compromised Ngly1 activity, ENGase-mediated deglycosylation of misfolded glycoproteins may cause excess formation of N-GlcNAc proteins in the cytosol, leading to detrimental effects in the mice. Whether endogenous N-GlcNAc proteins are really formed in Ngly1-KO cells/animals or not remains unclarified. Here, comprehensive identification of O- and N-GlcNAc proteins was carried out using purified cytosol from wild type, Ngly1-KO, Engase-KO, and Ngly1/Engase double KO mouse embryonic fibroblasts. It was revealed that while there is no dramatic change in the level of O-GlcNAc proteins among cells examined, there was a vast increase of N-GlcNAc proteins in Ngly1-KO cells upon proteasome inhibition. Importantly, few N-GlcNAc proteins were observed in Engase-KO or Ngly1/Engase double-KO cells, clearly indicating that the cytosolic ENGase is responsible for the formation of N-GlcNAc proteins. The excess formation of N-GlcNAc proteins may at least in part account for the pathogenesis of NGLY1-deficiency.

Rat models of human diseases and related phenotypes: a systematic inventory of the causative genes

The laboratory rat has been used for a long time as the model of choice in several biomedical disciplines. Numerous inbred strains have been isolated, displaying a wide range of phenotypes and providing many models of human traits and diseases. Rat genome mapping and genomics was considerably developed in the last decades. The availability of these resources has stimulated numerous studies aimed at discovering causal disease genes by positional identification. Numerous rat genes have now been identified that underlie monogenic or complex diseases and remarkably, these results have been translated to the human in a significant proportion of cases, leading to the identification of novel human disease susceptibility genes, helping in studying the mechanisms underlying the pathological abnormalities and also suggesting new therapeutic approaches. In addition, reverse genetic tools have been developed. Several genome-editing methods were introduced to generate targeted mutations in genes the function of which could be clarified in this manner [generally these are knockout mutations]. Furthermore, even when the human gene causing a disease had been identified without resorting to a rat model, mutated rat strains (in particular KO strains) were created to analyze the gene function and the disease pathogenesis. Today, over 350 rat genes have been identified as underlying diseases or playing a key role in critical biological processes that are altered in diseases, thereby providing a rich resource of disease models. This article is an update of the progress made in this research and provides the reader with an inventory of these disease genes, a significant number of which have similar effects in rat and humans.