Gut barrier defects, intestinal immune hyperactivation and enhanced lipid catabolism drive lethality in NGLY1-deficient Drosophila.

Intestinal barrier dysfunction leads to inflammation and associated metabolic changes. However, the relative impact of gut bacteria versus non-bacterial insults on animal health in the context of barrier dysfunction is not well understood. Here, we establish that loss of Drosophila N-glycanase 1 (Pngl) in a specific intestinal cell type leads to gut barrier defects, causing starvation and JNK overactivation. These abnormalities, along with loss of Pngl in enterocytes and fat body, result in Foxo overactivation, leading to hyperactive innate immune response and lipid catabolism and thereby contributing to lethality. Germ-free rearing of Pngl mutants rescued their developmental delay but not lethality. However, raising Pngl mutants on isocaloric, fat-rich diets partially rescued lethality. Our data indicate that Pngl functions in Drosophila larvae to establish the gut barrier, and that the lethality caused by loss of Pngl is primarily mediated through non-bacterial induction of immune and metabolic abnormalities.

NGLY1 deficiency: a prospective natural history study.

N-glycanase 1 (NGLY1) deficiency is a debilitating, ultra-rare autosomal recessive disorder caused by loss of function of NGLY1, a cytosolic enzyme that deglycosylates other proteins. It is characterized by severe global developmental delay and/or intellectual disability, hyperkinetic movement disorder, transient elevation of transaminases, (hypo)alacrima and progressive, diffuse, length-dependent sensorimotor polyneuropathy. A prospective natural history study (NHS) was conducted to elucidate clinical features and disease course. Twenty-nine participants were enrolled (15 onsite, 14 remotely) and followed for up to 32 months, representing ~29% of the ~100 patients identified worldwide. Participants exhibited profound developmental delays, with almost all developmental quotients below 20 on the Mullen Scales of Early Learning, well below the normative score of 100. Increased difficulties with sitting and standing suggested decline in motor function over time. Most patients presented with (hypo)alacrima and reduced sweat response. Pediatric quality of life was poor except for emotional function. Language/communication and motor skill problems including hand use were reported by caregivers as the most bothersome symptoms. Levels of the substrate biomarker, GlcNAc-Asn (aspartylglucosamine; GNA), were consistently elevated in all participants over time, independent of age. Liver enzymes were elevated for some participants but improved especially in younger patients and did not reach levels indicating severe liver disease. Three participants died during the study period. Data from this NHS informs selection of endpoints and assessments for future clinical trials for NGLY1 deficiency interventions. Potential endpoints include GNA biomarker levels, neurocognitive assessments, autonomic and motor function (particularly hand use), (hypo)alacrima and quality of life.

Gut barrier defects, increased intestinal innate immune response, and enhanced lipid catabolism drive lethality in N -glycanase 1 deficient Drosophila.

Intestinal barrier dysfunction leads to inflammation and associated metabolic changes. However, the relative impact of infectious versus non-infectious mechanisms on animal health in the context of barrier dysfunction is not well understood. Here, we establish that loss of Drosophila N -glycanase 1 (Pngl) leads to gut barrier defects, which cause starvation and increased JNK activity. These defects result in Foxo overactivation, which induces a hyperactive innate immune response and lipid catabolism, thereby contributing to lethality associated with loss of Pngl . Notably, germ-free rearing of Pngl mutants did not rescue lethality. In contrast, raising Pngl mutants on isocaloric, fat-rich diets improved animal survival in a dosage-dependent manner. Our data indicate that Pngl functions in Drosophila larvae to establish the gut barrier, and that the immune and metabolic consequences of loss of Pngl are primarily mediated through non-infectious mechanisms.

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.

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 four 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 with 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.

GlcNAc-Asn 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.

Loss of N-Glycanase 1 Alters Transcriptional and Translational Regulation in K562 Cell Lines.

N-Glycanase 1 (NGLY1) deficiency is an ultra-rare, complex and devastating neuromuscular disease. Patients display multi-organ symptoms including developmental delays, movement disorders, seizures, constipation and lack of tear production. NGLY1 is a deglycosylating protein involved in the degradation of misfolded proteins retrotranslocated from the endoplasmic reticulum (ER). NGLY1-deficient cells have been reported to exhibit decreased deglycosylation activity and an increased sensitivity to proteasome inhibitors. We show that the loss of NGLY1 causes substantial changes in the RNA and protein landscape of K562 cells and results in downregulation of proteasomal subunits, consistent with its processing of the transcription factor NFE2L1. We employed the CMap database to predict compounds that can modulate NGLY1 activity. Utilizing our robust K562 screening system, we demonstrate that the compound NVP-BEZ235 (Dactosilib) promotes degradation of NGLY1-dependent substrates, concurrent with increased autophagic flux, suggesting that stimulating autophagy may assist in clearing aberrant substrates during NGLY1 deficiency.

Liver-specific deletion of Ngly1 causes abnormal nuclear morphology and lipid metabolism under food stress.

The cytoplasmic peptide:N-glycanase (Ngly1) is a de-N-glycosylating enzyme that cleaves N-glycans from misfolded glycoproteins and is involved in endoplasmic reticulum-associated degradation. The recent discovery of NGLY1-deficiency, which causes severe systemic symptoms, drew attention to the physiological function of Ngly1 in mammals. While several studies have been carried out to reveal the physiological necessity of Ngly1, the semi-lethal nature of Ngly1-deficient animals made it difficult to analyze its function in adults. In this study, we focus on the physiological function of Ngly1 in liver (hepatocyte)-specific Ngly1-deficient mice generated using the cre-loxP system. We found that hepatocyte-specific Ngly1-deficient mice showed abnormal hepatocyte nuclear size/morphology with aging but did not show other notable defects in unstressed conditions. This nuclear phenotype did not appear to be related to the function of the only gene currently reported to rescue Ngly1-deficient murine lethality so far, endo-ß-N-acetylglucosaminidase. We also found that under a high fructose diet induced stress, the hepatocyte-specific Ngly1-deletion resulted in liver transaminases elevation and increased lipid droplet accumulation. We showed that the processing and localization of the transcription factor, nuclear factor erythroid 2-like 1 (Nfe2l1), was impaired in the Ngly1-deficient hepatocytes. Therefore, Nfe2l1, at least partially, contributes to the phenotypes observed in hepatocyte-specific Ngly1-deficient mice. Our results indicate that Ngly1 plays important roles in the adult liver impacting nuclear morphology and lipid metabolism. Hepatocyte-specific Ngly1-deficient mice could thus serve as a valuable animal model for assessing in vivo efficacy of drugs and/or treatment for NGLY1-deficiency.

Biological plasticity rescues target activity in CRISPR knock outs.

Gene knock outs (KOs) are efficiently engineered through CRISPR-Cas9-induced frameshift mutations. While the efficiency of DNA editing is readily verified by DNA sequencing, a systematic understanding of the efficiency of protein elimination has been lacking. Here we devised an experimental strategy combining RNA sequencing and triple-stage mass spectrometry to characterize 193 genetically verified deletions targeting 136 distinct genes generated by CRISPR-induced frameshifts in HAP1 cells. We observed residual protein expression for about one third of the quantified targets, at variable levels from low to original, and identified two causal mechanisms, translation reinitiation leading to N-terminally truncated target proteins or skipping of the edited exon leading to protein isoforms with internal sequence deletions. Detailed analysis of three truncated targets, BRD4, DNMT1 and NGLY1, revealed partial preservation of protein function. Our results imply that systematic characterization of residual protein expression or function in CRISPR-Cas9-generated KO lines is necessary for phenotype interpretation.

Inhibition of NGLY1 Inactivates the Transcription Factor Nrf1 and Potentiates Proteasome Inhibitor Cytotoxicity.

Proteasome inhibitors are used to treat blood cancers such as multiple myeloma (MM) and mantle cell lymphoma. The efficacy of these drugs is frequently undermined by acquired resistance. One mechanism of proteasome inhibitor resistance may involve the transcription factor Nuclear Factor, Erythroid 2 Like 1 (NFE2L1, also referred to as Nrf1), which responds to proteasome insufficiency or pharmacological inhibition by upregulating proteasome subunit gene expression. This "bounce-back" response is achieved through a unique mechanism. Nrf1 is constitutively translocated into the ER lumen, N-glycosylated, and then targeted for proteasomal degradation via the ER-associated degradation (ERAD) pathway. Proteasome inhibition leads to accumulation of cytosolic Nrf1, which is then processed to form the active transcription factor. Here we show that the cytosolic enzyme N-glycanase 1 (NGLY1, the human PNGase) is essential for Nrf1 activation in response to proteasome inhibition. Chemical or genetic disruption of NGLY1 activity results in the accumulation of misprocessed Nrf1 that is largely excluded from the nucleus. Under these conditions, Nrf1 is inactive in regulating proteasome subunit gene expression in response to proteasome inhibition. Through a small molecule screen, we identified a cell-active NGLY1 inhibitor that disrupts the processing and function of Nrf1. The compound potentiates the cytotoxicity of carfilzomib, a clinically used proteasome inhibitor, against MM and T cell-derived acute lymphoblastic leukemia (T-ALL) cell lines. Thus, NGLY1 inhibition prevents Nrf1 activation and represents a new therapeutic approach for cancers that depend on proteasome homeostasis.

SYGNALing a Red Light for Glioblastoma.

A new multiomic network inference pipeline, SYGNAL, integrates patient data with mechanistically accurate transcriptional regulatory networks to predict drug combinations with synergistic anti-proliferative effects on glioblastoma multiforme.

The Silent Sway of Splicing by Synonymous Substitutions.

Alternative splicing diversifies mRNA transcripts in human cells. This sequence-driven process can be influenced greatly by mutations, even those that do not change the protein coding potential of the transcript. Synonymous mutations have been shown to alter gene expression through modulation of splicing, mRNA stability, and translation. Using a synonymous position mutation library in SMN1 exon 7, we show that 23% of synonymous mutations across the exon decrease exon inclusion, suggesting that nucleotide identity across the entire exon has been evolutionarily optimized to support a particular exon inclusion level. Although phylogenetic conservation scores are insufficient to identify synonymous positions important for exon inclusion, an alignment of organisms filtered based on similar exon/intron architecture is highly successful. Although many of the splicing neutral mutations are observed to occur, none of the exon inclusion reducing mutants was found in the filtered alignment. Using the modified phylogenetic comparison as an approach to evaluate the impact on pre-mRNA splicing suggests that up to 45% of synonymous SNPs are likely to alter pre-mRNA splicing. These results demonstrate that coding and pre-mRNA splicing pressures co-evolve and that a modified phylogenetic comparison based on the exon/intron architecture is a useful tool in identifying splice altering SNPs.

The chromatin regulator Brg1 suppresses formation of intraductal papillary mucinous neoplasm and pancreatic ductal adenocarcinoma.

Pancreatic ductal adenocarcinoma (PDA) develops through distinct precursor lesions, including pancreatic intraepithelial neoplasia (PanIN) and intraductal papillary mucinous neoplasia (IPMN). However, genetic features resulting in IPMN-associated PDA (IPMN-PDA) versus PanIN-associated PDA (PanIN-PDA) are largely unknown. Here we find that loss of Brg1, a core subunit of SWI/SNF chromatin remodelling complexes, cooperates with oncogenic Kras to form cystic neoplastic lesions that resemble human IPMN and progress to PDA. Although Brg1-null IPMN-PDA develops rapidly, it possesses a distinct transcriptional profile compared with PanIN-PDA driven by mutant Kras and hemizygous p53 deletion. IPMN-PDA also is less lethal, mirroring prognostic trends in PDA patients. In addition, Brg1 deletion inhibits Kras-dependent PanIN development from adult acinar cells, but promotes Kras-driven preneoplastic transformation in adult duct cells. Therefore, this study implicates Brg1 as a determinant of context-dependent Kras-driven pancreatic tumorigenesis and suggests that chromatin remodelling may underlie the development of distinct PDA subsets.

In vitro assay of pre-mRNA splicing in mammalian nuclear extract.

The in vitro splicing assay is a valuable technique that can be used to study the mechanism and machinery involved in the splicing process. The ability to investigate various aspects of splicing and alternative splicing appears to be endless due to the flexibility of this assay. Here, we describe the tools and techniques necessary to carry out an in vitro splicing assay. Through the use of radiolabeled pre-mRNA and crude nuclear extract, spliced mRNAs can be purified and visualized by autoradiography for downstream analysis.

Kinetic analysis of in vitro pre-mRNA splicing in HeLa nuclear extract.

Kinetic analysis of in vitro splicing is a valuable technique for understanding splicing regulation. It allows the determination of specific contributions from functional elements for the efficient removal of introns. This chapter will describe the rationale and approach employed to use kinetic analysis to evaluate an in vitro splicing reaction using radiolabeled pre-mRNA incubated in splicing-competent HeLa nuclear extract (NE).

Position-dependent splicing activation and repression by SR and hnRNP proteins rely on common mechanisms.

Alternative splicing is regulated by splicing factors that modulate splice site selection. In some cases, however, splicing factors show antagonistic activities by either activating or repressing splicing. Here, we show that these opposing outcomes are based on their binding location relative to regulated 5' splice sites. SR proteins enhance splicing only when they are recruited to the exon. However, they interfere with splicing by simply relocating them to the opposite intronic side of the splice site. hnRNP splicing factors display analogous opposing activities, but in a reversed position dependence. Activation by SR or hnRNP proteins increases splice site recognition at the earliest steps of exon definition, whereas splicing repression promotes the assembly of nonproductive complexes that arrest spliceosome assembly prior to splice site pairing. Thus, SR and hnRNP splicing factors exploit similar mechanisms to positively or negatively influence splice site selection.

G Run-mediated recognition of proteolipid protein and DM20 5' splice sites by U1 small nuclear RNA is regulated by context and proximity to the splice site.

Highly conserved G runs, G1M2 and ISE, regulate the proteolipid protein (PLP)/DM20 ratio. We have investigated recruitment of U1 small nuclear ribonuclear protein (snRNP) by G1M2 and ISE and examined the effect of splice site strength, distance, and context on G run function. G1M2 is necessary for initial recruitment of U1snRNP to the DM20 5' splice site independent of the strength of the splice site. G1M2 regulates E complex formation and supports DM20 splicing when functional U1snRNP is reduced. By contrast, the ISE is not required for the initial recruitment of U1snRNP to the PLP 5' splice site. However, in close proximity to either the DM20 or the PLP 5' splice site, the ISE recruits U1snRNP to both splice sites. The ISE enhances DM20 splicing, whereas close to the PLP 5' splice site, it inhibits PLP splicing. Splicing enhancement and inhibition are mediated by heterogeneous nuclear ribonuclear protein (hnRNP)H/F. The data show that recognition of the DM20 5' splice site depends on G run-mediated recruitment of U1snRNA, whereas a complex interaction between the ISE G runs, context and position determines the functional outcome on splicing. The data suggest that different mechanisms underlie G run-mediated recognition of 5' splice sites and that context and position play a critical role.

Competing upstream 5' splice sites enhance the rate of proximal splicing.

Alternative 5' splice site selection is one of the major pathways resulting in mRNA diversification. Regulation of this type of alternative splicing depends on the presence of regulatory elements that activate or repress the use of competing splice sites, usually leading to the preferential use of the proximal splice site. However, the mechanisms involved in proximal splice site selection and the thermodynamic advantage realized by proximal splice sites are not well understood. Here, we have carried out a systematic analysis of alternative 5' splice site usage using in vitro splicing assays. We show that observed rates of splicing correlate well with their U1 snRNA base pairing potential. Weak U1 snRNA interactions with the 5' splice site were significantly rescued by the proximity of the downstream exon, demonstrating that the intron definition mode of splice site recognition is highly efficient. In the context of competing splice sites, the proximity to the downstream 3' splice site was more influential in dictating splice site selection than the actual 5' splice site/U1 snRNA base pairing potential. Surprisingly, the kinetic analysis also demonstrated that an upstream competing 5' splice site enhances the rate of proximal splicing. These results reveal the discovery of a new splicing regulatory element, an upstream 5' splice site functioning as a splicing enhancer.