Syndromic immune disorder caused by a viable hypomorphic allele of spliceosome component Snrnp40.

We report a new immunodeficiency disorder in mice caused by a viable hypomorphic mutation of Snrnp40, an essential gene encoding a subunit of the U5 small nuclear ribonucleoprotein (snRNP) complex of the spliceosome. Snrnp40 is ubiquitous but strongly expressed in lymphoid tissue. Homozygous mutant mice showed hypersusceptibility to infection by murine cytomegalovirus and multiple defects of lymphoid development, stability and function. Cell-intrinsic defects of hematopoietic stem cell differentiation also affected homozygous mutants. SNRNP40 deficiency in primary hematopoietic stem cells or T cells or the EL4 cell line increased the frequency of splicing errors, mostly intron retention, in several hundred messenger RNAs. Altered expression of proteins associated with immune cell function was also observed in Snrnp40-mutant cells. The immunological consequences of SNRNP40 deficiency presumably result from cumulative, moderate effects on processing of many different mRNA molecules and secondary reductions in the expression of critical immune proteins, yielding a syndromic immune disorder.

NLRP3 activation and mitosis are mutually exclusive events coordinated by NEK7, a new inflammasome component.

The NLRP3 inflammasome responds to microbes and danger signals by processing and activating proinflammatory cytokines, including interleukin 1ß (IL-1ß) and IL-18. We found here that activation of the NLRP3 inflammasome was restricted to interphase of the cell cycle by NEK7, a serine-threonine kinase previously linked to mitosis. Activation of the NLRP3 inflammasome required NEK7, which bound to the leucine-rich repeat domain of NLRP3 in a kinase-independent manner downstream of the induction of mitochondrial reactive oxygen species (ROS). This interaction was necessary for the formation of a complex containing NLRP3 and the adaptor ASC, oligomerization of ASC and activation of caspase-1. NEK7 promoted the NLRP3-dependent cellular inflammatory response to intraperitoneal challenge with monosodium urate and the development of experimental autoimmune encephalitis in mice. Our findings suggest that NEK7 serves as a cellular switch that enforces mutual exclusivity of the inflammasome response and cell division.

Disruption of the ZFP574-THAP12 complex suppresses B cell malignancies in mice.

Despite the availability of life-extending treatments for B cell leukemias and lymphomas, many of these cancers remain incurable. Thus, the development of new molecular targets and therapeutics is needed to expand treatment options. To identify new molecular targets, we used a forward genetic screen in mice to identify genes required for development or survival of lymphocytes. Here, we describe Zfp574, an essential gene encoding a zinc finger protein necessary for normal and malignant lymphocyte survival. We show that ZFP574 interacts with zinc finger protein THAP12 and promotes the G1-to-S-phase transition during cell cycle progression. Mutation of ZFP574 impairs nuclear localization of the ZFP574-THAP12 complex. ZFP574 or THAP12 deficiency results in cell cycle arrest and impaired lymphoproliferation. Germline mutation, acute gene deletion, or targeted degradation of ZFP574 suppressed Myc-driven B cell leukemia in mice, but normal B cells were largely spared, permitting long-term survival, whereas complete lethality was observed in control animals. Our findings support the identification of drugs targeting ZFP574-THAP12 as a unique strategy to treat B cell malignancies.

Essential requirement for IER3IP1 in B cell development.

In a forward genetic screen of mice with N-ethyl-N-nitrosourea-induced mutations for aberrant immune function, we identified animals with low percentages of B220+ cells in the peripheral blood. The causative mutation was in Ier3ip1, encoding immediate early response 3 interacting protein 1 (IER3IP1), an endoplasmic reticulum membrane protein mutated in an autosomal recessive neurodevelopmental disorder termed Microcephaly with simplified gyration, Epilepsy and permanent neonatal Diabetes Syndrome (MEDS) in humans. However, no immune function for IER3IP1 had previously been reported. The viable hypomorphic Ier3ip1 allele uncovered in this study, identical to a reported IER3IP1 variant in a MEDS patient, reveals an essential hematopoietic-intrinsic role for IER3IP1 in B cell development and function. We show that IER3IP1 forms a complex with the Golgi transmembrane protein 167A and limits activation of the unfolded protein response mediated by inositol-requiring enzyme-1α and X-box binding protein 1 in B cells. Our findings suggest that B cell deficiency may be a feature of MEDS.

Essential role of MFSD1-GLMP-GIMAP5 in lymphocyte survival and liver homeostasis.

We detected ENU-induced alleles of Mfsd1 (encoding the major facilitator superfamily domain containing 1 protein) that caused lymphopenia, splenomegaly, progressive liver pathology, and extramedullary hematopoiesis (EMH). MFSD1 is a lysosomal membrane-bound solute carrier protein with no previously described function in immunity. By proteomic analysis, we identified association between MFSD1 and both GLMP (glycosylated lysosomal membrane protein) and GIMAP5 (GTPase of immunity-associated protein 5). Germline knockout alleles of Mfsd1, Glmp, and Gimap5 each caused lymphopenia, liver pathology, EMH, and lipid deposition in the bone marrow and liver. We found that the interactions of MFSD1 and GLMP with GIMAP5 are essential to maintain normal GIMAP5 expression, which in turn is critical to support lymphocyte development and liver homeostasis that suppresses EMH. These findings identify the protein complex MFSD1-GLMP-GIMAP5 operating in hematopoietic and extrahematopoietic tissues to regulate immunity and liver homeostasis.

RNPS1 inhibits excessive tumor necrosis factor/tumor necrosis factor receptor signaling to support hematopoiesis in mice.

Null mutations of spliceosome components or cofactors are homozygous lethal in eukaryotes, but viable hypomorphic mutations provide an opportunity to understand the physiological impact of individual splicing proteins. We describe a viable missense allele (F181I) of Rnps1 encoding an essential regulator of splicing and nonsense-mediated decay (NMD), identified in a mouse genetic screen for altered immune cell development. Homozygous mice displayed a stem cell­intrinsic defect in hematopoiesis of all lineages due to excessive apoptosis induced by tumor necrosis factor (TNF)­dependent death signaling. Numerous transcript splice variants containing retained introns and skipped exons were detected at elevated frequencies in Rnps1F181I/F181I splenic CD8+ T cells and hematopoietic stem cells (HSCs), but NMD appeared normal. Strikingly, Tnf knockout rescued all hematopoietic cells to normal or near-normal levels in Rnps1F181I/F181I mice and dramatically reduced intron retention in Rnps1F181I/F181I CD8+ T cells and HSCs. Thus, RNPS1 is necessary for accurate splicing, without which disinhibited TNF signaling triggers hematopoietic cell death.

Neuroinflammatory disease signatures in SPG11-related hereditary spastic paraplegia patients.

Biallelic loss of SPG11 function constitutes the most frequent cause of complicated autosomal recessive hereditary spastic paraplegia (HSP) with thin corpus callosum, resulting in progressive multisystem neurodegeneration. While the impact of neuroinflammation is an emerging and potentially treatable aspect in neurodegenerative diseases and leukodystrophies, the role of immune cells in SPG11-HSP patients is unknown. Here, we performed a comprehensive immunological characterization of SPG11-HSP, including examination of three human postmortem brain donations, immunophenotyping of patients' peripheral blood cells and patient-specific induced pluripotent stem cell-derived microglia-like cells (iMGL). We delineate a previously unknown role of innate immunity in SPG11-HSP. Neuropathological analysis of SPG11-HSP patient brain tissue revealed profound microgliosis in areas of neurodegeneration, downregulation of homeostatic microglial markers and cell-intrinsic accumulation of lipids and lipofuscin in IBA1+ cells. In a larger cohort of SPG11-HSP patients, the ratio of peripheral classical and intermediate monocytes was increased, along with increased serum levels of IL-6 that correlated with disease severity. Stimulation of patient-specific iMGLs with IFNγ led to increased phagocytic activity compared to control iMGL as well as increased upregulation and release of proinflammatory cytokines and chemokines, such as CXCL10. On a molecular basis, we identified increased STAT1 phosphorylation as mechanism connecting IFNγ-mediated immune hyperactivation and SPG11 loss of function. STAT1 expression was increased both in human postmortem brain tissue and in an Spg11-/- mouse model. Application of an STAT1 inhibitor decreased CXCL10 production in SPG11 iMGL and rescued their toxic effect on SPG11 neurons. Our data establish neuroinflammation as a novel disease mechanism in SPG11-HSP patients and constitute the first description of myeloid cell/ microglia activation in human SPG11-HSP. IFNγ/ STAT1-mediated neurotoxic effects of hyperreactive microglia upon SPG11 loss of function indicate that immunomodulation strategies may slow down disease progression.

The clinical and molecular spectrum of ZFYVE26-associated hereditary spastic paraplegia: SPG15.

In the field of hereditary spastic paraplegia (HSP), progress in molecular diagnostics needs to be translated into robust phenotyping studies to understand genetic and phenotypic heterogeneity and to support interventional trials. ZFYVE26-associated hereditary spastic paraplegia (HSP-ZFYVE26, SPG15) is a rare, early-onset complex HSP, characterized by progressive spasticity and a variety of other neurological symptoms. While prior reports, often in populations with high rates of consanguinity, have established a general phenotype, there is a lack of systematic investigations and a limited understanding of age-dependent manifestation of symptoms. Here we delineate the clinical, neuroimaging and molecular features of 44 individuals from 36 families, the largest cohort assembled to date. Median age at last follow-up was 23.8 years covering a wide age range (11-61 years). While symptom onset often occurred in early childhood [median: 24 months, interquartile range (IQR) = 24], a molecular diagnosis was reached at a median age of 18.8 years (IQR = 8), indicating significant diagnostic delay. We demonstrate that most patients present with motor and/or speech delay or learning disabilities. Importantly, these developmental symptoms preceded the onset of motor symptoms by several years. Progressive spasticity in the lower extremities, the hallmark feature of HSP-ZFYVE26, typically presents in adolescence and involves the distal lower limbs before progressing proximally. Spasticity in the upper extremities was seen in 64%. We found a high prevalence of extrapyramidal movement disorders including cerebellar ataxia (64%) and dystonia (11%). Parkinsonism (16%) was present in a subset and showed no sustained response to levodopa. Cognitive decline and neurogenic bladder dysfunction progressed over time in most patients. A systematic analysis of brain MRI features revealed a common diagnostic signature consisting of thinning of the anterior corpus callosum, signal changes of the anterior forceps and non-specific cortical and cerebellar atrophy. The molecular spectrum included 45 distinct variants, distributed across the protein structure without mutational hotspots. Spastic Paraplegia Rating Scale scores, SPATAX Disability Scores and the Four Stage Functional Mobility Score showed moderate strength in representing the proportion of variation between disease duration and motor dysfunction. Plasma neurofilament light chain levels were significantly elevated in all patients (Mann-Whitney U-test, P < 0.0001) and were correlated inversely with age (Spearman's rank correlation coefficient r = -0.65, P = 0.01). In summary, our systematic cross-sectional analysis of HSP-ZFYVE26 patients across a wide age-range, delineates core clinical, neuroimaging and molecular features and identifies markers of disease severity. These results raise awareness to this rare disease, facilitate an early diagnosis and create clinical trial readiness.

Sulfatides are endogenous ligands for the TLR4-MD-2 complex.

Many endogenous molecules, mostly proteins, purportedly activate the Toll-like receptor 4 (TLR4)-myeloid differentiation factor-2 (MD-2) complex, the innate immune receptor for lipopolysaccharide (LPS) derived from gram-negative bacteria. However, there is no structural evidence supporting direct TLR4-MD-2 activation by endogenous ligands. Sulfatides (3-O-sulfogalactosylceramides) are natural, abundant sulfated glycolipids that have variously been shown to initiate or suppress inflammatory responses. We show here that short fatty acid (FA) chain sulfatides directly activate mouse TLR4-MD-2 independent of CD14, trigger MyD88- and TRIF-dependent signaling, and stimulate tumor necrosis factor α (TNFα) and type I interferon (IFN) production in mouse macrophages. In contrast to the agonist activity toward the mouse receptor, the tested sulfatides antagonize TLR4-MD-2 activation by LPS in human macrophage-like cells. The agonistic and antagonistic activities of sulfatides require the presence of the sulfate group and are inversely related to the FA chain length. The crystal structure of mouse TLR4-MD-2 in complex with C16-sulfatide revealed that three C16-sulfatide molecules bound to the MD-2 hydrophobic pocket and induced an active dimer conformation of the receptor complex similar to that induced by LPS or lipid A. The three C16-sulfatide molecules partially mimicked the detailed interactions of lipid A to achieve receptor activation. Our results suggest that sulfatides may mediate sterile inflammation or suppress LPS-stimulated inflammation, and that additional endogenous negatively charged lipids with up to six lipid chains of limited length might also bind to TLR4-MD-2 and activate or inhibit this complex.

Glucocerebrosidase reduces the spread of protein aggregation in a Drosophila melanogaster model of neurodegeneration by regulating proteins trafficked by extracellular vesicles.

Abnormal protein aggregation within neurons is a key pathologic feature of Parkinson's disease (PD). The spread of brain protein aggregates is associated with clinical disease progression, but how this occurs remains unclear. Mutations in glucosidase, beta acid 1 (GBA), which encodes glucocerebrosidase (GCase), are the most penetrant common genetic risk factor for PD and dementia with Lewy bodies and associate with faster disease progression. To explore how GBA mutations influence pathogenesis, we previously created a Drosophila model of GBA deficiency (Gba1b) that manifests neurodegeneration and accelerated protein aggregation. Proteomic analysis of Gba1b mutants revealed dysregulation of proteins involved in extracellular vesicle (EV) biology, and we found altered protein composition of EVs from Gba1b mutants. Accordingly, we hypothesized that GBA may influence pathogenic protein aggregate spread via EVs. We found that accumulation of ubiquitinated proteins and Ref(2)P, Drosophila homologue of mammalian p62, were reduced in muscle and brain tissue of Gba1b flies by ectopic expression of wildtype GCase in muscle. Neuronal GCase expression also rescued protein aggregation both cell-autonomously in brain and non-cell-autonomously in muscle. Muscle-specific GBA expression reduced the elevated levels of EV-intrinsic proteins and Ref(2)P found in EVs from Gba1b flies. Perturbing EV biogenesis through neutral sphingomyelinase (nSMase), an enzyme important for EV release and ceramide metabolism, enhanced protein aggregation when knocked down in muscle, but did not modify Gba1b mutant protein aggregation when knocked down in neurons. Lipidomic analysis of nSMase knockdown on ceramide and glucosylceramide levels suggested that Gba1b mutant protein aggregation may depend on relative depletion of specific ceramide species often enriched in EVs. Finally, we identified ectopically expressed GCase within isolated EVs. Together, our findings suggest that GCase deficiency promotes accelerated protein aggregate spread between cells and tissues via dysregulated EVs, and EV-mediated trafficking of GCase may partially account for the reduction in aggregate spread.

De novo germline mutation in the dual specificity phosphatase 10 gene accelerates autoimmune diabetes.

Insulin-dependent or type 1 diabetes (T1D) is a polygenic autoimmune disease. In humans, more than 60 loci carrying common variants that confer disease susceptibility have been identified by genome-wide association studies, with a low individual risk contribution for most variants excepting those of the major histocompatibility complex (MHC) region (40 to 50% of risk); hence the importance of missing heritability due in part to rare variants. Nonobese diabetic (NOD) mice recapitulate major features of the human disease including genetic aspects with a key role for the MHC haplotype and a series of Idd loci. Here we mapped in NOD mice rare variants arising from genetic drift and significantly impacting disease risk. To that aim we established by selective breeding two sublines of NOD mice from our inbred NOD/Nck colony exhibiting a significant difference in T1D incidence. Whole-genome sequencing of high (H)- and low (L)-incidence sublines (NOD/NckH and NOD/NckL) revealed a limited number of subline-specific variants. Treating age of diabetes onset as a quantitative trait in automated meiotic mapping (AMM), enhanced susceptibility in NOD/NckH mice was unambiguously attributed to a recessive missense mutation of Dusp10, which encodes a dual specificity phosphatase. The causative effect of the mutation was verified by targeting Dusp10 with CRISPR-Cas9 in NOD/NckL mice, a manipulation that significantly increased disease incidence. The Dusp10 mutation resulted in islet cell down-regulation of type I interferon signature genes, which may exert protective effects against autoimmune aggression. De novo mutations akin to rare human susceptibility variants can alter the T1D phenotype.

Development and validation of risk of CPS decline (RCD): a new prediction tool for worsening cognitive performance among home care clients in Canada.

BACKGROUND: To develop and validate a prediction tool, or nomogram, for the risk of a decline in cognitive performance based on the interRAI Cognitive Performance Scale (CPS). METHODS: Retrospective, population-based, cohort study using Canadian Resident Assessment Instrument for Home Care (RAI-HC) data, collected between 2010 and 2018. Eligible home care clients, aged 18+, with at least two assessments were selected randomly for model derivation (75%) and validation (25%). All clients had a CPS score of zero (intact) or one (borderline intact) on intake into the home care program, out of a possible score of six. All individuals had to remain as home care recipients for the six months observation window in order to be included in the analysis. The primary outcome was any degree of worsening (i.e., increase) on the CPS score within six months. Using the derivation cohort, we developed a multivariable logistic regression model to predict the risk of a deterioration in the CPS score. Model performance was assessed on the validation cohort using discrimination and calibration plots. RESULTS: We identified 39,292 eligible home care clients, with a median age of 79.0 years, 62.3% were female, 38.8% were married and 38.6% lived alone. On average, 30.3% experienced a worsening on the CPS score within the six-month window (i.e., a change from 0 or 1 to 2, 3, 4, 5, or 6). The final model had good discrimination (c-statistic of 0.65), with excellent calibration. CONCLUSIONS: The model accurately predicted the risk of deterioration on the CPS score over six months among home care clients. This type of predictive model may provide useful information to support decisions for home care clinicians who use interRAI data internationally.

Genetic and structural studies of RABL3 reveal an essential role in lymphoid development and function.

The small GTPase RABL3 is an oncogene of unknown physiological function. Homozygous knockout alleles of mouse Rabl3 were embryonic lethal, but a viable hypomorphic allele (xiamen [xm]) causing in-frame deletion of four amino acids from the interswitch region resulted in profound defects in lymphopoiesis. Impaired lymphoid progenitor development led to deficiencies of B cells, T cells, and natural killer (NK) cells in Rabl3xm/xm mice. T cells and NK cells exhibited impaired cytolytic activity, and mice infected with mouse cytomegalovirus (MCMV) displayed elevated titers in the spleen. Myeloid cells were normal in number and function. Biophysical and crystallographic studies demonstrated that RABL3 formed a homodimer in solution via interactions between the effector binding surfaces on each subunit; monomers adopted a typical small G protein fold. RABL3xm displayed a large compensatory alteration in switch I, which adopted a ß-strand configuration normally provided by the deleted interswitch residues, thereby permitting homodimer formation. Dysregulated effector binding due to conformational changes in the switch I-interswitch-switch II module likely underlies the xm phenotype. One such effector may be GPR89, putatively an ion channel or G protein-coupled receptor (GPCR). RABL3, but not RABL3xm, strongly associated with and stabilized GPR89, and an N-ethyl-N-nitrosourea (ENU)-induced mutation (explorer) in Gpr89 phenocopied Rabl3xm.

Forward genetic analysis using OCT screening identifies Sfxn3 mutations leading to progressive outer retinal degeneration in mice.

Retinal disease and loss of vision can result from any disruption of the complex pathways controlling retinal development and homeostasis. Forward genetics provides an excellent tool to find, in an unbiased manner, genes that are essential to these processes. Using N-ethyl-N-nitrosourea mutagenesis in mice in combination with a screening protocol using optical coherence tomography (OCT) and automated meiotic mapping, we identified 11 mutations presumably causative of retinal phenotypes in genes previously known to be essential for retinal integrity. In addition, we found multiple statistically significant gene-phenotype associations that have not been reported previously and decided to target one of these genes, Sfxn3 (encoding sideroflexin-3), using CRISPR/Cas9 technology. We demonstrate, using OCT, light microscopy, and electroretinography, that two Sfxn3-/- mouse lines developed progressive and severe outer retinal degeneration. Electron microscopy showed thinning of the retinal pigment epithelium and disruption of the external limiting membrane. Using single-cell RNA sequencing of retinal cells isolated from C57BL/6J mice, we demonstrate that Sfxn3 is expressed in several bipolar cell subtypes, retinal ganglion cells, and some amacrine cell subtypes but not significantly in Müller cells or photoreceptors. In situ hybridization confirmed these findings. Furthermore, pathway analysis suggests that Sfxn3 may be associated with synaptic homeostasis. Importantly, electron microscopy analysis showed disruption of synapses and synaptic ribbons in the outer plexiform layer of Sfxn3-/- mice. Our work describes a previously unknown requirement for Sfxn3 in retinal function.

Epstein-Barr virus-associated intracranial myopericytoma in a child: case report and review of literature.

BACKGROUND: Myopericytomas are benign soft tissue tumors which are rarely found as intracranial masses. METHODS: A review of SCOPUS and PubMed databases for case reports and case series was done for patients with intracranial myopericytomas. Data on demographics, clinical features, imaging, surgical management employed, and outcomes were collected. RESULTS: We found a total of 9 cases in the literature and we describe an additional case from our own experience. The mean age at presentation was 50.1 years (32-64 years), with a female predominance. Most tumors were in the posterior fossa and were multifocal in AIDS patients. The most common clinical manifestations were visual disturbances, headaches, and vomiting. An association with EBV was reported in two cases and was also found in our own case. Gross total excision and even subtotal excision were definitive therapies with no recurrences reported with a mean follow-up of 22.7 months. Our case is the first EBV-associated intracranial myopericytoma in a child. CONCLUSION: Intracranial myopericytomas are rare; some have an association with EBV and immunodeficient states. Surgery is the only necessary treatment and outcomes are generally favorable for these benign neoplasms.

Optic Perineuritis Associated With Cryptococcal Meningitis Presenting With a "Hot Orbit" in a Patient With Chronic Lymphocytic Leukemia.

ABSTRACT: A 75-year-old man presented with 3 days of progressive left retro-orbital pain, eyelid swelling, tearing, and pain with extraocular movement. His medical history was significant for type II diabetes mellitus and chronic lymphocytic leukemia, stable on no therapy since diagnosis 8 years prior. The initial examination was significant for diffuse restriction of left ocular motility, marked lid edema, and mild dyschromatopsia. Computed tomography demonstrated asymmetric left periorbital soft tissue swelling and intraconal fat stranding with an irregular left optic nerve sheath complex and clear paranasal sinuses. He was hospitalized for orbital cellulitis and treated empirically with broad-spectrum intravenous antibiotics, but his visual acuity declined over the ensuing 2 days. Subsequent MRI demonstrated left-greater-than-right circumferential optic nerve sheath enhancement, and leptomeningeal enhancement. An orbital biopsy demonstrated monoclonal B-cell lymphocyte aggregation, whereas a lumbar puncture was positive for Cryptococcus antigen with subsequent demonstration of abundant Cryptococcus by Papanicolaou stain. The final diagnosis was optic perineuritis secondary to cryptococcal meningitis presenting with orbital inflammation. Although his clinical course was complicated by immune reconstitution inflammatory syndrome, symptoms and signs of optic neuropathy ultimately resolved after 1 month of intensive antifungal therapy.

On the occurrence of cytochrome P450 in viruses.

Genes encoding cytochrome P450 (CYP; P450) enzymes occur widely in the Archaea, Bacteria, and Eukarya, where they play important roles in metabolism of endogenous regulatory molecules and exogenous chemicals. We now report that genes for multiple and unique P450s occur commonly in giant viruses in the Mimiviridae, Pandoraviridae, and other families in the proposed order Megavirales. P450 genes were also identified in a herpesvirus (Ranid herpesvirus 3) and a phage (Mycobacterium phage Adler). The Adler phage P450 was classified as CYP102L1, and the crystal structure of the open form was solved at 2.5 Å. Genes encoding known redox partners for P450s (cytochrome P450 reductase, ferredoxin and ferredoxin reductase, and flavodoxin and flavodoxin reductase) were not found in any viral genome so far described, implying that host redox partners may drive viral P450 activities. Giant virus P450 proteins share no more than 25% identity with the P450 gene products we identified in Acanthamoeba castellanii, an amoeba host for many giant viruses. Thus, the origin of the unique P450 genes in giant viruses remains unknown. If giant virus P450 genes were acquired from a host, we suggest it could have been from an as yet unknown and possibly ancient host. These studies expand the horizon in the evolution and diversity of the enormously important P450 superfamily. Determining the origin and function of P450s in giant viruses may help to discern the origin of the giant viruses themselves.

Enhanced susceptibility to chemically induced colitis caused by excessive endosomal TLR signaling in LRBA-deficient mice.

LPS-responsive beige-like anchor (LRBA) protein deficiency in humans causes immune dysregulation resulting in autoimmunity, inflammatory bowel disease (IBD), hypogammaglobulinemia, regulatory T (Treg) cell defects, and B cell functional defects, but the cellular and molecular mechanisms responsible are incompletely understood. In an ongoing forward genetic screen for N-ethyl-N-nitrosourea (ENU)-induced mutations that increase susceptibility to dextran sodium sulfate (DSS)-induced colitis in mice, we identified two nonsense mutations in Lrba Although Treg cells have been a main focus in LRBA research to date, we found that dendritic cells (DCs) contribute significantly to DSS-induced intestinal inflammation in LRBA-deficient mice. Lrba-/- DCs exhibited excessive IRF3/7- and PI3K/mTORC1-dependent signaling and type I IFN production in response to the stimulation of the Toll-like receptors (TLRs) 3, TLR7, and TLR9. Substantial reductions in cytokine expression and sensitivity to DSS in LRBA-deficient mice were caused by knockout of Unc93b1, a chaperone necessary for trafficking of TLR3, TLR7, and TLR9 to endosomes. Our data support a function for LRBA in limiting endosomal TLR signaling and consequent intestinal inflammation.

Dominant atopy risk mutations identified by mouse forward genetic analysis.

BACKGROUND: Atopy, the overall tendency to become sensitized to an allergen, is heritable but seldom ascribed to mutations within specific genes. Atopic individuals develop abnormally elevated IgE responses to immunization with potential allergens. To gain insight into the genetic causes of atopy, we carried out a forward genetic screen for atopy in mice. METHODS: We screened mice carrying homozygous and heterozygous N-ethyl-N-nitrosourea (ENU)-induced germline mutations for aberrant antigen-specific IgE and IgG1 production in response to immunization with the model allergen papain. Candidate genes were validated by independent gene mutation. RESULTS: Of 31 candidate genes selected for investigation, the effects of mutations in 23 genes on papain-specific IgE or IgG1 were verified. Among the 20 verified genes influencing the IgE response, eight were necessary for the response, while 12 repressed IgE. Nine genes were not previously implicated in the IgE response. Fifteen genes encoded proteins contributing to IgE class switch recombination or B-cell receptor signaling. The precise roles of the five remaining genes (Flcn, Map1lc3b, Me2, Prkd2, and Scarb2) remain to be determined. Loss-of-function mutations in nine of the 12 genes limiting the IgE response were dominant or semi-dominant for the IgE phenotype but did not cause immunodeficiency in the heterozygous state. Using damaging allele frequencies for the corresponding human genes and in silico simulations (Monte Carlo) of undiscovered atopy mutations, we estimated the percentage of humans with heterozygous atopy risk mutations. CONCLUSIONS: Up to 37% of individuals may be heterozygous carriers for at least one dominant atopy risk mutation.

Glucocerebrosidase deficiency promotes protein aggregation through dysregulation of extracellular vesicles.

Mutations in the glucosylceramidase beta (GBA) gene are strongly associated with neurodegenerative diseases marked by protein aggregation. GBA encodes the lysosomal enzyme glucocerebrosidase, which breaks down glucosylceramide. A common explanation for the link between GBA mutations and protein aggregation is that lysosomal accumulation of glucosylceramide causes impaired autophagy. We tested this hypothesis directly by measuring protein turnover and abundance in Drosophila mutants with deletions in the GBA ortholog Gba1b. Proteomic analyses revealed that known autophagy substrates, which had severely impaired turnover in autophagy-deficient Atg7 mutants, showed little to no overall slowing of turnover or increase in abundance in Gba1b mutants. Likewise, Gba1b mutants did not have the marked impairment of mitochondrial protein turnover seen in mitophagy-deficient parkin mutants. Proteasome activity, microautophagy, and endocytic degradation also appeared unaffected in Gba1b mutants. However, we found striking changes in the turnover and abundance of proteins associated with extracellular vesicles (EVs), which have been proposed as vehicles for the spread of protein aggregates in neurodegenerative disease. These changes were specific to Gba1b mutants and did not represent an acceleration of normal aging. Western blotting of isolated EVs confirmed the increased abundance of EV proteins in Gba1b mutants, and nanoparticle tracking analysis revealed that Gba1b mutants had six times as many EVs as controls. Genetic perturbations of EV production in Gba1b mutants suppressed protein aggregation, demonstrating that the increase in EV abundance contributed to the accumulation of protein aggregates. Together, our findings indicate that glucocerebrosidase deficiency causes pathogenic changes in EV metabolism and may promote the spread of protein aggregates through extracellular vesicles.