Simulated Colonic Fluid Replicates the In Vivo Growth Capabilities of Citrobacter rodentium cpxRA Mutants and Uncovers Additive Effects of Cpx-Regulated Genes on Fitness.

Citrobacter rodentium is an attaching and effacing (A/E) pathogen used to model enteropathogenic and enterohemorrhagic Escherichia coli infections in mice. During colonization, C. rodentium must adapt to stresses in the gastrointestinal tract, such as antimicrobial peptides, pH changes, and bile salts. The Cpx envelope stress response (ESR) is a two-component system used by some bacteria to remediate stress by modulating gene expression, and it is necessary for C. rodentium pathogenesis in mice. Here, we utilized simulated colonic fluid (SCF) to mimic the gastrointestinal environment, which we show strongly induces the Cpx ESR and highlights a fitness defect specific to the ΔcpxRA mutant. While investigating genes in the Cpx regulon that may contribute to C. rodentium pathogenesis, we found that the absence of the Cpx ESR resulted in higher expression of the locus of enterocyte effacement (LEE) master regulator, ler, and that the genes yebE, ygiB, bssR, and htpX relied on CpxRA for proper expression. We then determined that CpxRA and select gene mutants were essential for proper growth in SCF when in the presence of extraneous stressors and in competition. Although none of the Cpx-regulated gene mutants exhibited marked virulence phenotypes in vivo, the ΔcpxRA mutant had reduced colonization and attenuated virulence, as previously determined, which replicated the in vitro growth phenotypes specific to SCF. Overall, these results indicate that the ΔcpxRA virulence defect is not due to any single Cpx regulon gene examined. Instead, attenuation may be the result of defective growth in the colonic environment resulting from the collective impact of multiple Cpx-regulated genes.

Novel CARD9 mutation in a patient with chronic invasive dermatophyte infection (tinea profunda).

Caspase Recruitment Domain Family Member 9 (CARD9) is an adaptor molecule that drives antifungal activity of macrophages and neutrophils in the skin. Autosomal recessive loss-of-function mutations in CARD9 confer increased susceptibility to invasive disease with select fungi in non-immunosuppressed patients. We report on a patient with X-linked ichthyosis complicated by chronic cutaneous invasive dermatophyte infection. We identified a previously reported c.271T>C (p.Y91H) mutation and a novel intronic c.1269+18G>A mutation in CARD9 underlying recurrent deep dermatophytosis in this patient despite various antifungals for over three decades. Our case highlights susceptibility to invasive dermatophytosis related to autosomal recessive CARD9 deficiency and illustrates the range of CARD9 mutations to be pursued in immunocompetent patients with unexplained deep dermatophyte infections. Further studies are needed to define the best therapeutic regimen.

Loss of human ICOSL results in combined immunodeficiency.

Primary immunodeficiencies represent naturally occurring experimental models to decipher human immunobiology. We report a patient with combined immunodeficiency, marked by recurrent respiratory tract and DNA-based viral infections, hypogammaglobulinemia, and panlymphopenia. He also developed moderate neutropenia but without prototypical pyogenic infections. Using whole-exome sequencing, we identified a homozygous mutation in the inducible T cell costimulator ligand gene (ICOSLG; c.657C>G; p.N219K). Whereas WT ICOSL is expressed at the cell surface, the ICOSLN219K mutation abrogates surface localization: mutant protein is retained in the endoplasmic reticulum/Golgi apparatus, which is predicted to result from deleterious conformational and biochemical changes. ICOSLN219K diminished B cell costimulation of T cells, providing a compelling basis for the observed defect in antibody and memory B cell generation. Interestingly, ICOSLN219K also impaired migration of lymphocytes and neutrophils across endothelial cells, which normally express ICOSL. These defects likely contributed to the altered adaptive immunity and neutropenia observed in the patient, respectively. Our study identifies human ICOSLG deficiency as a novel cause of a combined immunodeficiency.

The genomic landscape of two Burkitt lymphoma cases and derived cell lines: comparison between primary and relapse samples.

Relapse occurs in 10-40% of Burkitt lymphoma (BL) patients that have completed intensive chemotherapy regimens and is typically fatal. While treatment-naive BL has been characterized, the genomic landscape of BL at the time of relapse (rBL) has never been reported. Here, we present a genomic characterization of two rBL patients. The diagnostic samples had mutations common in BL, including MYC and CCND3. Additional mutations were detected at relapse, affecting important pathways such as NFκB (IKBKB) and MEK/ERK (NRAS) signaling, glutamine metabolism (SIRT4), and RNA processing (ZFP36L2). Genes implicated in drug resistance were also mutated at relapse (TP53, BAX, ALDH3A1, APAF1, FANCI). This concurrent genomic profiling of samples obtained at diagnosis and relapse has revealed mutations not previously reported in this disease. The patient-derived cell lines will be made available and, along with their detailed genetics, will be a valuable resource to examine the role of specific mutations in therapeutic resistance.

Novel bi-allelic splice mutations in CARD9 causing adult-onset Candida endophthalmitis.

CARD9 deficiency (CANDF2; OMIM# 212050) is an autosomal-recessive monogenic inborn error of immunity conferring susceptibility to invasive fungal diseases, including the very distinct syndrome of spontaneous central nervous system candidiasis, in which opportunistic yeast of the genus Candida infect the central nervous system (either brain parenchyma and/or meninges) in the absence of trauma, chemotherapy or underlying systemic disease. We present a patient with spontaneous endophthalmitis of the right eye due to Candida albicans; further investigations revealed concomitant cerebral abscess. She had a history of left endophthalmitis due to the dematiaceous mould, Aureobasidium pullulans, 15 years earlier. Targeted sequencing of the CARD9 gene revealed 2 novel variants (c.184G>A and c.288C>T). Analysis in silico predicted each variant altered splicing, which was confirmed by sequencing of cDNA from proband and carrier offsprings: c.184G>A results in a 4-base pair frameshift deletion with loss of allelic expression; c.288C>T results in an in-frame 36-bp pair deletion with detectable protein. CARD9 deficiency can present with a phenotype of spontaneous candidal endophthalmitis. We report 2 novel mutations in CARD9, both affecting splicing, expanding the range of morbid variants causing CARD9 deficiency, emphasising the importance of both genomic and cDNA sequencing for this condition.

Impaired RASGRF1/ERK-mediated GM-CSF response characterizes CARD9 deficiency in French-Canadians.

BACKGROUND: Caspase recruitment domain-containing protein 9 (CARD9) deficiency is an autosomal recessive primary immunodeficiency conferring human susceptibility to invasive fungal disease, including spontaneous central nervous system candidiasis (sCNSc). However, clinical characterization of sCNSc is variable, hindering its recognition. Furthermore, an in-depth understanding of the bases for this susceptibility has remained elusive. OBJECTIVES: We sought to comprehensively characterize sCNSc and to dissect the mechanisms by which a hypomorphic CARD9 mutation causes susceptibility to Candida species. METHODS: We describe the clinical and radiologic findings of sCNSc caused by CARD9 deficiency in a French-Canadian cohort. We performed genetic, cellular, and molecular analyses to further decipher its pathophysiology. RESULTS: In our French-Canadian series (n = 4) sCNSc had onset in adulthood (median, 38 years) and was often misinterpreted radiologically as brain malignancies; 1 patient had additional novel features (eg, endophthalmitis and osteomyelitis). CARD9 deficiency resulted from a hypomorphic p.Y91H mutation and allelic imbalance established in this population through founder effects. We demonstrate a consistent cellular phenotype of impaired GM-CSF responses. The ability of CARD9 to complex with B-cell CLL/lymphoma 10 (BCL10) and mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) is intact in our series, arguing against its involvement in susceptibility to fungi. Instead, we show that the p.Y91H mutation impairs the ability of CARD9 to complex with Ras protein-specific guanine nucleotide-releasing factor 1 (RASGRF1), leading to impaired activation of nuclear factor κB and extracellular signal-regulated kinase (ERK) in monocytes and subsequent GM-CSF responses. Successful treatment of a second patient with adjunctive GM-CSF bolsters the clinical relevance of these findings. CONCLUSIONS: Hypomorphic CARD9 deficiency caused by p.Y91H results in adult-onset disease with variable penetrance and expressivity. Our findings establish the CARD9/RASGRF1/ERK/GM-CSF axis as critical to the pathophysiology of sCNSc.

The Fungal Exopolysaccharide Galactosaminogalactan Mediates Virulence by Enhancing Resistance to Neutrophil Extracellular Traps.

Of the over 250 Aspergillus species, Aspergillus fumigatus accounts for up to 80% of invasive human infections. A. fumigatus produces galactosaminogalactan (GAG), an exopolysaccharide composed of galactose and N-acetyl-galactosamine (GalNAc) that mediates adherence and is required for full virulence. Less pathogenic Aspergillus species were found to produce GAG with a lower GalNAc content than A. fumigatus and expressed minimal amounts of cell wall-bound GAG. Increasing the GalNAc content of GAG of the minimally pathogenic A. nidulans, either through overexpression of the A. nidulans epimerase UgeB or by heterologous expression of the A. fumigatus epimerase Uge3 increased the amount of cell wall bound GAG, augmented adherence in vitro and enhanced virulence in corticosteroid-treated mice to levels similar to A. fumigatus. The enhanced virulence of the overexpression strain of A. nidulans was associated with increased resistance to NADPH oxidase-dependent neutrophil extracellular traps (NETs) in vitro, and was not observed in neutropenic mice or mice deficient in NADPH-oxidase that are unable to form NETs. Collectively, these data suggest that cell wall-bound GAG enhances virulence through mediating resistance to NETs.

CARD9 deficiency and spontaneous central nervous system candidiasis: complete clinical remission with GM-CSF therapy.

We demonstrate autosomal-recessive Caspase Recruitment Domain-containing protein 9 (CARD9) deficiency in a patient with relapsing C. albicans meningoencephalitis. We identified a novel, hypomorphic mutation with intact Th17 responses, but impaired GM-CSF responses. We report complete clinical remission with adjunctive GM-CSF therapy, suggesting that a CARD9/GM-CSF axis contributes to susceptibility to candidiasis.

Patched1 haploinsufficiency impairs ependymal cilia function of the quaking viable mice, leading to fatal hydrocephalus.

The quaking viable (qk(v)) mice harbor an autosomal recessive mutation that deletes the parkin co-regulated gene (pacrg) and parkin (park2) genes, and alters the expression of the quaking (qkI) gene. qk(v) mice have been well-studied for their dysmyelination phenotype caused by the altered expression of the qkI gene. The qk(v) mice exhibit sterility in males and develop acquired mild hydrocephalus due to the lack of PACRG expression. To identify genetic interactors of the pacrg-parkin-qkI locus, we crossbred the qk(v) mice with various mouse strains including the patched1 (ptch1)-deficient mice. The ptch1 heterozygous mice exhibit increased Sonic Hedgehog (Shh) signaling and are prone to several malignancies including tumorigenesis. In the present study, we show that the qk(v/v); ptch1⁺/⁻ mice are distinguished by a dome-shaped skull at 4 to 6weeks of age and exhibit dilation of the lateral and third ventricles leading to fatal acquired hydrocephalus by ~5months of age, unlike their littermate controls that did not develop the condition. The qk(v/v); ptch1⁺/⁻ mice contained normal ciliated ependymal cells lining the ventricles of the brain, but these cells were functionally compromised with a severe cilial mediated flow defect. Our findings suggest that the ptch1 and the pacrg-parkin-qkI loci genetically interact to regulate cilia function of the ependymal cells.

Loss of p53 in quaking viable mice leads to Purkinje cell defects and reduced survival.

The qk(v) mutation is a one megabase deletion resulting in abnormal expression of the qkI gene. qk(v) mice exhibit hypomyelination of the central nervous system and display rapid tremors and seizures as adults. The qkI locus on 6q26-27 has also been implicated as a candidate tumor suppressor gene as the qkI locus maps to a region of genetic instability in Glioblastoma Multiforme (GBM), an aggressive brain tumor of astrocytic lineage. As GBM frequently harbors mutations affecting p53, we crossbred qk(v) and p53 mutant mice to examine whether qk(v) mice on a p53(-/-) background have an increased incidence of GBM. qk(v) (/v); p53(-/-) mice had a reduced survival rate compared to p53(-/-) littermates, and the cause of death of the majority of the mice remains unknown. In addition, immunohistochemistry revealed Purkinje cell degeneration in the cerebellum. These results suggest that p53 and qkI are genetically linked for neuronal maintenance and survival.

The QKI-6 RNA binding protein regulates actin-interacting protein-1 mRNA stability during oligodendrocyte differentiation.

The quaking viable (qk(v)) mice represent an animal model of dysmyelination. The absence of expression of the QKI-6 and QKI-7 cytoplasmic isoforms in oligodendrocytes (OLs) during CNS myelination causes the qk(v) mouse phenotype. The QKI RNA-binding proteins are known to regulate RNA metabolism of cell cycle proteins and myelin components in OLs; however, little is known of their role in reorganizing the cytoskeleton or process outgrowth during OL maturation and differentiation. Here, we identify the actin-interacting protein (AIP)-1 mRNA as a target of QKI-6 by using two-dimensional differential gel electrophoresis. The AIP-1 mRNA contains a consensus QKI response element within its 3'-untranslated region that, when bound by QKI-6, decreases the half-life of the AIP-1 mRNA. Although the expression of QKI-6 is known to increase during OL differentiation and CNS myelination, we show that this increase is paralleled with a corresponding decrease in AIP-1 expression in rat brains. Furthermore, qk(v)/qk(v) mice that lack QKI-6 and QKI-7 within its OLs had an increased level of AIP-1 in OLs. Moreover, primary rat OL precursors harboring an AIP-1 small interfering RNA display defects in OL process outgrowth. Our findings suggest that the QKI RNA-binding proteins regulate OL differentiation by modulating the expression of AIP-1.