Candida albicans Hexokinase 2 Challenges the Saccharomyces cerevisiae Moonlight Protein Model

Survival of the pathogenic yeast Candida albicans depends upon assimilation of fermentable and non-fermentable carbon sources detected in host microenvironments. Among the various carbon sources encountered in a human body, glucose is the primary source of energy. Its effective detection, metabolism and prioritization via glucose repression are primordial for the metabolic adaptation of the pathogen. In C. albicans, glucose phosphorylation is mainly performed by the hexokinase 2 (CaHxk2). In addition, in the presence of glucose, CaHxK2 migrates in the nucleus and contributes to the glucose repression signaling pathway. Based on the known dual function of the Saccharomyces cerevisiae hexokinase 2 (ScHxk2), we intended to explore the impact of both enzymatic and regulatory functions of CaHxk2 on virulence, using a site-directed mutagenesis approach. We show that the conserved aspartate residue at position 210, implicated in the interaction with glucose, is essential for enzymatic and glucose repression functions but also for filamentation and virulence in macrophages. Point mutations and deletion into the N-terminal region known to specifically affect glucose repression in ScHxk2 proved to be ineffective in CaHxk2. These results clearly show that enzymatic and regulatory functions of the hexokinase 2 cannot be unlinked in C. albicans.

Carbon metabolism snapshot by ddPCR during the early step of Candida albicans phagocytosis by macrophages

During Candida macrophage interactions, phagocytosed yeast cells feed in order to grow, develop hyphae and escape. Through numerous proteomic and transcriptomic studies, two metabolic phases have been described. A shift to a starvation mode is generally identified as early as one-hour post phagocytosis, followed by a glycolytic growth mode after C. albicans escaped from the macrophage. Healthy macrophages contain low amounts of glucose. To determine if this carbon source was sensed and metabolized by the pathogen, we explored the transcription level of a delimited set of key genes expressed in C. albicans cells during phagocytosis by macrophages, at an early stage of the interaction. This analysis was performed using a technical digital droplet PCR approach to quantify reliably the expression of carbon metabolic genes after 30 min of phagocytosis. Our data confirm the technique of digital droplet PCR for the detection of C. albicans transcripts using cells recovered after a short period of phagocytosis. At this stage, carbon metabolism is clearly oriented towards the use of alternative sources. However, the activation of high-affinity glucose transport system suggests that the low amount of glucose initially present in the macrophages is detected by the pathogen.

Hexokinase and Glucokinases Are Essential for Fitness and Virulence in the Pathogenic Yeast Candida albicans

The pathogenic yeast Candida albicans is both a powerful commensal and a pathogen of humans that can infect wide range of organs and body sites. Metabolic flexibility promotes infection and commensal colonization by this opportunistic pathogen. Yeast cell survival depends upon assimilation of fermentable and non-fermentable locally available carbon sources. Physiologically relevant sugars like glucose and fructose are present at low levels in host niches. However, because glucose is the preferred substrate for energy and biosynthesis of structural components, its efficient detection and metabolism are fundamental for the metabolic adaptation of the pathogen. We explored and characterized the C. albicans hexose kinase system composed of one hexokinase (CaHxk2) and two glucokinases (CaGlk1 and CaGlk4). Using a set of mutant strains, we found that hexose phosphorylation is mostly performed by CaHxk2, which sustains growth on hexoses. Our data on hexokinase and glucokinase expression point out an absence of cross regulation mechanisms at the transcription level and different regulatory pathways. In the presence of glucose, CaHxk2 migrates in the nucleus and contributes to the glucose repression signaling pathway. In addition, CaHxk2 participates in oxidative, osmotic and cell wall stress responses, while glucokinases are overexpressed under hypoxia. Hexose phosphorylation is a key step necessary for filamentation that is affected in the hexokinase mutant. Virulence of this mutant is clearly impacted in the Galleria mellonella and macrophage models. Filamentation, glucose phosphorylation and stress response defects of the hexokinase mutant prevent host killing by C. albicans. By contributing to metabolic flexibility, stress response and morphogenesis, hexose kinase enzymes play an essential role in the virulence of C. albicans.

Somatic tinnitus prevalence and treatment with tinnitus retraining therapy

OBJECTIVES

Somatic tinnitus originates from increased activity of the dorsal cochlear nucleus, a cross-point between the somatic and auditory systems. Its activity can be modified by auditory stimulation or somatic system manipulation. Thus, sound enrichment and white noise stimulation might decrease tinnitus and associated somatic symptoms. The present uncontrolled study sought to determine somatic tinnitus prevalence among tinnitus sufferers, and to investigate whether sound therapy with counselling (tinnitus retraining therapy; TRT) may decrease tinnitus-associated somatic symptoms.

METHODS

To determine somatic tinnitus prevalence, 70 patients following the TRT protocol completed the Jastreboff Structured Interview (JSI) with additional questions regarding the presence and type of somatic symptoms. Among 21 somatic tinnitus patients, we further investigated the effects of TRT on tinnitus-associated facial dysesthesia. Before and after three months of TRT, tinnitus severity was evaluated using the Tinnitus Handicap Inventory (THI), and facial dysesthesia was assessed with an extended JSI-based questionnaire.

RESULTS

Among the evaluated tinnitus patients, 56% presented somatic tinnitus-including 51% with facial dysesthesia, 36% who could modulate tinnitus by head and neck movements, and 13% with both conditions. Self-evaluation indicated that TRT significantly improved tinnitus and facial dysesthesia in 76% of patients. Three months of TRT led to a 50% decrease in mean THI and JSI scores regarding facial dysesthesia.

CONCLUSIONS

Somatic tinnitus is a frequent and underestimated condition. We suggest an extension of the JSI, including specific questions regarding somatic tinnitus. TRT significantly improved tinnitus and accompanying facial dysesthesia, and could be a useful somatic tinnitus treatment.

Spontaneous Pathology and Routine Clinical Pathology Parameters in Aging Beagle Dogs

AstraZeneca ran a bespoke study to generate age-matched clinical pathology and histopathology data from a cohort of Beagle dogs aged between 25 and 37 months to support the use of these older animals in routine preclinical toxicology studies. As the upper age range of Beagle dogs routinely used in toxicology studies does not normally exceed 24 months, there is an absence of appropriate age-matched historical control data. The generation of such data was crucial to understand whether age-related differences in spontaneous findings might confound the interpretation of toxicology study data. While the majority of the histopathology findings in all the older dogs occurred at a similar prevalence as those expected in young adult dogs (<24 months), a number of differences were observed in the thymus (involution), bone marrow (increased adiposity), testes (degenerative changes), and lung (fibrosis, pigment and alveolar hyperplasia) that could be misinterpreted as a test article effect. Minor differences in some clinical pathology values (hemoglobin, alkaline phosphatase, absolute reticulocytes) were of a small magnitude and considered unlikely to affect the interpretation of study data.

Glasgow supported self-management trial (GSuST) for patients with moderate to severe COPD: randomised controlled trial

OBJECTIVE

To determine whether supported self management in chronic obstructive pulmonary disease (COPD) can reduce hospital readmissions in the United Kingdom.

DESIGN

Randomised controlled trial.

SETTING

Community based intervention in the west of Scotland.

PARTICIPANTS

Patients admitted to hospital with acute exacerbation of COPD.

INTERVENTION

Participants in the intervention group were trained to detect and treat exacerbations promptly, with ongoing support for 12 months.

MAIN OUTCOME MEASURES

The primary outcome was hospital readmissions and deaths due to COPD assessed by record linkage of Scottish Morbidity Records; health related quality of life measures were secondary outcomes.

RESULTS

464 patients were randomised, stratified by age, sex, per cent predicted forced expiratory volume in 1 second, recent pulmonary rehabilitation attendance, smoking status, deprivation category of area of residence, and previous COPD admissions. No difference was found in COPD admissions or death (111/232 (48%) v 108/232 (47%); hazard ratio 1.05, 95% confidence interval 0.80 to 1.38). Return of health related quality of life questionnaires was poor (n=265; 57%), so that no useful conclusions could be made from these data. Pre-planned subgroup analysis showed no differential benefit in the primary outcome relating to disease severity or demographic variables. In an exploratory analysis, 42% (75/150) of patients in the intervention group were classified as successful self managers at study exit, from review of appropriateness of use of self management therapy. Predictors of successful self management on stepwise regression were younger age (P=0.012) and living with others (P=0.010). COPD readmissions/deaths were reduced in successful self managers compared with unsuccessful self managers (20/75 (27%) v 51/105 (49%); hazard ratio 0.44, 0.25 to 0.76; P=0.003).

CONCLUSION

Supported self management had no effect on time to first readmission or death with COPD. Exploratory subgroup analysis identified a minority of participants who learnt to self manage; this group had a significantly reduced risk of COPD readmission, were younger, and were more likely to be living with others.

TRIAL REGISTRATION

Clinical trials NCT 00706303.

[Somatic tinnitus (review). A consequence of plasticity and bimodal integration in the dorsal cochlear nucleus]

Somatic tinnitus is a peculiar tinnitus type that can be defined as a tinnitus that can be modulated in intensity and/or pitch by manipulating some regions of the head and neck but also as tinnitus associated with facial pain or dysesthesis in the same area. Those areas are innervated by the trigeminal nerve and the cervical plexus. This can be explained by functional connections between the trigeminal system and the auditory brainstem and mid-brain. A literature overview shows how different messages coming from the head and neck are able to modulate the hearing information. Tinnitus is generated by an increase of the spontaneous discharges of the dorsal cochlear nucleus neurons, tonotopic reorganisation and an increase of the neural synchronism in the auditory cortex. Trigeminal stimulations have an influence on the activity of the dorsal cochlear nucleus especially in case of an associated hearing loss.

Genomic analysis of the necrotrophic fungal pathogens Sclerotinia sclerotiorum and Botrytis cinerea

Sclerotinia sclerotiorum and Botrytis cinerea are closely related necrotrophic plant pathogenic fungi notable for their wide host ranges and environmental persistence. These attributes have made these species models for understanding the complexity of necrotrophic, broad host-range pathogenicity. Despite their similarities, the two species differ in mating behaviour and the ability to produce asexual spores. We have sequenced the genomes of one strain of S. sclerotiorum and two strains of B. cinerea. The comparative analysis of these genomes relative to one another and to other sequenced fungal genomes is provided here. Their 38-39 Mb genomes include 11,860-14,270 predicted genes, which share 83% amino acid identity on average between the two species. We have mapped the S. sclerotiorum assembly to 16 chromosomes and found large-scale co-linearity with the B. cinerea genomes. Seven percent of the S. sclerotiorum genome comprises transposable elements compared to <1% of B. cinerea. The arsenal of genes associated with necrotrophic processes is similar between the species, including genes involved in plant cell wall degradation and oxalic acid production. Analysis of secondary metabolism gene clusters revealed an expansion in number and diversity of B. cinerea-specific secondary metabolites relative to S. sclerotiorum. The potential diversity in secondary metabolism might be involved in adaptation to specific ecological niches. Comparative genome analysis revealed the basis of differing sexual mating compatibility systems between S. sclerotiorum and B. cinerea. The organization of the mating-type loci differs, and their structures provide evidence for the evolution of heterothallism from homothallism. These data shed light on the evolutionary and mechanistic bases of the genetically complex traits of necrotrophic pathogenicity and sexual mating. This resource should facilitate the functional studies designed to better understand what makes these fungi such successful and persistent pathogens of agronomic crops.

Amino acid changes during sunflower infection by the necrotrophic fungus B. cinerea

Metabolic changes that occur in host tissues during a necrotrophic plant/fungal interaction have been poorly investigated. Whereas carbon metabolism reprogramming and photosynthesis disturbances have been studied, data on plant amino acids stores during infection are scarce. Here we report an analysis of sunflower cotyledon amino acid content during infection with the necrotrophic fungus Botrytis cinerea, by using (13)C-NMR spectroscopy. A rapid disappearance of plant amino acids was observed, most probably due to fungal assimilation. In order to explore amino acid changes due to host reaction, we investigated the amino acid content in healthy and invaded region of infected leaves. During the course of infection, glutamate store was affected at distance in the non invaded region. Glutamate depletion was correlated to an enhanced sunflower glutamate dehydrogenase (GDH) transcription level in the area invaded by pathogen. Our data suggest that glutamate could be transferred to the invaded region to supply nitrogen. Such a strategy could delay cell death, and consequently disturb fungal progression in plant tissues.

Dynamic carbon transfer during pathogenesis of sunflower by the necrotrophic fungus Botrytis cinerea: from plant hexoses to mannitol

The main steps for carbon acquisition and conversion by Botrytis cinerea during pathogenesis of sunflower cotyledon were investigated here. A sequential view of soluble carbon metabolites detected by NMR spectroscopy during infection is presented. Disappearance of plant hexoses and their conversion to fungal metabolites were investigated by expression analysis of an extended gene family of hexose transporters (Bchxts) and of the mannitol pathway, using quantitative PCR. In order to analyse the main fungal metabolic routes used by B. cinerea in real time, we performed, for the first time, in vivo NMR analyses during plant infection. During infection, B. cinerea converts plant hexoses into mannitol. Expression analysis of the sugar porter gene family suggested predominance for transcription induced upon low glucose conditions and regulated according to the developmental phase. Allocation of plant hexoses by the pathogen revealed a conversion to mannitol, trehalose and glycogen for glucose and a preponderant transformation of fructose to mannitol by a more efficient metabolic pathway. Uptake of plant hexoses by B. cinerea is based on a multigenic flexible hexose uptake system. Their conversion into mannitol, enabled by two simultaneously expressed pathways, generates a dynamic intracellular carbon pool.

Metabolic processes and carbon nutrient exchanges between host and pathogen sustain the disease development during sunflower infection by Sclerotinia sclerotiorum

Interactions between the necrotrophic fungus Sclerotinia sclerotiorum and one of its hosts, Helianthus annuus L., were analyzed during fungal colonization of plant tissues. Metabolomic analysis, based on (13)C- and (31)P-NMR spectroscopy, was used to draw up the profiles of soluble metabolites of the two partners before interaction, and to trace the fate of metabolites specific of each partner during colonization. In sunflower cotyledons, the main soluble carbohydrates were glucose, fructose, sucrose and glutamate. In S. sclerotiorum extracts, glucose, trehalose and mannitol were the predominant soluble carbon stores. During infection, a decline in sugars and amino acids was observed in the plant and fungus total content. Sucrose and fructose, initially present almost exclusively in plant, were reduced by 85%. We used a biochemical approach to correlate the disappearance of sucrose with the expression and the activity of fungal invertase. The expression of two hexose transporters, Sshxt1 and Sshxt2, was enhanced during infection. A database search for hexose transporters homologues in the S. sclerotiorum genome revealed a multigenic sugar transport system. Furthermore, the composition of the pool of reserve sugars and polyols during infection was investigated. Whereas mannitol was produced in vitro and accumulated in planta, glycerol was exclusively produced in infected tissues and increased during colonization. The hypothesis that the induction of glycerol synthesis in S. sclerotiorum exerts a positive effect on osmotic protection of fungal cells and favors fungal growth in plant tissues is discussed. Taken together, our data revealed the importance of carbon-nutrient exchanges during the necrotrophic pathogenesis of S. sclerotiorum.

Widespread endoscopic mucosal resection of the esophagus with strategies for stricture prevention: a preclinical study

BACKGROUND AND STUDY AIMS

Circumferential endoscopic mucosal resection of the esophagus is complicated by stricture formation. Prophylactic measures for avoiding such strictures have not been well studied. The aim of this preclinical study was to assess strategies for prevention of esophageal strictures in a porcine model following widespread endoscopic mucosal resection (EMR).

METHODS

A total of 18 60-kg pigs were included in the study. The roles of strip width (group 1), prophylactic steroids (group 2), and prophylactic stents (group 3) in the prevention of post-mucosectomy strictures were studied. Six animals were included in each group. Esophageal mucosal resection was achieved using a novel widespread EMR technique previously described by our group. Animals in group 1 underwent partial (50% circumference) mucosal resection without prophylactic measures, while animals in the other two groups underwent circumferential mucosal resection. Animals in group 2 received 80 mg of triamcinolone injected directly into the exposed submucosal tissue (20 mg injection in four quadrants). Animals in group 3 received esophageal metal stents coated with small-intestine submucosa (SIS) that were deployed immediately post-resection. Animals were kept alive for 1 month.

RESULTS

Partial and circumferential widespread EMRs were achieved in all animals. There were no procedural complications. Repeat endoscopy at 1 month showed no strictures in group 1. Only four animals were studied in group 2, owing to the high complication rate (periesophageal abscess in all animals) with one early death. Three of the surviving animals developed mild to tight strictures. In group 3, all animals developed tight strictures; however, there was early stent migration in four animals and premature stent removal in two animals because of persistent vomiting.

CONCLUSIONS

Partial widespread EMR of the esophagus heals without stricture formation and does not require prophylactic intervention. The use of deep mural steroid injection following a circumferential resection does not appear to prevent strictures and may result in serious adverse events. Short-term use of esophageal stents is inadequate for stricture prevention. However, better results may be anticipated with longer term (at least 6 weeks) stent use.

Molecular characterization and in planta detection of Sclerotinia sclerotiorum endopolygalacturonase genes

Sclerotinia sclerotiorum, a plant pathogenic ascomycete, secretes multiple pectinolytic enzymes that facilitate penetration, colonization, and maceration of the plant tissues. Molecular analysis has previously revealed that the pectinolytic system of the fungus is organized as a multigene family, among which a subfamily of three members encoding for neutral endopolygalacturonase (endoPG) isoforms has been characterized. Here we describe the isolation and characterization of three additional endoPG-encoding genes ( pg5, pg6, and pg7) that belong to distinct phylogenetic groups. Pairwise sequence comparison between the known endoPGs from S. sclerotiorum revealed 43% to 97% identity, and the genomic organization of the pectinolytic system showed a great similarity to that of the related necrotroph Botrytis cinerea. During plant pathogenesis, a sequential expression of the endoPG-encoding genes was shown.

Ambient pH controls the expression of endopolygalacturonase genes in the necrotrophic fungusSclerotinia sclerotiorum

In the necrotrophic fungus Sclerotinia sclerotiorum, secretion of polygalacturonases (PGs) and decrease of the environmental pH via oxalic acid production are considered as the main pathogenicity determinants. In order to evaluate the relationship between these two aspects of the infection process, we analyzed the expression of the endoPG-encoding genes pg1-3. Transcription of pg1-3 was not carbon regulated but was strictly controlled by pH and highly favored in a narrow range of acidic pH. During plant infection, a pH gradient was established in relation to oxalic acid secretion. Transcripts of pg1-3 were localized to the zone of colonization of healthy tissues while transcripts of genes encoding other lytic enzymes were restricted to the more acidic zones of the infected tissues. Our results show that progressive acidification of the ambient medium by the fungus is a major strategy for the sequential expression of pathogenicity factors.

Characterization of a SNF1 homologue from the phytopathogenic fungus Sclerotinia sclerotiorum

In yeast, the SNF1 gene product is essential for the release of catabolic repression. We report the isolation and characterization of an SNF1 homologue from the necrotrophic pathogen Sclerotinia sclerotiorum. Ss snf1 encodes a 765-amino-acid protein in which the catalytic domain has an overall identity with the yeast proteins varying from 55 to 76% while the C-terminal half of Ss SNF1 has a weak homology of about 20% with the yeast sequences. Reverse transcription-polymerase chain reaction showed that its transcripts were weakly and constitutively expressed in planta and in vitro regardless of the nature of the carbon sources and of the presence or absence of glucose. Expression of Ss snf1 in yeast cells allowed the snf1 mutant cells to utilize sucrose, raffinose or glycerol for growth while expression of the Ss snf1 catalytic domain did not restore growth on raffinose or glycerol. Ss SNF1 is structurally homologous to Snf1p, suggesting that the interactions between the kinase and the accessory subunits to activate the enzymatic complex are conserved in fungi.

Characterization of PG2, an early endoPG produced by Sclerotinia sclerotiorum, expressed in yeast

Sclerotinia sclerotiorum, a plant pathogenic ascomycete, contains a neutral endopolygalacturonase (endoPG) subfamily of genes that was previously isolated. We report here that pg2, a member of this subfamily, is early and strongly expressed during the first steps of pathogenesis of sunflower cotyledons. The corresponding protein, PG2, was produced in the heterologous Kluyveromyces lactis system and purified. Characterization of the recombinant enzyme revealed a narrow pH activity curve with an optimal pH of 4.5. Hydrolysis of polygalacturonic acid by PG2 resulted in the accumulation of oligomers ranging from 2- to 9-mer. This degradation profile indicates a random attack on the polymer and demonstrates an endo-mode of action. These results provide evidence that pg2 contributes to the infection process during the early phase of host colonization.

Expression and compartmentation of the glucose repressor CRE1 from the phytopathogenic fungus Sclerotinia sclerotiorum

The glucose repressor from the phytopathogenic fungus Sclerotinia sclerotiorum is encoded by the cre1 gene. Polyclonal antibodies were raised against a fusion protein (gluthathione S-transferase) GST-CRE1 in order to study cre1 expression. Western blot analyses revealed that CRE1 synthesis is regulated by the nature of the extracellular carbon source. High CRE1 levels are induced by glucose and remain stable after transfer into pectin medium, suggesting the existence of post-translational mechanisms which inactivate CRE1 to allow transcription of glucose-repressed genes. Subcellular fractionation demonstrated that CRE1 is localized in the nuclei of glucose grown hyphae and in the cytoplasm when glucose is removed from the culture medium. CRE1 fused to green fluorescent protein (GFP) was introduced into Aspergillus nidulans. Fluorescence microscopy showed the nuclear localization of the GFP-CRE1 fusion protein according to the presence of glucose in the culture medium, suggesting homologous post-translational regulations of glucose repressors in fungi. We propose that filamentous fungi regulate the activity of the glucose repressor by controlling its nuclear translocation.

The glucose repressor CRE1 from Sclerotinia sclerotiorum is functionally related to CREA from Aspergillus nidulans but not to the Mig proteins from Saccharomyces cerevisiae

We isolated the putative glucose repressor gene cre1 from the phytopathogenic fungus Sclerotinia sclerotiorum. cre1 encodes a 429 amino acid protein 59% similar to the carbon catabolite repressor CREA from Aspergillus nidulans. In addition to the overall amino acid sequence relatedness between CRE1 and CREA proteins, cre1 can functionally complement the A. nidulans creAd30 mutation as assessed by repression of the alcohol dehydrogenase I gene expression. The CREI region carrying the two zinc fingers is also very similar to the DNA binding domains of the Saccharomyces cerevisiae glucose repressors Mig1p and Mig2p. Despite the presence in the CRE1 protein of several motifs involved in the regulation of Miglp activity, cre1 cannot complement mig deficiencies in S. cerevisiae. These data suggest that glucose repression pathways may have evolved differently in yeasts and filamentous fungi.

Pancreatic sphincter hypertension increases the risk of post-ERCP pancreatitis

BACKGROUND AND STUDY AIMS

The reason for the increased risk of pancreatitis after endoscopic retrograde cholangiopancreatography (ERCP) in patients with sphincter of Oddi dysfunction is not known. This study sought to determine whether pancreatic sphincter hypertension might explain some of the increased risk.

PATIENTS AND METHODS

The incidence of pancreatitis was determined from a cohort of patients who underwent pancreatic sphincter manometry. Additional data collected included: pancreatic and biliary sphincter manometry results, distal bile duct diameter, chronic pancreatitis grade by pancreatography, and endoscopic treatments.

RESULTS

Ten of 32 patients (31%) with pancreatic sphincter hypertension developed post-ERCP pancreatitis, compared to one of 33 (3%) with normal pancreatic manometry (P = 0.002). Patients with pancreatic sphincter hypertension were more likely to undergo endoscopic treatments (88%) compared to those with normal manometry (27%) (P = 0.001). The distal bile duct diameter was significantly smaller (4.5 +/- 0.5 mm) in patients who developed post-ERCP pancreatitis than in those who did not (6.2 +/- 0.3) (P = 0.025). Patients with small distal bile duct diameters (< 5 mm) were three times more likely to develop post-ERCP pancreatitis than those with larger ducts (relative risk [RR] 3.1, 95% confidence interval [CI] 0.9, 10.7). Patients with pancreatic sphincter hypertension were ten times more likely to develop post-ERCP pancreatitis than those with normal pancreatic manometry (RR 10.3, 95% CI 1.5, 76.0). In patients with a small bile duct size, pancreatic sphincter hypertension substantially increased the risk compared to those with normal manometry (RR 18.1, 95% CI 1.1, 287.6).

CONCLUSIONS

Pancreatic sphincter hypertension greatly increases the risk of post-ERCP pancreatitis in patients undergoing treatment or evaluation, or both, for sphincter of Oddi dysfunction.