Development of a murine model to study the cerebral pathogenesis of Aspergillus fumigatus

IMPORTANCE

Molds are environmental fungi that can cause disease in immunocompromised individuals. The most common pathogenic mold is Aspergillus fumigatus, which is typically inhaled into the lungs and causes invasive pulmonary disease. In a subset of these patients, this infection can spread from the lungs to other organs including the brain, resulting in cerebral aspergillosis. How A. fumigatus causes brain disease is not well understood and these infections are associated with extremely high mortality rates. Thus, we developed an animal model to study the pathogenesis of cerebral aspergillosis to better understand this disease and develop better treatments for these life-threatening infections.

CWHM-974 is a fluphenazine derivative with improved antifungal activity against Candida albicans due to reduced susceptibility to multidrug transporter-mediated resistance mechanisms

Multidrug resistance (MDR) transporters such as ATP-Binding Cassette (ABC) and Major Facilitator Superfamily proteins are important mediators of antifungal drug resistance, particularly with respect to azole class drugs. Consequently, identifying molecules that are not susceptible to this mechanism of resistance is an important goal for new antifungal drug discovery. As part of a project to optimize the antifungal activity of clinically used phenothiazines, we synthesized a fluphenazine derivative (CWHM-974) with 8-fold higher activity against Candida spp. compared to the fluphenazine and with activity against Candida spp. with reduced fluconazole susceptibility due to increased MDR transporters. Here, we show that the improved C. albicans activity is because fluphenazine induces its own resistance by triggering expression of Candida drug resistance (CDR) transporters while CWHM-974 induces expression but does not appear to be a substrate for the transporters or is insensitive to their effects through other mechanisms. We also found that fluphenazine and CWHM-974 are antagonistic with fluconazole in C. albicans but not in C. glabrata, despite inducing CDR1 expression to high levels. Overall, CWHM-974 is one of the few examples of a molecule in which relatively small structural modifications significantly reduced susceptibility to multidrug transporter-mediated resistance.

The anti-cancer efficacy of a novel phenothiazine derivative is independent of dopamine and serotonin receptor inhibition

Introduction

An attractive, yet unrealized, goal in cancer therapy is repurposing psychiatric drugs that can readily penetrate the blood-brain barrier for the treatment of primary brain tumors and brain metastases. Phenothiazines (PTZs) have demonstrated anti-cancer properties through a variety of mechanisms. However, it remains unclear whether these effects are entirely separate from their activity as dopamine and serotonin receptor (DR/5-HTR) antagonists.

Methods

In this study, we evaluated the anti-cancer efficacy of a novel PTZ analog, CWHM-974, that was shown to be 100-1000-fold less potent against DR/5-HTR than its analog fluphenazine (FLU).

Results

CWHM-974 was more potent than FLU against a panel of cancer cell lines, thus clearly demonstrating that its anti-cancer effects were independent of DR/5-HTR signaling. Our results further suggested that calmodulin (CaM) binding may be necessary, but not sufficient, to explain the anti-cancer effects of CWHM-974. While both FLU and CWHM-974 induced apoptosis, they induced distinct effects on the cell cycle (G0/G1 and mitotic arrest respectively) suggesting that they may have differential effects on CaM-binding proteins involved in cell cycle regulation.

Discussion

Altogether, our findings indicated that the anti-cancer efficacy of the CWHM-974 is separable from DR/5-HTR antagonism. Thus, reducing the toxicity associated with phenothiazines related to DR/5-HTR antagonism may improve the potential to repurpose this class of drugs to treat brain tumors and/or brain metastasis.

Novel Keto-Alkyl-Pyridinium Antifungal Molecules Active in Models of In Vivo Candida albicans Vascular Catheter Infection and Ex Vivo Candida auris Skin Colonization

New antifungal therapies are needed for both systemic, invasive infections in addition to superficial infections of mucosal and skin surfaces as well as biofilms associated with medical devices. The resistance of biofilm and biofilm-like growth phases of fungi contributes to the poor efficacy of systemic therapies to nonsystemic infections. Here, we describe the identification and characterization of a novel keto-alkyl-pyridinium scaffold with broad spectrum activity (2 to 16 μg/mL) against medically important yeasts and molds, including clinical isolates resistant to azoles and/or echinocandins. Furthermore, these keto-alkyl-pyridinium agents retain substantial activity against biofilm phase yeast and have direct activity against hyphal A. fumigatus. Although their toxicity precludes use in systemic infections, we found that the keto-alkyl-pyridinium molecules reduce Candida albicans fungal burden in a rat model of vascular catheter infection and reduce Candida auris colonization in a porcine ex vivo model. These initial preclinical data suggest that molecules of this class may warrant further study and development for nonsystemic applications.

CWHM-974 is a fluphenazine derivative with improved antifungal activity against Candida albicans due to reduced susceptibility to multidrug transporter-mediated resistance mechanisms

Multidrug resistance (MDR) transporters such as ATP Binding Cassette (ABC) and Major Facilitator Superfamily (MFS) proteins are important mediators of antifungal drug resistance, particularly with respect to azole class drugs. Consequently, identifying molecules that are not susceptible to this mechanism of resistance is an important goal for new antifungal drug discovery. As part of a project to optimize the antifungal activity of clinically used phenothiazines, we synthesized a fluphenazine derivative (CWHM-974) with 8-fold higher activity against Candida spp. compared to the fluphenazine and with activity against Candida spp. with reduced fluconazole susceptibility due to increased multidrug resistance transporters. Here, we show that the improved C. albicans activity is because fluphenazine induces its own resistance by triggering expression of CDR transporters while CWHM-974 induces expression but does not appear to be a substrate for the transporters or is insensitive to their effects through other mechanisms. We also found that fluphenazine and CWHM-974 are antagonistic with fluconazole in C. albicans but not in C. glabrata , despite inducing CDR1 expression to high levels. Overall, CWHM-974 represents a unique example of a medicinal chemistry-based conversion of chemical scaffold from MDR-sensitive to MDR-resistant and, hence, active against fungi that have developed resistance to clinically used antifungals such as the azoles.

A Dual-Readout High-Throughput Screening Assay for Small Molecules Active Against Aspergillus Fumigatus

Human fungal infections caused by molds have been on the rise in recent years. These infections have high mortality rates compared to other fungal infections, and yet treatment options are limited due to resistance to clinical antifungals and lack of broad-spectrum activity against molds. Technical challenges associated with molds have limited large-throughput screening efforts for anti-mold compounds: therefore, we adapted an assay for use with A. fumigatus to help fill the gap in robust screening platforms for these organisms. This assay measures the release of the cytosolic enzyme adenylate kinase (AK) as a measure of fungal cell lysis and can also detect inhibition of germination as a reduction in the secretion of AK during vegetative growth. The ability to detect both lysis and inhibition of germination facilitates the identification of a wide range of compounds with different mechanisms of action, creating a strong screening platform for the identification of novel, anti-mold compounds.

FKS1 Is Required for Cryptococcus neoformans Fitness In Vivo: Application of Copper-Regulated Gene Expression to Mouse Models of Cryptococcosis

There is an urgent need for new antifungals to treat cryptococcal meningoencephalitis, a leading cause of mortality in people living with HIV/AIDS. An important aspect of antifungal drug development is the validation of targets to determine whether they are required for the survival of the organism in animal models of disease. In Cryptococcus neoformans, a copper-regulated promoter (pCTR4-2) has been used previously to modulate gene expression in vivo. The premise for these experiments is that copper concentrations differ depending on the host niche. Here, we directly test this premise and confirm that the expression of CTR4, the promoter used to regulate gene expression, is much lower in the mouse lung compared to the brain. To further explore this approach, we applied it to the gene encoding 1,3-β-glucan synthase, FKS1. In vitro, reduced expression of FKS1 has little effect on growth but does activate the cell wall integrity stress response and increase susceptibility to caspofungin, a direct inhibitor of Fks1. These data suggest that compensatory pathways that reduce C. neoformans resistance do so through posttranscriptional effects. In vivo, however, a less pronounced reduction in FKS1 expression leads to a much more significant reduction in lung fungal burden (~1 log10 CFU), indicating that the compensatory responses to a reduction in FKS1 expression are not as effective in vivo as they are in vitro. In summary, use of copper-regulated expression of putative drug targets in vitro and in vivo can provide insights into the biological consequences of reduced activity of the target during infection. IMPORTANCE Conditional expression systems are widely used to genetically validate antifungal drug targets in mouse models of infection. Copper-regulated expression using the promoter of the CTR4 gene has been sporadically used for this purpose in C. neoformans. Here, we show that CTR4 expression is low in the lung and high in the brain, establishing the basic premise behind this approach. We applied the approach to the study of FKS1, the gene encoding the target of the echinocandin class of 1,3-β-glucan synthase inhibitors. Our in vitro and in vivo studies indicate that C. neoformans tolerates extremely low levels of FKS1 expression. This observation provides a potential explanation for the poor activity of 1,3-β-glucan synthase inhibitors toward C. neoformans.

Gluconate Kinase Is Required for Gluconate Assimilation and Sporulation in Cryptococcus neoformans

Cryptococcus neoformans is an environmental yeast and an opportunistic human pathogen. The ability to cause disease depends on the ability to adapt to the human host. Previous studies implicated infectivity-related kinase 3 (IRK3, CNAG_03048) as required for establishing an infection. We genetically and biochemically characterized IRK3 as a gluconate kinase and propose the name GNK1. This metabolic enzyme utilizes gluconate to produce 6-phosphogluconate as part of the alternative oxidative phase of the pentose phosphate pathway (AOXPPP). The presence of GNK1 confirms that the AOXPPP is present and able to compensate for loss of the traditional OXPPP, providing an explanation for its nonessentiality. C. neoformans can utilize gluconate as an alternative carbon source in a GNK1-dependent manner. In our efforts to understand the role of GNK1 in host adaptation and virulence, we found that GNK1-deficient mutants have variable virulence and carbon dioxide tolerance across multiple strains, suggesting that second site mutations frequently interact with GNK1 deletion mutations. In our effort to isolate these genetic loci by backcrossing experiments, we discovered that GNK1-deficient strains are unable to sporulate. These data suggest that gluconate metabolism is critical for sporulation of C. neoformans. IMPORTANCE Cryptococcus neoformans is a fungal pathogen that contributes to nearly 180,000 deaths annually. We characterized a gene named GNK1 that appears to interact with other genetic loci involved with the ability of C. neoformans to act as a pathogen. While these interacting genetic loci remain elusive, we discovered that GNK1 plays roles in both metabolism and mating/sporulation. Further interrogation of the mechanistic role for GNK1 in sexual reproduction may uncover a larger network of genes that are important for host adaptation and virulence.

An Alanine Aminotransferase Is Required for Biofilm-Specific Resistance of Aspergillus fumigatus to Echinocandin Treatment

Alanine metabolism has been suggested as an adaptation strategy to oxygen limitation in organisms ranging from plants to mammals. Within the pulmonary infection microenvironment, Aspergillus fumigatus forms biofilms with steep oxygen gradients defined by regions of oxygen limitation. An alanine aminotransferase, AlaA, was observed to function in alanine catabolism and is required for several aspects of A. fumigatus biofilm physiology. Loss of alaA, or its catalytic activity, results in decreased adherence of biofilms through a defect in the maturation of the extracellular matrix polysaccharide galactosaminogalactan (GAG). Additionally, exposure of cell wall polysaccharides is also impacted by loss of alaA, and loss of AlaA catalytic activity confers increased biofilm susceptibility to echinocandin treatment, which is correlated with enhanced fungicidal activity. The increase in echinocandin susceptibility is specific to biofilms, and chemical inhibition of alaA by the alanine aminotransferase inhibitor β-chloro-l-alanine is sufficient to sensitize A. fumigatus biofilms to echinocandin treatment. Finally, loss of alaA increases susceptibility of A. fumigatus to in vivo echinocandin treatment in a murine model of invasive pulmonary aspergillosis. Our results provide insight into the interplay of metabolism, biofilm formation, and antifungal drug resistance in A. fumigatus and describe a mechanism of increasing susceptibility of A. fumigatus biofilms to the echinocandin class of antifungal drugs. IMPORTANCE Aspergillus fumigatus is a ubiquitous filamentous fungus that causes an array of diseases depending on the immune status of an individual, collectively termed aspergillosis. Antifungal therapy for invasive pulmonary aspergillosis (IPA) or chronic pulmonary aspergillosis (CPA) is limited and too often ineffective. This is in part due to A. fumigatus biofilm formation within the infection environment and the resulting emergent properties, particularly increased antifungal resistance. Thus, insights into biofilm formation and mechanisms driving increased antifungal drug resistance are critical for improving existing therapeutic strategies and development of novel antifungals. In this work, we describe an unexpected observation where alanine metabolism, via the alanine aminotransferase AlaA, is required for several aspects of A. fumigatus biofilm physiology, including resistance of A. fumigatus biofilms to the echinocandin class of antifungal drugs. Importantly, we observed that chemical inhibition of alanine aminotransferases is sufficient to increase echinocandin susceptibility and that loss of alaA increases susceptibility to echinocandin treatment in a murine model of IPA. AlaA is the first gene discovered in A. fumigatus that confers resistance to an antifungal drug specifically in a biofilm context.

Genetic analysis of Hsp90 function in Cryptococcus neoformans highlights key roles in stress tolerance and virulence

The opportunistic human fungal pathogen Cryptococcus neoformans has tremendous impact on global health, causing 181,000 deaths annually. Current treatment options are limited, and the frequent development of drug resistance exacerbates the challenge of managing invasive cryptococcal infections. In diverse fungal pathogens, the essential molecular chaperone Hsp90 governs fungal survival, drug resistance, and virulence. Therefore, targeting this chaperone has emerged as a promising approach to combat fungal infections. However, the role of Hsp90 in supporting C. neoformans pathogenesis remains largely elusive due to a lack of genetic characterization. To help dissect the functions of Hsp90 in C. neoformans, we generated a conditional expression strain in which HSP90 is under control of the copper-repressible promoter CTR4-2. Addition of copper to culture medium depleted Hsp90 transcript and protein levels in this strain, resulting in compromised fungal growth at host temperature; increased sensitivity to stressors, including the azole class of antifungals; altered C. neoformans morphology; and impaired melanin production. Finally, leveraging the fact that copper concentrations vary widely in different mouse tissues, we demonstrated attenuated virulence for the CTR4-2p-HSP90 mutant specifically in an inhalation model of Cryptococcus infection. During invasion and establishment of infection in this mouse model, the pathogen is exposed to the relatively high copper concentrations found in the lung as compared to blood. Overall, this work generates a tractable genetic system to study the role of Hsp90 in supporting the pathogenicity of C. neoformans and provides proof-of-principle that targeting Hsp90 holds great promise as a strategy to control cryptococcal infection.

Enantioselective Synthesis of (+)-Hippolide J and Reevaluation of Antifungal Activity

A synthesis of the reported antifungal agent (+)-hippolide J is presented. The rapid assembly of the natural product was enabled through implementation of an enantioselective isomerization/[2 + 2]-cycloaddition sequence. Due to the simplicity of the route, >100 mg of the natural product were prepared in a single pass. Anitfungal assays of hippolide J, however, confirmed that it showed no activity against several fungal strains, contrary to the isolation report.

Antifungal drug screening: thinking outside the box to identify novel antifungal scaffolds

Invasive fungal infections are responsible for a significant disease burden worldwide. Drugs to treat these infections are limited to only four unique classes, and despite these available treatments, mortality rates remain unacceptably high. In this review, we will discuss antifungal drug screening and how the approach to identifying novel compounds needs move away from traditional growth-based assays in order to meet the demand for new drugs. We highlight specific examples of creative screening strategies that increase the likelihood of identifying compounds with desired activities and provide perspective to inspire development of novel screens for the identification of first-in-class antifungals.

Benzothiourea Derivatives Target the Secretory Pathway of the Human Fungal Pathogen Cryptococcus neoformans

Cryptococcus neoformans is one of the most important human fungal pathogens and causes life-threatening meningoencephalitis in immunocompromised patients. The current gold standard therapy for C. neoformans meningoencephalitis is based on medications that are over 50 years old and is not readily available in regions with high disease burden. Here, we report the mycologic, mechanistic, and pharmacologic characterization of a set of benzothioureas with highly selective fungicidal activity against C. neoformans. In addition, to direct antifungal activity, benzothioureas inhibit C. neoformans virulence traits. On the basis of a set of phenotypic, biochemical, and biophysical assays, the benzothioureas (BTUs) inhibit the late secretory pathway (post-Golgi), possibly through a direct interaction with Sav1, an orthologue of the Sec4-class small GTPase. Importantly, pharmacological characterization of the BTUs indicates it readily penetrates the blood-brain barrier. Together, our data support the further development of this scaffold as an antifungal agent with a novel mechanism of action against C. neoformans.

Characterizing the Pathogenic, Genomic, and Chemical Traits of Aspergillus fischeri, a Close Relative of the Major Human Fungal Pathogen Aspergillus fumigatus

Aspergillus fischeri is closely related to Aspergillus fumigatus, the major cause of invasive mold infections. Even though A. fischeri is commonly found in diverse environments, including hospitals, it rarely causes invasive disease. Why A. fischeri causes less human disease than A. fumigatus is unclear. A comparison of A. fischeri and A. fumigatus for pathogenic, genomic, and secondary metabolic traits revealed multiple differences in pathogenesis-related phenotypes. We observed that A. fischeri NRRL 181 is less virulent than A. fumigatus strain CEA10 in multiple animal models of disease, grows slower in low-oxygen environments, and is more sensitive to oxidative stress. Strikingly, the observed differences for some traits are of the same order of magnitude as those previously reported between A. fumigatus strains. In contrast, similar to what has previously been reported, the two species exhibit high genomic similarity; ∼90% of the A. fumigatus proteome is conserved in A. fischeri, including 48/49 genes known to be involved in A. fumigatus virulence. However, only 10/33 A. fumigatus biosynthetic gene clusters (BGCs) likely involved in secondary metabolite production are conserved in A. fischeri and only 13/48 A. fischeri BGCs are conserved in A. fumigatus Detailed chemical characterization of A. fischeri cultures grown on multiple substrates identified multiple secondary metabolites, including two new compounds and one never before isolated as a natural product. Additionally, an A. fischeri deletion mutant of laeA, a master regulator of secondary metabolism, produced fewer secondary metabolites and in lower quantities, suggesting that regulation of secondary metabolism is at least partially conserved. These results suggest that the nonpathogenic A. fischeri possesses many of the genes important for A. fumigatus pathogenicity but is divergent with respect to its ability to thrive under host-relevant conditions and its secondary metabolism.IMPORTANCEAspergillus fumigatus is the primary cause of aspergillosis, a devastating ensemble of diseases associated with severe morbidity and mortality worldwide. A. fischeri is a close relative of A. fumigatus but is not generally observed to cause human disease. To gain insights into the underlying causes of this remarkable difference in pathogenicity, we compared two representative strains (one from each species) for a range of pathogenesis-relevant biological and chemical characteristics. We found that disease progression in multiple A. fischeri mouse models was slower and caused less mortality than A. fumigatus Remarkably, the observed differences between A. fischeri and A. fumigatus strains examined here closely resembled those previously described for two commonly studied A. fumigatus strains, AF293 and CEA10. A. fischeri and A. fumigatus exhibited different growth profiles when placed in a range of stress-inducing conditions encountered during infection, such as low levels of oxygen and the presence of chemicals that induce the production of reactive oxygen species. We also found that the vast majority of A. fumigatus genes known to be involved in virulence are conserved in A. fischeri, whereas the two species differ significantly in their secondary metabolic pathways. These similarities and differences that we report here are the first step toward understanding the evolutionary origin of a major fungal pathogen.

Response to Comment on "Sterilizing immunity in the lung relies on targeting fungal apoptosis-like programmed cell death"

Aouacheria et al question the interpretation of contemporary assays to monitor programmed cell death with apoptosis-like features (A-PCD) in Aspergillus fumigatus Although our study focuses on fungal A-PCD for host immune surveillance and infectious outcomes, the experimental approach incorporates multiple independent A-PCD markers and genetic manipulations based on fungal rather than mammalian orthologs to circumvent the limitations associated with any single approach.

Sterilizing immunity in the lung relies on targeting fungal apoptosis-like programmed cell death

Humans inhale mold conidia daily and typically experience lifelong asymptomatic clearance. Conidial germination into tissue-invasive hyphae can occur in individuals with defects in myeloid function, although the mechanism of myeloid cell-mediated immune surveillance remains unclear. By monitoring fungal physiology in vivo, we demonstrate that lung neutrophils trigger programmed cell death with apoptosis-like features in Aspergillus fumigatus conidia, the most prevalent human mold pathogen. An antiapoptotic protein, AfBIR1, opposes this process by inhibiting fungal caspase activation and DNA fragmentation in the murine lung. Genetic and pharmacologic studies indicate that AfBIR1 expression and activity underlie conidial susceptibility to NADPH (reduced form of nicotinamide adenine dinucleotide phosphate) oxidase-dependent killing and, in turn, host susceptibility to invasive aspergillosis. Immune surveillance exploits a fungal apoptosis-like programmed cell death pathway to maintain sterilizing immunity in the lung.

Interleukin 1α Is Critical for Resistance against Highly Virulent Aspergillus fumigatus Isolates

Heterogeneity among Aspergillus fumigatus isolates results in unique virulence potential and inflammatory responses. How these isolates drive specific immune responses and how this affects fungally induced lung damage and disease outcome are unresolved. We demonstrate that the highly virulent CEA10 strain is able to rapidly germinate within the immunocompetent lung environment, inducing greater lung damage, vascular leakage, and interleukin 1α (IL-1α) release than the low-virulence Af293 strain, which germinates with a lower frequency in this environment. Importantly, the clearance of CEA10 was consequently dependent on IL-1α, in contrast to Af293. The release of IL-1α occurred by a caspase 1/11- and P2XR7-independent mechanism but was dependent on calpain activity. Our finding that early fungal conidium germination drives greater lung damage and IL-1α-dependent inflammation is supported by three independent experimental lines. First, pregermination of Af293 prior to in vivo challenge drives greater lung damage and an IL-1α-dependent neutrophil response. Second, the more virulent EVOL20 strain, derived from Af293, is able to germinate in the airways, leading to enhanced lung damage and IL-1α-dependent inflammation and fungal clearance. Third, primary environmental A. fumigatus isolates that rapidly germinate under airway conditions follow the same trend toward IL-1α dependency. Our data support the hypothesis that A. fumigatus phenotypic variation significantly contributes to disease outcomes.

Sniffing out the hypoxia volatile metabolic signature of Aspergillus fumigatus

Invasive aspergillosis (IA) is a life-threatening infectious disease caused by fungi from the genus Aspergillus, with an associated mortality as high as 90% in certain populations. IA-associated pulmonary lesions are characteristically depleted in oxygen relative to normal lung tissue, and it has been shown that the most common causal agent of IA, Aspergillus fumigatus, must respond to low-oxygen environments for pathogenesis and disease progression. Previous studies have demonstrated marked alterations to the Aspergillus fumigatus transcriptome in response to low-oxygen environments that induce a 'hypoxia response'. Consequently, we hypothesized that these transcriptomic changes would alter the volatile metabolome and generate a volatile hypoxia signature. In the present study, we analyzed the volatile molecules produced by A. fumigatus in both oxygen replete (normoxia) and depleted (hypoxia) environments via headspace solid-phase micro-extraction coupled to two-dimensional gas chromatography-time-of-flight mass spectrometry. Using the machine learning algorithm random forest, we identified 19 volatile molecules that were discriminatory between the four growth conditions assessed in this study (i.e., early hypoxia (1 h), late hypoxia (8 h), early normoxia (1 h), and late normoxia (8 h)), as well as a set of 19 that were discriminatory between late hypoxia cultures and all other growth conditions in aggregate. Nine molecules were common to both comparisons, while the remaining 20 were specific to only one of two. We assigned putative identifications to 13 molecules, of which six were most highly abundant in late hypoxia cultures. Previously acquired transcriptomic data identified putative biochemical pathways induced in hypoxia conditions that plausibly account for the production of a subset of these molecules, including 2,3-butanedione and 3-hydroxy-2-butanone. These two molecules may represent a novel hypoxia fitness pathway in A. fumigatus, and could be useful in the detection of hypoxia-associated A. fumigatus lesions that develop in established IA infections.

Filamentous fungal carbon catabolite repression supports metabolic plasticity and stress responses essential for disease progression

Aspergillus fumigatus is responsible for a disproportionate number of invasive mycosis cases relative to other common filamentous fungi. While many fungal factors critical for infection establishment are known, genes essential for disease persistence and progression are ill defined. We propose that fungal factors that promote navigation of the rapidly changing nutrient and structural landscape characteristic of disease progression represent untapped clinically relevant therapeutic targets. To this end, we find that A. fumigatus requires a carbon catabolite repression (CCR) mediated genetic network to support in vivo fungal fitness and disease progression. While CCR as mediated by the transcriptional repressor CreA is not required for pulmonary infection establishment, loss of CCR inhibits fungal metabolic plasticity and the ability to thrive in the dynamic infection microenvironment. Our results suggest a model whereby CCR in an environmental filamentous fungus is dispensable for initiation of pulmonary infection but essential for infection maintenance and disease progression. Conceptually, we argue these data provide a foundation for additional studies on fungal factors required to support fungal fitness and disease progression and term such genes and factors, DPFs (disease progression factors).

Aspergillus fumigatus strain-specific host response is regulated by glucose sensing

Our knowledge of how Aspergillus fumigatus growth is controlled within the respiratory tract is developing, but still enigmatic. Recruitment of neutrophils and inflammatory monocytes is critical to control fungal germination. We have recently found that the CEA10 and Af293 strains of A. fumigatus induce unique inflammatory leukocyte responses. Here, we aim to understand why these A. fumigatus strains induce different immune responses and how this affects fungal-induced immunopathology and disease outcome. We used an immunocompetent murine model of invasive pulmonary aspergillosis to evaluate the immune response induced by CEA10 and Af293. We observed that CEA10 undergoes significantly greater germination than Af293, which was regulated by its ability to sense glucose through CreA-mediated signaling. Moreover, the CEA10 strain induced greater lung damage, vascular leakage, and inflammation. These findings suggest the inflammatory response to A. fumigatus might be regulated in a stepwise manner in response to the threat posed by the specific A. fumigatus strain. Specifically, the Af293 strain, which swells but fails to germinate, activates the inflammasome leading to IL-1beta-dependent neutrophil recruitment. In contrast, the CEA10 strain is able to germinate efficiently within the lung, leading to necrotic host cell death, IL-1alpha release, and subsequent IL-1alpha dependent neutrophil recruitment. Clinically, our data support the idea that A. fumigatus strain phenotypic variation may significantly contribute to disease outcomes. Understanding why different A. fumigatus strains induce distinct immune pathology can reveal novel immunotherapeutic targets for the treatment of invasive aspergillosis.

The Janus transcription factor HapX controls fungal adaptation to both iron starvation and iron excess

Balance of physiological levels of iron is essential for every organism. In Aspergillus fumigatus and other fungal pathogens, the transcription factor HapX mediates adaptation to iron limitation and consequently virulence by repressing iron consumption and activating iron uptake. Here, we demonstrate that HapX is also essential for iron resistance via activating vacuolar iron storage. We identified HapX protein domains that are essential for HapX functions during either iron starvation or high-iron conditions. The evolutionary conservation of these domains indicates their wide-spread role in iron sensing. We further demonstrate that a HapX homodimer and the CCAAT-binding complex (CBC) cooperatively bind an evolutionary conserved DNA motif in a target promoter. The latter reveals the mode of discrimination between general CBC and specific HapX/CBC target genes. Collectively, our study uncovers a novel regulatory mechanism mediating both iron resistance and adaptation to iron starvation by the same transcription factor complex with activating and repressing functions depending on ambient iron availability.

Potent in vivo inhibitors of rat renin: analogues of human and rat angiotensinogen sequences containing different classes of pseudodipeptides at the scissile site

Using solid-phase methodology we have synthesised peptides based on the 8-14 or 6-14 human and rat angiotensinogen sequences, containing the following different isosteric units at the P1-P1' cleavage site: Leu-psi[CH2NH]Leu; Leu-psi[CH(OH)CH2]Val; Leu-psi[CH(OH)CH2]Leu and Leu-psi[CH(NH2)CH2]Val. In vitro, peptide Piv-His-Pro-Phe-His-Leu-psi[CH(OH)CH2]Leu-Tyr-Tyr-Ser-NH2(XXI) is the most potent inhibitor of rat plasma renin reported having an IC50 of 0.21 nM; it is a much weaker inhibitor of human renin (IC50 45 nM). Peptide Boc-His-Pro-Phe-His-Leu-psi[CH(OH)CH2] Leu-Val-Ile-His-NH2 (XX) was a highly effective inhibitor of rat renin in vivo. When infused (1 mg/kg/h) into two-kidney, one-clip chronic renal hypertensive rats, it lowered blood pressure and suppressed both plasma renin and angiotensin II. When given as a bolus (1 mg/kg) there was a divergence between the rapid rebound of renin levels and blood pressure, which remained suppressed. These results indicate that potent in vivo inhibitors of rat renin could be useful not only in examining the role of circulating renin but also in elucidating the equally important involvement of extracirculatory renin pools.

New renin inhibitors containing novel analogues of statine

Solid-phase methodology has been used to synthesize a series of peptides based on the N-terminal sequence of human angiotensinogen in which statine (Sta) or the novel analogues (3S,4S)-3,4-diamino- or (3R,4S)-3,4-diamino-6-methylheptanoic acid (Ads or R-Ads) and (3S,4S)-4-amino-3-aminomethyl- or (3R,4S)-4-amino-3-aminomethyl-6-methylheptanoic acid (Amd or R-Amd) replace either residue 10 or both residues 10-11 at the P1-P1' cleavage site. The synthesis of these novel analogues of statine together with biological results on the inhibition of human and rat renin by peptides derived from them is reported. The absolute stereochemistry of the (3S,4S) Ads was determined by an X-ray crystallographic analysis of its N gamma-Boc, B beta-Z, R(+)-1-methyl benzamide derivative. Peptide Boc-His-Pro-Phe-His-Sta-Val-Ile-His-NH2 (VI) is the best inhibitor of human renin containing Sta at position 10. However, peptides containing Ads and Amd gave better rat renin inhibitors than the corresponding Sta-containing peptides. Peptides Boc-His-Pro-Phe-His-Ads-Val-Ile-His-NH2 (VII) having Ads at position 10 had an IC50 of 12 nM against rat renin. Although Sta has come to be accepted as an isosteric replacement for a dipeptide unit rather than for a single amino acid residue, in our series of inhibitors Sta is more effective when replacing only the amino acid at position 10 in the natural angiotensinogen sequence. None of the peptides gave any effect in vivo in a hypertensive rat model.