Drosophila melanogaster as a model host to dissect the immunopathogenesis of zygomycosis

Disseminated Cunninghamella bertholletiae Infection From Latent Lower Limb Mass After Kidney Transplant: A Case Report

BACKGROUND

Cunninghamella bertholletiae (C. bertholletiae), a rare yet highly virulent species within the Mucorales order, predominantly affects individuals with compromised immune systems. Disseminated infections caused by this pathogen frequently lead to severe complications, underscoring the necessity for prompt diagnosis and aggressive therapeutic interventions. Invasive fungal diseases (IFDs) continue to be a major cause of morbidity and mortality among kidney transplant recipients, characterized by elevated incidence and mortality rates. The early and precise identification of fungal pathogens is crucial for optimizing patient outcomes.

CASE PRESENTATION

This report presents a case study of a 37-year-old male kidney transplant recipient who developed a disseminated C. bertholletiae infection from a latent lower limb lesion. Initially, he showed symptoms of high fever and dyspnea, leading to diagnoses of sepsis, severe pneumonia, acute respiratory distress syndrome, and allograft dysfunction. After surgery, he had recurrent pleural effusion and worsening pulmonary nodules. Metagenomic next-generation sequencing (mNGS) confirmed C. bertholletiae infection, and histopathology revealed mucormycosis with vascular invasion, thrombosis, and tissue necrosis. The patient underwent a 13-month antifungal treatment with amphotericin B lipid complex, posaconazole, and isavuconazole.

CONCLUSION

This case highlights the essential role of histopathology and mNGS in early detection of rare IFDs and stresses the need for a multidisciplinary approach combining surgery with antifungal therapy. The effective management of disseminated C. bertholletiae infection using a triple antifungal regimen offers important insights for future cases, underscoring the importance of early diagnosis and personalized treatment in immunocompromised patients.

Would global warming bring an increase of invertebrate-associated cutaneous invasive fungal infections?

Invasive mold-associated cutaneous disease is a rare but potentially catastrophic consequence of trauma. However, invertebrate bites are not well recognized as a mechanism for the inoculation of fungi into subcutaneous tissue that can also result in severe infections. Invertebrates often carry fungi with human pathogenic potential as part of their microbiome, and bites break the skin, providing a conduit for them to penetrate subcutaneous tissues where the establishment of infection can produce serious skin and soft tissue fungal diseases. In this essay, we review the existing data for invertebrate bite-associated cutaneous invasive fungal infections (IBA-cIFIs) and consider the potential consequences of global warming on their epidemiology. Climate changes will be associated with changes in the range of invertebrates and adaptation of their associated microbes to warmer temperatures. Fungal adaptation to higher temperatures can defeat the mammalian protective barrier and be associated with both more and different IBA-cIFIs.

Albumin orchestrates a natural host defense mechanism against mucormycosis

Mucormycosis is an emerging, life-threatening human infection caused by fungi of the order Mucorales. Metabolic disorders uniquely predispose an ever-expanding group of patients to mucormycosis via poorly understood mechanisms. Therefore, it is highly likely that uncharacterized host metabolic effectors confer protective immunity against mucormycosis. Here, we uncover a master regulatory role of albumin in host defense against Mucorales through the modulation of the fungal pathogenicity program. Our initial studies identified severe hypoalbuminemia as a prominent metabolic abnormality and a biomarker of poor outcome in independent cohorts of mucormycosis patients. Strikingly, we found that purified albumin selectively inhibits Mucorales growth among a range of human pathogens, and albumin-deficient mice display susceptibility specifically to mucormycosis. The antifungal activity of albumin is mediated by the release of bound free fatty acids (FFAs). Importantly, albumin prevents FFA oxidation, which results in loss of their antifungal properties. A high degree of FFA oxidation is found in the sera of patients with mucormycosis. Physiologically, albumin-bound FFAs blocks the expression of the mycotoxin mucoricin and renders Mucorales avirulent in vivo. Overall, we discovered a novel host defense mechanism that directs the pathogen to suppress its growth and the expression of virulence factors in response to unfavorable metabolic cues regulated by albumin. These findings have major implications for the pathogenesis and management of mucormycosis.

Functional characterization of two survival factor 1 genes in Mucor lusitanicus

Survival factor 1 (Svf1) protein has been described in some ascomycetous fungi where it was found to be contributing to several essential physiological processes, such as response to osmotic, oxidative and cold stresses, sphingolipid biosynthesis, morphogenesis, sporulation, antifungal resistance, and pathogenicity. It was also suggested that it can be a novel central regulator affecting the expression of various genes. In the present study, function of this protein and the encoding genes is described for the first time in a fungus (i.e., in Mucor lusitanicus) belonging to the order Mucorales. M. lusitanicus has two putative svf1 genes named svf1a and svf1b. Expression of both genes was proven. Although the expression of svf1a was affected by several environmental stresses and knocking out the gene affected adaptation to low temperatures and the sporulation ability, the main survival factor functions, such as participation in the maintenance of the viability, the response to oxidative and cold stresses, and the sphingolipid biosynthesis, could be associated with Svf1b, suggesting a central regulatory role to this protein. Interestingly, knockout of both genes affected the pathogenicity of the fungus in a Drosophila model.

IMPORTANCE

Mucor lusitanicus is a widely used model organism to study various biological processes in the basal fungal group Mucorales. Several members of this group can be agents of mucormycosis, an opportunistic fungal infection, which is associated with high mortality, rapid progression, and wide resistance to the commonly used antifungal agents. Svf1 proteins have so far only been identified in fungi, where they have been involved in pathogenicity and resistance to antifungal agents in many cases. Only a limited number of factors affecting the stress response, antifungal resistance, and virulence of Mucorales fungi have been revealed. Elucidating the function of a fungus-specific protein that may regulate these processes may bring us closer to understanding the pathogenesis of these fungi.

Pharmacology of Aging: Drosophila as a Tool to Validate Drug Targets for Healthy Lifespan

Finding effective therapies to manage age-related conditions is an emerging public health challenge. Although disease-targeted treatments are important, a preventive approach focused on aging can be more efficient. Pharmacological targeting of aging-related processes can extend lifespan and improve health in animal models. However, drug development and translation are particularly challenging in geroscience. Preclinical studies have survival as a major endpoint for drug screening, which requires years of research in mammalian models. Shorter-lived invertebrates can be exploited to accelerate this process. In particular, the fruit fly Drosophila melanogaster allows the validation of new drug targets using precise genetic tools and proof-of-concept experiments on drugs impacting conserved aging processes. Screening for clinically approved drugs that act on aging-related targets may further accelerate translation and create new tools for aging research. To date, 31 drugs used in clinical practice have been shown to extend the lifespan of flies. Here, we describe recent advances in the pharmacology of aging, focusing on Drosophila as a tool to repurpose these drugs and study age-related processes.

Co-Existing Fungi: An Unforeseen Combo Creating a Dilemma in Diagnostic Morale

Mucormycosis is a rare fungal infection belonging to Mucorales order fungi. Rhino-cerebral form is more noted in patients with diabetes mellitus, but pulmonary mucormycosis is a rare manifestation with hematological malignancy, malignant tumors, and transplant recipient patients. Aspergillus species are also known to cause allergic bronchopulmonary aspergillosis, aspergilloma, chronic pulmonary aspergillosis, and invasive aspergillosis in immunocompromised individuals. We report a case of pulmonary mucormycosis superimposed with aspergillus infection presenting in an immunocompromised patient with metastatic prostate cancer on chemotherapy, initially misdiagnosed as aspergillus infection.

The Impact of Dimitrios P. Kontoyiannis on Mucormycosis Research

Dimitrios P [...].

Molecular mechanisms that govern infection and antifungal resistance in Mucorales

SUMMARYThe World Health Organization has established a fungal priority pathogens list that includes species critical or highly important to human health. Among them is the order Mucorales, a fungal group comprising at least 39 species responsible for the life-threatening infection known as mucormycosis. Despite the continuous rise in cases and the poor prognosis due to innate resistance to most antifungal drugs used in the clinic, Mucorales has received limited attention, partly because of the difficulties in performing genetic manipulations. The COVID-19 pandemic has further escalated cases, with some patients experiencing the COVID-19-associated mucormycosis, highlighting the urgent need to increase knowledge about these fungi. This review addresses significant challenges in treating the disease, including delayed and poor diagnosis, the lack of accurate global incidence estimation, and the limited treatment options. Furthermore, it focuses on the most recent discoveries regarding the mechanisms and genes involved in the development of the disease, antifungal resistance, and the host defense response. Substantial advancements have been made in identifying key fungal genes responsible for invasion and tissue damage, host receptors exploited by the fungus to invade tissues, and mechanisms of antifungal resistance. This knowledge is expected to pave the way for the development of new antifungals to combat mucormycosis. In addition, we anticipate significant progress in characterizing Mucorales biology, particularly the mechanisms involved in pathogenesis and antifungal resistance, with the possibilities offered by CRISPR-Cas9 technology for genetic manipulation of the previously intractable Mucorales species.

Experimental Models to Study the Pathogenesis and Treatment of Mucormycosis

Mucormycosis presents a formidable challenge to clinicians and researchers. Animal models are an essential part of the effort to decipher the pathogenesis of mucormycosis and to develop novel pharmacotherapeutics against it. Diverse model systems have been established, using a range of animal hosts, immune and metabolic perturbations, and infection routes. An understanding of the characteristics, strengths, and drawbacks of these models is needed to optimize their use for specific research aims.

Iron chelation and supplementation: A comparison in the management of inflammatory bowel disease using drosophila

AIMS

Inflammatory Bowel Disease (IBD) is associated with systemic iron deficiency and has been managed with iron supplements which cause adverse side effects. Conversely, some reports highlight iron depletion to ameliorate IBD. The underlying intestinal response and comparative benefit of iron depletion and supplementation in IBD is unknown. The aims of this work were to characterize and compare the effects of iron supplementation and iron depletion in IBD.

MAIN METHODS

IBD was induced in Drosophila melanogaster using 3 % dextran sodium sulfate (DSS) in diet for 7 days. Using this model, we investigated the impacts of acute iron depletion (using bathophenanthroline disulfonate, BPS) and supplementation (using ferrous sulphate, FS), before and after IBD induction, on gut iron homeostasis, cell death, gut permeability, inflammation, antioxidant defence, antimicrobial response and several fly phenotypes.

KEY FINDINGS

DSS decreased fly mass (p < 0.001), increased gut permeability (p < 0.001) and shortened lifespan (p = 0.035) compared to control. The DSS-fed flies also showed significantly elevated lipid peroxidation (p < 0.001), and the upregulated expression of apoptotic marker- drice (p < 0.001), tight junction protein - bbg (p < 0.001), antimicrobial peptide - dpta (p = 0.002) and proinflammatory cytokine - upd2 (p < 0.001). BPS significantly (p < 0.05) increased fly mass and lifespan, decreased gut permeability, decreased lipid peroxidation and decreased levels of drice, bbg, dpta and upd2 in IBD flies. This iron chelation (using BPS) showed better protection from DSS-induced IBD than iron supplementation (using FS). Preventive and curative interventions, by BPS or FS, also differed in outcomes.

SIGNIFICANCE

This may inform precise management strategies aimed at tackling IBD and its recurrence.

Repression of Staphylococcus aureus and Escherichia coli by Lactiplantibacillus plantarum Strain AG10 in Drosophila melanogaster In Vivo Model

Probiotic bacteria exhibiting antagonistic activities against pathogenic bacteria are widely considered as potential options for the prevention and treatment of various infectious diseases and represent potential substitutes of antibiotics. Here we show that the L. plantarum AG10 strain represses the growth of Staphylococcus aureus and Escherichia coli in vitro and diminishes their negative effects in vivo in a Drosophila melanogaster model of survival on embryonic (larvae) and pupa stages. In an agar drop diffusion test, L. plantarum AG10 exhibited antagonistic properties against Escherichia coli, Staphylococcus aureus, Serratia marcescens and Pseudomonas aeruginosa, and repressed the growth of E. coli and S. aureus during milk fermentation. In a Drosophila melanogaster model, L. plantarum AG10 alone did not provide any significant effect, either during the embryonic stage or during further development of the flies. Despite this, it was able to restore the viability of groups infected with either E. coli and S. aureus, almost to the level of non-treated control at all stages of development (larvae, pupa and adult). Moreover, in the presence of L. plantarum AG10, pathogens-induced mutation rates and recombination events reduced 1.5-2-fold. The genome of L. plantarum AG10 was sequenced and deposited at NCBI under the accession number PRJNA953814 and consists of annotated genome and raw sequence data. It consists of 109 contigs and is 3,479,919 bp in length with a GC content of 44.5%. The analysis of the genome has revealed considerably few putative virulence factors and three genes responsible for the biosynthesis of putative antimicrobial peptides, with one of them exhibiting a high probability of antimicrobial properties. Taken together, these data allow the suggestion that the L. plantarum AG10 strain is promising for use in both dairy production and probiotics as a preservative from foodborne infections.

What Is New in Pulmonary Mucormycosis?

Mucormycosis is a rare but life-threatening fungal infection due to molds of the order Mucorales. The incidence has been increasing over recent decades. Worldwide, pulmonary mucormycosis (PM) presents in the lungs, which are the third main location for the infection after the rhino-orbito-cerebral (ROC) areas and the skin. The main risk factors for PM include hematological malignancies and solid organ transplantation, whereas ROC infections are classically favored by diabetes mellitus. The differences between the ROC and pulmonary locations are possibly explained by the activation of different mammalian receptors—GRP78 in nasal epithelial cells and integrin β1 in alveolar epithelial cells—in response to Mucorales. Alveolar macrophages and neutrophils play a key role in the host defense against Mucorales. The diagnosis of PM relies on CT scans, cultures, PCR tests, and histology. The reversed halo sign is an early, but very suggestive, sign of PM in neutropenic patients. Recently, the serum PCR test showed a very encouraging performance for the diagnosis and follow-up of mucormycosis. Liposomal amphotericin B is the drug of choice for first-line therapy, together with correction of underlying disease and surgery when feasible. After a stable or partial response, the step-down treatment includes oral isavuconazole or posaconazole delayed release tablets until a complete response is achieved. Secondary prophylaxis should be discussed when there is any risk of relapse, such as the persistence of neutropenia or the prolonged use of high-dose immunosuppressive therapy. Despite these novelties, the mortality rate from PM remains higher than 50%. Therefore, future research must define the place for combination therapy and adjunctive treatments, while the development of new treatments is necessary.

Focusing COVID-19-associated mucormycosis: a major threat to immunocompromised COVID-19

COVID-19 disease has been identified to cause remarkable increase of mucormycosis infection cases in India, with the majority of cases being observed in individuals recovering from COVID-19. Mucormycosis has emanated as an outcome of the recent COVID-19 pandemic outbreak as rapidly developing fatal illness which was acquired by Mucorales fungus which is a subcategory of molds known as mucormycetes. Mucormycosis is one of the serious, sporadic mycotic illnesses which is a great threat to immunocompromised COVID-19 patients and affects people of all ages, including children with COVID-19 infections. This is associated with tissue damaging property and, therefore, causes serious clinical complications and elevated death rate. The COVID-19-associated mucormycosis or "black fungus" are the terms used interchangeably. The rapid growth of tissue necrosis presenting as "rhino-orbital-cerebral, pulmonary, cutaneous, gastrointestinal, and disseminated disease" are various clinical forms of mucormycosis. The patient's prognosis and survival can be improved with proper surgeries using an endoscopic approach for local tissue protection in conjunction with course of appropriate conventional antifungal drug like Amphotericin-B and novel drugs like Rezafungin, encochleated Amphotericin B, Orolofim, and SCY-078 which have been explored in last few years. This review provides an overview of mucormycosis including its epidemiology, pathophysiology, risk factors, its clinical forms, and therapeutic approaches for disease management like antifungal therapy, surgical debridement, and iron chelators. The published patents and ongoing clinical trials related to mucormycosis have also been mentioned in this review.

COVID-19-associated Mucormycosis: A clinico-epidemiological study

BACKGROUND

There was an unprecedented increase in COVID-19-associated-Mucormycosis (CAM) cases during the second pandemic wave in India.

METHODS

This observational study was done to know the epidemiological profile of CAM cases andincluded all patients admitted with mucormycosis between May 2021 and July 2021.

RESULTS

Out of the enrolled 208 CAM cases (either SARS-CoV-2 RT-PCR or serology positive), 204, three and one had rhino-orbital-cerebral, pulmonary and gastrointestinal mucormycosis, respectively. 95.7 % of the patients had diabetes, out of which 42.3 % were recently diagnosed. Mean HbA1c was 10.16 ± 2.56 %. 82.5 % of the patients were unvaccinated. During their COVID-19 illness, 86.5 % were prescribed antibiotics, 84.6 % zinc preparations, 76.4 % ivermectin, and 64.9 % steroids, while only 39.5 % required oxygen therapy. The frequency of blood groups A, B, O and AB in our CAM patients was 29.5 %, 18.9 %, 38.9 % &12.6 %, respectively. At three months follow up, 60 (28.8 %) patients died, four (1.9 %) stopped antifungal treatment, and 144(69.23 %) were on antifungal treatment. 55 % (n = 33) of deaths occurred within 15 days of admission. Mortality was significantly associated with higher age, RT-PCR positive for SARS-CoV-2, raised serum creatinine and alkaline phosphatase during treatment. At 6 months follow-up, eight more patients died, three due to chronic kidney disease, four patients who had stopped treatment and one patient who was on a ventilator due to COVID-19 associated pneumonia and the rest 140(67.3 %) survived.

CONCLUSION

Uncontrolled hyperglycemia, SARS-CoV-2 infection, rampant use of antibiotics, zinc supplementation and steroids were some of the risk factors for mucormycosis. Despite the overwhelming number of patients with an uncommon disease like mucormycosis, the six months mortality was much lower than expected.

Mucormycosis and COVID-19-Associated Mucormycosis: Insights of a Deadly but Neglected Mycosis

The ongoing COVID-19 pandemic has quickly become a health threat worldwide, with high mortality and morbidity among patients with comorbidities. This viral infection promotes the perfect setting in patients for the development of opportunistic infections, such as those caused by fungi. Mucormycosis, a rare but deadly fungal infection, has recently increased its incidence, especially in endemic areas, since the onset of the pandemic. COVID-19-associated mucormycosis is an important complication of the pandemic because it is a mycosis hard to diagnose and treat, causing concern among COVID-19-infected patients and even in the already recovered population. The risk factors for the development of mucormycosis in these patients are related to the damage caused by the SARS-CoV-2 itself, the patient's overstimulated immune response, and the therapy used to treat COVID-19, causing alterations such as hyperglycemia, acidosis, endothelial and lung damage, and immunosuppression. In this review, the molecular aspects of mucormycosis and the main risk factors for the development of COVID-19-associated mucormycosis are explained to understand this virus-fungi-host interaction and highlight the importance of this neglected mycosis.

A bacterial endosymbiont of the fungus Rhizopus microsporus drives phagocyte evasion and opportunistic virulence

Opportunistic infections by environmental fungi are a growing clinical problem, driven by an increasing population of people with immunocompromising conditions. Spores of the Mucorales order are ubiquitous in the environment but can also cause acute invasive infections in humans through germination and evasion of the mammalian host immune system. How they achieve this and the evolutionary drivers underlying the acquisition of virulence mechanisms are poorly understood. Here, we show that a clinical isolate of Rhizopus microsporus contains a Ralstonia pickettii bacterial endosymbiont required for virulence in both zebrafish and mice and that this endosymbiosis enables the secretion of factors that potently suppress growth of the soil amoeba Dictyostelium discoideum, as well as their ability to engulf and kill other microbes. As amoebas are natural environmental predators of both bacteria and fungi, we propose that this tri-kingdom interaction contributes to establishing endosymbiosis and the acquisition of anti-phagocyte activity. Importantly, we show that this activity also protects fungal spores from phagocytosis and clearance by human macrophages, and endosymbiont removal renders the fungal spores avirulent in vivo. Together, these findings describe a new role for a bacterial endosymbiont in Rhizopus microsporus pathogenesis in animals and suggest a mechanism of virulence acquisition through environmental interactions with amoebas.

The roles of metals in insect-microbe interactions and immunity

Metal ions play essential roles in diverse physiological processes in insects, including immunity and interactions with microbes. Some, like iron, are essential nutrients and therefore are the subject of a tug-of-war between insects and microbes. Recent findings showed that the hypoferremic response mediated by Transferrin 1 is an essential defense mechanism against pathogens in insects. Transferrin 1 and the overall iron metabolism were also implicated in mediating interactions between insects and beneficial microbes. Other metals, like copper and zinc, can interfere with insect immune effectors, and either enhance (antimicrobial peptides) or reduce (reactive oxygen species) their activity. By covering recent advances in the field, this review emphasizes the importance of metals as essential mediators of insect-microbe interactions.

Drosophila melanogaster as a Rapid and Reliable In Vivo Infection Model to Study the Emerging Yeast Pathogen Candida auris

While mammalian models remain the gold standard to study invasive mycoses, mini-host invertebrate models have provided complementary platforms for explorative investigations of fungal pathogenesis, host-pathogen interplay, and antifungal therapy. Specifically, our group has established Toll-deficient Drosophila melanogaster flies as a facile and cost-effective model organism to study candidiasis, and we have recently expanded these studies to the emerging and frequently multidrug-resistant yeast pathogen Candida auris. Our proof-of-concept data suggest that fruit flies could hold a great promise for large-scale applications in antifungal drug discovery and the screening of C. auris (mutant) libraries with disparate pathogenic capacity. This chapter discusses the advantages and limitations of D. melanogaster to study C. auris candidiasis and provides a step-by-step guide for establishing and troubleshooting C. auris infection and antifungal treatment of Toll-deficient flies along with essential downstream readouts.

Mucormycosis: A triple burden in patients with diabetes during COVID-19 Pandemic

With the upsurge in the cases of COVID-19 around the world, plenty of potential COVID-19 complications are becoming more prevalent, including a higher risk of secondary bacterial and fungal infections. Mucormycosis is one such condition which has high prevalence among individuals with diabetes who were infected with COVID-19.The usage of steroids in the treatment further inflates the risk of infection and exacerbation of disease in pre-existent mucormycosis patients. Generally, Corticosteroid-induced diabetes can arise on long-term steroid medication, increasing the likelihood of mucormycosis. In patients with COVID-19, the indications and dose of corticosteroids should be properly regulated, and persons with diabetes who take insulin or oral anti-diabetic medicines should be cautious. To avoid poor outcomes, strategies to improve glycemic management should be emphasized. This narrative review elucidates different disciplines on rampant use of steroids, iron and zinc supplements as well as the methods utilized as primary or adjunctive treatment of this fatal condition. This article may help to pave the way for robust research that needs to be done to tackle the deadly triple burden of the disease.

Epidemiology and Pathophysiology of COVID-19-Associated Mucormycosis: India Versus the Rest of the World

The coronavirus disease 2019 (COVID-19) pandemic has led to a concerning resurgence of mucormycosis. More than 47,000 cases of mucormycosis were reported in three months from India. We update our systematic review on COVID-19-associated mucormycosis (CAM) till June 21st, 2021, comparing cases reported from India and elsewhere. We included individual patient details of 275 cases of CAM, of which 233 were reported from India and 42 from the rest of the world. Diabetes mellitus was the most common underlying risk factor for CAM in India than in other countries. The fatality rate of cases reported from India (36.5%) was less than the globally reported cases (61.9%), probably due to the predominance of rhino-orbital mucormycosis. On a multivariate analysis, we found that pulmonary or disseminated mucormycosis cases and admission to the intensive care unit were associated with increased mortality, while combination medical therapy improved survival. The paucity of pulmonary and disseminated mucormycosis cases from India suggests that these cases were either not diagnosed or reported, further supported by a trend of search data from the Google search engine. In this review, we discuss the factors explaining the substantial rise in cases of CAM. We also propose a hypothetical model describing the epidemiologic triad of CAM.

Haemocyte-mediated immunity in insects: Cells, processes and associated components in the fight against pathogens and parasites

The host defence of insects includes a combination of cellular and humoral responses. The cellular arm of the insect innate immune system includes mechanisms that are directly mediated by haemocytes (e.g., phagocytosis, nodulation and encapsulation). In addition, melanization accompanying coagulation, clot formation and wound healing, nodulation and encapsulation processes leads to the formation of cytotoxic redox-cycling melanin precursors and reactive oxygen and nitrogen species. However, demarcation between cellular and humoral immune reactions as two distinct categories is not straightforward. This is because many humoral factors affect haemocyte functions and haemocytes themselves are an important source of many humoral molecules. There is also a considerable overlap between cellular and humoral immune functions that span from recognition of foreign intruders to clot formation. Here, we review these immune reactions starting with the cellular mechanisms that limit haemolymph loss and participate in wound healing and clot formation and advancing to cellular functions that are critical in restricting pathogen movement and replication. This information is important because it highlights that insect cellular immunity is controlled by a multilayered system, different components of which are activated by different pathogens or during the different stages of the infection.

Aspergillus fumigatus and aspergillosis: From basics to clinics

The airborne fungus Aspergillus fumigatus poses a serious health threat to humans by causing numerous invasive infections and a notable mortality in humans, especially in immunocompromised patients. Mould-active azoles are the frontline therapeutics employed to treat aspergillosis. The global emergence of azole-resistant A. fumigatus isolates in clinic and environment, however, notoriously limits the therapeutic options of mould-active antifungals and potentially can be attributed to a mortality rate reaching up to 100 %. Although specific mutations in CYP 51A are the main cause of azole resistance, there is a new wave of azole-resistant isolates with wild-type CYP 51A genotype challenging the efficacy of the current diagnostic tools. Therefore, applications of whole-genome sequencing are increasingly gaining popularity to overcome such challenges. Prominent echinocandin tolerance, as well as liver and kidney toxicity posed by amphotericin B, necessitate a continuous quest for novel antifungal drugs to combat emerging azole-resistant A. fumigatus isolates. Animal models and the tools used for genetic engineering require further refinement to facilitate a better understanding about the resistance mechanisms, virulence, and immune reactions orchestrated against A. fumigatus. This review paper comprehensively discusses the current clinical challenges caused by A. fumigatus and provides insights on how to address them.

Connecting the Dots: Interplay of Pathogenic Mechanisms between COVID-19 Disease and Mucormycosis

Coronavirus disease (COVID-19)-associated mucormycosis (CAM) is an emerging threat globally, especially in India. More than 40,000 CAM cases have been reported in India. The emergence of CAM cases in India has been attributed to environmental, host, and iatrogenic factors. Mucorales spore burden has been reported globally; however, their presence is higher in tropical countries such as India, contributing to the emergence of CAM. Before the COVID-19 pandemic, patients with diabetes mellitus, haematological malignancies, solid organ transplants, corticosteroid therapy and neutropenia were more prone to mucormycosis, whereas in COVID-19 patients, virus-induced endothelial dysfunction, hyperglycaemia, and immune dysfunction following corticosteroid use increase the risk of acquiring mucormycosis. The interaction of Mucorales spores with the epithelial cells, followed by endothelial invasion, is a crucial step in the pathogenesis of mucormycosis. Endothelial damage and increased endothelial receptor expression induced by COVID-19 infection may predispose patients to CAM. COVID-19 infection may directly induce hyperglycaemia by damaging beta cells of the pancreas or by corticosteroid therapy, which may contribute to CAM pathogenesis. Iron acquisition from the host, especially in diabetic ketoacidosis (DKA) or deferoxamine therapy, is an important virulence trait of Mucorales. Similarly, the hyperferritinaemia caused by COVID-19 may act as a source of iron for Mucorales growth and invasion. In addition, corticosteroid treatment reduces or abolishes the innate immune functions of phagocytic cells contributing to the pathogenesis of CAM. This review aims to discuss primarily the host and iatrogenic factors shared between COVID-19 and mucormycosis that could explain the emergence of CAM.

Lactoferrin, a potential iron-chelator as an adjunct treatment for mucormycosis - A comprehensive review

Mucormycosis is a deadly infection which is caused by fungi of the order Mucorales including species belonging to the genus Rhizopus, Mucor, Mycocladus, Rhizomucor, Cunninghamella, and Apophysomyces. Despite antifungal therapy and surgical procedures, the mortality rate of this disease is about 90-100% which is exceptionally high. The hypersensitivity of patients with raised available serum iron indicates that the Mucorales are able to use host iron as a critical factor of virulence. This is because iron happens to be a crucial element playing its role in the growth of cells and development. In this review, we have described Lactoferrin (Lf) as a potential iron-chelator. Lf is a naturally occurring glycoprotein which is expressed in most of the biological fluids. Moreover, Lf possesses exclusive anti-inflammatory effects along with several anti-fungal effects that could prove to be helpful to the pathological physiology of inexorable mucormycosis cases. This literature summarises the biological insights into the Lf being considered as a potential fungistatic agent and an immune regulator. The review also proposes that unique potential of Lf as an iron-chelator can be exploited as the adjunct treatment for mucormycosis infection.

In vitro pharmacokinetics/pharmacodynamics modeling and efficacy against systemic candidiasis in Drosophila melanogaster of a bisaryloxypropanamine derivative

The number of deaths due to systemic fungal infections is increasing alarmingly, which is aggravated by the limitations of traditional treatments and multidrug resistance. Therefore, the research and development of new therapeutic options against pathogenic fungi is an urgent need. To evaluate the fungicidal activity of a synthetic compound, 1,3-bis-(3,4-dichlorophenoxy)propan-2-aminium chloride (2j), through time-kill studies and pharmacokinetics/pharmacodynamics (PK/PD) modeling. The protective effect of the compound was also evaluated using the Drosophila melanogaster minihost model of candidiasis. Mathematical modeling of time-kill data of compound 2j was performed to obtain PD characteristics. Additionally, Toll-deficient D. melanogaster flies were infected with a Candida albicans strain and treated with 2j. We observed that compound 2j demonstrated a time- and dose-dependent fungicidal effect against Candida spp. and dermatophytes, even at low concentrations, and rapidly achieved kill rates reaching the maximum effect in less than one hour. The efficacy of the compound against systemic candidiasis in D. melanogaster flies was comparable to that achieved by fluconazole. These results support the potential of compound 2j as a systemic antifungal agent candidate and serve as a starting point for further studies involving mammalian animal models.

A guide to changing paradigms of glucocorticoid receptor function-a model system for genome regulation and physiology

The glucocorticoid receptor (GR) is a bona fide ligand-regulated transcription factor. Cloned in the 80s, the GR has become one of the best-studied and clinically most relevant members of the nuclear receptor superfamily. Cooperative activity of GR with other transcription factors and a plethora of coregulators contribute to the tissue- and context-specific response toward the endogenous and pharmacological glucocorticoids (GCs). Furthermore, nontranscriptional activities in the cytoplasm are emerging as an additional function of GR. Over the past 40 years, the concepts of GR mechanisms of action had been constantly changing. Different methodologies in the pregenomic and genomic era of molecular biological research and recent cutting-edge technology in single-cell and single-molecule analysis are steadily evolving the views, how the GR in particular and transcriptional regulation in general act in physiological and pathological processes. In addition to the development of technologies for GR analysis, the use of model organisms provides insights how the GR in vivo executes GC action in tissue homeostasis, inflammation, and energy metabolism. The model organisms, namely the mouse, but also rats, zebrafish, and recently fruit flies carrying mutations of the GR became a major driving force to analyze the molecular function of GR in disease models. This guide provides an overview of the exciting research and paradigm shifts in the GR field from past to present with a focus on GR transcription factor networks, GR DNA-binding and single-cell analysis, and model systems.

Corticosteroids alter alveolar macrophage control of Lichtheimia corymbifera spores in an ex vivo mouse model

Alveolar macrophages (AM) are the first-line lung defense against Mucorales in pulmonary mucormycosis. Since corticosteroid use is a known risk factor for mucormycosis, the aim of this study was to describe the role of corticosteroids on AM capacities to control Lichtheimia corymbifera spore growth using a new ex vivo model. An in vivo mouse model was developed to determine the acetate cortisone dose able to trigger pulmonary invasive infection. Then, in the ex vivo model, male BALB/c mice were pretreated with the corticosteroid regimen triggering invasive infection, before AM collection through bronchoalveolar lavage. AMs from corticosteroid-treated mice and untreated control AMs were then exposed to L. corymbifera spores in vitro (ratio 1:5). AM control of fungal growth, adherence/phagocytosis, and oxidative burst were assessed using optical densities by spectrophotometer, flow cytometry, and 2', 7'-dichlorofluoresceine diacetate fluorescence, respectively. Cortisone acetate at 500 mg/kg, at D-3 and at D0, led to pulmonary invasive infection at D3. Co-incubated spores and AMs from corticosteroid-treated mice had significantly higher absorbance (fungal growth) than co-incubated spores and control AMs, at 24 h (P = .025), 36 h (P = .004), and 48 h (P = .001). Colocalization of spores with AMs from corticosteroid-treated mice was significantly lower than for control AMs (7.6 ± 1.9% vs 22.3 ± 5.8%; P = .003), reflecting spore adherence and phagocytosis inhibition. Finally, oxidative burst was significantly increased when control AMs were incubated with spores (P = 0.029), while corticosteroids hampered oxidative burst from treated AMs (P = 0.321). Corticosteroids enhanced fungal growth of L. corymbifera through AM phagocytosis inhibition and burst oxidative decrease in our ex vivo model.

LAY SUMMARY

The aim of this study was to describe the impact of corticosteroids on alveolar macrophage (AM) capacities to control Mucorales growth in a new murine ex vivo model. Corticosteroids enhanced fungal growth of L. corymbifera through AM phagocytosis inhibition and burst oxidative decrease.

Antifungal activity and toxicological parameters of 8-hydroxyquinoline-5-sulfonamides using alternative animal models

AIM

The purpose of this study was to evaluate the antifungal activity and toxicological parameters of 8-hydroxyquinoline derivatives PH151 and PH153 using alternative animal models, to understand their behaviour when subjected to in vivo experiments.

METHODS AND RESULTS

We used Toll-deficient Drosophila melanogaster to test the protective effect of compounds against Candida albicans infection. Toxicological parameters were investigated in chicken and zebrafish embryos. PH151 and PH153 showed low toxicity and the treated flies with these compounds had a significantly higher survival rate than untreated flies after 7 days of infection. The compounds did not cause interruption of chicken embryogenesis. Zebrafish embryos exposed to compounds showed dose-dependent toxicity.

CONCLUSIONS

The data supported the potential of PH151 and PH153 for the treatment of systemic candidiasis and demonstrated to be appropriate drug candidates for further studies using mammalian models.

SIGNIFICANCE AND IMPACT OF THE STUDY

The increased incidence of Candida infections resistant to antifungals currently available requires acceleration of the discovery of new agents with properties of inhibiting this fungal pathogen. In this study, we have described the antifungal potential and toxicity of two 8-hydroxyquinoline derivatives using in vivo alternative models, and the results confirm their potential to be developed as new drug candidates.

Understanding Mucormycoses in the Age of "omics"

Mucormycoses are deadly invasive infections caused by several fungal species belonging to the subphylum Mucoromycotina, order Mucorales. Hallmarks of disease progression include angioinvasion and tissue necrosis that aid in fungal dissemination through the blood stream, causing deeper infections and resulting in poor penetration of antifungal agents to the site of infection. In the absence of surgical removal of the infected focus, antifungal therapy alone is rarely curative. Even when surgical debridement is combined with high-dose antifungal therapy, the mortality associated with mucormycoses is >50%. The unacceptably high mortality rate, limited options for therapy and the extreme morbidity of highly disfiguring surgical therapy provide a clear mandate to understand the molecular mechanisms that govern pathogenesis with the hopes of developing alternative strategies to treat and prevent mucormycoses. In the absence of robust forward and reverse genetic systems available for this taxonomic group of fungi, unbiased next generation sequence (NGS)-based approaches have provided much needed insights into our understanding of many aspects of Mucormycoses, including genome structure, drug resistance, diagnostic development, and fungus-host interactions. Here, we will discuss the specific contributions that NGS-based approaches have made to the field and discuss open questions that can be addressed using similar approaches.

Tornadic Shear Stress Induces a Transient, Calcineurin-Dependent Hypervirulent Phenotype in Mucorales Molds

Trauma-related necrotizing myocutaneous mucormycosis (NMM) has a high morbidity and mortality in victims of combat-related injuries, geometeorological disasters, and severe burns. Inspired by the observation that several recent clusters of NMM have been associated with extreme mechanical forces (e.g., during tornados), we studied the impact of mechanical stress on Mucoralean biology and virulence in a Drosophila melanogaster infection model. In contrast to other experimental procedures to exert mechanical stress, tornadic shear challenge (TSC) by magnetic stirring induced a hypervirulent phenotype in several clinically relevant Mucorales species but not in Aspergillus or Fusarium Whereas fungal growth rates, morphogenesis, and susceptibility to noxious environments or phagocytes were not altered by TSC, soluble factors released in the supernatant of shear-challenged R. arrhizus spores rendered static spores hypervirulent. Consistent with a rapid decay of TSC-induced hypervirulence, minimal transcriptional changes were revealed by comparative RNA sequencing analysis of static and shear-challenged Rhizopus arrhizus However, inhibition of the calcineurin/heat shock protein 90 (hsp90) stress response circuitry by cyclosporine and tanespimycin abrogated the increased pathogenicity of R. arrhizus spores following TSC. Similarly, calcineurin loss-of-function mutants of Mucor circinelloides displayed no increased virulence capacity in flies after undergoing TSC. Collectively, these results establish that TSC induces hypervirulence specifically in Mucorales and point out the calcineurin/hsp90 pathway as a key orchestrator of this phenotype. Our findings invite future studies of topical calcineurin inhibitor treatment of wounds as an adjunct mitigation strategy for NMM following high-energy trauma.IMPORTANCE Given the limited efficacy of current medical treatments in trauma-related necrotizing mucormycosis, there is a dire need to better understand the Mucoralean pathophysiology in order to develop novel strategies to counteract fungal tissue invasion following severe trauma. Here, we describe that tornadic shear stress challenge transiently induces a hypervirulent phenotype in various pathogenic Mucorales species but not in other molds known to cause wound infections. Pharmacological and genetic inhibition of calcineurin signaling abrogated hypervirulence in shear stress-challenged Mucorales, encouraging further evaluation of (topical) calcineurin inhibitors to improve therapeutic outcomes of NMM after combat-related blast injuries or violent storms.

Drosophila as a Model Organism in Host-Pathogen Interaction Studies

Owing to the genetic similarities and conserved pathways between a fruit fly and mammals, the use of the Drosophila model as a platform to unveil novel mechanisms of infection and disease progression has been justified and widely instigated. Gaining proper insight into host-pathogen interactions and identifying chief factors involved in host defense and pathogen virulence in Drosophila serves as a foundation to establish novel strategies for infectious disease prevention and control in higher organisms, including humans.

Identification of glucocorticoid receptor in Drosophila melanogaster

BACKGROUND

Vertebrate glucocorticoid receptor (GR) is an evolutionary-conserved cortisol-regulated nuclear receptor that controls key metabolic and developmental pathways. Upon binding to cortisol, GR acts as an immunosuppressive transcription factor. Drosophila melanogaster, a model organism to study innate immunity, can also be immunosuppressed by glucocorticoids. However, while the genome of fruit fly harbors 18 nuclear receptor genes, the functional homolog of vertebrate GR has not been identified.

RESULTS

In this study, we demonstrated that while D. melanogaster is susceptible to Saccharomyces cerevisiae oral infection, the oral exposure to cortisol analogs, cortisone acetate or estrogen, increases fly sensitivity to yeast challenge. To understand the mechanism of this steroid-induced immunosuppression, we identified the closest genetic GR homolog as D. melanogaster Estrogen Related Receptor (ERR) gene. We discovered that Drosophila ERR is necessary for cortisone acetate- and estrogen-mediated increase in sensitivity to fungal infection: while ERR mutant flies are as sensitive to the fungal challenge as the wildtype flies, the yeast-sensitivity of ERR mutants is not increased by these steroids. Interestingly, the fungal cortisone analog, ergosterol, did not increase the susceptibility of Drosophila to yeast infection. The immunosuppressive effect of steroids on the sensitivity of flies to fungi is evolutionary conserved in insects, as we show that estrogen significantly increases the yeast-sensitivity of Culex quinquefasciatus mosquitoes, whose genome contains a close ortholog of the fly ERR gene.

CONCLUSIONS

This study identifies a D. melanogaster gene that structurally resembles vertebrate GR and is functionally necessary for the steroid-mediated immunosuppression to fungal infections.

Iron sequestration by transferrin 1 mediates nutritional immunity in Drosophila melanogaster

Iron sequestration is a recognized innate immune mechanism against invading pathogens mediated by iron-binding proteins called transferrins. Despite many studies on antimicrobial activity of transferrins in vitro, their specific in vivo functions are poorly understood. Here we use Drosophila melanogaster as an in vivo model to investigate the role of transferrins in host defense. We find that systemic infections with a variety of pathogens trigger a hypoferremic response in flies, namely, iron withdrawal from the hemolymph and accumulation in the fat body. Notably, this hypoferremia to infection requires Drosophila nuclear factor κB (NF-κB) immune pathways, Toll and Imd, revealing that these pathways also mediate nutritional immunity in flies. Next, we show that the iron transporter Tsf1 is induced by infections downstream of the Toll and Imd pathways and is necessary for iron relocation from the hemolymph to the fat body. Consistent with elevated iron levels in the hemolymph, Tsf1 mutants exhibited increased susceptibility to Pseudomonas bacteria and Mucorales fungi, which could be rescued by chemical chelation of iron. Furthermore, using siderophore-deficient Pseudomonas aeruginosa, we discover that the siderophore pyoverdine is necessary for pathogenesis in wild-type flies, but it becomes dispensable in Tsf1 mutants due to excessive iron present in the hemolymph of these flies. As such, our study reveals that, similar to mammals, Drosophila uses iron limitation as an immune defense mechanism mediated by conserved iron-transporting proteins transferrins. Our in vivo work, together with accumulating in vitro studies, supports the immune role of insect transferrins against infections via an iron withholding strategy.

Pattern recognition receptors in Drosophila immune responses

Insects, which lack the adaptive immune system, have developed sophisticated innate immune system consisting of humoral and cellular immune responses to defend against invading microorganisms. Non-self recognition of microbes is the front line of the innate immune system. Repertoires of pattern recognition receptors (PRRs) recognize the conserved pathogen-associated molecular patterns (PAMPs) present in microbes, such as lipopolysaccharide (LPS), peptidoglycan (PGN), lipoteichoic acid (LTA) and β-1, 3-glucans, and induce innate immune responses. In this review, we summarize current knowledge of the structure, classification and roles of PRRs in innate immunity of the model organism Drosophila melanogaster, focusing mainly on the peptidoglycan recognition proteins (PGRPs), Gram-negative bacteria-binding proteins (GNBPs), scavenger receptors (SRs), thioester-containing proteins (TEPs), and lectins.

Stress resistance and lifespan enhanced by downregulation of antimicrobial peptide genes in the Imd pathway

Biological behaviors and longevity of ectothermic animals are remarkably influenced by ambient temperature. Development at 18°C significantly enhances the stress resistance of adult flies with more accumulation of nutrients (especially fat) in the body than development at 25°C. Gene expression analysis between the flies developed at 18°C and 25°C revealed that the Immune deficiency (Imd) pathway, including the downstream antimicrobial peptides (AMPs), is downregulated in the flies developed at 18°C. When hypomorphic imd mutant flies with reduced AMP expressions were developed at 25°C, they showed induced stress resistance with higher fat content in the body similar to the wild-type flies developed at 18°C. However, severe hypomorphic imd mutants could not enhance stress resistance due to the downregulation of another downstream JNK pathway that expresses stress tolerance genes. Interestingly, the downregulation of AMP genes, itself, extended lifespan with increased stress resistance. Especially, fat body-specific downregulation of Imd AMP genes exhibited a longer lifespan with higher heat resistance. The fat body is known to function in metabolic homeostasis, stress tolerance, growth, and longevity in Drosophila. Here, we provide the first evidence that mild downregulation of the Imd pathway with AMP genes increases fat content, stress resistance, and lifespan in adult flies.

Phagocytosis in Drosophila: From molecules and cellular machinery to physiology

Phagocytosis is an evolutionarily conserved mechanism that plays a key role in both host defence and tissue homeostasis in multicellular organisms. A range of surface receptors expressed on different cell types allow discriminating between self and non-self (or altered) material, thus enabling phagocytosis of pathogens and apoptotic cells. The phagocytosis process can be divided into four main steps: 1) binding of the phagocyte to the target particle, 2) particle internalization and phagosome formation, through remodelling of the plasma membrane, 3) phagosome maturation, and 4) particle destruction in the phagolysosome. In this review, we describe our present knowledge on phagocytosis in the fruit fly Drosophila melanogaster, assessing each of the key steps involved in engulfment of both apoptotic cells and bacteria. We also assess the physiological role of phagocytosis in host defence, development and tissue homeostasis.

Pathogenicity patterns of mucormycosis: epidemiology, interaction with immune cells and virulence factors

Fungi of the basal lineage order Mucorales are able to cause infections in animals and humans. Mucormycosis is a well-known, life-threatening disease especially in patients with a compromised immune system. The rate of mortality and morbidity caused by mucormycosis has increased rapidly during the last decades, especially in developing countries. The systematic, phylogenetic, and epidemiological distributions of mucoralean fungi are addressed in relation to infection in immunocompromised patients. The review highlights the current achievements in (i) diagnostics and management of mucormycosis, (ii) the study of the interaction of Mucorales with cells of the innate immune system, (iii) the assessment of the virulence of Mucorales in vertebrate and invertebrate infection models, and (iv) the determination of virulence factors that are key players in the infection process, for example, high-affinity iron permease (FTR1), spore coat protein (CotH), alkaline Rhizopus protease enzyme (ARP), ADP-ribosylation factor (ARF), dihydrolipoyl dehydrogenase, calcineurin (CaN), serine and aspartate proteases (SAPs). The present mini-review attempts to increase the awareness of these difficult-to-manage fungal infections and to encourage research in the detection of ligands and receptors as potential diagnostic parameters and drug targets.

Animal Models to Study Mucormycosis

Mucormycosis is a rare but often fatal or debilitating infection caused by a diverse group of fungi. Animal models have been crucial in advancing our knowledge of mechanisms influencing the pathogenesis of mucormycoses, and to evaluate therapeutic strategies. This review describes the animal models established for mucormycosis, summarizes how they have been applied to study mucormycoses, and discusses the advantages and limitations of the different model systems.

Mucor circinelloides Thrives inside the Phagosome through an Atf-Mediated Germination Pathway

Mucormycosis is an emerging fungal infection that is often lethal due to the ineffectiveness of current therapies. Here, we have studied the first stage of this infection-the germination of Mucor circinelloides spores inside phagocytic cells-from an integrated transcriptomic and functional perspective. A relevant fungal gene network is remodeled in response to phagocytosis, being enriched in crucial functions to survive and germinate inside the phagosome, such as nutritional adaptation and response to oxidative stress. Correspondingly, the phagocytic cells induced a specific proinflammatory and apoptotic response to the pathogenic strain. Deletion of fungal genes encoding putative transcription factors (atf1, atf2, and gcn4), extracellular proteins (chi1 and pps1), and an aquaporin (aqp1) revealed that these genes perform important roles in survival following phagocytosis, germination inside the phagosome, and virulence in mice. atf1 and atf2 play a major role in these pathogenic processes, since their mutants showed the strongest phenotypes and both genes control a complex gene network of secondarily regulated genes, including chi1 and aqp1 These new insights into the initial phase of mucormycosis define genetic regulators and molecular processes that could serve as pharmacological targets.IMPORTANCE Mucorales are a group of ancient saprophytic fungi that cause neglected infectious diseases collectively known as mucormycoses. The molecular processes underlying the establishment and progression of this disease are largely unknown. Our work presents a transcriptomic study to unveil the Mucor circinelloides genetic network triggered in fungal spores in response to phagocytosis by macrophages and the transcriptional response of the host cells. Functional characterization of differentially expressed fungal genes revealed three transcription factors and three extracellular proteins essential for the fungus to survive and germinate inside the phagosome and to cause disease in mice. Two of the transcription factors, highly similar to activating transcription factors (ATFs), coordinate a complex secondary gene response involved in pathogenesis. The significance of our research is in characterizing the initial stages that lead to evasion of the host innate immune response and, in consequence, the dissemination of the infection. This genetic study offers possible targets for novel antifungal drugs against these opportunistic human pathogens.

Preexposure to Isavuconazole Increases the Virulence of Mucorales but Not Aspergillus fumigatus in a Drosophila melanogaster Infection Model

Breakthrough mucormycosis in patients receiving isavuconazole prophylaxis or therapy has been reported. We compared the impact of isavuconazole and voriconazole exposure on the virulence of clinical isolates of Aspergillus fumigatus and different Mucorales species in a Drosophila melanogaster infection model. In contrast to A. fumigatus, a hypervirulent phenotype was found in all tested Mucorales upon preexposure to either voriconazole or isavuconazole. These findings may contribute to the explanation of breakthrough mucormycosis in isavuconazole-treated patients.

Longer lifespan in the Rpd3 and Loco signaling results from the reduced catabolism in young age with noncoding RNA

Downregulation of Rpd3 (histone deacetylase) or Loco (regulator of G-protein signaling protein) extends Drosophila lifespan with higher stress resistance. We found rpd3-downregulated long-lived flies genetically interact with loco-upregulated short-lived flies in stress resistance and lifespan. Gene expression profiles between those flies revealed that they regulate common target genes in metabolic enzymes and signaling pathways, showing an opposite expression pattern in their contrasting lifespans. Functional analyses of more significantly changed genes indicated that the activities of catabolic enzymes and uptake/storage proteins are reduced in long-lived flies with Rpd3 downregulation. This reduced catabolism exhibited from a young age is considered to be necessary for the resultant longer lifespan of the Rpd3- and Loco-downregulated old flies, which mimics the dietary restriction (DR) effect that extends lifespan in the several species. Inversely, those catabolic activities that break down carbohydrates, lipids, and peptides were high in the short lifespan of Loco-upregulated flies. Long noncoding gene, dntRL (CR45923), was also found as a putative target modulated by Rpd3 and Loco for the longevity. Interestingly, this dntRL could affect stress resistance and lifespan, suggesting that the dntRL lncRNA may be involved in the metabolic mechanism of Rpd3 and Loco signaling.

An Adult Zebrafish Model Reveals that Mucormycosis Induces Apoptosis of Infected Macrophages

Mucormycosis is a life-threatening fungal infection caused by various ubiquitous filamentous fungi of the Mucorales order, although Rhizopus spp. and Mucor spp. are the most prevalent causal agents. The limited therapeutic options available together with a rapid progression of the infection and a difficult early diagnosis produce high mortality. Here, we developed an adult zebrafish model of Mucor circinelloides infection which allowed us to confirm the link between sporangiospore size and virulence. Transcriptomic studies revealed a local, strong inflammatory response of the host elicited after sporangiospore germination and mycelial tissue invasion, while avirulent and UV-killed sporangiospores failed to induce inflammation and were rapidly cleared. Of the 857 genes modulated by the infection, those encoding cytokines, complement factors, peptidoglycan recognition proteins, and iron acquisition are particularly interesting. Furthermore, neutrophils and macrophages were similarly recruited independently of sporangiospore virulence and viability, which results in a robust depletion of both cell types in the hematopoietic compartment. Strikingly, our model also reveals for the first time the ability of mucormycosis to induce the apoptosis of recruited macrophages but not neutrophils. The induction of macrophage apoptosis, therefore, might represent a key virulence mechanism of these fungal pathogens, providing novel targets for therapeutic intervention in this lethal infection.

Iron restriction inside macrophages regulates pulmonary host defense against Rhizopus species

Mucormycosis is a life-threatening respiratory fungal infection predominantly caused by Rhizopus species. Mucormycosis has incompletely understood pathogenesis, particularly how abnormalities in iron metabolism compromise immune responses. Here we show how, as opposed to other filamentous fungi, Rhizopus spp. establish intracellular persistence inside alveolar macrophages (AMs). Mechanistically, lack of intracellular swelling of Rhizopus conidia results in surface retention of melanin, which induces phagosome maturation arrest through inhibition of LC3-associated phagocytosis. Intracellular inhibition of Rhizopus is an important effector mechanism, as infection of immunocompetent mice with swollen conidia, which evade phagocytosis, results in acute lethality. Concordantly, AM depletion markedly increases susceptibility to mucormycosis. Host and pathogen transcriptomics, iron supplementation studies, and genetic manipulation of iron assimilation of fungal pathways demonstrate that iron restriction inside macrophages regulates immunity against Rhizopus. Our findings shed light on the pathogenetic mechanisms of mucormycosis and reveal the role of macrophage-mediated nutritional immunity against filamentous fungi.

Mucormycosis is a life-threatening respiratory fungal infection that typically occurs in patients with abnormalities in iron metabolism. Here the authors show that iron restriction inside the phagosome of macrophages is an essential component of the host defense against Rhizopus, the main species causing mucormycosis.

Robust Phagocyte Recruitment Controls the Opportunistic Fungal Pathogen Mucor circinelloides in Innate Granulomas In Vivo

Mucormycosis is an emerging fungal infection with extremely high mortality rates in patients with defects in their innate immune response, specifically in functions mediated through phagocytes. However, we currently have a limited understanding of the molecular and cellular interactions between these innate immune effectors and mucormycete spores during the early immune response. Here, the early events of innate immune recruitment in response to infection by Mucor circinelloides spores are modeled by a combined in silico modeling approach and real-time in vivo microscopy. Phagocytes are rapidly recruited to the site of infection in a zebrafish larval model of mucormycosis. This robust early recruitment protects from disease onset in vivoIn silico analysis identified that protection is dependent on the number of phagocytes at the infection site, but not the speed of recruitment. The mathematical model highlights the role of proinflammatory signals for phagocyte recruitment and the importance of inhibition of spore germination for protection from active fungal disease. These in silico data are supported by an in vivo lack of fungal spore killing and lack of reactive oxygen burst, which together result in latent fungal infection. During this latent stage of infection, spores are controlled in innate granulomas in vivo Disease can be reactivated by immunosuppression. Together, these data represent the first in vivo real-time analysis of innate granuloma formation during the early stages of a fungal infection. The results highlight a potential latent stage during mucormycosis that should urgently be considered for clinical management of patients.IMPORTANCE Mucormycosis is a dramatic fungal infection frequently leading to the death of patients. We know little about the immune response to the fungus causing this infection, although evidence points toward defects in early immune events after infection. Here, we dissect this early immune response to infectious fungal spores. We show that specialized white blood cells (phagocytes) rapidly respond to these spores and accumulate around the fungus. However, we demonstrate that the mechanisms that enable phagocytes to kill the fungus fail, allowing for survival of spores. Instead a cluster of phagocytes resembling an early granuloma is formed around spores to control the latent infection. This study is the first detailed analysis of early granuloma formation during a fungal infection highlighting a latent stage that needs to be considered for clinical management of patients.

The mucormycete-host interface

Mucormycosis is a fungal infection with fulminant angioinvasion leading to high morbidity and mortality in susceptible individuals. The major predisposing conditions are uncontrolled diabetes, neutropenia, malignancies, receipt of a transplant and traumatic injury [1]. Over the past decade, mucormycosis has become an emerging fungal infection due to the increase in patient groups presenting with these pre-disposing conditions and our medical advances in diagnosing the infection [2-4]. Yet, we currently lack clinical interventions to treat mucormycosis effectively. This in turn is due to a lack of understanding of mucormycosis pathogenesis. Here, we discuss our current understanding of selected aspects of interactions at the mucormycete-host interface. We will highlight open questions that might guide future research directions for investigations into the pathogenesis of mucormycosis and potential innovative therapeutic approaches.

Innate and Adaptive Immunity to Mucorales

Mucormycosis is an invasive fungal infection characterised by rapid filamentous growth, which leads to angioinvasion, thrombosis, and tissue necrosis. The high mortality rates (50-100%) associated with mucormycosis are reflective of not only the aggressive nature of the infection and the poor therapeutics currently employed, but also the failure of the human immune system to successfully clear the infection. Immune effector interaction with Mucorales is influenced by the developmental stage of the mucormycete spore. In a healthy immune environment, resting spores are resistant to phagocytic killing. Contrarily, swollen spores and hyphae are susceptible to damage and degradation by macrophages and neutrophils. Under the effects of immune suppression, the recruitment and efficacy of macrophage and neutrophil activity against mucormycetes is considerably reduced. Following penetration of the endothelial lining, Mucorales encounter platelets. Platelets adhere to both mucormycete spores and hyphae, and exhibit germination suppression and hyphal damage capacity in vitro. Dendritic cells are activated in response to Mucorales hyphae only, and induce adaptive immunity. It is crucial to further knowledge regarding our immune system's failure to eradicate resting spores under intact immunity and inhibit fungal growth under immunocompromised conditions, in order to understand mucormycosis pathogenicity and enhance therapeutic strategies for mucormycosis.

The Drosophila melanogaster Muc68E Mucin Gene Influences Adult Size, Starvation Tolerance, and Cold Recovery

Mucins have been implicated in many different biological processes, such as protection from mechanical damage, microorganisms, and toxic molecules, as well as providing a luminal scaffold during development. Nevertheless, it is conceivable that mucins have the potential to modulate food absorption as well, and thus contribute to the definition of several important phenotypic traits. Here we show that the Drosophila melanogaster Muc68E gene is 40- to 60-million-yr old, and is present in Drosophila species of the subgenus Sophophora only. The central repeat region of this gene is fast evolving, and shows evidence for repeated expansions/contractions. This and/or frequent gene conversion events lead to the homogenization of its repeats. The amino acid pattern P[ED][ED][ST][ST][ST] is found in the repeat region of Muc68E proteins from all Drosophila species studied, and can occur multiple times within a single conserved repeat block, and thus may have functional significance. Muc68E is a nonessential gene under laboratory conditions, but Muc68E mutant flies are smaller and lighter than controls at birth. However, at 4 d of age, Muc68E mutants are heavier, recover faster from chill-coma, and are more resistant to starvation than control flies, although they have the same percentage of lipids as controls. Mutant flies have enlarged abdominal size 1 d after chill-coma recovery, which is associated with higher lipid content. These results suggest that Muc68E has a role in metabolism modulation, food absorption, and/or feeding patterns in larvae and adults, and under normal and stress conditions. Such biological function is novel for mucin genes.