Biology subjects

Bojarczuk, A.

Publications and source records attributed to Bojarczuk, A..

6 recordsLinked to original sources

bioRxiv2018

Alternative oxidase induction protects Candida albicans from respiratory stress and promotes hyphal growth

The human fungal pathogen Candida albicans possesses two genes expressing a cyanide-insensitive Alternative Oxidase (Aox) enzymes in addition to classical and parallel electron transfer chains (ETC). In this study, we examine the role of Aox in C. albicans under conditions of respiratory stress, which may be inflicted during its interaction with the human host or co-colonising bacteria. We find that the level of Aox expression is sufficient to modulate resistance to classical ETC inhibition under respiratory stress and are linked to gene expression changes that can promote both survival and pathogenicity. For example we demonstrate that Aox function is important for the regulation of filamentation in C. albicans and observe that cells lacking Aox function lose virulence in a zebrafish infection model. Our investigations also identify that pyocyanin, a phenazine produced by the co-colonising bacterium Pseudomonas aeruginosa, inhibits Aox-based respiration in C. albicans. These results suggest that Aox plays important roles within respiratory stress response pathways which C. albicans may utilise both as a commensal organism and as a pathogen.

microbiology↗

bioRxiv2018

Inhibition of classical and alternative modes of respiration in C. albicans leads to cell wall remodelling and increased macrophage recognition

The human fungal pathogen C. albicans requires respiratory function for normal growth, morphogenesis and virulence. As such the mitochondria represent an enticing target for the development of new antifungal strategies. This possibility is further bolstered by the presence of fungal specific characteristics. However, respiration in C. albicans, as is the case in many fungal organisms, is facilitated by redundant electron transport mechanisms that makes direct inhibition a challenge. In addition, many chemicals known to target the electron transport chain are highly toxic. Here we make use of chemicals with low toxicity in mammals to efficiently inhibit respiration in C. albicans. We find that use of the Nitric Oxide donor, Sodium Nitroprusside (SNP), and the alternative oxidase inhibitor, SHAM, prevent respiration, lead to a loss in viability and to cell wall rearrangements that increase the rate of uptake by macrophages in vitro and in vivo. We propose that SNP+SHAM treatment leads to transcriptional changes that drive cell wall re-arrangement but which also prime cells to activate transition to hyphal growth. In line with this we find that pre-treatment of C. albicans with SNP+SHAM leads to an increase in virulence. Our data reveals strong links between respiration, cell wall remodelling and activation of virulence factors. Our findings also demonstrate that respiration in C. albicans can be efficiently inhibited with chemicals which are not damaging to the mammalian host, but that we need to develop a deeper understanding of the roles of mitochondria in cellular signalling if they are to be developed successfully as a target for new antifungals.\n\nAuthor SummaryCurrent approaches to tackling fungal infections are limited and new targets must be identified to protect against the emergence of resistant strains. We investigate the potential of targeting mitochondria, organelles required for energy production, growth and virulence, in the yeast human fungal pathogen Candida albicans. Our findings suggest that mitochondria can be targeted using drugs that can be tolerated by humans and that this treatment enhances their recognition by immune cells. However release of C. albicans cells from mitochondrial inhibition appears to activate a stress response that increases traits associated with virulence. Our results make it clear that mitochondria are a valid target for the development of anti-fungal strategies but that we must determine the mechanisms by which they regulate stress signalling and virulence ahead of successful therapeutic advance.

microbiology↗

bioRxiv2017

Dissemination of Cryptococcus neoformans via localised proliferation and blockage of blood vessels

Cryptococcus neoformans is an opportunistic fungal pathogen that can cause life-threatening cryptoccocal meningitis, predominantly within immunocompromised individuals. Cortical infarcts are observed in as many as 30% of cryptococcal meningitis cases, being particularly common in severe infection. Limited clinical case studies suggest infarcts are secondary to vasculitis and blood vessel damage caused by cryptococcal infection. However, the cause of infarcts in cryptococcal infection has not been determined. To examine potential causes of vascular damage and cryptococcal dissemination in cryptococcal infection, the zebrafish C. neoformans infection model was used. We demonstrate that spread of cryptococci from the vasculature occurs at sites where cryptococci grow within the blood vessels, originating from a single or small number of cryptococci. We find that cryptococcal cells become trapped within the vasculature and can proliferate there resulting in vasodilation. Localised cryptococcal growth in the vasculature is also associated with sites of dissemination - in some cases simultaneously with a loss of blood vessel integrity. Using a cell-cell junction protein reporter (VE-cadherin) we identified sites dissemination associated with both intact blood vessels and where vessel rupture occurred. Thus, we have identified a mechanism for blood vessel damage during cryptococcal infection that may represent a cause of the vascular damage and cortical infarction observed in cryptococcal meningitis.\n\nAuthor summaryHuman infection by the fungal pathogen, Cryptococcus neoformans, can lead to life-threatening cryptococcal meningitis. In severe cases of cryptococcal meningitis, a lack of blood supply can cause tissue death and a resulting area of dead tissue (infarct) in the brain. Although vasculature inflammation in known to occur in cryptococcal meningitis, the cause of infarcts in unknown. Using a zebrafish model of cryptococcal infection, the growth and dissemination of fungal cells was observed over time. We show that cryptococcal cells become trapped and proliferate in the vasculature, resulting in cryptococcoma that damage the blood vessels. We propose that vessel damage results from increased blood pressure caused by cryptococci blocking blood vessels suggesting that the vascular damage that ensues on cryptococcoma formation may in turn be a cause of infarct formation seen in cryptococcal meningitis.

microbiology↗

bioRxiv2017

A transgenic zebrafish model for the in vivo study of the blood and choroid plexus brain barriers using claudin 5

The central nervous system (CNS) has specific barriers that protect the brain from potential threats and tightly regulate molecular transport. Despite the critical functions of the CNS barriers, the mechanisms underlying their development and function are not well understood, and there are very limited experimental models for their study. Claudin 5 is a tight junction protein required for blood brain barrier (BBB) and choroid plexus (CP) barrier structure and function in humans. Here, we show that the gene claudin 5a is the zebrafish orthologue with high fidelity expression, in the BBB and CP barriers, that demonstrates the conservation of the BBB and CP between humans and zebrafish. Expression of claudin 5a correlates with developmental tightening of the BBB and is restricted to a subset of the brain vasculature clearly delineating the BBB. We show that claudin 5a expressing cells of the CP are ciliated ependymal cells that drive fluid flow in the brain ventricles. Finally, we find that CP development precedes BBB development and that claudin 5a expression occurs simultaneously with angiogenesis. Thus, our novel transgenic zebrafish represents an ideal model to study CNS barrier development and function, critical in understanding the mechanisms underlying CNS barrier function in health and disease.

developmental biology↗

bioRxiv2017

Mycophenolate Mofetil Increases Inflammation Resolution In Zebrafish Via Neutrophil Apoptosis

Mycophenolate mofetil (MMF) is an immunosuppressive agent used in the treatment of autoimmune and inflammatory conditions, and following organ transplant. MMF treatment results in lymphopenia via the depletion of purines required for DNA synthesis. While the primary effect of MMF treatment is thought to be via the depletion of lymphocytes, MMF has also been associated with innate immune defects, including neutropenia and neutrophil dysplasia. Here, we address the question of MMF specific effects on neutrophils in an in vivo model of neutrophil inflammation in zebrafish. We find that, following tissue injury, MMF increases resolution of neutrophilic inflammation via increased neutrophil apoptosis. Critically, we identify that the effect of MMF is distinct from DNA synthesis inhibition by using the competitive inhibitor of purine nucleotide incorporation, azathioprine. Therefore, we propose that increased neutrophil cell death during inflammatory insult may play a role in neutrophil defects associated with MMF treatment.

immunology↗

bioRxiv2017

Mycophenolate mofetil increases susceptibility toopportunistic fungal infection independent of lymphocytes

Anti-proliferative agents that target lymphoid cells are common immunosuppressive agents used in the treatment of diverse autoimmune, graft versus host and inflammatory diseases. Mycophenolate mofetil (MMF) is an anti-proliferative agent that targets lymphoid dependence on inosine monophosphate dehydrogenase for the de novo purine synthesis of deoxyguanosine triphosphate (dGTP) for DNA replication. Here we show that MMF has a distinct and specific in vivo effect on macrophages, in the absence of lymphoid cells. This results in increased macrophage cell death that is dependent on the depletion of cellular GTP, independent of DNA synthesis. Furthermore, the macrophage specific effect of MMF treatment causes an increase in susceptibility to the opportunistic fungal infection Cryptococcus neoformans by reducing phagocytosis and increasing the release of intracellular pathogens via macrophage lysis. Our study demonstrates the need for a better mechanistic understanding of immunosuppressive treatments used in clinical practice and of the specific infection risks associated with certain treatment regimens.

immunology↗