Biology subjects

Oehlers, S. H.

Publications and source records attributed to Oehlers, S. H..

At least 19 recordsLinked to original sources

bioRxiv2026

Loss of 7-Dehydrocholesterol Reductase-mediated cholesterol biosynthesis activates IRF3 and inhibits control of Mycobacterium marinum infection

Cholesterol immunometabolism is a critical controller of immunopathology in respiratory infections such as tuberculosis. Smith-Lemli-Opitz syndrome (SLOS) patients are affected by a loss of 7-dehydrocholesterol reductase (DHCR7) function and have elevated 7-dehydrocholesterol (7DHC) and reduced cholesterol. Increased 7DHC has been found to be protective against viral infections in a range of infection models however SLOS patients have a higher susceptibility to respiratory infection. Here we use the zebrafish-Mycobacterium marinum infection model to demonstrate a compromised innate immune response to bacterial infection in the absence of dhcr7. We correlate increased 7DHC with increased activation of the IRF3/type I interferon axis and demonstrate Irf3 is a targetable signaling node to restore anti-bacterial immunity in a dhcr7-depleted background. Plain English summaryLoss of 7-dehydrocholesterol reductase causes Smith-Lemli-Opitz syndrome. One of the metabolic features of Smith-Lemli-Opitz syndrome is increased 7-dehydrocholesterol (7DHC). We find increased 7DHC inhibits the ability of zebrafish to control mycobacterial infection by mis-activating an antiviral immune response at the expense of a protective anti-bacterial immune response. Our study suggests the susceptibility to respiratory infections and increased neuroinflammation in Smith-Lemli-Opitz syndrome could be treated by targeting the antiviral protein IRF3.

immunology↗

bioRxiv2025

A bioluminescence-based chemical screen identifies a bactericidal naphthalene scaffold targeting MmpL3 in Mycobacterium abscessus

Mycobacterium abscessus pulmonary disease (Mabs-PD) presents a significant and growing global health threat, particularly in individuals with underlying lung conditions like cystic fibrosis and chronic obstructive pulmonary disease. A key challenge in treating Mabs-PD is the lack of bactericidal antibiotics effective at therapeutically relevant concentrations, underscoring an urgent need for drug discovery. Targeting cell-wall synthesis is a promising approach, as evidenced by the success of broad-spectrum {beta}-lactam antibiotics and the frontline antituberculosis drug isoniazid. However, these agents exhibit limited efficacy against Mabs, often requiring concentrations unachievable in lung tissues. Here, we used a bioluminescence-based whole-cell assay optimized to identify drugs targeting both cell-wall synthesis and the oxidative phosphorylation pathway. Screening a small drug library against Mabs revealed multiple hits, including {beta}-lactam antibiotics, validating the effectiveness of this approach to identify cell wall-targeting agents. Among these, we identified a chemically tractable naphthalene scaffold with potent bactericidal activity. The optimized derivative GM47-1 targets MmpL3, disrupting cell wall integrity, inducing ATP leakage into the extracellular milieu, and uncoupling respiration, predominantly through the cytochrome bcc:aa3 branch. Further chemical optimization resulted in a new derivative exhibiting a nanomolar minimum inhibitory concentration, with potent activity against intracellular Mabs and in a zebrafish model of infection. This study offers a promising scaffold for future therapeutic development and highlights the utility of this approach as a rapid assay platform for identifying bactericidal compounds against Mabs.

microbiology↗

bioRxiv2025

Telomerase reverse transcriptase is required for resistance to mycobacterial infection

Age is an important risk factor for infections such as tuberculosis (TB). Telomerase is expressed in immune cells yet leukocyte telomere length declines during ageing suggesting an age-dependent loss of telomerase activity in the immune system. Leukocyte telomere length has been correlated with worse outcomes in TB patients, however the mechanisms linking telomere biology to TB susceptibility and response to therapy are unexplored. Here we use the zebrafish-Mycobacterium marinum model to investigate the role of telomerase in TB resistance. We find depletion and inhibition of Tert, the catalytic subunit of telomerase, increases bacterial burden in zebrafish embryos. The Tert depletion infection susceptibility phenotype could not be rescued by p53 or STING depletion suggesting a non-canonical role for Tert in controlling mycobacterial infection. Consistent with a previously described role for Tert in developmental hematopoiesis, we find Tert is necessary for demand-driven emergency myelopoiesis to support containment of extended mycobacterial infection. Our findings establish a previously undescribed role for host telomerase in supporting infection demand-driven hematopoiesis to control infection.

immunology↗

bioRxiv2025

GplR1, an unusual TetR-like transcription factor in Mycobacterium abscessus, controls the production of cell wall glycopeptidolipids, colony morphology, and virulence

Mycobacterium abscessus is a major human pathogen, mostly infecting people with pre-existing lung conditions such as cystic fibrosis. The production of glycopeptidolipids (GPL) is a major determinant of virulence of this bacterium, with clinical isolates that lack GPL generally exhibiting more aggressive clinical behavior. The current paradigm is that GPL production is abolished in vivo via irreversible, spontaneous mutations taking place as part of in-host evolution. Little is known about the mechanisms or extent to which GPL production may be regulated. Here we describe an unusual TetR-like transcription factor of M. abscessus, MAB_1638, that appears to be a strong positive regulator of the entire GPL biosynthesis and export gene cluster through a combination of direct and indirect mechanisms. The inactivation of mab_1638 abolished GPL production and thus led to stable rough colony morphology, as well as increased virulence in infection models, characteristic of rough, non-GPL-producers. Transcriptome analysis found the mab_1638 mutant had 118 differentially expressed genes, including the GPL locus and a second, recently described GPL-like locus that produces a related glycosylated lipopeptide called GP8L. Chromatin Immunoprecipitation and sequencing revealed a consensus inverted-repeat DNA sequence motif characteristic of genes regulated by mab_1638. Together, mab_1638 appears to encode a transcription factor required for production of GPL and therefore having a profound effect on virulence traits. We propose naming this gene GPL regulator 1 (gplR1). This finding raises the important possibility that M. abscessus strains appearing smooth in laboratory growth conditions may nonetheless downregulate GPL-cluster genes in other conditions, including in-patient conditions, and thus acquire the phenotypic characteristics of rough strains. ImportanceMycobacterium abscessus is an important human pathogen, causing disease that is difficult to treat. M. abscessus strains have been observed to have two distinct colony morphologies, smooth and rough, which substantially impact clinical presentation. Rough strains are associated with later-stage, more severe disease and are more virulent in animal models. Smooth morphology is conferred by a molecule called glycopeptidolipid in the outer cell envelope, and rough morphology is known to occur when mutations inactivate genes required for glycopeptidolipid biosynthesis. Little is known about the possibility that glycopeptidolipid production could be regulated. Here we have identified a transcription factor that is required for glycopeptidolipid biosynthesis, indicating that glycopeptidolipid production is indeed a regulated process, and raising the important possibility that strains exhibiting smooth morphology in the lab may down-regulated GPL production in the human host and thereby acquire the virulence properties of rough strains.

microbiology↗

bioRxiv2025

Primary tuberculous mycobacterial granulomas provide a niche for superinfecting Mycobacterium abscessus

Prior and concurrent tuberculosis infection are among the most important susceptibility factors for nontuberculous mycobacterial infection in Asia. Here we model this process in zebrafish with a primary Mycobacterium marinum infection followed by a secondary M. abscessus infection. We demonstrate preferential growth of secondary M. abscessus infection inside primary M. marinum granulomas. Granuloma-resident secondary M. abscessus is protected from macrophage-mediated immune control and antibiotic therapy. Successful colonization is driven by expansion of M. abscessus feeding on caseum produced by the primary M. marinum ESX-1 virulence program in a nutritionally separate niche from M. marinum. Our data suggest tuberculous granulomas may provide a long-lasting niche for the growth of the opportunistic pathogen Mycobacterium abscessus.

microbiology↗

bioRxiv2024

The repurposed STAT3 inhibitor pyrimethamine controls mycobacterial infection-induced vascular permeability and mycobacterial burden

Infection-induced vascular pathologies are a side effect of the immune response to contact with a range of pathogens. Mycobacteria, including Mycobacterium tuberculosis, are particularly adept at co-opting vascular leakiness as a survival mechanism to shape the host immune response and impede the delivery of antibiotics to sites of infection. Here using the zebrafish-Mycobacterium marinum infection model, we confirm a critical role for Signal transducer and activator of transcription 3 (STAT3) in mediating infection-induced vascular permeability, and demonstrate the ability of FDA-approved drugs atovaquone and pyrimethamine to restore vascular barrier function without compromising immune control of mycobacterial infection. Additionally, we find an antibiotic effect of pyrimethamine against Mycobacterium marinum via inhibition of bacterial dihydrofolate reductase. Together our findings suggest pyrimethamine could be used as adjunctive therapy against mycobacterial infection.

microbiology↗

bioRxiv2021

Treatment of infection-induced vascular pathologies is protective against persistent rough morphotype Mycobacterium abscessus infection in zebrafish

Mycobacterium abscessus infections are of increasing global prevalence and are often difficult to treat due to complex antibiotic resistance profiles. While there are similarities between the pathogenesis of M. abscessus and tuberculous mycobacteria, including granuloma formation and stromal remodeling, there are distinct molecular differences at the host-pathogen interface. Here we have used a zebrafish-M. abscessus model and host-directed therapies that were previously identified in the zebrafish-M. marinum model to identify potential host-directed therapies against M. abscessus infection. We find efficacy of anti-angiogenic and vascular normalizing therapies against rough M. abscessus infection, but no effect of anti-platelet drugs.

microbiology↗

bioRxiv2021

Inhibition of infection-induced vascular permeability modulates host leukocyte recruitment to Mycobacterium marinum granulomas in zebrafish

Mycobacterial granuloma formation involves significant stromal remodeling and the growth of leaky, granuloma-associated vasculature. These permeable blood vessels aid mycobacterial growth, as anti-angiogenic or vascular normalizing therapies are beneficial host-directed therapies in pre-clinical models of tuberculosis. Here we demonstrate that vascular normalization through vascular endothelial-protein tyrosine phosphatase inhibition decreases granuloma hypoxia, the opposite effect of hypoxia-inducing anti-angiogenic therapy. Vascular normalization leads to increased T cell and decreased neutrophil recruitment to granulomas, correlates of a protective immune response against mycobacterial infection.

immunology↗

bioRxiv2021

Infection-induced miR-126 suppresses tsc1- and cxcl12a-dependent permissive macrophages during mycobacterial infection

Regulation of host microRNA (miRNA) expression is a contested node that controls the host immune response to mycobacterial infection. The host must overcome concerted subversive efforts of pathogenic mycobacteria to launch and maintain a protective immune response. Here we examine the role of miR-126 in the zebrafish model of Mycobacterium marinum infection and identify a protective role for this infection-induced miRNA through multiple effector pathways. Specifically, we analyse the impact of the miR-126 knockdown-induced tsc1a and cxcl12a/ccl2/ccr2 signalling axes during early host-M. marinum interactions. We find a strong detrimental effect of tsc1a upregulation that renders zebrafish embryos susceptible to higher bacterial burden and increased cell death despite dramatically higher recruitment of macrophages to the site of infection. We demonstrate that infection-induced miR-126 suppresses tsc1 and cxcl12a expression thus improving macrophage function early in infection, partially through activation of mTOR signalling and strongly through preventing the recruitment of Ccr2+ permissive macrophages, resulting in the recruitment of protective tnfa-expressing macrophages. Together our results demonstrate an important role for infection-induced miR-126 in shaping an effective immune response to M. marinum infection in zebrafish embryos.

immunology↗

bioRxiv2021

Exposure to the gut microbiota from cigarette smoke-exposed mice exacerbates cigarette smoke extract-induced inflammation in zebrafish larvae

Cigarette smoke (CS)-induced inflammation leads to a range of diseases including chronic obstructive pulmonary disease and cancer. The gut microbiota is a major modifying environmental factor that determine the severity of cigarette smoke-induced pathology. Microbiomes and metabolites from CS-exposed mice exacerbate lung inflammation via the gut-lung axis of shared mucosal immunity in mice but these systems are expensive to establish and analyse. Zebrafish embryos and larvae have been used to model the effects of cigarette smoking on a range of physiological processes and offer an amenable platform for screening modifiers of cigarette smoke-induced pathologies with key features of low cost and rapid visual readouts. Here we exposed zebrafish larvae to cigarette smoke extract (CSE) and characterised a CSE-induced leukocytic inflammatory phenotype with increased neutrophilic and macrophage inflammation in the gut. The CSE-induced phenotype was exacerbated by co-exposure to microbiota from the faeces of CS-exposed mice, but not control mice. Microbiota could be recovered from the gut of zebrafish and studied in isolation in a screening setting. This demonstrates the utility of the zebrafish-CSE exposure platform for identifying environmental modifiers of cigarette smoking-associated pathology and demonstrates that the CS-exposed mouse gut microbiota potentiates the inflammatory effects of CSE across host species.

immunology↗

bioRxiv2021

Heme oxygenase limits mycobacterial infection-induced ferroptosis

Iron homeostasis is essential for both sides of the host-pathogen interface. Restricting access of iron slows bacterial growth while iron is also a necessary co-factor for host immunity. Heme oxygenase 1 (HMOX1) is a critical regulator of iron homeostasis that catalyses the liberation of iron during degradation of heme. It is also a stress-responsive protein that can be rapidly upregulated and confers protection to the host. Although a protective role of HMOX1 has been demonstrated in a variety of diseases, the role of HMOX1 in Mycobacterium tuberculosis infection is equivocal across experiments with different host-pathogen combinations. Here we use the natural host-pathogen pairing of the zebrafish-Mycobacterium marinum infection platform to study the role of zebrafish heme oxygenase in mycobacterial infection. We identify zebrafish Hmox1a as the relevant functional paralog of mammalian HMOX1 and demonstrate a conserved role for Hmox1a in protecting the host from mycobacterial infection. Using genetic and chemical tools, we show zebrafish Hmox1a protects the host against mycobacterial infection by reducing infection-induced iron accumulation and ferroptosis.

immunology↗

bioRxiv2021

Transplantation of high fat fed mouse microbiota into zebrafish embryos identifies pathobiont species

Gut dysbiosis is an important modifier of pathologies including cardiovascular disease but our understanding of the role of individual microbes is limited. Here, we have used transplantation of mouse microbiota into microbiota-deficient zebrafish larvae to study the interaction between members of a mammalian high fat diet-associated gut microbiota with a lipid rich diet challenge in a tractable model species. We find zebrafish larvae are more susceptible to hyperlipidaemia when exposed to the mouse high fat-diet-associated microbiota and that this effect can be driven by two individual bacterial species fractionated from the mouse high fat-diet-associated microbiota. We find Stenotrophomonas maltophilia increases the hyperlipidaemic potential of chicken egg yolk to zebrafish larvae independent of direct interaction between S. maltophilia and the zebrafish host. Colonisation by live, or exposure to heat-killed, Enterococcus faecalis accelerates hyperlipidaemia via host Myd88 signalling. The hyperlipidaemic effect is replicated by exposure to the Gram positive Toll-like receptor agonists peptidoglycan and lipoteichoic acid in a MyD88-dependent manner. In this work, we demonstrate the applicability of zebrafish as a tractable host for the identification of gut microbes that can induce conditional host phenotypes via microbiota transplantation and subsequent challenge with a high fat diet.

microbiology↗

bioRxiv2021

OXSR1 inhibits inflammasome activation by limiting potassium efflux during mycobacterial infection

Pathogenic mycobacteria inhibit inflammasome activation as part of their pathogenesis. While it is known that potassium efflux is a trigger for inflammasome activation, the interaction between mycobacterial infection, potassium efflux and inflammasome activation has not been investigated. Here we use Mycobacterium marinum infection of zebrafish embryos and Mycobacterium tuberculosis of human THP-1 cells to demonstrate that pathogenic mycobacteria upregulate the host WNK signalling pathway kinases SPAK and OXSR1 which control intracellular potassium balance. We show that genetic depletion or inhibition of OXSR1 decreases bacterial burden and intracellular potassium levels. The protective effects of OXSR1 depletion are mediated by NLRP3 inflammasome activation and are dependent on caspase-mediated release of IL-1{beta} and the downstream activation of protective TNF-. The elucidation of this druggable pathway to potentiate inflammasome activation provides a new avenue for the development of host-directed therapies against intracellular infections.

immunology↗

bioRxiv2021

Zebrafish heme oxygenase 1a is necessary for normal development and macrophage migration

Heme oxygenase function is highly conserved between vertebrates where it plays important roles in normal embryonic development and controls oxidative stress. Expression of the zebrafish heme oxygenase 1 genes are known to be responsive to oxidative stress suggesting a conserved physiological function. Here we generate a knockout allele of zebrafish hmox1a and characterize the effects of hmox1a and hmox1b loss on embryonic development. We find that loss of hmox1a or hmox1b causes developmental defects in only a minority of embryos, in contrast to Hmox1 gene deletions in mice that causes loss of most embryos. Using a tail wound inflammation assay we find a conserved role for hmox1a, but not hmox1b, in normal macrophage migration to the wound site. Together our results indicate zebrafish hmox1a has clearly a partitioned role from hmox1b that is more consistent with conserved functions of mammalian Heme oxygenase 1.

developmental biology↗

bioRxiv2021

Common anti-hemostatic medications increase the severity of uropathogenic Escherichia coli sepsis

Uropathogenic Escherichia coli (UPEC) causes urinary tract infections that can result in sepsis. The haemostatic system is protective in the pyelonephritis stage of ascending UPEC infection, but the role of the haemostatic system has not been investigated during sepsis. Here we utilize a zebrafish-UPEC systemic infection model to visualize infection-induced coagulation and examine the effects of commonly prescribed anti-haemostatic medications on the infection severity. Treatment of systemically infected zebrafish with warfarin, aspirin, or ticagrelor reduced host survival, while stabilization of clots with aminocaproic acid increased host survival. Anti-haemostatic drug treatment increased UPEC burden. Our findings provide evidence that commonly prescribed anti-haemostatic medications may worsen the outcome of severe UPEC infection.

immunology↗

bioRxiv2020

Mycobacterial infection-induced miR-206 inhibits protective neutrophil recruitment via the CXCL12/CXCR4 signalling axis

Pathogenic mycobacteria actively dysregulate protective host immune signalling pathways during infection to drive the formation of permissive granuloma microenvironments. Dynamic regulation of host microRNA (miRNA) expression is a conserved feature of mycobacterial infections across host-pathogen pairings. Here we examine the role of miR-206 in the zebrafish model of Mycobacterium marinum infection, which allows investigation of the early stages of granuloma formation. We find miR-206 is upregulated following infection by pathogenic M. marinum and that antagomir-mediated knockdown of miR-206 is protective against infection. We observed striking upregulation of cxcl12a and cxcr4b in infected miR-206 knockdown zebrafish embryos and live imaging revealed enhanced recruitment of neutrophils to sites of infection. We used Crispr/Cas9-mediated knockdown of cxcl12a and cxcr4b expression and AMD3100 inhibition of Cxcr4 to show that the enhanced neutrophil response and reduced bacterial burden caused by miR-206 knockdown was dependent on the Cxcl12/Cxcr4 signalling axis. Together, our data illustrate a pathway through which pathogenic mycobacteria induce host miR-206 expression to suppress Cxcl12/Cxcr4 signalling and prevent protective neutrophil recruitment to granulomas. Author summaryMycobacterial infections cause significant disease burden to humans and animals, the most widely known example being tuberculosis which has killed more humans than any other infectious disease throughout history. Infectious mycobacteria are highly evolved to hijack host processes, including the very immune cells tasked with destroying them. microRNAs are host molecules that control wide-ranging programs of host gene expression and are important in the immune response to infections. Here we use the zebrafish model of mycobacterial infection to determine the role of the infection-induced microRNA miR-206 in the host response to infection. We found pathogenic mycobacteria trigger the host to produce more miR-206 in order to suppress the otherwise protective recruitment of neutrophils to sites of infection via the host Cxcl12/Cxcr4 signalling pathway. Our study provides new insight into the role of mycobacterial infection-induced miR-206 function in the context of a whole host.

immunology↗

bioRxiv2020

Conserved anti-inflammatory effects and sensing of butyrate in zebrafish

Short chain fatty acids (SCFAs) are produced by microbial fermentation of dietary fiber in the gut. Butyrate is a particularly important SCFA with anti-inflammatory properties and is generally present at lower levels in inflammatory diseases associated with gut microbiota dysbiosis in mammals. We aimed to determine if SCFAs are produced by the zebrafish microbiome and if SCFAs exert conserved effects on zebrafish immunity as an example of the non-mammalian vertebrate immune system. We demonstrate that bacterial communities from adult zebrafish intestines synthesize all three main SCFA in vitro, although SCFA were below our detectable limits in zebrafish intestines in vivo. Immersion in butyrate, but not acetate or propionate, reduced the recruitment of neutrophils and M1-type pro-inflammatory macrophages to wounds. We found conservation of butyrate sensing by neutrophils via orthologs of the hydroxycarboxylic acid receptor 1 (hcar1) gene. Neutrophils from Hcar1-depeleted embryos were no longer responsive to the anti-inflammatory effects of butyrate, while macrophage sensitivity to butyrate was independent of Hcar1. Our data demonstrate conservation of anti-inflammatory butyrate effects and identify the presence of a conserved molecular receptor in fish.

immunology↗

bioRxiv2019

Chronic infection of adult zebrafish with rough or smooth variant Mycobacterium abscessus causes necrotising inflammation and differential activation of host immunity

Infections caused by Mycobacterium abscessus are increasing in prevalence within patient groups with respiratory comorbidities. Initial colonisation by the smooth colony M. abscessus (S) can be followed by an irreversible genetic switch into a highly inflammatory rough colony M. abscessus (R), often associated with a decline in pulmonary function. Our understanding of the role of adaptive immunity in M. abscessus pathogenesis is largely unknown. Here, we have used intraperitoneal infection of adult zebrafish to model M. abscessus pathogenesis in the context of fully functioning host immunity. We find infection with the R variant penetrates host organs causing an inflammatory immune response leading to necrotic granuloma formation within 2 weeks. The R bacilli are targeted by T cell-mediated immunity and burden is constrained. Strikingly, the S variant colonises host internal surfaces at high loads and is met with a robust innate immune response but little T cell-mediated immunity. Invasive granuloma formation is delayed in S variant infection compared to R variant infection upon which T cell-mediated immunity is required to control infection. In mixed infections, the S variant outcompetes the R variant. We also find the R variant activates host immunity to the detriment of S variant M. abscessus in mixed infections. These findings demonstrate the applicability of the adult zebrafish to model persistent M. abscessus infection and provide insight into the immunopathogenesis of chronic M. abscessus infection.

microbiology↗