Biology subjects

Bartlett, S.

Publications and source records attributed to Bartlett, S..

8 recordsLinked to original sources

bioRxiv2026

MinC influences the Min oscillation period in Escherichia coli by priming MinD on the membrane

Spatial organization during bacterial fission is critical to ensure that division results in identical, viable progeny cells. In Escherichia coli, one important system that accomplishes this is the Min system, comprising MinC, MinD, and MinE proteins. The Min system regulates assembly of the FtsZ-ring to ensure proper placement of the division machinery at midcell. We explored the dynamics of the Min system and demonstrate that Min oscillation and release of MinD from the membrane is modulated by MinC. Deletion of the minC gene from a strain expressing minD fused to the gene encoding green fluorescent protein (Gfp) resulted in faster pole-to-pole oscillation of Gfp-MinD in vivo, leading to a shorter period. This was also observed in a strain expressing the MinC(R133A), a variant mutated at the MinC-MinD interface. In phospholipid binding and release assays in vitro, we observed that the concentration of MinE required to release MinD was lower with MinC, suggesting that MinC activates MinD for MinE-dependent release. Oscillation is produced by a diffusion-capture-release mechanism occurring at the membrane with proteins proceeding toward a pole. To determine if an increase in the diffusive proportion of MinD leads to faster oscillation, we constructed MinD membrane targeting sequence (MTS) variants to reduce the membrane associated pool of MinD. MTS variants induced a range of oscillation defects, with MinD(KR265AA) oscillating faster in vivo. Together our results show that MinC is an effector that modifies Min oscillation by priming MinD for MinE-dependent membrane release and fine-tunes the Min oscillation rate in dividing cells.

microbiology↗

bioRxiv2026

SARS-CoV-2 ORF8 modulates the upper respiratory tract inflammatory response to facilitate transmission

The ability of respiratory viruses to exploit host immune responses to promote transmission is a defining feature of pandemics. SARS-CoV-2 remains a major global public health threat because of its persistent evolution and capacity to counteract evolving immune defenses. Although the immune evasion properties of the SARS-CoV-2 Spike protein are well characterized, the contributions of other viral proteins to transmission remain poorly understood. Here, we used the infant mouse model to define the role of the accessory protein ORF8 in SARS-CoV-2 spread. We demonstrate that ORF8 supports efficient upper respiratory tract (URT) infection, infectious virus shedding, and host-to-host transmission. Mice infected with a recombinant SARS-CoV-2 strain lacking ORF8 (r{Delta}ORF8) had less infectious virus recovered from URT tissues and nasal secretions and transmitted less efficiently than mice infected with the isogenic ancestral strain rWA-1, which contains an intact ORF8. Recombinant viruses encoding naturally occurring ORF8 mutations exhibited distinct transmission phenotypes, with ORF8-deficient viruses resembling r{Delta}ORF8. Infection with ORF8-sufficient viruses induced greater macrophage recruitment, inflammatory cytokine production, and type-I interferon (IFN-I) signaling programs than ORF8-deficient viruses. Intranasal IFN{beta} supplementation partially restored URT shedding by r{Delta}ORF8-infected mice and rescued transmission to contacts, whereas blockade of the type I interferon receptor (IFNAR) in rWA-1-infected index mice reduced contact infection and transmission. Together, these findings demonstrate that ORF8 promotes SARS-CoV-2 transmission by engaging an IFN-I-associated inflammatory and secretory program in the URT that supports virus shedding from the infected host. These data identify ORF8 as a viral determinant of host mucosal responses that promote contagiousness. ImportanceEfficient host-to-host transmission underlies the success of respiratory viruses. Although SARS-CoV-2 research has largely focused on the Spike protein, accessory proteins can also shape viral fitness and spread. We previously identified ORF8 as a determinant of SARS-CoV-2 transmission. Here we show that ORF8 promotes SARS-CoV-2 infectious viral shedding and transmission by engaging IFN-I-associated inflammatory and secretory responses in the URT. These findings reveal how a SARS-CoV-2 accessory protein can exploit mucosal antiviral responses to increase host contagiousness.

microbiology↗

bioRxiv2026

IFNγ-Driven Inflammatory Responses in the Nasal Mucosa Drive Influenza Virus Shedding and Transmission

What determines host infectiousness during influenza A virus (IAV) infection remains a fundamental unanswered question in virology. While upper respiratory tract (URT) replication is necessary for transmission, its insufficient to explain host-to-host variation in contagiousness. Using the infant mouse model of influenza transmission, we show that viruses containing H3 hemagglutinin shed at higher levels than non-H3-containing viruses, despite comparable URT replication. H3-containing virus infection was associated with higher URT inflammation, characterized by increased cytokine production, immune cell recruitment, and mucus hypersecretion, which directly correlated with shedding efficiency. Transcriptomic profiling identified enrichment of interferon-stimulated gene programs, with a dominant interferon gamma (IFN{gamma}) signature during H3 infections. Functional studies demonstrated that IFN{gamma} deficiency reduced mucus production, shedding, and transmission, whereas IFN{gamma} supplementation restored these phenotypes. Together, these findings identify IFN{gamma}-driven mucosal inflammation key host determinant of influenza infectiousness, reframing contagiousness as a consequence of host inflammatory clearance rather than viral replication alone.

microbiology↗

bioRxiv2023

Targeting host sialic acids in the upper respiratory tract with a broadly-acting neuraminidase to inhibit influenza virus transmission

The ongoing transmission of influenza A viruses (IAV) for the past century continues to be a burden to humans. IAV binds terminal sialic acids (SA) of sugar molecules present within the upper respiratory tract (URT) in order to successfully infect hosts. The two most common SA structures that are important for IAV infection are those with 2,3- and 2,6-linkages. While mice were once considered to be an unsuitable system for studying IAV transmission due to their lack of 2,6-SA in the trachea, we have successfully demonstrated that IAV transmission in infant mice is remarkably efficient. This finding led us to reevaluate the SA composition of the URT of mice using in situ immunofluorescence and examine its in vivo contribution to transmission for the first time. We demonstrate that mice express both 2,3- and 2,6-SA in the URT and that the difference in expression between infants and adults contribute to the variable transmission efficiencies observed. Furthermore, selectively blocking 2,3-SA or 2,6-SA within the URT of infant mice using lectins was necessary but insufficient at inhibiting transmission, and simultaneous blockade of both receptors was crucial in achieving the desired inhibitory effect. By employing a broadly-acting neuraminidase (ba-NA) to indiscriminately remove both SA moieties in vivo, we effectively suppressed viral shedding and halted the transmission of different strains of influenza viruses. These results emphasize the utility of the infant mouse model for studying IAV transmission, and strongly indicate that broadly targeting host SA is an effective approach that inhibits IAV contagion. IMPORTANCEInfluenza virus transmission studies have historically focused on viral mutations that alter hemagglutinin binding to sialic acid (SA) receptors in vitro. However, SA binding preference doesnt fully account for the complexities of IAV transmission in humans. Our previous findings reveal that viruses that are known to bind 2,6-SA in vitro have different transmission kinetics in vivo, suggesting that diverse SA interactions may occur during their life-cycle. In this study, we examine the role of host SA on viral replication, shedding, and transmission in vivo. We highlight the critical role of SA presence during virus shedding, such that attachment to SA during virion egress is equally important as detachment from SA during virion release. These insights support the potential of broadly-acting neuraminidases as therapeutic agents capable of restraining viral transmission in vivo. Our study unveils intricate virus-host interactions during shedding, highlighting the necessity to develop innovative strategies to effectively target transmission.

microbiology↗

bioRxiv2022

Oxysterols drive inflammation via GPR183 during influenza virus and SARS-CoV-2 infection

RationaleSevere viral respiratory infections are often characterized by extensive myeloid cell infiltration and activation and persistent lung tissue injury. However, the immunological mechanisms driving excessive inflammation in the lung remain elusive. ObjectivesTo identify the mechanisms that drive immune cell recruitment in the lung during viral respiratory infections and identify novel drug targets to reduce inflammation and disease severity. MethodsPreclinical murine models of influenza virus and SARS-CoV-2 infection. ResultsOxidized cholesterols and the oxysterol-sensing receptor GPR183 were identified as drivers of monocyte-macrophage infiltration to the lung during influenza virus (IAV) and SARS-CoV-2 infections. Both IAV and SARS-CoV-2 infections upregulated the enzymes cholesterol 25-hydroxylase (CH25H) and cytochrome P450 family 7 subfamily member B1 (CYP7B1) in the lung, resulting in local production of the oxidized cholesterols 25-hydroxycholesterol and 7,25-dihydroxycholesterol (7,25-OHC). Loss-of-function mutation of GPR183, or treatment with a GPR183 antagonist, reduced macrophage infiltration and inflammatory cytokine production in the lungs of IAV- or SARS-CoV-2-infected mice. The GPR183 antagonist also significantly attenuated the severity of SARS-CoV-2 infection by reducing weight loss and viral loads. ConclusionThis study demonstrates that oxysterols drive inflammation in the lung and provides the first preclinical evidence for therapeutic benefit of targeting GPR183 during severe viral respiratory infections. Author SummaryViral infections trigger oxysterol production in the lung, attracting macrophages via GPR183. Blocking GPR183 reduced inflammation and disease severity in SARS-CoV-2 infection, making GPR183 a putative target for therapeutic intervention.

immunology↗

bioRxiv2022

A blunted GPR183/oxysterol axis during dysglycemia results in delayed recruitment of macrophages to the lung during M. tuberculosis infection

We previously reported that the oxidised cholesterol-sensing receptor GPR183 is significantly downregulated in blood from tuberculosis (TB) patients with diabetes compared to TB patients without co-morbidities and that lower GPR183 expression in blood is associated with more severe pulmonary TB on chest-x-ray consistent with observations in dysglycemic mice. To further elucidate the role of this receptor and its endogenous high affinity agonist 7,25-di-hydroxycholesterol (7,25-OHC) in the lung, we studied high fat diet (HFD)-induced dysglycemic mice infected with M.tuberculosis. We found that the 7,25-OHC-producing enzymes cholesterol 25-hydroxylase (CH25H) and cytochrome P450 family 7 subfamily member B1 (CYP7B1) were highly upregulated upon M. tuberculosis infection in the lungs of normoglycemic mice, and this was associated with increased expression of GPR183 indicative of effective recruitment of GPR183-expressing immune cells to the site of infection. We demonstrated that CYP7B1 was predominantly expressed by macrophages in the centre of TB granulomas. Expression of CYP7B1 was significantly blunted in lungs from HFD-fed dysglycemic animals and this coincided with delayed recruitment of macrophages to the lung during early infection and more severe lung pathology. GPR183 deficient mice similarly had reduced macrophage recruitment during early infection demonstrating a requirement of the GPR183/oxysterol axis for macrophage infiltration into the lung in TB. Together our data demonstrate that oxidised cholesterols and GPR183 play an important role in positioning macrophages to the site of M. tuberculosis infection and that this is impaired by HFD-induced dysglycemia, adding a mechanistic explanation to the poorer TB outcomes in patients with diabetes.

immunology↗

bioRxiv2021

Pre-diabetes increases tuberculosis disease severity, while high body fat without impaired glucose tolerance is protective

Type 2 diabetes (T2D) is a well-known risk factor for tuberculosis (TB), but little is known about pre-diabetes and the relative contribution of impaired glucose tolerance vs. obesity towards susceptibility to TB. Here, we developed a preclinical model of pre-diabetes and TB. Mice fed a high fat diet (HFD) for 12 weeks presented with impaired glucose tolerance and hyperinsulinemia compared to mice fed normal chow diet (NCD). Infection with M. tuberculosis (Mtb) H37Rv after the onset of dysglycemia was associated with significantly increased lung pathology, lower concentrations of TNF-a, IFN-g, IFN-{beta} and IL-10 and a trend towards higher bacterial burden at 3 weeks post infection. To determine whether the increased susceptibility of pre-diabetic mice to TB is reversible and is associated with dysglycemia or increased body fat mass, we performed a diet reversal experiment. Pre-diabetic mice were fed a NCD for 10 additional weeks (HFD/NCD) at which point glucose tolerance was restored, but body fat mass remained higher compared to control mice that consumed NCD throughout the entire experiment (NCD/NCD). Upon Mtb infection HFD/NCD mice had significantly lower bacterial burden compared to NCD/NCD mice and this was accompanied by restored IFN-{gamma} responses. Our findings demonstrate that pre-diabetes increases susceptibility to TB, but a high body mass index without dysglycemia is protective. This murine model offers the opportunity to further study the underlying immunological, metabolic and endocrine mechanisms of this association.

immunology↗

bioRxiv2020

GPR183 regulates interferons and bacterial growth during Mycobacterium tuberculosis infection: interaction with type 2 diabetes and TB disease severity

Oxidized cholesterols have emerged as important signaling molecules of immune function, but little is known about the role of these oxysterols during mycobacterial infections. We found that expression of the oxysterol-receptor GPR183 was reduced in blood from patients with tuberculosis (TB) and type 2 diabetes (T2D) compared to TB patients without T2D and was associated with TB disease severity on chest x-ray. GPR183 activation by 7,25-hydroxycholesterol (7,25-OHC) reduced growth of Mycobacterium tuberculosis (Mtb) and Mycobacterium bovis BCG in primary human monocytes, an effect abrogated by the GPR183 antagonist GSK682753. Growth inhibition was associated with reduced IFN-{beta} and IL-10 expression and enhanced autophagy. Mice lacking GPR183 had significantly increased lung Mtb burden and dysregulated IFNs during early infection. Together, our data demonstrate that GPR183 is an important regulator of intracellular mycobacterial growth and interferons during mycobacterial infection. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=112 SRC="FIGDIR/small/203398v1_ufig1.gif" ALT="Figure 1"> View larger version (21K): org.highwire.dtl.DTLVardef@76c86dorg.highwire.dtl.DTLVardef@60a3bcorg.highwire.dtl.DTLVardef@9dc233org.highwire.dtl.DTLVardef@138db01_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗