PLoS Pathogens最新文献

Dengue virus (DENV) is a mosquito-transmitted flavivirus that circulates globally as four distinct serotypes and poses a substantial threat to public health. There are an estimated ~96 million symptomatic infections yearly, including severe cases of dengue fever, underscoring the urgency of identifying effective therapeutics targeting all four serotypes. Nucleoside analogs, which mimic endogenous nucleosides to inhibit viral RNA replication, offer a promising strategy for broad-spectrum antiviral development. Here, we conducted a high-throughput screen of 1,101 nucleoside analogs against DENV serotype 2 (DENV2) in a panel of human cell models, including human epithelial cells, hepatocytes, and fibroblasts. Candidates that were active against DENV2 were screened against all four serotypes. Since flaviviruses including West Nile virus and Zika virus are also important human pathogens, we screened these compounds for activity and identified compounds that were broadly active in these cellular and viral models. We further evaluated antivirals in primary human keratinocytes and fibroblasts, which are early targets of mosquito-transmitted DENV infection. From this screen, we identified 23 nucleoside analogs with broad antiviral activity against DENV and focused on two purine analogs UPGNUC255 and UPGNUC558, that demonstrated potent pan-flaviviral activity achieving >10-fold viral load reduction across all four DENV serotypes and other flaviviruses across cell models. Mechanistic studies revealed that both compounds target the viral RNA-dependent RNA polymerase (RdRp) domain of NS5. Resistance to UPGNUC558 was associated with a conserved S604T substitution, conferring cross-resistance to other 2'C-substituted nucleoside analogs. Resistance to UPGNUC255 was linked to a previously unknown R355Q mutation, located near the catalytic GDD motif of RdRp. These findings highlight UPGNUC255 and UPGNUC558 as promising leads for the development of broad-spectrum antiviral agents against flaviviruses.

Translocation of Campylobacter concisus from the oral cavity to the intestinal tract is increasingly recognised as a contributor to inflammatory bowel disease (IBD). The C. concisus secreted protein Csep1 has emerged as a molecular marker of C. concisus strains associated with Crohn's disease, a form of IBD. However, its structure and role in inflammation remain unknown. Here, we report the X-ray crystal structure of plasmid-encoded Csep1P that reveals a unique α-helical fold with structural similarity to Helicobacter pylori cysteine-rich proteins HcpB and HcpC. Because HcpA, another Hcp family member, is known to affect monocyte differentiation, this structural similarity led us to hypothesise that Csep1P may modulate monocyte differentiation and macrophage function. Transcriptomic analysis revealed that Csep1P induced a chemokine-dominant inflammatory state in macrophages, M1-chem. Protein-level validation in both THP-1-derived and primary human macrophages confirmed this selective chemokine response. While Csep1P alone did not upregulate proinflammatory cytokines, THP-1-derived macrophages pre-incubated with Csep1P produced a higher level of proinflammatory cytokines in response to commensal Escherichia coli, which was validated on primary human macrophages. Furthermore, silencing the delta like canonical notch ligand 4 (DLL4) gene decreased the proinflammatory response of Csep1P-mediated macrophages to E. coli. Collectively, our data demonstrate that the structurally unique Csep1P reprograms macrophage response, which provides a mechanistic link between C. concisus infection and Crohn's disease pathogenesis, and identifies Csep1P as a potential target for therapeutic intervention.

Bordetella atropi is an intracellular bacterial pathogen that infects the intestinal epithelia of the nematode host Oscheius tipulae. We previously showed that the bacteria use filamentation as a novel cell-to-cell spreading mechanism once inside the intestinal cell. However, how the bacteria invade the host cells and what factors contribute to B. atropi infection process remain unknown. In this study, we investigate the roles of type III (T3SS) and type VI secretion systems (T6SS) in B. atropi pathogenesis, which are employed by many bacterial pathogens, both extracellular and intracellular, to deliver effectors that manipulate host physiology to their advantage. We found that the two T6SSs encoded in B. atropi genome played no obvious roles in the invasion or intracellular spreading. In contrast, a T3SS was required for intestinal cell invasion. T3SS mutants showed loss of host cell protrusions from the apical surface that normally engulf invading wild type bacteria, as seen by both electron microscopy and confocal fluorescent microscopy. These protrusions bear morphological similarities to membrane ruffles triggered by the T3SS-mediated invasion seen in other pathogens such as Salmonella and Shigella spp. Additionally, we conducted dual transcriptomics and saw upregulation of T3SS in vivo, along with several putative effectors and the virulence regulator BvgS of the genus Bordetellae. We knocked out these effector candidates and found that deletion of one of these genes, deiA (decreased invasion protein A), leads to a reduction in the number of invasion events and overall percentage of infected animals in the population. In addition, deletion of the virulence regulator bvgS resulted in a complete loss of B. atropi invasion, suggesting it may regulate T3SS for host cell invasion.

The World Health Organisation has identified Acinetobacter baumannii as a critical priority antimicrobial resistant (AMR) pathogen for which new therapeutics are needed. Despite this, currently there are no antibody or vaccine candidates in advanced clinical development for A. baumannii. To help address this, we designed a protein microarray approach to identify multiple A. baumannii protein antigens for further investigation as potential targets for vaccination or an antibody therapy. An 868-protein microarray was constructed containing mainly highly conserved A. baumannii proteins, and was enriched for those predicted to be surface localised and for which the corresponding gene is highly expressed during culture in ex vivo human serum. Probing the protein microarray with sera obtained from mice after non-lethal infection with multiple different A. baumannii strains identified IgG responses to 66 proteins. Four proteins (three previously poorly described outer membrane proteins and BamA, a known protective vaccine antigen selected as a positive control) were selected for further investigation. Polyclonal rabbit IgG to all four protein antigens recognised multiple clinical AMR A. baumannii strains, and for selected strains promoted opsonisation with IgG and complement, improved neutrophil phagocytosis, and increased membrane attack complex formation. Passive immunisation with polyclonal IgG to each antigen partially protected mice against A. baumannii sepsis, and a combination of polyclonal to two antigens completely protected against A. baumannii murine sepsis. Repeating passive immunisation experiments in mice depleted of complement, neutrophils or tissue macrophages demonstrated protection against systemic infection was dependent on complement and neutrophils but not macrophages. Overall, the data demonstrate that our protein microarray is a novel approach that can rapidly identify multiple new protein antigens as potential antibody targets for preventing or treating AMR bacterial infections.

Staphylococcus aureus (S. aureus)-driven senescence of bovine mammary epithelial cells is a key determinant of mammary gland health, yet its molecular basis remains poorly defined. Sirtuin 5 (SIRT5), a mitochondria-localized desuccinylase, may play an important regulatory role in this process. This study aimed to elucidate the mechanisms by which S. aureus drives cellular senescence and to define the contribution of the SIRT5-mitochondrial axis to delaying senescence. We found pronounced oxidative stress and cellular senescence in mammary tissues from cows with S. aureus mastitis, accompanied by marked downregulation of SIRT5. In an S. aureus-infected epithelial cell model, infection induced mitochondrial stress characterized by excessive mitochondrial fragmentation, loss of membrane potential, and increased mitochondrial superoxide, along with oxidative damage and cellular senescence. Mechanistically, S. aureus toxins and the toxin-induced inflammatory response cooperatively drove mitochondrial stress, which in turn increased intracellular bacterial burden and exacerbated cell death. During infection, SIRT5 protein abundance was significantly reduced. Mass spectrometry and co-immunoprecipitation analyses indicated that infection upregulated the ubiquitin-conjugating enzyme ubiquitin C (UBC), enhanced its interaction with SIRT5, and promoted ubiquitin-mediated degradation of SIRT5. Loss of SIRT5 increased succinylation of dynamin-related protein 1 (DRP1), inhibited its ubiquitin-mediated degradation, and led to its excessive accumulation on the outer mitochondrial membrane, thereby promoting excessive mitochondrial fission. Functionally, SIRT5 overexpression markedly alleviated mitochondrial stress, oxidative damage, and senescence phenotypes. When mitochondrial fission was forcibly enhanced, the cytoprotective effect of SIRT5 was substantially weakened, confirming that SIRT5 acts through a pathway dependent on mitochondrial integrity. Collectively, S. aureus infection releases toxins and induces inflammatory injury, during which UBC-mediated SIRT5 degradation activates DRP1-dependent mitochondrial hyper-fragmentation, aggravating mitochondrial stress, oxidative stress, and mammary epithelial cell senescence. These findings identify SIRT5 as a critical regulator of redox and mitochondrial homeostasis in mammary epithelial cells and a potential therapeutic target for mitigating oxidative damage associated with bovine mastitis.

The caseinolytic protease (ClpP) is an emerging antibacterial target. Pseudomonas plecoglossicida (Pp), a pathogen causing visceral white spot disease in Larimichthys crocea, encodes two ClpP paralogs, PpClpP1 and PpClpP2. This study characterizes their distinct structural and functional properties. Phylogenetic and biochemical analysis revealed that PpClpP2 functions as a canonical serine protease with high peptidase activity, while PpClpP1 is evolutionarily divergent, exhibiting low inherent activity due to an unconventional Ser-His-Pro catalytic triad and a truncated N-terminal domain. Cryo-EM structure determination of PpClpP1 confirmed a homotetradecameric assembly with a dilated axial pore and a non-canonical catalytic geometry. In contrast, AlphaFold-predicted PpClpP2 displayed a compact structure with a canonical Ser-His-Asp triad. The subunits formed a stable heterotetradecamer (PpClpP1P2) with enhanced proteolytic activity compared to individual homotetradecameric. Pull-down assays demonstrated that PpClpP2, but not PpClpP1, specifically interacts with the unfoldase PpClpX, and the PpClpP1P2 heterotetradecamer further augmented PpClpX-mediated degradation of model substrates. Notably, the proteasome inhibitor bortezomib (BTZ) selectively inhibited PpClpP1 by binding to a unique pocket near the active site without engaging the catalytic serine, thereby suppressing bacterial growth in a PpClpP1-dependent manner. This study elucidates the structural basis of functional divergence between PpClpP paralogs, highlights their synergistic interplay in proteolysis, and identifies PpClpP1 as a druggable target for antibacterial development.

Sepsis is a life-threatening condition characterized by a dysregulated immune response to infection, often leading to organ dysfunction and even death. During the recovery phase of sepsis, patients frequently exhibit impaired antimicrobial function of immune cells, which exacerbates the state of immunosuppression and increases the risk of secondary infections. However, therapeutic strategies targeting sepsis-induced immunosuppression have yet to achieve breakthrough progress, with the core challenge lying in the significant gaps in understanding the molecular mechanisms underlying immunosuppression. In this study, we integrated clinical samples, mouse models, and molecular mechanisms to reveal that the reduction in macrophage function and epigenetic dysregulation, particularly histone ubiquitination, are central drivers of sepsis-induced immunosuppression. Further investigation demonstrated that MYSM1, a deubiquitinase, plays a pivotal role in regulating this ubiquitination process. Targeted deletion of the N-terminal domain of MYSM1 markedly enhances the inflammatory response during the early phase of secondary infection in sepsis, facilitating bacterial clearance and significantly mitigating tissue damage in the late phase of secondary infection, thereby improving the survival outcomes in mice. Overall, our study elucidates the role of MYSM1-mediated dysregulation of epigenetic modifications in the immune response during the late phase of sepsis, providing a novel therapeutic approach for addressing sepsis-related immune dysfunction.

Careful regulation of type I interferons (IFN) like IFN-β is vital for balancing tissue damage and protection against infections. Heterogeneity in type I IFN expression among virally infected cells is a common phenomenon that may help limit IFN responses, but the source of this heterogeneity is poorly understood. We previously found that during Kaposi's sarcoma-associated herpesvirus replication, type I IFN induction was limited to a small percentage of infected cells. This heterogeneity was not explained by viral gene expression. Here, we used a fluorescent reporter and fluorescence activated cell sorting to investigate the source of the heterogeneity. Surprisingly, the canonical IFN induction pathway culminating in the activation of the IRF3 transcription factor was similarly activated between cells that made high vs. low/no IFN-β. In contrast, the activation or expression of the two other IFN transcription factors, the NF-κB subunit RelA and the AP-1 subunit ATF2, correlated with IFN-β induction. Our results suggest that during viral infection, activation of IRF3 does not automatically result in IFN responses at the level of individual cells, but that other factors, such as NF-κB and AP-1, are limiting for type I IFN induction.