PLoS Pathogens最新文献

Sterile alpha motif and histidine-aspartate domain-containing protein 1 (SAMHD1) restricts a broad spectrum of viruses through multifaceted mechanisms. It also limits spontaneous- and virus-induced innate immune responses by suppressing proinflammatory cytokine and type-I interferon (IFN-I) production. Some viruses escape SAMHD1 restriction and utilize SAMHD1-mediated innate immune suppression to establish effective infection through IFN antagonism. Our previous studies showed that SAMHD1 is a proviral factor facilitating replication of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) in human macrophages, monocytic THP-1 and epithelial-like HEK293T cell lines by suppressing IFN responses. However, it is unclear about the function of SAMHD1 in lung epithelial cells during SARS-CoV-2 infection. Here, we report that SAMHD1 knockout (KO) restricts SARS-CoV-2 replication in lung epithelial Calu-3 cells by suppressing endogenous expression of the viral receptor angiotensin-converting enzyme 2 (ACE2) via hepatocyte nuclear factor 1-alpha (HNF1α) and HNF1β. Using pseudotyped SARS-CoV-2 and lentiviral vectors, we found that SARS-CoV-2 spike protein-mediated viral entry was suppressed in SAMHD1 KO Calu-3 cells. SAMHD1 KO repressed ACE2 expression in Calu-3 cells at mRNA and protein levels. Functional analyses revealed that HNF1α and HNF1β were crucial for the endogenous ACE2 expression in Calu-3 cells. Additionally, SAMHD1 KO led to a reduction in the expression levels and ACE2-promoting function of HNF1α and HNF1β. Inhibition of IFN antiviral response by baricitinib, a Janus kinase 1 and 2 (JAK 1/2) inhibitor, did not revert the suppression of SARS-CoV-2 in SAMHD1 KO Calu-3 cells. SAMHD1 knock-in and deoxynucleoside supplementation experiments indicated that SAMHD1 expression and dNTP pool balance collectively regulated HNF1-mediated ACE2 expression in Calu-3 cells. Our findings demonstrate that SAMHD1 depletion hinders HNF1-mediated ACE2 expression and SARS-CoV-2 replication in Calu-3 cells via a novel mechanism beyond its IFN-suppressive function.

[This corrects the article DOI: 10.1371/journal.ppat.1013136.].

The tegument protein UL51 is conserved among herpesviruses, but the mechanisms underlying its role in viral pathogenesis remain unclear. In this study, using Anatid herpesvirus 1 (AnHV-1) as a model, we show that deletion of UL51 markedly attenuates viral replication and virulence in ducks. Immunoprecipitation coupled with LC-MS/MS identified interactions between pUL51 and multiple viral proteins, among which the association with pUL10 depends on pUL51 palmitoylation. This modification promotes pUL10 stability and its localization to the Golgi apparatus. Further analysis revealed that the palmitoylation of pUL51 is mediated by the host palmitoyltransferases DHHC9 and DHHC18 and is required to maintain pUL51 stability by preventing ubiquitin-proteasome-mediated degradation. Moreover, the deletion of pUL51 led to the accumulation of incompletely enveloped viral particles in the cytoplasm, and fewer viral particles were present within multivesicular bodies (MVBs), suggesting that pUL51 facilitates viral particle recruitment to MVBs for secondary envelopment. A palmitoylation-deficient (C9A) mutant of pUL51 also exhibited impaired viral replication, defective secondary envelopment, and attenuated virulence. These findings indicate that palmitoylation is a critical modification for pUL51 function, ensuring proper subcellular localization and promoting virion maturation, and highlight its potential as an antiviral target.

Hepatitis E virus genotype 1 (HEV-1) has long been considered human-specific, with no known natural animal hosts. Here, we demonstrate that three wild rodent species-Apodemus peninsulae, Clethrionomys rufocanus, and Lasiopodomys brandtii-are susceptible to HEV-1 infection. Among them, A. peninsulae infected with HEV-1 exhibited the highest susceptibility, characterized by robust fecal viral shedding, systemic viral replication, seroconversion, and mild liver pathology mimicking human acute HEV-1 infection. Intrahepatic transcriptomic analysis of infected animals revealed activation of inflammatory pathways, including upregulation of IL-1β and IL-18. Re-inoculation experiments confirmed infection-induced protective immunity, and ribavirin treatment effectively suppressed viral replication. HEV-1 infection can be established by oral gavage inoculation, close contact and vertical transmission. These results provide solid evidence that wild rodents can serve as potential hosts for HEV-1, highlighting the potential role of wild rodents in HEV-1 ecology and cross-species transmission.

As a first line of host defense, macrophages must be able to effectively sense and respond to diverse types of pathogens, and while a particular response may be beneficial in some circumstances, it can be detrimental in others. Upon infection, Mycobacterium tuberculosis (Mtb) induces proinflammatory cytokines and activates antibacterial responses. Surprisingly, Mtb also triggers antiviral responses that actually hinder the ability of macrophages to restrict Mtb growth. In Mtb-infected macrophages, the ubiquitin ligase CBL suppresses antiviral responses and preserves the antibacterial capacity of the macrophage. However, the mechanisms by which CBL regulates immune signaling are unknown. We found that CBL controls responses to multiple immune stimuli and broadly suppresses the expression of antiviral response genes. We used mass spectrometry to identify potential CBL substrates, and found, in total, over 46,000 ubiquitylated peptides in Mtb-infected macrophages, including roughly 400 peptides with CBL-dependent ubiquitylation. We then performed genetic interaction analysis of CBL and its putative substrates, and identified the Fas-associated factor 2 (FAF2) adapter protein as a key signaling molecule downstream of CBL. Together, these analyses reveal thousands of new ubiquitin-mediated signaling events and identify an important new regulator of immune signaling.

Malaria control is challenged by the emergence of resistance to virtually all antimalarial drugs, from the frontline artemisinin to other classes, highlighting the critical need for new therapies. This study demonstrates that the human antimicrobial peptide LL-37 exhibits antiplasmodial activity against both drug-sensitive and drug-resistant parasites in vitro. LL-37 selectively targets infected red blood cells through membrane disruption mediated by phosphatidylserine externalization and cholesterol depletion. Elevated plasma LL-37/CRAMP levels were observed in malaria patients and infected mice, and exogenous LL-37/CRAMP administration reduced parasitemia, improved survival, and modulated pro-inflammatory cytokine levels in a mouse model. CRAMP-deficient mice showed higher susceptibility to infection, underscoring its role in host defense. Our findings reveal a naturally occurring host defense mechanism centered on LL-37/CRAMP, which acts through direct targeting of the infected erythrocyte membrane. However, therapeutic administration after infection establishment showed limited efficacy, likely due to rapid peptide degradation in vivo, and the effective concentrations required for direct killing in vitro are substantially higher than endogenous systemic levels. The reduction in systemic cytokines observed in treated mice is likely primarily attributable to decreased parasite burden rather than direct immunomodulation. Further studies are needed to evaluate stabilized analogs, optimized delivery strategies, and combination approaches before therapeutic applications can be considered.

The mosaic penA allele (penA41) from H041, the most ceftriaxone-resistant Neisseria gonorrhoeae strain identified to date, encodes a variant of the essential Penicillin-Binding Protein 2 (PBP2) with 60 amino acid mutations compared to PBP2 from the antimicrobial-susceptible strain, FA19. Based on previous work from our lab and others, we identified a minimal set of 10 mutations that, when introduced into the β-lactam antibiotic-susceptible penA allele from FA19 (penA19), confers two-thirds of the ceftriaxone and cefixime resistance compared to the penA41 allele. Three mutations (A311V, I312M, and V316P) are in the α2 helix of PBP2 containing the catalytic serine (Ser310), two (F504L and N512Y) are in the β3-β4 loop that is important in binding and acylation, and one (G545S) interacts with conserved amino acids in the active site. The seventh mutation, T483S, confers substantial resistance to ceftriaxone within the minimal mutant set but requires the presence of three epistatic mutations located on the other side of the protein that do not alter resistance on their own yet are necessary to retain essential function. These epistatic mutations change the backbone dihedral angles at position-447, which may increase flexibility of the enzyme and help maintain enzymatic function. Our results highlight the complex balance necessary for evolving cephalosporin resistance in PBP2 while also retaining sufficient transpeptidase function to support growth.

Trichinella spiralis (T. spiralis), a zoonotic nematode that causes severe myositis and systemic morbidity, sustains chronic muscle parasitism through evolutionary adaptations; however, this globally prevalent disease lacks targeted therapies to disrupt chronic infection. Although the heme transport protein HRG-1 has been characterized as an intervention target in free-living species (e.g., Caenorhabditis elegans) and hematophagous parasites (e.g., Haemonchus contortus), the molecular machinery governing heme acquisition in the nonhematophagous parasite T. spiralis remains uncharacterized, and no drugs targeting HRG-1 have been reported until now. Herein, we demonstrate that T. spiralis, a parasite that lacks the ability to synthesize heme autonomously, has evolved a sophisticated mechanism to scavenge and utilize heme from its host. By employing an aspartic protease to degrade host hemoglobin and myoglobin in the parasitic niche, T. spiralis is able to liberate heme for its own growth and survival. The structurally and functionally conserved Ts-HRG-1 protein plays a key role in transporting heme to the entire worm, particularly to functional organs, such as the cuticle and stichosome. More importantly, we discovered that the interaction between Ts-HRG-1 and Ts-ATP6V0C results in the formation of a functional complex that is essential for the parasite's heme acquisition. The intervention effect achieved by Ts-ATP6V0C RNAi or inhibiting the activity of Ts-ATP6V0C with bafilomycin A1 (BafA1) was consistent with Ts-HRG-1 RNAi, resulting in impaired heme uptake, developmental arrest and a reduced larval burden in mouse hosts. These findings enhance our understanding of the parasite's heme acquisition mechanism and identify the development of drugs that target proteins that interact with HRG-1 as a new direction in anthelminthic drug research.

Tissue resident memory CD4+ T cells (TRMs) populate mucosal sites and play a critical role in local immune responses. Gut TRM cells persist for extended periods in the gut mucosa where they rapidly respond to invading pathogens and provide long lasting protection. This study investigates the factors that mediate differentiation of naïve CD4+ T cells into cells presenting a gut TRM phenotype. Naïve CD4+ T cells were cultured under conditions that mimicked mucosal environments. This included signaling through MAdCAM-1 in the presence of Retinoic Acid (RA) and TGF-β. This combination of stimuli primed naïve CD4+ T cells to adopt a TRM phenotype. However, to fully differentiate into TRMs an additional soluble factor provided by memory T cells was required. Our results identified IL-6 as one of the key factors that induces the expression of TRM -associated markers, including CD69, CD103 and CCR5. This unique combination of stimuli promoted TRM differentiation despite low level proliferation. TRM differentiation was mediated through JAK/STAT signaling, and antagonists that target JAK/STAT pathways suppressed MAdCAM-1 mediated TRM cell formation. Our findings revealed that MAdCAM-1 works together with TGF-β, RA and IL-6 in this process. Such information may aid in the design of next generation adjuvants and effective mucosal vaccines. Additionally, each of these factors may be targeted to treat excessive gut inflammation associated with conditions like inflammatory bowel disease. Overall, these findings provide new strategies aimed at modulating immune responses to invading pathogens and identify therapeutic approaches toward regulating gut inflammation.

Leishmania amastigotes ingested by female phlebotomine sand flies are exposed to a harsh and dynamic environment that differs markedly from the intracellular niche in the mammalian host in temperature, pH and nutrient availability. Membrane transporter proteins, channels and pumps play a crucial role in maintaining cellular physiology under changing environments. A systematic loss-of-function screen of the L. mexicana transporter deletion mutants in macrophage and mouse infections previously identified transporter genes important for the amastigote stage. To test which transporters are important for the promastigote stage in the insect vector, we measured the fitness of gene deletion mutants in Lu. longipalpis sand flies. Pooled libraries of different complexities, consisting of 71-317 barcoded parasite lines allowed for an estimation of the bottleneck size in experimental infections, providing a foundation for similar experimental bar-seq studies. The fitness of each mutant parasite line was measured by tracking population composition over a course of 9 days in the sand flies and compared with the growth fitness of promastigotes over 7 days in laboratory cultures. There was a high correlation of fitness scores in vitro and in vivo, but 34 mutants showed a loss of fitness only in vivo, including deletion mutants of vacuolar H + ATPase (V-ATPase) subunits. V-ATPase deletion mutants expressed low levels of the metacyclic-specific transcript sherp in vitro and failed to generate metacyclic promastigotes in sand flies, indicating that V-ATPase function is required for parasite differentiation and progression through the Leishmania life cycle.