Folate metabolism negatively regulates OAS-mediated antiviral innate immunity via ADAR3/endogenous dsRNA pathway

Research progress on immune mechanism and control strategy of dsRNA impurities in mRNA vaccine

INTRODUCTION

Double-stranded RNA (dsRNA) is a key impurities of mRNA vaccines prepared by in vitro transcription (IVT) and is primarily transcribed by T7 RNA polymerase. It can trigger innate immunity and induce a series of side effects that may influence the safety of mRNA vaccines.

AREAS COVERED

This manuscript summarizes dsRNA generation mechanisms and immunity activation and analyzes the current challenges in dsRNA detection and control strategies. Regulatory standards for dsRNA impurities in mRNA vaccines have also been discussed.

EXPERT OPINION

dsRNA as a critical quality attribute (CQA), the structural heterogeneity of it (including length and structure) and its precise immunomodulatory mechanisms affecting vaccine safety are poorly understood. Regulatory authorities have not released specific standards for dsRNA. Additionally, there is a lack of comparative analysis data on different corporate testing methods. Therefore, to ensure the safety of dsRNA containing mRNA vaccines, and improve mRNA-based platforms, it is of great significance to establish standardized detection methods and standards for dsRNA; to design mRNA production with low dsRNA impurities by adopting the quality by design (QbD) approach; and to evaluate the immune stimulation mechanism of dsRNA impurities in mRNA vaccines.

Astrocytes-derived LCN2 triggers EV-A71-induced muscle soreness via accumulating lactate

Viral muscle soreness (VMS) is a common feature during acute viral infections, including those caused by enteroviruses, and it substantially diminishes patients' quality of life. At present, we aim to establish the "brain-muscle" axis to explore the underlying mechanisms of VMS. We initially observed that diminished pain threshold occurred in enterovirus A71 (EV-A71)-infected C57BL/6J and AG6 mice. Subsequently, RNA sequencing data showed that lipocalin 2 (LCN2) was up-regulated during multiple viral infections, including EV-A71, Japanese encephalitis virus, vesicular stomatitis virus, and West Nile virus, which all caused VMS. As expected, Lcn2-deficient C57BL/6 J (Lcn2-/-) mice exhibited greater pain tolerance, as shown by stronger grip force and stable motor function after EV-A71 infection. Mechanistically, EV-A71-induced high-mobility group 1 (HMGB1) stimulated astrocyte-derived LCN2 secreted into the circulatory system, which enhanced glycolysis and induced lactate buildup in muscle through increasing pyruvate dehydrogenase kinase 1 (PDK1) expression and decreasing pyruvate dehydrogenase (PDH) activity. Together, HMGB1/LCN2/PDK1/lactate pathway in the brain-muscle axis promoted VMS development.

High throughput recurrent pregnancy loss screening: urine metabolic fingerprints via LDI-MS and machine learning

Infertility is a significant challenge faced by many families worldwide, with recurrent pregnancy loss (RPL) being a prevalent cause of infertility among women. This condition causes immense emotional and physical distress for affected individuals and their families. In this study, we present a rapid, efficient, and high-throughput analytical method using PS@Fe3O4-NH2 magnetic beads as a matrix for the detection of urinary metabolite fingerprints in RPL patients via laser desorption/ionization mass spectrometry (LDI-MS) combined with machine learning (ML). This approach offers rich metabolic information from urine samples, through subsequent analysis we identify 17 metabolites that significantly differ between RPL patients and healthy controls (HC). The application of mass spectrometry features in conjunction with ML enabled effective screening of RPL patients and the identification of dysregulated metabolic pathways. This method presents a promising, non-invasive, and rapid screening approach for early detection of RPL, facilitating timely intervention and contributing to women's health.

FTO-associated osteoclastogenesis promotes alveolar bone resorption in apical periodontitis male rat via the HK1/USP14/RANK pathway

Alveolar bone resorption (ABR) is a key pathological manifestation in the development of apical periodontitis (AP) and contributes to the AP-associated tooth loss among AP patients in the clinic. However, the underlying mechanism of ABR development is largely unknown. Here we show, the total levels of N6-methyladenosine (m6A) were reduced in AP male rat alveolar bone tissues and BMDM-derived osteoclasts (OC), which was associated with the up-regulation of obesity-associated protein (FTO). Subsequently FTO-mediated hexokinase (HK1) demethylation modification enhancing glycolytic pathway that stabilizes receptor activator of NF-κB (RANK) protein via the deubiquitination activity of ubiquitin-specific protease 14 (USP14), which further promotes osteoclastogenesis to participate in the AP-related ABR development. Finally, Dac51 (an FTO inhibitor) and 2-DG (an HK1 inhibitor) both exhibit the inhibitory activity of osteoclastogenesis. Our current study reveals a molecular mechanism on osteoclastogenesis-related ABR and provides a therapeutic target of AP via modulating the FTO/HK1/USP14/RANK axis.

6-thioguanine inhibits EV71 replication by reducing BIRC3-mediated autophagy

BACKGROUND

Enterovirus 71 (EV71) is one of the major causative agents of hand, foot, and mouth disease (HFMD), and can cause severe cerebral complications and even fatality in children younger than 5 years old. However, there is no specific medication for EV71 infection in clinical practice. Our previous studies had identified the 6-thioguanine (6-TG), an FDA-approved anticancer drug, as a potential antiviral agent, but its anti-EV71 activity is largely unknown, therefore, we aim to explore the antiviral effect of 6-TG on EV71.

RESULTS

6-TG significantly suppressed EV71 mRNA level, VP1 protein expression, and viral progeny production in HT-29 cells. In EV71-infected HT-29 cells, the 50% cytotoxicity concentration of 6-TG (CC50) was > 2000 µM and the 50% inhibitory concentration of 6-TG against EV71 (IC50) was 0.9302 µM. Interestingly, the selectivity index (SI) value of 6-TG against EV71 was > 2150.1, which was higher than the SI value (> 66.7) of ribavirin. Mechanistically, 6-TG treatment reduced the expression of baculoviral IAP repeat containing 3 (BIRC3), and further inhibited EV71 replication by attenuating BIRC3-mediated the complete autophagy.

CONCLUSIONS

6-TG exerted a significant inhibitory effect on EV71 infection in vitro and prevented EV71-induced the complete autophagy by decreasing BIRC3 expression. Our work provided a basis for the further development of 6-TG as a therapy for EV71-associated HFMD.

Trained immunity of intestinal tuft cells during infancy enhances host defense against enteroviral infections in mice

Innate immune cells have been acknowledged as trainable in recent years. While intestinal tuft cells are recognized for their crucial roles in the host defense against intestinal pathogens, there remains uncertainty regarding their trainability. Enterovirus 71 (EV71), a prevalent enterovirus that primarily infects children but rarely infects adults. At present, there is a significant expansion of intestinal tuft cells in the EV71-infected mouse model, which is associated with EV71-induced interleukin-25 (IL-25) production. Further, we found that IL-25 pre-treatment at 2 weeks old mouse enabled tuft cells to acquire immune memory. This was evidenced by the rapid expansion and stronger response of IL-25-trained tuft cells in response to EV71 infection at 6 weeks old, surpassing the reactivity of naïve tuft cells in mice without IL-25-trained progress. Interestingly, IL-25-trained intestinal tuft cells exhibit anti-enteroviral effect via producing a higher level of IL-25. Mechanically, IL-25 treatment upregulates spermidine/spermine acetyl-transferase enzyme (SAT1) expression, mediates intracellular polyamine deficiency, further inhibits enterovirus replication. In summary, tuft cells can be trained by IL-25, which supports faster and higher level IL-25 production in response to EV71 infection and further exhibits anti-enteroviral effect via SAT1-mediated intracellular polyamine deficiency. Given that IL-25 can be induced by multiple gut microbes during human growth and development, including shifts in gut flora abundance, which may partially explain the different susceptibility to enteroviral infections between adults and children.

Nuclear aggregates of NONO/SFPQ and A-to-I-edited RNA in Parkinson's disease and dementia with Lewy bodies

Neurodegenerative diseases are commonly classified as proteinopathies that are defined by the aggregation of a specific protein. Parkinson's disease (PD) and dementia with Lewy bodies (DLB) are classified as synucleinopathies since α-synuclein (α-syn)-containing inclusions histopathologically define these diseases. Unbiased biochemical analysis of PD and DLB patient material unexpectedly revealed novel pathological inclusions in the nucleus comprising adenosine-to-inosine (A-to-I)-edited mRNAs and NONO and SFPQ proteins. These inclusions showed no colocalization with Lewy bodies and accumulated at levels comparable to α-syn. NONO and SFPQ aggregates reduced the expression of the editing inhibitor ADAR3, increasing A-to-I editing mainly within human-specific, Alu-repeat regions of axon, synaptic, and mitochondrial transcripts. Inosine-containing transcripts aberrantly accumulated in the nucleus, bound tighter to recombinant purified SFPQ in vitro, and potentiated SFPQ aggregation in human dopamine neurons, resulting in a self-propagating pathological state. Our data offer new insight into the inclusion composition and pathophysiology of PD and DLB.

Analyzing the impact of synthetic and natural steroids: a study of cytochrome P450 metabolism, morphological alterations through metabolomics, and histopathological Examination

This study focuses on the comparative metabolic profiling and effects of two steroid types: natural and synthetic, specifically 17α-methyl testosterone (17α-MT) at varying concentrations (1.5, 2, and 3 mg/kg) in rainbow trout (Oncorhynchus mykiss). Over a 75-day feeding trial, growth metrics, such as feed efficiency, daily specific growth, live weight gain, total weight gain, and survival rate were systematically monitored every 15 days. At the end of the feeding trial, histopathology, immunohistochemistry, and metabolome analyses were performed in the high-concentration groups (3 mg/kg natural and 3 mg/kg synthetic), in which the lowest survival rate was determined. Key findings reveal that the type of hormone significantly influences growth parameters. While some natural steroids enhanced certain growth aspects, synthetic variants often yielded better results. The metabolomic analysis highlighted significant shifts in the metabolism of tryptophan, purine, folate, primary bile acids, phosphonates, phosphinates, and xenobiotics via cytochrome P450 pathways. Histopathologically, the natural hormone groups showed similar testicular, hepatic, muscular, gill, cerebral, renal, and intestinal tissue structures to the control, with minor DNA damage and apoptosis observed through immunohistochemistry. Conversely, the synthetic hormone groups exhibited moderate DNA damage and mild degenerative and necrotic changes in histopathology.

Unraveling the Role of RNase L Knockout in Alleviating Immune Response Activation in Mice Bone Marrow after Irradiation

Ionizing radiation (IR) induces severe hematopoietic injury by causing DNA and RNA damage as well as activating the immune responses, necessitating the development of effective therapeutic strategies. Ribonuclease L (RNase L) as an innate immune response pathway is triggered by exogenous and endogenous abnormal dsRNA under viral infection and dyshomeostasis, thereby activating the immune responses. Thus, we investigated the effect of RNase L on irradiation-induced bone marrow damage using RNase L knockout (RNase L-/-) mice. Phenotypic analysis revealed that RNase L knockout mitigates irradiation-induced injury in the bone marrow. Further investigation into the mechanism of RNase L by RNA-seq, qRT-PCR, and CBA analysis demonstrated that RNase L deficiency counteracts the upregulation of genes related to immune responses induced by irradiation, including cytokines and interferon-stimulated genes. Moreover, RNase L deficiency inhibits the increased levels of immunoglobulins in serum induced by irradiation. These findings indicate that RNase L plays a role in the immune response induced by irradiation in the bone marrow. This study further enhances our understanding of the biological functions of RNase L in the immune response induced by irradiation and offers a novel approach for managing irradiation-induced bone marrow injury through the regulation of RNase L activation.

Folate supports IL-25-induced tuft cell expansion following enteroviral infections

Intestinal tuft cells, a kind of epithelial immune cells, rapidly expand in response to pathogenic infections, which is associated with infection-induced interleukin 25 (IL-25) upregulation. However, the metabolic mechanism of IL-25-induced tuft cell expansion is largely unknown. Folate metabolism provides essential purine and methyl substrates for cell proliferation and differentiation. Thus, we aim to investigate the roles of folate metabolism playing in IL-25-induced tuft cell expansion by enteroviral infection and recombinant murine IL-25 (rmIL-25) protein-stimulated mouse models. At present, enteroviruses, such as EV71, CVA16, CVB3, and CVB4, upregulated IL-25 expression and induced tuft cell expansion in the intestinal tissues of mice. However, EV71 did not induce intestinal tuft cell expansion in IL-25-/- mice. Interestingly, compared to the mock group, folate was enriched in the intestinal tissues of both the EV71-infected group and the rmIL-25 protein-stimulated group. Moreover, folate metabolism supported IL-25-induced tuft cell expansion since both folate-depletion and anti-folate MTX-treated mice had a disrupted tuft cell expansion in response to rmIL-25 protein stimulation. In summary, our data suggested that folate metabolism supported intestinal tuft cell expansion in response to enterovirus-induced IL-25 expression, which provided a new insight into the mechanisms of tuft cell expansion from the perspective of folate metabolism.

Pralatrexate inhibited the replication of varicella zoster virus and vesicular stomatitis virus: An old dog with new tricks

Varicella zoster virus (VZV) is associated with herpes zoster (HZ) or herpes zoster ophthalmicus (HZO). All antiviral agents currently licensed for the management of VZV replication via modulating different mechanisms, and the resistance is on the rise. There is a need to develop new antiviral agents with distinct mechanisms of action and adequate safety profiles. Pralatrexate (PDX) is a fourth-generation anti-folate agent with an inhibitory activity on folate (FA) metabolism and has been used as an anti-tumor drug. We observed that PDX possessed potent inhibitory activity against VZV infection. In this study, we reported the antiviral effects and the underlying mechanism of PDX against VZV infection. The results showed that PDX not only inhibited VZV replication in vitro and in mice corneal tissues but also reduced the inflammatory response and apoptosis induced by viral infection. Furthermore, PDX treatment showed a similar anti-VSV inhibitory effect in both in vitro and in vivo models. Mechanistically, PDX inhibited viral replication by interrupting the substrate supply for de novo purine and thymidine synthesis. In conclusion, this study discovered the potent antiviral activity of PDX with a novel mechanism and presented a new strategy for VZV treatment that targets a cellular metabolic mechanism essential for viral replication. The present study provided a new insight into the development of broad-spectrum antiviral agents.

Characterization and function of Japanese flounder (Paralichthys olivaceus) slc2a6 in response to lymphocystis disease virus infection

Slc2a6 is a member of the slc2 family (solute carrier 2 family) and previous reports have indicated its involvement in the inflammatory response. Slc2a6 is regulated by the NF-ĸB signaling pathway. This study investigated the differential expression of slc2a6 in the early embryonic development of Japanese flounder, revealing that the early gastrula stage had the highest level of slc2a6 expression. Moreover, slc2a6 expression was increased in vitro after stimulation by lymphocystis disease virus (LCDV), and in vivo experiments also showed significantly elevated levels in the spleen and muscle tissues following LCDV stimulation. Subcellular localization revealed that Slc2a6 was expressed in both the nucleus and cytoplasm of cells. The pcDNA3.1-slc2a6 overexpression plasmid was successfully constructed; the si-slc2a6 interfering strand was screened and samples were collected. The expression of NF-ĸB signaling pathway-related genes il-1β, il-6, nf-ĸb, and tnf-α was evaluated in overexpressed, silenced, and LCDV-stimulated samples. The results showed that slc2a6 is involved in viral regulation in Japanese flounder by regulating innate immune responses.

FOLR1-induced folate deficiency reduces viral replication via modulating APOBEC3 family expression

Folate receptor alpha (FOLR1) is vital for cells ingesting folate (FA). FA plays an indispensable role in cell proliferation and survival. However, it is not clear whether the axis of FOLR1/FA has a similar function in viral replication. In this study, we used vesicular stomatitis virus (VSV) to investigate the relationship between FOLR1-mediated FA deficiency and viral replication, as well as the underlying mechanisms. We discovered that FOLR1 upregulation led to the deficiency of FA in HeLa cells and mice. Meanwhile, VSV replication was notably suppressed by FOLR1 overexpression, and this antiviral activity was related to FA deficiency. Mechanistically, FA deficiency mainly upregulated apolipoprotein B mRNA editing enzyme catalytic subunit 3B (APOBEC3B) expression, which suppressed VSV replication in vitro and in vivo. In addition, methotrexate (MTX), an FA metabolism inhibitor, effectively inhibited VSV replication by enhancing the expression of APOBEC3B in vitro and in vivo. Overall, our present study provided a new perspective for the role of FA metabolism in viral infections and highlights the potential of MTX as a broad-spectrum antiviral agent against RNA viruses.