Peli1 signaling blockade attenuates congenital zika syndrome

c-FLIP facilitates ZIKV infection by mediating caspase-8/3-dependent apoptosis

c-FLIP functions as a dual regulator of apoptosis and inflammation, yet its implications in Zika virus (ZIKV) infection remain partially understood, especially in the context of ZIKV-induced congenital Zika syndrome (CZS) where both apoptosis and inflammation play pivotal roles. Our findings demonstrate that c-FLIP promotes ZIKV infection in placental cells and myeloid-derived macrophages, involving inflammation and caspase-8/3-mediated apoptosis. Moreover, our observations reveal that c-FLIP augments ZIKV infection in multiple tissues, including blood cell, spleen, uterus, testis, and the brain of mice. Notably, the partial deficiency of c-FLIP provides protection to embryos against ZIKV-induced CZS, accompanied by a reduction in caspase-3-mediated apoptosis. Additionally, we have found a distinctive parental effect of c-FLIP influencing ZIKV replication in fetal heads. In summary, our study reveals the critical role of c-FLIP as a positive regulator in caspase-8/3-mediated apoptosis during ZIKV infection, significantly contributing to the development of CZS.

Role of microglia in brain development after viral infection

Microglia are immune cells in the brain that originate from the yolk sac and enter the developing brain before birth. They play critical roles in brain development by supporting neural precursor proliferation, synaptic pruning, and circuit formation. However, microglia are also vulnerable to environmental factors, such as infection and stress that may alter their phenotype and function. Viral infection activates microglia to produce inflammatory cytokines and anti-viral responses that protect the brain from damage. However, excessive or prolonged microglial activation impairs brain development and leads to long-term consequences such as autism spectrum disorder and schizophrenia spectrum disorder. Moreover, certain viruses may attack microglia and deploy them as "Trojan horses" to infiltrate the brain. In this brief review, we describe the function of microglia during brain development and examine their roles after infection through microglia-neural crosstalk. We also identify limitations for current studies and highlight future investigated questions.

Biology of Pellino1: a potential therapeutic target for inflammation in diseases and cancers

Pellino1 (Peli1) is a highly conserved E3 Ub ligase that exerts its biological functions by mediating target protein ubiquitination. Extensive evidence has demonstrated the crucial role of Peli1 in regulating inflammation by modulating various receptor signaling pathways, including interleukin-1 receptors, Toll-like receptors, nuclear factor-κB, mitogen-activated protein kinase, and phosphoinositide 3-kinase/AKT pathways. Peli1 has been implicated in the development of several diseases by influencing inflammation, apoptosis, necrosis, pyroptosis, autophagy, DNA damage repair, and glycolysis. Peli1 is a risk factor for most cancers, including breast cancer, lung cancer, and lymphoma. Conversely, Peli1 protects against herpes simplex virus infection, systemic lupus erythematosus, esophageal cancer, and toxic epidermolysis bullosa. Therefore, Peli1 is a potential therapeutic target that warrants further investigation. This comprehensive review summarizes the target proteins of Peli1, delineates their involvement in major signaling pathways and biological processes, explores their role in diseases, and discusses the potential clinical applications of Peli1-targeted therapy, highlighting the therapeutic prospects of Peli1 in various diseases.

Pellino 3 promotes the colitis-associated colorectal cancer through suppression of IRF4-mediated negative regulation of TLR4 signalling

The incidence of colitis-associated colorectal cancer (CAC) has increased due to a high-nutrient diet, increased environmental stimuli and inherited gene mutations. To adequately treat CAC, drugs should be developed by identifying novel therapeutic targets. E3 ubiquitin-protein ligase pellino homolog 3 (pellino 3; Peli3) is a RING-type E3 ubiquitin ligase involved in inflammatory signalling; however, its role in the development and progression of CAC has not been elucidated. In this study, we studied Peli3-deficient mice in an azoxymethane/dextran sulphate sodium-induced CAC model. We observed that Peli3 promotes colorectal carcinogenesis with increased tumour burden and oncogenic signalling pathways. Ablation of Peli3 reduced inflammatory signalling activation at the early stage of carcinogenesis. Mechanistic studies indicate that Peli3 enhances toll-like receptor 4 (TLR4)-mediated inflammation through ubiquitination-dependent degradation of interferon regulatory factor 4, a negative regulator of TLR4 in macrophages. Our study suggests an important molecular link between Peli3 and colonic inflammation-mediated carcinogenesis. Furthermore, Peli3 can be a therapeutic target in the prevention and treatment of CAC.

Pellino Proteins in Viral Immunity and Pathogenesis

Pellino proteins are a family of evolutionarily conserved ubiquitin ligases involved in intracellular signaling in a wide range of cell types. They are essential for microbe detection and the initiation of innate and adaptive immune responses. Some viruses specifically target the Pellino proteins as part of their immune evasion strategies. Through studies of mouse models of viral infections in the central nervous system, heart, lungs, and skin, the Pellino proteins have been linked to both beneficial and detrimental immune responses. Only in recent years have some of the involved mechanisms been identified. The objective of this review is to highlight the many diverse aspects of viral immunity and pathogenesis that the Pellino proteins have been associated with, in order to promote further research into their functions. After a brief introduction to the cellular signaling mechanisms involving Pellino proteins, their physiological roles in the initiation of immune responses, pathogenesis through excess inflammation, immune regulation, and cell death are presented. Known viral immune evasion strategies are also described. Throughout, areas that require more in-depth investigation are identified. Future research into the functions of the Pellino protein family may reveal fundamental insights into how our immune system works. Such knowledge may be leveraged in the fight against viral infections and their sequala.

Viral Protein Accumulation of Zika Virus Variants Links with Regulation of Innate Immunity for Differential Control of Viral Replication, Spread, and Response to Interferon

Asian lineage Zika virus (ZIKV) strains emerged globally, causing outbreaks linked with critical clinical disease outcomes unless the virus is effectively restricted by host immunity. We have previously shown that retinoic acid-inducible gene-I (RIG-I) senses ZIKV to trigger innate immunity to direct interferon (IFN) production and antiviral responses that can control ZIKV infection. However, ZIKV proteins have been demonstrated to antagonize IFN. Here, we conducted in vitro analyses to assess how divergent prototypic ZIKV variants differ in virologic properties, innate immune regulation, and infection outcome. We comparatively assessed African lineage ZIKV/Dakar/1984/ArD41519 (ZIKV/Dakar) and Asian lineage ZIKV/Malaysia/1966/P6740 (ZIKV/Malaysia) in a human epithelial cell infection model. De novo viral sequence determination identified amino acid changes within the ZIKV/Dakar genome compared to ZIKV/Malaysia. Viral growth analyses revealed that ZIKV/Malaysia accumulated viral proteins and genome copies earlier and to higher levels than ZIKV/Dakar. Both ZIKV strains activated RIG-I/IFN regulatory factor (IRF3) and NF-κB pathways to induce inflammatory cytokine expression and types I and III IFNs. However, ZIKV/Malaysia, but not ZIKV/Dakar, potently blocked downstream IFN signaling. Remarkably, ZIKV/Dakar protein accumulation and genome replication were rescued in RIG-I knockout (KO) cells late in acute infection, resulting in ZIKV/Dakar-mediated blockade of IFN signaling. We found that RIG-I signaling specifically restricts viral protein accumulation late in acute infection where early accumulation of viral proteins in infected cells confers enhanced ability to limit IFN signaling, promoting viral replication and spread. Our results demonstrate that RIG-I-mediated innate immune signaling imparts restriction of ZIKV protein accumulation, which permits IFN signaling and antiviral actions controlling ZIKV infection. IMPORTANCE ZIKV isolates are classified under African or Asian lineages. Infection with emerging Asian lineage-derived ZIKV strains is associated with increased incidence of neurological symptoms that were not previously reported during infection with African or preemergent Asian lineage viruses. In this study, we utilized in vitro models to compare the virologic properties of and innate immune responses to two prototypic ZIKV strains from distinct lineages: African lineage ZIKV/Dakar and Asian lineage ZIKV/Malaysia. Compared to ZIKV/Dakar, ZIKV/Malaysia accumulates viral proteins earlier, replicates to higher levels, and robustly blocks IFN signaling during acute infection. Early accumulation of ZIKV/Malaysia NS5 protein confers enhanced ability to antagonize IFN signaling, dampening innate immune responses to promote viral spread. Our data identify the kinetics of viral protein accumulation as a major regulator of host innate immunity, influencing host-mediated control of ZIKV replication and spread. Importantly, these findings provide a novel framework for evaluating the virulence of emerging variants.

Pellino1 Restricts Herpes Simplex Virus Infections in the Epidermis and Dissemination to Sebaceous Glands

Nearly all adults are infected with one or more herpes viruses. The most common are herpes simplex virus (HSV)-1 and HSV-2, which upon reactivation can cause painful skin and mucosal erosions. Patients who are immune compromised often experience frequent, atypical, or chronic lesions and thus a greatly diminished QOL. Pellino1 is a ubiquitin ligase involved in IL-1 and toll-like receptor signaling; however, the role of Pellino1 in skin immunity against HSV is unknown. In this study, using the mouse-flank HSV-1 skin infection model, we show that Pellino1 has several critical functions during active viral replication. Peli1‒/‒ mice succumb more than wild-type mice to systemic disease and develop larger zosteriform skin lesions along affected dermatomes. In Pellino1-deficient mice, the virus spread extensively through the epidermis and follicular infundibulum into sebaceous glands where sebocytes were found positive for the virus. The latter did not appear to involve a shift in how the virus migrated through the nervous system. Immunohistochemistry revealed delayed recruitment of myeloid and T cells to the infected epidermis in Peli1‒/‒ mice. This was associated with decreased expression of the cytokine mRNAs Il1a, Il36b and 2610528A11Rik; the latter also known as Gpr15l. In conclusion, Pellino1 plays important roles in restricting viral dissemination, and the involved pathways may represent novel therapeutic targets in patients with frequent or chronic HSV infections.

Pathogenesis of Zika Virus Infection

Zika virus (ZIKV) is an emerging virus from the Flaviviridae family that is transmitted to humans by mosquito vectors and represents an important health problem. Infections in pregnant women are of major concern because of potential devastating consequences during pregnancy and have been associated with microcephaly in newborns. ZIKV has a unique ability to use the host machinery to promote viral replication in a tissue-specific manner, resulting in characteristic pathological disorders. Recent studies have proposed that the host ubiquitin system acts as a major determinant of ZIKV tropism by providing the virus with an enhanced ability to enter new cells. In addition, ZIKV has developed mechanisms to evade the host immune response, thereby allowing the establishment of viral persistence and enhancing viral pathogenesis. We discuss recent reports on the mechanisms used by ZIKV to replicate efficiently, and we highlight potential new areas of research for the development of therapeutic approaches.

Maternal Inflammation Exaggerates Offspring Susceptibility to Cerebral Ischemia–Reperfusion Injury via the COX-2/PGD2/DP2 Pathway Activation

The pathogenesis of cerebral ischemia–reperfusion (I/R) injury is complex and does not exhibit an effective strategy. Maternal inflammation represents one of the most important factors involved in the etiology of brain injury in newborns. We aimed to investigate the effect of maternal inflammation on offspring susceptibility to cerebral I/R injury and the mechanisms by which it exerts its effects. Pregnant SD rats were intraperitoneally injected with LPS (300 μg/kg/day) at gestational days 11, 14, and 18. Pups were subjected to MCAO/R on postnatal day 60. Primary neurons were obtained from postnatal day 0 SD rats and subjected to OGD/R. Neurological deficits, brain injury, neuronal viability, neuronal damage, and neuronal apoptosis were assessed. Oxidative stress and inflammation were evaluated, and the expression levels of COX-2/PGD2/DP pathway-related proteins and apoptotic proteins were detected. Maternal LPS exposure significantly increased the levels of oxidative stress and inflammation, significantly activated the COX-2/PGD2/DP₂ pathway, and increased proapoptotic protein expression. However, maternal LPS exposure significantly decreased the antiapoptotic protein expression, which subsequently increased neurological deficits and cerebral I/R injury in offspring rats. The corresponding results were observed in primary neurons. Moreover, these effects of maternal LPS exposure were reversed by a COX-2 inhibitor and DP₁ agonist but exacerbated by a DP₂ agonist. In conclusion, maternal inflammatory exposure may increase offspring susceptibility to cerebral I/R injury. Moreover, the underlying mechanism might be related to the activation of the COX-2/PGD2/DP₂ pathway. These findings provide a theoretical foundation for the development of therapeutic drugs for cerebral I/R injury.

The Emerging Roles of Pellino Family in Pattern Recognition Receptor Signaling

The Pellino family is a novel and well-conserved E3 ubiquitin ligase family and consists of Pellino1, Pellino2, and Pellino3. Each family member exhibits a highly conserved structure providing ubiquitin ligase activity without abrogating cell and structure-specific function. In this review, we mainly summarized the crucial roles of the Pellino family in pattern recognition receptor-related signaling pathways: IL-1R signaling, Toll-like signaling, NOD-like signaling, T-cell and B-cell signaling, and cell death-related TNFR signaling. We also summarized the current information of the Pellino family in tumorigenesis, microRNAs, and other phenotypes. Finally, we discussed the outstanding questions of the Pellino family in immunity.

Gain-of-function genetic screening identifies the antiviral function of TMEM120A via STING activation

Zika virus (ZIKV) infection can be associated with neurological pathologies, such as microcephaly in newborns and Guillain-Barre syndrome in adults. Effective therapeutics are currently not available. As such, a comprehensive understanding of virus-host interactions may guide the development of medications for ZIKV. Here we report a human genome-wide overexpression screen to identify host factors that regulate ZIKV infection and find TMEM120A as a ZIKV restriction factor. TMEM120A overexpression significantly inhibits ZIKV replication, while TMEM120A knockdown increases ZIKV infection in cell lines. Moreover, Tmem120a knockout in mice facilitates ZIKV infection in primary mouse embryonic fibroblasts (MEF) cells. Mechanistically, the antiviral activity of TMEM120A is dependent on STING, as TMEM120A interacts with STING, promotes the translocation of STING from the endoplasmic reticulum (ER) to ER-Golgi intermediate compartment (ERGIC) and enhances the phosphorylation of downstream TBK1 and IRF3, resulting in the expression of multiple antiviral cytokines and interferon-stimulated genes. In summary, our gain-of-function screening identifies TMEM120A as a key activator of the antiviral signaling of STING.

Understanding the interplay between host and viral factors during infection is essential for the interactome of infection. Here the authors perform a gain-of-function screen to identify factors involved during Zika virus infection and identify TMEM120A as a key factor in the STING mediated immune responses.

Dendritic Cell-Specific Role for Pellino2 as a Mediator of TLR9 Signaling Pathway

Ubiquitination regulates immune signaling, and multiple E3 ubiquitin ligases have been studied in the context of their role in immunity. Despite this progress, the physiological roles of the Pellino E3 ubiquitin ligases, especially Pellino2, in immune regulation remain largely unknown. Accordingly, this study aimed to elucidate the role of Pellino2 in murine dendritic cells (DCs). In this study, we reveal a critical role of Pellino2 in regulation of the proinflammatory response following TLR9 stimulation. Pellino2-deficient murine DCs show impaired secretion of IL-6 and IL-12. Loss of Pellino2 does not affect TLR9-induced activation of NF-κB or MAPKs, pathways that drive expression of IL-6 and IL-12. Furthermore, DCs from Pellino2-deficient mice show impaired production of type I IFN following endosomal TLR9 activation, and it partly mediates a feed-forward loop of IFN-β that promotes IL-12 production in DCs. We also observe that Pellino2 in murine DCs is downregulated following TLR9 stimulation, and its overexpression induces upregulation of both IFN-β and IL-12, demonstrating the sufficiency of Pellino2 in driving these responses. This suggests that Pellino2 is critical for executing TLR9 signaling, with its expression being tightly regulated to prevent excessive inflammatory response. Overall, this study highlights a (to our knowledge) novel role for Pellino2 in regulating DC functions and further supports important roles for Pellino proteins in mediating and controlling immunity.

Pellino2 mediates TLR9-induced cytokine production in dendritic cells.

Pellino2 does not play a role in TLR9 signaling in macrophages.

Pellino2 is a limiting factor for TLR9 signaling in dendritic cells.

The roles of microglia in viral encephalitis: from sensome to therapeutic targeting

Viral encephalitis is a devastating disease with high mortality, and survivors often suffer from severe neurological complications. Microglia are innate immune cells of the central nervous system (CNS) parenchyma whose turnover is reliant on local proliferation. Microglia express a diverse range of proteins, which allows them to continuously sense the environment and quickly react to changes. Under inflammatory conditions such as CNS viral infection, microglia promote innate and adaptive immune responses to protect the host. However, during viral infection, a dysregulated microglia-T-cell interplay may result in altered phagocytosis of neuronal synapses by microglia that causes neurocognitive impairment. In this review, we summarize the current knowledge on the role of microglia in viral encephalitis, propose questions to be answered in the future and suggest possible therapeutic targets.