Viperin Deficiency Promotes Polarization of Macrophages and Secretion of M1 and M2 Cytokines

Unexpected regulatory functions of cyprinid Viperin on inflammation and metabolism

BACKGROUND

Viperin, also known as radical S-adenosyl-methionine domain containing protein 2 (RSAD2), is an interferon-inducible protein that is involved in the innate immune response against a wide array of viruses. In mammals, Viperin exerts its antiviral function through enzymatic conversion of cytidine triphosphate (CTP) into its antiviral analog ddhCTP as well as through interactions with host proteins involved in innate immune signaling and in metabolic pathways exploited by viruses during their life cycle. However, how Viperin modulates the antiviral response in fish remains largely unknown.

RESULTS

For this purpose, we developed a fathead minnow (Pimephales promelas) clonal cell line in which the unique viperin gene has been knocked out by CRISPR/Cas9 genome-editing. In order to decipher the contribution of fish Viperin to the antiviral response and its regulatory role beyond the scope of the innate immune response, we performed a comparative RNA-seq analysis of viperin-/- and wildtype cell lines upon stimulation with recombinant fathead minnow type I interferon.

CONCLUSIONS

Our results revealed that Viperin does not exert positive feedback on the canonical type I IFN but acts as a negative regulator of the inflammatory response by downregulating specific pro-inflammatory genes and upregulating repressors of the NF-κB pathway. It also appeared to play a role in regulating metabolic processes, including one carbon metabolism, bone formation, extracellular matrix organization and cell adhesion.

Viperin inhibits interferon-γ production to promote Mycobacterium tuberculosis survival by disrupting TBK1-IKKε-IRF3-axis and JAK-STAT signaling

OBJECTIVES AND DESIGN

As an interferon-inducible protein, Viperin has broad-spectrum antiviral effects and regulation of host immune responses. We aim to investigate how Viperin regulates interferon-γ (IFN-γ) production in macrophages to control Mycobacterium tuberculosis (Mtb) infection.

METHODS

We use Viperin deficient bone-marrow-derived macrophage (BMDM) to investigate the effects and machines of Viperin on Mtb infection.

RESULTS

Viperin inhibited IFN-γ production in macrophages and in the lung of mice to promote Mtb survival. Further insight into the mechanisms of Viperin-mediated regulation of IFN-γ production revealed the role of TANK-binding kinase 1 (TBK1), the TAK1-dependent inhibition of NF-kappa B kinase-epsilon (IKKε), and interferon regulatory factor 3 (IRF3). Inhibition of the TBK1-IKKε-IRF3 axis restored IFN-γ production reduced by Viperin knockout in BMDM and suppressed intracellular Mtb survival. Moreover, Viperin deficiency activated the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling pathway, which promoted IFN-γ production and inhibited Mtb infection in BMDM. Additionally, a combination of the anti-TB drug INH treatment in the absence of Viperin resulted in further IFN-γ production and anti-TB effect.

CONCLUSIONS

This study highlights the involvement of TBK1-IKKε-IRF3 axis and JAK-STAT signaling pathways in Viperin-suppressed IFN-γ production in Mtb infected macrophages, and identifies a novel mechanism of Viperin on negatively regulating host immune response to Mtb infection.

RSAD2 is abundant in atherosclerotic plaques and promotes interferon-induced CXCR3-chemokines in human smooth muscle cells

In atherosclerotic lesions, monocyte-derived macrophages are major source of interferon gamma (IFN-γ), a pleotropic cytokine known to regulate the expression of numerous genes, including the antiviral gene RSAD2. While RSAD2 was reported to be expressed in endothelial cells of human carotid lesions, its significance for the development of atherosclerosis remains utterly unknown. Here, we harnessed publicly available human carotid atherosclerotic data to explore RSAD2 in lesions and employed siRNA-mediated gene-knockdown to investigate its function in IFN-γ-stimulated human aortic smooth muscle cells (hAoSMCs). Silencing RSAD2 in IFN-γ-stimulated hAoSMCs resulted in reduced expression and secretion of key CXCR3-chemokines, CXCL9, CXCL10, and CXCL11. Conditioned medium from RSAD2-deficient hAoSMCs exhibited diminished monocyte attraction in vitro compared to conditioned medium from control cells. Furthermore, RSAD2 transcript was elevated in carotid lesions where it was expressed by several different cell types, including endothelial cells, macrophages and smooth muscle cells. Interestingly, RSAD2 displayed significant correlations with CXCL10 (r =  0.45, p = 0.010) and CXCL11 (r = 0.53, p = 0.002) in human carotid lesions. Combining our findings, we uncover a novel role for RSAD2 in hAoSMCs, which could potentially contribute to monocyte recruitment in the context of atherosclerosis.

Viperin mutation is linked to immunity, immune cell dynamics, and metabolic alteration during VHSV infection in zebrafish

Viperin is a prominent antiviral protein found in animals. The primary function of Viperin is the production of 3'-deoxy-3',4'-didehydro-cytidine triphosphate (ddhCTP), an inhibitory nucleotide involved in viral RNA synthesis. Studies in mammalian models have suggested that ddhCTP interferes with metabolic proteins. However, this hypothesis has yet to be tested in teleost. In this study, the role of Viperin in regulating metabolic alterations during viral hemorrhagic septicemia virus (VHSV) infection was tested. When infected with VHSV, viperin -/- fish showed considerably higher mortality rates. VHSV copy number and the expression of the NP gene were significantly increased in viperin -/- fish. Metabolic gene analysis revealed significant differences in soda, hif1a, fasn, and acc expression, indicating their impact on metabolism. Cholesterol analysis in zebrafish larvae during VHSV infection showed significant upregulation of cholesterol production without Viperin. In vitro analysis of ZF4 cells suggested a considerable reduction in lipid production and a significant upregulation of reactive oxygen species (ROS) generation with the overexpression of viperin. Neutrophil and macrophage recruitment were significantly modulated in viperin -/- fish compared to the wild-type (WT) fish. Thus, we have demonstrated that Viperin plays a role in interfering with metabolic alterations during VHSV infection.

Chemoenzymatic Synthesis of 3'-Deoxy-3',4'-didehydro-cytidine triphosphate (ddhCTP)

3'-Deoxy-3',4'-didehydro-cytidine triphosphate (ddhCTP) is a novel antiviral molecule produced by the enzyme viperin during the early stages of the innate immune response. ddhCTP has been shown to act as a chain terminator of flavivirus RNA-dependent RNA polymerases. To date, synthesis of ddhCTP requires complicated synthetic protocols or isolation of the enzyme viperin to catalyze the production of ddhCTP from CTP. Recombinant viperin approaches preclude the production of highly pure ddhCTP (free of contaminants such as CTP), whereas the chemical synthesis involves techniques or equipment not readily available to most laboratories. Herein, we describe the chemoenzymatic synthesis of ddhCTP, starting from commercially available ddhC. We utilize these methods to produce milligram quantities of ddhCTP, ddhCDP, and ddhCMP. Using purified semisynthetic ddhCTP and fully synthetic ddhCTP, we also show ddhCTP does not inhibit NAD+-dependent enzymes such as glyceraldehyde 3-phosphate dehydrogenase, malate dehydrogenase, or lactate dehydrogenase, contrary to a recent report.

Molecular pathogenicity of 1-nonadecene and L-lactic acid, unique metabolites in radicular cysts and periapical granulomas

Recently, 1-nonadecene and L-lactic acid were identified as unique metabolites in radicular cysts and periapical granuloma, respectively. However, the biological roles of these metabolites were unknown. Therefore, we aimed to investigate the inflammatory and mesenchymal-epithelial transition (MET) effects of 1-nonadecene, and the inflammatory and collagen precipitation effects of L-lactic acid on both periodontal ligament fibroblasts (PdLFs) and peripheral blood mononuclear cells (PBMCs). PdLFs and PBMCs were treated with 1-nonadecene and L-lactic acid. Cytokines' expression was measured using quantitative real-time polymerase chain reaction (qRT-PCR). E-cadherin, N-cadherin, and macrophage polarization markers were measured using flow cytometry. The collagen, matrix metalloproteinase (MMP)-1, and released cytokines were measured using collagen assay, western blot, and Luminex assay, respectively. In PdLFs, 1-nonadecene enhances inflammation through the upregulation of some inflammatory cytokines including IL-1β, IL-6, IL-12A, monocyte chemoattractant protein (MCP)-1, and platelet-derived growth factor (PDGF) α. 1-Nonadecene also induced MET through the upregulation of E-cadherin and the downregulation of N-cadherin in PdLFs. 1-Nonadecene polarized macrophages to a pro-inflammatory phenotype and suppressed their cytokines' release. L-lactic acid exerted a differential impact on the inflammation and proliferation markers. Intriguingly, L-lactic acid induced fibrosis-like effects by enhancing collagen synthesis, while inhibiting MMP-1 release in PdLFs. These results provide a deeper understanding of 1-nonadecene and L-lactic acid's roles in modulating the microenvironment of the periapical area. Consequently, further clinical investigation can be employed for target therapy.

A Cysteine Residue of Human Cytomegalovirus vMIA Protein Plays a Crucial Role in Viperin Trafficking to Control Viral Infectivity

Viperin is a multifunctional interferon-inducible protein that is directly induced in cells by human cytomegalovirus (HCMV) infection. The viral mitochondrion-localized inhibitor of apoptosis (vMIA) interacts with viperin at the early stages of infection and translocates it from the endoplasmic reticulum to the mitochondria, where viperin modulates the cellular metabolism to increase viral infectivity. Viperin finally relocalizes to the viral assembly compartment (AC) at late stages of infection. Despite the importance of vMIA interactions with viperin during viral infection, their interacting residues are unknown. In the present study, we showed that cysteine residue 44 (Cys44) of vMIA and the N-terminal domain (amino acids [aa] 1 to 42) of viperin are necessary for their interaction and for the mitochondrial localization of viperin. In addition, the N-terminal domain of mouse viperin, which is structurally similar to that of human viperin, interacted with vMIA. This indicates that the structure, rather than the sequence composition, of the N-terminal domain of viperin, is required for the interaction with vMIA. Recombinant HCMV, in which Cys44 of vMIA was replaced by an alanine residue, failed to translocate viperin to the mitochondria at the early stages of infection and inefficiently relocalized it to the AC at late stages of infection, resulting in the impairment of viperin-mediated lipid synthesis and a reduction in viral replication. These data indicate that Cys44 of vMIA is therefore essential for the intracellular trafficking and function of viperin to increase viral replication. Our findings also suggest that the interacting residues of these two proteins are potential therapeutic targets for HCMV-associated diseases. IMPORTANCE Viperin traffics to the endoplasmic reticulum (ER), mitochondria, and viral assembly compartment (AC) during human cytomegalovirus (HCMV) infection. Viperin has antiviral activity at the ER and regulates cellular metabolism at the mitochondria. Here, we show that Cys44 of HCMV vMIA protein and the N-terminal domain (aa 1 to 42) of viperin are necessary for their interaction. Cys44 of vMIA also has a critical role for viperin trafficking from the ER to the AC via the mitochondria during viral infection. Recombinant HCMV expressing a mutant vMIA Cys44 has impaired lipid synthesis and viral infectivity, which are attributed to mislocalization of viperin. Cys44 of vMIA is essential for the trafficking and function of viperin and may be a therapeutic target for HCMV-associated diseases.

Viperin deficiency promotes dendritic cell activation and function via NF-kappaB activation during Mycobacterium tuberculosis infection

OBJECTIVES AND DESIGN

Dendritic cells (DCs) are one of the key immune cells in bridging innate and adaptive immune response against Mycobacterium tuberculosis (Mtb) infection. Interferons (IFNs) play important roles in regulating DC activation and function. Virus-inhibitory protein, endoplasmic reticulum-associated, interferon-inducible (Viperin) is one of the important IFN-stimulated genes (ISGs), and elicits host defense against infection.

METHODS

We investigated the effects and mechanisms of Viperin on DC activation and function using Viperin deficient bone marrow-derived dendritic cells (BMDCs) during Mtb infection.

RESULTS

Viperin deficiency enhanced phagocytic activity and increased clearance of Mtb in DCs, produced higher abundance of NO, cytokine including interleukin-12 (IL-12), Tumor necrosis factor-α (TNF-α), IL-1β, IL-6 and chemokine including CXCL1, CXCL2 and CXCL10, elevated MHC I, MHC II and co-stimulatory molecules expression, and enhanced CD4⁺ and CD8⁺ T cell responses. Mechanistically, Viperin deficiency promoted DC activation and function through NF-κB p65 activation. NF-κB p65 inhibitor prevented cytokine and chemokine production, and co-stimulatory molecules expression promoted by Viperin deficiency.

CONCLUSIONS

These results suggest that Mtb induced Viperin expression could impair the activation of host defense function of DCs and DC-T cell cross talk during Mtb infection. This research may provide a potential target for future HDT in TB therapy.

Viperin impairs the innate immune response through the IRAK1-TRAF6-TAK1 axis to promote Mtb infection

Mycobacterium tuberculosis (Mtb) infection is a long-standing public health threat, and the development of host-directed therapy for eradicating Mtb infection requires better insights into Mtb-host interactions. Viperin [virus-inhibitory protein, endoplasmic reticulum-associated, interferon (IFN) inducible] is an IFN-inducible protein with broad antiviral activities. Here, we demonstrated that Viperin was increased in abundance in patients with lymphatic and pulmonary tuberculosis (TB). Viperin-deficient mice had decreased Mtb bacterial loads and enhanced macrophage responses compared with their wild-type counterparts. Viperin suppressed the formation of a complex containing interleukin-1 receptor-associated kinase 1, TNF receptor-associated factor 6, and transforming growth factor β-activated kinase 1 (TAK1) and inhibited the TAK1-dependent activation of IκB kinase α/β, thereby impairing the production of nitric oxide and proinflammatory cytokines. These results suggest that Viperin promotes Mtb infection by inhibiting host innate immune responses in macrophages, suggesting that Viperin may be a candidate target for adjunct host-directed therapy in patients with TB.

Characterisation of key biomarkers in diabetic ulcers via systems bioinformatics

Diabetic ulcers (DUs) are characterised by a high incidence and disability rate. However, its pathogenesis remains elusive. Thus, a deep understanding of the underlying mechanisms for the pathogenesis of DUs has vital implications. The weighted gene co-expression network analysis was performed on the main data from the Gene Expression Omnibus database. Gene Ontology (GO) terms, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were adopted to analyse the potential biological function of the most relevant module. Furthermore, we utilised CytoHubba and protein-protein interaction network to identify the hub genes. Finally, the hub genes were validated by animal experiments in diabetic ulcer mice models. The expression of genes from the turquoise module was found to be strongly related to DUs. GO terms, KEGG analysis showed that biological functions are closely related to immune response. The hub genes included IFI35, IFIT2, MX2, OASL, RSAD2, and XAF1, which were higher in wounds of DUs mice than that in normal lesions. Additionally, we also demonstrated that the expression of hub genes was correlated with the immune response using immune checkpoint, immune cell infiltration, and immune scores. These data suggests that IFI35, IFIT2, MX2, OASL, RSAD2, and XAF1 are crucial for DUs.

Granulocyte Macrophage-Colony Stimulating Factor Produces a Splenic Subset of Monocyte-Derived Dendritic Cells That Efficiently Polarize T Helper Type 2 Cells in Response to Blood-Borne Antigen

Dendritic cells (DCs) are key antigen-presenting cells that prime naive T cells and initiate adaptive immunity. Although the genetic deficiency and transgenic overexpression of granulocyte macrophage-colony stimulating factor (GM-CSF) signaling were reported to influence the homeostasis of DCs, the in vivo development of DC subsets following injection of GM-CSF has not been analyzed in detail. Among the treatment of mice with different hematopoietic cytokines, only GM-CSF generates a distinct subset of XCR1^-33D1^- DCs which make up the majority of DCs in the spleen after three daily injections. These GM-CSF-induced DCs (GMiDCs) are distinguished from classical DCs (cDCs) in the spleen by their expression of CD115 and CD301b and by their superior ability to present blood-borne antigen and thus to stimulate CD4⁺ T cells. Unlike cDCs in the spleen, GMiDCs are exceptionally effective to polarize and expand T helper type 2 (Th2) cells and able to induce allergic sensitization in response to blood-borne antigen. Single-cell RNA sequencing analysis and adoptive cell transfer assay reveal the sequential differentiation of classical monocytes into pre-GMiDCs and GMiDCs. Interestingly, mixed bone marrow chimeric mice of Csf2rb^+/+ and Csf2rb^-/- demonstrate that the generation of GMiDCs necessitates the cis expression of GM-CSF receptor. Besides the spleen, GMiDCs are generated in the CCR7-independent resident DCs of the LNs and in some peripheral tissues with GM-CSF treatment. Also, small but significant numbers of GMiDCs are generated in the spleen and other tissues during chronic allergic inflammation. Collectively, our present study identifies a splenic subset of CD115^hiCD301b⁺ GMiDCs that possess a strong capacity to promote Th2 polarization and allergic sensitization against blood-borne antigen.

Viperin is anti-viral in vitro but is dispensable for restricting dengue virus replication or induction of innate and inflammatory responses in vivo

Viperin has antiviral function against many viruses, including dengue virus (DENV), when studied in cells in culture. Here, the antiviral actions of viperin were defined both in vitro and in a mouse in vivo model of DENV infection. Murine embryonic fibroblasts (MEFs) derived from mice lacking viperin (vip^−/−) showed enhanced DENV infection, accompanied by increased IFN-β and induction of ISGs; IFIT1 and CXCL-10 but not IRF7, when compared to wild-type (WT) MEFs. In contrast, subcutaneous challenge of immunocompetent WT and vip^−/− mice with DENV did not result in enhanced infection. Intracranial infection with DENV resulted in body weight loss and neurological disease with a moderate increase in mortality in vip^−/− compared with WT mice, although this was not accompanied by altered brain morphology, immune cell infiltration or DENV RNA level in the brain. Similarly, DENV induction of IFN-β, IFIT1, CXCL-10, IRF7 and TNF-α was not significantly different in WT and vip^−/− mouse brain, although there was a modest but significant increase in DENV induction of IL-6 and IfI27la in the absence of viperin. NanoString nCounter analysis confirmed no significant difference in induction of a panel of inflammatory genes in WT compared to vip^−/− DENV-infected mouse brains. Further, polyI:C stimulation of bone marrow-derived macrophages (BMDMs) induced TNF-α, IFN-β, IL-6 and Nos-2, but responses were not different in BMDMs generated from WT or vip^−/− mice. Thus, while there is significant evidence of anti-DENV actions of viperin in some cell types in vitro, for DENV infection in vivo a lack of viperin does not affect systemic or brain susceptibility to DENV or induction of innate and inflammatory responses.

Interferon-stimulated gene products as regulators of central carbon metabolism

In response to viral infections, the innate immune system rapidly activates expression of several interferon-stimulated genes (ISGs), whose protein and metabolic products are believed to directly interfere with the viral life cycle. Here, we argue that biochemical reactions performed by two specific protein products of ISGs modulate central carbon metabolism to support a broad-spectrum antiviral response. We demonstrate that the metabolites generated by metalloenzymes nitric oxide synthase and the radical S-adenosylmethionine (SAM) enzyme RSAD2 inhibit the activity of the housekeeping and glycolytic enzyme glyceraldehyde 3-phosphate dehydrogenase (GAPDH). We discuss that this inhibition is likely to stimulate a range of metabolic and signalling processes to support a broad-spectrum immune response. Based on these analyses, we propose that inhibiting GAPDH in individuals with deteriorated cellular innate immune response like elderly might help in treating viral diseases such as COVID-19.

Viperin Reveals Its True Function

Most cells respond to viral infections by activating innate immune pathways that lead to the induction of antiviral restriction factors. One such factor, viperin, was discovered almost two decades ago based on its induction during viral infection. Since then, viperin has been shown to possess activity against numerous viruses via multiple proposed mechanisms. Most recently, however, viperin was demonstrated to catalyze the conversion of cytidine triphosphate (CTP) to 3'-deoxy-3',4'-didehydro-CTP (ddhCTP), a previously unknown ribonucleotide. Incorporation of ddhCTP causes premature termination of RNA synthesis by the RNA-dependent RNA polymerase of some viruses. To date, production of ddhCTP by viperin represents the only activity of viperin that links its enzymatic activity directly to an antiviral mechanism in human cells. This review examines the multiple antiviral mechanisms and biological functions attributed to viperin.

ddhCTP produced by the radical-SAM activity of RSAD2 (viperin) inhibits the NAD+ -dependent activity of enzymes to modulate metabolism

Radical S-adenosylmethionine (SAM) domain-containing protein 2 (RSAD2; viperin) is a key enzyme in innate immune responses that is highly expressed in response to viral infection and inflammatory stimuli in many cell types. Recently, it was found that RSAD2 catalyses transformation of cytidine triphosphate (CTP) to its analogue 3'-deoxy-3',4'-didehydro-CTP (ddhCTP). The cellular function of this metabolite is unknown. Here, we analysed the extra- and intracellular metabolite levels in human induced pluripotent stem cell (hiPSC)-derived macrophages using high-resolution LC-MS/MS. The results together with biochemical assays and molecular docking simulations revealed that ddhCTP inhibits the NAD⁺ -dependent activity of enzymes including that of the housekeeping enzyme glyceraldehyde 3-phosphate dehydrogenase (GAPDH). We propose that ddhCTP regulates cellular metabolism in response to inflammatory stimuli such as viral infection, pointing to a broader function of RSAD2 than previously thought.

Middle East Respiratory Syndrome-Coronavirus Infection into Established hDPP4-Transgenic Mice Accelerates Lung Damage Via Activation of the Pro-Inflammatory Response and Pulmonary Fibrosis

Middle East respiratory syndrome coronavirus (MERS-CoV) infects the lower respiratory airway of humans, leading to severe acute respiratory failure. Unlike human dipeptidyl peptidase 4 (hDPP4), a receptor for MERS-CoV, mouse DPP4 (mDPP4) failed to support MERS-CoV infection. Consequently, diverse transgenic mouse models expressing hDPP4 have been developed using diverse methods, although some models show no mortality and/or only transient and mild-to-moderate clinical signs following MERS-CoV infection. Additionally, overexpressed hDPP4 is associated with neurological complications and breeding difficulties in some transgenic mice, resulting in impeding further studies. Here, we generated stable hDPP4-transgenic mice that were sufficiently susceptible to MERS-CoV infection. The transgenic mice showed weight loss, decreased pulmonary function, and increased mortality with minimal perturbation of overexpressed hDPP4 after MERS-CoV infection. In addition, we observed histopathological signs indicative of progressive pulmonary fibrosis, including thickened alveolar septa, infiltration of inflammatory monocytes, and macrophage polarization as well as elevated expression of profibrotic molecules and acute inflammatory response in the lung of MERS-CoV-infected hDPP4-transgenic mice. Collectively, we suggest that this hDPP4-transgenic mouse is useful in understanding the pathogenesis of MERS-CoV infection and for antiviral research and vaccine development against the virus.

Viperin Differentially Induces Interferon-Stimulated Genes in Distinct Cell Types

Viperin is an IFN-stimulated gene (ISG)-encoded protein that was identified in human primary macrophages treated with IFN-γ and in human primary fibroblasts infected with cytomegalovirus (CMV). This protein plays multiple roles in various cell types. It inhibits viral replication, mediates signaling pathways, and regulates cellular metabolism. Recent studies have shown that viperin inhibits IFN expression in macrophages, while it enhances TLR7 and TLR9-mediated IFN production in plasmacytoid dendritic cells, suggesting that viperin can play different roles in activation of the same pathway in different cell types. Viperin also controls induction of ISGs in macrophages. However, the effect of viperin on induction of ISGs in cell types other than macrophages is unknown. Here, we show that viperin differentially induces ISGs in 2 distinct cell types, macrophages and fibroblasts isolated from wild type and viperin knockout mice. Unlike in bone marrow-derived macrophages (BMDMs), viperin downregulates the expression levels of ISGs such as bone marrow stromal cell antigen-2, Isg15, Isg54, myxovirus resistance dynamin like GTPase 2, and guanylate binding protein 2 in murine embryonic fibroblasts (MEFs) treated with type I or II IFN. However, viperin upregulates expression of these ISGs in both BMDMs and MEFs stimulated with polyinosinic-polycytidylic acid or CpG DNA and infected with murine CMV. The efficiency of viral entry is inversely proportional to the expression levels of ISGs in both cell types. The data indicate that viperin differentially regulates induction of ISGs in a cell type-dependent manner, which might provide different innate immune responses in distinct cell types against infections.

Intrinsic expression of viperin regulates thermogenesis in adipose tissues

Viperin is an interferon (IFN)-inducible multifunctional protein. Recent evidence from high-throughput analyses indicates that most IFN-inducible proteins, including viperin, are intrinsically expressed in specific tissues; however, the respective intrinsic functions are unknown. Here we show that the intrinsic expression of viperin regulates adipose tissue thermogenesis, which is known to counter metabolic disease and contribute to the febrile response to pathogen invasion. Viperin knockout mice exhibit increased heat production, resulting in a reduction of fat mass, improvement of high-fat diet (HFD)-induced glucose tolerance, and enhancement of cold tolerance. These thermogenic phenotypes are attributed to an adipocyte-autonomous mechanism that regulates fatty acid β-oxidation. Under an HFD, viperin expression is increased, and its function is enhanced. Our findings reveal the intrinsic function of viperin as a novel mechanism regulating thermogenesis in adipose tissues, suggesting that viperin represents a molecular target for thermoregulation in clinical contexts.

Two Distinct Subsets Are Identified from the Peritoneal Myeloid Mononuclear Cells Expressing both CD11c and CD115

To this date, the criteria to distinguish peritoneal macrophages and dendritic cells (DCs) are not clear. Here we delineate the subsets of myeloid mononuclear cells in the mouse peritoneal cavity. Considering phenotypical, functional, and ontogenic features, peritoneal myeloid mononuclear cells are divided into 5 subsets: large peritoneal macrophages (LPMs), small peritoneal macrophages (SPMs), DCs, and 2 MHCII⁺CD11c⁺CD115⁺ subpopulations (i.e., MHCII⁺CD11c⁺CD115⁺CD14⁻CD206⁻ and MHCII⁺CD11c⁺CD115⁺CD14⁺CD206⁺). Among them, 2 subsets of competent Ag presenting cells are demonstrated with distinct functional characteristics, one being DCs and the other being MHCII⁺CD11c⁺CD115⁺CD14⁻CD206⁻ cells. DCs are able to promote fully activated T cells and superior in expanding cytokine producing inflammatory T cells, whereas MHCII⁺CD11c⁺CD115⁺CD14⁻CD206⁻ cells generate partially activated T cells and possess a greater ability to induce Treg under TGF-β and retinoic acid conditions. While the development of DCs and MHCII⁺CD11c⁺CD115⁺CD14⁻CD206⁻ cells are responsive to the treatment of FLT3 ligand and GM-CSF, the number of LPMs, SPMs, and MHCII⁺CD11c⁺CD115⁺CD14⁺CD206⁺ cells are only influenced by the injection of GM-CSF. In addition, the analysis of gene expression profiles among MHCII⁺ peritoneal myeloid mononuclear cells reveals that MHCII⁺CD11c⁺CD115⁺CD14⁺CD206⁺ cells share high similarity with SPMs, whereas MHCII⁺CD11c⁺CD115⁺CD14⁻CD206⁻ cells are related to peritoneal DC2s. Collectively, our study identifies 2 distinct subpopulations of MHCII⁺CD11c⁺CD115⁺ cells, 1) MHCII⁺CD11c⁺CD115⁺CD14⁻CD206⁻ cells closely related to peritoneal DC2s and 2) MHCII⁺CD11c⁺CD115⁺CD14⁺CD206⁺ cells to SPMs.

Viperin controls chikungunya virus-specific pathogenic T cell IFNγ Th1 stimulation in mice

This study shows that Viperin controls the microenvironment pro-inflammatory response and CD4 T cell–mediated pathogenesis during anti-chikungunya virus immune response in mice.

Chikungunya virus (CHIKV) has been a worldwide threat since its reemergence in La Reunion Island in 2004. Expression of the interferon-stimulated protein Viperin correlates with viral load burden in patients, and studies in mice have demonstrated its role to limit disease severity against CHIKV infection. Using Viperin^−/− mice, we aimed to understand the contribution of Viperin to the T-cell immune response against CHIKV. CD4 T-cell depletion in Viperin^−/− mice showed that increased late acute joint inflammation (5–8 d postinfection) was exclusively mediated by T cells. Specifically, CHIKV-infected Viperin^−/− mice showed an increased INFγ Th1 profile of CD4 T cells, enhanced INFγ stimulation by APCs, an increased INFγ secretion profile in the joint microenvironment, and increased numbers of inflammatory monocytes in virus-infected joints compared with WT mice. Bone marrow grafting experiments showed that Viperin expression in both hematopoietic and non-hematopoietic cells is instrumental in reducing disease severity associated with a CD4 T-cell response.