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

Abstract

Viperin is a multifunctional protein that was first identified in human primary macrophages treated with interferon-γ and in human fibroblasts infected with human cytomegalovirus. This protein plays a role as an anti-viral protein and a regulator of cell signaling pathways or cellular metabolism when induced in a variety of cells such as fibroblasts, hepatocytes and immune cells including T cells and dendritic cells. However, the role of viperin in macrophages is unknown. Here, we show that viperin is basally expressed in murine bone marrow cells including monocytes. Its expression is maintained in bone marrow monocyte-derived macrophages (BMDMs) depending on macrophage colony-stimulating factor (M-CSF) treatment but not on granulocyte-macrophage colony-stimulating factor (GM-CSF) treatment. In wild type (WT) and viperin knockout (KO) BMDMs differentiated with M-CSF or G-MCSF, there are little differences at the gene expression levels of M1 and M2 macrophage markers such as inducible nitric oxide synthase (iNOS) and arginase-1, and cytokines such as IL-6 and IL-10, indicating that viperin expression in BMDMs does not affect the basal gene expression of macrophage markers and cytokines. However, when BMDMs are completely polarized, the levels of expression of macrophage markers and secretion of cytokines in viperin KO M1 and M2 macrophages are significantly higher than those in WT M1 and M2 macrophages. The data suggest that viperin plays a role as a regulator in polarization of macrophages and secretion of M1 and M2 cytokines.

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

“…This T-cell polarization identified as IFNγ-producing Th1 (Fig 3), could be a result of the increased stimulation potential of Viperin −/− APCs via soluble mediators after viral stimulation (Figs 4 and 5, and S8). Consistent with this, it was recently shown in vitro that mice BMDM deficient for Viperin were more polarized to either M1 or M2 and had enhanced secretion of immune mediators upon stimulation (Eom et al, 2018). Similarly, Viperin −/− was shown to be necessary for inhibition of type I IFN production in macrophages (Hee & Cresswell, 2017).…”

“…Notably, Viperin enzymatic function was recently shown to be a convertase of CTP in 3′-deoxy-3′,4′-didehydro-CTP (ddhCTP) which was also reported to have chain reaction termination properties on RNA polymerase of flaviviruses (Gizzi et al, 2018). Our results, taken together with the observed phenotypes of Viperin −/− on macrophage polarization and cytokine production (Eom et al, 2018), interferon response signaling (Hee & Cresswell, 2017), and TLR-7/9 signaling pathway (Jiang & Chen, 2011; Saitoh et al, 2011), raise very intriguing questions on the main role of Viperin during immune responses. Is the enzymatic activity of Viperin linked to these immune regulatory functions, which would imply a role of CTP or ddhCTP in immune signaling and/or polarization, or are Viperin functions on immune responses unrelated to this enzymatic activity but rather to other Viperin protein partners because the SAM domain of Viperin is dispensable for flavivirus restriction (Helbig et al, 2011, 2013)?…”

“…In addition, IL-22 production was increased following CHIKV infection only in CD4 T cell–depleted Viperin −/− mice, suggesting a potential involvement of Viperin in a negative signaling feedback loop on non–T-cell IL-22 production during CHIKV infection. Importantly, others have reported that Viperin can inhibit the macrophage interferon response (Hee & Cresswell, 2017), restrain BMDM polarization and cytokine production (Eom et al, 2018), modulate NF-κB and AP-1 expression in T cells (Qiu et al, 2009), and modulate TLR-7 and TLR-9 signaling in plasmacytoid dendritic cells (Jiang & Chen, 2011; Saitoh et al, 2011).…”

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

“…However, based on available data regarding the antiviral activity of RSAD2, different mechanisms can be postulated: (i) it is shown that the intracellular NAD + levels modulate TNF‐α protein synthesis [42]. It is known that TNF has antiviral activity [43–45], and it is observed that expression of TNF‐α in RSAD2‐KO cells decreases approximately two‐fold [46]. These data together with our findings suggest that ddhCTP inhibits the NAD + ‐dependent reactions to modulate the cellular level of TNF‐α and restrict viral replication.…”

Intrinsic expression of viperin regulates thermogenesis in adipose tissues

“…Cytokines, including IL-10 and IL-13, from immune cells such as macrophages and eosinophils reportedly regulate thermogenesis in adipose tissues (33)(34)(35). We recently showed that viperin deficiency promotes the secretion of proinflammatory and antiinflammatory cytokines from completely differentiated bone marrow-derived macrophages (36). However, viperin was not detected in macrophages in the BAT of mice fed RC.…”