Priming of the cGAS-STING-TBK1 Pathway Enhances LPS-Induced Release of Type I Interferons.

Alessandra Tesser,Giulia Maria Piperno,Federica Benvenuti,Elisa Piscianz,Alberto Tommasini,Valentina Boz,Alessia Pin

doi:10.3390/cells10040785

Abstract

Cytoplasmic nucleic acids sensing through cGAS-STING-TBK1 pathway is crucial for the production of antiviral interferons (IFNs). IFN production can also be induced by lipopolysaccharide (LPS) stimulation through Toll-like receptor 4 (TLR4) in appropriate conditions. Of note, both IFN production and dysregulated LPS-response could play a role in the pathogenesis of Systemic Lupus Erythematosus (SLE). Indeed, LPS can trigger SLE in lupus-prone mice and bacterial infections can induce disease flares in human SLE. However, the interactions between cGAS and TLR4 pathways to IFNs have been poorly investigated. To address this issue, we studied LPS-stimulation in cellular models with a primed cGAS-STING-TBK1 pathway. cGAS-stimulation was naturally sustained by undigested self-nucleic acids in fibroblasts from DNase2-deficiency interferonopathy, whilst it was pharmacologically obtained by cGAMP-stimulation in THP1 cells and murine bone marrow-derived dendritic cells. We showed that cells with a primed cGAS-STING-TBK1 pathway displayed enhanced IFNs production after TLR4-challenge. STING-inhibition did not affect IFN production after LPS alone, but prevented the amplified IFN production in cGAMP-primed cells, suggesting that functional STING is required for priming-dependent enhancement. Furthermore, we speculated that an increased PIK3AP1 expression in DNase2-deficient fibroblasts may link cGAMP-priming with increased LPS-induced IFN production. We showed that both the hyper-expression of PIK3API and the enhanced LPS-induced IFN production can be contrasted by STING inhibitors. Our results may explain how bacterial LPS can synergize with cGAS-pathway in promoting the development of SLE-like autoimmunity.

Highlights

Triggering cytoplasmic sensors with nucleic acids results in inflammatory response dominated by type I interferon (IFN) production, considered as a physiological and conserved defense mechanism against viral infections [1]. several proteins can recognize nucleic acids in the cytoplasm, only the cyclic GMP-AMP synthase has emerged as the crucial sensor in all experimental settings [2], as well as in distinct mendelian IFN-related disorders [3]. cGAS senses cytoplasmic double-stranded DNA and DNA:RNA hybrids [4], catalyzing the production of the dinucleotide cyclic GMP-AMP [5], a second messenger that activates the STING protein, which is considered the principal stimulator of IFN genes
Fibroblasts from DNase2 interferonopathy (D2I) present a constitutive primed IFN signaling, witnessed by increased IFN signature compared with the control (Figure 1a)
We hypothesized that the effect observed in D2I fibroblasts could be due to a permissive effect of an activated cGAS pathway on the Toll-like receptor 4 (TLR4)-TBK1 pathway

Summary

Introduction

Triggering cytoplasmic sensors with nucleic acids results in inflammatory response dominated by type I interferon (IFN) production, considered as a physiological and conserved defense mechanism against viral infections [1]. several proteins can recognize nucleic acids in the cytoplasm, only the cyclic GMP-AMP synthase (cGAS) has emerged as the crucial sensor in all experimental settings [2], as well as in distinct mendelian IFN-related disorders [3]. cGAS senses cytoplasmic double-stranded DNA and DNA:RNA hybrids [4], catalyzing the production of the dinucleotide cyclic GMP-AMP (cGAMP) [5], a second messenger that activates the STING protein, which is considered the principal stimulator of IFN genes. Triggering cytoplasmic sensors with nucleic acids results in inflammatory response dominated by type I interferon (IFN) production, considered as a physiological and conserved defense mechanism against viral infections [1]. Several proteins can recognize nucleic acids in the cytoplasm, only the cyclic GMP-AMP synthase (cGAS) has emerged as the crucial sensor in all experimental settings [2], as well as in distinct mendelian IFN-related disorders [3]. CGAS senses cytoplasmic double-stranded DNA and DNA:RNA hybrids [4], catalyzing the production of the dinucleotide cyclic GMP-AMP (cGAMP) [5], a second messenger that activates the STING protein, which is considered the principal stimulator of IFN genes. TBK1-mediated production of type I IFN can be triggered by the stimulation of Toll-like receptor 4 (TLR4) with bacterial lipopolysaccharide (LPS) in murine models of autoimmunity [8]. It is well recognized that bacterial infections can trigger disease relapses in SLE [9,10,11]

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Conclusion