Golgi apparatus-synthesized sulfated glycosaminoglycans mediate polymerization and activation of the cGAMP sensor STING.

Activation of the cyclic guanosine monophosphate (GMP)-AMP (cGAMP) sensor STING requires its translocation from the endoplasmic reticulum to the Golgi apparatus and subsequent polymerization. Using a genome-wide CRISPR-Cas9 screen to define factors critical for STING activation in cells, we identified proteins critical for biosynthesis of sulfated glycosaminoglycans (sGAGs) in the Golgi apparatus. Binding of sGAGs promoted STING polymerization through luminal, positively charged, polar residues. These residues are evolutionarily conserved, and selective mutation of specific residues inhibited STING activation. Purified or chemically synthesized sGAGs induced STING polymerization and activation of the kinase TBK1. The chain length and O-linked sulfation of sGAGs directly affected the level of STING polymerization and, therefore, its activation. Reducing the expression of Slc35b2 to inhibit GAG sulfation in mice impaired responses to vaccinia virus infection. Thus, sGAGs in the Golgi apparatus are necessary and sufficient to drive STING polymerization, providing a mechanistic understanding of the requirement for endoplasmic reticulum (ER)-to-Golgi apparatus translocation for STING activation.

STING-associated vasculopathy with onset in infancy (SAVI) presenting with skin lesions.

STING-associated vasculopathy with onset in infancy (SAVI) is caused by pathogenic gain-of-function variants in the gene TMEM173 (also named stimulator of interferon genes, STING1). This report details the case of an 11-year-old girl with SAVI who presented with skin-limited symptoms and discusses the phenotype-genotype correlations of the TMEM173 variant present in our patient. Treatment of SAVI focuses on preventing the development or progression of organ damage by reducing systemic inflammation. We summarize the available treatments for this syndrome.

Development of nitroalkene-based inhibitors to target STING-dependent inflammation.

Stimulator of Interferon Genes (STING) is essential for the inflammatory response to cytosolic DNA. Despite that aberrant activation of STING is linked to an increasing number of inflammatory diseases, the development of inhibitors has been challenging, with no compounds in the pipeline beyond the preclinical stage. We previously identified endogenous nitrated fatty acids as novel reversible STING inhibitors. With the aim of improving the specificity and efficacy of these compounds, we developed and tested a library of nitroalkene-based compounds for in vitro and in vivo STING inhibition. The structure-activity relationship study revealed a robustly improved electrophilicity and reduced degrees of freedom of nitroalkenes by conjugation with an aromatic moiety. The lead compounds CP-36 and CP-45, featuring a ß-nitrostyrene moiety, potently inhibited STING activity in vitro and relieved STING-dependent inflammation in vivo. This validates the potential for nitroalkene compounds as drug candidates for STING modulation to treat STING-driven inflammatory diseases, providing new robust leads for preclinical development.

Case report: JAK1/2 inhibition with baricitinib in the treatment of STING-associated vasculopathy with onset in infancy.

BACKGROUND: Gain-of-function mutations in STING1 (also known as TMEM173) which result in constitutive activation of STING, have been reported to cause STING-associated vasculopathy with onset in infancy (SAVI). Although a wider spectrum of associated manifestations and perturbations in disease onset have been observed since its description, the genotype-phenotype correlations are not definite, and there is no established treatment protocol for SAVI. CASE PRESENTATION: Herein, we report a kindred, heterozygous STING mutation (p.V155M) in which the 2-year-old proband suffered from severe interstitial lung disease (ILD) while her father was initially misdiagnosed with connective tissue disease associated with ILD at an adult age. Baricitinib was initiated after the diagnosis of SAVI in the proband combined with steroids, and during the 14-month follow-up, the respiratory symptoms were improved. However, as the improvement of laboratory indicators was limited, especially in autoimmune indices, and the lung CT images remained unaltered, it seems that JAK1/2 inhibition was unsatisfactory in completely controlling the inflammation of the disease in our study. CONCLUSIONS: Baricitinib was shown to elicit some effect on the ILD but failed to control the inflammation of the disease completely. Further exploration of JAK inhibitors or other therapeutic strategies are needed to more optimally treat this inflammatory disease.

The activity of disease-causative STING variants can be suppressed by wild-type STING through heterocomplex formation.

Stimulator of interferon genes (STING) is essential for the type I interferon response induced by microbial DNA from viruses or self-DNA from mitochondria/nuclei. Recently, gain-of-function mutations in STING have been identified in patients with STING-associated vasculopathy with onset in infancy (SAVI). The SAVI patients exhibit complex systemic vascular inflammation and interstitial lung disease, resulting in pulmonary fibrosis and respiratory failure. SAVI mouse models have recently developed, harbouring common SAVI mutations, such as N153S and V154M, which correspond to the human N154S and V155M, respectively. Interestingly, crosses of heterozygous SAVI mice did not yield homozygous SAVI mice as of embryonic day 14, indicating that homozygous SAVI embryos were not viable and that wild-type (WT) allele would function dominantly over SAVI alleles in terms of viability. However, the molecular mechanism underlying the dominance has not been understood. In the present study, we show that STING (WT) and STING (SAVI) can form heterocomplex. The heterocomplex localized primarily in the endoplasmic reticulum (ER) and failed to reach the trans-Golgi network (TGN), where STING activates the downstream kinase TBK1. SURF4 is the essential protein functioning in the retrieval of STING from the Golgi to the ER. The amount of SURF4 bound to STING (SAVI) significantly increased in the presence of STING (WT). These results suggest that STING (WT) can suppress the activity of STING (SAVI) by tethering STING (SAVI) to the ER through heterocomplex formation. The dormant heterocomplex formation may underlie, at least in part, the dominance of STING WT allele over SAVI alleles in the STING-triggered inflammatory response.

STING-associated vasculopathy with onset in infancy: a familial case series report and literature review.

Stimulator of interferon genes (STING1) is a key intermediary in activating the type I IFN response. STING-associated vasculopathy with onset in infancy (SAVI) is a very rare autoinflammatory disease that is caused by heterozygous gain-of-function mutations in STING1. SAVI typically manifests as neonatal-onset systemic inflammation, interstitial lung disease (ILD), and severe cutaneous vasculopathy located in acral regions, including fingers, toes, ears, and nose. Severity of ILD and recurrent pulmonary infections are crucial for the prognosis. Therapeutic options for SAVI are quite limited, and JAK inhibitors are considered to be a promising treatment according to several recent case reports. We report on a familial case series of SAVI with the R281Q mutation in the STING1 gene with predominant ILD manifestations, absence of cutaneous lesions, and poor response to ruxolitinib. Moreover, we reviewed all the case reports of SAVI in English published in the PubMed database. The atypical phenotype of the current cases adds to the growing list of inflammatory syndromes associated with SAVI. The literature analysis suggests that the severity and natural courses of the disease seem to be independent of the mutation type. Although JAK inhibitors may be a promising treatment, the therapeutic effect for different phenotypes and disease statuses of SAVI warrants further investigation.