STING-Mediated Lung Inflammation and Beyond

Mendelian autoinflammatory diseases characterized by constitutive activation of the type I interferon pathway, the so-called type I interferonopathies, constitute a rapidly expanding group of inborn errors of immunity. Among the type I interferonopathies, STING-associated vasculopathy with onset in infancy (SAVI) and COPA syndrome were described in the last 6 years, both manifesting a major inflammatory lung component associated with significant morbidity and increased mortality. There is striking clinical and histopathological overlap between SAVI and COPA syndrome, although distinct features are also present. Of note, there is a remarkably high frequency of clinical non-penetrance among individuals harboring pathogenic COPA mutations. SAVI is caused by, principally heterozygous, gain-of-function mutations in STING1 (previously referred to as TMEM173) encoding STING, a key adaptor of the interferon signaling pathway induced by DNA. COPA syndrome results from heterozygous dominant-negative mutations in the coatomer protein subunit alpha, forming part of a complex involved in intracellular cargo protein transport between the Golgi and the endoplasmic reticulum (ER). Of importance, a role for COPA in regulating the trafficking of STING, an ER-resident protein which translocates to the Golgi during the process of its activation, was recently defined, thereby possibly explaining some aspects of the phenotypic overlap between SAVI and COPA syndrome. Here, we review the expanding phenotype of these diseases, highlighting common as well as specific features, and recent advances in our understanding of STING biology that have informed therapeutic decision-making in both conditions. Beyond these rare Mendelian disorders, DNA sensing through STING is likely relevant to the pathology of several diseases associated with lung inflammation, including systemic lupus erythematosus, dermatomyositis, environmental toxin exposure, and viral infection.