LUBAC modulates signalling by various immune receptors. In TNF signalling, linear (also known as M1) ubiquitin enables full gene-activation and prevents cell death. However, the mechanisms underlying cell-death prevention remain ill-defined. We show that LUBAC activity enables TBK1 and IKKε recruitment to and activation at the TNFR1-signalling complex (TNFR1-SC). Whilst exerting only limited effects on TNF-induced gene-activation, TBK1/IKKε are essential to prevent TNF-induced cell death. Mechanistically, TBK1/IKKε phosphorylate RIPK1 in the TNFR1-SC, thereby preventing RIPK1-kinase-activity-dependent cell death. This activity is essential in vivo , as it prevents TNF-induced lethal shock. Strikingly, NEMO/IKKγ, which mostly, but not exclusively, binds to the TNFR1-SC via M1-ubiquitin, mediates recruitment of the adaptors TANK and NAP1/AZI2 which are constitutively associated with TBK1/IKKε and TBK1, respectively. We here discover a previously unrecognised TBK1/IKKε-mediated cell-death checkpoint and uncover an essential survival function for NEMO by enabling recruitment and activation of these noncanonical IKKs to prevent TNF-induced cell death.

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) constitutes life-threatening autoimmune diseases affecting every organ, including the kidneys, where they cause necrotizing crescentic glomerulonephritis. ANCA activates neutrophils and activated neutrophils damage the endothelium, leading to vascular inflammation and necrosis. Better understanding of neutrophil-mediated AAV disease mechanisms may reveal novel treatment strategies. Here we report that ANCA induces neutrophil extracellular traps (NETs) via receptor-interacting protein kinase (RIPK) 1/3- and mixed-lineage kinase domain-like (MLKL)-dependent necroptosis. NETs from ANCA-stimulated neutrophils caused endothelial cell (EC) damage in vitro. This effect was prevented by () pharmacologic inhibition of RIPK1 or () enzymatic NET degradation. The alternative complement pathway (AP) was recently implicated in AAV, and C5a inhibition is currently being tested in clinical studies. We observed that NETs provided a scaffold for AP activation that in turn contributed to EC damage. We further established the in vivo relevance of NETs and the requirement of RIPK1/3/MLKL-dependent necroptosis, specifically in the bone marrow-derived compartment, for disease induction using murine AAV models and in human kidney biopsies. In summary, we identified a mechanistic link between ANCA-induced neutrophil activation, necroptosis, NETs, the AP, and endothelial damage. RIPK1 inhibitors are currently being evaluated in clinical trials and exhibit a novel therapeutic strategy in AAV.

Metabolic diseases are associated with an increased risk of severe COVID-19 and conversely, new-onset hyperglycemia and complications of preexisting diabetes have been observed in COVID-19 patients. Here, we performed a comprehensive analysis of pancreatic autopsy tissue from COVID-19 patients using immunofluorescence, immunohistochemistry, RNA scope and electron microscopy and detected SARS-CoV-2 viral infiltration of beta-cells in all patients. Using SARS-CoV-2 pseudoviruses, we confirmed that isolated human islet cells are permissive to infection. In eleven COVID-19 patients, we examined the expression of ACE2, TMPRSS and other receptors and factors, such as DPP4, HMBG1 and NRP1, that might facilitate virus entry. Whereas 70% of the COVID-19 patients expressed ACE2 in the vasculature, only 30% displayed ACE2-expression in beta-cells. Even in the absence of manifest new-onset diabetes, necroptotic cell death, immune cell infiltration and SARS-CoV-2 viral infection of pancreatic beta-cells may contribute to varying degrees of metabolic dysregulation in patients with COVID-19.