In Vivo Study of Optineurin in Immunity and Inflammation

Optineurin is a multifunctional protein with sequence similarity with NEMO, the regulatory subunit of IκB kinase complex. NEMO preferentially binds K63-linked ubiquitin chains, and OPTN was shown to compete with NEMO for poly-ubiquitinated RIP1 dampening TNF-induced NF-κB signalling. Since OPTN is also an NF-κB target gene, it could act as a negative feedback regulator preventing uncontrolled inflammation. OPTN was also shown to be crucial for the phosphorylation of IRF3 and IFN type I production after LPS, and was shown to function as an autophagy receptor needed for the autophagic clearance of cytosolic Salmonella enterica. However, the vast majority of these data comes from in vitro studies and no full knockout mouse has been described. Therefore, we generated full OPTN-knockout mice to study the role of OPTN in vivo. OPTN-KO mice are indistinguishable from their wild-type littermates, develop normally and do not show any signs of spontaneous organ abnormality. Also upon DSS challenge OPTN-deficient mice do not show higher susceptibility to colitis. Unexpectedly, TNF-treated embryonic fibroblasts show normal NF-κB responses and also in vivo no differences could be observed upon TNF injection. However, in primary bone marrow derived macrophages, OPTN-deficiency leads to a reduced TBK1 and IRF3 phosphorylation and IFN type I production after LPS or poly(I;C), suggesting that OPTN is involved in innate immune responses upon pathogen infection. Finally, we inoculated mice with Salmonella enterica sv. Typhimurium and observed that in agreement with a role for OPTN in autophagy and bacterial clearance, OPTN deficiency sensitizes mice to Salmonella infection.