Cytosolic Cathepsin Inhibitor Stefin B (Cystatin B) Regulate Caspase‐11 Expression

Abstract

Stefin B (cystatin B) is an endogenous cysteine cathepsin inhibitor, and the loss‐of‐function mutations in the stefin B gene were reported in patients with Unverricht‐Lundborg disease (EPM1). In this study we demonstrated that stefin B‐deficient (StB KO) mice were significantly more sensitive to the lethal LPS‐induced sepsis and secreted higher amounts of pro‐inflammatory cytokines IL‐1β and IL‐18 in the serum. We further showed that increased caspase‐11 gene expression and better pro‐inflammatory caspase‐1 and ‐11 activation determined in StB KO bone marrow‐derived macrophages resulted in enhanced IL‐1β processing. Pretreatment of macrophages with the cathepsin inhibitor E‐64d did not affect secretion of IL‐1β, suggesting that the increased cathepsin activity determined in StB KO bone marrow‐derived macrophages is not essential for inflammasome activation. Upon LPS stimulation, stefin B was targeted into the mitochondria, and the lack of stefin B resulted in the increased destabilization of mitochondrial membrane potential and mitochondrial superoxide generation. Collectively, our study demonstrates that the LPS‐induced sepsis in StB KO mice is dependent on caspase‐11 and mitochondrial reactive oxygen species but is not associated with the lysosomal destabilization and increased cathepsin activity in the cytosol.