A role for stefin B (cystatin B) in inflammation and endotoxemia [Cell Biology]

October 6th, 2014 by Maher, K., Jerič–Kokelȷ, B., Butinar, M., Mikhaylov, G., Manček–Keber, M., Stoka, V., Vasilȷeva, O., Turk, B., Grigoryev, S. A., Kopitar–Jerala, N.

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 the present 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 (BMDMs) resulted in enchanced IL-1β processing. Pretreatment of macrophages with a cathepsin inhibitor E-64d did not affect secretion of IL-1β, suggesting that the increased cathepsin activity determined in StB KO BMDMs is not essential for the inflammasome activation. Upon LPS stimulation stefin B was targeted into 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 oxygene species (mtROS), but is not associated with the lysosomal destabilization and increased cathepsin activity in the cytosol.