Deletion of toll-like receptor-4 downregulates protein kinase C-ζ and attenuates liver injury in experimental pancreatitis

Background. Toll-like receptor-4 (TLR4) and protein kinase C-zeta (PKC-zeta) play a role in macrophage activation. We hypothesized that deletion of TLR4 downregulates PKC-zeta and attenuates liver cell apoptosis in experimental pancreatitis. Methods. Acute pancreatitis was induced by choline-deficient ethionine diet in C57/BL6 (TLR4+/+ and TLR4-/-) mice. Results. During pancreatitis, staining for TLR4 and PKC-zeta, which colocalized in Kupffer cells but not in hepatocytes, increased in TLR4+/+ mice and decreased in TLR4-/- mice. In TLR4+/+ mice, pancreatitis increased TLR4 protein and mRNA and PKC-zeta protein and activity, nuclear factor (NF)-kappa B, ERK1/2, caspase-3 cleavage, and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining; all P <.01 versus controls. In TLR4-/- mice with pancreatitis, PKc-zeta mRNA and activity were reduced, ERK1/2 and caspase 3 did not increase, and NF-kappa B and TUNEL (mostly in hepatocytes) increased mildly (all P <.01 vs control). PKC-zeta. did not interact directly with NF-kappa B; however during pancreatitis, coimmunoprecipitation of PKC-zeta with ERK1/2 was increased in TLR4+/+ mice and was attenuated in TLR4-/- mice (all P <.01 vs control), indicating that PKC-zeta interacts with ERK1/2. Conclusion. Acute pancreatitis upregulates TLR4, PKC-zeta, Nf-kappa B, and ERK1/2, and increases apoptosis in mice livers. PKC-zeta induces nuclear translocation of NF-kappa B via ERK1/2-dependent mechanisms. Deletion of TLR4 downregulates PKC-zeta, NF-kappa B, and ERK1/2, and attenuates pancreatitis-induced liver cell apoptosis.