Central role of liver in anticancer and radioprotective activities of Toll-like receptor 5 agonist.

Vertebrate Toll-like receptor 5 (TLR5) recognizes bacterial flagellin proteins and activates innate immune responses to motile bacteria. In addition, activation of TLR5 signaling can inhibit growth of TLR5-expressing tumors and protect normal tissues from radiation and ischemia-reperfusion injuries. To understand the mechanisms behind these phenomena at the organismal level, we assessed nuclear factor kappa B (NF-κB) activation (indicative of TLR5 signaling) in tissues and cells of mice treated with CBLB502, a pharmacologically optimized flagellin derivative. This identified the liver and gastrointestinal tract as primary CBLB502 target organs. In particular, liver hepatocytes were the main cell type directly and specifically responding to systemic administration of CBLB502 but not to that of the TLR4 agonist LPS. To assess CBLB502 impact on other pathways, we created multireporter mice with hepatocytes transduced in vivo with reporters for 46 inducible transcription factor families and found that along with NF-κB, CBLB502 strongly activated STAT3-, phenobarbital-responsive enhancer module (PREM), and activator protein 1 (AP-1-) -driven pathways. Livers of CBLB502-treated mice displayed induction of numerous immunomodulatory factors and massive recruitment of various types of immune cells. This led to inhibition of growth of liver metastases of multiple tumors regardless of their TLR5 status. The changed liver microenvironment was not, however, hepatotoxic, because CBLB502 induced resistance to Fas-mediated apoptosis in normal liver cells. Temporary occlusion of liver blood circulation prevented CBLB502 from protecting hematopoietic progenitors in lethally irradiated mice, indicating involvement of a factor secreted by responding liver cells. These results define the liver as the key mediator of TLR5-dependent effects in vivo and suggest clinical applications for TLR5 agonists as hepatoprotective and antimetastatic agents.

Topical bacterial lipopolysaccharide application affects inflammatory response and promotes wound healing.

The mechanisms underlying the complex and multistage wound-healing process are not yet completely understood. One of the most important and intriguing questions remaining is the effect of the interactions between wounds and the microflora that are present in wounds. In this report, we describe the first study of the effect of treating murine skin wounds with topical bacterial lipopolysaccharide (LPS), the main exogenous ligand of Toll-like receptor 4. Our findings demonstrate that LPS treatment strongly affects the wound-healing process by accelerating the resolution of inflammation, increasing macrophage infiltration, enhancing collagen synthesis, and altering the secretion of a number of mediators that are involved in the skin regeneration process. Topical LPS treatment upregulated the secretion of proinflammatory cytokines [interleukin (IL)-6, IL-1ß, and leukemia inhibitory factor (LIF)] and CC-chemokines (CCL2/MCP-1, CCL7/MCP-3, CCL3/MIP-1α, and CCL5/RANTES), but not CXC-chemokines (CXCL2/MIP-2 and CXCL9/MIG). The secretion of growth factors (vascular endothelial growth factor, transforming growth factor-ß1 (TGF-ß1), and fibroblast growth factor 2) at the wound site was also upregulated. Taken together, these results suggest that the topical application of LPS at the wound surface affects the inflammatory process and promotes the wound healing of injured skin.