GUT BARRIER DYSFUNCTION: THE TRIGGER FOR CACHEXIA IN APCMIN/+ MICE

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Cancer cachexia is a condition of whole body wasting that is more common with gastrointestinal tract and lung cancers; cachexia accounts for 30-50% deaths with colon cancer. Thus, the prevention of cachexia is an important objective for the improvement of clinical outcomes in colon cancer patients. Studies on cellular mechanisms involved in muscle wasting indicate that cachexia is initiated by inflammatory signaling, which then activates ATP-dependent ubiquitin-dependent proteasomal degradation of protein, causing loss of muscle mass. Understanding the regulatory mechanisms that integrate inflammatory signaling and muscle proteolysis is critical for understanding cachexia. The PI currently has a RO1 grant funded through the National Cancer Institute to examine inflammatory cytokine IL-6 regulation of muscle protein synthesis and degradation, and muscle mitochondrial function in cachectic ApcMin/+ mice. The source of chronic low level inflammation in ApcMin/+ mice is not well established, but is thought to be related to the immune response to intestinal and colon tumors, and may also involve direct tumor cell secretion of cytokines. A question not addressed by our current funding is the cause of the systemic inflammation that is thought to initiate the skeletal muscle wasting in ApcMin/+ mice. Gut barrier dysfunction (GBD) is a condition where tight junctions between intestinal epithelial cells no longer form an impermeable barrier against bacterial infiltration into the submucosa and muscularis mucosa of the intestine.8 This can lead to endotoxemia (bacterial cell wall fragments in blood) or sepsis (viable bacteria in blood), leading to multiple organ dysfunction syndrome (MODS).7, 21 GBD has been well documented in hemorrhage shock models, and is associated with, and dependent on, increased circulating IL-6 levels; rats with knock-out of IL-6 do not develop GBD.27 We have recently shown that knockout of IL-6 also inhibits development of cachexia and that IL-6 over-expression induces cachexia in ApcMin/+ mice.5 Our preliminary studies demonstrate that a subset of 30 week old ApcMin/+ mice test positive for circulating endotoxin in the blood, and bacteria in the mesenteric lymph nodes. It is not known if GBD with low-level endotoxemia or sepsis, combined with increased expression of IL-6, is a significant source of inflammation that promotes tumorigenesis, tumor growth, and/or cachexia in ApcMin/+ mice. The overall purpose of the current proposal is to determine if gut barrier dysfunction is the primary cause of cachexia in ApcMin/+ mice. To the best of our knowledge the working hypothesis is completely novel. We hypothesize that cachexia is initiated by increased inflammation that results from endotoxin (bacterial lipopolysaccharide or intact bacteria) leakage across the gastrointestinal barrier in ApcMin/+ mice. Additionally, we hypothesize that elevated circulating IL-6 will be necessary to induce endotoxin leakage across the gastrointestinal barrier in ApcMin/+ and ApcMin/+ x Il-6-/- mice. This proposal merges Dr. John Baynes experience in analytical biochemistry, clinical biochemistry, and metabolism with Dr. Carson's understanding of physiology using whole animal models, including the ApcMin/+ mouse. This proposal also servers as a novel project that can bring Dr. Baynes's research expertise closer to the colorectal cancer research group at the University of South Carolina. Completion of this work will lead to a better understanding of the role of GBD and IL-6 signaling in regulation on cachexia, and identify potential novel therapeutic targets to both treat and prevent the cachectic condition. This proposal will provide essential preliminary data for further study in a multi-year RO1 application. Aim 1. Determine if gut barrier dysfunction increases with tumor burden and cachexia in the ApcMin/+ mouse. Aim 2. Determine if inflammatory cytokine IL-6 induces gut barrier dysfunction, in concert with the development of cachexia, in ApcMin/+ and ApcMin/+ x IL-6 -/- mice.