Teresa Zimmers - US grants

DESCRIPTION (provided by applicant): Cachexia, or progressive wasting of fat and skeletal muscle despite adequate nutrition, is a devastating complication of cancer. Cachexia results in weakness, diminished quality of life, poor response to therapy, and susceptibility to illness. Cachexia afflicts more than half of all cancer patients and is responsible for 25-30% of all cancer-related deaths. Currently, there are no approved effective treatments for muscle wasting in cancer. In cancer patients, cachexia and mortality correlate closely with elevated serum IL-6 levels. In mice, IL-6 administration causes systemic wasting and IL-6 inhibition ameliorates cancer cachexia. However, the molecular mechanisms linking IL-6 and skeletal muscle wasting are unknown. Our long term goal is to establish the key regulatory pathways that mediate muscle wasting in cancer for the purpose of developing therapeutics. The objective of this application is to elucidate the mechanisms by which IL-6 results in skeletal muscle wasting in cancer. Our hypothesis is that IL-6 signaling in mature myofibers activates STAT3 and STAT3 target genes that together result in increased proteolysis and reduced hypertrophy. The net result is myofiber wasting. We base this hypothesis on considerable preliminary data. In skeletal muscle of 5 mouse models of cachexia, we have observed phosphorylated STAT3 and expression of known STAT3 target genes, including acute phase proteins. The IL-6/STAT3 transcriptome is also activated in skeletal muscle from patients with pancreatic cancer cachexia. We show that constitutively activated STAT3 is sufficient to cause wasting in myofibers and normal mouse skeletal muscle. Furthermore, over-expression of STAT3 inhibitors, abrogated IL-6-induced wasting of myotubes. Taken together, these results strongly implicate STAT3 as a causative factor in muscle wasting in cancer cachexia. The studies proposed here will determine definitively the role of the IL-6/gp130/STAT3 signaling pathway in muscle growth regulation in mature myofibers, both in normal physiology and in cancer cachexia. When these studies are complete, we will have identified potential targets for muscle preservation in cancer cachexia, as well as new regulators of skeletal muscle growth. The specific aims of this study are as follows: 1) Determine the role of the IL-6/STAT3 pathway and target genes in myotube hypertrophy and wasting in vitro, 2) Determine STAT3 and target gene functions in regulating mature myofiber growth in normal mice and in mouse models of cancer cachexia, and 3) Determine the contribution of skeletal muscle STAT3 to IL-6 induced wasting and cancer cachexia using skeletal muscle specific STAT3 null mice and our panel of MLC-SOCS3 transgenics. PUBLIC HEALTH RELEVANCE: Muscle wasting in cancer is associated with high levels of Interleukin-6, a blood-borne protein involved in inflammation and host defense. Using cell culture and mouse models, this study will determine how Interleukin- 6 activates muscle wasting in cancer in order to identify future therapeutic targets.

DESCRIPTION (provided by applicant): Muscle protein and adipose catabolism after burn or other life-threatening injury is likely an acute, adaptive response to preserve organ function and promote survival. However, persistent cachexia in the convalescent phase is pathological in itself. Hypermetabolism and catabolism of skeletal muscle mass for up to 2 years after burn injury renders patients vulnerable to injury and infection, retards wound healing, reduces overall function and diminishes quality of life. Myostatin is a skeletal muscle-specific member of the Transforming Growth Factor- 2 superfamily and a potent, tonic muscle growth inhibitor .Our long term goal is to define the key regulatory pathways mediating muscle wasting after burn injury for the purpose of developing therapeutics. The objective of this application is to determine the role of the myostatin signaling pathway in muscle wasting after burn injury. Our hypothesis is that myostatin and related ligands promote muscle wasting after burn injury, and that altering myostatin family signaling after burn will change burn survival, muscle mass and function. In the acute post-burn period, myostatin signaling and muscle wasting may facilitate survival. In the longer term, myostatin action and muscle wasting becomes maladaptive, reducing function and increasing vulnerability. We base this hypothesis on considerable preliminary data. We developed a mouse model of burn injury that causes long- term hyperinflammation and catabolism despite hyperphagia. Myostatin family signaling was increased in skeletal muscle after burn. Paradoxically, myostatin null mice exhibited enhanced wasting but also increased survival after burn. Administration of a myostatin inhibitor reduced muscle loss after burn injury. However, abolishing signaling from all myostatin-family ligands using a dominant negative ACVR2B transgenic resulted in 100% mortality after burn injury. These data indicate that myostatin family signaling plays an important, temporally regulated role in muscle size control after burn-injury. To study myostatin in burn, we have assembled a highly interactive, multidisciplinary team. The PI is a molecular biologist and expert in muscle wasting and the co-investigators are the world-leader in myostatin research, a highly accomplished academic surgeon-scientist, and the director of one of the country's largest and busiest burn centers. Each is necessary for the ultimate translation of these findings to therapeutics. Together we will determine the role of myostatin and myostatin-related ligand activity in burn-induced muscle wasting;determine the role of the myostatin family receptors ACVR2 and ACVR2B in burn-induced muscle wasting;and determine the role of SMAD2 activity in burn-induced muscle wasting. PUBLIC HEALTH RELEVANCE: The studies will result in new insights into the molecular pathways by which myostatin and related ligands regulate muscle mass in normal physiology and in burn wasting. They are essential pre-clinical studies for determining the potential clinical benefit of modulating myostatin for increasing survival and function after burn injury.

PROJECT SUMMARY: PROJECT 1 Cancer cachexia, or progressive weight loss featuring immunodysmetabolism, causes ~1/3 of cancer deaths. Loss of muscle mass reduces performance status, predisposes to illness, and increases treatment toxicity while reducing efficacy. Not merely a feature of end-stage cancer, cachexia is a disease with specific, targetable mechanisms. Pre-clinical studies prove that targeting those mechanisms can preserve muscle and lengthen survival, with or without chemotherapy. Cachexia is especially devastating in pancreatic ductal adenocarcinoma (PDAC), afflicting 85% of PDAC patients, most of whom present with weight loss. There is no effective treatment for PDAC and 5-year survival is ~9%. Thus, until PDAC can be cured early in its course, we must manage cachexia, because preserving muscle mass and function will promote response to cancer treatment, improve quality of life, and increase survival. Overall, our Program team hypothesizes that PDAC tumor progression and cachexia is highly orchestrated by an IL-6/IL6R/STAT3/NF-?B signaling axis. Project 2 will test NF-?B in muscle inflammation and tumor progression, and Project 3 will study IL-6/STAT3/NF-?B in tumor-stroma- immune interactions and the macroenvironment. Project 1 of this Program focuses on the crosstalk between adipose and skeletal muscle induced by PDAC tumors, and how IL6R, STAT3, and NF-?B combine to produce fat and muscle loss in the PDAC macroenvironment. Abundant data demonstrate that weight loss in PDAC is primarily fat loss in PDAC. Moreover, we showed that fat loss is as predictive of mortality in PDAC as muscle loss, regardless of response to therapy, suggesting a central role for adipose wasting in cachexia. Now we demonstrate that tumor-induced, muscle-derived soluble IL6R appears to induce IL-6 mediated adipocyte lipolysis, products of which feed forward to induce myosteatosis, lipotoxicity, dysmetabolism, weakness and atrophy through a novel PKC-? to PDK4 axis. Thus, we hypothesize that PDAC induces a feed-forward loop among tumor, fat, and muscle whereby tumor-induced IL-6 and other signals activate adipose STAT3 and lipolysis, products of which are taken up by muscle leading to myosteatosis, PKC-? activation and subsequent myofiber STAT3, NF-?B and PDK4 activation, which promote dysmetabolism, local inflammation and production of soluble IL6R to feed-forward activate adipose wasting. Blocking this cycle will preserve adipose and muscle wasting in PDAC. Using genetic mouse models, human specimens, advanced single cell resolution sequencing as well as correlative cachexia studies in a clinical trial, we will test our hypothesis in these specific aims: AIM 1. Interrogate the mechanisms of adipose-to-muscle crosstalk in the macroenvironment of PDAC cachexia. AIM 2. Interrogate mechanisms of muscle-to-adipose crosstalk in the macroenvironment of PDAC cachexia. AIM 3. Interrogate manifestations and mechanisms of the IL-6/IL6R/STAT3/NF-?B pathway in patients with PDAC cachexia.