Mice bearing the Colon-26 (C26) carcinoma represent a classical model of cancer cachexia. Progressive muscle wasting occurs in association with tumor growth, over-expression of muscle-specific ubiquitin ligases, and reductions in muscle cross-sectional area. Fat loss is also observed. Cachexia is studied in a time-dependent manner with increasing severity of wasting.
Cancer cachexia is the progressive loss of skeletal muscle mass and adipose tissue, negative nitrogen balance, anorexia, fatigue, inflammation, and activation of lipolysis and proteolysis systems. Cancer patients with cachexia benefit less from anti-neoplastic therapies and show increased mortality1. Several animal models have been established in order to investigate the molecular causes responsible for body and muscle wasting as a result of tumor growth. Here, we describe methodologies pertaining to a well-characterized model of cancer cachexia: mice bearing the C26 carcinoma2-4. Although this model is heavily used in cachexia research, different approaches make reproducibility a potential issue. The growth of the C26 tumor causes a marked and progressive loss of body and skeletal muscle mass, accompanied by reduced muscle cross-sectional area and muscle strength3-5. Adipose tissue is also lost. Wasting is coincident with elevated circulating levels of pro-inflammatory cytokines, particularly Interleukin-6 (IL-6)3, which is directly, although not entirely, responsible for C26 cachexia. It is well-accepted that a primary mechanism by which the C26 tumor induces muscle tissue depletion is the activation of skeletal muscle proteolytic systems. Thus, expression of muscle-specific ubiquitin ligases, such as atrogin-1/MAFbx and MuRF-1, represent an accepted method for the evaluation of the ongoing muscle catabolism2. Here, we present how to execute this model in a reproducible manner and how to excise several tissues and organs (the liver, spleen, and heart), as well as fat and skeletal muscles (the gastrocnemius, tibialis anterior, and quadriceps). We also provide useful protocols that describe how to perform muscle freezing, sectioning, and fiber size quantification.
Muscle wasting is a serious complication of various clinical conditions such as cancer, sepsis, liver, cirrhosis, heart and kidney failure, chronic obstructive pulmonary disease, and AIDS. In particular, muscle wasting is evident in at least 50% of patients with cancer1. Loss of skeletal muscle in cancer results from increased protein degradation due to the over-activation of the skeletal muscle proteolytic systems and/or from decreased protein synthesis6. Lipolysis is also evident, leading to the depletion of adipose tissue. Clinically, cachexia is associated with reduced quality and length of life and is estimated to be the cause of death in 20 – 30% of cancer patients7. Use of experimental models that resemble the human disease as closely as possible would be beneficial. An optimal animal model is characterized by high reproducibility, as well as by limited interference from different therapies and the unpredictable factors of diet, sex, and genetic background that are usually associated with the clinical condition8. So far, cancer cachexia has been studied mainly in animal models characterized by transplantation of cancer cells or injection of carcinogens, although a new method is to use genetically modified mice susceptible to the development of cancer.
Mice bearing the C26 carcinoma (also referred to as colon-26 and adenocarcinoma) represent a well-characterized and extensively used model of cancer cachexia2,5. The growth of the C26 tumor results in body and muscle weight loss, mainly through enhanced fat and protein catabolism9. Generally, a 10% tumor weight versus total body weight is associated with a reduction of 20-25% in skeletal muscle weight and a greater depletion of fat3,10. Hepatomegaly and splenomegaly are also observed with tumor growth, along with the activation of the acute phase response and the elevation of pro-inflammatory cytokine levels3,11. Among these, it is well known that IL-6 plays a pivotal role in mediating muscle wasting in the C26 model, even though this cytokine is probably not the only inducer of cachexia12. Elevated IL-6 causes muscle atrophy through activation of the JAK/STAT3 pathway, and inhibiting this transcription factor can prevent muscle wasting3,4.
During C26-induced muscle wasting, as in many conditions of muscle atrophy, muscle mass is lost largely through reductions in muscle protein content across muscle fibers, not through cell death or loss of fibers13. In C26 cachexia, a shift towards smaller cross-sectional areas is observed in both glycolytic and oxidative fibers2. This is also consistent with reduced muscle strength5. Many groups worldwide have taken advantage of the C26 model in order to discover new mediators of muscle wasting or clinically relevant drugs for cancer cachexia. However, many different procedures for the use of this model have been reported, raising concerns about the consistency of the obtained data and posing barriers to reproducibility in different experimental conditions. Here we report a typical use of this model for the study of cancer cachexia that yields standardized and reproducible data.
Especially in its latest stages, colorectal cancer is associated with the development of cachexia, which is responsible for poorer outcomes and reductions in patient quality of life. Many studies have focused on the treatment of conditions secondary to cancer; however, despite many efforts in this direction, there is still no approved therapy for cancer cachexia21. Thus, it is imperative that animal models resemble the human pathology as closely as possible in order to maximize the translation of findings.
…The authors have nothing to disclose.
We thank Richard Lieber and Shannon Bremner for their ImageJ macro and instructions. While at Thomas Jefferson University, this work was supported by the Pennsylvania Department of Health CURE Grant TJU No. 080-37038-AI0801. Subsequently, this study was supported by a grant to AB from the National Institutes of Health (R21CA190028), and by grants to TAZ from the National Institutes of Health (R01CA122596, R01CA194593), the IU Simon Cancer Center, the Lustgarten Foundation, the Lilly Foundation, Inc., and the IUPUI Pancreas Signature Center.
Cell culture Flasks | Falcon – Becton Dickinson | 35-5001 | |
DMEM | Cellgro | 10-017-CV | |
FBS | Gibco | 26140 | |
Streptomycin-Penicillin | Cellgro | 30-002-CI | |
CD2F1 mice | Harlan | 060 | |
Anesthesia apparatus | EZ-Anesthesia | EZ-7000 | |
2-Methyl Butane | Sigma-Aldrich | M32631 | |
OCT | Tissue-Tek | 4583 | |
Cryostat | Leica | CM1850 | |
Cork disks | Electron Microscopy Sciences | 63305 | |
Superfrost plus glass slides | VWR | 48311-703 | |
Anti-Laminin Rabbit polyclonal antibody | Sigma-Aldrich | L9393 | |
Anti-Dystrophin Mouse Monoclonal antibody | Vector Laboratories | VP-D508 | |
Alexa Flour 594 anti-mouse IgG | Life Technologies | A11062 | |
Alexa Flour 594 anti-rabbit IgG | Life Technologies | A21211 | |
Hematoxylin | Sigma-Aldrich | GHS216 | |
Eosin | Sigma-Aldrich | HT110332 | |
Xylene | Acros Organics | 422680025 | |
Cytoseal-XYL | Thermo | 8312-4 | |
Microscope | Zeiss | Observer.Z1 | |
Bamboo Tablet | Wacom | CTH-661 | |
Prism 7.0 for Mac OS X | GraphPad Software, Inc. | ||
Excel for Mac 2011 | Microsoft Corp. | ||
Image J | US National Institutes of Health | IJ1.46 | http://rsbweb.nih.gov/ij/download.html |
Microtainer | BD | 365873 |