Skeletal muscle is enriched in hematopoietic stem cells and not inflammatory cells in cachectic mice Emanuele Berardi, Paola Aulino, Ivana Murfuni, Angelica Toschi, Fabrizio Padula, Bianca M. Scicchitano, Dario Coletti and Sergio Adamo Department of Histology and Medical Embryology, Sapienza University of Rome, and Interuniversity Institute of Myology, Via Scarpa, 14 00161 Rome, Italy Objective: Cachexia, a debilitating syndrome characterized by skeletal muscle wasting, is associated to many chronic diseases and diminishes the quality of life and survival of patients. Tumor-derived factors and proinflammatory cytokines, including TNF-alpha, IL-6 and IL-1beta, mediate cachexia. In response to elevated cytokine levels, increased proteasome-mediated proteolysis and auto-phagocytosis result in muscle wasting. The histologic features of muscle cachexia are not fully elucidated. Therefore, we analysed alterations of different cell populations in cachectic muscle. Methods: By immunohistochemical and cytological approaches, we characterized changes in the abundance of cellular populations in the musculature of a murine model of cancer cachexia (C26-bearing mice). Results: Cachectic muscle displayed a decreased DNA content proportional to muscle mass wastage. A decrease in the number of nuclei occurred in the muscular but not in the stromal compartment. Cachectic muscle showed: mild modulation of myeloperoxidase activity, a neutrophil marker; reduction of macrophages in the endomysium; decrease in CD3 z lymphocyte number. Conversely, a statistically significant enrichment in Sca-1 z CD45 z hematopoietic stem cells (HSCs) occurred in cachectic muscle. Discussion: The elevated levels of cytokines which characterize cachexia may represent a trigger for inflammatory cell activation. However, we find that in cachexia, inflammatory cells in muscle are not increased while muscle tissue nuclei decline. Our data suggest that the inflammatory cell-mediated stress is not an etiologic component of muscle wasting in cachexia. The relative increase in HSCs in cachectic skeletal muscle suggests an attempt to maintain muscle homeostasis by recruitment and/or activation of stem cells. [Neurol Res 2008; 30: 160– 169] Keywords: Cancer cachexia; hematopoietic stem cells; inflammatory cells; muscle inflamma- tion; muscle injury; muscle wasting INTRODUCTION Cachexia is a syndrome characterized by extreme weight loss due to skeletal muscle wasting associated to many chronic diseases, including cancer 1 . Cachexia lowers the patients’ responsiveness to therapy contribut- ing to poor prognosis and reducing both quality of life and survival. In vivo models of cachexia are based on a chronic, systemic inflammatory state obtained by several approaches including: cytokine gene delivery to a variety of tissues 2,3 , recombinant cytokine injection 4 and transplant of tumor cells 5 . Transgenic mouse models developing cachexia include the mice activating NF-kB 6 , resulting in muscle wasting and the Apc min/z mice, prematurely developing colon cancer and the associated cachexia 7,8 . Tumor growth and muscle wasting depend on factors of both tumor and host origin, such as tumor necrosis factor a (TNF-a), IL-1b, IL- 6, TGF-b, proteolysis-inducing factor and parathyroid hormone-related peptide. These factors lead to muscle wasting through reduced food intake and/or hyperme- tabolism 9 . Cytokines induce the transcriptional activity of MuRF1 and Atrogin-1/MAFbx which encode E3 ubiquitin ligase proteins mediating degradation of structural and functional muscular proteins 10 . Muscle tissue homeostasis depends not only on the protein synthesis/degradation ratio, but also on the balance between muscle damage and repair. The latter is operated by satellite cells and by stem cells of various origins 11 . Various cell surface markers have been employed to purify adult stem cell populations from skeletal muscle, including CD45, Sca-1, c-kit, CD34 12 . Co-expression of CD45 and Sca-1 characterizes hema- topoietic stem cells (HSC) of bone marrow origin, which Correspondence and reprint requests to: Dario Coletti, Department of Histology and Medical Embryology, Sapienza University of Rome, Via Scarpa, 14 00161 Rome, Italy. [dario.coletti@uniroma1.it] Accepted for publication August 2007. 160 Neurological Research, 2008, Volume 30, March # 2008 W. S. Maney & Son Ltd 10.1179/174313208X281046