A goal of our research is to understand interactions between the immune system and skeletal muscle that are important in regulating muscle repair, growth and regeneration. By better understanding these relationships, therapeutic manipulations of the immune system or its products can be designed to improve muscle growth and regeneration following acute trauma, disuse or chronic disease. Over the last several years, knowledge in this area has advanced substantially, showing that immune cells called M2 macrophages play a major role in muscle growth and regeneration. However, the identity of the specific, M2 macrophage-derived molecules that drive regeneration remains unknown. We propose to test the novel hypothesis that the protein Klotho generated by M2 macrophages is essential for normal growth and regeneration of muscle following injury. In addition, we will develop a novel, cell-based mechanism for targeting Klotho to injured muscle on demand, so that expression of the therapeutic protein is elevated specifically at the location and time of muscle regeneration. We propose to use an acute, muscle-injury model in mice to address the following aims:
Aim 1 : Test the hypothesis that genetic or pharmacological interventions that modulate Klotho levels affect muscle regeneration. We will manipulate Klotho levels in mice that experience muscle injury by expressing a Klotho transgene, by ablating the Klotho gene, by transplanting bone marrow-derived cells (BMCs) from Klotho transgenic mice and by administering Klotho protein. Mice will be assessed by molecular, physiological and morphological assays to determine the effects of modified Klotho levels on muscle growth and regeneration.
Aim 2 : Test the hypothesis that Klotho modulates shifts in inflammatory cells from pro-inflammatory M1 macrophages to pro-regenerative M2 macrophages following muscle injury. We will test whether genetic or pharmacological manipulations of Klotho affect macrophage phenotype or function following muscle injury.
Aim 3. Test the hypothesis that myeloid cells can be designed to target elevated Klotho expression to injured muscle during regeneration. We will generate a transgenic mouse line in which Klotho expression is driven by a promoter that is most-highly activated in myeloid cells in the context of inflammation and then assay whether transplanting BMCs from those mice promotes growth and regeneration of injured muscle in the recipients. We anticipate that these findings will establish the importance of Klotho in driving growth and regeneration of injured muscle. We also believe that this work can provide a basis for a new, cell-based delivery of therapeutic molecules to sites of injury and repair that may have significance beyond the treatment of muscle injuries.

Public Health Relevance

Muscle damage is a major component of injuries in the work-place, in recreational activities, in vehicle accidents and in combat; collectively, the medical costs for treating the effects of trauma to muscle to attempt to regain normal ambulation and function are immense and growing. Our investigation will elucidate mechanisms through which the immune system can promote growth and regeneration of injured muscle and we will develop a novel, cell-based strategy to improve muscle regeneration.

National Institute of Health (NIH)
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Research Project (R01)
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Skeletal Muscle Biology and Exercise Physiology Study Section (SMEP)
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Boyce, Amanda T
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University of California Los Angeles
Schools of Arts and Sciences
Los Angeles
United States
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Wehling-Henricks, Michelle; Welc, Steven S; Samengo, Guiseppina et al. (2018) Macrophages escape Klotho gene silencing in the mdx mouse model of Duchenne muscular dystrophy and promote muscle growth and increase satellite cell numbers through a Klotho-mediated pathway. Hum Mol Genet 27:14-29
Tidball, James G (2017) Regulation of muscle growth and regeneration by the immune system. Nat Rev Immunol 17:165-178
Chadwick, Jessica A; Swager, Sarah A; Lowe, Jeovanna et al. (2016) Myeloid cells are capable of synthesizing aldosterone to exacerbate damage in muscular dystrophy. Hum Mol Genet 25:5167-5177
Wehling-Henricks, Michelle; Li, Zhenzhi; Lindsey, Catherine et al. (2016) Klotho gene silencing promotes pathology in the mdx mouse model of Duchenne muscular dystrophy. Hum Mol Genet 25:2465-2482
Tidball, James G; Wehling-Henricks, Michelle (2015) Shifts in macrophage cytokine production drive muscle fibrosis. Nat Med 21:665-6
Tidball, James G; Welc, Steven S (2015) Macrophage-Derived IGF-1 Is a Potent Coordinator of Myogenesis and Inflammation in Regenerating Muscle. Mol Ther 23:1134-1135
Tidball, James G; Wehling-Henricks, Michelle (2014) Nitric oxide synthase deficiency and the pathophysiology of muscular dystrophy. J Physiol 592:4627-38
Tidball, James G; Bertoni, Carmen (2014) Purloined mechanisms of bacterial immunity can cure muscular dystrophy. Cell Metab 20:927-9