Mechanisms of mineralocorticoid receptor antagonism on inflammation in muscular dystrophy

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PROJECT SUMMARY Gene therapy for Duchenne Muscular Dystrophy (DMD) is currently being tested in clinical trials in young patients. However, limitations of the adeno-associated virus (AAV) delivery system, including its small carrying capacity and its low efficiency transfection of muscle stem cells, will remain a barrier to a cure. The miniaturized transgene being delivered that is based on a Becker muscular dystrophy dystrophin (micro- dystrophin) will still result in some skeletal muscle turnover with subsequent inflammation and cardiomyopathy. Additionally, injury resulting from normal muscle use will be repaired with muscle stem cells that will likely not express dystrophin. Both of these issues will result in at least low-level chronic inflammation, which will likely exacerbate muscle damage and ultimate loss of transgene expression, limiting efficacy. Prednisone, which has served as the standard of care for DMD, but has many severe side effects, continues to be given as an anti- inflammatory to prevent an immune response to the transgene. Published and preliminary data support the scientific premise that mineralocorticoid receptor (MR) antagonists, which have clinical benefit for DMD cardiomyopathy, stabilize muscle membranes, improve skeletal muscle force, and reduce fibrosis, are also anti-inflammatory and represent an ideal drug for combination with gene transfer. However, the anti- inflammatory properties of MR antagonists in muscular dystrophy have not been explored. Since prednisone directly competes with MR antagonist binding to its receptors, these studies are crucial for clinical use of MR antagonists as an adjunct therapy to replace prednisone. In this application, we will test whether prednisone and MR antagonists have the same or different effects on specific immune cell populations in dystrophic muscles, whether cytokine reductions by MR antagonists are dependent on MR signaling mechanisms in muscle fibers or myeloid cells, and whether MR antagonists limit accumulated damage after acute injury in dystrophic mice treated with micro-dystrophin gene therapy. We have developed methods to flow sort immune cell populations from single muscles from the mdx genotypic model of DMD that will allow the first identification of the immune cell populations suppressed by prednisone, despite decades of clinical use, and a direct comparison with MR antagonists. These methods will also allow for the unbiased identification of gene expression changes in inflammatory myeloid cells induced by MR antagonists and prednisone. These studies will inform optimal MR antagonist clinical use as a co-therapy to extend efficacy of emerging genetic therapies for DMD and potentially other forms of muscular dystrophies. The data generated will also identify novel potential anti-inflammatory treatment targets.