New pharmacological strategies modulating PGC1alpha signalling and mitochondrial biogenesis to restore skeletal and cardiac muscle functionality in Duchenne Muscular Dystrophy

Duchenne’s muscular dystrophy (DMD) is a progressive, fatal muscle wasting disorder caused by mutations within the dystrophin gene with an estimated prevalence of 1:5000–10000 boys [1]. Glucocorticoids, the current standard of care in DMD, slow loss of motor function and muscle turnover [2]. However, their use is associated with severe adverse effects that are at odds with their beneficial effects in DMD. For heart dysfunction classical approaches with ACE inhibitors and beta-adrenoceptor antagonists are still the only available option. Cell based approaches including genome editing technology to repair DMD mutations and reprogramme satellite cells are still experimental [3]; issues of delivery, effectiveness, and safety of exon skipping and other genetic approaches are not optimal [4]. Hence the need to develop additional strategies ideally suited to act alone or as add on to the above therapies. A reasonable aim is to limit not only skeletal but also cardiac muscle wasting, since heart dysfunction contributes significantly to determine DMD prognosis. Mitochondria are key players in muscle homeostasis and a mitochondrial dysfunction is among the earliest cellular deficits in muscles of mdx mice (being deficient for dystrophin), reducing the ability of muscle cells to repair [5]. Approaches understanding and correcting mitochondrial dysfunctions are thus of absolute interest and might be explored in therapeutic perspective. Using well-established mouse models of DMD and human DMD samples we propose here to deepen the investigation on mitochondrial impairments during DMD progression at different stages of disease to identify specific molecular alterations that will be then tested for potential therapeutic effects. In preliminary studies we have identified low mitochondrial DNA (mtDNA) levels and PGC1a (peroxisomal proliferator-activated receptor coactivator 1 alpha) expression in adult mdx mice, in both skeletal and cardiac muscle, suggesting an impairment in the mitochondrial biogenetic pathway. Importantly, at earlier stages such an impairment is observed in conditions of forced exercise that is able to blunt the compensatory mechanisms typical of the benign mdx phenotype and to disclose a mechanical-metabolic uncoupling [6,7]. We thus intend to design therapeutic approaches based on the correction of mitochondrial biogenesis defect; this will be pursued through the three interconnected research AIMs described below. AIM1 is intended to assess the mitochondrial biogenesis process occurring during DMD progression, investigating both skeletal and cardiac muscle. We will unravel how and at which step mitochondrial biogenesis is impaired, whether this defect is progressive with the disease and how it is related to mechano-transduction defects, whether this accounts for the reduction of mitochondrial functionality and whether other processes, such as autophagy/mitophagy, could be involved in the mitochondrial phenotype of the diseases. We will investigate whether the defect affects a specific mitochondrial population and whether it results in changes of mitochondria distribution and localization. We will also evaluate whether the defect is present also in myogenic precursor cells affecting myogenic differentiation and regeneration. Noteworthy, the use of DMD patients’ specimens and myoblasts will allow us to investigate the possibility of translating our findings to humans. AIM 2 will be focused on PGC1a regulation, defining the molecular signatures of its blockade at transcriptional and post-translational level. To sustain a transcriptional impairment we will explore epigenetic modifications on the PGC1a promoter; besides we will investigate the nuclear “druggable” receptors REV-ERB and ROR that are emerging as new regulators of mitochondrial biogenesis and PGC1a, with potential therapeutic relevance in DMD. At post-translational level, PGC1a protein is activated by the Sirtui