Project Summary/Abstract Disruption of mitochondrial oxidative phosphorylation (OXPHOS) is associated with the development of biochemical alterations that typically affect tissues with a high energy demand, particularly skeletal and cardiac muscle. An inherited autosomal recessive skeletal myopathy and hypertrophic cardiomyopathy has been linked to loss of function of a nuclear DNA-encoded mitochondrial protein, due to a frameshift mutation in solute carrier family 25, member 4 (SLC25A4; c.523delC, p.Q175RfxX38). SLC25A4 encodes the heart-muscle isoform of the adenine nucleotide translocator-1 (ANT1, SLC25A4), which in the wild-type state is a critical component of mitochondrial metabolism. Patients with SLC25A4 deficiency display lactic acidosis, persistent adrenergic activation, and exertional intolerance secondary to both a general skeletal muscle myopathy as well as a hypertrophic cardiomyopathy. Ultimately, myocardial thickening and cardiac dysfunction progress to end- stage heart failure necessitating cardiac transplantation. There are not currently any disease-modifying therapies available for this patient cohort. However, adeno- associated viral (AAV) mediated gene replacement therapies have emerged as a powerful strategy for disease modification of inherited monogenic disorders. The long-term goal of our research is to develop a therapeutic gene replacement strategy to treat SLC25A4 deficiency. The objective of this proposal is to further characterize the disease phenotype as well as to synthesize and evaluate the efficacy of a recombinant AAV (rAAV) vector in an in vitro model of patient-derived cell lines and organoid models. The central hypothesis of this proposal is that AAV-mediated gene replacement can ameliorate the biochemical and functional effects of SLC25A4 deficiency and can more decisively prevent disease progression. The specific aims of this proposal are: 1. Characterize the SLC25A4 deficiency phenotype in patient-derived cell lines. 2. Synthesize a recombinant AAV vector for delivery of codon-optimized SLC25A4 cDNA to skeletal and cardiac myocytes. 3. Evaluate the efficacy of AAV-SLC25A4 viral transduction in patient-derived cell lines. These experiments will improve our understanding of the molecular mechanisms underlying SLC25A4 deficiency as well as allow us to evaluate the efficacy of an AAV platform in a relevant preclinical model. Moreover, the skills I will acquire during this fellowship will help to establish me as an independent investigator and a surgeon-scientist focused on the development of translational gene replacement therapies.

PROJECT NARRATIVE SLC25A4 deficiency is an inherited disorder that manifests as a progressive skeletal myopathy and hypertrophic cardiomyopathy; there are no effective systemic therapies for affected patients. Preliminary data from our laboratory demonstrate that recombinant AAV vectors with specific tropism for skeletal muscle cells and cardiomyocytes can be synthesized. Here, we investigate the efficacy of myotropic AAV-mediated gene replacement as a therapeutic option for SLC25A4 deficiency.