Generation of a Medaka Fish Model of Propionic Acidemia for Development of Novel Therapies.

Propionic acidemia (PA) is an autosomal recessive inborn error of metabolism caused by deficiency of the mitochondrial enzyme propionyl-CoA carboxylase (PCC). The disease presents with acute, recurrent and life-threatening crises of metabolic decompensation starting from the newborn period. Patients also suffer from multi-organ complications, neurological dysfunction, and cardiomyopathy. Despite available treatments, disease mortality and morbidity remain elevated and investigation of novel and more effective therapies is highly needed. I have generated a PA model in medaka fishes (Oryzias latipes) using TALENs targeting the pccb medaka gene, encoding one of the subunits of PCC. The pccbdel/del medaka recapitulates the clinical and biochemical phenotype of human patients. Affected medaka larvae showed early lethality and severe neurological impairment as shown by reduced and abnormal movements. Livers and hearts of pccbdel/del larvae exhibited increased lipid droplets, likely as a consequence of impaired mitochondrial β-oxidation. Importantly, pccbdel/del larvae showed a significant increase in the levels of propionylcarnitine (C3), the biochemical hallmark of the disease. Administration of a low-protein diet improved the survival of pccbdel/del larvae. Because PCC deficiency induces depletion of Krebs cycle intermediates, I investigated the efficacy of an anaplerotic therapy in pccbdel/del medaka fishes. The anaplerotic therapy comprising sodium citrate, ornithine α-ketoglutarate, and glutamine resulted in significant improvements of both survival and locomotor activity in pccbdel/del larvae. Given its small size, easy handling and large number of progeny, the PA medaka model is suitable for rapid investigation of novel drugs by large-scale drug screening. I have set a drug screening assay on whole fishes using the clinically relevant locomotor activity as read-out of the assay. This large drug screening has the potential to lead to the identification of small molecule drugs already approved for use in humans that have the potential to be rapidly translated in clinical applications