AAV9 gene replacement therapy for respiratory insufficiency in very‐long chain acyl‐CoA dehydrogenase deficiency

Very‐long chain acyl‐CoA dehydrogenase (VLCAD) deficiency (VLCADD) is an autosomal recessive disorder of fatty acid oxidation. Fatty acids are a major source of energy during catabolic stress, so the absence of VLCAD can result in a metabolic crises and respiratory insufficiency. The etiology of this respiratory insufficiency is unclear. Thus, our aims were: (1) to characterize respiratory pathophysiology in VLCADD mice (VLCAD −/− ), and (2) to determine if AAV9‐mediated gene therapy improves respiratory function. For the first aim, VLCAD −/− and wild‐type (WT) mice underwent an exercise/fast “stress protocol” and awake spontaneous breathing was evaluated using whole‐body plethysmography (WBP) both at baseline and during a hypercapnic respiratory challenge (FiO 2 : 0.21; FiCO 2 : 0.07; nitrogen balance). During hypercapnia, VLCAD −/− mice had a significantly lower frequency, tidal volume, minute ventilation, and peak inspiratory and expiratory flow, all of which indicate respiratory insufficiency. Histologically, the cardiac and respiratory muscles of stressed VLCAD −/− animals had an accumulation of intramyocellular lipids. For the second aim, a single systemic injection of AAV9‐VLCAD gene therapy improved this respiratory pathology by normalizing breathing frequency and enhancing peak inspiratory flow. In addition, following gene therapy, there was a moderate reduction of lipid accumulation in the respiratory muscles. Furthermore, VLCAD protein expression was robust in cardiac and respiratory muscle. This was confirmed by immuno‐staining with anti‐human VLCAD antibody. In summary, stress with exercise and fasting induces respiratory insufficiency in VLCAD −/− mice and a single injection with AAV9‐VLCAD gene therapy ameliorates breathing.