A genetically engineered vertebrate animal model of NAA15-related heart disease uncovers myocardial growth, contractility, and mitochondrial defects

Delineating the genetic and environmental instigators of congenital heart disease (CHD), affecting up to 1% of newborns, will improve preventative, diagnostic, and therapeutic efforts to mitigate the disease. Although mutations in the N-alpha-acetyltransferase subunit gene NAA15 were recently associated with CHD in humans, a genetically engineered whole animal model of NAA15-related heart disease in a vertebrate species has yet to be described. We generated and characterized zebrafish carrying null mutations in paralogs naa15a and naa15b. Double homozygous naa15-deficient larvae suffered from diminutive, lowly contractile, and bradycardic ventricles composed of fewer and smaller cardiomyocytes incapable of proliferation. Myocardial re-expression of wild-type naa15a from a stable transgene partially rescued the contractile deficit. Moreover, transient, ubiquitous expression of WT human NAA15 achieved complete rescue, allowing for pathogenicity testing of human CHD variants of unknown significance. On a subcellular level, naa15-deficient CMs exhibited mild disruptions in sarcomere structure. Unlike double homozygous animals, animals carrying three mutant alleles and a reduced genetic dosage (RD) of naa15 grew to adulthood, sharing some phenotypes with double homozygous larvae, including reduced ventricular and cardiomyocyte size, as well as sarcomere disarray. Quantitative proteomics analysis of adult naa15RD hearts identified downregulation of proteins and acetylated N-terminal peptides from mitochondrial respiratory complex I. Abnormal mitochondrial density, size, and content were also documented in the myocardium of naa15-deficient larvae. Taken together, our studies demonstrate that a vertebrate animal model of naa15 disruption causes defects in cardiac development and function, with likely contributions from mitochondrial abnormalities, providing additional evidence that loss-of-function mutations in NAA15 are pathogenic for CHD.