No abstract

Cardiovascular disease (CVD) is one of the leading causes of death worldwide. The most significant risk factors associated with the development of heart diseases include genetic and environmental factors such as hypertension, high blood cholesterol levels, diabetes, smoking, and obesity. Coronary artery disease accounts for the highest percentage of CVD deaths and stroke, cardiomyopathies, congenital heart diseases, heart valve defects and arrhythmias follow. The causes, prevention, and treatment of all forms of cardiovascular disease remain active fields of biomedical research, with hundreds of scientific studies published on a weekly basis. Generating animal models of cardiovascular diseases is the main approach used to understand the mechanism of pathogenesis and also design and test novel therapies. Here, we will focus on recent advances to finding the genetic cause and the molecular mechanisms of CVDs as well as novel drugs to treat them, using a small tropical freshwater fish native to Southeast Asia: the zebrafish (Danio rerio). Zebrafish emerged as a high-throughput but low-cost model organism that combines the advantages of forward and reverse genetics with phenotype-driven drug screenings. Noninvasive imaging allows in vivo analyses of cardiovascular phenotypes. Functional verification of candidate genes from genome-wide association studies has verified the role of several genes in the pathophysiology of CVDs. Also, zebrafish hearts maintain their ability to regenerate throughout their lifetime, providing novel insights to understand human cardiac regeneration.

Protein Kinase D2 belongs to a family of evolutionarily conserved enzymes regulating several biological processes. In a forward genetic screen for zebrafish cardiovascular mutants, we identified a mutation in the prkd2 gene. Homozygous mutant embryos develop as wild-type up to 36hours post-fertilization and initiate blood flow, but fail to maintain it, resulting in a complete outflow tract stenosis. We identified a mutation in the prkd2 gene that results in a T757A substitution at a conserved residue in the kinase domain activation loop (T714A in human PRKD2) that disrupts catalytic activity and drives this phenotype. Homozygous mutants survive without circulation for several days, allowing us to study the extreme phenotype of no intracardiac flow, in the background of a functional heart. We show dysregulation of atrioventricular and outflow tract markers in the mutants and higher sensitivity to the Calcineurin inhibitor, Cyclosporin A. Finally we identify TBX5 as a potential regulator of PRKD2. Our results implicate PRKD2 catalytic activity in outflow tract development in zebrafish.