Inherited arrhythmogenic cardiac diseases and the kir2.1-nav1.5 channelosome

Resumen

Sudden cardiac death in children and young adults is a relatively rare but tragic event whose pathophysiology is unknown at the molecular level. The objective of this PhD Thesis in Physiology is to understand the emerging role of macromolecular ion channel complexes in the mechanisms of arrhythmias and sudden death in hereditary diseases of young individuals. Our recent identification of the interaction at the molecular level of the main sodium channel (NaV1.5) with the strong inward rectifying potassium channel (Kir2.1) in the control of cardiac excitability has led us to propose a new paradigm to establish the molecular bases of sudden cardiac death. Evidence indicates that these two ion channels form "channelosomes" in which they physically interact with common partners including adapter, scaffolding regulatory proteins. Both channels have direct links to hereditary human diseases. For example, certain mutations in the KCNJ2 gene encoding the Kir2.1 protein impede ion channel traffic to the membrane and result in Andersen-Tawil syndrome type 1 (also known as long QT syndrome type 7). Similarly, trafficking-deficient mutations in the gene encoding the NaV1.5 protein (SCN5A) result in Brugada syndrome. On the other hand, defects in the dystrophin gene (DMD) also lead to ion channel dysfunction and sudden cardiac death in Duchenne Muscular Dystrophy, further highlighting the relevance of macromolecular protein complexes in heart disease. By using mutant proteins that interrupt Kir2.1 or NaV1.5 trafficking from the sarcoplasmic reticulum or the Golgi apparatus, we have recently discovered that NaV1.5 and Kir2.1 can traffic together to their eventual membrane microdomains. Therefore, we proposed two working hypotheses: 1) the expression of a traffic-deficient Kir2.1 mutant protein will disrupt the traffic and functional expression of the associated NaV1.5 channels, and vice versa, thereby altering cellular excitability and establishing the substrate for arrhythmogenesis in genetically modified mouse models to reproduce Andersen-Tawil syndrome or Brugada syndrome. 2) In the case of Duchenne muscular dystrophy, by interfering with the dystrophin protein complex, the mutations that lead to a truncation of the Dp427 dystrophin isoform, alter the functional expression of the channelosome formed by NaV1.5 and Kir2.1, which controls cardiac excitability and conduction velocity causing arrhythmias and sudden cardiac death. We have used adeno-associated virus mediated gene transfer in mice and human cardiomyocytes derived from induced pluripotent stem cells (hiPSC-CMs) to define for the first time the mechanistic framework for interactions between NaV1.5 and Kir2.1 in human cells in vitro and the heart in vivo, and how deregulation of the NaV1.5-Kir2.1 channelosome caused by inherited mutations can result in arrhythmias and sudden death in three different cardiac diseases.