New research reveals the underlying mechanism for a dangerous heart disorder in which low oxygen levels in the heart produce life-threatening arrhythmias.
The discovery, made with human heart muscle cells derived from pluripotent stem cells, offers new targets for therapies aimed at preventing sudden death from heart attack.
“Our research shows that within seconds, at low levels of oxygen (hypoxia), a protein called small ubiquitin-like modifier (SUMO) is linked to the inside of the sodium channels which are responsible for starting each heartbeat,” says Steve A. N. Goldstein, vice chancellor for health affairs at the University of California, Irvine and professor in the School of Medicine departments of pediatrics and physiology and biophysics.
“And, while SUMOylated channels open as they should to start the heartbeat, they re-open when they should be closed. The result is abnormal sodium currents that predispose to dangerous cardiac rhythms.”
Every heartbeat begins when sodium channels open and ions to rush into heart cells—this starts the action potential that causes the heart muscle to contract. When functioning normally, the sodium channels close quickly after opening and stay closed. After that, potassium channels open, ions leave the heart cells, and the action potential ends in a timely fashion, so the muscle can relax in preparation for the next beat.
If sodium channels re-open and produce late sodium currents, as observed in this study with low oxygen levels, the action potential is prolonged and new electrical activity can begin before the heart has recovered risking dangerous, disorganized rhythms.
Fifteen years ago, the Goldstein group reported SUMO regulation of ion channels at the surface of cells. It was an unexpected finding because the SUMO pathway had been thought to operate solely to control gene expression in the nucleus.
“This new research shows how rapid SUMOylation of cell surface cardiac sodium channels causes late sodium current in response to hypoxia, a challenge that confronts many people with heart disease,” says Goldstein. “Previously, the danger of late sodium current was recognized in patients with rare, inherited mutations of sodium channels that cause cardiac Long QT syndrome, and to result from a common polymorphism in the channel we identified in a subset of babies with sudden infant death syndrome (SIDS).”
The information gained through the current study offers new targets for therapeutics to prevent late current and arrhythmia associated with heart attacks, chronic heart failure, and other life-threatening low oxygen cardiac conditions.
The National Institutes of Health funded the study, which appears in Cell Reports.
Source: UC Irvine