Cardiac neurons expressing a glucagon-like receptor mediate cardiac arrhythmia induced by high-fat diet in Drosophila

Abstract

Cardiac arrhythmia leads to increased risks for stroke, heart failure, and cardiac arrest. Arrhythmic pathology is often rooted in the cardiac conduction system, but the mechanism is complex and not fully understood. For example, how metabolic diseases, like obesity and diabetes, increase the risk for cardiac arrhythmia. Glucagon regulates glucose production, mobilizes lipids from the fat body, and affects cardiac rate and rhythm, attributes of a likely key player. Drosophila is an established model to study metabolic diseases and cardiac arrhythmias. Since glucagon signaling is highly conserved, we used high-fat diet (HFD)-fed flies to study its effect on heart function. HFD led to increased heartbeat and an irregular rhythm. The HFD-fed flies showed increased levels of adipokinetic hormone (Akh), the functional equivalent to human glucagon. Both genetic reduction of Akh and eliminating the Akh producing cells (APC) rescued HFD-induced arrhythmia, whereas heart rhythm was normal in Akh receptor mutants (AkhRnull). Furthermore, we discovered a pair of cardiac neurons that express high levels of Akh receptor. These are located near the posterior heart, make synaptic connections at the heart muscle, and regulate heart rhythm. Altogether, this Akh signaling pathway provides new understanding of the regulatory mechanisms between metabolic disease and cardiac arrhythmia. HIGHLIGHTSO_LIHigh-fat diet activates Akh (glucagon-like)-producing neurons near the esophagus in Drosophila C_LIO_LIReducing Akh prevents high-fat diet-induced cardiac arrhythmia in flies C_LIO_LIDiscovery of two neurons located at the posterior end of the heart that express the Akh receptor (AkhR) and innervate the heart C_LIO_LIEliminating one of the two AkhR-expressing cardiac neurons (ACN) results in cardiac arrhythmia, whereas the absence of functional AkhR prevents high-fat diet-induced cardiac arrhythmia in flies C_LI