Electrophysiological signatures of BDNF/TrkB in human iPSC-derived cardiomyocytes

Abstract

Cardiovascular diseases are on the rise worldwide, with ischemic heart disease being the primary cause of death. Brain-derived neurotrophic factor (BDNF) and its high-affinity receptor, Tropomyosin-related kinase receptor B (TrkB), have emerged as potential cardioprotective factors that could mitigate cardiac damage following ischemic events. Also, BDNF/TrkB signaling has been implicated in regulating cardiac contractility in murine models, where it modulates calcium (Ca2+) cycling, which is necessary for normal cardiac contraction and relaxation. Here, we evaluated whether BDNF/TrkB signaling regulates electrophysiology and Ca2+ signaling in human cardiomyocytes derived from iPSC using bi- and tri-dimensional culture approaches. We differentiated iPSC into cardiomyocytes using dual Wnt modulation protocols and matured them with thyroid hormone and dexamethasone. We evaluated excitation-contraction coupling by assessing action potentials (FluoVolt), Ca2+ transients (Cal590), and contractility (contrast pixel correlation algorithm). We also evaluated wave propagation in monolayers using Ca2+ optical mapping to assess the effects of BDNF on conduction. We used engineered heart tissues (EHT) made of iPSC-CM and human fibroblasts to determine the impact of BDNF on cardiac contraction. T3/dexamethasone increased CM maturation, correlating with increased TrkB mRNA levels. BDNF stimulation increased Ca2+ spark frequency and increased spontaneous Ca2+ activity in hiPSC-CMs. Intriguingly, BDNF treatment increased spiral Ca2+ waves, which are characteristic of arrhythmic activity, likely due to RyR Ca2+ leaking. TrkB knockdown blunted these effects. BDNF treatment did not change Ca2+ levels in single cells but increased action potential duration and contraction. In EHT, we found that BDNF treatment preliminarily showed an increased contraction, as was previously reported on murine models, showing the advantages of bioengineered tissues. Here, we used iPSC-CMs and EHTs as an approximation to human physiology. We found that BDNF/TrkB altered electrophysiological properties in 2D monolayers and single-cell measurements. Furthermore, in 3D-cultured cardiomyocytes, BDNF increased contraction, suggesting that changes might rely on a cardiac structural component. This finding helps translate the cardioprotective role of this factor into a therapeutic approach and better understand this trophic factor's role and its receptor in human cardiac physiology.