Investigating a novel catecholamine-associated cardiomyocyte subpopulation

Thesis

Excessive sympathetic stimulation of the heart, via catecholamines, is involved in a range of cardiac disease, from takotsubo cardiomyopathy to heart failure. Canonically, there are two main sources of catecholamines for sympathoexcitation. 1) Adrenaline, secreted by chromaffin cells in the adrenal medulla and carried by the bloodstream to the heart. 2) Noradrenaline, released by sympathetic nerve terminals within the heart. However, there is a growing body of literature highlighting a non-neuronal cellular source of catecholamines within the heart. This project aimed to characterise a cellular cardiac subpopulation associated with the gene expression of a catecholamine-synthesising enzyme. Mouse embryos and hearts from embryonic day 8.5 to neonates were single-cell RNA-sequenced. RNA velocity, a form of in-silico lineage inference, in combination with differential gene expression analysis and pseudotime inference suggested first heart field splanchnic mesoderm as the developmental origin for this subpopulation. An optogenetic lineage tracing mouse line for the gene encoding this catecholamine-synthesising enzyme was generated. Langendorff-perfused ex-vivo hearts from this mouse line were subjected to pulsed light stimulation. In addition, fluorescent microscopy of immunostained heart sections and genetic fluorescence was performed. These methods showed that the subpopulation was spatially distributed in the ventricular endocardium, subendocardium, atria and interventricular septum. The refractory periods of the cells were not significantly heterogeneous across the heart. The cells of the subpopulation had the size, morphology, striations and protein expression of cardiomyocytes. The subpopulation was shown to be proximal to sympathetic nerve terminals. Characterising subpopulations associated with intrinsic cardiac catecholaminergic signalling could lead to a better understanding of, and potential therapeutics for, cardiac pathologies where excessive catecholaminergic signalling plays a key role.

Authors: Lipov, A

• DOI: 10.5287/ora-w4vjan1bk
• Type of award: MSc by Research
• Level of award: Masters
• Awarding institution: University of Oxford
• Language: English
• Keywords: electrophysiology; sympathoexcitation; RNA velocity; lineage inference; RNA sequencing; optogenetics; heart; catecholamines
• Subjects: Cardiovascular pharmacology