CARDIAC CONDUCTION SYSTEM IN ex vivo HUMAN HEARTS IN AGEING, OBESITY, AND HEART FAILURE - INNOVATIVE 3D ANATOMICAL RECONSTRUCTION, MORPHOLOGY, AND MOLECULAR PROPERTIES

Abstract

Background: Ageing and obesity are the common risk factors for cardiovascular diseases, and heart failure is one common outcome. With the increased ageing and obese population worldwide, it is crucial to analyse and understand the morphological alterations caused by ageing, obesity and heart failure. The cardiac conduction system (CCS) is a group of cells that work together to generate and propagate electrical impulses. It comprises the sinus node (SN), the atrioventricular conduction axis and the His-Purkinje networks. The SN is the main pacemaker site of the heart. In this thesis, the human cardiac structures were visualised and compared between the hearts of healthy and heart failure individuals, with an emphasis on the CCS. Then, the micro-anatomy of the SN and the surrounding RA regions were visualised and the impact of ageing and obesity on the morphology were determined. The sex differences were also determined. Finally, the molecular makeup of the healthy SN was determined, and the specific interactions of miRNAs (miRs), transcription factors (TFs) and mRNA were also determined. Methods: (1). Five post-mortem human hearts were obtained for research. Micro-computed tomography was used on these hearts. Amira software was used for high-resolution visualisations and various cardiac structures were segmented. (2). Human SN/RA tissue blocks were dissected from 23 post-mortem hearts. Paraffin was used to embed the block and Masson's Trichrome was used for histological staining. (3). Human SN/RA tissue blocks were dissected from 25 post-mortem hearts. The blocks were embedded in paraffin, and Masson's Trichrome staining and immunohistochemistry were performed. (4). The bioinformatics software, RStudio and Ingenuity Pathway Analysis were used to classify the mRNAs into contractile, mitochondrial and glycogen related mRNAs. These mRNAs were combined with miRs and TFs to predict the interactions. Main findings: (1). 3D segmented CV structures in the myocardial infarction hearts elicited diverse macro-/micro- anatomical changes, such as thickening valve leaflets, thickened aortic walls, enlarged aortic lumens, formation of new coronary arteries, increased or reduced thicknesses of pectinate and papillary muscles and Purkinje fibres, thinner left bundle branches, sinoatrial nodal atrophy and general atrioventricular conduction axis fragmentation, as well as increased epicardial fat in some hearts. (2). Ageing and obesity are two risk factors for extensive fibrosis and cellular hypertrophy in SN and RA, and obesity exacerbates the morphological alterations, especially hypertrophy of nodal and atrial myocytes. These morphological alterations might lead to functional alterations and eventually cause cardiovascular diseases. (3). In the SN and the surrounding RA, females, especially aged females are more likely to be impacted by morphological alterations, such as apoptosis, fibrosis, microvascular alterations, and cellular hypertrophy caused by obesity than males. (4). In human SN, TFs (such as MYCN and SOX2) mainly regulate mitochondrial mRNAs (such as COX5A, SLC25A11 and NDUFA8), while miRs (such as miR-153-3p, miR-654-5p, miR-10a-5p and miR-215-5p) mainly regulate contractile mRNAs (such as RYR2, CAMK2A and PRKAR1A). These interactions provide a further understanding of the molecular makeup of the SN and potential therapeutic targets for cardiovascular treatments.

Date of Award	14 Oct 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Halina Dobrzynski (Main Supervisor), Andrew Atkinson (Co Supervisor) & Tao Wang (Co Supervisor)