Introduction: Cardiac fibroblasts (CFs) are abundant in the heart, where they play a major role in

cardiac homeostasis and disease development. However, a role for CF derived small extracellular

vesicles (sEV) in cardiac disease remains unclear. In this thesis, sEV derived from hypertrophic

cardiomyopathy (HCM) patient CFs and non-activated CFs (ICFs) have been cultured with

cardiomyocytes (CMs) to assess their effect on electrical and contractile activity of CMs.

Methodology: CFs isolated from tissue collected from HCM patients were characterised using flow

cytometry, RT-qPCR and immunohistochemistry. sEV were isolated from CF conditioned media using

ultrafiltration paired with size exclusion chromatography and characterised using nanoparticle tracking

analysis, electron microscopy and staining for the tetraspanins. These sEV were co-cultured with hiPSC

derived CMs for 48 hours at increasing concentrations to generate a dose response curve. The

electrophysiology and calcium cycling were measured using optical mapping and molecular changes

were measured using RT-qPCR and RNA sequencing.

Results: The results collected have provided evidence that HCM-CF sEV alter the contractility and

calcium handling of CMs by inducing hypercontractility and decreasing the calcium transient duration.

The ICF sEV also altered calcium handling but unlike HCM-CF sEV there was no induction of

hypercontractility. The mRNA expression of calcium handling genes such as RYR2 and Cav1.2 was

significantly altered with CF sEV treatment. Hypertrophy was evident in HCM-CF sEV treated CMs

with an increase in cell size and mRNA expression of atrial natriuretic peptide and brain natriuretic

peptide but not in CMs treated with ICF sEV.

Conclusion: This thesis has provided evidence that human CF sEV alter CM contractility and calcium

handling, with HCM-CF sEV but not ICF sEV, inducing a disease like phenotype reminiscent of CMs

from HCM patients.