Abstract 502: Resynchronization of Separated Rat Cardiomyocyte Fields Using Genetically Modified Human Ventricular Scar Fibroblasts: A Novel Approach in Reducing Dyssynchrony.
Background: Non-response to cardiac resynchronization therapy (CRT) is associated with the presence of slow or non-conducting scar tissue. Genetic modification of scar tissue, aimed at improving conduction, may be a novel approach to achieve effective resynchronization of cardiac tissue. Therefore we studied in a co-culture model the feasibility of resynchronization using genetically modified human ventricular scar fibroblasts (hVSFs).
Methods: hVSFs were transduced with lentivirus vectors either expressing the gene encoding for the cardiac transcription factor Myocardin (MyoC), or LacZ as control. A standardized in vitro model was used to investigate the effects of forced expression of MyoC in hVSFs on the resynchronization of two rat cardiomyocyte (CMC) fields, separated by a strip of hVSFs, and cultured on micro-electrode arrays. Also, the effects of MyoC expression on the capacity of hVSFs to serve as pacing site were studied using an external pipette electrode. MyoC-dependent gene activation in hVSFs was further examined by genetic and immunohistochemical analysis.
Results: Forced MyoC expression in hVSFs decreased dyssynchrony between the two CMC fields (control hVSFs: 27.6±0.2 ms, n=11, vs MyoC-hVSFs: 3.6±0.3 ms, n=11, at day 8, p<0.01). Conduction velocity across MyoC-hVSFs increased to 18±1.2 cm/s at day 8 (p<0.01 vs control hVSFs), thereby reaching values of CMCs. In addition, MyoC-hVSFs could be electrically stimulated, resulting in simultaneous activation of the two adjacent CMC fields, this in contrast to stimulation of control hVSFs. Importantly, forced MyoC expression in hVSFs led to a time-dependent upregulation of the expression or induction of various cardiac ion channel genes (e.g. SCN5A and CACNA1C) and those of connexins (Cx40 and Cx45).
Conclusions: Forced MyoC gene expression in hVSFs allowed electrical stimulation of these cells and endowed the capability to conduct an electrical impulse over a considerable distance, both resulting in resynchronization of two separated CMC fields. Both phenomena are most likely mediated by MyoC-induced expression of ion channels, involved in excitation, and the expression of connexins, mediating intra-cellular electrical coupling.