Mimicking Isovolumic Contraction with Combined Electromechanical Stimulation Improves the Development of Engineered Cardiac Constructs

Abstract

Electrical and mechanical stimulation have both been used extensively to improve the function of cardiac engineered tissue as each of these stimuli is present in the physical environment during normal development in vivo. However, to date, there has been no direct comparison between electrical and mechanical stimulation and current published data are difficult to compare due to the different systems used to create the engineered cardiac tissue and the different measures of functionality studied as outcomes. The goals of this study were twofold. First, we sought to directly compare the effects of mechanical and electrical stimulation on engineered cardiac tissue. Second, we aimed to determine the importance of the timing of the two stimuli in relation to each other in combined electromechanical stimulation. We hypothesized that delaying electrical stimulation after the beginning of mechanical stimulation to mimic the biophysical environment present during isovolumic contraction would improve construct function by improving proteins responsible for cell-cell communication and contractility. To test this hypothesis, we created a bioreactor system that would allow us to electromechanically stimulate engineered tissue created from neonatal rat cardiac cells entrapped in fibrin gel during 2 weeks in culture. Contraction force was higher for all stimulation groups as compared with the static controls, with the delayed combined stimulation constructs having the highest forces. Mechanical stimulation alone displayed increased final cell numbers but there were no other differences between electrical and mechanical stimulation alone. Delayed combined stimulation resulted in an increase in SERCA2a and troponin T expression levels, which did not happen with synchronous combined stimulation, indicating that the timing of combined stimulation is important to maximize the beneficial effect. Increases in Akt protein expression levels suggest that the improvements are at least in part induced by hypertrophic growth. In summary, combined electromechanical stimulation can create engineered cardiac tissue with improved functional properties over electrical or mechanical stimulation alone, and the timing of the combined stimulation greatly influences its effects on engineered cardiac tissue.

Depolarization of Cellular Resting Membrane Potential Promotes Neonatal Cardiomyocyte Proliferation In Vitro

“…In order to assess the potential cell signaling pathways involved in any measured effect of depolarization, we identified pathways previously implicated in proliferation and cell survival and studied them using Western blot techniques previously described by our lab [32]. Briefly, after the 4 days in culture cells were lysed and analyzed with a BCA assay (Pierce, Rockford, Illinois) to determine the protein concentration for each sample.…”

It's all in the timing: Modeling isovolumic contraction through development and disease with a dynamic dual electromechanical bioreactor system

“…1 The aim of this commentary is to provide additional insights into the rationale behind the simulation of isovolumic contractions in a dual stimulation bioreactor system, introduce new data that supports our claims that the timing of combined stimulation is important, and highlight potential uses of this technology in the study of various cardiac diseases.…”

“…1 The ability to vary the timing between electrical and mechanical stimulation is a powerful tool that allows us to mimic both normal developmental processes that are likely important in cardiomyocyte and myocardial tissue maturation as well as diseased tissues, such as those that exist in aortic valve stenosis and heart failure. Future studies will aim to investigate the effects of elongated and shortened isovolumic contraction time and its effects on tissue development with the goal of simulating a disease model system in vitro for studying potential treatment options.…”

Cardiac Tissue Engineering for the Treatment of Heart Failure Post-Infarction

“…Electrical stimulation has been used in concert with perfusion and resulted in an increase in cell elongation, enhanced expression of gap junction protein connexin-43, increase in cell number, and an increase in contractile performance [52,53]. However, the combination of stretch and β-adrenergic stimulation resulted in no additional benefit [53].…”