Research

Our research is focused on the physiological and pathophysiological function of cardiac cells in a tissue context.

Methods that we employ for our studies include tissue culture, optical mapping, microfabrication, immunohistochemistry, protein and gene analysis, confocal microscopy, whole cell patch clamp, viral gene delivery, and genome editing. Our work is currently directed within the following areas:

 

APD80 map calculated from optical map of an hEB derived from H9 line of human embryonic stem cells, showing heterogeneity in action potentials within the hEB.

(Zhu, R., et al. Sci Rep 6, 18544 2016.)



Cardiomyocytes from Human Pluripotent Stem Cells
Human pluripotent stem cells can be differentiated into many different cell types, including cardiomyocytes (hPSC-CMs) that are potentially valuable resources for cardiac regenerative medicine and experimental models of the human cardiac tissue. We are interested in studying the electrophysiology of these derived cardiomyocytes in a variety of in vitro culture models, including spontaneously formed cell aggregates (human embryoid bodies, hEBs) and monolayers. Using optical mapping, we record high spatial resolution maps of action potentials and calcium transients from hPSC-CM populations, and study their heterogeneity and drug responses. We are working with other labs to develop automated algorithms to analyze action potential shapes by machine learning techniques that can assist the identification of phenotypes among populations of hPSC-CMs. We are also investigating cardiomyocytes derived from human induced pluripotent stem cell lines with certain mutations related to cardiac diseases, including Long QT syndrome (LQT) and Arrhythmogenic Right Ventricular Dysplasia (ARVD).

Phase contrast image of a cardiac microtissue.
  Engineered Cardiac Tissues
While traditional monolayer (planar 2D) cultures of cardiac myocytes are an important platform for in vitro investigations, they lack the complex spatial organization and biochemical signaling found in the native myocardium. We are interested in recapitulating important aspects of the natural 3D tissue environment so that cultured cardiac myocytes derived from a variety of sources will acquire the mature phenotype and organization of the post-natal heart. To achieve this, we are utilizing several tissue engineering approaches: decellularized cardiac slices, cardiac hydrogels, and cardiac microtissues. Optical mapping techniques are used to investigate the electrical activity of cardiac cells within these preparations.

Representative trace for Tetanizing Burst Therapy, a novel waveform for less painful ventricular defibrillation. 

AC stimulation for Cardiac Therapy 
We developed High Frequency Alternating Current (HFAC), a novel electrical waveform capable of blocking conduction across the entire myocardium. This property has been exploited to terminate complex arrhythmias like fibrillation in the whole heart. Our current research has grown out of this initial exploration of HFAC stimulation and is focused on the translation of a combined HFAC burst with a traditional defibrillation shock. The HFAC component results in a tetanized muscle that cannot further contract during defibrillation. This 'Tetanizing Burst Therapy,' or 'TBT,' has shown initial promise as a less painful alternative to traditional defibrillation. We are also exploring entirely high frequency (>5 kHz) pacing strategies to reduce the pain associated with transcutaneous pacing. 

 

                 
Fibrotic neonatal rat ventricular cell model with smooth muscle actin (SMA) staining indicating myofibroblasts and α-actinin staining indicating ventricular myocytes. (Thompson SA et al. Circulation. 2011;123:2083-2093)
  Myofibroblast - Cardiomyocyte Interactions
Because cardiac myofibroblasts are activated following cardiac injury, we are interested in investigating potential cellular interactions between myofibroblasts and cardiomyocytes, and subsequent effects on tissue electrophysiology. Our laboratory has shown that myofibroblast-myocyte mechanical interactions impair cardiac conduction and increase the vulnerability for reentrant waves in cultured cell monolayers through the application of contractile forces via heterocellular N-cadherin junctions. Additionally, we have shown that the impairment of conduction can be rescued by engraftment of cardiomyocytes derived from human embryonic stem cells (hESC-CMs).