Sandra I. Grijalva                 

BME Ph.D. Defense Presentation

Date: Thursday, August 29, 2019

Time:10:00 am

Location: HSRB E-182 (Emory University)

Advisor: Hee Cheol Cho, PhD (Emory, BME and Pediatrics)

Committee Members:

Bum-Rak Choi, PhD (Brown University, Medicine)

Flavio Fenton, PhD (GaTech, Physics)

Rebecca Levit, PhD (Emory, Medicine)

Chunhui Xu, PhD (Emory, Medicine)

Title: Engineering cardiac biological pacemaker tissues to dissect source-sink mismatch in the heart

Abstract: Each and every heartbeat is initiated from, and driven by, the pacemaker cells in the sinoatrial node (SAN). More than 10 billion cardiac myocytes and non-myocytes make up the heart, but remarkably, it takes only a few thousand pacemaker (<10,000) cells to pace-and-drive the entire heart. Although we have a general understanding of how individual cardiac pacemaker cells beat automatically, there is a lack of understanding in how a few pacemaker cells can drive the beating of the entire heart. This problem, known as a “source-sink mismatch”, is a fundamental concept that has been difficult to study due to it being painfully low-throughput to study these pacemaker cells. Recently, we have demonstrated conversion of ventricular cardiomyocytes to induced pacemaker cells (iPMs) by singular expression of TBX18. In this thesis we develop a cardiac pacemaker tissue model of the SAN by exploiting the de novo iPMs.

We have examined four design principles of the native SAN, i) number of iPMs required to pace a given number of neighboring ventricular myocytes, ii) influence of autonomic nervous system on pacemaking, iii) role of non-myocyte population in pacemaking, and iv) the need for exit pathways. Our 3D model uses patterned cardiac spheroids, by 3D –printed silicone mold stenciling techniques. We have created a population of iPMs co-cultured with ventricular cardiomyocytes. The major readout is fast, high-resolution optical mapping using a calcium dye.

This work demonstrates the ability to reverse-engineer the SAN (eSAN) to i) provide the mechanistic insights on generating sinus rhythm at the tissue level, ii) exploit the insights gained to better engineer biological pacemakers.