Abstract 20574: Engineered Biological Pacing Nodes Created From Induced Pacemaker Cells
Background: We have previously demonstrated transformation of ordinary cardiac myocytes to pacemaker cells by a transient expression of TBX18. Noting that the sinus rhythm originates from a unified automaticity of the sinoatrial node (SAN) rather than the individual pacemaker cells, we hypothesized that a 3-dimensional ensemble of TBX18-induced pacemaker cells (iPCs) would be superior to scattered single iPCs in pacing and driving the neighboring myocardium.
Methods: The iPCs were created by adenoviral gene transfer of TBX18 to neonatal rat ventricular myocytes. The control group consisted of the same cells transduced with a GFP vector. TBX18 or GFP spheroids were created by exploiting the self-assembling properties of the cardiac myocytes and subjecting them to hanging drops (1000 iPCs/drop). The spheroids were allowed to mature in suspension for one week.
Results: Three weeks after the spheroid formation, TBX18 spheroids maintained spontaneous pacing at 100±4 bpm while GFP spheroids were rarely active (0.01±0.01 bpm, p=0.0106). Monolayers of TBX18 cells exhibited automaticity, but such automaticity were often asynchronous, and the monolayers ceased to be viable in <2 weeks. Reflecting the weak electrical coupling in the SA node, the conduction velocity of TBX18 spheroids (1.3 ±0.9 cm/s) was 15-fold lower than that of GFP spheroids (19±12 cm/s). The slow conduction velocity in TBX18 spheroids was attributed to 17-fold increase in a small conductance gap junction, Cx45, transcripts (p<0.0001) and a 2-fold decrease in myocardial gap junction, Cx43 (p=0.003), compared to GFP-spheroids. When a cluster of 15-20 spheroids was surrounded by a monolayer of ventricular myocytes, TBX18, but not GFP, spheroids were able to pace and drive the neighboring sheet of ventricular myocytes. A monolayer of TBX18 cells failed to pace and drive the neighboring sheet of ventricular myocytes at the same source-to-sink ratio.
Conclusions: Taken together, TBX18 spheroids represent the first engineered SAN, with enhanced viability and the ability to overcome source-to-sink mismatch. The technology provides a convenient platform on which other SAN design principles may be built toward persistent biological pacemakers.
Author Disclosures: J. Sung: None. S. Gonzalez: None. J. Li: None. D. Wolfson: None. H. Cho: None.
- © 2016 by American Heart Association, Inc.