Inhibition of Tgfβ signaling enables durable ventricular pacing by TBX18 gene transfer

Implantable cardiac pacemaker devices are generally effective for patients with symptomatic bradyarrhythmia. However, device-dependent cardiac pacing is far from ideal and often inadequate, particularly for pediatric patients who need to go through invasive revision of the indwelling hardware. Biological pacemakers have been proposed as device-free alternatives to the current treatment, but sustained, unwavering biological pacing beyond days after the biologic delivery has not been demonstrated. We have previously demonstrated that re-expression of an embryonic transcription factor, TBX18, could reprogram ventricular cardiomyocytes into induced pacemaker myocytes (iPMs). Here, we report that exogenous expression of TBX18 per se leads to severe fibrosis in situ, impairing the iPMs ability to pace together. Acute fibrosis is accompanied with proliferation and activation of cardiac fibroblasts via Tgf{beta}-Smad2/3 pathway. Small molecule inhibition of Tgf{beta} signaling mitigated the interstitial remodeling, independent from TBX18-induced iPM reprogramming at the single-cell level. Direct and focal gene transfer of TBX18 into the left ventricular myocardium created ventricular pacing in a rat model of chronic atrioventricular block, but such activity began to wane in a week. In contrast, a combination therapy consisting of TBX18 gene transfer and Tgf{beta} inhibition enabled sustained biological pacing beyond the four-week study period. Our data demonstrate that inhibition of Tgf{beta} signaling suffices to achieve durable cardiac pacing by TBX18-induced biological pacemakers.