Abstract 15180: Inhibition of Tgfβ Signaling Enables Durable Ventricular Pacing by TBX18 Gene Transfer

Introduction: Somatic gene transfer of an embryonic transcription factor, TBX18, could directly reprogram ventricular myocytes to induced pacemaker myocytes. We and others have previously reported that direct myocardial gene delivery of TBX18 created ventricular pacing in heart block animals in vivo. However, the de novo biological pacing was short-lived, diminishing its translational value.

Hypothesis: Our preliminary RNAseq and mass spec data indicate pronounced Tgfβ signaling in TBX18-transduced cardiomyocytes. Tgfβ signaling induces fibrosis in multiple organs including the heart. We hypothesized that TBX18 triggers Tgfβ signaling and results in fibrosis, leading to loss of durable ventricular pacing.

Methods: Adenoviral vectors expressing TBX18 or GFP was delivered to neonatal rat ventricular myocytes (NRVMs) in vitro or to the left ventricular apex of adult rats with complete atrioventricular block (CAVB).

Results: In vitro experiments showed increased population of vimentin+ fibroblasts and alpha smooth muscle actin+ myofibroblasts in TBX18-NRVMs compared to GFP-NRVMs at 2 weeks after gene transfer. Single cell transcriptome data indicated that TBX18 triggered substantial changes in extracellular matrix-related gene expression and Tgfβ signaling. Quantitative RT-PCR and ELISA validated scRNA-seq data, indicating fibroblast activation. TBX18-NRVMs showed faster automaticity than that control did, but their automaticity began wavering after day 7. Treatment of TBX18-NRVMs with a Tgfβ signaling inhibitor, A83-01, mitigated fibroblast activation by TBX18 and preserved their automaticity.

Direct delivery of TBX18 into ventricular myocardium resulted in focal fibrosis as well as expansion of vimentin+ fibroblasts at day 7. TBX18 gene transfer initiated ventricular pacing in a rat model of CAVB, but ventricular pacing diminished after one week. In contrast, treating TBX18-injected animals with A83-01 enabled sustained biological pacing beyond three weeks of after gene delivery, accompanied by reduced fibrosis in situ.

Conclusions: Inhibition of Tgfβ signaling is sufficient to achieve durable cardiac pacing by TBX18-induced biological pacemakers.