Stereotactic arrhythmia radioablation at 25 Gy induced early fibroblast activation, ECM remodelling gene expression changes, and endothelial injury without mature fibrosis at 10 weeks in pigs.
Does stereotactic arrhythmia radioablation (STAR) induce fibrotic remodelling and fibroblast activation in a pig myocardial infarction model?
STAR induces early fibroblast and endothelial activation with intramyocardial hemorrhage at 10 weeks in a pig model, preceding mature macroscopic fibrosis.
Abstract Background Ventricular tachycardia (VT) is a common and often therapy-refractory clinical problem in structurally abnormal hearts. Stereotactic arrhythmia radioablation (STAR) is hypothesized to reduce VT by inducing localized tissue remodelling and fibrosis, thereby homogenizing the myocardial scar and disrupting re-entry circuits. This non-invasive approach delivers a single, high-dose (25 Gy) fraction of radiation targeted to arrhythmogenic substrates. While clinical outcomes are promising, the cellular and molecular mechanisms driving this remodelling remain poorly defined. Purpose To investigate how STAR induces fibrotic remodelling through fibroblast activation and altered extracellular matrix (ECM) composition, that may underlie homogenization of the arrhythmogenic substrate in a pig myocardial infarction (MI) model. Methods A single 25 Gy dose was delivered to the scar and border zone (N=2), 4 weeks after inducing the MI. An additional planned low-dose (5 Gy) was targeted to the posterior wall. Healthy weight-matched pigs (N=4) received anatomically matched dosing (Ctrl). Non-irradiated healthy pigs (non-IR) served as controls (N=4). At 10 weeks post-STAR, myocardial samples from the 25 Gy and 5 Gy regions were collected for histology, immunofluorescence, and RT-qPCR using a predefined panel of genes related to fibrosis, fibroblast activation, and endothelial function. Results Preliminary data showed no macroscopic fibrosis in the irradiated regions in both MI and Ctrl (25 Gy 4.29±0.74% in MI vs 6.32±1.24% in Ctrl; 5 Gy 4.29±0.74% in MI vs 6.29±3.90% in Ctrl), with values comparable to previously published non-IR pigs. Initial analysis revealed changes in collagen gene expression in the 25 Gy region. Relative to non-IR animals, COL1A1 (-1.5-fold in MI, -1.8-fold in Ctrl), COL1A2 (-1.5-fold in MI, -2.3-fold in Ctrl), and COL3A1 (-6.1-fold in MI, -4.9-fold in Ctrl) were consistently downregulated, whereas COL8A1 was upregulated (+3.0-fold in MI, +3.2-fold in Ctrl). Early fibroblast activation demonstrated by altered gene expression of POSTN (+5.9-fold in MI, +6.8-fold in Ctrl) and ACTA2 (+1.4-fold in MI, +2.3-fold in Ctrl) compared to non-IR controls, and supported by similar protein-level observations was observed in the 25 Gy region. Initial histological assessment identified intramyocardial hemorrhage (IMH) localized to the 25 Gy region in both MI and Ctrl. This was accompanied by changes in endothelial marker expression, including CD31 (-55.9-fold in MI, -2.9-fold in Ctrl), ENG (-4.5-fold in MI, -1.1-fold in Ctrl), and ICAM1 (+1.3-fold in MI, +2.2-fold in Ctrl), suggesting endothelial activation and injury. All findings were confined to the 25 Gy region and were not observed in the 5 Gy region. Conclusion STAR induces early fibroblast activation and gene expression changes related to ECM remodelling, alongside endothelial injury, indicating early remodelling without mature fibrosis at 10 weeks post-treatment.
Nys et al. (Fri,) conducted a other in Myocardial infarction and ventricular tachycardia (n=10). Stereotactic arrhythmia radioablation (STAR) vs. Non-irradiated healthy pigs was evaluated on Fibrotic remodelling through fibroblast activation and altered extracellular matrix composition. Stereotactic arrhythmia radioablation at 25 Gy induced early fibroblast activation, ECM remodelling gene expression changes, and endothelial injury without mature fibrosis at 10 weeks in pigs.