Background: In patients with heart failure (HF), concomitant cardiac conduction system (CCS) dysfunction is an important predictor of mortality. Despite this, the molecular mechanisms underlying HF-induced CCS disease are poorly understood. Inflammation is a hallmark and mechanistic proponent of ventricular remodelling in chronic HF but its involvement in CCS dysfunction is presently unknown.

 

Methods and Results:  We assessed the global signature of HF-induced molecular remodelling of the sinoatrial (SAN) and atrioventricular node (AVN) in the mouse transverse aortic constriction model of HF. Transcriptomic analysis using RNAseq and mass spectrometry-based proteomics combined with single nucleus RNAseq data intersection determined that downregulated proteins were predominantly enriched for ion channels involved in pacemaking, whereas upregulated proteins annotated to the immune-inflammatory response. In particular, striking enrichment of the macrophage population was observed in the failing CCS alongside a significant increase in expression of the macrophage-secreted proinflammatory protein Galectin-3 (Gal-3), a biotarget and biomarker in human HF.

To investigate a functional role for Gal-3 in HF-induced CCS remodelling, sham-operated and HF animals were randomised into anti-Gal-3 treated and untreated groups. Animals in the anti-Gal-3 treated group received 100 mg/kg/day modified citrus pectin (MCP), a well-characterised and clinically utilized Gal-3 inhibitor, starting from the day of surgery and continuing for 8 weeks. At termination, the impact of Gal-3 inhibition on CCS electrophysiological parameters was tested in vivo and in Langendorff-perfused hearts: MCP treatment significantly blunted prolongation of sinus cycle length, corrected SAN recovery time and the rate-corrected PR interval seen in untreated HF animals, whereas the Wenckebach cycle length and AVN effective refractory period were unaffected. To further evaluate SAN remodelling, high resolution unipolar multielectrode array mapping was carried out on the endocardial surface of isolated SAN preparations from the four groups of animals. Analysis of activation maps demonstrated that HF SAN had an inferior leading pacemaker site as well as slower conduction than control animals, changes that were restored to control levels in the MCP treated TAC group. Unipolar fractionated electrograms – indicative of structural and electrical remodelling resulting in asynchronous activation of myocytes – were significantly more prevalent in untreated HF animals, and the incidence of complex fractionated electrograms were also restored to control levels in the HF group receiving MCP treatment. Finally, using sharp microelectrodes, intracellular action potentials were recorded from the compact AVN. Strikingly, MCP treatment abrogated the HF-induced reduction in the resting membrane potential, upstroke velocity, action potential amplitude and slope of diastolic depolarisation.

 

Conclusions: These data provide novel proof-of-concept that Gal-3 inhibition prevents CCS dysfunction in HF of a pressure overload pathophysiology.  Studies incorporating precision transgenics to study the impact of CCS-specific inflammation, coupled with state-of-the-art imaging mass cytometry to characterise the precise Gal-3 secreting macrophage population infiltrating the failing human and mouse CCS are underway.