In heart failure (HF), myocardial telomere shortening has been observed. The underlying mechanisms and the clinical significance of this phenomenon remain unclear: in adult mammals cardiomyocyte (CM) regeneration is limited and CM cell division thus cannot account for telomere shortening. How telomere shortening in turn affects myocardial recovery remains unexplored.

We put forth to investigate underlying mechanisms employing a model of chronic cardiac injury induced by excess neurohormonal activation (NHA), a universal dysregulation in the pathogenesis of HF of diverse etiologies. 

Male C57BL/6J (B6) mice were subjected to AngII-infusion, uninephrectomy and high-salt (AngII++) to induce excess NHA for 5 weeks. Cardiac function was assessed by ultrasound. Human iPSC-derived CMs, mouse adult CMs and rat ventricular CM-derived cells (H9C2) were stimulated with AngII. Human endomyocardial biopsies from non-ischemic heart failure with reduced ejection fraction (HFrEF) were grouped depending on cardiac recovery after initial admission. Telomere length was quantified by Q-FISH after staining with a C-rich telomere probe (TelC). ROS-induced DNA/RNA-damage was evaluated after staining for 8-oxo-7,8-dihydro-2'-deoxyguanosine, -guanine and – guanosine-residues (8-oxo-dG). H9C2-cells were co-stained for TelC and 8-oxo-dG, telomere-specific DNA-damage was quantified by automated colocalization analysis. Superoxide (O₂^-) was quantified by 2-hydroxyethidium (2-HE) using HPLC analysis. In cardiac sections, immune cells were quantified by staining for H&E, CD45, fibrosis was quantified by Sirius red staining.

AngII++-mice exhibited left ventricular (LV) hypertrophy (p<0.0001 vs B6) along with reduced LV ejection fraction (p=0.03 vs B6), reduced global longitudinal strain (p<0.001 vs B6) along with significant telomere shortening in CMs isolated from AngII++-mice (p=0.0082 vs B6). Telomere length showed a significant correlation with LV systolic function (r²=0.64, p=0.006) but no correlation with LV hypertrophy (r²=0.05, p=0.433). AngII++-mice showed significantly increased myocardial fibrosis (p<0.01 vs B6) with inhomogeneous adverse remodeling along with immune-cell infiltration as confirmed by H&E/CD45-staining. While 8-oxo-dG-staining revealed significantly increased ROS-induced DNA/RNA damage in AngII++-myocardial sections overall (p<0.0001 vs B6), DNA/RNA-damage was highest in areas of fibrotic adverse remodeling and inflammation congruent with significant telomere shortening (p<0.0122 fibrotic vs non-fibrotic AngII++-myocardium, p<0.0001 vs B6). Excess NHA-induced telomere shortening could be corroborated in-vitro in all cells tested (iPSC-derived CM, mouse adult CM, H9C2). As a potential explanation, CMs stimulated with AngII revealed significantly increased, dose-dependent O₂^--production (AngII 10 nM p=0.03, AngII 50 nm p=0.0004 vs H9C2), while colocalization analysis revealed a significantly increased ROS-induced damage to the telomeric DNA (AngII 10/50 nm p<0.05 vs H9C2). 

HFrEF-patients that had recovered cardiac function (∆LVEF +5-30%) showed significantly longer myocardial telomeres than patients with no recovery/worsening (∆LVEF -10-0%) (p=0.008). Moreover, overall the telomere signal correlated significantly with ∆LVEF (r²=0.41, p=0.03).

Our data provides evidence that ROS-induced DNA-damage significantly causes myocardial telomere shortening in HF and further that the extend of telomere shortening determines cardiac recovery.