https://doi.org/10.1007/s00392-025-02625-4
1Kath. Klinikum Bochum Institut für Forschung und Lehre (IFL), St. Josef Hospital Bochum, Deutschland; 2Kath. Klinikum Bochum Molekulare und experimentelle Kardiologie (IFL) Bochum, Deutschland; 3Charité - Universitätsmedizin Berlin BIH Center für regenerative Therapien (BCRT) Berlin, Deutschland; 4Charité - Universitätsmedizin Berlin CC11: Med. Klinik m.S. Kardiologie Berlin, Deutschland; 5Klinikum der Ruhr-Universität Bochum Medizinische Klinik II, Kardiologie Bochum, Deutschland; 6Academic Medical Center University of Amsterdam Department of Cardiology Amsterdam, Niederlande; 7Universitätsklinikum Gießen und Marburg GmbH Medizinische Klinik I - Kardiologie und Angiologie Gießen, Deutschland; 8Cardiology Deparment of Physiology Augusta, USA; 9Kath. Klinikum Bochum Cellular Physiology Bochum, Deutschland
Introduction:
Heart failure with preserved ejection fraction (HFpEF) is characterized by increased diastolic stiffness and impaired relaxation of the left ventricle (LV) and is highly prevalent, affecting approximately 50% of HF patients. HFpEF is associated with increased mortality and is closely linked to a range of comorbidities that promote systemic inflammation. This inflammation contributes to endothelial dysfunction, an increase in reactive oxygen species (ROS), nitrosative stress, a decrease in nitric oxide (NO) availability, and downregulation of cGMP-dependent protein kinase G (PKG). Oxidative stress and inflammation play a crucial role in the pathophysiology of HFpEF, partly by influencing LV stiffness through modulation of the myocardial cGMP-PKG signaling pathway. Our study aims to investigate the contribution of Phosphodiesterase 9 (PDE9) to the increased stiffness observed in HFpEF and whether this effect can be reversed with PDE9 inhibitor treatment.
Methods:
We measured cardiomyocyte function, PDE9 oxidation and its distribution in different cell compartments, pro-inflammatory cytokines, oxidative stress levels, protein expression, and phosphorylation in human HFpEF samples before and after acute treatment of myocardial biopsies with the PDE9A inhibitor PF04447943, as well as in the ZSF1 obese rat model of HFpEF. Chronic treatment (2 weeks) with the PDE9A inhibitor (3 mg/kg) or vehicle was administered to 18-week-old HFpEF rats via daily oral gavage. At 20 weeks of age, LV diastolic dysfunction in HFpEF rats was assessed by transthoracic echocardiography.
Results:
Both HFpEF patients and HFpEF rats showed significantly higher levels of PDE9 oxidation, particularly in the membrane compartment, compared to control groups. Pro-inflammatory cytokines and oxidative stress markers were markedly elevated in both HFpEF patients and rats relative to controls. These changes were associated with increased PDE9 activity due to oxidation, reduced nitric oxide (NO) and soluble guanylyl cyclase levels, and diminished PKG activity. In healthy cardiomyocytes, oxidized PDE9 significantly increased passive stiffness (Fpassive). In contrast, it did not affect HFpEF cardiomyocytes from both HFpEF myocardial biopsies and HFpEF ZSF1 rats, which already have elevated stiffness at baseline. PDE9 oxidation reduced calcium transient and increased the slope of diastolic force in the non-failing cardiomyocyte compared to HFpEF cardiomyocytes. This suggests that the increase in PDE9 activity caused by oxidation partially contributes to the elevated diastolic stiffness observed in HFpEF. Furthermore, key signaling pathways involved in titin phosphorylation were differentially regulated in HFpEF compared to controls, with significant reductions in the phosphorylation status of myofilament proteins in HFpEF. Several other proteins were also dysregulated in HFpEF patients compared to controls. Treatment with the PDE9A inhibitor decreased PDE9 oxidation, improved cardiomyocyte function, and enhanced myofilament protein phosphorylation. Reductions in inflammation and oxidative stress accompanied these beneficial effects.
Conclusion:
This study reveals that PDE9 oxidation due to increased oxidative stress and inflammation in HFpEF contributes to elevated LV stiffness. Targeted inhibitors of PDE9 oxidation may reverse diastolic dysfunction, suggesting a promising therapeutic approach for HFpEF.