Our working group focuses on endogenous protective cardiac mechanisms in patients with heart failure with reduced ejection fraction (HFrEF). While heart failure with preserved ejection fraction (HFpEF) differs in pathophysiology, both share stress-responsive pathways regulating cardiac adaptation. To explore these shared adaptive mechanisms, we investigate how β-adrenergic stress influences endogenous cardioprotection.
In this context, we discovered that under physiological stress such as exercise, a proteolytic fragment of HDAC4, termed HDAC4-NT, is induced by beta-adrenergic signaling. It is produced by PKA-mediated activation of the serine protease ABHD5. HDAC4-NT exerts its cardioprotective effect by suppressing hexosamine biosynthesis pathway-promoting gene programs via the MEF2/NR4A1 axis.
We observed that, in contrast to males, female Abhd5/Nr4a1 double knockout mice (DKO) were protected from HFrEF. This is documented by improved ejection fraction in female DKO mice. Thus, the PKA/ABHD5/HDAC4-NT/MEF2/NR4A1 axis may be part of sex-specific mechanisms that modulate disease progression.
In line with these findings, our latest experiments in a HFpEF mouse model revealed that exercise training increases levels of HDAC4-NT and improves diastolic function. These observations further support the concept that physiological stressors such as exercise activate the PKA/ABHD5/HDAC4-NT axis and promote endogenous cardioprotective mechanisms across different forms of heart failure.
The project aims to translate HDAC4-NT production in cardiomyocytes into a therapeutic application. To this end, we engineered a bioluminescence-based reporter that can be used to monitor HDAC4-NT production. To do so, we use a firefly/renilla dual-luciferase system. The system includes a 21-amino-acid sequence flanking the HDAC4 cleavage site. When this site is cleaved by NT producing enzyme, it triggers an increase in the firefly luciferase signal. Initial experiments showed an 8-fold increase in the firefly/renilla ratio upon PKA stimulation compared to controls and non-transfected cells, indicating that the assay is robustly detecting HDAC4 proteolysis (n = 3 independent experiments).
In parallel, we generated a stably expressing reporter hiPSC line to monitor HDAC4 cleavage in hiPSC-derived cardiomyocytes (hiPSC-CMs). Recent data demonstrated that HDAC4 cleavage can be effectively induced in hiPSC-CMs by combined treatment with Forskolin and IBMX, both of which elevate intracellular cAMP levels and thereby enhance PKA activity.
We are in the process of using this reporter to screen small molecules and gene candidates enhancing HDAC4-NT formation. We also want to apply it in vivo to monitor sex-specific HDAC4 proteolysis and to determine whether this protective mechanism can also be effectively activated in males.
This project offers a novel, cause-oriented therapeutic approach to HFrEF and HFpEF by pharmacologically enhancing endogenous protection mechanisms. It also contributes to the advancement of gender-specific medicine by addressing biological differences in disease mechanisms and therapeutic response.
