Interleukin-6 (IL-6) is elevated in cardiometabolic heart failure with preserved ejection fraction (HFpEF) and correlates with disease severity and mortality. However, the cardiomyocyte-specific mechanisms linking IL-6 signaling to HFpEF pathogenesis remain poorly understood. In a porcine HFpEF model (high-fat diet plus 11-deoxycorticosterone; in collaboration with David Lefer), myocardial IL-6 protein abundance was increased and associated with reduced expression of the mitochondrial fusion protein OPA1, suggesting impaired mitochondrial homeostasis.
To investigate the direct effects of IL-6 on cardiomyocytes, human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) were exposed to IL-6. IL-6 treatment reduced OPA1 protein levels and increased phosphorylation of DRP1 at Ser616, indicating enhanced mitochondrial fission and disruption of mitochondrial network integrity. To assess mitochondrial organization in a physiologically relevant setting, hiPSC-CMs were cultured on two-photon polymerization (2PP)-printed three-dimensional scaffolds and analyzed by high-resolution Airyscan confocal microscopy. Under baseline conditions, mitochondria exhibited close alignment with sarcomeres, whereas IL-6 exposure markedly disrupted this spatial organization. In addition, IL-6 increased mitochondrial reactive oxygen species production, reduced mitochondrial membrane potential (TMRM live cell imaging), and promoted lipid droplet accumulation under fatty acid-enriched culture conditions.
Mechanistically, IL-6 induced a dose-dependent increase in class IIa histone deacetylase (HDAC) activity. We therefore investigated whether IL-6 regulates mitochondrial homeostasis through coordinated signaling between STAT3 and HDAC4. Under basal conditions, STAT3 localized predominantly to the mitochondrial compartment, whereas IL-6 stimulation promoted its redistribution to the nucleus. In contrast, HDAC4 accumulated at the outer mitochondrial membrane following IL-6 exposure, revealing reciprocal STAT3/HDAC4 compartmental shuttling. Similar observations were obtained under hypoxic stress in HDAC4-Flag-transfected HEK293T cells and in both wild-type and CRISPR/Cas9-HDR-engineered HDAC4-Flag hiPSC-CMs, suggesting a conserved stress-response mechanism.
Functionally, pharmacological inhibition of class IIa HDACs restored mitochondrial-sarcomere co-localization in hiPSC-CMs. To evaluate translational relevance, mice subjected to high-fat diet and L-NAME treatment developed diastolic dysfunction, as assessed by echocardiographic E/e′ measurements. Treatment with the class IIa HDAC inhibitor TMP195 significantly improved diastolic function within 96 Hours compared to vehicle treated mice.
Collectively, our findings identify a previously unrecognized IL-6-driven signaling axis characterized by reciprocal STAT3/HDAC4 shuttling that disrupts mitochondrial architecture and function in cardiomyocytes. Targeting class IIa HDAC signaling may represent a novel therapeutic strategy to restore mitochondrial homeostasis and improve diastolic dysfunction in cardiometabolic HFpEF.
