OR06-08 Thyroid Hormone Prevents TNFα-induced β-Adrenergic Receptor Desensitization In Cardiomyocytes—Implications For Septic Shock Cardiomyopathy

Abstract Disclosure: A. Fathi: None. A. Fernandez-Pombo: None. C. Zhu: None. S. Bahriz: None. V.R. Salemme: None. B. Xu: None. J. Lado-Abeal: None. Y.K. Xiang: None. Objective: Septic cardiomyopathy is an early complication of septic shock that increases the risk of death. β-adrenergic receptor (βAR) desensitization leading to decreased ventricular contractility is a key player in septic cardiomyopathy. Tumor necrosis factor-alpha (TNF-α) is a major inflammatory cytokine in sepsis, inhibiting βAR signaling and impairing cardiac function. Non-thyroidal illness syndrome (NTIS), a condition for myocardial hypothyroidism, is a universal complication of septic shock. Thyroid hormones (TH) increase myocardial contractility. We hypothesize that thyroid hormone (T3) replacement can prevent TNF-α-induced βAR desensitization through a thyroid hormone receptor (Thrs) mediated nongenomic mechanism. Methods: Isolated adult ventricular myocytes (AVMs) from mice and rabbits, along with H9c2 myoblast cells, were transfected with FRET-based biosensors to monitor intracellular compartmental cAMP levels (H187) and PKA activity (AKAR3). Protein expression and phosphorylation status were evaluated using Western blot, focusing on phospholamban (PLB). CV1 cells transfected with plasmids encoding Thrα and Thrβ were used to investigate their role in the TH-preventing role on βAR desensitization. Results: TNFα caused a dose-dependent inhibition of isoproterenol (ISO)-induced PKA activity and cAMP increase in AVMs and H9c2 cells. TNFα inhibition was prevented by adding T3 (100 nM) to the cell culture medium 60 min before ISO stimulation. T3 also prevented TNFα-mediated inhibition of ISO-induced PKA phosphorylation of PLB in AVMs. Moreover, T3 prevented the inhibitory effects of TNFα on the ISO-induced increases in calcium transient amplitude and sarcomere shortening in AVMs. Treating the cells with I-850, a compound that inhibits the binding of T3 to Thrs, abolished the T3 preventive effect. Through selective transfection studies in Thr-deficient CV1 cells, Thrα was identified as the receptor mediating T3 effects. Mechanistic investigations revealed that inhibition of PI3K (with Wortmannin) or GRK2 (with Paroxetine) prevents TNFα inhibitory effects on βAR-cAMP-PKA signaling. In AVMs, selective inhibition of PI3Kα or PI3Kγ similarly blocked TNFα effects on β2AR-cAMP-PKA signaling. Conclusion: Our study showed that TNFα-induced desensitization of the βAR and inhibition of calcium transients and sarcomere shortening, a mechanism at the root of septic cardiomyopathy, was prevented by a rapid effect of T3 acting through TRα. These novel findings in thyroid hormone actions open new avenues for future studies investigating the role of thyroid hormone replacement in animal models or humans with septic cardiomyopathy. Presentation: Saturday, July 12, 2025