Abstract 1444: Reversal of Sepsis-induced Contractile Dysfunction by Targeting Cardiac TnI Phosphorylation
Systemic sepsis is associated with an intrinsic impairment of cardiomyocyte contraction due in part to a decrease in myofilament Ca2+ sensitivity associated with a sustained increase in cardiac troponin I (cTnI) phosphorylation at serines 23/24. Dephosphorylation of cTnI is under regulatory control. Thus, muscarinic and adenosine A1 agonists antagonise β-adrenergic stimulation via activation of protein phosphatase 2A (PP2A). The aim of this study was to determine whether modulation of PP2A and thus cTnI phosphorylation could improve sepsis-induced contractile dysfunction. Cardiac myocytes were isolated from control (Con) or septic mice 16–18h after an injection of saline or lipopolysaccharide (LPS; 9mg/kg i.p.) respectively. LPS reduced contraction amplitude (1Hz, 32° C) by 37± 2% (6.3 ± 0.4% to 3.9 ± 0.3%; P<0.01; 3 hearts/gp, n>100 cells) with no effect on Ca2+ transients. Western blot analysis confirmed increased cTnI phosphorylation at Ser23/24 in septic myocytes (3.0± 0.6 fold increase vs Con; P<0.05). Incubation with the A1 agonist CPA (1 μ M) or the PKA inhibitor H89 (1 μ M) significantly attenuated the LPS-induced contractile dysfunction by 56± 17% and 47± 13% (P<0.05) (Fig⇓) with no effect on Ca2+ transients. Treatment of septic cells with both CPA and H89 completely reversed the contractile dysfunction (7.0± 0.5%) vs Con (6.8± 0.4%). Conversely the PP2A inhibitor, okadaic acid (1 nM) mimicked the effects of LPS by significantly decreasing shortening in Con myocytes by 43± 3% and increasing cTnI phosphorylation (2.47±0.52 fold). In conclusion, these data support the hypothesis that sustained cTnI phosphorylation underlies the contractile dysfunction seen in sepsis.