Abstract 17362: Cardiac Suppressor of Cytokine Signaling-3 (SOCS3)-Deficiency Leads to Hypo-Phosphorylation of Troponin I (Ser23/24) Through the Increase in Intracellular [Na+] ([Na+]i), Resulting in Contractile Dysfunction
Cardiac-specific SOCS3 knockout mice (SOCS3 cKO) develop heart failure without abnormalities in ultrastructure of myofibrils and Ca2+ transients. This suggests a malfunction of contractile machinery in SOCS3 cKO. Although the phenotype was associated with augmented expression of voltage-gated Na+ channel and its current density, the pathophysiological connection between the increased Na+ channel function and contractile dysfunction remains unclear.
Hypothesis: The augmented Na+ channel function increases Na+ influx during depolarization, leading to the increase in [Na+]i. This induces malfunction of contractile machinery by changing phosphorylation status of the contractile proteins.
Methods: To detect primary abnormalities in SOCS3 cKO, the mice with normal cardiac function (20 weeks old) were used for this study. We examined as follows: 1) phosphorylation status of contractile proteins in SOCS3 cKO by western-blot. 2) [Na+]i in adult cardiomyocytes isolated from SOCS3 cKO using the fluorescence indicator SBFI/AM at rest and during stimulation (0.5 and 2.0 Hz). The signal intensity ratio 340/380 nm was calculated and converted to [Na+]i by calibration at the end of each experiment. 3) the effect of [Na+]i on Troponin I (TnI) phosphorylation (Ser23/24) post isoproterenol (ISP, 100 μM) stimulation. The [Na+]i was changed by calibration buffers for [Na+]i measurement.
Results: 1) Of the proteins examined, phospho-TnI (p-TnI) (Ser23/24) was significantly decreased in SOCS3 cKO compared to wild-type (WT) littermates (relative p-TnI level in SOCS3 cKO compared to WT: 0.41±0.02, mean±SE, p<0.00051, n=3). 2) [Na+]i (mM) was significantly higher in SOCS3-deficient myocytes compared to WT myocytes both at rest and during stimulation (At rest; 11.6±2.1 vs. 5.9±2.0, 0.5 Hz; 16.4±4.4 vs. 7.2±3.3, 2.0 Hz; 20.0±3.0 vs. 9.8±3.3, SOCS3 cKO vs. WT, mean±SE, p<0.001, n=10). 3) p-TnI level (Ser23/24) was significantly decreased at 20 mM of [Na+]i compared to 5 mM of [Na+]i (relative p-TnI level at 20 mM compared to 5 mM: 0.39±0.033, mean±SE, p<0.001, n=3).
Conclusions: These results indicate that SOCS3-deficiency increases [Na+]i through augmented voltage-gated Na+ current, resulting in contractile dysfunction through hypo-phosphorylation of TnI.
- © 2010 by American Heart Association, Inc.