Our results are the first to support the possibility that abnormalities in SOCS3 regulation of cardiac gp130 signaling could be an important disease mechanism underlying fatal arrhythmias and DCM in humans

Our results are the first to support the possibility that abnormalities in SOCS3 regulation of cardiac gp130 signaling could be an important disease mechanism underlying fatal arrhythmias and DCM in humans. == Clinical Summary. (WT) hearts. We also found that Ser23/24 residues of troponin I were hypophosphorylated in SOCS3 cKO hearts before the manifestation BMS-1166 hydrochloride of cardiac dysfunction. These data suggested the presence of abnormalities in myofilament Ca2+sensitivity in SOCS3 cKO mice. In addition to the contractile dysfunction, we found various ventricular arrhythmias in SOCS3 cKO non-failing hearts accompanied by a sarcoplasmic reticulum Ca2+overload. To determine the contribution of gp130 signaling to the cardiac phenotype that occurs with SOCS3 deficiency, we BMS-1166 hydrochloride generated cardiac-specific gp130 and SOCS3 double knockout mice. Double KO mice lived significantly longer and had different histological abnormalities when compared to SOCS3 cKO mice; thus, demonstrating the importance of gp130 signaling in the SOCS3 cKO cardiac phenotype. == Conclusions == Our results demonstrate an important role of SOCS3 regulation on cardiac gp130 signaling in the pathogenesis of contractile dysfunction and ventricular arrhythmias. Keywords:SOCS3, gp130, heart failure, ventricular arrhythmia, cardiomyopathy, myofilament Ca2+sensitivity, SR Ca2+overload == Introduction == Suppressor of cytokine signaling-3 (SOCS3) is a key BMS-1166 hydrochloride negative-feedback regulator of gp130, which is a common receptor component of the interleukin-6 (IL-6) family of cytokines. The IL-6 family of cytokines activates the JAK-STAT signaling pathway through gp130 and induces the expression of the cytokine-responsive genes, including SOCS3. Subsequently, SOCS3 binds to gp130 and inhibits the downstream signaling cascade that includes activation of JAK-STAT, SH2 homology containing tyrosine phosphatase 2 (SHP2)-Ras/ERK and SHP2-AKT.13Accordingly, SOCS3 regulates tightly the duration and intensity of gp130 signaling in a classic negative-feedback manner. While cardiac gp130 signaling has been shown to affect significantly cardiomyocyte survival following acute pressure overload, the role of SOCS3 regulation on cardiac gp130 signaling remains unclear.4 Germ-line knockout (KO) of SOCS3 causes embryonic lethality, via placental deficiency associated with an abnormality of trophoblast giant cell differentiation.5,6When placental deficiency is rescued by a tetraploid embryo complementation approach, SOCS3 KO embryos show a perinatal lethality with a markedly enlarged heart and hypertrophy. Furthermore, the placental defect and cardiac abnormalities can be rescued in the embryos with leukemia inhibitory factor (LIF) receptor null background.6These data demonstrate that SOCS3 is an essential regulator of LIF-gp130 signaling. Moreover, these data suggest that unregulated gp130 activation without SOCS3 regulation leads to cardiac hypertrophy during embryonic development. However, due to embryonic lethality, the ultimate physiological role of SOCS3 regulation on gp130 signaling in the adult heart remains unclear. In isolated adult cardiomyocytes, gp130 stimulation by IL-6 has been reported to decrease myocyte contractility during acute exposure. In addition, chronic IL-6 stimulation induces cardiac hypertrophy.79These findings indicate a potentially pathological role of gp130 signaling in the cardiomyocyte. In humans, the serum level of IL-6 is known to be elevated in patients with congestive heart failure (CHF) and the elevated levels correspond to worsening functional class, increased hospitalization rates, and poor survival.1012In the Framingham heart study, elevated serum IL-6 has been associated with increased risk of CHF in seniors without previous myocardial infarction.13Furthermore, during heart transplant, myocardial IL-6 manifestation has been reported to be significantly increased in BMS-1166 hydrochloride donor hearts with dysfunction compared to those with normal function.14Despite the strong association between the activation of gp130 signaling and CHF in humans, the primary part of gp130 activation during the development of cardiac dysfunction has not been thoroughly evaluated using animal models. It has been reported that SOCS3 protein and mRNA levels LKB1 are decreased in failing human being myocardium.1517In many cancer cells, the hypermethylation of CpG islands in the SOCS3 promoter inhibits the transcription of SOCS3 mRNA, resulting in epigenetic silencing of SOCS3 protein.18,19These data suggest that abnormalities of SOCS3 regulation about cardiac gp130 signaling could occur in diseased states. Accordingly, we hypothesized that the loss of gp130-mediated upregulation of SOCS3 induces sustained activation of gp130 signaling in the cardiomyocyte, leading to cardiomyopathy and heart failure. With this study, we found that the absence of SOCS3 rules in the cardiomyocyte results in early mortality that is inhibited by BMS-1166 hydrochloride deletion of gp130 and is accompanied by contractile dysfunction and ventricular arrhythmias. These findings highlight a crucial part of SOCS3 and its apparent effect on gp130 signaling in the homeostasis of adult cardiomyocytes and demonstrate a previously unidentified part of gp130 signaling in the pathogenesis of cardiomyopathy. == Methods == == Mice == Floxed SOCS3 (SOCS3F/+, a kind gift from Dr. Kenneth R. Chien, MGH),20floxed gp130 (gp130F/+),21and alpha myosin weighty chain-Cre (MHC-Cre) were bred in UCSD vivarium relating to institutional recommendations. These mice were backcrossed into Balb/c for at least five decades. == Immunoblot analysis.