| Heart failure is a chronic disease needing lifelong management. However, with treatment, signs and symptoms of heart failure can improve and the heart sometimes becomes stronger. Nitroxyl donors have positive inotropic and lusitropic effects that may have therapeutic potential for treating heart failure, but their effects on signaling pathways, especially JAk-STAT, are not well studied. Previously we showed that leukemia inhibitory factor (LIF)-induced signaling is inhibited by oxidative stress, which targets JAK1 activation. In addition, we recently reported evidence for a cysteine-based redox switch in the JH1 catalytic domain of JAK 1 and 2. Since nitroxyl is thiophylic, we postulated that nitroxyl donors would inhibit LIFinduced JAK-STAT3 activation. Pretreatment of HMEC-1 or neonatal rat ventricular myocytes with the nitroxyl donors Angeli's salt and the recently-described nitrosocyclohexyl acetate (NCA) inhibited LIF-induced STAT3 activation as indexed by Y705 phosphorylation. Pretreatment of HMEC-1 with NCA also blocked LIF-induced expression of the inflammation-related genes, ICAM-1 and CEBPD. The related acyloxy nitroso compound 1-nitrosocyclohexyl pivalate (NCP), which is not a nitroxyl donor, was equally effective in inhibiting STAT3 activation, suggesting that these compounds were acting as electrophiles on a thiolate residue. NCA had no effect on the catalytic activity of JAK1 and modestly affected JAK1-induced tyrosine phosphorylation of the LIF receptor. Thus, the JH1 redox switch is not a direct target of the acyloxy nitroso compound. However, pretreatment of recombinant human STAT3 with NCA or NCP reduced the labeling of free sulfhydryl residues with fluorescein-5-maleimide. In addition, we document by dimedone labeling that oxidation of STAT3 is associated with formation of sulfenic acid residues, a hallmark of redox-sensitive proteins. Altogether our evidence indicates that STAT3 has redox-sensitive cysteines that regulate its activation and are targeted by nitroxyl donors and related acyloxy nitroso compounds. These findings raise the possibility of new therapeutic strategies to target STAT3 signaling.;LIF is produced by cardiac myocytes and is reported to have protective effects on heart cells and against myocardial IR injury or infarction. These beneficial actions of LIF are attributed in part to the stimulation of angiogenesis, protection of the mitochondria against oxidative stress, and upregulation of MnSOD, Bcl-xl, and VEGF. On the other hand, LIF was also shown to have effects on the growth, metabolism, contractility, and Ca2+ handling of cardiac myocytes, which could be characterized as disadvantageous; however, these studies relied on cultured cells or isolated muscle and thus the physiological significance of these effects is uncertain. As a first step in establishing whether LIF may have therapeutic potential in preventing injury to the heart or repairing the injured myocardium, we carried out an in vivo study giving mice daily intraperitoneal injections of LIF (∼2 μg/30 g) over 10 days. Our hypothesis is that chronic treatment of mice with LIF will not adversely affect cardiac function or induce cardiac remodeling. We observed an increase in ejection fraction and fractional shortening with LIF treatment of mice, inducting that LW positively affects cardiac contractility. We found that STAT3 was activated in hearts of mice treated with LIF. Moreover, levels of STAT3 were increased, which is consistent with reports of STAT3-induced STAT3 expression. Notably, no increase in expression levels of SOD2 or Bcl-xL was observed in the present study. LIF treatment tended to increase levels of miR-17, miR-21, and miR-199a, although these changes did not reach statistical significance. In conclusion, the effects of chronic LIF treatment on the heart were modest, although this cytokine has been implicated in cardiac repair and remodeling. One possibility is that the actions of LIF on the heart may be manifested only under stress or with injury.;The findings of these studies lend credence to the conclusion that JAKSTAT3 signaling is adversely affected by oxidative stress. Thus, while sustained STAT3 signaling in the context of LIF is not harmful, as I report here, and may offer advantages in cardiac repair as suggested by others, the beneficial actions of this signaling pathway may be compromised in pathological conditions of increased oxidative stress, such as heart failure. Therapeutic strategies that seek to utilize STAT3 activity to repair or protect the heart will need to take into consideration this feature of STAT3. (Abstract shortened by UMI.). |
