ST2 is an IL-1 receptor family member with transmembrane (ST2L) and soluble (sST2) isoforms. sST2 is a mechanically induced cardiomyocyte protein, and serum sST2 levels predict outcome in patients with acute myocardial infarction or chronic heart failure. Recently, IL-33 was identified as a functional ligand of ST2L, allowing exploration of the role of ST2 in myocardium. We found that IL-33 was a biomechanically induced protein predominantly synthesized by cardiac fibroblasts. IL-33 markedly antagonized angiotensin II-and phenylephrine-induced cardiomyocyte hypertrophy. Although IL-33 activated NF-κB, it inhibited angiotensin II-and phenylephrine-induced phosphorylation of inhibitor of NF-κBα (IκBα) and NF-κB nuclear binding activity. sST2 blocked antihypertrophic effects of IL-33, indicating that sST2 functions in myocardium as a soluble decoy receptor. Following pressure overload by transverse aortic constriction (TAC), ST2 -/-mice had more left ventricular hypertrophy, more chamber dilation, reduced fractional shortening, more fibrosis, and impaired survival compared with WT littermates. Furthermore, recombinant IL-33 treatment reduced hypertrophy and fibrosis and improved survival after TAC in WT mice, but not in ST2 -/-littermates. Thus, IL-33/ST2 signaling is a mechanically activated, cardioprotective fibroblast-cardiomyocyte paracrine system, which we believe to be novel. IL-33 may have therapeutic potential for beneficially regulating the myocardial response to overload.

Background-Local delivery of chemotactic factors represents a novel approach to tissue regeneration. However, successful chemokine protein delivery is challenged by barriers including the rapid diffusion of chemokines and cleavage of chemokines by proteases that are activated in injured tissues. Stromal cell-derived factor-1 (SDF-1) is a well-characterized chemokine for attracting stem cells and thus a strong candidate for promoting regeneration. However, SDF-1 is cleaved by exopeptidases and matrix metalloproteinase-2, generating a neurotoxin implicated in some forms of dementia. Methods and Results-We designed a new chemokine called S-SDF-1(S4V) that is resistant to matrix metalloproteinase-2 and exopeptidase cleavage but retains chemotactic bioactivity, reducing the neurotoxic potential of native SDF-1. To deliver S-SDF-1(S4V), we expressed and purified fusion proteins to tether the chemokine to self-assembling peptides, which form nanofibers and allow local delivery. Intramyocardial delivery of S-SDF-1(S4V) after myocardial infarction recruited CXCR4 ϩ /c-Kit ϩ stem cells (46Ϯ7 to 119Ϯ18 cells per section) and increased capillary density (from 169Ϯ42 to 283Ϯ27 per 1 mm 2 ). Furthermore, in a randomized, blinded study of 176 rats with myocardial infarction, nanofiber delivery of the protease-resistant S-SDF-1(S4V) improved cardiac function (ejection fraction increased from 34.0Ϯ2.5% to 50.7Ϯ3.1%), whereas native SDF-1 had no beneficial effects. Conclusions-The combined advances of a new, protease-resistant SDF-1 and nanofiber-mediated delivery promoted recruitment of stem cells and improved cardiac function after myocardial infarction. These data demonstrate that driving chemotaxis of stem cells by local chemokine delivery is a promising new strategy for tissue regeneration. (Circulation.

Background-ST2 is a member of the interleukin-1 receptor family with a soluble form that is markedly upregulated on application of biomechanical strain to cardiac myocytes. Circulating ST2 levels are elevated in the setting of acute myocardial infarction, but the predictive value of ST2 independent of traditional clinical factors and of an established biomarker of biomechanical strain, N-terminal prohormone B-type natriuretic peptide (NT-proBNP), has not been established. Methods and Results-We measured ST2 at baseline in 1239 patients with ST-elevation myocardial infarction from the CLopidogrel as Adjunctive ReperfusIon TherapY-Thrombolysis in Myocardial Infarction 28 (CLARITY-TIMI 28) trial. Per trial protocol, patients were to undergo coronary angiography after 2 to 8 days and were followed up for 30 days for clinical events. In contrast to NT-proBNP, ST2 levels were independent of clinical factors potentially related to chronic increased left ventricular wall stress, including age, hypertension, prior myocardial infarction, and prior heart failure; levels also were only modestly correlated with NT-proBNP (rϭ0.14). After adjustment for baseline characteristics and NT-proBNP levels, an ST2 level above the median was associated with a significantly greater risk of cardiovascular death or heart failure (third quartile: adjusted odds ratio, 1.42; 95% confidence interval, 0.68 to 3.57; fourth quartile: adjusted odds ratio, 3.57; 95% confidence interval, 1.87 to 6.81; PϽ0.0001 for trend). When both ST2 and NT-proBNP were added to a model containing traditional clinical predictors, the c statistic significantly improved from 0.82 (95% confidence interval, 0.77 to 0.87) to 0.86 (95% confidence interval, 0.81 to 0.90) (Pϭ0.017). Conclusions-In ST-elevation myocardial infarction, high baseline ST2 levels are a significant predictor of cardiovascular death and heart failure independently of baseline characteristics and NT-proBNP, and the combination of ST2 and NT-proBNP significantly improves risk stratification. These data highlight the prognostic value of multiple, complementary biomarkers of biomechanical strain in ST-elevation myocardial infarction.

The thioredoxin system plays an important role in maintaining a reducing environment in the cell. Recently, several thioredoxin binding partners have been identified and proposed to mediate aspects of redox signaling, but the significance of these interactions is unclear in part due to incomplete understanding of the mechanism for thioredoxin binding. Thioredoxin-interacting protein (Txnip) is critical for regulation of glucose metabolism, the only currently known function of which is to bind and inhibit thioredoxin. We explored the mechanism of the Txnip-thioredoxin interaction and present evidence that Txnip and thioredoxin form a stable disulfide-linked complex. We identified two Txnip cysteines that are important for thioredoxin binding and showed that this interaction is consistent with a disulfide exchange reaction between oxidized Txnip and reduced thioredoxin. These cysteines are not conserved in the broader family of arrestin domain-containing proteins, and we demonstrate that the thioredoxin-binding property of Txnip is unique. These data suggest that Txnip is a target of reduced thioredoxin and provide insight into the potential role of Txnip as a redox-sensitive signaling protein.Thioredoxin is a ubiquitous disulfide oxidoreductase that, along with the glutathione system, plays a major role in maintaining the cytoplasm in a reducing environment. Thioredoxin activity is mediated by a pair of cysteine thiols at its active site (human thioredoxins C32 and C35) that are oxidized during reduction of the substrate. By maintaining this reducing environment, thioredoxin is a critical defense against excess concentrations of reactive oxygen species, which are deleterious to cells and implicated in the pathophysiology of diseases such as atherosclerosis (1, 2), diabetes (3), and arthritis (4, 5). The reducing environment of the cell is also important for keeping protein thiols reduced, so that under normal conditions proteins contain many free sulfhydryl groups and relatively rare accessible disulfides (6).In addition to the classic reducing activity of thioredoxin, recent evidence suggests that the redox state of thioredoxin may itself be an important component of redox signaling pathways. Thioredoxin reportedly binds a number of transcription factors and signaling molecules, including NF-B p50 subunit (7), Ref-1 (8), Jab-1 (9), Oct-4 (10), and PTEN (11). One of the better characterized interactions is that of reduced thioredoxin with apoptosis signal-regulating kinase 1 (ASK1), 2 which plays a key role in promoting stress-induced apoptosis (12). Because only reduced thioredoxin is thought to bind ASK1, the interaction can be controlled by the redox state of the cell: during conditions of oxidative stress, ASK1 is released from thioredoxin and promotes apoptosis. The identification of thioredoxin and ASK1 cysteines required for the interaction (13) supports the hypothesis that thioredoxin forms a mixed disulfide complex with ASK1. However, the implications of this interaction are not clear in part due to (i) ...