Postpartum cardiomyopathy (PPCM) is a disease of unknown etiology and exposes women to high risk of mortality after delivery. Here, we show that female mice with a cardiomyocyte-specific deletion of stat3 develop PPCM. In these mice, cardiac cathepsin D (CD) expression and activity is enhanced and associated with the generation of a cleaved antiangiogenic and proapoptotic 16 kDa form of the nursing hormone prolactin. Treatment with bromocriptine, an inhibitor of prolactin secretion, prevents the development of PPCM, whereas forced myocardial generation of 16 kDa prolactin impairs the cardiac capillary network and function, thereby recapitulating the cardiac phenotype of PPCM. Myocardial STAT3 protein levels are reduced and serum levels of activated CD and 16 kDa prolactin are elevated in PPCM patients. Thus, a biologically active derivative of the pregnancy hormone prolactin mediates PPCM, implying that inhibition of prolactin release may represent a novel therapeutic strategy for PPCM.

Abstract-The transcription factor signal transducer and activator of transcription 3 (STAT3) participates in a wide variety of physiological processes and directs seemingly contradictory responses such as proliferation and apoptosis. To elucidate its role in the heart, we generated mice harboring a cardiomyocyte-restricted knockout of STAT3 using Cre/loxP-mediated recombination. STAT3-deficient mice developed reduced myocardial capillary density and increased interstitial fibrosis within the first 4 postnatal months, followed by dilated cardiomyopathy with impaired cardiac function and premature death. Conditioned medium from STAT3-deficient cardiomyocytes inhibited endothelial cell proliferation and increased fibroblast proliferation, suggesting the presence of paracrine factors attenuating angiogenesis and promoting fibrosis in vitro. STAT3-deficient mice showed enhanced susceptibility to myocardial ischemia/reperfusion injury and infarction with increased cardiac apoptosis, increased infarct sizes, and reduced cardiac function and survival. Our study establishes a novel role for STAT3 in controlling paracrine circuits in the heart essential for postnatal capillary vasculature maintenance, interstitial matrix deposition balance, and protection from ischemic injury and heart failure. Key Words: mouse Ⅲ signal transduction Ⅲ angiogenesis Ⅲ ischemia Ⅲ heart failure A ctivation of signal transducer and activator of transcription 3 (STAT3) in the heart has been observed in acute myocardial infarction (MI), ischemic preconditioning, and pressure overload. [1][2][3] In this regard, activation of the stressresponsive Janus kinase (JAK)-STAT signaling pathway during ischemia/reperfusion (I/R) injury and MI has been proposed to provide protection against ischemic stress via transcriptional activation of cytoprotective genes. 1,4 Cell culture studies have ascribed some of the cytoprotective actions of the JAK-STAT pathway in cardiomyocytes specifically to STAT3 activation. 5 However, although STAT3 activation is clearly associated with an upregulation of a wide array of target genes in cardiomyocytes, it is unclear which of the reported cardiac responses associated with STAT3 activation are indeed required in vivo for controlling cardiac growth, function, tissue architecture, or protection against cardiovascular stress such as ischemic injury. Importantly, although increased circulating levels of interleukin (IL)-6 -related cytokines predict mortality in patients with heart failure and may enhance gp130 activation in the failing human heart, expression and phosphorylation levels of STAT3 are severely depressed in myocardium obtained from patients with dilated cardiomyopathy, 6 raising the possibility that decreased STAT3 activation may contribute to development of cardiac failure in patients.To elucidate the potential role of STAT3 in cardiac muscle and, in particular, for cardiac protection against physiological and pathophysiological stress, we created mice with a cardiomyocyte-restricted STAT3 deletion. Materials and...

No abstract

Circulating levels of interleukin (IL)-6 are elevated after myocardial infarction (MI) and associated with increased morbidity and mortality. Its myocardial expression post-MI suggests a pathophysiological role in this condition. To explore the role of endogenous IL-6, we analyzed MI size, left ventricular (LV) remodeling, and mortality after permanent coronary ligation in IL-6 knockout mice (IL-6-/-) and wild-type controls (WT). Six weeks after MI, IL-6-/- and WT had similar mortality rates, MI sizes, LV remodeling, and LV dysfunction in vivo, determined by catheterization. Infarct size 24 h post-MI, shown by 2,3,5-triphenyltetrazolium chloride (TTC) staining, was similar at 24 h. Treatment with exogenous IL-6 did not alter MI size in WT. Infarction resulted in marked phosphorylation of STAT3, without differences between genotypes. Leukemia inhibitory factor (LIF) protein was increased 48 h post-MI in IL-6-/-, and angiotensin II and AT1 receptor (AT1R) protein were strongly increased in IL-6-/- baseline and post-MI, suggesting compensatory up-regulation. Lack of IL-6 does not affect long-term MI size or LV function, remodeling, and survival. In mice lacking IL-6, other members of the IL-6 family such as LIF and other factors signaling via JAK/STAT such as angiotensin may act in a compensatory manner to activate the JAK/STAT pathway, thereby maintaining STAT3 phosphorylation, which is crucial for the cellular effects of IL-6 cytokines.

Background-The renin-angiotensin system is thought to be involved in development and progression of arteriosclerosis, thereby contributing to adverse cardiovascular events. To elucidate the role of angiotensin II (Ang II) at a cellular level, we analyzed the Ang II-induced gene expression profile. Methods and Results-Genes induced on Ang II stimulation (10 Ϫ7 mol/L, 45 minutes) in rat smooth muscle cells were analyzed by polymerase chain reaction selected subtraction. In addition to known genes, such as interleukin 6, leukemia inhibitory factor, and c-fos, we identified CYR61, an angiogenic immediate early gene. Northern blot analysis revealed a rapid 2.5-fold increase of CYR61 transcript levels by Ang II, peaking at 30 minutes, which was blunted by Ang II type 1 receptor blockade. Exposure of rat aortic rings to Ang II (30 minutes) revealed a 2-fold, and intraperitoneal injection of Ang II (30 minutes) in mice a 3-fold, increase of aortic CYR61 transcripts. In arteriosclerotic aortas of apolipoprotein E-deficient mice, CYR61 transcripts confirmed by in situ hybridization and proteins shown by immunohistochemistry were elevated, whereas they were hardly detectable in wild types. In human carotid atherectomies and arteriosclerotic coronary arteries, immunohistochemical analysis revealed expression of CYR61 within connective tissue in neointima, adventitia, and surrounding small capillaries and blood vessels, colocalized with ACE and Ang II. Normal human arteries showed no significant staining for CYR61. Conclusions-CYR61, an angiogenic factor, is induced by Ang II in vascular cells and tissue. The expression of CYR61, colocalized with Ang II and ACE, in small vessels of human arteriosclerotic lesions is consistent with the notion that the activated renin-angiotensin system may contribute to plaque neovascularization by enhancing regulators of microvessel formation and cell proliferation.

No abstract

Background-The Jun family of activator protein 1 (AP-1) transcription factors (c-Jun, JunB, and JunD) is involved in fundamental biological processes such as proliferation, apoptosis, tumor angiogenesis, and hypertrophy. The role of individual AP-1 transcription factors in the stressed heart is not clear. In the present study we analyzed the role of JunD in survival, hypertrophy, and angiogenesis in the pressure-overloaded mouse heart after thoracic aortic constriction. Methods and Results-Mice lacking JunD (knockout [KO]) showed increased mortality and enhanced cardiomyocyte apoptosis and fibrosis associated with increased levels of hypoxia-induced factor-1␣, vascular endothelial growth factor (VEGF), p53, and Bax protein and reduced levels of Bcl-2 protein after 7 days of severe pressure overload compared with wild-type (WT) siblings. Cardiomyocyte hypertrophy in surviving KO mice was enhanced compared with that in WT mice. Chronic moderate pressure overload for 12 weeks caused enhanced left ventricular hypertrophy in KO mice, and survival and interstitial fibrosis were comparable with WT mice. Cardiac function, 12 weeks after operation, was comparable among shams and pressure-overloaded mice of both genotypes. In addition, KO mice exposed to chronic pressure overload showed higher cardiac capillary density associated with increased protein levels of VEGF. Conclusions-Thus, JunD limits cardiomyocyte hypertrophy and protects the pressure-overloaded heart from cardiac apoptosis. These beneficial effects of JunD, however, are associated with antiangiogenic properties.

No abstract