Adverse left ventricular remodeling by glycoprotein nonmetastatic melanoma protein B in myocardial infarction.

Cardiac diseases are the leading cause of death. Available treatment approaches are not sufficient to reverse persistent cardiac damage after injury; thus, the search for new therapeutic targets is essential. Our microarray-based screening in rat hearts 24 h after myocardial infarction (MI) yielded glycoprotein nonmetastatic melanoma protein B (GPNMB), which is known to be involved in inflammation and fibrosis after tissue injury. However, its role in the heart was elusive. We found increased cardiac expression levels of GPNMB in rats and mice after MI. Analysis of DBA/2J mice, which lack functional GPNMB due to a spontaneous point mutation, showed that systemic GPNMB deficiency was associated with preserved cardiac function and less left ventricular dilation after MI compared with DBA/2J mice with reconstituted GPNMB expression. These improvements were associated with decreased expression of matrix metalloproteinase 9, the cardiac stress genes for natriuretic peptides (atrial natriuretic peptide and brain natriuretic peptide), and ß-myosin heavy chain after MI. Moreover, GPNMB deficiency attenuated the dilated cardiomyopathy in muscle lim protein knockout mice but could not prevent cardiac hypertrophy induced by isoprenaline infusion. This is the first experimental study to show that GPNMB adversely influences myocardial remodeling.-Järve, A., Mühlstedt, S., Qadri, F., Nickl, B., Schulz, H., Hübner, N., Özcelik, C., Bader, M. Adverse left ventricular remodeling by glycoprotein nonmetastatic melanoma protein B in myocardial infarction.

Cardiomyocyte-derived CXCL12 is not involved in cardiogenesis but plays a crucial role in myocardial infarction.

UNLABELLED: The chemokine CXCL12/SDF-1 is crucial for heart development and affects cardiac repair processes due to its ability to attract leukocytes and stem cells to injured myocardium. However, there is a great controversy whether CXCL12 is beneficial or detrimental after myocardial infarction (MI). The divergence in the reported CXCL12 actions may be due to the cellular source and time of release of the chemokine after MI. This study was designed to evaluate the role of cardiomyocyte-derived CXCL12 for cardiogenesis and heart repair after MI. We generated two rodent models each targeting CXCL12 in only one cardiac cell type: cardiomyocyte-specific CXCL12-overexpressing transgenic (Tg) rats and CXCL12 conditional knockout (cKO) mice. Animals of both models did not show any signs of cardiac abnormalities under baseline conditions. After induction of MI, cKO mice displayed preserved cardiac function and remodeling. Moreover, fibrosis was less pronounced in the hearts of cKO mice after MI. Accordingly, CXCL12 Tg rats revealed impaired cardiac function post-MI accompanied by enhanced fibrosis. Furthermore, we observed decreased numbers of infiltrating Th1 cells in the hearts of cKO mice. Collectively, our findings demonstrate that cardiomyocyte-derived CXCL12 is not involved in cardiac development but has adverse effects on the heart after injury via promotion of inflammation and fibrosis. KEY MESSAGES: • CXCL12 in cardiomyocytes is not involved in cardiac development. • CXCL12 deficiency in cardiomyocytes improves outcome of myocardial infarction. • CXCL12 overexpression in cardiomyocytes worsens outcome of myocardial infarction. • CXCL12 increases fibrosis and invasion of Th1 cells in the heart after infarction.

Critical role for stromal interaction molecule 1 in cardiac hypertrophy.

BACKGROUND: Cardiomyocytes use Ca2+ not only in excitation-contraction coupling but also as a signaling molecule promoting, for example, cardiac hypertrophy. It is largely unclear how Ca2+ triggers signaling in cardiomyocytes in the presence of the rapid and large Ca2+ fluctuations that occur during excitation-contraction coupling. A potential route is store-operated Ca2+ entry, a drug-inducible mechanism for Ca2+ signaling that requires stromal interaction molecule 1 (STIM1). Store-operated Ca2+ entry can also be induced in cardiomyocytes, which prompted us to study STIM1-dependent Ca2+ entry with respect to cardiac hypertrophy in vitro and in vivo. METHODS AND RESULTS: Consistent with earlier reports, we found drug-inducible store-operated Ca2+ entry in neonatal rat cardiomyocytes, which was dependent on STIM1. Although this STIM1-dependent, drug-inducible store-operated Ca2+ entry was only marginal in adult cardiomyocytes isolated from control hearts, it increased significantly in cardiomyocytes isolated from adult rats that had developed compensated cardiac hypertrophy after abdominal aortic banding. Moreover, we detected an inwardly rectifying current in hypertrophic cardiomyocytes that occurs under native conditions (i.e., in the absence of drug-induced store depletion) and is dependent on STIM1. By manipulating its expression, we found STIM1 to be both sufficient and necessary for cardiomyocyte hypertrophy in vitro and in the adult heart in vivo. Stim1 silencing by adeno-associated viruses of serotype 9-mediated gene transfer protected rats from pressure overload-induced cardiac hypertrophy. CONCLUSION: By controlling a previously unrecognized sarcolemmal current, STIM1 promotes cardiac hypertrophy.

SDF-1α as a therapeutic stem cell homing factor in myocardial infarction.

Myocardial infarction is associated with persistent muscle damage, scar formation and depressed cardiac performance. Recent studies have demonstrated the clinical significance of stem cell-based therapies after myocardial infarction with the aim to improve cardiac remodeling and function by inducing the reconstitution of functional myocardium and formation of new blood vessels. Stem cell homing signals play an important role in stem cell mobilization from the bone marrow to the ischemic cardiac environment and are therefore crucial for myocardial repair. To date, the most prominent stem cell homing factor is the chemokine SDF-1α/CXCL12. This protein was shown to be significantly upregulated in many experimental models of myocardial infarction and in patients suffering from ischemic cardiac diseases, suggesting the involvement in the pathophysiology of these disorders. A number of studies focused on manipulating SDF-1α and its receptor CXCR4 as central regulators of the stem cell mobilization process. Targeted expression of SDF-1α after myocardial infarction was shown to result in increased engraftment of bone marrow-derived stem cells into infarcted myocardium. This was accompanied by beneficial effects on cardiomyocyte survival, neovascularization and cardiac function. Thus, the SDF-1/CXCR4 axis seems to be a promising novel therapeutic approach to improve post-infarction therapy by attracting circulating stem cells to remain, survive and possibly differentiate in the infarct area. This review will summarize clinical trials of stem cell therapy in patients with myocardial infarction. We further discuss the basic findings about SDF-1α in stem cell recruitment and its therapeutic implications in experimental myocardial infarction.

An EF hand mutation in Stim1 causes premature platelet activation and bleeding in mice.

Changes in cytoplasmic Ca2+ levels regulate a variety of fundamental cellular functions in virtually all cells. In nonexcitable cells, a major pathway of Ca2+ entry involves receptor-mediated depletion of intracellular Ca2+ stores followed by the activation of store-operated calcium channels in the plasma membrane. We have established a mouse line expressing an activating EF hand motif mutant of stromal interaction molecule 1 (Stim1), an ER receptor recently identified as the Ca2+ sensor responsible for activation of Ca2+ release-activated (CRAC) channels in T cells, whose function in mammalian physiology is not well understood. Mice expressing mutant Stim1 had macrothrombocytopenia and an associated bleeding disorder. Basal intracellular Ca2+ levels were increased in platelets, which resulted in a preactivation state, a selective unresponsiveness to immunoreceptor tyrosine activation motif-coupled agonists, and increased platelet consumption. In contrast, basal Ca2+ levels, but not receptor-mediated responses, were affected in mutant T cells. These findings identify Stim1 as a central regulator of platelet function and suggest a cell type-specific activation or composition of the CRAC complex.