Mst1 is a central Ser-Thr kinase in the Hippo pathway, which promotes apoptosis and inhibits cell proliferation. We have shown previously that, in cardiomyocytes, oxidative stress activates Mst1 at mitochondria, where Mst1 phosphorylates Bcl-xL at Ser14, inducing dissociation of Bcl-xL from Bax and thereby promoting apoptosis. However, the functional significance of Ser14 phosphorylation of endogenous Bcl-xL in vivo remains elusive. We generated knockin (KI) mice in which Ser14 of Bcl-xL is replaced with Ala. KI mice were born at the expected Mendelian ratio, and adult KI mice exhibited normal cardiac morphology and function at baseline. However, KI mice were protected from myocardial ischemia/reperfusion (I/R) injury and exhibited reduced cardiomyocyte apoptosis. Although suppression of endogenous Mst1 also reduced I/R injury, there was no additive protective effect when Mst1 was inhibited in KI mice. The development of dilated cardiomyopathy induced by cardiac-specific overexpression of Mst1 was also ameliorated in KI mice. Lats2 and YAP, two other key components of the Hippo pathway, were not affected in KI mice. These results suggest that Ser14 phosphorylation of Bcl-xL plays an essential role in mediating both cardiomyocyte apoptosis and myocardial injury by acting as a key downstream mediator of Mst1 independently of the canonical Hippo pathway.
Michinari Nakamura, Peiyong Zhai, Dominic P. Del Re, Yasuhiro Maejima, Junichi Sadoshima
We recently discovered that endothelial Nogo-B, a membrane protein of the ER, regulates vascular function by inhibiting the rate-limiting enzyme, serine palmitoyltransferase (SPT), in de novo sphingolipid biosynthesis. Here, we show that endothelium-derived sphingolipids, particularly sphingosine-1-phosphate (S1P), protect the heart from inflammation, fibrosis, and dysfunction following pressure overload and that Nogo-B regulates this paracrine process. SPT activity is upregulated in banded hearts in vivo as well as in TNF-α–activated endothelium in vitro, and loss of Nogo removes the brake on SPT, increasing local S1P production. Hence, mice lacking Nogo-B, systemically or specifically in the endothelium, are resistant to the onset of pathological cardiac hypertrophy. Furthermore, pharmacological inhibition of SPT with myriocin restores permeability, inflammation, and heart dysfunction in Nogo-A/B–deficient mice to WT levels, whereas SEW2871, an S1P1 receptor agonist, prevents myocardial permeability, inflammation, and dysfunction in WT banded mice. Our study identifies a critical role of endothelial sphingolipid biosynthesis and its regulation by Nogo-B in the development of pathological cardiac hypertrophy and proposes a potential therapeutic target for the attenuation or reversal of this clinical condition.
Yi Zhang, Yan Huang, Anna Cantalupo, Paula S. Azevedo, Mauro Siragusa, Jacek Bielawski, Frank J. Giordano, Annarita Di Lorenzo
To elucidate the mechanisms for reverse LV remodeling, we generated a conditional (doxycycline [dox] off) transgenic mouse tetracycline transactivating factor–TRAF2 (tTA-TRAF2) that develops a dilated heart failure (HF) phenotype upon expression of a proinflammatory transgene, TNF receptor–associated factor 2 (TRAF2), and complete normalization of LV structure and function when the transgene is suppressed. tTA-TRAF2 mice developed a significant increase in LV dimension with decreased contractile function, which was completely normalized in the tTA-TRAF2 mice fed dox for 4 weeks (tTA-TRAF2dox4W). Normalization of LV structure and function was accompanied by partial normalization (~60%) of gene expression associated with incident HF. Similar findings were observed in patients with dilated cardiomyopathy who underwent reverse LV remodeling following mechanical circulatory support. Persistence of the HF gene program was associated with an exaggerated hypertrophic response and increased mortality in tTA-TRAF2dox4W mice following transaortic constriction (TAC). These effects were no longer observed following TAC in tTA-TRAF2dox8W, wherein there was a more complete (88%) reversal of the incident HF genes. These results demonstrate that reverse LV remodeling is associated with improvements in cardiac myocyte biology; however, the persistence of the abnormal HF gene program may be maladaptive following perturbations in hemodynamic loading conditions.
Veli K. Topkara, Kari T. Chambers, Kai-Chien Yang, Huei-Ping Tzeng, Sarah Evans, Carla Weinheimer, Attila Kovacs, Jeffrey Robbins, Philip Barger, Douglas L. Mann
The cardioprotective inducible enzyme heme oxygenase-1 (HO-1) degrades prooxidant heme into equimolar quantities of carbon monoxide, biliverdin, and iron. We hypothesized that HO-1 mediates cardiac protection, at least in part, by regulating mitochondrial quality control. We treated WT and HO-1 transgenic mice with the known mitochondrial toxin, doxorubicin (DOX). Relative to WT mice, mice globally overexpressing human HO-1 were protected from DOX-induced dilated cardiomyopathy, cardiac cytoarchitectural derangement, and infiltration of CD11b+ mononuclear phagocytes. Cardiac-specific overexpression of HO-1 ameliorated DOX-mediated dilation of the sarcoplasmic reticulum as well as mitochondrial disorganization in the form of mitochondrial fragmentation and increased numbers of damaged mitochondria in autophagic vacuoles. HO-1 overexpression promotes mitochondrial biogenesis by upregulating protein expression of NRF1, PGC1α, and TFAM, which was inhibited in WT animals treated with DOX. Concomitantly, HO-1 overexpression inhibited the upregulation of the mitochondrial fission mediator Fis1 and resulted in increased expression of the fusion mediators, Mfn1 and Mfn2. It also prevented dynamic changes in the levels of key mediators of the mitophagy pathway, PINK1 and parkin. Therefore, these findings suggest that HO-1 has a novel role in protecting the heart from oxidative injury by regulating mitochondrial quality control.
Travis D. Hull, Ravindra Boddu, Lingling Guo, Cornelia C. Tisher, Amie M. Traylor, Bindiya Patel, Reny Joseph, Sumanth D. Prabhu, Hagir B. Suliman, Claude A. Piantadosi, Anupam Agarwal, James F. George
Myocardial fuel and energy metabolic derangements contribute to the pathogenesis of heart failure. Recent evidence implicates posttranslational mechanisms in the energy metabolic disturbances that contribute to the pathogenesis of heart failure. We hypothesized that accumulation of metabolite intermediates of fuel oxidation pathways drives posttranslational modifications of mitochondrial proteins during the development of heart failure. Myocardial acetylproteomics demonstrated extensive mitochondrial protein lysine hyperacetylation in the early stages of heart failure in well-defined mouse models and the in end-stage failing human heart. To determine the functional impact of increased mitochondrial protein acetylation, we focused on succinate dehydrogenase A (SDHA), a critical component of both the tricarboxylic acid (TCA) cycle and respiratory complex II. An acetyl-mimetic mutation targeting an SDHA lysine residue shown to be hyperacetylated in the failing human heart reduced catalytic function and reduced complex II–driven respiration. These results identify alterations in mitochondrial acetyl-CoA homeostasis as a potential driver of the development of energy metabolic derangements that contribute to heart failure.
Julie L. Horton, Ola J. Martin, Ling Lai, Nicholas M. Riley, Alicia L. Richards, Rick B. Vega, Teresa C. Leone, David J. Pagliarini, Deborah M. Muoio, Kenneth C. Bedi Jr., Kenneth B. Margulies, Joshua J. Coon, Daniel P. Kelly
Stimulation of β1-adrenergic receptor (β1AR), a GPCR, and the receptor for advanced glycation end-products (RAGE), a pattern recognition receptor (PRR), have been independently implicated in the pathogenesis of cardiomyopathy caused by various etiologies, including myocardial infarction, ischemia/reperfusion injury, and metabolic stress. Here, we show that the two distinctly different receptors, β1AR and RAGE, are mutually dependent in mediating myocardial injury and the sequelae of cardiomyopathy. Deficiency or inhibition of RAGE blocks β1AR- and RAGE-mediated myocardial cell death and maladaptive remodeling. Ablation or blockade of β1AR fully abolishes RAGE-induced detrimental effects. Mechanistically, RAGE and β1AR form a complex, which in turn activates Ca2+/calmodulin-dependent kinase II (CaMKII), resulting in loss of cardiomyocytes and myocardial remodeling. These results indicate that RAGE and β1AR not only physically crosstalk at the receptor level, but also functionally converge at the common mediator, CaMKII, highlighting a combined inhibition of RAGE and β1AR as a more effective therapy to treat diverse cardiovascular diseases, such as myocardial infarction, ischemia/reperfusion injury, and diabetic cardiovascular complications.
Weizhong Zhu, Sharon Tsang, David M. Browe, Anthony Y.H. Woo, Ying Huang, Chanjuan Xu, Jian-Feng Liu, Fengxiang Lv, Yan Zhang, Rui-ping Xiao
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