Ca2+ channel β-subunit interactions with pore-forming α-subunits are long-thought to be obligatory for channel trafficking to the cell surface and for tuning of basal biophysical properties in many tissues. Unexpectedly, we demonstrate that transgenic expression of mutant cardiac α1C subunits lacking capacity to bind CaVβ because of alanine-substitutions of three conserved residues — Y467, W470, and I471 in the α-interaction domain of rabbit α1C — can traffic to the sarcolemma in adult cardiomyocytes in vivo and sustain normal excitation-contraction coupling. However, these β-less Ca2+ channels cannot be stimulated by β-adrenergic pathway agonists, and thus adrenergic-augmentation of contractility is markedly impaired in isolated cardiomyocytes and in hearts. Similarly, viral-mediated expression of a β-subunit-sequestering-peptide sharply curtailed β-adrenergic stimulation of wild-type Ca2+ channels, identifying an approach to specifically modulate β-adrenergic regulation of cardiac contractility. Our data demonstrate that β subunits are required for β-adrenergic regulation of CaV1.2 channels and positive inotropy in the heart, but are dispensable for CaV1.2 trafficking to the adult cardiomyocyte cell surface, and for basal function and excitation-contraction coupling.
Lin Yang, Alexander Katchman, Jared S. Kushner, Alexander Kushnir, Sergey I. Zakharov, Bi-xing Chen, Zunaira Shuja, Prakash Subramanyam, Guoxia Liu, Arianne Papa, Daniel D. Roybal, Geoffrey S. Pitt, Henry M. Colecraft, Steven O. Marx
Emerging evidence indicates that angiopoietin-2 (Angpt2), a well-recognized vascular destabilizing factor, is a biomarker of poor outcome in ischemic heart disease. However, its precise role in postischemic cardiovascular remodeling is poorly understood. Here, we show that Angpt2 plays multifaceted roles in the exacerbation of cardiac hypoxia and inflammation after myocardial ischemia. Angpt2 was highly expressed in endothelial cells at the infarct border zone after myocardial infarction (MI) or ischemia/reperfusion injury in mice. In the acute phase of MI, endothelial-derived Angpt2 antagonized Angpt1/Tie2 signaling, which was greatly involved in pericyte detachment, vascular leakage, increased adhesion molecular expression, degradation of the glycocalyx and extracellular matrix, and enhanced neutrophil infiltration and hypoxia in the infarct border area. In the chronic remodeling phase after MI, endothelial- and macrophage-derived Angpt2 continuously promoted abnormal vascular remodeling and proinflammatory macrophage polarization through integrin α5β1 signaling, worsening cardiac hypoxia and inflammation. Accordingly, inhibition of Angpt2 either by gene deletion or using an anti-Angpt2 blocking antibody substantially alleviated these pathological findings and ameliorated postischemic cardiovascular remodeling. Blockade of Angpt2 thus has potential as a therapeutic option for ischemic heart failure.
Seung-Jun Lee, Choong-kun Lee, Seok Kang, Intae Park, Yoo Hyung Kim, Seo Ki Kim, Seon Pyo Hong, Hosung Bae, Yulong He, Yoshiaki Kubota, Gou Young Koh
Heart failure (HF) remains a major source of morbidity and mortality in the U.S. The multifunctional Ca2+/calmodulin-dependent kinase II (CaMKII) has emerged as a critical regulator of cardiac hypertrophy and failure, although the mechanisms remain unclear. Previous studies have established that the cytoskeletal protein βIV-spectrin coordinates local CaMKII signaling. Here we sought to determine the role of a spectrin/CaMKII complex in maladaptive remodeling in HF. Chronic pressure overload (6 weeks transaortic constriction, TAC) induced a decrease in cardiac function in WT mice but not in animals expressing truncated βIV-spectrin lacking spectrin/CaMKII interaction (qv3J). Underlying observed differences in function was an unexpected differential regulation of STAT3-related genes in qv3J TAC hearts. In vitro experiments demonstrate that βIV-spectrin serves as a target for CaMKII phosphorylation, which regulates its stability. Cardiac-specific βIV-spectrin knockout (βIV-cKO) mice show STAT3 dysregulation, fibrosis and decreased cardiac function at baseline similar to WT TAC. STAT3 inhibition restored normal cardiac structure and function in βIV-cKO and WT TAC hearts. Our studies identify a novel spectrin-based complex essential for regulation of the cardiac response to chronic pressure overload. We anticipate that strategies targeting the new spectrin-based “statosome” will be effective at suppressing maladaptive remodeling in response to chronic stress.
Sathya D. Unudurthi, Drew M. Nassal, Amara Greer-Short, Nehal J. Patel, Taylor Howard, Xianyao Xu, Birce Onal, Tony Satroplus, Deborah Y. Hong, Cemantha M. Lane, Alyssa Dalic, Sara N. Koenig, Adam C. Lehnig, Lisa A. Baer, Hassan Musa, Kristin I. Stanford, Sakima A. Smith, Peter J. Mohler, Thomas J. Hund
The ubiquitin-proteasome system (UPS) degrades a protein molecule via two main steps: ubiquitination and proteasomal degradation. Extraproteasomal ubiquitin receptors are thought to couple the two steps but this proposition has not been tested in vivo with vertebrate animals. More importantly, impaired UPS performance plays a major role in cardiac pathogenesis including myocardial ischemia-reperfusion injury (IRI) but the molecular basis of the UPS impairment remains poorly understood. Ubiquilin1 is a bona fide extra-proteasomal ubiquitin receptor. Here we report that cardiomyocyte-restricted knockout of Ubiquilin1 (Ubqln1-CKO) in mice accumulated a surrogate UPS substrate (GFPdgn) and increased myocardial ubiquitinated proteins without altering proteasome activities, and resulted in a late-onset cardiomyopathy and a significantly shortened lifespan. When subject to regional myocardial ischemia-reperfusion, young Ubqln1-CKO mice showed significantly exacerbated cardiac malfunction and enlarged infarct size and, conversely, mice with transgenic Ubqln1 overexpression displayed attenuated IRI. Furthermore, Ubqln1 overexpression facilitated proteasomal degradation of oxidized proteins and the degradation of a UPS surrogate substrate in cultured cardiomyocytes without increasing autophagic flux. These findings demonstrate that Ubiquilin1 is essential to cardiac ubiquitination-proteasome coupling and that an inadequacy in the coupling represents a major pathogenic factor to myocardial IRI, identifying strengthening the coupling as a potential strategy to reduce IRI.
Chengjun Hu, Yihao Tian, Hongxin Xu, Bo Pan, Erin M. Terpstra, Penglong Wu, Hongmin Wang, Faqian Li, Jinbao Liu, Xuejun Wang
Cardiac two pore domain potassium channels (K2P) exist in organisms from Drosophila to humans, however their role in cardiac function is not known. We identified a K2P gene, CG8713 (sandman), in a Drosophila genetic screen and show that sandman is critical to cardiac function. Mice lacking an ortholog of sandman, TWIK related potassium channel (TREK-1 or Kcnk2), exhibit exaggerated pressure overload induced concentric hypertrophy and alterations in fetal gene expression, yet retain preserved systolic and diastolic cardiac function. While cardiomyocyte specific deletion of TREK-1 in response to in vivo pressure overload resulted in cardiac dysfunction, TREK-1 deletion in fibroblasts prevented deterioration in cardiac function. The absence of pressure overload induced dysfunction in TREK-1 KO mice was associated with diminished cardiac fibrosis and reduced activation of c-Jun N-terminal kinase activity (JNK) in cardiomyocytes and fibroblasts. These findings indicate a central role for cardiac fibroblast TREK-1 in the pathogenesis of pressure overload-induced cardiac dysfunction and serve as a conceptual basis for its inhibition for as a potential therapy.
Dennis M. Abraham, Teresa E. Lee, Lewis J. Watson, Lan Mao, Gurangad S. Chandok, Hong-Gang Wang, Stephan Frangakis, Geoffrey S. Pitt, Svati H. Shah, Matthew J. Wolf, Howard A. Rockman
The superoxide-generating enzyme Nox2 contributes to hypertension and cardiovascular remodeling triggered by activation of the renin-angiotensin system. Multiple Nox2-expressing cells are implicated in angiotensin II (AngII)-induced pathophysiology, but the importance of Nox2 in leukocyte subsets is poorly understood. Here, we investigated the role of Nox2 in T cells, particularly Tregs. Mice globally deficient in Nox2 displayed increased numbers of Tregs in the heart at baseline whereas AngII-induced T-effector cell (Teffs) infiltration was inhibited. To investigate the role of Treg Nox2, we generated a mouse line with CD4-targeted Nox2 deficiency (Nox2fl/flCD4Cre+). These animals showed inhibition of AngII-induced hypertension and cardiac remodeling related to increased tissue-resident Tregs and reduction in infiltrating Teffs, including Th17 cells. The protection in Nox2fl/flCD4Cre+ mice was reversed by anti-CD25 Ab-depletion of Tregs. Mechanistically, Nox2–/y Tregs showed higher in vitro suppression of Teffs proliferation than WT Tregs, increased nuclear levels of FoxP3 and NF-κB, and enhanced transcription of CD25, CD39, and CD73. Adoptive transfer of Tregs confirmed that Nox2-deficient cells had greater inhibitory effects on AngII-induced heart remodeling than WT cells. These results identify a previously unrecognized role of Nox2 in modulating suppression of Tregs, which acts to enhance hypertension and cardiac remodeling.
Amber Emmerson, Silvia Cellone Trevelin, Heloise Mongue-Din, Pablo D. Becker, Carla Ortiz, Lesley A. Smyth, Qi Peng, Raul Elgueta, Greta Sawyer, Aleksandar Ivetic, Robert I. Lechler, Giovanna Lombardi, Ajay M. Shah
Fibroblasts are a dynamic cell type that achieve selective differentiated states to mediate acute wound healing and long-term tissue remodeling with scarring. With myocardial infarction injury, cardiomyocytes are replaced by secreted extracellular matrix proteins produced by proliferating and differentiating fibroblasts. Here, we employed 3 different mouse lineage-tracing models and stage-specific gene profiling to phenotypically analyze and classify resident cardiac fibroblast dynamics during myocardial infarction injury and stable scar formation. Fibroblasts were activated and highly proliferative, reaching a maximum rate within 2 to 4 days after infarction injury, at which point they expanded 3.5-fold and were maintained long term. By 3 to 7 days, these cells differentiated into myofibroblasts that secreted abundant extracellular matrix proteins and expressed smooth muscle α-actin to structurally support the necrotic area. By 7 to 10 days, myofibroblasts lost proliferative ability and smooth muscle α-actin expression as the collagen-containing extracellular matrix and scar fully matured. However, these same lineage-traced initial fibroblasts persisted within the scar, achieving a new molecular and stable differentiated state referred to as a matrifibrocyte, which was also observed in the scars of human hearts. These cells express common and unique extracellular matrix and tendon genes that are more specialized to support the mature scar.
Xing Fu, Hadi Khalil, Onur Kanisicak, Justin G. Boyer, Ronald J. Vagnozzi, Bryan D. Maliken, Michelle A. Sargent, Vikram Prasad, Iñigo Valiente-Alandi, Burns C. Blaxall, Jeffery D. Molkentin
SCN5A encodes the voltage-gated Na+ channel NaV1.5 that is responsible for depolarization of the cardiac action potential and rapid intercellular conduction. Mutations disrupting the SCN5A coding sequence cause inherited arrhythmias and cardiomyopathy, and single-nucleotide polymorphisms (SNPs) linked to SCN5A splicing, localization, and function associate with heart failure–related sudden cardiac death. However, the clinical relevance of SNPs that modulate SCN5A expression levels remains understudied. We recently generated a transcriptome-wide map of microRNA (miR) binding sites in human heart, evaluated their overlap with common SNPs, and identified a synonymous SNP (rs1805126) adjacent to a miR-24 site within the SCN5A coding sequence. This SNP was previously shown to reproducibly associate with cardiac electrophysiological parameters, but was not considered to be causal. Here, we show that miR-24 potently suppresses SCN5A expression and that rs1805126 modulates this regulation. We found that the rs1805126 minor allele associates with decreased cardiac SCN5A expression and that heart failure subjects homozygous for the minor allele have decreased ejection fraction and increased mortality, but not increased ventricular tachyarrhythmias. In mice, we identified a potential basis for this in discovering that decreased Scn5a expression leads to accumulation of myocardial reactive oxygen species. Together, these data reiterate the importance of considering the mechanistic significance of synonymous SNPs as they relate to miRs and disease, and highlight a surprising link between SCN5A expression and nonarrhythmic death in heart failure.
Xiaoming Zhang, Jin-Young Yoon, Michael Morley, Jared M. McLendon, Kranti A. Mapuskar, Rebecca Gutmann, Haider Mehdi, Heather L. Bloom, Samuel C. Dudley, Patrick T. Ellinor, Alaa A. Shalaby, Raul Weiss, W.H. Wilson Tang, Christine S. Moravec, Madhurmeet Singh, Anne L. Taylor, Clyde W. Yancy, Arthur M. Feldman, Dennis M. McNamara, Kaikobad Irani, Douglas R. Spitz, Patrick Breheny, Kenneth B. Margulies, Barry London, Ryan L. Boudreau
Congenital long QT syndrome (LQTS) is an inherited channelopathy associated with life-threatening arrhythmias. LQTS type 2 (LQT2) is caused by mutations in KCNH2, which encodes the potassium channel hERG. We hypothesized that modifier genes are partly responsible for the variable phenotype severity observed in some LQT2 families. Here, we identified contributors to variable expressivity in an LQT2 family by using induced pluripotent stem cell–derived cardiomyocytes (iPSC-CMs) and whole exome sequencing in a synergistic manner. We found that iPSC-CMs recapitulated the clinical genotype-phenotype discordance in vitro. Importantly, iPSC-CMs derived from the severely affected LQT2 patients displayed prolonged action potentials compared with cells from mildly affected first-degree relatives. The iPSC-CMs derived from all patients with hERG R752W mutation displayed lower IKr amplitude. Interestingly, iPSC-CMs from severely affected mutation-positive individuals exhibited greater L-type Ca2+ current. Whole exome sequencing identified variants of KCNK17 and the GTP-binding protein REM2, providing biologically plausible explanations for this variable expressivity. Genome editing to correct a REM2 variant reversed the enhanced L-type Ca2+ current and prolonged action potential observed in iPSC-CMs from severely affected individuals. Thus, our findings showcase the power of combining complementary physiological and genomic analyses to identify genetic modifiers and potential therapeutic targets of a monogenic disorder. Furthermore, we propose that this strategy can be deployed to unravel myriad confounding pathologies displaying variable expressivity.
Sam Chai, Xiaoping Wan, Angelina Ramirez-Navarro, Paul J. Tesar, Elizabeth S. Kaufman, Eckhard Ficker, Alfred L. George Jr., Isabelle Deschênes
Isolated left ventricular noncompaction (LVNC) results from excessive trabeculation and impaired myocardial compaction during heart development. The extracellular matrix (ECM) that separates endocardium from myocardium plays a critical but poorly understood role in ventricular trabeculation and compaction. In an attempt to characterize solute carrier family 39 member 8–null (Slc39a8-null) mice, we discovered that homozygous null embryos do not survive embryogenesis, and exhibit a cardiac phenotype similar to human LVNC. Slc39a8 encodes a divalent metal cation importer that has been implicated in ECM degradation through the zinc/metal regulatory transcription factor 1 (Zn/MTF1) axis, which promotes the expression of ECM-degrading enzymes, including Adamts metalloproteinases. Here, we have shown that Slc39a8 is expressed by endothelial cells in the developing mouse heart, where it serves to maintain cellular Zn levels. Furthermore, Slc39a8-null hearts exhibited marked ECM accumulation and reduction of several Adamts metalloproteinases. Consistent with the in vivo observations, knockdown of SLC39A8 in HUVECs decreased ADAMTS1 transcription by decreasing cellular Zn uptake, and as a result, MTF1 transcriptional activity. Our study thus identifies a gene underlying ventricular trabeculation and compaction development, and a pathway regulating ECM during myocardial morphogenesis.
Wen Lin, Deqiang Li, Lan Cheng, Li Li, Feiyan Liu, Nicholas J. Hand, Jonathan A. Epstein, Daniel J. Rader