Tbx6 induces cardiomyocyte proliferation in postnatal and adult mouse hearts.

Cardiovascular disease is a leading cause of death worldwide. Mammalian cardiomyocytes (CMs) proliferate during embryonic development, whereas they largely lose their regenerative capacity after birth. Defined factors expressed in cardiac progenitors or embryonic CMs may activate the cell cycle and induce CM proliferation in postnatal and adult hearts. Here, we report that the overexpression of Tbx6, enriched in the cardiac mesoderm (progenitor cells), induces CM proliferation in postnatal and adult mouse hearts. By screening 24 factors enriched in cardiac progenitors or embryonic CMs, we found that only Tbx6 could induce CM proliferation in primary cultured postnatal rat CMs. Intriguingly, it did not induce the proliferation of cardiac fibroblasts. We next generated a recombinant adeno-associated virus serotype 9 vector encoding Tbx6 (AAV9-Tbx6) for transduction into mouse CMs in vivo. The subcutaneous injection of AAV9-Tbx6 into neonatal mice induced CM proliferation in postnatal and adult mouse hearts. Mechanistically, Tbx6 overexpression upregulated multiple cell cycle activators including Aurkb, Mki67, Ccna1, and Ccnb2 and suppressed the tumor suppressor Rb1. Thus, Tbx6 promotes CM proliferation in postnatal and adult mouse hearts by modifying the expression of cell cycle regulators.

Distinct expression patterns of Flk1 and Flt1 in the coronary vascular system during development and after myocardial infarction.

The coronary vascular system is critical for myocardial growth and cardiomyocyte survival. However, the molecular mechanism regulating coronary angiogenesis remains elusive. Vascular endothelial growth factor (VEGF) regulates angiogenesis by binding to the specific receptors Flk1 and Flt1, which results in different functions. Despite the importance of Flk1 and Flt1, their expression in the coronary vasculature remains largely unknown due to the lack of appropriate antibodies for immunostaining. Here, we analyzed multiple reporter mice including Flk1-GFP BAC transgenic (Tg), Flk1-LacZ knock-in, Flt1-DsRed BAC Tg, and Flk1-GFP/Flt1-DsRed double Tg animals to determine expression patterns in mouse hearts during cardiac growth and after myocardial infarction (MI). We found that Flk1 was expressed in endothelial cells (ECs) with a pattern of epicardial-to-endocardial transmural gradients in the neonatal mouse ventricle, which was downregulated in adult coronary vessels with development. In contrast, Flt1 was homogeneously expressed in the ECs of neonatal mouse hearts and expression was maintained until adulthood. After MI, expression of both Flk1 and Flt1 was induced in the regenerating coronary vessels at day 7. Intriguingly, Flk1 expression was downregulated thereafter, whereas Flt1 expression was maintained in the newly formed coronary vessels until 30 days post-MI, recapitulating their expression kinetics during development. This is the first report demonstrating the spatiotemporal expression patterns of Flk1 and Flt1 in the coronary vascular system during development and after MI; thus, this study suggests that these factors have distinct and important functions in coronary angiogenesis.

Evaluation of Lecithinized Superoxide Dismutase for the Prevention of Acute Respiratory Distress Syndrome in Animal Models.

For acute respiratory distress syndrome (ARDS), mechanical ventilation (MV) is a life-saving intervention without alternative; however, MV can cause ventilator-induced lung injury. Reactive oxygen species (ROS) play important roles in the pathogenesis of both ARDS and ventilator-induced lung injury. Lecithinized superoxide dismutase (PC-SOD) overcomes the limitations of superoxide dismutase such as low tissue affinity and low stability in plasma. In this study, we examined the effect of PC-SOD on tissue injury, edema, and inflammation in the lung and other organs of mice subjected to cecal ligation and puncture (CLP), LPS administration, or MV. The severity of the lung injury was assessed on the basis of vascular permeability, histopathologic evaluation, and lung mechanics. Intravenous PC-SOD administration (the first administered just before CLP) increased the survival rate and decreased vascular permeability in mice subjected to CLP. PC-SOD, but not dexamethasone or sivelestat sodium hydrate (sivelestat), suppressed CLP-induced kidney injury and systemic inflammation. PC-SOD also suppressed vascular permeability, tissue injury, and inflammation in the lung induced by LPS administration. Moreover, PC-SOD, but not dexamethasone or sivelestat, suppressed vascular permeability, edema, tissue injury, and mechanical alterations in the lung induced by MV. In vivo imaging analysis of ROS revealed that CLP, LPS administration, and MV increased the level of ROS and that this increase was suppressed by PC-SOD. The results of this study thus suggest that, on the basis of its ROS-reducing properties, intravenous administration of PC-SOD may be beneficial for patients at high risk of developing ARDS.

Single-Construct Polycistronic Doxycycline-Inducible Vectors Improve Direct Cardiac Reprogramming and Can Be Used to Identify the Critical Timing of Transgene Expression.

Direct reprogramming is a promising approach in regenerative medicine. Overexpression of the cardiac transcription factors Gata4, Mef2c, and Tbx5 (GMT) or GMT plus Hand2 (GHMT) directly reprogram fibroblasts into cardiomyocyte-like cells (iCMs). However, the critical timing of transgene expression and the molecular mechanisms for cardiac reprogramming remain unclear. The conventional doxycycline (Dox)-inducible temporal transgene expression systems require simultaneous transduction of two vectors (pLVX-rtTA/pLVX-cDNA) harboring the reverse tetracycline transactivator (rtTA) and the tetracycline response element (TRE)-controlled transgene, respectively, leading to inefficient cardiac reprogramming. Herein, we developed a single-construct-based polycistronic Dox-inducible vector (pDox-cDNA) expressing both the rtTA and TRE-controlled transgenes. Fluorescence activated cell sorting (FACS) analyses, quantitative RT-PCR, and immunostaining revealed that pDox-GMT increased cardiac reprogramming three-fold compared to the conventional pLVX-rtTA/pLVX-GMT. After four weeks, pDox-GMT-induced iCMs expressed multiple cardiac genes, produced sarcomeric structures, and beat spontaneously. Co-transduction of pDox-Hand2 with retroviral pMX-GMT increased cardiac reprogramming three-fold compared to pMX-GMT alone. Temporal Dox administration revealed that Hand2 transgene expression is critical during the first two weeks of cardiac reprogramming. Microarray analyses demonstrated that Hand2 represses cell cycle-promoting genes and enhances cardiac reprogramming. Thus, we have developed an efficient temporal transgene expression system, which could be invaluable in the study of cardiac reprogramming.

Superoxide dismutase overexpression protects against glucocorticoid-induced depressive-like behavioral phenotypes in mice.

In the stress response, activation of the hypothalamic-pituitary-adrenal axis, and particularly the release of glucocorticoids, plays a critical role. However, dysregulation of this system and sustained high plasma levels of glucocorticoids can result in depression. Recent studies have suggested the involvement of reactive oxygen species (ROS), such as superoxide anion, in depression. However, direct evidence for a role of ROS in the pathogenesis of this disorder is lacking. In this study, using transgenic mice expressing human Cu/Zn-superoxide dismutase (SOD1), an enzyme that catalyzes the dismutation of superoxide anions, we examined the effect of SOD1 overexpression on depressive-like behavioral phenotypes in mice. Depressive-like behaviors were induced by daily subcutaneous administration of the glucocorticoid corticosterone for 4 weeks, and was monitored with the social interaction test, the sucrose preference test and the forced swim test. These tests revealed that transgenic mice overexpressing SOD1 are more resistant to glucocorticoid-induced depressive-like behavioral disorders than wild-type animals. Furthermore, compared with wild-type mice, transgenic mice showed a reduction in the number of 8-hydroxy-2'-deoxyguanosine (a marker of oxidative stress)-positive cells in the hippocampal CA3 region following corticosterone administration. These results suggest that overexpression of SOD1 protects mice against glucocorticoid-induced depressive-like behaviors by decreasing cellular ROS levels.

The Effect of a Synthetic Estrogen, Ethinylestradiol, on the hERG Block by E-4031.

Inhibition of K+-conductance through the human ether-a-go-go related gene (hERG) channel leads to QT prolongation and is associated with cardiac arrhythmias. We previously reported that physiological concentrations of some estrogens partially suppress the hERG channel currents by interacting with the S6 residue F656 and increase the sensitivity of hERG blockade by E-4031. Although these studies suggested that clinically used synthetic estrogens with similar structures have the marked potential to alter hERG functions, the hERG interactions with synthetic estrogens have not been assessed. We therefore examined whether ethinylestradiol (EE2), a synthetic estrogen used in oral contraceptives, affects hERG function and blockade by drugs. Supratherapeutic concentrations of EE2 did not alter amplitudes or kinetics of the hERG currents elicited by train pulses at 20 mV (0.1 Hz). On the other hand, EE2 at therapeutic concentrations reduced the degree of hERG current suppression by E-4031. The administration of EE2 followed by E-4031 blockade reversed the current suppression, suggesting that the interaction of EE2 and E-4031 alters hERG at the drug-binding site. The effects of EE2 on hERG blockade raised the possibility that other estrogens, including synthetic estrogens, can alter hERG blockade by drugs that cause QT prolongation and ventricular arrhythmias.

Soft Matrix Promotes Cardiac Reprogramming via Inhibition of YAP/TAZ and Suppression of Fibroblast Signatures.

Direct cardiac reprogramming holds great potential for regenerative medicine. However, it remains inefficient, and induced cardiomyocytes (iCMs) generated in vitro are less mature than those in vivo, suggesting that undefined extrinsic factors may regulate cardiac reprogramming. Previous in vitro studies mainly used hard polystyrene dishes, yet the effect of substrate rigidity on cardiac reprogramming remains unclear. Thus, we developed a Matrigel-based hydrogel culture system to determine the roles of matrix stiffness and mechanotransduction in cardiac reprogramming. We found that soft matrix comparable with native myocardium promoted the efficiency and quality of cardiac reprogramming. Mechanistically, soft matrix enhanced cardiac reprogramming via inhibition of integrin, Rho/ROCK, actomyosin, and YAP/TAZ signaling and suppression of fibroblast programs, which were activated on rigid substrates. Soft substrate further enhanced cardiac reprogramming with Sendai virus vectors via YAP/TAZ suppression, increasing the reprogramming efficiency up to ∼15%. Thus, mechanotransduction could provide new targets for improving cardiac reprogramming.

Role of cyclooxygenase-2-mediated prostaglandin E2-prostaglandin E receptor 4 signaling in cardiac reprogramming.

Direct cardiac reprogramming from fibroblasts can be a promising approach for disease modeling, drug screening, and cardiac regeneration in pediatric and adult patients. However, postnatal and adult fibroblasts are less efficient for reprogramming compared with embryonic fibroblasts, and barriers to cardiac reprogramming associated with aging remain undetermined. In this study, we screened 8400 chemical compounds and found that diclofenac sodium (diclofenac), a non-steroidal anti-inflammatory drug, greatly enhanced cardiac reprogramming in combination with Gata4, Mef2c, and Tbx5 (GMT) or GMT plus Hand2. Intriguingly, diclofenac promoted cardiac reprogramming in mouse postnatal and adult tail-tip fibroblasts (TTFs), but not in mouse embryonic fibroblasts (MEFs). Mechanistically, diclofenac enhanced cardiac reprogramming by inhibiting cyclooxygenase-2, prostaglandin E2/prostaglandin E receptor 4, cyclic AMP/protein kinase A, and interleukin 1ß signaling and by silencing inflammatory and fibroblast programs, which were activated in postnatal and adult TTFs. Thus, anti-inflammation represents a new target for cardiac reprogramming associated with aging.

Direct In Vivo Reprogramming with Sendai Virus Vectors Improves Cardiac Function after Myocardial Infarction.

Direct cardiac reprogramming holds great promise for regenerative medicine. We previously generated directly reprogrammed induced cardiomyocyte-like cells (iCMs) by overexpression of Gata4, Mef2c, and Tbx5 (GMT) using retrovirus vectors. However, integrating vectors pose risks associated with insertional mutagenesis and disruption of gene expression and are inefficient. Here, we show that Sendai virus (SeV) vectors expressing cardiac reprogramming factors efficiently and rapidly reprogram both mouse and human fibroblasts into integration-free iCMs via robust transgene expression. SeV-GMT generated 100-fold more beating iCMs than retroviral-GMT and shortened the duration to induce beating cells from 30 to 10 days in mouse fibroblasts. In vivo lineage tracing revealed that the gene transfer of SeV-GMT was more efficient than retroviral-GMT in reprogramming resident cardiac fibroblasts into iCMs in mouse infarct hearts. Moreover, SeV-GMT improved cardiac function and reduced fibrosis after myocardial infarction. Thus, efficient, non-integrating SeV vectors may serve as a powerful system for cardiac regeneration.

Tbx6 Induces Nascent Mesoderm from Pluripotent Stem Cells and Temporally Controls Cardiac versus Somite Lineage Diversification.

The mesoderm arises from pluripotent epiblasts and differentiates into multiple lineages; however, the underlying molecular mechanisms are unclear. Tbx6 is enriched in the paraxial mesoderm and is implicated in somite formation, but its function in other mesoderms remains elusive. Here, using direct reprogramming-based screening, single-cell RNA-seq in mouse embryos, and directed cardiac differentiation in pluripotent stem cells (PSCs), we demonstrated that Tbx6 induces nascent mesoderm from PSCs and determines cardiovascular and somite lineage specification via its temporal expression. Tbx6 knockout in mouse PSCs using CRISPR/Cas9 technology inhibited mesoderm and cardiovascular differentiation, whereas transient Tbx6 expression induced mesoderm and cardiovascular specification from mouse and human PSCs via direct upregulation of Mesp1, repression of Sox2, and activation of BMP/Nodal/Wnt signaling. Notably, prolonged Tbx6 expression suppressed cardiac differentiation and induced somite lineages, including skeletal muscle and chondrocytes. Thus, Tbx6 is critical for mesoderm induction and subsequent lineage diversification.

Preventive Effects of Carnosine on Lipopolysaccharide-induced Lung Injury.

Acute respiratory distress syndrome (ARDS) is a potentially devastating form of acute lung injury, which involves neutrophilic inflammation and pulmonary cell death. Reactive oxygen species (ROS) play important roles in ARDS development. New compounds for inhibiting the onset and progression of ARDS are required. Carnosine (ß-alanyl-L-histidine) is a small di-peptide with numerous activities, including antioxidant effects, metal chelation, proton buffering capacity and the inhibition of protein carbonylation and glycoxidation. We have examined the preventive effects of carnosine on tissue injury, oedema and inflammation in a murine model for ARDS. Oral administration of carnosine suppressed lipopolysaccharide (LPS)-induced vascular permeability, tissue injury and inflammation in the lung. In vivo imaging analysis revealed that LPS administration increased the level of ROS and that this increase was inhibited by carnosine administration. Carnosine also suppressed LPS-induced neutrophilic inflammation (evaluated by activation of myeloperoxidase in the lung and increased extracellular DNA in bronchoalveolar lavage fluid). Furthermore, carnosine administration suppressed the LPS-induced endoplasmic reticulum stress response in vivo. These results suggest that the oral administration of carnosine suppresses LPS-induced lung injury via carnosine's ROS-reducing activity. Therefore, carnosine may be beneficial for suppressing the onset and progression of ARDS.

Protective and therapeutic effect of felodipine against bleomycin-induced pulmonary fibrosis in mice.

Idiopathic pulmonary fibrosis (IPF) involves alveolar epithelial injury and abnormal collagen production caused by activated fibroblasts; transforming growth factor (TGF)-ß1 is implicated in this activation. In this study, we screened for chemicals capable of inhibiting TGF-ß1-induced collagen production in cultured fibroblasts from medicines already in clinical use. We selected felodipine based on its extent of collagen production inhibition, clinical safety profile, and other pharmacological activity. Felodipine is a dihydropyridine Ca2+ channel blocker that has been used clinically to treat patients with high blood pressure. Felodipine suppressed collagen production within LL29 cells in the presence of TGF-ß1, but not in its absence. Intratracheal administration of felodipine prevented bleomycin-induced pulmonary fibrosis, alteration of lung mechanics and respiratory dysfunction. Felodipine also improved pulmonary fibrosis, as well as lung and respiratory function when administered after fibrosis development. Furthermore, administration of felodipine suppressed a bleomycin-induced increase in activated fibroblasts in the lung. We also found other dihydropyridine Ca2+ channel blockers (nifedipine and benidipine) inhibited collagen production in vitro and partially prevented bleomycin-induced pulmonary fibrosis, alteration of lung mechanics and respiratory dysfunction in vivo. We propose that these Ca2+ channel blockers may be therapeutically beneficial for IPF patients.

Encapsulation of beraprost sodium in nanoparticles: analysis of sustained release properties, targeting abilities and pharmacological activities in animal models of pulmonary arterial hypertension.

Prostaglandin I2 (PGI2) and its analogues (such as beraprost sodium, BPS) are beneficial for the treatment of pulmonary arterial hypertension (PAH). The encapsulation of BPS in nanoparticles to provide sustained release and targeting abilities would improve both the therapeutic effect of BPS on PAH and the quality of life of patients treated with this drug. BPS was encapsulated into nanoparticles prepared from a poly(lactic acid) homopolymer and monomethoxy poly(ethyleneglycol)-poly(lactide) block copolymer. The accumulation of nanoparticles in damaged pulmonary arteries was examined using fluorescence-emitting rhodamine S-encapsulated nanoparticles. The monocrotaline-induced PAH rat model and the hypoxia-induced mouse model were used to examine the pharmacological activity of BPS-encapsulated nanoparticles. A nanoparticle, named BPS-NP, was selected among various types of BPS-encapsulated nanoparticles tested; this was based on the sustained release profile in vitro and blood clearance profile in vivo. Fluorescence-emitting rhodamine S-encapsulated nanoparticles were prepared in a similar manner to that of BPS-NP, and showed accumulation and prolonged residence in monocrotaline-damaged pulmonary peripheral arteries. Intravenous administration of BPS-NP (once per week, 20µg/kg) protected against monocrotaline-induced pulmonary arterial remodeling and right ventricular hypertrophy. The extent of this protection was similar to that observed with oral administration (once per day, 100µg/kg) of BPS alone. The once per week intravenous administration of BPS-NP (20µg/kg) also exhibited an ameliorative effect on hypoxia-induced pulmonary arterial remodeling and right ventricular hypertrophy. The beneficial effects of BPS-NP on PAH animal models seem to be mediated by its sustained release and tissue targeting profiles. BPS-NP may be useful for the treatment of PAH patients due to reduced dosages and frequency of BPS administration.