Cardiac reprogramming reduces inflammatory macrophages and improves cardiac function in chronic myocardial infarction

Cardiomyocytes (CMs) have little regenerative capacity. After myocardial infarction (MI), scar formation and myocardial remodeling proceed in the infarct and non-infarct areas, respectively, leading to heart failure (HF). Prolonged activation of cardiac fibroblasts (CFs) and inflammatory cells may contribute to this process; however, therapies targeting these cell types remain lacking. Cardiac reprogramming converts CFs into induced CMs, reduces fibrosis, and improves cardiac function in chronic MI through the overexpression of Mef2c/Gata4/Tbx5/Hand2 (MGTH). However, whether cardiac reprogramming reduces inflammation in infarcted hearts remains unclear. Moreover, the mechanism through which MGTH overexpression in CFs affects inflammatory cells remains unknown. Here, we showed that inflammation persists in the myocardium until three months after MI, which can be reversed with cardiac reprogramming. Single-cell RNA sequencing demonstrated that CFs expressed pro-inflammatory genes and exhibited strong intercellular communication with inflammatory cells, including macrophages, in chronic MI. Cardiac reprogramming suppressed the inflammatory profiles of CFs and reduced the relative ratios and pro-inflammatory signatures of cardiac macrophages. Moreover, fluorescence-activated cell sorting analysis (FACS) revealed that cardiac reprogramming reduced the number of chemokine receptor type 2 (CCR2)-positive inflammatory macrophages in the non-infarct areas in chronic MI, thereby restoring myocardial remodeling. Thus, cardiac reprogramming reduced the number of inflammatory macrophages to exacerbate cardiac function after MI.

Flk1 Deficiency and Hypoxia Synergistically Promote Endothelial Dysfunction, Vascular Remodeling, and Pulmonary Hypertension

BACKGROUND

The mechanisms underlying pulmonary hypertension (PH) remain largely unknown; further, why advanced vascular remodeling preferentially occurs in arterioles is yet to be answered. VEGF (vascular endothelial growth factor) regulates angiogenesis through Flk1 (fetal liver kinase 1) and Flt1 (fms-like tyrosine kinase 1) on endothelial cells (ECs), which may be related to PH pathogenesis. However, spatiotemporal expression patterns of Flk1 and Flt1 in the pulmonary vascular system and the role of endothelial Flk1 in PH development remain poorly understood.

METHODS

We analyzed multiple reporter mice, including Flk1-GFP (green fluorescent protein) bacterial artificial chromosome transgenic (Tg), Flt1-DsRed bacterial artificial chromosome Tg, and Flk1-GFP/Flt1-DsRed double Tg mice, to determine the spatiotemporal expression of Flk1 and Flt1 in hypoxia-induced PH. We also used Cdh5CreERT2/Flk1f/f/Tomato (Flk1-KO [knockout]) mice to induce EC-specific Flk1 deletion and lineage tracing in chronic hypoxia.

RESULTS

Flk1 was specifically expressed in the ECs of small pulmonary vessels, including arterioles. Conversely, Flt1 was more broadly expressed in the ECs of large- to small-sized vessels in adult mouse lungs. Intriguingly, Flk1+ ECs were transiently increased in hypoxia with proliferation, whereas Flt1 expression was unchanged. Flk1-KO mice did not exhibit pulmonary vascular remodeling nor PH in normoxia; however, the arteriolar ECs changed to a cuboidal shape with protrusion. In hypoxia, Flk1 deletion exacerbated EC dysfunction and reduced their number via apoptosis. Additionally, Flk1 deletion promoted medial thickening and neointimal formation in arterioles and worsened PH. Mechanistically, lineage tracing revealed that neointimal cells were derived from Flk1-KO ECs. Moreover, RNA sequencing in pulmonary ECs demonstrated that Flk1 deletion and hypoxia synergistically activated multiple pathways, including cell cycle, senescence/apoptosis, and cytokine/growth factor, concomitant with suppression of cell adhesion and angiogenesis, to promote vascular remodeling.

CONCLUSIONS

Flk1 and Flt1 were differentially expressed in pulmonary ECs. Flk1 deficiency and hypoxia jointly dysregulated arteriolar ECs to promote vascular remodeling. Thus, dysfunction of Flk1+ ECs may contribute to the pathogenesis of advanced vascular remodeling in pulmonary arterioles.

MEF2C/p300-mediated epigenetic remodeling promotes the maturation of induced cardiomyocytes

Cardiac transcription factors (TFs) directly reprogram fibroblasts into induced cardiomyocytes (iCMs), where MEF2C acts as a pioneer factor with GATA4 and TBX5 (GT). However, the generation of functional and mature iCMs is inefficient, and the molecular mechanisms underlying this process remain largely unknown. Here, we found that the overexpression of transcriptionally activated MEF2C via fusion of the powerful MYOD transactivation domain combined with GT increased the generation of beating iCMs by 30-fold. Activated MEF2C with GT generated iCMs that were transcriptionally, structurally, and functionally more mature than those generated by native MEF2C with GT. Mechanistically, activated MEF2C recruited p300 and multiple cardiogenic TFs to cardiac loci to induce chromatin remodeling. In contrast, p300 inhibition suppressed cardiac gene expression, inhibited iCM maturation, and decreased the beating iCM numbers. Splicing isoforms of MEF2C with similar transcriptional activities did not promote functional iCM generation. Thus, MEF2C/p300-mediated epigenetic remodeling promotes iCM maturation.

Generation of a MyoD knock-in reporter mouse line to study muscle stem cell dynamics and heterogeneity

Myoblast determination protein 1 (MyoD) dynamics define the activation status of muscle stem cells (MuSCs), aiding in muscle tissue regeneration after injury. However, the lack of experimental platforms to monitor MyoD dynamics in vitro and in vivo has hampered the investigation of fate determination and heterogeneity of MuSCs. Herein, we report a MyoD knock-in (MyoD-KI) reporter mouse expressing tdTomato at the endogenous MyoD locus. Expression of tdTomato in MyoD-KI mice recapitulated the endogenous MyoD expression dynamics in vitro and during the early phase of regeneration in vivo. Additionally, we showed that tdTomato fluorescence intensity defines MuSC activation status without immunostaining. Based on these features, we developed a high-throughput screening system to assess the effects of drugs on the behavior of MuSCs in vitro. Thus, MyoD-KI mice are an invaluable resource for studying the dynamics of MuSCs, including their fate decisions and heterogeneity, and for drug screening in stem cell therapy.

Development of direct cardiac reprogramming for clinical applications

The incidence of cardiovascular diseases is increasing worldwide, and cardiac regenerative therapy has great potential as a new treatment strategy, especially for ischemic heart disease. Direct cardiac reprogramming is a promising new cardiac regenerative therapy that uses defined factors to induce transdifferentiation of endogenous cardiac fibroblasts (CFs) into induced cardiomyocyte-like cells (iCMs). In vivo reprogramming is expected to restore lost cardiac function without necessitating cardiac transplantation by converting endogenous CFs that exist abundantly in cardiac tissues directly into iCMs. Indeed, we and other groups have demonstrated that in vivo cardiac reprogramming improves cardiac contractile function and reduces scar area after acute myocardial infarction (MI). Recently, we demonstrated that in vivo cardiac reprogramming is an innovative cardiac regenerative therapy that not only regenerates the myocardium, but also reverses fibrosis by inducing the quiescence of pro-fibrotic fibroblasts, thereby improving heart failure in chronic MI. In this review, we summarize the recent progresses in in vivo cardiac reprogramming, and discuss its prospects for future clinical applications and the challenges of direct human reprogramming, which has been a longstanding issue.

Direct Reprogramming Improves Cardiac Function and Reverses Fibrosis in Chronic Myocardial Infarction

BACKGROUND

Because adult cardiomyocytes have little regenerative capacity, resident cardiac fibroblasts (CFs) synthesize extracellular matrix after myocardial infarction (MI) to form fibrosis, leading to cardiac dysfunction and heart failure. Therapies that can regenerate the myocardium and reverse fibrosis in chronic MI are lacking. The overexpression of cardiac transcription factors, including Mef2c/Gata4/Tbx5/Hand2 (MGTH), can directly reprogram CFs into induced cardiomyocytes (iCMs) and improve cardiac function under acute MI. However, the ability of in vivo cardiac reprogramming to repair chronic MI with established scars is undetermined.

METHODS

We generated a novel Tcf21^iCre/reporter/MGTH2A transgenic mouse system in which tamoxifen treatment could induce both MGTH and reporter expression in the resident CFs for cardiac reprogramming and fibroblast lineage tracing. We first tested the efficacy of this transgenic system in vitro and in vivo for acute MI. Next, we analyzed in vivo cardiac reprogramming and fusion events under chronic MI using Tcf21^iCre/Tomato/MGTH2A and Tcf21^iCre/mTmG/MGTH2A mice, respectively. Microarray and single-cell RNA sequencing were performed to determine the mechanism of cardiac repair by in vivo reprogramming.

RESULTS

We confirmed the efficacy of transgenic in vitro and in vivo cardiac reprogramming for acute MI. In chronic MI, in vivo cardiac reprogramming converted ≈2% of resident CFs into iCMs, in which a majority of iCMs were generated by means of bona fide cardiac reprogramming rather than by fusion with cardiomyocytes. Cardiac reprogramming significantly improved myocardial contraction and reduced fibrosis in chronic MI. Microarray analyses revealed that the overexpression of MGTH activated cardiac program and concomitantly suppressed fibroblast and inflammatory signatures in chronic MI. Single-cell RNA sequencing demonstrated that resident CFs consisted of 7 subclusters, in which the profibrotic CF population increased under chronic MI. Cardiac reprogramming suppressed fibroblastic gene expression in chronic MI by means of conversion of profibrotic CFs to a quiescent antifibrotic state. MGTH overexpression induced antifibrotic effects partly by suppression of Meox1, a central regulator of fibroblast activation.

CONCLUSIONS

These results demonstrate that cardiac reprogramming could repair chronic MI by means of myocardial regeneration and reduction of fibrosis. These findings present opportunities for the development of new therapies for chronic MI and heart failure.

A biomimetic hydrogel culture system to facilitate cardiac reprogramming

Direct cardiac reprogramming, in which fibroblasts are converted into induced cardiomyocytes (iCMs) with cardiogenic transcription factors, may be a promising approach for myocardial regeneration. Here, we present a protocol for cardiac reprogramming using a handmade hydrogel culture system. This system can recapitulate substrate stiffness comparable to that of the native myocardium. This protocol features improved efficiency of cardiac reprogramming by generating threefold more beating iCMs on the Matrigel-based hydrogel culture system compared to that on conventional polystyrene dishes.

For complete details on the use and execution of this protocol, please refer to Kurotsu et al. (2020)

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Protocol for cardiac reprogramming using a soft hydrogel system

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Generation of beating iCMs with 3% efficiency on hydrogel culture

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Detailed approaches for generating Matrigel-based hydrogel culture systems

Direct reprogramming with Sendai virus vectors repaired infarct hearts at the chronic stage

Adult hearts have limited regenerative capacity. Hence, after acute myocardial infarction (MI), dead myocardial tissues are digested by immune cells and replaced by fibrosis, leading to ventricular remodeling and heart failure at the chronic stage. Direct reprogramming of the cardiac fibroblasts (CFs) into induced cardiomyocytes (iCMs) with cardiac transcription factors, including Gata4, Mef2c, and Tbx5 (GMT), may have significant potential for cardiac repair. Sendai virus (SeV) vectors expressing GMT have been reported to reprogram the mouse cardiac fibroblasts into iCMs without any risk of insertional mutagenesis. In vivo reprogramming improved the cardiac function after acute MI in immunodeficient mice. However, it is unknown whether the newly generated iCMs could exist in infarct hearts for a prolonged period and SeV-GMT can improve cardiac function after MI at the chronic stage in immunocompetent mice. Here, we show that SeV vectors efficiently infect CFs in vivo and reprogram them into iCMs, which existed for at least four weeks after MI, in fibroblast-linage tracing mice. Moreover, SeV-GMT improved cardiac function and reduced fibrosis and collagen I expression at 12 weeks after MI in immunocompetent mice. Thus, direct cardiac reprogramming with SeV vectors could be a promising therapy for MI.

In vivo reprogramming as a new approach to cardiac regenerative therapy

Cardiovascular diseases are a common cause of death worldwide. Adult cardiomyocytes have limited regenerative capacity after injury, and there is growing interest in cardiac regeneration as a new therapeutic strategy. There are several limitations of induced pluripotent stem cell-based transplantation therapy with respect to efficiency and risks of tumorigenesis. Direct reprogramming enables the conversion of terminally differentiated cells into target cell types using defined factors. In most cardiac diseases, activated fibroblasts proliferate in the damaged heart and contribute to the progression of heart failure. In vivo cardiac reprogramming, in which resident cardiac fibroblasts are converted into cardiomyocytes in situ, is expected to become a new cardiac regenerative therapy. Indeed, we and other groups have demonstrated that in vivo reprogramming improves cardiac function and reduces fibrosis after myocardial infarction. In this review, we summarize recent discoveries and developments related to in vivo reprogramming. In addition, issues that need to be resolved for clinical application are described.

Generation of Efficient Knock-in Mouse and Human Pluripotent Stem Cells Using CRISPR-Cas9

A knock-in can generate fluorescent or Cre-reporter under the control of an endogenous promoter. It also generates knock-out or tagged-protein with fluorescent protein and short tags for tracking and purification. Recent advances in genome editing with clustered regularly interspaced short palindromic repeat (CRISPR) and CRISPR-associated protein 9 (Cas9) significantly increased the efficiencies of making knock-in cells. Here we describe the detailed protocols of generating knock-in mouse and human pluripotent stem cells (PSCs) by electroporation and lipofection, respectively.

Direct Cardiac Reprogramming ― Converting Cardiac Fibroblasts to Cardiomyocytes ―

Cardiovascular disease is the leading cause of death and disability worldwide. Despite advances in cardiovascular therapy, mortality in heart disease still remains high. Direct cardiac reprogramming is a promising approach for cardiac tissue repair involving in situ generation of new cardiomyocytes from endogenous cardiac fibroblasts. Although, initially, the reprogramming efficiency was low, several developments in reprogramming methods have improved the in vitro cardiac reprogramming efficiency. Subsequently, in vivo cardiac reprogramming has demonstrated improvement in cardiac function and fibrosis after myocardial infarction. Here, we review recent progress in cardiac reprogramming as a new technology for cardiac regeneration.

A high BNP level predicts an improvement in exercise tolerance after a successful catheter ablation of persistent atrial fibrillation

INTRODUCTION

Restoration of sinus rhythm (SR) by catheter ablation (CA) of atrial fibrillation (AF) improves exercise tolerance. However, it is still unclear what characteristics of patients are contributing to an improvement in exercise tolerance after CA of AF without heart failure.

METHODS AND RESULTS

This study consisted of 51 consecutive patients with persistent or long-standing persistent AF without heart failure who were restored to SR for over 6 months by a successful CA. Exercise tolerance was evaluated by cardiopulmonary exercise testing before and 3 and 6 months after CA. The clinical characteristics contributing to an improvement in exercise tolerance was elucidated. The peak oxygen uptake (VO₂ )% significantly increased from 101.4 ± 20.3% to 110.9 ± 19.9% 3 months after the CA (P < .001). The improvement rate in the peak VO₂ % exhibited a positive correlation to the baseline brain natriuretic peptide (BNP; ρ = 0.39, P < .01), but not to the age, AF duration, left ventricular ejection fraction, or left atrial size. The linear regression analysis revealed that the baseline BNP was an independent predictor of an improvement in the peak VO₂ % (coefficients = 0.32; 95% confidence interval = 0.08, 0.54; P = .01). The peak VO₂ % improved significantly in the patients whose baseline BNP level was greater than 100 pg/mL, compared to the others (P < .01). These favorable findings were also observed 6 months after the CA.

CONCLUSION

Elimination of persistent AF by CA was associated with an improvement in exercise tolerance. This was particularly true in patients with high BNP values at baseline.

Cardiac regeneration with pluripotent stem cell-derived cardiomyocytes and direct cardiac reprogramming

Cardiovascular disease is the leading cause of death globally. Cardiomyocytes (CMs) have poor regenerative capacity, and pharmacological therapies have limited efficacy in severe heart failure. Currently, there are several promising strategies for cardiac regeneration. The most promising approach to remuscularize failing hearts is cell transplantation therapy using newly generated CMs from exogenous sources, such as pluripotent stem cells. Alternatively, approaches to generate new CMs from endogenous cell sources in situ may also repair the injured heart and improve cardiac function. Direct cardiac reprogramming has emerged as a novel therapeutic approach to regenerate injured hearts by directly converting endogenous cardiac fibroblasts into CM-like cells. Through cell transplantation and direct cardiac reprogramming, new CMs can be generated and scar tissue reduced to improve cardiac function; therefore, cardiac regeneration may serve as a powerful strategy for treatment of severe heart failure. While substantial progress has been made in these two strategies for cardiac regeneration over the past several years, challenges remain for clinical translation. This review provide an overview of previous reports and current challenges in this field.

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.

Rapid and high-efficient generation of mutant mice using freeze-thawed embryos of the C57BL/6J strain

BACKGROUND

The CRISPR/Cas9 technique has undergone many modifications to decrease the effort and shorten the time needed for efficient production of mutant mice. The use of fresh embryos consumes time and effort during oocytes preparation and fertilization before every experiment, and freeze-thawed embryos overcome this limitation. However, cryopreservation of 1-cell embryos is challenging.

NEW METHOD

We introduce a protocol that combines a modified method for cryopreserving 1-cell C57BL/6J embryos with optimized electroporation conditions that were used to deliver CRISPR reagents into embryos, 1 h after thawing.

RESULTS

Freeze-thawed 1-cell embryos showed similar survival rates and surprisingly high developmental rates compared to fresh embryos. Using our protocol, we generated several lines of mutant mice: knockout mice via non-homologous end joining (NHEJ) and knock-in mice via homology-directed repair (HDR) with high-efficient mutation rates (100%, 75% respectively) and a low mosaic rate within 4 weeks.

COMPARISON WITH EXISTING METHOD (S)

Our protocol associates the use of freeze-thawed embryos from an inbred strain and electroporation, and can be performed by laboratory personnel with basic training in embryo manipulation to generate mutant mice within short time periods.

CONCLUSION

We developed a simple, economic, and robust protocol facilitating the generation of genetically modified mice, bypassing the need of backcrossing, with a high efficiency and a low mosaic rate. It makes the preparation of mouse models of human diseases a simple task with unprecedented ease, pace, and efficiency.

Progress and Challenge of Cardiac Regeneration to Treat Heart Failure

Cardiac muscle has limited proliferative capacity, and regenerative therapies are highly in demand as a new treatment strategy. Pharmacological and non-pharmacological therapies have been developed, but these medical therapies have limited effects to cure patients with severe heart failure. Moreover, heart transplantation is limited due to the low number of donor organs. Thus, heart regeneration holds great potential to offer innovative therapy to treat heart failure patients. Currently, there are several strategies for heart regeneration. Transplantation of somatic stem cells was safe and modestly improved cardiac function after myocardial infarction mainly through paracrine mechanisms. Alternatively, new cardiomyocytes could be generated from induced pluripotent stem cells (iPSCs) to transplant into injured hearts. However, several issues remain to be resolved prior to using iPSC-derived cardiomyocytes, such as a potential risk of tumorigenesis and poor survival of transplanted cells in the injured heart. More recently, direct cardiac reprogramming has emerged as a novel technology to regenerate damaged myocardium by directly converting endogenous cardiac fibroblasts into induced cardiomyocyte-like cells to restore cardiac function. Following our first report of cardiac reprogramming, an improvement in cardiac reprogramming efficiency, in vivo direct cardiac reprogramming, and cardiac reprogramming in human cells were reported by many investigators. While these previous studies have advanced regenerative research, many challenges remain. Here, we review the current status of cardiac regenerative technology, a great hope to treat cardiovascular diseases.

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.

Real-Time Analysis of the Heart Rate Variability During Incremental Exercise for the Detection of the Ventilatory Threshold

Background

It has never been possible to immediately evaluate heart rate variability (HRV) during exercise. We aimed to visualize the real‐time changes in the power spectrum of HRV during exercise and to investigate its relationship to the ventilatory threshold (VT).

Methods and Results

Thirty healthy subjects (29.1±5.7 years of age) and 35 consecutive patients (59.0±13.2 years of age) with myocardial infarctions underwent cardiopulmonary exercise tests with an RAMP protocol ergometer. The HRV was continuously assessed with power spectral analyses using the maximum entropy method and projected on a screen without delay. During exercise, a significant decrease in the high frequency (HF) was followed by a drastic shift in the power spectrum of the HRV with a periodic augmentation in the low frequency/HF (L/H) and steady low HF. When the HRV threshold (HRVT) was defined as conversion from a predominant high frequency (HF) to a predominant low frequency/HF (L/H), the VO₂ at the HRVT (HRVT‐VO₂) was substantially correlated with the VO₂ at the lactate threshold and VT) in the healthy subjects (r=0.853 and 0.921, respectively). The mean difference between each threshold (0.65 mL/kg per minute for lactate threshold and HRVT, 0.53 mL/kg per minute for VT and HRVT) was nonsignificant (P>0.05). Furthermore, the HRVT‐VO₂ was also correlated with the VT‐VO₂ in these myocardial infarction patients (r=0.867), and the mean difference was −0.72 mL/kg per minute and was nonsignificant (P>0.05).

Conclusions

A HRV analysis with our method enabled real‐time visualization of the changes in the power spectrum during exercise. This can provide additional information for detecting the VT.

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.

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.

Fibroblast Growth Factors and Vascular Endothelial Growth Factor Promote Cardiac Reprogramming under Defined Conditions

Fibroblasts can be directly reprogrammed into cardiomyocyte-like cells (iCMs) by overexpression of cardiac transcription factors, including Gata4, Mef2c, and Tbx5; however, this process is inefficient under serum-based culture conditions, in which conversion of partially reprogrammed cells into fully reprogrammed functional iCMs has been a major hurdle. Here, we report that a combination of fibroblast growth factor (FGF) 2, FGF10, and vascular endothelial growth factor (VEGF), termed FFV, promoted cardiac reprogramming under defined serum-free conditions, increasing spontaneously beating iCMs by 100-fold compared with those under conventional serum-based conditions. Mechanistically, FFV activated multiple cardiac transcriptional regulators and converted partially reprogrammed cells into functional iCMs through the p38 mitogen-activated protein kinase and phosphoinositol 3-kinase/AKT pathways. Moreover, FFV enabled cardiac reprogramming with only Mef2c and Tbx5 through the induction of cardiac reprogramming factors, including Gata4. Thus, defined culture conditions promoted the quality of cardiac reprogramming, and this finding provides new insight into the mechanism of cardiac reprogramming.

MRI and serum high-sensitivity C reactive protein predict long-term mortality in non-ischaemic cardiomyopathy

Objective

Myocardial fibrosis related to non-specific inflammation can be detected using late gadolinium-enhancement cardiovascular MR (LGE-CMR), which is an important prognostic indicator for dilated cardiomyopathy (DCM). The aims of this study were to define the prognostic factors for DCM with LGE-CMR, and to evaluate the impact of the prognostic factors on adverse effects.

Methods

We performed a retrospective analysis of a prospectively maintained single centre registry. We analysed the data from 76 patients with DCM who had been admitted for acute heart failure. The primary combined end point was defined as all-cause mortality and rehospitalisation.

Results

LGE-CMR was present in 39 patients (51%), and the mean follow-up period was 813±54 days. The primary end point occurred in 20 patients (5 (13.5%) patients without LGE-CMR and 15 (38.5%) patients with LGE-CMR, p=0.006). Sixteen of 39 patients with LGE-CMR exhibited elevated high-sensitivity C reactive protein (hs-CRP >0.3 mg/dL). Patients with elevated hs-CRP and LGE-CMR had a significantly higher incidence of the primary end point compared with patients with normal hs-CRP and LGE-CMR (62.5%; 10 patients, 22.7%; 5 patients, respectively, p=0.001). Elevated hs-CRP was significantly associated with the primary end point (HR: 4.04; 95% CI 1.67 to 9.76; p=0.002). After elevated hs-CRP was adjusted for known predictors of DCM, it was still associated with the primary end point (HR: 2.91; 95% CI 1.19 to 7.15; p=0.02).

Conclusions

Among patients with DCM, LGE-CMR and elevated hs-CRP are associated with a higher incidence of the long-term combined end point of all-cause mortality and hospitalisation.

Trial registration number:

UMIN000001171.

MiR-133 promotes cardiac reprogramming by directly repressing Snai1 and silencing fibroblast signatures

Fibroblasts can be directly reprogrammed into cardiomyocyte-like cells (iCMs) by overexpression of cardiac transcription factors or microRNAs. However, induction of functional cardiomyocytes is inefficient, and molecular mechanisms of direct reprogramming remain undefined. Here, we demonstrate that addition of miR-133a (miR-133) to Gata4, Mef2c, and Tbx5 (GMT) or GMT plus Mesp1 and Myocd improved cardiac reprogramming from mouse or human fibroblasts by directly repressing Snai1, a master regulator of epithelial-to-mesenchymal transition. MiR-133 overexpression with GMT generated sevenfold more beating iCMs from mouse embryonic fibroblasts and shortened the duration to induce beating cells from 30 to 10 days, compared to GMT alone. Snai1 knockdown suppressed fibroblast genes, upregulated cardiac gene expression, and induced more contracting iCMs with GMT transduction, recapitulating the effects of miR-133 overexpression. In contrast, overexpression of Snai1 in GMT/miR-133-transduced cells maintained fibroblast signatures and inhibited generation of beating iCMs. MiR-133-mediated Snai1 repression was also critical for cardiac reprogramming in adult mouse and human cardiac fibroblasts. Thus, silencing fibroblast signatures, mediated by miR-133/Snai1, is a key molecular roadblock during cardiac reprogramming.

Induction of cardiomyocyte-like cells in infarct hearts by gene transfer of Gata4, Mef2c, and Tbx5

RATIONALE

After myocardial infarction (MI), massive cell death in the myocardium initiates fibrosis and scar formation, leading to heart failure. We recently found that a combination of 3 cardiac transcription factors, Gata4, Mef2c, and Tbx5 (GMT), reprograms fibroblasts directly into functional cardiomyocytes in vitro.

OBJECTIVE

To investigate whether viral gene transfer of GMT into infarcted hearts induces cardiomyocyte generation.

METHODS AND RESULTS

Coronary artery ligation was used to generate MI in the mouse. In vitro transduction of GMT retrovirus converted cardiac fibroblasts from the infarct region into cardiomyocyte-like cells with cardiac-specific gene expression and sarcomeric structures. Injection of the green fluorescent protein (GFP) retrovirus into mouse hearts, immediately after MI, infected only proliferating noncardiomyocytes, mainly fibroblasts, in the infarct region. The GFP expression diminished after 2 weeks in immunocompetent mice but remained stable for 3 months in immunosuppressed mice, in which cardiac induction did not occur. In contrast, injection of GMT retrovirus into α-myosin heavy chain (αMHC)-GFP transgenic mouse hearts induced the expression of αMHC-GFP, a marker of cardiomyocytes, in 3% of virus-infected cells after 1 week. A pooled GMT injection into the immunosuppressed mouse hearts induced cardiac marker expression in retrovirus-infected cells within 2 weeks, although few cells showed striated muscle structures. To transduce GMT efficiently in vivo, we generated a polycistronic retrovirus expressing GMT separated by 2A "self-cleaving" peptides (3F2A). The 3F2A-induced cardiomyocyte-like cells in fibrotic tissue expressed sarcomeric α-actinin and cardiac troponin T and had clear cross striations. Quantitative RT-PCR also demonstrated that FACS-sorted 3F2A-transduced cells expressed cardiac-specific genes.

CONCLUSIONS

GMT gene transfer induced cardiomyocyte-like cells in infarcted hearts.

Usefulness of plasma exchange plus continuous hemodiafiltration to reduce adverse effects associated with plasma exchange in patients with acute liver failure

OBJECTIVE

To efficiently remove middle-molecular-weight substances such as hepatic toxins and minimize adverse effects associated with plasma exchange implementation, we have performed plasma exchange slowly in combination with continuous hemodiafiltration. This study was designed to determine the usefulness of plasma exchange with continuous hemodiafiltration in reducing the adverse effects associated with implementation of plasma exchange alone.

DESIGN

A retrospective clinical study.

SETTING

University teaching hospital.

PATIENTS

The study involved 90 patients with liver failure who had been treated with plasma exchange in our department over the past 12 yrs. We examined these patients by dividing them into two groups (48 patients treated with plasma exchange alone and 42 patients treated with plasma exchange plus continuous hemodiafiltration at the time of plasma exchange implementation).

MEASUREMENTS AND MAIN RESULTS

Baseline blood Na+ concentration, HCO3- concentration, and colloid osmotic pressure were followed after implementation of plasma exchange to compare the frequency of development of three adverse effects (hypernatremia, metabolic alkalosis, and sharp decrease in colloid osmotic pressure) in the two groups. Hypernatremia was found in 26.7% of treatments in the group with plasma exchange alone and 3.3% in the group of plasma exchange plus continuous hemodiafiltration, and metabolic alkalosis was found in 30.6% of treatments in the group with plasma exchange alone and 4.9% in the group of plasma exchange plus continuous hemodiafiltration; both percentages were significantly higher in the group with plasma exchange alone (p <.001). A sharp decrease in colloid osmotic pressure occurred in 13.3% of treatments in the group with plasma exchange alone but was not observed at all in the patients treated with plasma exchange plus continuous hemodiafiltration.

CONCLUSIONS

We conclude that adverse effects associated with plasma exchange for artificial liver support for liver failure can be alleviated with use of plasma exchange plus continuous hemodiafiltration instead of plasma exchange alone.

Comparison of Sepsis-related Organ Failure Assessment (SOFA) score and CIS (cellular injury score) for scoring of severity for patients with multiple organ dysfunction syndrome (MODS)

OBJECTIVE

To evaluate the usefulness of cellular injury score (CIS) and Sepsis-related Organ Failure Assessment (SOFA) score for determination of the severity of multiple organ dysfunction syndrome (MODS).

DESIGN

A prospective observational study.

SETTING

A medical and surgical intensive care unit (ICU) of a teaching hospital.

PATIENTS

Forty-seven consecutive MODS patients.

MEASUREMENTS AND RESULTS

SOFA score and CIS were measured every day for 12 months for 47 MODS patients. Comparison was made of the SOFA score and CIS for usefulness in the scoring of severity of MODS in 26 survivors and 21 non-survivors. In addition, receiver operating characteristics (ROC) analysis was used to determine the usefulness of these two indexes as predictors of prognosis. No significant differences were found on admission between the survivors and non-survivors, but significant differences between the two subgroups (p < 0.001) were found in maximum value within 1 week after admission and maximum value during the course of treatment for both indexes. Analysis of changes after admission indicated that significant differences between survivors and non-survivors began to appear on day 3 of admission for both indexes; at that time SOFA score began to deteriorate in the non-survivors while CIS began to improve in the survivors. ROC analysis demonstrated that the area under the ROC curve was 0.769 for SOFA scores and 0.760 for CIS.

CONCLUSIONS

Both SOFA score and CIS sequentially reflected the severity of MODS. Furthermore, they were comparable in diagnostic value as predictors of prognosis. These findings may indicate the possibility that MODS is a summation of effects of cellular injury. In addition, sequential evaluation of both SOFA score and CIS would provide a more accurate prediction of prognosis than conventional methods.

Low induction of varicella-zoster virus-specific secretory IgA antibody after vaccination

Breakthrough after varicella vaccination occurs in approximately 2. 6% approximately 18.6% of immunocompetent children, but the reason has not been demonstrated clearly. As a first defense, specific secretory IgA antibody on the mucosa plays an important role in preventing invasion of microorganisms. To examine induction of varicella-zoster virus (VZV) specific secretory IgA after natural infection and vaccination and its booster mechanisms, 143 salivary samples were tested by ELISA. The VZV-secretory IgA values were significantly higher in the matched children after natural chickenpox than in those after vaccination, although the total secretory IgA did not differ between them. Two (7%) of the vaccinees lacked the sIgA antibody. In the elderly and in immunocompromised children, the VZV-secretory IgA values were no lower than those in healthy children, and they did not lack VZV-secretory IgA. The doctors and nurses taking care of patients with chickenpox had higher values than the other groups as did individuals who had had herpes zoster recently. VZV-secretory IgA was thought to be stimulated by exogenous and reactivated endogenous VZV to neutralize VZV with weak activity. These results suggest that low or no induction of VZV-secretory IgA antibody after vaccination may be one of the possible explanations for a breakthrough.

Efficacy and limitation of apheresis therapy in critical care

Apheresis therapy such as plasma exchange and plasma adsorption has become therapeutic tools in critical care. The indications for apheresis therapy in ICU patients include fulminant hepatic failure, thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS), autoimmune disease, and sepsis. During the past 11 years, 150 patients with various kinds of critical illnesses were treated with apheresis therapy in our ICU, and the overall survival rate was 50%. Apheresis therapy is especially useful in the treatment of a patient with fulminant hepatic failure because liver transplantation is seldom performed in Japan; therefore, the patient should be treated with artificial liver support. When plasma exchange is performed on the critically ill, continuous hemodiafiltration should be performed simultaneously to overcome the adverse effects of plasma exchange such as hypernatremia, metabolic alkalosis, and abrupt changes in colloid osmotic pressure and to enhance the removal rate of the causative middle molecular weight substances of hepatic failure or hepatic coma.

[The adventitia wrapping technique in microvascular surgery]

The success of microvascular anastomosis on fine vessels is essential not only for expanding the possibility of surgical treatment in such cases as replanting severed fingers of children, and vascularized nerve and joint grafting, but also for diminishing the damage to donors as well. This report describes the details of our study on a adventitia wrapping technique in which the adventitia was utilized for wrapping anastomosis. This study demonstrates that the advantages of the adventitia wrapping technique are as follows; (1) Adventitia wrapping technique provides a higher patency rate in smaller microvascular anastomosis. (2) Adventitia wrapping technique aids in reducing operative time and stitches. (3) Adventitia wrapping technique increases tolerable pressure of the anastomosis site and prevents aneurysm. (4) Immediate postoperative hemorrhage at the anastomosis site is lesser than that of the standard suture technique. These results indicate that this technique utilizes the tissue in site, therefore, is simple and useful for microvascular anastomoses.

Continuous blood-letting for congestion in replantation of the amputated finger

Experimental and clinical studies have been made on the function of the venous system in the replantation of the contused severed finger. In experiments on rats replantation of severed limbs was more successful in a group treated by continuous blood-letting and anastomosis of the artery alone, compared with controls in which only the artery was anastomosed. Histologically, in the first group there was less congestion, thrombus-formation, oedema and exudative haemorrhage in the initial stage; in the reparative phase there was less granulation and the degree of muscular degeneration was very slight. Clinically, contused, severed fingers were successfully replanted when venous anastomosis was impossible or incomplete, by using the fish-mouth incision for continuous blood-letting. The resulting scar caused no problem aesthetically or functionally.