Essential thrombocythemia complicated with simultaneous two-vessel acute myocardial infarction in the subacute phase of takotsubo cardiomyopathy: A case report.

We report the case of a 79-year-old woman with essential thrombocythemia who presented with simultaneous two-vessel acute myocardial infarction (AMI) in the subacute phase of takotsubo cardiomyopathy. Despite sufficient anticoagulation therapy with warfarin to prevent thrombus formation in the left ventricle, the patient developed simultaneous two-vessel AMI in the right and left circumflex coronary arteries 16 days after the onset of takotsubo cardiomyopathy. Thromboembolism from the left ventricle associated with takotsubo cardiomyopathy was considered a potential cause of this event. However, macroscopic and pathological findings of the aspirated thrombi revealed that the primary cause of AMI was non-organized white platelet thrombi associated with essential thrombocythemia. In addition to oral anticoagulation therapy with warfarin, low-dose aspirin was started. The patient was discharged without any symptoms, and the clinical course has been uneventful for >5 years. This case highlights the potential risk of fatal complications associated with essential thrombocythemia, including simultaneous multivessel AMI. Additionally, pathological findings of the thrombi may play a crucial role in clarifying the etiology in such complicated cases. Appropriate antithrombotic therapy should be selected according to the pathogenesis of the condition. Learning objective: We describe a 79-year-old woman with essential thrombocythemia complicated with simultaneous two-vessel acute myocardial infarction (AMI) in the subacute phase of takotsubo cardiomyopathy. Although patients with essential thrombocythemia are highly predisposed to thrombotic events including AMI, the appropriate antithrombotic regimen remains controversial. The macroscopic and pathological findings of the thrombi play a pivotal role in clarifying the etiology, which may lead to the appropriate antithrombotic therapy.

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.

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.

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.

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.