Feifei Su

High-Mobility Group Box 1 Induces Calcineurin-Mediated Cell Hypertrophy in Neonatal Rat Ventricular Myocytes

Cardiac hypertrophy is an independent predictor of cardiovascular morbidity and mortality. In recent years, evidences suggest that high-mobility group box 1 (HMGB1) protein, an inflammatory cytokine, participates in cardiac remodeling; however, the involvement of HMGB1 in the pathogenesis of cardiac hypertrophy remains unknown. The aim of this study was to investigate whether HMGB1 is sufficient to induce cardiomyocyte hypertrophy and to identify the possible mechanisms underlying the hypertrophic response. Cardiomyocytes isolated from 1-day-old Sprague-Dawley rats were treated with recombinant HMGB1, at concentrations ranging from 50 ng/mL to 200 ng/mL. After 24 hours, cardiomyocytes were processed for the evaluation of atrial natriuretic peptide (ANP) and calcineurin A expression. Western blot and real-time RT-PCR was used to detect protein and mRNA expression levels, respectively. The activity of calcineurin was also evaluated using a biochemical enzyme assay. HMGB1 induced cardiomyocyte hypertrophy, characterized by enhanced expression of ANP, and increased protein synthesis. Meanwhile, increased calcineurin activity and calcineurin A protein expression were observed in cardiomyocytes preconditioned with HMGB1. Furthermore, cyclosporin A pretreatment partially inhibited the HMGB1-induced cardiomyocyte hypertrophy. Our findings suggest that HMGB1 leads to cardiac hypertrophy, at least in part through activating calcineurin.

Magnolol administration in normotensive young spontaneously hypertensive rats postpones the development of hypertension: role of increased PPAR gamma, reduced TRB3 and resultant alleviative vascular insulin resistance.

Patients with prehypertension are more likely to progress to manifest hypertension than those with optimal or normal blood pressure. However, the mechanisms underlying the development from prehypertension to hypertension still remain largely elusive and the drugs for antihypertensive treatment in prehypertension are absent. Here we determined the effects of magnolol (MAG) on blood pressure and aortic vasodilatation to insulin, and investigated the underlying mechanisms. Four-week-old male spontaneous hypertensive rats (SHR) and age-matched normotensive Wistar-Kyoto (WKY) control rats were used. Our results shown that treatment of young SHRs with MAG (100 mg/kg/day, o.g.) for 3 weeks decreased blood pressure, improved insulin-induced aorta vasodilation, restored Akt and eNOS activation stimulated by insulin, and increased PPARγ and decreased TRB3 expressions. In cultured human umbilical vein endothelial cells (HUVECs), MAG incubation increased PPARγ, decreased TRB3 expressions, and restored insulin-induced phosphorylated Akt and eNOS levels and NO production, which was blocked by both PPARγ antagonist and siRNA targeting PPARγ. Improved insulin signaling in HUVECs by MAG was abolished by upregulating TRB3 expression. In conclusion, treatment of young SHRs with MAG beginning at the prehypertensive stage decreases blood pressure via improving vascular insulin resistance that is at least partly attributable to upregulated PPARγ, downregulated TRB3 and consequently increased Akt and eNOS activations in blood vessels in SHRs.

Programmed cell death-1 deficiency results in atrial remodeling in C57BL/6 mice.

Deficiency of the programmed cell death-1 (PD-1) gene enhances T-cell activation and increases inflammation levels. It has been reported that atrial fibrillation (AF) is closely related to inflammation. The aim of the present study was to investigate the role of PD-1 deficiency in the pathogenesis of AF. Two groups of mice were used in our experiment: the C57BL/6 and the C57BL/6-PD-(1-/-) group. The expression of the inflammatory cytokines interleukin (IL)-2, -4, -6, -10, -17, interferon-γ and tumor necrosis factor were detected. Furthermore, the levels of atrial myocyte oxidative stress, the atrial effective refractory period (AERP) and the atrial myocardial fibrosis levels were determined. Compared with the C57BL/6 group, we found that the inflammatory cytokines were significantly increased in the PD-1(-/-) group and the levels of atrial myocyte oxidative stress in the PD-1(-/-) group were also higher. The AERP became shorter and the dispersion of AERP was increased in the PD-1(-/-) group. Moreover, the PD-1(-/-) group presented significant atrial myocardial fibrosis but the C57BL/6 group did not. Our findings strongly suggest that the higher levels of inflammatory cytokines and atrial myocyte oxidative stress were present in the PD-1(-/-) mice and resulted in atrial electricity and structural remodeling. Due to the atrial remodeling, the PD-1(-/-) mice were more likely to develop AF.

The Long-Term Differentiation of Embryonic Stem Cells into Cardiomyocytes: An Indirect Co-Culture Model

Background Embryonic Stem Cells (ESCs) can differentiate into cardiomyocytes (CMs) in vitro but the differentiation level from ESCs is low. Here we describe a simple co-culture model by commercially available Millicell™ hanging cell culture inserts to control the long-term differentiation of ESCs into CMs. Methodology/Principal Findings Mouse ESCs were cultured in hanging drops to form embryoid bodies (EBs) and treated with 0.1 mmol/L ascorbic acid to induce the differentiation of ESCs into CMs. In the indirect co-culture system, EBs were co-cultured with epidermal keratinocytes (EKs) or neonatal CMs (NCMs) by the hanging cell culture inserts (PET membranes with 1 µm pores). The molecular expressions and functional properties of ESC-derived CMs in prolonged culture course were evaluated. During time course of ESC differentiation, the percentages of EBs with contracting areas in NCMs co-culture were significantly higher than that without co-culture or in EKs co-culture. The functional maintenance of ESC-derived CMs were more prominent in NCMs co-culture model. Conclusions/Significance These results indicate that NCMs co-culture promote ESC differentiation and has a further effect on cell growth and differentiation. We assume that the improvement of the differentiating efficiency of ESCs into CMs in the co-culture system do not result from the effect of co-culture directly on cell differentiation, but rather by signaling effects that influence the cells in proliferation and long-term function maintenance.

Simvastatin inhibits angiotensin II-induced cardiac cell hypertrophy: Role of Homer 1a

1 The scaffolding protein Homer 1a is constitutively expressed in the myocardium, although its function in cardiomyocytes remains poorly understood. The aim of the present study was to investigate Homer 1a expression in hypertrophic cardiac cells and its role in angiotensin (Ang) II‐induced cardiac hypertrophy. 2 After serum starvation for 24 h, cells were treated with 1 μmol/L simvastatin, 100 nmol/L angiotensin (Ang) II or their combination added to Dulbeccos modified Eagles medium containing 0.5% serum. For combination treatment with AngII plus simvastatin, cells were exposed to simvastatin 12 h before the addition of AngII to the medium and cells were then incubated in the presence of both drugs for a further 24 h. Western blotting was used to determine Homer 1a protein expression. Hypertrophy was evaluated by determining the protein content per cell. 3 Homer 1a protein levels were upregulated following AngII‐induced hypertrophy in H9C2 cells and neonatal rat cardiomyocytes, and these increases were augmented by simvastatin pretreatment. Concomitantly, simvastatin pretreatment inhibited extracellular signal‐regulated kinase (ERK) 1/2 phosphorylation and AngII‐induced hypertrophy. 4 The inhibitory effects of simvastatin against AngII‐induced hypertrophy were attenuated by Homer 1a silencing, suggesting that simvastatin suppresses cardiac hypertrophy in a Homer 1a‐dependent manner. Furthermore, AngII‐induced hypertrophy and ERK1/2 phosphorylation in neonatal rat cardiomyocytes were significantly inhibited following the overexpression of Homer 1a using an adenovirus. 5 These results suggest a possible role for Homer 1a in inhibiting cardiac hypertrophy perhaps in part through inhibition of ERK1/2 activation.

Tetrahydroxystilbene Glycoside Improves Microvascular Endothelial Dysfunction and Ameliorates Obesity-Associated Hypertension in Obese ZDF Rats Via Inhibition of Endothelial Autophagy

Aims: Obesity is a major risk for hypertension. Endothelial dysfunction contributes to increased peripheral vascular resistance and subsequent hypertension. Autophagy regulates endothelial function, however, whether autophagy is related to hypertension in obesity remains largely unclear. We wished to ascertain: (i) the role of autophagy in obesity-induced hypertension and the underlying mechanisms; (ii) if tetrahydroxystilbene glycoside (TSG) influences endothelial dysfunction and obesity-associated hypertension. Methods: (TSG-treated) male Zucker diabetic fatty (ZDF) rats and cultured human umbilical vein endothelial cells (HUVECs) were used. Blood pressure was measured non-invasively with a tail-cuff system. Westernblotting was performed to determine the expression of autophagy-associated proteins. Autophagy flux was assessed by transfection HUVECs with the Ad-mGFP–RFP–LC3. Results: Compared with their lean counterparts, obese ZDF rats exhibited hypertension and endothelial dysfunction, along with impaired Akt/mTOR signaling and upregulated expression of autophagy-associated proteins beclin1, microtubule-associated protein 1 light chain 3 II/I, autophagy protein (ATG)5 and ATG7. Two-week TSG administration restored blood pressure and endothelial function, reactivated Akt/mTOR pathway and decreased endothelial autophagy in ZDF rats. Rapamycin pretreatment blocked the hypotensive effect of TSG in ZDF rats. Suppression of Akt/mTOR expression with siRNA significantly blunted the anti-autophagic effect of TSG in HUVECs as evidenced by abnormal autophagic flux and increased expression of autophagy-associated proteins. Conclusion: Endothelial dysfunction in ZDF rats is partially attributable to excessive autophagy. TSG improves endothelial function and exerts hypotensive effects via regulation of endothelial autophagy.

Non- Isolation Treatment of Atrial Fibrillation: Does Autonomic Nerve Modulation Really Act?

Atrial fibrillation (AF) is an abnormal heart rhythm that originates in the top chambers of the heart (atria). Pulmonary vein (PV) ablation is an effective treatment for AF, which has been used widely in clinic; however, significant side effects are difficult to avoid including potential recurrence, pulmonary vein stenosis, systemic thromboembolism, pericardial effusion, cardiac tamponade, esophageal perforation, and phrenic nerve paralysis. These limitations suggest that PV isolation is not a majority determinant of clinical success and promote research toward the development of less aggressive, but equally effective, procedures. First, researchers focus on some non-anti-arrhythmic drug therapy. There is accumulating evidence in support of the anti-arrhythmic effects of non-anti-arrhythmic drugs. Treatments with angiotensin-converting enzyme inhibitors, angiotensin-receptor blockers, statins, and omega-3 fatty acids all seem promising, over and above any effect related to the treatment of underlying heart disease. Despite exciting results from animal experiments and promising outcomes from retrospective analyses, there is no robust evidence of specific effects of these drugs to transform current clinical practice (Ardell et al., 2001). Therefore, autonomic nerve modulation has recently become a new strategy for AF management. This chapter aims to study the relationship between ANS and AF; and to investigate the effect of autonomic nerve modulation on AF.

Simvastatin Protects Heart from Pressure Overload Injury by Inhibiting Excessive Autophagy

Cardiac hypertrophy is an independent predictor of cardiovascular morbidity and mortality. To identify the mechanisms by which simvastatin inhibits cardiac hypertrophy induced by pressure overload, we determined effects of simvastatin on 14-3-3 protein expression and autophagic activity. Simvastatin was administered intragastrically to Sprague-Dawley (SD) rats before abdominal aortic banding (AAB). Neonatal rat cardiomyocytes (NRCs) were treated with simvastatin before angiotensin II (AngII) stimulation. 14-3-3, LC3, and p62 protein levels were determined by western blot. Autophagy was also measured by the double-labeled red fluorescent protein-green fluorescent protein autophagy reporter system. Simvastatin alleviated excessive autophagy, characterized by a high LC3II/LC3I ratio and low level of p62, and blunted cardiac hypertrophy while increasing 14-3-3 protein expression in rats that had undergone AAB. In addition, it increased 14-3-3 expression and inhibited excessive autophagy in NRCs exposed to AngII. Our study demonstrated that simvastatin may inhibit excessive autophagy, increase 14-3-3 expression, and finally exert beneficial effects on cardioprotection against pressure overload.

Low-Level Electrical Stimulation of Aortic Root Ventricular Ganglionated Plexi Attenuates Autonomic Nervous System–Mediated Atrial Fibrillation

OBJECTIVES This study investigated the effect of electrical stimulation of aortic root ventricular ganglionated plexi (GP) on atrial fibrillation (AF) inducibility. BACKGROUND The ventricular GP are interconnected with atrial GP to govern heart function, although the effect of ventricular GP modification on control of AF remains unknown. METHODS Effective refractory periods (ERPs) of test pulmonary veins (PVs) were measured at baseline and during high-level (HL-ES) and low-level (LL-ES) electrical stimulation of the aortic root GP. The arrhythmogenic threshold of acetylcholine and isoproterenol was determined at baseline and during HL-ES and LL-ES. Moreover, AF was induced at PVs by programmed electrical stimulation after HL-ES or LL-ES. Immunohistochemistry staining was performed to examine the autonomic activity from aortic root GP to the PVs. RESULTS Compared with the baseline group, HL-ES of aortic root GP significantly shortened atrial ERP (95 ± 13 ms vs. 122 ± 9 ms) and PV ERP (104 ± 11 ms vs. 131 ± 12 ms); decreased the threshold concentration of AF by both acetylcholine (1.3 ± 0.2 μmol/l vs. 3.2 ± 0.3 μmol/l) and isoproterenol (0.3 ± 0.1 μmol/l vs. 1.3 ± 0.2 μmol/l); and increased the AF-inducing rate from PVs (90% vs. 30%). In contrast, LL-ES of the GP prevented the shortening of ERP and PV ERP to 125 ± 10 ms and 133 ± 11 ms, respectively; increased threshold levels of acetylcholine and isoproterenol to 5.7 ± 0.4 μmol/l and 3.2 ± 0.3 μmol/l; and decreased the AF-inducing rate to 5%. We also found that the biotinylated dextran amine-containing varicose fibers projected directly from the aortic root GP to the left PVs. CONCLUSIONS These findings suggest that autonomic innervations of left PVs partly originated from aortic root ventricular GP. Moreover, LL-ES of aortic root ventricular GP suppressed AF inducibility and arose from PVs mediated by the autonomic nervous system.

Autonomic Innervation from the Aortic Root Ventricular Ganglionated Plexi to the Pulmonary Vein: A Novel Pathway

Background: Autonomic nerve innervation pathway from the ventricular GP to the pulmonary veins (PV) remains unclear. Aim:This study investigates the autonomic innervations from aortic root ventricular GP to the PVs. Nissls staining and fluorescent dual label staining were performed to determine the neuron structure in the aortic root GP in five dogs. Avidin Biotin Complex (ABC) staining were performed to study the efferent autonomic pathway from the aortic root GP to the PVs. Results:Adrenergic and cholinergic neurons were both present in the aortic root GP, with the majorities were cholinergic. ABC positive nerve fibers that contained both cholinergic and adrenergic neurotransmitters penetrated directly from the aortic root GP to the left PVs. Conclusion: Autonomic innervation of the Left PVs is partly originated from the aortic root ventricular GP.