Zhiyun Xu

Implantation of sinoatrial node cells into canine right ventricle: biological pacing appears limited by the substrate.

Biological pacing has been proposed as a physiologic counterpart to electronic pacing, and the sinoatrial node (SAN) is the general standard for biological pacemakers. We tested the expression of SAN pacemaker cell activity when implanted autologously in the right ventricle (RV). We induced complete heart block and implanted electronic pacemakers in the RV of adult mongrel dogs. Autologous SAN cells isolated enzymatically were studied by patch clamp to confirm SAN identity. SAN cells (400,000) were injected into the RV subepicardial free wall and dogs were monitored for 2 weeks. Pacemaker function was assessed by overdrive pacing and IV epinephrine challenge. SAN cells expressed a time-dependent inward current (I(f)) activating on hyperpolarization: density = 4.3 ± 0.6 pA/pF at -105 mV. Four of the six dogs demonstrated >50% of beats originating from the implant site at 24 h. Biological pacemaker rates on days 7-14 = 45-55 bpm and post-overdrive escape times = 1.5-2.5 s. Brisk catecholamine responsiveness occurred. Dogs implanted with autologous SAN cells manifest biological pacing properties dissimilar from those of the anatomic SAN. This highlights the importance of cell and substrate interaction in generating biological pacemaker function.

In Vivo Self-Powered Wireless Cardiac Monitoring via Implantable Triboelectric Nanogenerator

Harvesting biomechanical energy in vivo is an important route in obtaining sustainable electric energy for powering implantable medical devices. Here, we demonstrate an innovative implantable triboelectric nanogenerator (iTENG) for in vivo biomechanical energy harvesting. Driven by the heartbeat of adult swine, the output voltage and the corresponding current were improved by factors of 3.5 and 25, respectively, compared with the reported in vivo output performance of biomechanical energy conversion devices. In addition, the in vivo evaluation of the iTENG was demonstrated for over 72 h of implantation, during which the iTENG generated electricity continuously in the active animal. Due to its excellent in vivo performance, a self-powered wireless transmission system was fabricated for real-time wireless cardiac monitoring. Given its outstanding in vivo output and stability, iTENG can be applied not only to power implantable medical devices but also possibly to fabricate a self-powered, wireless healthcare monitoring system.

MicroRNA-30b is a multifunctional regulator of aortic valve interstitial cells

OBJECTIVE Calcific aortic valve disease is an active process involving a wide range of pathologic changes. Valve interstitial cells are the most prevalent cells in the heart valve and maintain normal valve structure and function. MicroRNAs (miRNAs) are essential posttranscriptional modulators of gene expression, and miRNA-30b is a known repressor of bone morphogenetic protein 2-mediated osteogenesis. We hypothesized that miRNA-30b is a multifunctional regulator of aortic valve interstitial cells during calcification. METHODS To determine the role of miRNA-30b in calcific aortic valve disease, we evaluated miRNA expression in human calcific aortic valve leaflets obtained intraoperatively. Furthermore, human valve interstitial cells were evaluated with regard to miRNA-30b expression and osteogenesis by quantitative real-time polymerase chain reaction, Western blotting, flow cytometry, and alkaline phosphatase assays. RESULTS In this study, we demonstrated that miRNA-30b attenuates bone morphogenetic protein 2-induced osteoblast differentiation by targeting Runx2, Smad1, and caspase-3. Transfection of a mimic of miRNA-30b led to decreases in alkaline phosphatase activity and expressions of Runx2, Smad1, and caspase-3. Furthermore, dual luciferase reporter assays confirmed that Runx2, Smad1, and caspase-3 are direct targets of miRNA-30b. CONCLUSIONS We demonstrated a remarkable role of miRNA-30b in calcific aortic valve disease as a regulator of human aortic valvular calcification and apoptosis through direct targeting of Runx2, Smad1, and caspase-3. Targeting of miRNA-30b could serve as a novel therapeutic strategy to limit progressive calcification in aortic stenosis.

BRG1 expression is increased in thoracic aortic aneurysms and regulates proliferation and apoptosis of vascular smooth muscle cells through the long non-coding RNA HIF1A-AS1 in vitro

OBJECTIVES Brahma-related gene 1 (BRG1) and long non-coding RNAs (lncRNAs) play important roles in cellular processes. However, little is known regarding their roles in thoracic aortic aneurysms. We investigated BRG1 expression in thoracic aortic aneurysms and the roles of BRG1 and the lncRNA HIF 1 alpha-antisense RNA 1 in regulating the proliferation and apoptosis of aortic smooth muscle cells in vitro. METHODS BRG1 mRNA and protein expression in human aortic media specimens were examined by quantitative real-time polymerase chain reaction, immunohistochemical staining and western blot. BRG1 expression was up-regulated by lentiviral vectors. Vascular smooth muscle cell proliferation and apoptosis were studied using Cell Counting Kit-8 and terminal deoxynucleotidyl transferase dUTP nick-end labelling assays. We performed western blots to detect Caspase3 and Bcl2 protein expression. LncRNAs regulated by BRG1 were identified through microarray in BRG1 gain- and loss-of-function vascular smooth muscle cells. Finally, the expression of HIF 1 alpha-antisense RNA 1 was reduced by siRNA and cell proliferation and apoptosis was studied using Cell Counting Kit-8 assays, caspase-3 activity assays and western blot. RESULTS BRG1 expression in the aortic media was significantly higher in thoracic aortic aneurysms than in normal controls. Overexpression of BRG1 in human aortic smooth muscle cells promoted apoptosis and reduced proliferation. The expression of HIF 1 alpha-antisense RNA 1 was significantly down- and up-regulated in BRG1 knock-down and overexpressing vascular smooth muscle cells, respectively. We further demonstrated that suppression of HIF 1 alpha-antisense RNA 1 by siRNA in vascular smooth muscle cells reduced apoptosis and promoted proliferation. CONCLUSIONS BRG1 is overexpressed in the aortic media of thoracic aortic aneurysms and the interaction between BRG1 and HIF 1 alpha-antisense RNA 1 plays a key role in the proliferation and apoptosis of vascular smooth muscle cells in vitro, which may contribute to the pathogenesis of thoracic aortic aneurysms.

MSCs transfected with hepatocyte growth factor or vascular endothelial growth factor improve cardiac function in the infarcted porcine heart by increasing angiogenesis and reducing fibrosis

BACKGROUND Cell transplantation and gene therapy have been demonstrated to have beneficial effects after a myocardial infarction (MI). Here, we used a large animal model of MI to investigate the beneficial effects of mesenchymal stem cells (MSCs) transfected with hepatocyte growth factor (HGF) or vascular endothelial growth factor (VEGF) genes. METHODS A porcine MI model was created by balloon occlusion of the distal left anterior descending artery for 90 min followed by reperfusion. At 1 week after MI, the pigs were infused via the coronary vein with saline (n=8), MSCs + AdNull(n=8), MSC+VEGF(n=10), or MSC+HGF(n=10). Cardiac function and myocardial perfusion were evaluated by using echocardiography and gated cardiac perfusion imaging before and 4 weeks after transplantation. Morphometric and histological analyses were performed. RESULTS All cell-implanted groups had better cardiac function than the saline control group. There were further functional improvements in the MSC+HGF group, accompanied by smaller infarct sizes, increased cell survival, and less collagen deposition. Blood vessel densities in the damaged area and cardiac perfusion were significantly greater in the MSC+AdNull group than in the saline control group, and further increased in the MSC+VEGF/HGF groups. Tissue fibrosis was significantly less extensive in the MSC and MSC+VEGF groups than in the saline control group and was most reduced in the MSC+HGF group. CONCLUSION MSCs (alone or transfected with VEGF/HGF) delivered into the infarcted porcine heart via the coronary vein improved cardiac function and perfusion, probably by increasing angiogenesis and reducing fibrosis. MSC+HGF was superior to MSC+VEGF, possibly owing to its enhanced antifibrotic effect.

Synergistic effect of fibronectin and hepatocyte growth factor on stable cell-matrix adhesion, re-endothelialization, and reconstitution in developing tissue-engineered heart valves.

Stable cell-matrix adhesion, re-endothelialization, and reconstitution represent important issues in creating autologous living heart valve, a close collaboration between growth factors and the extracellular matrix in these processes appears crucial. To prove this action, porcine decellularized valve constructs were precoated with fibronectin and seeded with hepatocyte growth factor-transferred marrow stromal cells (MSCs) and grown in vitro in a pulsatile-flow bioreactor. Results showed hepatocyte growth factor stimulated adhesion of MSCs to fibronectin in a time-dependent manner with a range of 8–128 ng/ml. Histological observation demonstrated a time course of MSC growth on decellularized valve constructs. A handful of cells, a loose cellular layer, a confluent monolayer coverage, a 2-layer structure and a 3-layer structure were observed at weeks 2, 3, 4, 6, and 8, respectively. Immunohistochemical analysis revealed cellular reconstitution of endothelial cells (von Willebrand factor positive) and myofibroblasts (α-smooth muscle actin and vimentin double-positive) at week 8. Importantly, endothelial cell retention (17.3 ± 2.6/mm) remained high under exposure to high flow and pressure conditions in a bioreactor. These results demonstrated that the combination of fibronectin and hepatocyte growth factor contributed to creating autologous living heart valve.

Does PGA external stenting reduce compliance mismatch in venous grafts

BackgroundAutogenous vein grafting is widely used in regular bypassing procedures. Due to its mismatch with the host artery in both mechanical property and geometry, the graft often over expands under high arterial blood pressure and forms a step-depth where eddy flow develops, thus causing restenosis, fibrous graft wall, etc. External stents, such as sheaths being used to cuff the graft, have been introduced to eliminate these mismatches and increase the patency. Although histological and immunochemical studies have shown some positive effects of the external stent, the mechanical mismatch under the protection of an external stent remains poorly analyzed.MethodsIn this study, the jugular veins taken from hypercholesterolemic rabbits were transplanted into the carotid arteries, and non-woven polyglycolic acid (PGA) fabric was used to fabricate the external stents to study the effect of the biodegradable external stent. Eight weeks after the operation, the grafts were harvested to perform mechanical tests and histological examinations. An arc tangent function was suggested to describe the relationship between pressure and cross-sectional area to analyse the compliance of the graft.ResultsThe results from the mechanical tests indicated that grafts either with or without external stents displayed large compliance in the low-pressure range and were almost inextensible in the high-pressure range. This was very different from the behavior of the arteries or veins in vivo. The data from histological tests showed that, with external stents, collagen fibers were more compact, whilst those in the graft without protection were looser and thicker. No elastic fiber was found in either kind of grafts. Furthermore, grafts without protection were over-expanded which resulted in much bigger cross-sectional areas.ConclusionThe PGA external extent contributes little to the reduction of the mechanical mismatch between the graft and its host artery while remodeling develops. For the geometric mismatch, it reduces the cross-section area, therefore matching with the host artery much better. Although there are some positive effects, conclusively the PGA is not an ideal material for external stent.

Performance of EuroSCORE II in patients who have undergone heart valve surgery: a multicentre study in a Chinese population

OBJECTIVES The EuroSCORE II is an updated version of the EuroSCORE. This multicentre study validated the EuroSCORE II and logistic EuroSCORE in Chinese patients who underwent heart valve surgery. METHODS A total of 11 170 adult patients underwent heart valve surgery from January 2008 to December 2011. Model discrimination and calibration were assessed for both EuroSCORE II and logistic EuroSCORE. The patients were divided into three subgroups according to the weight of the procedures, and the performance of EuroSCORE II for each group was assessed. A correlation analysis was performed for operative complications and EuroSCORE II. RESULTS The in-hospital mortality of this series was 2.02% (226 of 11 170), and the predicted mortality rate was 2.62±5.75% by EuroSCORE II and 2.55±6.51% by logistic EuroSCORE (LES). The C-statistics of EuroSCORE II and LES were 0.72 [95% confidence interval (CI) 0.69-0.75] and 0.67 (95% CI 0.63-0.70), respectively. Both models failed the Hosmer-Lemeshow goodness-of-fit test, with a P<0.05. According to the weight of the procedure, the isolated non-CABG subgroup had the best discrimination (C-statistics: 0.76 in the non-CABG group, 0.67 in the 2 procedures group and 0.73 in the 3+ procedures group). The complication ratio was strongly related to the EuroSCORE II-predicted mortality (Pearson correlation coefficient: 0.90 for ARDS, 0.97 for acute renal failure, 0.97 for prolonged ventilation and 0.94 for a prolonged ICU stay). CONCLUSIONS EuroSCORE II was an improvement upon its original logistic model for Chinese patients who underwent heart valve surgery, particularly for a single-valve procedure. The EuroSCORE II-predicted mortality correlated with the operative complications.

Impact of preoperative atrial fibrillation on mortality and cardiovascular outcomes of mechanical mitral valve replacement for rheumatic mitral valve disease

OBJECTIVES The prognostic significance of preoperative atrial fibrillation on mitral valve replacement remains unclear. The aim of this study was to explore the effects of the presence of preoperative atrial fibrillation on mortality and cardiovascular outcomes of mitral valve replacement for rheumatic valve disease. METHODS A retrospective analysis was performed on a total of 793 patients who underwent mitral valve replacement with or without tricuspid valve repair in our hospital. The patients selected were divided into two groups according to preoperative rhythm status. Patients with preoperative atrial fibrillation were assigned to the AF group, while patients in preoperative sinus rhythm were assigned to the SR group. Postoperative follow-up was performed by outpatient visits, as well as by telephone and written correspondence. Data gathered included survivorship, postoperative complications, left ventricular function and tricuspid regurgitation. RESULTS For patients with atrial fibrillation vs those in sinus rhythm, there was no difference in postoperative mortality and morbidity. Follow-up was a mean of 8.6 ± 2.4 years. For patients with preoperative atrial fibrillation, 10-year survival from a Kaplan-Meier curve was 88.7%, compared with 96.6% in patients with preoperative sinus rhythm (P = 0.002). Multivariate analysis identified low left ventricular ejection fraction, older age, large left atrium and preoperative atrial fibrillation as significant adverse predictors for overall survival. Freedom from thromboembolism complications at 13 years was lower for patients with preoperative atrial fibrillation without maze procedure and left atrial appendage ligation, compared with that for patients with preoperative sinus rhythm without maze procedure and left atrial appendage ligation, and patients with concomitant maze procedure and left atrial appendage ligation (76.3 vs 94.8 vs 94.0%, respectively; P = 0.001). On echocardiography, the proportion of patients with significant tricuspid regurgitation was 38.7% (atrial fibrillation patients) vs 25.4% (patients in sinus rhythm; P < 0.001). Left ventricular ejection fraction measured 5 years after surgery increased by an average of 1.2% in the AF group, while it increased by 5.3% in the SR group (P = 0.028). CONCLUSIONS Preoperative atrial fibrillation is a risk factor for long-term mortality, thromboembolism complications and tricuspid regurgitation, and it also has an adverse effect on the degree of improvement when considering left ventricular function.

Twist-related protein 1 negatively regulated osteoblastic transdifferentiation of human aortic valve interstitial cells by directly inhibiting runt-related transcription factor 2.

OBJECTIVE Valve calcification involves transdifferentiation of valve interstitial cells (VICs) into osteoblasts. Twist-related protein 1 (TWIST1) has been established as a negative regulator of osteoblast differentiation in both mouse and human mesenchymal stem cells, but its function in human aortic VICs is unknown. In our study, we determined the mechanism of TWIST1 action in regulating osteoblastic transdifferentiation of human aortic VICs. METHODS Human calcified and noncalcified aortic valves were examined for TWIST1 expression. Human aortic VICs were isolated and cultured. RESULTS The data showed that calcified aortic valves express lower levels of TWIST1. In vitro experiments showed that TWIST1 overexpression inhibited the transdifferentiation of VICs into osteoblasts by decreasing the expression of runt-related transcription factor 2 (RUNX2) and its downstream osteoblastic markers. Through chromatin immunoprecipitation and dual luciferase assays, we found that TWIST1 repressed the expression of RUNX2 by directly binding to an E-box located at -820 bp of the RUNX2 P2 promoter region and inhibiting its activity. CONCLUSIONS Our study results suggest that TWIST1 could play an important role in preventing human aortic valve calcification by negatively regulating osteoblastic transdifferentiation of human aortic VICs through direct inhibition of RUNX2.