Poor cell homing limits the efficacy of cardiac cellular therapy. The homing peptide, cysteine-arginine-glutamic acid-lysine-alanine (CREKA), targets fibrin effectively which is involved in the repair process of tissue injury. Here, we assessed if CREKA-modified stem cells had enhanced fibrin-mediated homing ability resulting in better functional recovery and structural preservation in a rat myocardial injury model. CREKA-modified mesenchymal stem cells (CREKA-MSCs) were obtained via membrane fusion with CREKA-modified liposomes. The fibrin targeting ability of CREKA-MSCs was examined both in vitro and in vivo. Under both static and flow conditions in vitro, CREKA significantly enhanced MSCs binding ability to fibrin clots (2.6- and 2.3-fold, respectively). CREKA-MSCs showed 6.5-fold higher accumulation than unmodified MSCs in injured rat myocardium one day after administration, resulting in better structural preservation and functional recovery. Fibrin is, therefore, a novel target for enhancing homing of transplanted cells to injured myocardium, and the delivery system of fibrin-targeting is on behalf of a universalizable platform technology for regenerative medicine. Stem Cells 2019;37:663–676

The poor survival of stem cells seriously limits their therapeutic efficacy for myocardial infarction (MI). Mineralocorticoid receptor (MR) activation plays an important role in the pathogenesis of multiple cardiovascular diseases. Here, we examined whether MR silencing in bone marrow derived mesenchymal stem cells (MSCs) could improve MSCs’ survival and enhance their cardioprotective effects in MI. MSCs from male Sprague‐Dawley rats were transfected with adenoviral small interfering RNA to silence MR (siRNA‐MR). MR silencing decreased hypoxia‐induced MSCs’ apoptosis, as demonstrated by Annexin V/7‐AAD staining. The mechanisms contributing to the beneficial effects of MR depletion were associated with inhibiting intracellular reactive oxygen species production and increased Bcl‐2/Bax ratio. In vivo study, 1 × 106 of MSCs with or without siRNA‐MR were injected into rat hearts immediately after MI. Depletion of MR could improve the MSCs’ survival significantly in infarcted myocardium, associated with more cardiac function improvement and smaller infarct size. Capillary density were also significantly higher in siRNA group with increased expression of vascular endothelial growth factor. Our study demonstrated that silencing MR promoted MSCs’ survival and repair efficacy in ischaemic hearts. MR might be a potential target for enhancing the efficacy of cell therapy in ischaemic heart disease.

Background New-onset atrial fibrillation (AF) is common after atrial flutter (AFL) ablation, but it was unclear whether AF ablation could reduce the incidence of AF in AFL patients without AF history. The present meta-analysis was conducted to evaluate the benefit of prophylactic AF ablation in reducing the occurrence of AF in typical AFL patients. Material/Methods We systematically searched PubMed, EMBASE, and the Cochrane Library from inception to December 2017 for randomized controlled trials (RCTs) that assessed the efficacy of AF ablation in reducing the occurrence of AF in AFL patients without AF. Trial sequential analysis (TSA) was used to control random errors and calculate the required information size. Results Four trials (n=357 patients) met the inclusion criteria and were included in our meta-analysis. The incidence of AF after AFL ablation was 46.4%. We observed that prophylactic AF ablation reduced the AF incidence compared with simple AFL ablation (26.1% versus 46.4%, RR: 0.57, 95% CIs: 0.42–0.76, P=0.0002) with a prolonged procedure duration (P<0.00001) and fluoroscopy time (P=0.004). Further TSA indicated that more RCTs were needed to reach more conclusive results. There was no significant difference in clinical complications (P=0.33) between the 2 groups. Conclusions This meta-analysis provides evidence that prophylactic AF ablation may be more effective than simple AFL ablation in reducing AF incidence after AFL ablation. Large prospective RCTs are warranted to confirm the benefit of prophylactic AF ablation in AFL patients without AF history.

AIMS:The meta-analysis was aimed to search for candidate blood markers whose pre-ablation level was associated with atrial fibrillation (AF) recurrence after radiofrequency catheter ablation (RFCA).METHODS AND RESULTS:A systematic literature search of PubMed, EMBASE, Springer Link, Web of Science, Wiley-Cochrane library, and supplemented with Google scholar search engine was performed. Thirty-six studies covering 11 blood markers were qualified for this meta-analysis. Compared with the nonrecurrence group, the recurrence group had increased pre-ablation level of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), N-terminal pro-brain natriuretic peptide (NT-pro-BNP), interleukin-6 (IL-6), C-reactive protein, low density lipoprotein (LDL), and tissue inhibitor of metal loproteinase-2 (TIMP-2) [standardized mean difference (95% confidence interval): 0.37 (0.13-0.61), 0.77 (0.40-1.14), 1.25 (0.64-1.87), 0.37 (0.21-0.52), 0.35 (0.10-0.60), 0.24 (0.07-0.42), 0.17 (0.00-0.34), respectively], while no statistical difference of pre-ablation level of white blood cell, total cholesterol, triglyceride, and transforming growth factor-β1 was found. Subgroup analysis demonstrated that ANP was associated with AF recurrence in participants who had no concomitant structural heart diseases (SHD); however, not in participants who had SHD, C-reactive protein was associated with AF recurrence in Asian studies, whereas not in European studies.CONCLUSION:Increased pre-ablation level of ANP, BNP, NT-pro-BNP, IL-6, C-reactive protein, LDL, and TIMP-2 was associated with greater risk of AF recurrence after RFCA.

BackgroundLong‐term effects of ganglionated plexi (GP) ablation on sinoatrial node (SAN) and atrioventricular node (AVN) remain unclear. This study is to investigate the long‐term effects of ablation of cardiac anterior right GP (ARGP) and inferior right GP (IRGP) on function and structure of SAN and AVN in canine.MethodsThirty‐two dogs were randomly divided into an operated group (n = 24) and sham‐operated group (n = 8). ARGP and IRGP were ablated in operated group which was randomly divided into three subgroups according to the period of evaluation after operation (1 month, 6 months, 12 months). The functional and histological characteristics of SAN and AVN, as well as the expression of connexin (Cx) 43 and Cx 45 in SAN and AVN, were evaluated before and after ablation.ResultsResting heart rate was increased and AVN effective refractory period was prolonged and sinus node recovery time (SNRT) and corrected SNRT were shortened immediately after ablation. These changes were reverted to preablation level after 1 month. At 1 month, ventricular rate during atrial fibrillation was slowed, atria‐His intervals were prolonged, and Cx43 and Cx45 expression in SAN and AVN were downregulated. At 6 months, all changes were reverted to preablation level. The histological characteristics of SAN and AVN did not change.ConclusionAblation of ARGP and IRGP has short‐term effects on function and structure of SAN and AVN rather than long‐term effects, which suggests that ablation of ARGP and IRGP is safe. Atrioventricular conduction dysfunction after ablation may be related to downregulated Cx43 and Cx45 expression in AVN.

Intrinsic cardiac autonomic neural remodeling (ANR) has been reported to be involved in the initiation and maintenance of atrial fibrillation (AF). Long non-coding RNAs (lncRNAs) are important orchestrators of gene regulatory networks. However, little is known about the relationships between lncRNAs and cardiac ANR in AF. In this study, second-generation RNA sequencing was performed to examine the transcriptomes of lncRNAs in AF and non-AF canine cardiac fat pads. A total of 61,616 putative lncRNAs were yielded, in which 166 were downregulated and 410 were upregulated with more than twofold change. Bioinformatics analysis showed that the aberrantly expressed genes were associated with neural development, migration and neurodegenerative disorders. On the basis of a series of filtering pipelines, two new lncRNAs, namely, TCONS_00032546 and TCONS_00026102, were selected. Silencing of TCONS_00032546 or TCONS_00026102 with lentiviruses in vivo could significantly shorten or prolong the atrial effective refractory period thereby increasing or preventing AF inducibility by promoting or inhibiting the neurogenesis. Besides, the expression of CCND1-FGF19-FGF4-FGF3 gene cluster and SLC25A4, the nearby genes of TCONS_00032546 and TCONS_00026102, were negatively correlated with that of lncRNAs. Furthermore, combining bioinformatics analysis with literature review, TCONS_00032546 and TCONS_00026102 may induce effects by increasing the CCND1-FGF19-FGF3-FGF4 gene cluster and SLC25A4 via complex mechanisms during neural remodeling. Taken together, dysregulated lncRNAs may play regulatory roles in AF neural remodeling, which may further provide potential therapeutic targets for prophylaxis and treatment of AF. J. Cell. Biochem. 116: 809-821, 2015. (C) 2015 Wiley Periodicals, Inc.

Background A critical mechanism in atrial fibrillation (AF) is cardiac autonomic nerve remodeling (ANR). MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression at the post-transcriptional level. Numerous miRNAs are involved in diseases of the nervous and cardiovascular systems. Objective We aimed to assess the underlying role of miRNAs in regulating cardiac ANR in AF by right atrial tachypacing (A-TP) in canines. Methods and Results Following 4-week A-TP, the superior left ganglionated plexuses (SLGPs), which are embedded in the fat pads of the left atrium, were subjected to miRNA expression profiling to screen preferentially expressed miRNAs. Sixteen miRNAs showed significantly differential expression between the control and A-TP groups, including miR-206, miR-203, miR-224 and miR-137. In particular, we focused on miR-206, which was elevated ~10-fold in A-TP dogs. Forced expression of miR-206 through lentiviral infection based on A-TP in vivo significantly shortened the atrial effective refractory period (AERP) (81 ± 7 vs. 98 ± 7 ms, P < 0.05). Immunohistochemical analysis showed that the regeneration of nerves increased more than 2-fold by miR-206 overexpression (P < 0.01). The expression of superoxide dismutase 1 (SOD1) was repressed by miR-206 overexpression by Western blot and luciferase assay, indicative of SOD1 as a direct target of miR-206. Overexpression of miR-206 increased reactive oxygen species (ROS) levels in vitro and in vivo, whereas miR-206 silencing attenuated irradiation- or A-TP-induced ROS. Knockdown of SOD1 effectively abolished ROS reduction caused by miR-206 silencing. Conclusions Our results found the differential expression of miRNAs in response to ANR in AF and elucidated the important role of miR-206 by targeting SOD1. The study illustrated the novel molecular mechanism of ANR and indicated a potential therapeutic target for AF.

Background— The long-term effects of ganglionated plexi ablation on electrophysiological characteristics and neuron remodeling in target atrial tissues remain unclear. Methods and Results— Dogs in group 1 (control, n=8) were not subjected to ganglionated plexi ablation and observed for 1 month, and dogs in groups 2 to 4 (ablation groups, n=8 each) underwent ablation of the right-sided ganglionated plexi and observed for 1, 6, and 12 months, respectively. Atrial electrophysiological characteristics were examined before ablation, immediately and continuously after ablation. Target atrial tissues were subjected to immunohistochemical staining and Western blot analysis. Atrial effective refractory period was significantly prolonged immediately after ablation ( P <0.001), and persisted for 1 month ( P <0.05). Nerve densities decreased 1 month after ablation ( P <0.001). These parameters reverted to preablation levels after 6 and 12 months. In the ablation groups, atrial fibrillation was induced in 5 of 8 dogs after 1 month and in all animals after 6 and 12 months. Atrial fibrillation was not observed in the control group and in the experimental groups immediately after ablation. Moreover, the expression of the growth-associated protein 43 was upregulated after ablation. Conclusions— Ganglionated plexi ablation effectively prolonged atrial effective refractory period for a short period, but the long-term effects on atrial effective refractory period and the suppression of atrial fibrillation induction were not persistent. Targeted atrial neuron remodeling may be an important mechanism underlying the observed electrophysiological changes.

OBJECTIVE:The purpose of this study was to verify the hypothesis that rosuvastatin attenuates atrial structural remodelling in rats with myocardial infarction (MI) through the regulation of the p38 mitogen-activated protein kinase (MAPK) signalling pathway. METHODS:A total of 66 rats were used in this study to establish a model of MI. The 56 rats that survived the first 24h after surgery were randomly divided into four groups: the control group (C group), the rosuvastatin group (R group), the low-dose torasemide group (T1 group), and the high-dose torasemide group (T2 group). The four groups of rats received daily intragastric administration of normal saline, rosuvastatin, or torasemide (T1: 1mg/kg body weight; T2: 2mg/kg body weight) for a total of four weeks. The rats in the sham-operated group (n=14) also received daily intragastric administration of normal saline for four weeks. After four weeks of intervention, the left ventricular end-diastolic pressure (LVEDP) was measured in all groups of rats by haemodynamic methods. The rats were then sacrificed, and the left atrial tissues were collected. The collagen volume fractions (CVFs) in the left atrial tissues were determined using Masson's trichrome staining. The expression of phosphorylated p38 (P-p38) MAPK in the left atrial tissues was examined by immunohistochemistry and western blot analysis. RESULTS:The results showed that LVEDP, CVF, and P-p38 MAPK expression were drastically elevated in the four MI groups in comparison to the sham-operated group (p<0.001). Rosuvastatin elevated the left ventricular fractional shortening (LVFS) and left ventricular ejection fraction (LVEF). Both rosuvastatin and torasemide improved the haemodynamic parameters. No significant difference was detected in LVEDP between the R group and the T1 group (p=0.37). In contrast, LVEDP was significantly higher in the R group than in the T2 group (p <0.05). CVF (%) was markedly decreased in the R group compared to the C, T1, and T2 groups (decreased by 47.4%, 28%, and 20.1%, respectively). Immunohistochemical analysis showed that the indices of P-p38 MAPK positive cells were significantly decreased in the R group in comparison with the C, T1, and T2 groups (decreased by 44.6%, 36.6%, and 21.4%, respectively). Western blot analysis demonstrated that P-p38 MAPK expression was markedly reduced in the R group compared with the C and T1 groups (reduced by 67% and 40.5%, respectively). The level of P-p38 MAPK in the R group was slightly higher than in the T2 group. However, the difference was not statistically significant (p>0.05). CONCLUSION:Rosuvastatin attenuates atrial structural remodelling in rats with MI. The mechanism underlying this phenomenon may be associated with the downregulation of P-p38 MAPK by rosuvastatin.

Background: The potential mechanisms of microRNA-1 (miR-1) in the electrical remodeling of atrial fibrillation remain unclear. The purpose of this study was to evaluate the effects of miR-1 on the atrial effective refractory period (AERP) in a right atrial tachypacing model and to elucidate the potential mechanisms.Methods and Results: QRT-PCR and western blot were used to detect the expression of the miR-1, KCNE1, and KCNB2 genes after 1-week of right atrial tachypacing in New Zealand white rabbits. The AERP was measured using a programmable multichannel stimulator, and atrial fibrillation was induced by burst stimulation in vivo. The slowly activating delayed rectifier potassium current (IKs) and AERP in atrial cells were measured by whole cell patch clamp in vitro. Right atrial tachypacing upregulated miR-1 expression and downregulated KCNE1 and KCNB2 in this study, while the AERP was decreased and the atrial IKs increased. The downregulation of KCNE1 and KCNB2 levels was greater when miR-1 was further upregulated through in vivo lentiviral infection. Electrophysiological tests indicated a shorter AERP, a great increase in the IKs and a higher atrial fibrillation inducibility. In addition, similar results were found when the levels of KCNE1 and KCNB2 were downregulated by small interfering RNA while keeping miR-1 level unaltered. Conversely, knockdown of miR-1 by anti-miR-1 inhibitor oligonucleotides alleviated the downregulation of KCNE1 and KCNB2, the shortening of AERP, and the increase in the IKs. KCNE1 and KCNB2 as the target genes for miR-1 were confirmed by luciferase activity assay.Conclusions: These results indicate that miR-1 accelerates right atrial tachypacing-induced AERP shortening by targeting potassium channel genes, which further suggests that miR-1 plays an important role in the electrical remodeling of atrial fibrillation and exhibits significant clinical relevance as a potential therapeutic target for atrial fibrillation.

The aim of this study was to investigate the correlation between the altered expression of genes involved in the regulation of ion channels in atrial myocytes and the risk of atrial fibrillation (AF) in patients with heart failure (HF). Right atrial appendages were obtained from 18 HF patients and 18 patients with normal cardiac functions who had undergone surgery. The mRNA expression levels of Kv4.3α, KvLQT1, Kv1.5, L-Caα1c and NCX were measured by reverse transcription-PCR (RT-PCR). Protein expression levels were also detected by western blotting. In comparison with the control group exhibiting normal cardiac functions, the mRNA and protein expression levels of Kv4.3α, KvLQT1 and L-Caα1c were significantly reduced in HF patients. By contrast, the mRNA and protein expression levels of NCX were significantly increased in HF patients compared with the control group (P<0.01). The mRNA expression levels of Kv1.5 were not evidently altered. We demonstrated that increased levels of Kv4.3α, KvLQT1 and L-Caα1c and decreased levels of NCX are correlated with the risk of AF in HF patients. Changes in the gene expression of ion channel-related proteins may therefore be used as biological markers of AF occurring in HF patients in future studies.

OBJECTIVE:This study was designed to assess whether angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) could prevent the recurrence of atrial fibrillation (AF).METHODS:A systemic literature search of PubMed, EMBASE, and Cochrane Controlled Trials Register till 2012 was performed to identify randomized controlled trials involving the prevention of recurrence of AF with renin-angiotensin system blockade therapy. Subgroup analysis and meta-regression were performed. Publication bias was checked through funnel plot and Egger's test.RESULTS:Twenty-one randomized controlled trials including 13,184 patients with AF were identified. Overall, the recurrence of AF was significantly reduced in patients using ACEI/ARBs [odds ratio (OR), 0.43; 95% confidence interval (CI), 0.32-0.56; P < 0.00001], especially both in irbesartan subgroup (OR, 0.38; 95% CI, 0.21-0.68; P = 0.001) and in patients receiving antiarrhythmic drug (AAD) (OR, 0.37; 95% CI, 0.29-0.48; P < 0.00001), and there was no significant difference between ACEIs and ARBs (ACEIs: OR, 0.42; 95% CI, 0.31-0.57 and ARBs: OR, 0.42; 95% CI, 0.31-0.57). Moreover, it was found that the benefits of ACEI/ARBs revealed positive correlation to systolic blood pressure (regression coefficient: -0.0700257, P = 0.000) in no-AAD users.CONCLUSIONS:ACEI/ARBs are effective on the secondary prevention of AF, especially in patients receiving AAD and suffering from hypertension.

Aim: To investigate the mechanism of rosuvastatin in preserving cardiac function after acute myocardial infarction (AMI) in a rat model. Methods: Sprague-Dawley rats were randomized to receive either rosuvastatin (5 mg/kg every day) or placebo (0.5% CMC-Na), respectively, by daily gavage from 7 days before AMI. Acute myocardial infarction (AMI) model was induced by left anterior descending coronary artery ligation through a lateral thoracotomy in rats. The expressions of stromal-cell-derived factor 1 (SDF-1), chemokine motif CXC receptor 4 (CXCR-4), vascular endothelial growth factor (VEGF), and intercellular adhesion molecule 1 (ICAM-1) in peri-infarction region and nonischemic region at different time points were determined by the Western blot analysis. Immunohistochemistry analysis was performed on the 28th day after AMI to investigate the accumulation of CD90+, CD133+, and c-kit+ progenitor cells in the peri-infarction region. Masson staining and echocardiograph were performed to evaluate the left ventricular remodeling and postinfarction cardiac function 4 weeks after AMI. Results: Western blot analysis showed that rosuvastatin could change the cytokine expressions in the peri-infarction region by upregulating the SDF-1 expression and downregulating the expressions of CXCR-4, ICAM-1, and VEGF in 4 to 14 days after AMI. Immunohistochemistry analysis showed that rosuvastatin treatment was associated with increased accumulation of CD90+, CD133+, and c-kit+ progenitor cells in the peri-infarction region. Masson staining and echocardiograph confirmed that rosuvastatin could attenuate left ventricular remodeling and improve postinfarction systolic function. Conclusion: The data suggest that rosuvastatin can protect the heart from ischemic injury and preserve the cardiac function in rats in vivo. The changing expressions of SDF-1, CXCR-4, ICAM-1, and VEGF, and the accumulation of progenitor cells were involved in this process.

Background A meta‐analysis of randomized controlled trials (RCTs) was conducted to compare the effects of right ventricular nonapical (RVNA) and right ventricular apical (RVA) pacing on cardiac function. Methods A systematic literature search was performed using MEDLINE, EMBASE, and the Cochrane Library to identify RCTs comparing RVNA pacing with RVA pacing with follow‐up ≥2 months. Twenty RCTs involving 1,114 patients were included. Results Compared with RVA pacing, RVNA (mainly right ventricular septum [RVS]) pacing exhibited not only excellent pacing threshold and R‐wave amplitude but also higher impedance. RVNA pacing showed a significant increase in left ventricular ejection fraction (LVEF) at the end of follow‐up (weighted mean difference = 3.58, 95% confidence interval = 1.80–5.35), and the effects were observed in the following subgroups: 6‐month follow‐up, ≤12‐month follow‐up, >12‐month follow‐up, baseline LVEF ≤45%, and baseline LVEF >45%. RVS and RVA pacing significantly differed in improving LVEF (weighted mean difference = 4.82, 95% confidence interval = 2.78–6.87). In addition, RVNA pacing resulted in a narrower QRS duration, a smaller left ventricular end‐systolic volume, and a lower New York Heart Association functional class. Conclusions This meta‐analysis found that RVNA (mainly RVS) pacing exhibited satisfactory long‐term lead performance compared with RVA pacing and demonstrated beneficial effects in improving LVEF after the 6‐month follow‐up. Furthermore, it proved superior to RVA pacing in terms of interventricular synchrony and cardiac function.

High-density lipoprotein (HDL) possesses protective properties in cardiovascular diseases. However, the effect of HDL on the mesenchymal stem cells (MSCs), which could be mobilized to the damaged myocardial tissue, has not been well elucidated yet. In the current study, we investigated the effect of HDL on the proliferation of MSCs so as to reveal its molecular mechanisms. MSCs derived from rats were treated with HDL in different concentrations and for different periods. The proliferation of MSCs was measured with MTT and BrdU cell proliferation assay. The phosphorylation of Akt, ERK1/2 and the expression of p21 were evaluated by Western blotting. After the activity of respective pathways was down-regulated by the specific inhibitor and the gene of scavenger receptor-B type I (SR-BI) was knocked down by RNA interference, BrdU assay was performed to examine this effect of HDL on MSCs. We found that the proliferation of MSCs induced by HDL, in a time- and concentration-dependent manner, was the phosphorylation of Akt- and ERK1/2-dependent, which was significantly attenuated by the specific inhibitor to respective pathways. Moreover, MAPK/ERK1/2 pathway exerted a more dominating effect on this process. SR-BI contributed to HDL-induced proliferation of MSCs, which was effectively abolished by the silencing of SR-BI. The results suggested that HDL was capable of improving MSCs proliferation, in which MAPK/ERK1/2 and PI3K/Akt pathways involved and SR-BI played a critical role as well.

Given the adult heart's minimal capacity for endogenous regeneration, cell therapy has emerged as a promising approach to the regeneration of damaged vascular and cardiac tissue after acute myocardial infarction and heart failure. However, systematic review suggests only mild improvement in global heart function, and high degree of heterogeneity among clinical trials 1. The first prerequisite for cell therapy success is the engraftment and thus, homing of transplanted cells to the target area. Poor cell homing, retention and engraftment are major obstacles in achieving a significant functional benefit irrespective of the cell type or delivery route used. Data showed only 1–3% of the delivered cells were recruited at the infarct sites via intracoronary administration. The retention of cells in the heart is extremely low, even undetectable after a few weeks when administered by the intravenous route 2-5. The predominant number of cells was found in non-targeting organs such as liver, spleen and lung. To induce migration and homing of transplanted cells to optimize the efficacy of cell-based therapies, much efforts have been made in identifying chemokine and its receptors (CXCR4/SDF-1 axis, et al.) in the last decades 6, 7. However, due to the extreme complicity of the ‘cell-extracellular matrix-cytokine’ network and the homing molecular mechanisms, the chemoattractant molecules-targeted method has been far away from being able to precisely and effectively regulate stem cell migrating to target tissue 8, 9. Magnetic targeting strategy, traditionally used in chemotherapy for tumour 10, had been introduced to localize magnetic nanoparticle-loaded cell delivery to target lesion in vivo in recent years 11-17. The accumulation and retention of the magnetic responsive cells can be enhanced by using an external magnetic field produced by electromagnet, which is focused on the area of interest 18. Cheng K et al. 19 were the first to introduce magnetic targeting strategy to attract transplanted cells to the heart. Using a 1.3 Tesla magnet applied above the rat apex during the intramyocardial injection of magnetic responsive cardiosphere-derived cells, they found that cell retention and engraftment in the recipient hearts increased by approximately threefold compared to non-targeted cells. Chaudeurge A et al. 20 adopted subcutaneous insertion of a magnet over the chest cavity during therapeutic intracavitary stem cell infusion, found that the average number of engrafted cells was significantly 10 times higher with than without magnetic targeting. This magnetically enhanced intracoronary cell delivery was confirmed by another study 21. Thus, magnetic targeting is proved to enhance cell retention, engraftment and this novel method to improve cell therapy outcome offers the potential for clinical applications. However, the magnetic field has some inherent limitations as the magnetic flux density is maximal at the magnet pole face and cannot be focused at a distance from the magnet 10. For conventional electromagnet therefore magnetically loaded cells are predominantly attracted to the surface of magnetic materials, and hard to be targeted to tissues localized deeper in the body. To promote the cell retention at targeting sites remote from the magnet surface, a greater magnetic force or invasive approaches (e.g. implant magnetized stent, magnetic particles or magnet at the target site) will be required. Magnetically loaded endothelial cells were homing to the magnetized stent deployed in rat arteries in the presence of a uniform magnetic field 12, 13. However, achievement of the cell engraftment necessary for therapeutic effects by using a ‘safe magnet force’ would be challenging. Moreover, it is not feasible that there could be the invasive implantation of a magnet or magnetized materials in parenchymatous organs such as heart. To overcome these limitations, it is of great significance to develope a magnetic field which can be focused at a distance from the magnet surface. Recently, we proposed that the spatially focused magnetic field is feasible in theoretical considerations 22. Its deep capture property of this special magnetic field has been testified in our preliminary in vitro study 22, 23. The deep accumulation of magnetically loaded mesenchymal stem cells was observed while cells flowed through a tube served as a model of blood vessels in such a magnetic field. The cell capture efficiency was positively influenced by the magnetic flux density, and negatively influenced by the flow velocity. The capture efficiency reached 89.3% with 640 mT of the magnetic flux density, 38.4 T/m of the magnetic intensity gradient and 0.8 mm/sec. of flow velocity in our in vitro study 23. Based on available studies, it is logical to assume that spatially focused magnetic targeting strategy should be a novel method to deliver stem cells to the injured heart. The hypothesis could be verified in animal study. First, stem cells (such as bone marrow mesenchymal stem cells, et al.) are preloaded with biodegradable superparamagnetic iron oxide nanoparticles (SPIO) and became magnetically responsive. Secondly, the magnetically loaded cells are administered intravenously into rats with myocardial infarction, meanwhile a spatially focusing magnetic field is adopted at the area of injured heart. As a result, systemically delivered stem cells will be localized to infarcted heart. The mechanism of this phenomenon should be studied based on electrodynamic and magnetomechanic principles. This magnetic spatial localization strategy may revive the route of peripheral intravenous administration for cell therapy. Peripheral systemic intravenous administration is the most convenient rout of cell delivery, offering the advantages of a non-surgical and non-interventional method that can be performed repeatedly. However, it's efficacy was not efficient because the majority of intravenously injected cells were entrapped in lung, and chemoattractant factors secreted by the infarcted heart might be too diluted to attract stem cells 24. The spatial localization strategy can also performed non-invasively and repeatedly, without the need of a magnet applied on the surface of the heart. So more benefits may be reasonably expected from the combination of the novel magnetic strategy and the systemic intravenous transplantation method, which offers a brand-new, attracting method to effectively overcome the shortcoming of low homing, and subsequently improve the efficacy of cell transplantation for myocardial infarction and heart failure. More importantly, the magnetic spatial localization strategy may be a breakthrough in targeting therapy, with the potential for widening the indication of magnetic cells/drugs targeting for lesions localized deeper in the body. Its indications are more than just cell therapy in heart. It can be applied in any organ or lesions, as long as the patient or animal could be placed within the magnetic field, and the lesion deep-seated in body could be positioned at the focus site to localize systemically delivered cells/drugs to targeted site. In conclusion, poor cell homing, retention and engraftment limit the efficacy of stem cell therapy. Our hypothesis might be a novel strategy worth to try to localize systemically delivered cells to targeted lesion which deep-seated in body, included the injured heart, subsequently enhance the efficacy of stem cell therapy. This work was supported by National Natural Science Fundation of China (81000043, 81000105) and Research Fund for the Doctoral Program of Higher Education of China (20100071120072).

The therapeutic effect of transplantation of mesenchymal stem cells (MSCs) in myocardial infarction (MI) appears to be limited by poor cell viability in the injured tissue, which is a consequence of oxidative stress and pro-apoptotic factors. High density lipoprotein (HDL) reverses cholesterol transport and has anti-oxidative and anti-apoptotic properties. We, therefore, investigated whether HDL could protect MSCs from oxidative stress-induced apoptosis. MSCs derived from the bone marrow of rats were pre-incubated with or without HDL, and then were exposed to hydrogen peroxide (H2O2) in vitro, or were transplanted into experimentally infarcted hearts of rats in vivo. Pre-incubation of MSCs with HDL increased cell viability, reduced apoptotic indices and resulted in parallel decreases in reactive oxygen species (ROS) in comparison with control MSCs. Each of the beneficial effects of HDL on MSCs was attenuated by inhibiting the PI3K/Akt pathway. Preconditioning with HDL resulted in higher MSC survival rates, improved cardiac remodeling and better myocardial function than in the MSC control group. Collectively, these results suggest that HDL may protect against H2O2-induced apoptosis in MSCs through activation of a PI3K/Akt pathway, and by suppressing the production of ROS.

Objectives To investigate the effect of high density lipoprotein (HDL) on the proliferation of mesenchymal stem cells (MSCs), and to elucidate the molecular mechanisms involved. Methods MSCs derived from rats was treated with HDL in different concentration or for different periods. The proliferation of MSCs was measured with MTT and BrdU assay. The expressions of p21 and phosphorylation of Akt, ERK1/2 were evaluated by western blot. The activity of pathways was down-regulated by the respective specific inhibitor, and the gene of Scavenger Receptor-B Type I (SR-BI) was knocked down by RNA interference. Results We found that HDL promoted MSCs proliferation in a time- and concentration-dependent manner, in which the phosphorylation of Akt, ERK1/2 were up-regulated and the level of p21 was down-regulated. When MSCs was preconditioned with the specific inhibitor to respective pathways, the decrease of p21 induced by HDL was significantly attenuated compared with that without preconditioning (LY294002: 1.03±0.16 vs 0.691±0.13, p<0.05; U0126: 1.68±0.17 vs 0.76±0.15, p<0.05). SR-BI contributed to HDL-induced proliferation of MSCs, which was effectively abolished by the knock-down of SR-BI. Compared with respective PBS-treatment groups, MSCs transfected with mock siRNA displayed a higher BrdU incorporation rate after administration of HDL (0.98±0.16 vs 1.57±0.23, p<0.05), while the MSCs transfected with SR-BI siRNA showed no change (1.08±0.15 vs1.08±0.14, p > 0.05). Conclusions HDL improves the proliferation of MSCs in a time- and concentration-dependent manner through PI3K/Akt and MAPK/ERK1/2 pathways and binding SR-BI receptor.