Intramyocardial Injection of Pig Pluripotent Stem Cells Improves Left Ventricular Function and Perfusion: A Study in a Porcine Model of Acute Myocardial Infarction

Induced pluripotent stem (iPS) cells have the potential to differentiate to various types of cardiovascular cells to repair an injured heart. The potential therapeutic benefits of iPS cell based treatment have been established in small-animal models of myocardial infarction (MI). We hypothesize that porcine iPS (piPS) cell transplantation may be an effective treatment for MI. After a 90-minute occlusion of the left anterior descending artery in a porcine model, undifferentiated piPS cells or PBS were injected into the ischemic myocardium. Cardiac function, myocardial perfusion and cell differentiation were investigated. One week after piPS cell delivery, global left ventricular ejection fraction (LVEF) significantly decreased in both the iPS group and the PBS group compared to the Sham group (p<0.05, respectively). Six weeks after piPS cell delivery, LVEF of the iPS group significantly improved compared to the PBS group (56.68% vs. 50.93%, p = 0.04) but was still lower than the Sham group. Likewise, the piPS cell transplantation improved the regional perfusion compared to the PBS injection (19.67% vs. 13.67%, p = 0.02). The infarct area was significantly smaller in the iPS group than the PBS group (12.04% vs. 15.98% p = 0.01). PiPS cells engrafted into the myocardium can differentiate into vessel cells, which result in increased formation of new vessels in the infarcted heart. Direct intramyocardial injection of piPS cells can decrease infarct size and improve left ventricular function and perfusion for an immunosuppressed porcine AMI model.     

Functional and bioenergetic modulations in the infarct border zone following autologous mesenchymal stem cell transplantation

Preclinical and clinical studies have demonstrated that stem cell transplantation can improve the left ventricular (LV) contractile performance, yet the underlying mechanisms remain unknown. We examined whether mesenchymal stem cell (MSC) transplantation-induced beneficial effects are secondary to paracrine-associated improvements in LV contractile performance, wall stress, and myocardial bioenergetics in hearts with postinfarction LV remodeling. Myocardial contractile function and bioenergetics were compared 4 wk after acute myocardial infarction in normal pigs (n = 6), untreated pigs with myocardial infarction (MI group; n = 6), and pigs receiving autologous MSC transplantation (MI + MSC group; n = 5). A distal occlusion of the left anterior descending coronary artery instigated significant myocardial hypertrophy. Ejection fraction decreased from 55.3 +/- 3.1% (normal) to 30.4 +/- 2.3% (MI group; P < 0.01) and to 45.4 +/- 3.1% (MI + MSC group; P < 0.01 vs. MI). Hearts in the MI group developed severe contractile dyskinesis in the infarct zone and border zone (BZ). MSC transplantation significantly improved contractile performance from dyskinesis to active contraction (P < 0.01 vs. MI). BZ systolic wall stress was severely increased in MI hearts but significantly improved after MSC transplantation (P < 0.01 vs. MI). The BZ demonstrated profound bioenergetic abnormalities in MI pigs; this was significantly improved after MSC transplantation (P < 0.01 vs. MI). Patchy spared myocytes were found in the infarct zone of hearts receiving MSC transplantation but not in control hearts. These data demonstrate that MSC transplantation into the BZ causes significant improvements in myocardial contractile performance and reduction in wall stress, which ultimately results in significant bioenergetic improvements. Low cell engraftment indicates that MSCs did not provide a structural contribution to the damaged heart and that the observed beneficial effects likely resulted from paracrine repair mechanisms.     

Effects of hepatocyte growth factor overexpressed bone marrow-derived mesenchymal stem cells on prevention from left ventricular remodelling and functional improvement in infarcted rat hearts

Bone marrow-derived mesenchymal stem cells (BM-MSCs ) transplantation has been reported to be a promising therapy for myocardial infarction (MI). However, low survival rate of BM-MSCs in infarcted heart is one of the major limitations for the perspective clinical application. In this study, we aimed to investigate the effect of hepatocyte growth factor (HGF) on left ventricular function improvement of HGF gene-modified BM-MSCs (HGF-MSCs) after its delivery into the infarcted rat hearts. BM-MSCs were isolated with fibroblast-like morphology and expressed CD44+CD29+CD90+/CD34-CD45-CD31-CD11a. After 5-azacytidine induction in vitro, 20%-30% of the cells were positively stained for desmin, cardiac-specific cardiac troponin I and connexin-43. Histological staining revealed that 2?weeks after MI is an optimal time point with decreased neutrophil infiltration and increased vascular number. Minimal infarct size and best haemodynamic analysis were also observed after cell injection at 2?weeks compared with that of 1?h, 1?week or 4?weeks. Echocardiogram confirmed that transplantation with HGF-MSCs significantly improved left ventricular function compared with other groups in rat MI models. MSCs and HGF-MSCslabelled with DAPI were detected 4?weeks after MI in the infarcted area. Decreased infarcted scar area and increased angiogenesis formation could be found in HGF-MSCs group than in other groups as demonstrated by hematoxylin and eosin (H&E) staining and factor VIII staining. These results indicate that HGF-MSCs transplantation could enhance the contractile function and attenuate left ventricular remodelling efficiently in rats with MI. Copyright ? 2012 John Wiley & Sons, Ltd.     

Intramyocardial transplantation of cardiac telocytes decreases myocardial infarction and improves post‐infarcted cardiac function in rats

The midterm effects of cardiac telocytes (CTs) transplantation on myocardial infarction (MI) and the cellular mechanisms involved in the beneficial effects of CTs transplantation are not understood. In the present study, we have revealed that transplantation of CTs was able to significantly decrease the infarct size and improved cardiac function 14 weeks after MI. It has established that CT transplantation exerted a protective effect on the myocardium and this was maintained for at least 14 weeks. The cellular mechanism behind this beneficial effect on MI was partially attributed to increased cardiac angiogenesis, improved reconstruction of the CT network and decreased myocardial fibrosis. These combined effects decreased the infarct size, improved the reconstruction of the LV and enhanced myocardial function in MI. Our findings suggest that CTs could be considered as a potential cell source for therapeutic use to improve cardiac repair and function following MI, used either alone or in tandem with stem cells.     

Mesenchymal stem cell transplantation for the infarcted heart: a role in minimizing abnormalities in cardiac-specific energy metabolism

Intense interest has been focused on cell-based therapy for the infarcted heart given that stem cells have exhibited the ability to reduce infarct size and mitigate cardiac dysfunction. Despite this, it is unknown whether mesenchymal stem cell (MSC) therapy can prevent metabolic remodeling following a myocardial infarction (MI). This study examines the ability of MSCs to rescue the infarcted heart from perturbed substrate uptake in vivo. C57BL/6 mice underwent chronic ligation of the left anterior descending coronary artery to induce a MI. Echocardiography was performed on conscious mice at baseline as well as 7 and 23 days post-MI. Twenty-eight days following the ligation procedure, hyperinsulinemic euglycemic clamps assessed in vivo insulin sensitivity. Isotopic tracer administration evaluated whole body, peripheral tissue, and cardiac-specific glucose and fatty acid utilization. To gain insight into the mechanisms by which MSCs modulate metabolism, mitochondrial function was assessed by high-resolution respirometry using permeabilized cardiac fibers. Data show that MSC transplantation preserves insulin-stimulated fatty acid uptake in the peri-infarct region (4.25 ± 0.64 vs. 2.57 ± 0.34 vs. 3.89 ± 0.54 μmol·100 g(-1)·min(-1), SHAM vs. MI + PBS vs. MI + MSC; P < 0.05) and prevents increases in glucose uptake in the remote left ventricle (3.11 ± 0.43 vs. 3.81 ± 0.79 vs. 6.36 ± 1.08 μmol·100 g(-1)·min(-1), SHAM vs. MI + PBS vs. MI + MSC; P < 0.05). This was associated with an enhanced efficiency of mitochondrial oxidative phosphorylation with a respiratory control ratio of 3.36 ± 0.18 in MSC-treated cardiac fibers vs. 2.57 ± 0.14 in the infarct-only fibers (P < 0.05). In conclusion, MSC therapy exhibits the potential to rescue the heart from metabolic aberrations following a MI. Restoration of metabolic flexibility is important given the metabolic demands of the heart and the role of energetics in the progression to heart failure.     

Effects of hepatocyte growth factor overexpressed bone marrow‐derived mesenchymal stem cells on prevention from left ventricular remodelling and functional improvement in infarcted rat hearts

Bone marrow‐derived mesenchymal stem cells (BM‐MSCs ) transplantation has been reported to be a promising therapy for myocardial infarction (MI). However, low survival rate of BM‐MSCs in infarcted heart is one of the major limitations for the perspective clinical application. In this study, we aimed to investigate the effect of hepatocyte growth factor (HGF) on left ventricular function improvement of HGF gene‐modified BM‐MSCs (HGF‐MSCs) after its delivery into the infarcted rat hearts. BM‐MSCs were isolated with fibroblast‐like morphology and expressed CD44+CD29+CD90+/CD34‐CD45‐CD31‐CD11a. After 5‐azacytidine induction in vitro, 20%–30% of the cells were positively stained for desmin, cardiac‐specific cardiac troponin I and connexin‐43. Histological staining revealed that 2 weeks after MI is an optimal time point with decreased neutrophil infiltration and increased vascular number. Minimal infarct size and best haemodynamic analysis were also observed after cell injection at 2 weeks compared with that of 1 h, 1 week or 4 weeks. Echocardiogram confirmed that transplantation with HGF‐MSCs significantly improved left ventricular function compared with other groups in rat MI models. MSCs and HGF‐MSCslabelled with DAPI were detected 4 weeks after MI in the infarcted area. Decreased infarcted scar area and increased angiogenesis formation could be found in HGF‐MSCs group than in other groups as demonstrated by hematoxylin and eosin (H&E) staining and factor VIII staining. These results indicate that HGF‐MSCs transplantation could enhance the contractile function and attenuate left ventricular remodelling efficiently in rats with MI. Copyright © 2012 John Wiley & Sons, Ltd.     

Central zone of myocardial infarction: a neglected target area for heart cell therapy

The purpose of this study was to investigate the fate of transplanted cells in the central zone of myocardial infarction (MI), and to clarify the relationship between the injection-site impact and the efficacy of cell therapy. MI was created by coronary ligation in female rats. Three weeks later, 3-million labelled male bone marrow mesenchymal stem cells (BMSCs) were directly injected into the border (BZC group) or central zone (CZC group) of MI area. As a control, culture medium was injected into the same sites. Cell survival was evaluated by quantitative real-time polymerase chain reaction, and apoptosis was assayed with TUNEL and caspase-3 staining. Four weeks after transplantation, heart function and cardiac morphometry were evaluated by echocardiography and Masson's Trichrome staining, respectively. Angiogenesis and myogenesis were detected by immunofluorescence staining. After cell transplantation into the border or central zone, there was no cell migration between the different zones of MI. BMSCs in the CZC group exhibited no difference in apoptotic percentage, in the long-term survival, when compared with those in the BZC group. However, they did effectively promote angiogenesis and cellular myogenic differentiation. Although cell delivery in the central zone of MI had no effect on the recovery of heart function compared with the BZC group, the retained BMSCs could still increase the scar thickness, and subsequently exhibit a trend in the reverse remodelling of ventricular dilation. Hence, we concluded that the central zone of MI should not be ignored during cell-based therapy. Multiple site injection (border+central zone) is strongly recommended during the procedure of cell transplantation.     

骨髓间质干细胞向大鼠损伤心肌组织的迁移

实验旨在动态观察骨髓间充质干细胞（mesenchymal stem cells,MSCs）向不同微环境下心肌组织的迁移特点,明确组织损伤在干细胞迁移中的作用,为提高干细胞治疗的靶向性和高效性奠定初步试验基础。分离纯化雄性Sprague-Dawley（SD）大鼠的骨髓MSCs,输注入雌性SD大鼠。实验分为4组：正常大鼠＋MSCs移植组,假手术＋MSCs移植组,心肌缺血＋MSCs移植组,心肌缺血对照组（心肌缺血＋培养基移植）。结扎冠状动脉前降支制造心肌缺血模型,将相等数量的雄性MSCs经尾静脉注射移植入前3组雌性大鼠体内,对照组注射等体积培养基,分别于移植后1周及8周取心脏组织标本,采用荧光原位杂交方法（fluorescence in situ hybridization,FISH）检测大鼠Y染色体雄性鉴别基因sty片段的表达,用透射电镜观察大鼠心肌组织超微结构改变。结果发现,移植后1周和8周,正常大鼠移植组和对照组大鼠的心肌组织中均未见sry基因的表达,但假手术移植组和心肌缺血移植组的心肌组织中均可见sty基因的表达,心肌缺血移植组的Y染色体sty基因阳性细胞数量在两个时间点均显著高于假手术移植组（P〈0．01）。分别比较心肌缺血移植组和假手术组在移植后1周和8周的Y染色体sry基因阳性细胞的数量,两个时间点无明显差异。心肌组织的超微结构观察发现心肌缺血移植组大鼠的心肌梗死周边区域可见一些细胞,其形态类似于体外培养的MSCs。研究结果提示MSCs具有向损伤心肌组织迁移的特性,迁移的高峰期可能在组织损伤1周左右,组织损伤及其程度在干细胞迁移中起重要作用。     

Effects of hydrogel injection on borderzone contractility post-myocardial infarction

Injectable hydrogels are a potential therapy for mitigating adverse left ventricular (LV) remodeling after myocardial infarction (MI). Previous studies using magnetic resonance imaging (MRI) have shown that hydrogel treatment improves systolic strain in the borderzone (BZ) region surrounding the infarct. However, the corresponding contractile properties of the BZ myocardium are still unknown. The goal of the current study was to quantify the in vivo contractile properties of the BZ myocardium post-MI in an ovine model treated with an injectable hydrogel. Contractile properties were determined 8 weeks following posterolateral MI by minimizing the difference between in vivo strains and volume calculated from MRI and finite element model predicted strains and volume. This was accomplished by using a combination of MRI, catheterization, finite element modeling, and numerical optimization. Results show contractility in the BZ of animals treated with hydrogel injection was significantly higher than untreated controls. End-systolic (ES) fiber stress was also greatly reduced in the BZ of treated animals. The passive stiffness of the treated infarct region was found to be greater than the untreated control. Additionally, the wall thickness in the infarct and BZ regions was found to be significantly higher in the treated animals. Treatment with hydrogel injection significantly improved BZ function and reduced LV remodeling, via altered MI properties. These changes are linked to a reduction in the ES fiber stress in the BZ myocardium surrounding the infarct. The current results imply that injectable hydrogels could be a viable therapy for maintaining LV function post-MI.     

Immuno‐modification of enhancing stem cells targeting for myocardial repair

Despite the controversy in mechanism, rodent and clinical studies have demonstrated beneficial effects of stem/progenitor cell therapy after myocardial infarction (MI). In a rat ischaemic reperfusion MI model, we investigated the effects of immunomodification of CD 34⁺ cells on heart function and myocardial conduction. Bispecific antibody (BiAb), consisting of an anti‐myosin light chain antibody and anti‐CD45 antibody, injected intravenously was used to direct human CD34⁺ cells to injured myocardium. Results were compared to echocardiography guided intramyocardial (IM) injection of CD34⁺ cells and PBS injected intravenously. Treatment was administered 2 days post MI. Echocardiography was performed at 5 weeks and 3 months which demonstrated LV dilatation prevention and fractional shortening improvement in both the BiAb and IM injection approaches, with BiAb achieving better results. Histological analyses demonstrated a decrease in infarct size and increase in arteriogenesis in both BiAb and IM injection. Electrophysiological properties were studied 5 weeks after treatments by optical mapping. Conduction velocity (CV), action potential duration (APD) and rise time were significantly altered in the MI area. The BiAb treated group demonstrated a more normalized activation pattern of conduction and normalization of CV at shorter pacing cycle lengths. The ventricular tachycardia inducibility was lowest in the BiAb treatment group. Intravenous administration of BiAb offers an effective means of stem cell delivery for myocardial repair post‐acute MI. Such non‐invasive approach was shown to offer a distinct advantage to more invasive direct IM delivery.     

Characterization of photo-cross-linked oligo[poly(ethylene glycol) fumarate] hydrogels for cartilage tissue engineering

Photo-cross-linkable oligo[poly(ethylene glycol) fumarate] (OPF) hydrogels have been developed for use in tissue engineering applications. We demonstrated that compressive modulus of these hydrogels increased with increasing polymer concentration, and hydrogels with different mechanical properties were formed by altering the ratio of cross-linker/polymer in precursor solution. Conversely, swelling of hydrogels decreased with increasing polymer concentration and cross-linker/polymer ratio. These hydrogels are degradable and degradation rates vary with the change in cross-linking level. Chondrocyte attachment was quantified as a method for evaluating adhesion of cells to the hydrogels. These data revealed that cross-linking density affects cell behavior on the hydrogel surfaces. Cell attachment was greater on the samples with increased cross-linking density. Chondrocytes on these samples exhibited spread morphology with distinct actin stress fibers, whereas they maintained their rounded morphology on the samples with lower cross-linking density. Moreover, chondrocytes were photoencapsulated within various hydrogel networks. Our results revealed that cells encapsulated within 2-mm thick OPF hydrogel disks remained viable throughout the 3-week culture period, with no difference in viability across the thickness of hydrogels. Photoencapsulated chondrocytes expressed the mRNA of type II collagen and produced cartilaginous matrix within the hydrogel constructs after three weeks. These findings suggest that photo-cross-linkable OPF hydrogels may be useful for cartilage tissue engineering and cell delivery applications.     

培养于生物降解支架膜内的胚胎干细胞可修复小鼠的梗塞心肌

我们以往的研究表明,直接在心肌梗塞（myocardial infarction,MI）动物的心脏缺血区注射胚胎干细胞（embryonic stemceils,ESCs）可以提高其心肌功能,干细胞组织工程学可以使组织再生、修复。本研究旨在观察将ESCs接种到生物降解膜内并移植到梗塞部位的效果。通过结扎小鼠左冠状动脉制作MI模型,将培养3d的带有小鼠ESCs的聚羟基乙酸膜（polyglycolicacid,PGA）移植到心肌缺血及边缘区表面。实验小鼠分成4组：假手术组、MI组、MI＋PGA组、MI＋ESC组,移植操作8周后检测血流动力学和心肌功能。MI组的血压和左心室功能显著降低。与MI组和MI＋PGA组相比,MI＋ESC组的血压和心室功能显著改善,存活率也显著增高,在梗塞区检测到GFP阳性组织,表明ESCs存活,并可能有心肌再生。以上结果表明,移植生物降解膜内的ESCs可修复小鼠梗塞区心肌细胞并提高心脏功能。将ESCs和生物降解材料联合运用可能为修复受损心脏提供一个新的治疗方法。     

Controlled intramyocardial release of engineered chemokines by biodegradable hydrogels as a treatment approach of myocardial infarction

Myocardial infarction (MI) induces a complex inflammatory immune response, followed by the remodelling of the heart muscle and scar formation. The rapid regeneration of the blood vessel network system by the attraction of hematopoietic stem cells is beneficial for heart function. Despite the important role of chemokines in these processes, their use in clinical practice has so far been limited by their limited availability over a long time‐span in vivo. Here, a method is presented to increase physiological availability of chemokines at the site of injury over a defined time‐span and simultaneously control their release using biodegradable hydrogels. Two different biodegradable hydrogels were implemented, a fast degradable hydrogel (FDH) for delivering Met‐CCL5 over 24 hrs and a slow degradable hydrogel (SDH) for a gradual release of protease‐resistant CXCL12 (S4V) over 4 weeks. We demonstrate that the time‐controlled release using Met‐CCL5‐FDH and CXCL12 (S4V)‐SDH suppressed initial neutrophil infiltration, promoted neovascularization and reduced apoptosis in the infarcted myocardium. Thus, we were able to significantly preserve the cardiac function after MI. This study demonstrates that time‐controlled, biopolymer‐mediated delivery of chemokines represents a novel and feasible strategy to support the endogenous reparatory mechanisms after MI and may compliment cell‐based therapies.     

Intracardiac injection of matrigel induces stem cell recruitment and improves cardiac functions in a rat myocardial infarction model

Matrigel promotes angiogenesis in the myocardium from ischemic injury and prevents remodelling of the left ventricle. We assessed the therapeutic efficacy of intracardiac matrigel injection and matrigel‐mediated stem cell homing in a rat myocardial infarction (MI) model. Following MI, matrigel (250 μl) or phosphate‐buffered solution (PBS) was delivered by intracardiac injection. Compared to the MI control group (MI‐PBS), matrigel significantly improved left ventricular function (n= 11, P < 0.05) assessed by pressure–volume loops after 4 weeks. There is no significant difference in infarct size between MI‐matrigel (MI‐M; 21.48 ± 1.49%, n= 10) and MI‐PBS hearts (20.98 ± 1.25%, n= 10). The infarct wall thickness of left ventricle is significantly higher (P < 0.01) in MI‐M (0.72 ± 0.02 mm, n= 10) compared with MI‐PBS (0.62 ± 0.02 mm, n= 10). MI‐M hearts exhibited higher capillary density (border 130.8 ± 4.7 versus 115.4 ± 6.0, P < 0.05; vessels per high‐power field [HPF; 400×], n= 6) than MI‐PBS hearts. c‐Kit⁺ stem cells (38.3 ± 5.3 versus 25.7 ± 1.5 c‐Kit⁺ cells per HPF [630×], n= 5, P < 0.05) and CD34⁺ cells (13.0 ± 1.51 versus 5.6 ± 0.68 CD34⁺ cells per HPF [630×], n= 5, P < 0.01) were significantly more numerous in MI‐M than in MI‐PBS in the infarcted hearts (n= 5, P < 0.05). Intracardiac matrigel injection restores myocardial functions following MI, which may attribute to the improved recruitment of CD34⁺ and c‐Kit⁺ stem cells.     

Engineered heart tissue enables study of residual undifferentiated embryonic stem cell activity in a cardiac environment

Embryonic stem cell (ESC) derivatives are a promising cell source for cardiac cell therapy. Mechanistic studies upon cell injection in conventional animal models are limited by inefficient delivery and poor cell survival. As an alternative, we have used an engineered heart tissue (EHT) based on neonatal rat cardiomyocytes (CMs) cultivated with electrical field stimulation as an in vitro model to study cell injection. We injected (0.001, 0.01, and 0.1 million) and tracked (by qPCR and histology) undifferentiated yellow‐fluorescent protein transgenic mouse ESCs and Flk1 + /PDGFRα+ cardiac progenitor (CPs) cells, to investigate the effect of the cardiac environment on cell differentiation, as well as to test whether our in vitro model system could recapitulate the formation of teratoma‐like structures commonly observed upon in vivo ESC injection. By 8 days post‐injection, ESCs were spatially segregated from the cardiac cell population; however, ESC injection increased survival of CMs. The presence of ESCs blocked electrical conduction through the tissue, resulting in a 46% increase in the excitation threshold. Expression of mouse cardiac troponin I, was markedly increased in CP injected constructs compared to ESC injected constructs at all time points and cell doses tested. As early as 2 weeks, epithelial and ganglion‐like structures were observed in ESC injected constructs. By 4 weeks of ESC injection, teratoma‐like structures containing neural, epithelial, and connective tissue were observed in the constructs. Non‐cardiac structures were observed in the CP injected constructs only after extended culture (4 weeks) and only at high cell doses, suggesting that these cells require further enrichment or differentiation prior to transplantation. Our data indicate that the cardiac environment of host tissue and electrical field stimulation did not preferentially guide the differentiation of ESCs towards the cardiac lineage. In the same environment, injection of CP resulted in a more robust cardiac differentiation than injection of ESC. Our data demonstrate that the model‐system developed herein can be used to study the functional effects of candidate stem cells on the host myocardium, as well as to measure the residual activity of undifferentiated cells present in the mixture. Biotechnol. Bioeng. 2011; 108:704–719. © 2010 Wiley Periodicals, Inc.     

Overexpression of phosphoinositide-3-kinase class II alpha enhances mesenchymal stem cell survival in infarcted myocardium

The efficacy of mesenchymal stem cell (MSC) therapy for myocardial regeneration is limited by the poor survival of stem cells after transplantation into the infarcted heart. To improve the cell survival of MSCs in the infarcted heart, MSCs were genetically engineered to overexpress phosphoinositide-3-kinase class II alpha (PI3K-C2α). PI3K-C2α overexpression increased PI3K expression and the cell viability of MSCs. Furthermore, levels of survival-related phosphorylation were elevated in PI3K-C2α-MSCs. But, the level of apoptotic proteins downregulated and the number of PI-positive cells decreased in PI3K-C2α-MSCs compared to hypoxic MSCs. Nine rats per group had 1 × 10⁶ cells (20 μl PBS) transplanted after myocardial infarction. One week after transplantation, infarct size and area of fibrosis were reduced in the PI3K-C2α-MSC-transplanted group. The number of TUNEL positive cells declined, while the mean microvessel count per field was higher in the PI3K-C2α-MSC group than the MSC-injected group. Heart function was improved in the PI3K-C2α-MSCs group as assessed using a Millar catheter at 3 weeks after transplantation. These findings suggest that overexpression of PI3K-C2α in MSCs can assist cell survival and enhance myocardial regeneration.     

Delayed erythropoietin therapy reduces post-MI cardiac remodeling only at a dose that mobilizes endothelial progenitor cells

We examined the cardiac effects of chronic erythropoietin (EPO) therapy initiated 7 days after myocardial infarction (MI) in rats. A single high dose of EPO has been shown to reduce infarct size by preventing apoptosis when injected immediately after myocardial ischemia. The proangiogenic potential of EPO has also been reported, but the effects of chronic treatment with standard doses after MI are unknown. In this study, rats underwent coronary occlusion followed by reperfusion or a sham procedure. Infarcted rats were assigned to one of three treatment groups: 1) 0.75 microg/kg darbepoetin (MI+darb 0.75, n = 12); 2) 1.5 microg/kg darbepoetin (MI+darb 1.5, n = 12); 3) vehicle (MI+PBS, n = 16), once a week from day 7 postsurgery. Sham rats received the vehicle alone (n = 10). After 8 wk of treatment, the animals underwent echocardiography, left ventricular pressure-volume measurements, and peripheral blood endothelial progenitor cell (EPC) counting. MI size and capillary density in the border zone and the area at risk (AAR) were measured postmortem. The AAR was similar in the three MI groups. Compared with MI+PBS, the MI+darb 1.5 group showed a reduction in the MI-to-AAR ratio (20.8% vs. 38.7%; P < 0.05), as well as significantly reduced left ventricle dilatation and improved cardiac function. This reduction in post-MI remodeling was accompanied by increased capillary density (P < 0.05) and by a higher number of EPC (P < 0.05). Both darbepoetin doses increased the hematocrit, whereas MI+darb 0.75 did not increase EPC numbers or capillary density and had no functional effect. We found that chronic EPO treatment reduces MI size and improves cardiac function only at a dose that induces EPC mobilization in blood and that increases capillary density in the infarct border zone.     

In vitro cytotoxicity of unsaturated oligo[poly(ethylene glycol) fumarate] macromers and their cross-linked hydrogels

Currently, oligo[poly(ethylene glycol) fumarate] (OPF) hydrogels are being investigated as an injectable and biodegradable system for tissue engineering applications. In this study, cytotoxicity of each component of the OPF hydrogel formulation and the resulting cross-linked network was examined. Specifically, OPF synthesized with poly(ethylene glycol) (PEG) of different molecular weights (MW), the cross-linking agent [PEG-diacrylate (PEG-DA)], and the redox initiator pair [ammonium persulfate (APS) and ascorbic acid (AA)] were evaluated for cytotoxicity at 2 and 24 h using marrow stromal cells (MSCs) as model cells. The effect of leachable byproducts of OPF hydrogels on cytotoxicity was also investigated. Upon exposure to various concentrations of OPF for 2 h, greater than 50% of the MSCs were viable, regardless of OPF molecular weight or concentration in the media. After 24 h, the MSCs maintained more than 75% viability except for OPF concentrations higher than 25% (w/v). When examining the cross-linking agent, PEG-DA of higher MW (3400) demonstrated significantly higher viability compared to PEG-DA with MW 575 at all concentrations tested. Considering initiators, when MSCs were exposed to AA and APS, as well as the combination of AA and APS, higher viability was observed at lower concentrations. Once cross-linked, the leachable products from the OPF hydrogels had minimal adverse effects on the viability of MSCs (percentage of live cells was higher than 90% regardless of hydrogel types). The results suggest that, after optimization of cross-linking parameters, OPF-based hydrogels hold promise as novel injectable scaffolds or cell carriers in tissue engineering.     

Comparison of Human Induced Pluripotent Stem-Cell Derived Cardiomyocytes with Human Mesenchymal Stem Cells following Acute Myocardial Infarction

Introduction

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have recently been shown to express key cardiac proteins and improve in vivo cardiac function when administered following myocardial infarction. However, the efficacy of hiPSC-derived cell therapies, in direct comparison to current, well-established stem cell-based therapies, is yet to be elucidated. The goal of the current study was to compare the therapeutic efficacy of human mesenchymal stem cells (hMSCs) with hiPSC-CMs in mitigating myocardial infarction (MI).

Methods

Male athymic nude hyrats were subjected to permanent ligation of the left-anterior-descending (LAD) coronary artery to induce acute MI. Four experimental groups were studied: 1) control (non-MI), 2) MI, 3) hMSCs (MI+MSC), and 4) hiPSC-CMs (MI+hiPSC-derived cardiomyocytes). The hiPSC-CMs and hMSCs were labeled with superparamagnetic iron oxide (SPIO) in vitro to track the transplanted cells in the ischemic heart by high-field cardiac MRI. These cells were injected into the ischemic heart 30-min after LAD ligation. Four-weeks after MI, cardiac MRI was performed to track the transplanted cells in the infarct heart. Additionally, echocardiography (M-mode) was performed to evaluate the cardiac function. Immunohistological and western blot studies were performed to assess the cell tracking, engraftment and cardiac fibrosis in the infarct heart tissues.

Results

Echocardiography data showed a significantly improved cardiac function in the hiPSC-CMs and hMSCs groups, when compared to MI. Immunohistological studies showed expression of connexin-43, α-actinin and myosin heavy chain in engrafted hiPSC-CMs. Cardiac fibrosis was significantly decreased in hiPSC-CMs group when compared to hMSCs or MI groups. Overall, this study demonstrated improved cardiac function with decreased fibrosis with both hiPSC-CMs and hMSCs groups when compared with MI group.     

Modified hyaluronan hydrogels support the maintenance of mouse embryonic stem cells and human induced pluripotent stem cells

These studies provide evidence for the ability of a commercially available, defined, hyaluronan-gelatin hydrogel, HyStem-C?, to maintain both mouse embryonic stem cells (mESCs) and human induced pluripotent stem cells (hiPSCs) in culture while retaining their growth and pluripotent characteristics. Growth curve and doubling time analysis show that mESCs and hiPSCs grow at similar rates on HyStem-C? hydrogels and mouse embryonic fibroblasts and Matrigel?, respectively. Immunocytochemistry, flow cytometry, gene expression and karyotyping reveal that both human and murine pluripotent cells retain a high level of pluripotency on the hydrogels after multiple passages. The addition of fibronectin to HyStem-C? enabled the attachment of hiPSCs in a xeno-free, fully defined medium.