Functionally Improved Mesenchymal Stem Cells to Better Treat Myocardial Infarction

Myocardial infarction (MI) is one of the leading causes of death worldwide. Mesenchymal stem cell (MSC) transplantation is considered a promising approach and has made significant progress in preclinical studies and clinical trials for treating MI. However, hurdles including poor survival, retention, homing, and differentiation capacity largely limit the therapeutic effect of transplanted MSCs. Many strategies such as preconditioning, genetic modification, cotransplantation with bioactive factors, and tissue engineering were developed to improve the survival and function of MSCs. On the other hand, optimizing the hostile transplantation microenvironment of the host myocardium is also of importance. Here, we review the modifications of MSCs as well as the host myocardium to improve the efficacy of MSC-based therapy against MI.

Cardiac cell–integrated microneedle patch for treating myocardial infarction

We engineered a microneedle patch integrated with cardiac stromal cells (MN-CSCs) for therapeutic heart regeneration after acute myocardial infarction (MI). To perform cell-based heart regeneration, cells are currently delivered to the heart via direct muscle injection, intravascular infusion, or transplantation of epicardial patches. The first two approaches suffer from poor cell retention, while epicardial patches integrate slowly with host myocardium. Here, we used polymeric MNs to create “channels” between host myocardium and therapeutic CSCs. These channels allow regenerative factors secreted by CSCs to be released into the injured myocardium to promote heart repair. In the rat MI model study, the application of the MN-CSC patch effectively augmented cardiac functions and enhanced angiomyogenesis. In the porcine MI model study, MN-CSC patch application was nontoxic and resulted in cardiac function protection. The MN system represents an innovative approach delivering therapeutic cells for heart regeneration.

11β-HSD1 suppresses cardiac fibroblast CXCL2, CXCL5 and neutrophil recruitment to the heart post MI

We have previously demonstrated that neutrophil recruitment to the heart following myocardial infarction (MI) is enhanced in mice lacking 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) that regenerates active glucocorticoid within cells from intrinsically inert metabolites. The present study aimed to identify the mechanism of regulation. In a mouse model of MI, neutrophil mobilization to blood and recruitment to the heart were higher in 11β-HSD1-deficient (Hsd11b1−/−) relative to wild-type (WT) mice, despite similar initial injury and circulating glucocorticoid. In bone marrow chimeric mice, neutrophil mobilization was increased when 11β-HSD1 was absent from host cells, but not when absent from donor bone marrow-derived cells. Consistent with a role for 11β-HSD1 in ‘host’ myocardium, gene expression of a subset of neutrophil chemoattractants, including the chemokines Cxcl2 and Cxcl5, was selectively increased in the myocardium of Hsd11b1−/− mice relative to WT. SM22α-Cre directed disruption of Hsd11b1 in smooth muscle and cardiomyocytes had no effect on neutrophil recruitment. Expression of Cxcl2 and Cxcl5 was elevated in fibroblast fractions isolated from hearts of Hsd11b1−/− mice post MI and provision of either corticosterone or of the 11β-HSD1 substrate, 11-dehydrocorticosterone, to cultured murine cardiac fibroblasts suppressed IL-1α-induced expression of Cxcl2 and Cxcl5. These data identify suppression of CXCL2 and CXCL5 chemoattractant expression by 11β-HSD1 as a novel mechanism with potential for regulation of neutrophil recruitment to the injured myocardium, and cardiac fibroblasts as a key site for intracellular glucocorticoid regeneration during acute inflammation following myocardial injury.

Intramyocardially Transplanted Neonatal Cardiomyocytes (NCMs) Show Structural and Electrophysiological Maturation and Integration and Dose-Dependently Stabilize Function of Infarcted Rat Hearts

Cardiac cell replacement therapy is a promising therapy to improve cardiac function in heart failure. Persistence, structural and functional maturation, and integration of transplanted cardiomyocytes into recipients' hearts are crucial for a safe and efficient replacement of lost cells. We studied histology, electrophysiology, and quantity of intramyocardially transplanted rat neonatal cardiomyocytes (NCMs) and performed a detailed functional study with repeated invasive (pressure–volume catheter) and noninvasive (echocardiography) analyses of infarcted female rat hearts including pharmacological stress before and 3 weeks after intramyocardial injection of 5 × 106 (low NCM) or 25 × 106 (high NCM) syngeneic male NCMs or medium as placebo (Ctrl). Quantitative real-time polymerase chain reaction (PCR) for Y-chromosome confirmed a fivefold higher persisting male cell number in high NCM versus low NCM after 3 weeks. Sharp electrode measurements within viable slices of recipient hearts demonstrated that transplanted NCMs integrate into host myocardium and mature to an almost adult phenotype, which might be facilitated through gap junctions between host myocardium and transplanted NCMs as indicated by connexin43 in histology. Ejection fraction of recipient hearts was severely impaired after ligation of left anterior descending (LAD; pressure–volume catheter: 39.2 ± 3.6%, echocardiography: 39.9 ± 1.4%). Repeated analyses revealed a significant further decline within 3 weeks in Ctrl and a dose-dependent stabilization in cell-treated groups. Consistently, stabilized cardiac function/morphology in cell-treated groups was seen in stroke volume, cardiac output, ventricle length, and wall thickness. Our findings confirm that cardiac cell replacement is a promising therapy for ischemic heart disease since immature cardiomyocytes persist, integrate, and mature after intramyocardial transplantation, and they dose-dependently stabilize cardiac function after myocardial infarction.

Abstract 123: Optical Mapping of Host and Human Embryonic Stem Cell-Derived Cardiomyocyte Graft Electrical Activity in Injured Hearts

Human embryonic stem cell-derived cardiomyocytes (hESC-CMs) show tremendous promise for cardiac repair, but more information is required as to their electrical behavior in vivo. hESC-CMs expressing the protein calcium sensor GCaMP3 provide a graft autonomous reporter of activation, which we have used to show hESC-CM grafts can couple with host myocardium in injured hearts. When we sought to assess host-graft electrical interactions by optical voltage mapping, we found the commonly used lipophilic voltage dyes RH237 and di-4-ANEPPS label host but not graft tissue. We hypothesized the water-soluble voltage dye di-2-ANEPEQ could overcome this limitation and efficiently label both host and graft. After confirming good spectral separation of GCaMP3 and di-2-ANEPEQ signals by spectrofluorimetry and confocal spectral imaging, we transplanted 1x10^8 GCaMP3+ hESC-CMs into guinea pig hearts (n=6) at 4 weeks following cardiac injury and then imaged engrafted hearts at 2 weeks post-transplantation with a dual-channel CCD-based system. We found a differential time-course of di-2-ANEPEQ labeling between host and graft tissues, with stable optical action potentials (APs) obtained in host and graft tissue after ~4 and ~13 minutes of dye perfusion, respectively. This differential labeling kinetics, which was also observed on washout, presumably reflects sluggish graft perfusion and provides another tool for distinguishing host and graft signals. No regions of 1:1 host-graft coupling were identified, and graft tissue had spontaneous rates from 0.1-2 Hz and long optical AP durations from 500-1090 ms. Activation maps based on di-2-ANEPEQ and GCaMP3 signals indicated relatively slow conduction velocities in graft tissue, as well as patterns of propagation that commonly occurred along a vector distinct from that in host tissue. These imaging studies reveal multiple potentially pro-arrhythmic properties in hESC-CM graft tissue including slow propagation, ultralong AP duration, as well as aberrant patterns of activation that can vary from beat to beat. We conclude the electrical behavior of both graft and host myocardium can be reliably assessed by the simultaneous imaging of a graft-autonomous fluorescent reporter of activation and a water-soluble voltage dye.

Xenogenic cardiomyocytes transplantation for the treatment of curing acute myocardial infarction

The autogenic cardiomyocytes transplantation presents numerous challenges in clinical application, such as the difficulty to obtain the autogenic cells, etc. Therefore, it is necessary to investigate allogenic or xenogenic cardiomyocytes transplantation. In this study, the experimental rabbits with acute infarcted myocardium were randomly divided into 3 groups: the 7-day cultured cardiomyocytes group, the 2-day cultured cardiomyocytes group and the control group. Neonate rat cardiomyocytes were labeled by DAPI and then injected into the acute infarcted myocardium of rabbits. After transplantation, results showed that, compared to the control group, the survival number of grafted cardiomyocytes in the cultured group is significantly larger (P < 0.05), with the implanted cardiomyocytes parallel to the host myocardium in an aligning direction. However, compared to the control group, the ventricular wall of the two experimental groups is thicker and the condition of myocardial fibrosis is better, especially to 7-day cultured cardiomyocytes group. These results suggested that the transplantation of xenogenic cardiomyocytes into curing acute ischemic heart of animal model is possible.