A fibrin-supported myocardial organ culture for isolation of cardiac stem cells via the recapitulation of cardiac homeostasis

Tanshinone‑IIA inhibits myocardial infarct via decreasing of the mitochondrial apoptotic signaling pathway in myocardiocytes

Myocardial ischemia triggers an inflammatory reaction and oxidative stress that increases apoptosis of myocardiocytes. It has been evidenced that tanshinone‑IIA (Tan‑IIA) protects against heart failure post‑myocardial infarction via inhibition of the apoptotic pathway. The purpose of the present study was to investigate the therapeutic effect of Tan‑IIA in a rat model of myocardial ischemia, and explore the possible mechanism of Tan‑IIA in myocardiocytes. The rat model of myocardial ischemia was established by left anterior descending coronary artery and rats received treatment with either Tan‑IIA (10 mg/kg) or PBS for 20 days continuously. The cardiac function in the experimental rat model was detected using the Sequoia 512 echocardiography system on day 21. The cell viability of myocardiocytes was assessed by CCK‑8 assay. Apoptosis of myocardiocytes and myocardial tissue was evaluated by TUNEL assay. The infarct size of the myocardial ischemia rat was determined through 2,3,5‑triphenyltetrazolium chloride (TTC) and Evan blue double staining assay. The expression levels of apoptotic factors were assessed by immunohistochemistry, western blotting and immunofluorescence. The results demonstrated that Tan‑IIA reduced myocardial infarct size and improved the myocardial function in myocardial ischemia rats. Compared with PBS, Tan‑IIA treatment decreased myocardial tissue apoptosis and the expression levels of caspase‑3, Cyto c and Apaf‑1 in myocardial tissue. Tan‑IIA increased the viability of impaired myocardiocytes, inhibited apoptosis of impaired myocardiocytes and increased Bcl‑2 and Bak expression in myocardiocytes. In addition, Tan‑IIA increased Bim and CHOP, decreased TBARS, ROS and H2O2 production, decreased ATF4 and IRE1α expression, and reduced intracellular calcium and oxidative stress in myocardiocytes. Furthermore, caspase‑3 overexpression blocked Tan‑IIA‑decreased apoptosis of myocardiocytes. In conclusion, the data in the present study indicated that Tan‑IIA improved myocardial infarct and apoptosis via the endoplasmic reticulum stress‑dependent pathway and mitochondrial apoptotic signaling pathway.

Intramyocardial delivery of human cardiac stem cell spheroids with enhanced cell engraftment ability and cardiomyogenic potential for myocardial infarct repair

Strategies for stem cell-based cardiac regeneration and repair are key issues for the ischemic heart disease (IHD) patients with chronic complications related to ischemic necrosis. Cardiac stem cells (CSCs) have demonstrated high therapeutic efficacy for IHD treatment owing to their specific cardiac-lineage commitment. The therapeutic potential of CSCs could be further enhanced by designing a cellular spheroid formulation. The spheroid culture condition of CSCs was optimized to ensure regulated size and minimal core necrosis in the spheroids. The CSC spheroids revealed mRNA profiles of the factors related to cardiac regeneration, angiogenesis, anti-inflammatory, and cardiomyocyte differentiation with a higher expression level than the CSCs. Intramyocardially delivered CSC spheroids in the rat IHD model resulted in a significant increase in retention rate by 1.82-fold (day 3) and 1.98-fold (day 14) compared to CSCs. Endothelial cell differentiation and neovascularization of the engrafted CSC spheroids were noted in the infarcted myocardium. CSC spheroids significantly promoted cardiac regeneration: i.e., decreased infarction and fibrotic area (11.22% and 4.18%) and increased left ventricle thickness (0.62 mm) compared to the untreated group. Cardiac performance was also improved by 2.04-fold and 1.44-fold increase in the ejection fraction and fractional shortening, respectively. Intramyocardial administration of CSC spheroids might serve as an advanced therapeutic modality with enhanced cell engraftment and regenerative abilities for cardiac repair after myocardial infarction.

Biodegradable Nanopolymers in Cardiac Tissue Engineering: From Concept Towards Nanomedicine

Cardiovascular diseases are the number one cause of heart failure and death in the world, and the transplantation of the heart is an effective and viable choice for treatment despite presenting many disadvantages (most notably, transplant heart availability). To overcome this problem, cardiac tissue engineering is considered a promising approach by using implantable artificial blood vessels, injectable gels, and cardiac patches (to name a few) made from biodegradable polymers. Biodegradable polymers are classified into two main categories: natural and synthetic polymers. Natural biodegradable polymers have some distinct advantages such as biodegradability, abundant availability, and renewability but have some significant drawbacks such as rapid degradation, insufficient electrical conductivity, immunological reaction, and poor mechanical properties for cardiac tissue engineering. Synthetic biodegradable polymers have some advantages such as strong mechanical properties, controlled structure, great processing flexibility, and usually no immunological concerns; however, they have some drawbacks such as a lack of cell attachment and possible low biocompatibility. Some applications have combined the best of both and exciting new natural/synthetic composites have been utilized. Recently, the use of nanostructured polymers and polymer nanocomposites has revolutionized the field of cardiac tissue engineering due to their enhanced mechanical, electrical, and surface properties promoting tissue growth. In this review, recent research on the use of biodegradable natural/synthetic nanocomposite polymers in cardiac tissue engineering is presented with forward looking thoughts provided for what is needed for the field to mature.

Characterization of human cardiac mesenchymal stromal cells and their extracellular vesicles comparing with human bone marrow derived mesenchymal stem cells

Cardiac regeneration with adult stem-cell (ASC) therapy is a promising field to address advanced cardiovascular diseases. In addition, extracellular vesicles (EVs) from ASCs have been implicated in acting as paracrine factors to improve cardiac functions in ASC therapy. In our work, we isolated human cardiac mesenchymal stromal cells (h-CMSCs) by means of three-dimensional organ culture (3D culture) during ex vivo expansion of cardiac tissue, to compare the functional efficacy with human bone-marrow derived mesenchymal stem cells (h-BM-MSCs), one of the actively studied ASCs. We characterized the h-CMSCs as CD90^low, c-kit^negative, CD105^positive phenotype and these cells express NANOG, SOX2, and GATA4. To identify the more effective type of EVs for angiogenesis among the different sources of ASCs, we isolated EVs which were derived from CMSCs with either normoxic or hypoxic condition and BM-MSCs. Our in vitro tube-formation results demonstrated that the angiogenic effects of EVs from hypoxia-treated CMSCs (CMSC-Hpx EVs) were greater than the well-known effects of EVs from BM-MSCs (BM-MSC EVs), and these were even comparable to human vascular endothelial growth factor (hVEGF), a potent angiogenic factor. Therefore, we present here that CD90^lowc-kit^negativeCD105^positive CMSCs under hypoxic conditions secrete functionally superior EVs for in vitro angiogenesis. Our findings will allow more insights on understanding myocardial repair.

Engineered extracellular microenvironment with a tunable mechanical property for controlling cell behavior and cardiomyogenic fate of cardiac stem cells

Endogenous cardiac stem cells (CSCs) are known to play a certain role in the myocardial homeostasis of the adult heart. The extracellular matrix (ECM) surrounding CSCs provides mechanical signals to regulate a variety of cell behaviors, yet the impact in the adult heart of these mechanical properties of ECM on CSC renewal and fate decisions is mostly unknown. To elucidate CSC mechanoresponses at the individual cell and myocardial level, we used the sol-to-gel transitional gelatin-poly(ethylene glycol)-tyramine (GPT) hydrogel with a tunable mechanical property to construct a three-dimensional (3D) matrix for culturing native myocardium and CSCs. The elastic modulus of the GPT hydrogel was controlled by adjusting cross-linking density using hydrogen peroxide. The GPT hydrogel showed an ability to transduce integrin-mediated signals into the myocardium and to permit myocardial homeostatic processes in vitro, including CSC migration and proliferation into the hydrogel from the myocardium. Decreasing the elastic modulus of the hydrogel resulted in upregulation of phosphorylated integrin-mediated signaling molecules in CSCs, which were associated with significant increases in cell spreading, migration, and proliferation of CSCs in a modulus-dependent manner. However, increasing the elastic modulus of hydrogel induced the arrest of cell growth but led to upregulation of cardiomyocyte-associated mRNAs in CSCs. This work demonstrates that tunable 3D-engineered microenvironments created by GPT hydrogel are able to control CSC behavior and to direct cardiomyogenic fate. Our system may also be appropriate for studying the mechanoresponse of CSCs in a 3D context as well as for developing therapeutic strategies for in situ myocardial regeneration.

STATEMENT OF SIGNIFICANCE

The extracellular matrix (ECM) provides a physical framework of myocardial niches in which endogenous cardiac stem cells (CSCs) reside, renew, differentiate, and replace cardiac cells. Interactions between ECM and CSCs might be critical for the maintenance of myocardial homeostasis in the adult heart. Yet most studies done so far have used irrelevant cell types and have been performed at the individual cell level, none able to reflect the in vivo situation. By the use of a chemically defined hydrogel to create a tunable 3D microenvironment, we succeeded in controlling CSC behavior at the myocardial and individual cell level and directing the cardiomyogenic fate. Our work may provide insight into the design of biomaterials for in situ myocardial regeneration as well as for tissue engineering.

How Biomaterials Can Influence Various Cell Types in the Repair and Regeneration of the Heart after Myocardial Infarction

The healthy heart comprises many different cell types that work together to preserve optimal function. However, in a diseased heart the function of one or more cell types is compromised which can lead to many adverse events, one of which is myocardial infarction (MI). Immediately after MI, the cardiac environment is characterized by excessive cardiomyocyte death and inflammatory signals leading to the recruitment of macrophages to clear the debris. Proliferating fibroblasts then invade, and a collagenous scar is formed to prevent rupture. Better functional restoration of the heart is not achieved due to the limited regenerative capacity of cardiac tissue. To address this, biomaterial therapy is being investigated as an approach to improve regeneration in the infarcted heart, as they can possess the potential to control cell function in the infarct environment and limit the adverse compensatory changes that occur post-MI. Over the past decade, there has been considerable research into the development of biomaterials for cardiac regeneration post-MI; and various effects have been observed on different cell types depending on the biomaterial that is applied. Biomaterial treatment has been shown to enhance survival, improve function, promote proliferation, and guide the mobilization and recruitment of different cells in the post-MI heart. This review will provide a summary on the biomaterials developed to enhance cardiac regeneration and remodeling post-MI with a focus on how they control macrophages, cardiomyocytes, fibroblasts, and endothelial cells. A better understanding of how a biomaterial interacts with the different cell types in the heart may lead to the development of a more optimized biomaterial therapy for cardiac regeneration.

Intracellular transduction of TAT-Hsp27 fusion protein enhancing cell survival and regeneration capacity of cardiac stem cells in acute myocardial infarction

Myocardial infarction (MI) results in the substantial loss of functional cardiomyocytes, which frequently leads to intractable heart disorders. Cardiac stem cells (CSCs) that retain the capacity to replace all cardiac cells might be a promising strategy for providing a source of new functional cardiomyocytes; however, the poor survival and engraftment of transplanted CSCs in the hostile environment of MI critically mitigate their therapeutic benefits. To capitalize their therapeutic potential, an ex vivo strategy in which CSCs were introduced to the recombinant heat shock protein 27 (Hsp27) through a TAT protein transduction domain for increasing the viability and engraftment in the infarcted myocardium was designed. A recombinant TAT fused Hsp27 (TAT-Hsp27) was able to enter CSCs in a dose-dependent manner. CSCs transduced with TAT-Hsp27 expressed not only endogenous Hsp27 but externally introduced Hsp27, resulting in substantial increase of their anti-oxidative and anti-apoptotic properties via suppressing reactive oxygen species production, the MAPKs signaling pathway, and caspase activation. TAT-Hsp27 enabled CSCs to be protected from apoptotic- and hypoxic-induced cell death during in vitro cardiomyogenic differentiation. In vivo studies demonstrated that CSCs transduced TAT-Hsp27 significantly increased the survival and engraftment in the acutely infarcted myocardium, which is closely related to caspase activity suppression. Finally, CSCs transduced TAT-Hsp27 improved cardiac function and attenuated cardiac remodeling in comparison with non-transduced CSCs. Overall, our approach, which is based on the ex vivo intracellular transduction of TAT-Hsp27 into CSCs before myocardial delivery, might be effective in treating MI.