Cardiac stem cell therapy: stemness or commitment?

Recent advances in mesenchymal stem cell therapy for myocardial infarction

Myocardial infarction refers to the ischemic necrosis of myocardium, characterized by a sharp reduction or interruption of blood flow in the coronary arteries due to the coronary artery occlusion, resulting in severe and prolonged ischemia in the corresponding myocardium and ultimately leading to ischemic necrosis of the myocardium. Given its high risk, it is considered as one of the most serious health threats today. In current clinical practice, multiple approaches have been explored to diminish myocardial oxygen consumption and alleviate symptoms, but notable success remains elusive. Accumulated clinical evidence has showed that the implantation of mesenchymal stem cell for treating myocardial infarction is both effective and safe. Nevertheless, there persists controversy and variability regarding the standardizing MSC transplantation protocols, optimizing dosage, and determining the most effective routes of administration. Addressing these remaining issues will pave the way of integration of MSCs as a feasible mainstream cardiac treatment.

Bisphosphonate of Zoledronate Has Antiapoptotic Effect on Hypoxia/Reoxygenation Injury in Human Embryonic Stem Cell-Derived Cardiomyocytes Through Trk Signaling Pathway

In this work, we investigated the in vitro and in vivo functions of bisphosphonate of zoledronate (Zd) in hypoxia/reoxygenation (H/R) injured human embryonic stem cell-derived cardiomyocytes (hES-CMs). In the in vitro setting, the effects of Zd on hES-CM survival and differentiation were examined. We found that low and medium concentrations (<2 µm) of Zd did not induce cell death of hES-CMs. 0.5 µm Zd protected H/R-induced hES-CM apoptosis but did not affect key differentiation proteins, including hcTnl, PECM-1 Cnx43 and Pan-Cadherin. In addition, Zd-induced TrkA/B phosphorylation and promoted VEGF to counter the apoptotic effect of H/R injury. In the in vivo animal model of myocardial infarction, Zd treatment promoted the survival of hES-CMs by inducing PECAM1 and hcTnl. Thus, we concluded that Zd protected H/R-induced hES-CM apoptosis in vitro and promoted hES-CM survival in vivo. These data may facilitate the development of human embryonic stem cells into clinical applications for patients with ischemic heart disease.

Exosomal Expression of CXCR4 Targets Cardioprotective Vesicles to Myocardial Infarction and Improves Outcome after Systemic Administration

Cell therapy has been evaluated to enhance heart function after injury. Delivered cells mostly act via paracrine mechanisms, including secreted growth factors, cytokines, and vesicles, such as exosomes (Exo). Intramyocardial injection of cardiac-resident progenitor cells (CPC)-derived Exo reduced scarring and improved cardiac function after myocardial infarction in rats. Here, we explore a clinically relevant approach to enhance the homing process to cardiomyocytes (CM), which is crucial for therapeutic efficacy upon systemic delivery of Exo. By overexpressing exosomal CXCR4, we increased the efficacy of plasmatic injection of cardioprotective Exo-CPC by increasing their bioavailability to ischemic hearts. Intravenous injection of Exo^CXCR4 significantly reduced infarct size and improved left ventricle ejection fraction at 4 weeks compared to Exo^CTRL (p < 0.01). Hemodynamic measurements showed that Exo^CXCR4 improved dp/dt min, as compared to Exo^CTRL and PBS group. In vitro, Exo^CXCR4 was more bioactive than Exo^CTRL in preventing CM death. This in vitro effect was independent from SDF-1α, as shown by using AMD3100 as specific CXCR4 antagonist. We showed, for the first time, that systemic administration of Exo derived from CXCR4-overexpressing CPC improves heart function in a rat model of ischemia reperfusion injury These data represent a substantial step toward clinical application of Exo-based therapeutics in cardiovascular disease.

iPSC-derived human cardiac progenitor cells improve ventricular remodelling via angiogenesis and interstitial networking of infarcted myocardium

We investigate the effects of myocardial transplantation of human induced pluripotent stem cell (iPSC)‐derived progenitors and cardiomyocytes into acutely infarcted myocardium in severe combined immune deficiency mice. A total of 2 × 10⁵ progenitors, cardiomyocytes or cell‐free saline were injected into peri‐infarcted anterior free wall. Sham‐operated animals received no injection. Myocardial function was assessed at 2‐week and 4‐week post‐infarction by using echocardiography and pressure‐volume catheterization. Early myocardial remodelling was observed at 2‐week with echocardiography derived stroke volume (SV) in saline (20.45 ± 7.36 μl, P < 0.05) and cardiomyocyte (19.52 ± 3.97 μl, P < 0.05) groups, but not in progenitor group (25.65 ± 3.61 μl), significantly deteriorated as compared to sham control group (28.41 ± 4.41 μl). Consistently, pressure–volume haemodynamic measurements showed worsening chamber dilation in saline (EDV: 23.24 ± 5.01 μl, P < 0.05; ESV: 17.08 ± 5.82 μl, P < 0.05) and cardiomyocyte (EDV: 26.45 ± 5.69 μl, P < 0.05; ESV: 18.03 ± 6.58 μl, P < 0.05) groups by 4‐week post‐infarction as compared to control (EDV: 15.26 ± 2.96 μl; ESV: 8.41 ± 2.94 μl). In contrast, cardiac progenitors (EDV: 20.09 ± 7.76 μl; ESV: 13.98 ± 6.74 μl) persistently protected chamber geometry against negative cardiac remodelling. Similarly, as compared to sham control (54.64 ± 11.37%), LV ejection fraction was preserved in progenitor group from 2‐(38.68 ± 7.34%) to 4‐week (39.56 ± 13.26%) while cardiomyocyte (36.52 ± 11.39%, P < 0.05) and saline (35.34 ± 11.86%, P < 0.05) groups deteriorated early at 2‐week. Improvements of myocardial function in the progenitor group corresponded to increased vascularization (16.12 ± 1.49/mm² to 25.48 ± 2.08/mm² myocardial tissue, P < 0.05) and coincided with augmented networking of cardiac telocytes in the interstitial space of infarcted zone.

Cardiac-Derived Extracellular Matrix Enhances Cardiogenic Properties of Human Cardiac Progenitor Cells

The use of biomaterials has been demonstrated as a viable strategy to promote cell survival and cardiac repair. However, limitations on combinational cell-biomaterial therapies exist, as cellular behavior is influenced by the microenvironment and physical characteristics of the material. Among the different scaffolds employed for cardiac tissue engineering, a myocardial matrix hydrogel has been shown to promote cardiogenesis in murine cardiac progenitor cells (mCPCs) in vitro. In this study, we investigated the influence of the hydrogel on Sca-1-like human fetal and adult CPCs (fCPCs and aCPCs) when encapsulated in three-dimensional (3D) material in vitro. fCPCs encapsulated in the myocardial matrix showed an increase in the gene expression level of cardiac markers GATA-4 and MLC2v and the vascular marker vascular endothelial growth factor receptor 2 (VEGFR2) after 4 days in culture, and a significant increase in GATA-4 up to 1 week. Increased gene expression levels of Nkx2.5, MEF2c, VEGFR2, and CD31 were also observed when aCPCs were cultured in the matrix compared to collagen. Cell survival was sustained in both hydrogels up to 1 week in culture with the myocardial matrix capable of enhancing the expression of the proliferation marker Ki-67 after 4 days in culture. When encapsulated CPCs were treated with H₂O₂, an improved survival of the cells cultured in the myocardial matrix was observed. Finally, we evaluated the use of the myocardial matrix as hydrogel for in vivo cell transplantation and demonstrated that the gelation properties of the hydrogel are not influenced by the cells. In summary, we showed that the myocardial matrix hydrogel promotes human CPC cardiogenic potential, proliferation, and survival and is a favorable hydrogel for 3D in vitro culture. Furthermore, we demonstrated the in vivo applicability of the matrix as a potential vehicle for cell transplantation.

iPSC-derived human mesenchymal stem cells improve myocardial strain of infarcted myocardium

We investigated global and regional effects of myocardial transplantation of human induced pluripotent stem cell (iPSC)-derived mesenchymal stem cells (iMSCs) in infarcted myocardium. Acute myocardial infarction (MI) was induced by ligation of left coronary artery of severe combined immunodeficient mice before 2 × 10⁵ iMSCs or cell-free saline were injected into peri-infarcted anterior free wall. Sham-operated animals received no injection. Global and regional myocardial function was assessed serially at 1-week and 8-week by segmental strain analysis by using two dimensional (2D) speckle tracking echocardiography. Early myocardial remodelling was observed at 1-week and persisted to 8-week with global contractility of ejection fraction and fractional area change in saline- (32.96 ± 14.23%; 21.50 ± 10.07%) and iMSC-injected (32.95 ± 10.31%; 21.00 ± 7.11%) groups significantly depressed as compared to sham control (51.17 ± 11.69%, P < 0.05; 34.86 ± 9.82%, P < 0.05). However, myocardial dilatation was observed in saline-injected animals (4.40 ± 0.62 mm, P < 0.05), but not iMSCs (4.29 ± 0.57 mm), when compared to sham control (3.74 ± 0.32 mm). Furthermore, strain analysis showed significant improved basal anterior wall strain (28.86 ± 8.16%, P < 0.05) in the iMSC group, but not saline-injected (15.81 ± 13.92%), when compared to sham control (22.18 ± 4.13%). This was corroborated by multi-segments deterioration of radial strain only in saline-injected (21.50 ± 5.31%, P < 0.05), but not iMSC (25.67 ± 12.53%), when compared to sham control (34.88 ± 5.77%). Improvements of the myocardial strain coincided with the presence of interconnecting telocytes in interstitial space of the infarcted anterior segment of the heart. Our results show that localized injection of iMSCs alleviates ventricular remodelling, sustains global and regional myocardial strain by paracrine-driven effect on neoangiogenesis and myocardial deformation/compliance via parenchymal and interstitial cell interactions in the infarcted myocardium.

A multistep procedure to prepare pre-vascularized cardiac tissue constructs using adult stem sells, dynamic cell cultures, and porous scaffolds

The vascularization of tissue engineered products represents a key issue in regenerative medicine which needs to be addressed before the translation of these protocols to the bedside can be foreseen. Here we propose a multistep procedure to prepare pre-vascularized three-dimensional (3D) cardiac bio-substitutes using dynamic cell cultures and highly porous biocompatible gelatin scaffolds. The strategy adopted exploits the peculiar differentiation potential of two distinct subsets of adult stem cells to obtain human vascularized 3D cardiac tissues. In the first step of the procedure, human mesenchymal stem cells (hMSCs) are seeded onto gelatin scaffolds to provide interconnected vessel-like structures, while human cardiomyocyte progenitor cells (hCMPCs) are stimulated in vitro to obtain their commitment toward the cardiac phenotype. The use of a modular bioreactor allows the perfusion of the whole scaffold, providing superior performance in terms of cardiac tissue maturation and cell survival. Both the cell culture on natural-derived polymers and the continuous medium perfusion of the scaffold led to the formation of a densely packaged proto-tissue composed of vascular-like and cardiac-like cells, which might complete maturation process and interconnect with native tissue upon in vivo implantation. In conclusion, the data obtained through the approach here proposed highlight the importance to provide stem cells with complementary signals in vitro able to resemble the complexity of cardiac microenvironment.