Biomaterial strategies to improve the efficacy of bone marrow cell therapy for myocardial infarction

VE-cadherin-based matrix promoting the self-reconstruction of pro-vascularization microenvironments and endothelial differentiation of human mesenchymal stem cells

Regulating the secretion and endothelial differentiation of human mesenchymal stem cells (hMSCs) plays an important role in the vascularization in tissue engineering and regenerative medicine. In this study, a recombinant cadherin fusion protein consisting of a human vascular endothelial-cadherin extracellular domain and immunoglobulin IgG Fc region (hVE-cad-Fc) was developed as a bioartificial matrix for modulating hMSCs. The hVE-cad-Fc matrix significantly enhanced the secretion of angiogenic factors, activated the VE-cadherin-VEGFR2/FAK-AKT/PI3K signaling pathway in hMSCs, and promoted the endothelial differentiation of hMSCs even without extra VEGF. Furthermore, the hVE-cad-Fc matrix was applied for the surface modification of a poly (lactic-co-glycolic acid) (PLGA) porous scaffold, which significantly improved the hemocompatibility and vascularization of the PLGA scaffold in vivo. These results revealed that the hVE-cad-Fc matrix should be a superior bioartificial ECM for remodeling the pro-vascularization extracellular microenvironment by regulating the secretion of hMSCs, and showed great potential for the vascularization in tissue engineering.

An Injectable Oxygen Release System to Augment Cell Survival and Promote Cardiac Repair Following Myocardial Infarction

Oxygen deficiency after myocardial infarction (MI) leads to massive cardiac cell death. Protection of cardiac cells and promotion of cardiac repair are key therapeutic goals. These goals may be achieved by re-introducing oxygen into the infarcted area. Yet current systemic oxygen delivery approaches cannot efficiently diffuse oxygen into the infarcted area that has extremely low blood flow. In this work, we developed a new oxygen delivery system that can be delivered specifically to the infarcted tissue, and continuously release oxygen to protect the cardiac cells. The system was based on a thermosensitive, injectable and fast gelation hydrogel, and oxygen releasing microspheres. The fast gelation hydrogel was used to increase microsphere retention in the heart tissue. The system was able to continuously release oxygen for 4 weeks. The released oxygen significantly increased survival of cardiac cells under the hypoxic condition (1% O₂) mimicking that of the infarcted hearts. It also reduced myofibroblast formation under hypoxic condition (1% O₂). After implanting into infarcted hearts for 4 weeks, the released oxygen significantly augmented cell survival, decreased macrophage density, reduced collagen deposition and myofibroblast density, and stimulated tissue angiogenesis, leading to a significant increase in cardiac function.

Bone marrow CD34+ cell subset under induction of moderate stiffness of extracellular matrix after myocardial infarction facilitated endothelial lineage commitment in vitro

BACKGROUND

The stiffness of the myocardial extracellular matrix (ECM) and the transplanted cell type are vitally important in promoting angiogenesis. However, the combined effect of the two factors remains uncertain. The purpose of this study is to investigate in vitro the combined effect of myocardial ECM stiffness postinfarction with a bone marrow-derived cell subset expressing or not expressing CD34 on endothelial lineage commitment.

METHODS

Myocardial stiffness of the infarct zone was determined in mice at 1 h, 24 h, 7 days, 14 days, and 28 days after coronary artery ligation. Polyacrylamide (PA) gel substrates of different stiffnesses were prepared to mechanically mimic the myocardial ECM after infarction. Mouse bone marrow-derived CD34⁺ and CD34^- cells were seeded on the flexible PA gels. The double-positive expression for DiI-acetylated low-density lipoprotein (acLDL) uptake and fluorescein isothiocyanate-Ulex europaeus agglutinin-1 (FITC-UEA-1) binding, the endothelial lineage antigens CD31, von Willebrand factor (vWF), Flk-1, and VE-cadherin, as well as cytoskeleton were measured by immunofluorescent staining on day 7. Cell apoptosis was evaluated by both immunofluorescent staining and flow cytometry at 24 h after culture.

RESULTS

We found that the numbers of the CD34⁺ cell subset adherent to the flexible substrates (4-72 kPa) was much larger than that of the CD34^- subset. More double-positive cells for DiI-acLDL uptake/FITC-UEA-1 binding were seen on the 42-kPa (moderately stiff) substrate, corresponding to the stiffness of myocardial ECM at 7-14 days postinfarction, compared with those on substrates of other stiffnesses. Similarly, the moderately stiff substrate showed benefits in promoting the positive expressions of the endothelial lineage markers CD31, vWF, Flk-1, and VE-cadherin. In addition, the cytoskeleton F-actin network within CD34⁺ cells was organized more significantly at the leading edge of the adherent cells on the moderately stiff (42 kPa) or stiff (72 kPa) substrates as compared with those on the soft (4 kPa and 15 kPa) substrates. Moreover, the moderately stiff or stiff substrates showed a lower percentage of cell apoptosis than the soft substrates.

CONCLUSIONS

Infarcted myocardium-like ECM of moderate stiffness (42 kPa) more beneficially regulated the endothelial lineage commitment of a bone marrow-derived CD34⁺ subset. Thus, the combination of a CD34⁺ subset with a "suitable" ECM stiffness might be an optimized strategy for cell-based cardiac repair.