Jeong-Kee Yoon

Graphene-Regulated Cardiomyogenic Differentiation Process of Mesenchymal Stem Cells by Enhancing the Expression of Extracellular Matrix Proteins and Cell Signaling Molecules

The potential of graphene as a mesenchymal stem cell (MSC) culture substrate to promote cardiomyogenic differentiation is demonstrated. Graphene exhibits no sign of cytotoxicity for stem cell culture. MSCs are committed toward cardiomyogenic lineage by simply culturing them on graphene. This may be attributed, at least partially, to the regulation of expression levels of extracellular matrix and signaling molecules.

Mesenchymal Stem Cells Aggregate and Deliver Gold Nanoparticles to Tumors for Photothermal Therapy

Gold nanoparticles (AuNPs) have been extensively studied for photothermal cancer therapy because AuNPs can generate heat upon near-infrared irradiation. However, improving their tumor-targeting efficiency and optimizing the nanoparticle size for maximizing the photothermal effect remain challenging. We demonstrate that mesenchymal stem cells (MSCs) can aggregate pH-sensitive gold nanoparticles (PSAuNPs) in mildly acidic endosomes, target tumors, and be used for photothermal therapy. These aggregated structures had a higher cellular retention in comparison to pH-insensitive, control AuNPs (cAuNPs), which is important for the cell-based delivery process. PSAuNP-laden MSCs (MSC-PSAuNPs) injected intravenously to tumor-bearing mice show a 37-fold higher tumor-targeting efficiency (5.6% of the injected dose) and 8.3 °C higher heat generation compared to injections of cAuNPs after irradiation, which results in a significantly enhanced anticancer effect.

Graphene enhances the cardiomyogenic differentiation of human embryonic stem cells

Graphene has drawn attention as a substrate for stem cell culture and has been reported to stimulate the differentiation of multipotent adult stem cells. Here, we report that graphene enhances the cardiomyogenic differentiation of human embryonic stem cells (hESCs) at least in part, due to nanoroughness of graphene. Large-area graphene on glass coverslips was prepared via the chemical vapor deposition method. The coating of the graphene with vitronectin (VN) was required to ensure high viability of the hESCs cultured on the graphene. hESCs were cultured on either VN-coated glass (glass group) or VN-coated graphene (graphene group) for 21 days. The cells were also cultured on glass coated with Matrigel (Matrigel group), which is a substrate used in conventional, directed cardiomyogenic differentiation systems. The culture of hESCs on graphene promoted the expression of genes involved in the stepwise differentiation into mesodermal and endodermal lineage cells and subsequently cardiomyogenic differentiation compared with the culture on glass or Matrigel. In addition, the culture on graphene enhanced the gene expression of cardiac-specific extracellular matrices. Culture on graphene may provide a new platform for the development of stem cell therapies for ischemic heart diseases by enhancing the cardiomyogenic differentiation of hESCs.

Graphene oxide reinforced hydrogels for osteogenic differentiation of human adipose-derived stem cells

Polyethylene glycol (PEG)-based hydrogels are attractive biomaterials for stem cell culture due to their tunable material properties and mechanical strength. However, the lack of cell adhesion sites has been one of the major obstacles in generating functional tissue constructs using PEG-based hydrogels. To overcome this limitation, we designed graphene oxide (GO)-functionalized polyethylene glycol diacrylate (PEGDA) hydrogels to assign cell adhesion-dependent biofunctionality. The incorporation of GO into three-dimensional PEGDA networks improved cell attachment, engaged focal adhesion, and activated focal adhesion kinase (FAK) signaling of hydrogel-encapsulated human adipose-derived stem cells (hADSCs). Compared to the control PEGDA hydrogel, GO functionalized PEGDA hydrogel (PEGDA-GO) resulted in enhanced cell viability and survival. When subsequently cultured under osteoinductive condition, PEGDA-GO enhanced osteogenic differentiation and stimulated osteogenic phenotypes compared to those in its PEGDA counterpart. Taken together, GO could serve as an effective biofunctionalizing moiety to modulate stem cell adhesion and differentiation.

Enhancing Therapeutic Efficacy and Reducing Cell Dosage in Stem Cell Transplantation Therapy for Ischemic Limb Diseases by Modifying the Cell Injection Site

In conventional stem cell transplantation therapies for ischemic limb diseases, stem cells are generally transplanted into the ischemic region (IR), and most of the transplanted cells undergo hypoxia-mediated cell death. Due to massive cell death, the therapeutic efficacy is reduced and a high dose of stem cells is necessitated for the therapies. In this study, we investigated whether the therapeutic efficacy can be improved and the cell dosage can be reduced in the therapy for limb ischemia simply by modifying the stem cell injection site to a site where cell engraftment is improved and blood vessel sprouting is efficiently stimulated. Human mesenchymal stem cells (hMSCs) cultured under hypoxic condition, which simulates cells transplanted to IR, underwent extensive cell death in vitro. Importantly, cell death was significantly attenuated when hMSCs adhered first under normoxic condition for 24 h and then were exposed to hypoxic condition, which simulates cells transplanted to the border zone (BZ) in the upper thigh and migrated to IR. hMSCs, at doses of 2 × 10(5) or 2 × 10(6) cells, were injected into the IR or BZ of 5-week-old female athymic mice after ischemic hindlimb induction. Compared with human mesenchymal stem cell (hMSC) transplantation to the IR of mouse ischemic limbs, transplantation to the BZ significantly enhanced cell engraftment and paracrine factor secretion, which effectively stimulated vessel sprouting, enhanced blood perfusion in IR, and enabled the cell dosage reduction. Therefore, modification of the stem cell transplantation site would improve the current stem cell therapies for ischemic limb diseases in terms of cell dosage reduction and therapeutic efficacy enhancement.

Therapeutic angiogenesis using tumor cell-conditioned medium

Stem cell‐conditioned medium (CM), which contains angiogenic factors that are secreted by stem cells, represents a potential therapy for ischemic diseases. Along with stem cells, tumor cells also secrete various angiogenic factors. Here, tumor cells as a cell source of CM for therapeutic angiogenesis was evaluated and the therapeutic efficacy of tumor cell CM in mouse hindlimb ischemia models was demonstrated. CM obtained from a human fibrosarcoma HT1080 cell line culture was compared with CM obtained from a human bone marrow‐derived mesenchymal stem cell (MSC) culture. HT1080 CM contained higher concentrations of angiogenic factors compared with MSC CM, which was attributable to the higher cell density that resulted from a much faster growth rate of HT1080 cells compared with MSCs. For use in in vitro and in vivo angiogenesis studies, HT1080 CM was diluted such that HT1080 CM and MSC CM would have the same cell number basis. The two types of CMs induced the same extent of human umbilical vein endothelial cell (HUVEC) proliferation in vitro. The injection of HT1080 CM into mouse ischemic limbs significantly improved capillary density and blood perfusion compared with the injection of fresh medium. Although the therapeutic outcome of HT1080 CM was similar to that of MSC CM, the preparation of CM by tumor cell line culture would be much more efficient due to the faster growth and unlimited life‐time of the tumor cell line. These data suggest the potential application of tumor cell CM as a therapeutic modality for angiogenesis and ischemic diseases.

Therapeutic Efficacy-Potentiated and Diseased Organ-Targeting Nanovesicles Derived from Mesenchymal Stem Cells for Spinal Cord Injury Treatment

Human mesenchymal stem cell (hMSC)-derived exosomes have been spotlighted as a promising therapeutic agent for cell-free regenerative medicine. However, poor organ-targeting ability and insufficient therapeutic efficacy of systemically injected hMSC-exosomes were identified as critical limitations for their further applications. Therefore, in this study we fabricated iron oxide nanoparticle (IONP)-incorporated exosome-mimetic nanovesicles (NV-IONP) from IONP-treated hMSCs and evaluated their therapeutic efficacy in a clinically relevant model for spinal cord injury. Compared to exosome-mimetic nanovesicles (NV) prepared from untreated hMSCs, NV-IONP not only contained IONPs which act as a magnet-guided navigation tool but also carried greater amounts of therapeutic growth factors that can be delivered to the target cells. The increased amounts of therapeutic growth factors inside NV-IONP were attributed to IONPs that are slowly ionized to iron ions which activate the JNK and c-Jun signaling cascades in hMSCs. In vivo systemic injection of NV-IONP with magnetic guidance significantly increased the amount of NV-IONP accumulating in the injured spinal cord. Accumulated NV-IONP enhanced blood vessel formation, attenuated inflammation and apoptosis in the injured spinal cord, and consequently improved spinal cord function. Taken together, these findings highlight the development of therapeutic efficacy-potentiated extracellular nanovesicles and demonstrate their feasibility for repairing injured spinal cord.

A Disposable Photovoltaic Patch Controlling Cellular Microenvironment for Wound Healing

Electrical stimulation (ES) is known to affect the wound healing process by modulating skin cell behaviors. However, the conventional clinical devices that can generate ES for promoting wound healing require patient hospitalization due to large-scale of the extracorporeal devices. Herein, we introduce a disposable photovoltaic patch that can be applied to skin wound sites to control cellular microenvironment for promoting wound healing by generating ES. In vitro experiment results show that exogenous ES could enhance cell migration, proliferation, expression of extracellular matrix proteins, and myoblast differentiation of fibroblasts which are critical for wound healing. Our disposable photovoltaic patches were attached to the back of skin wound induced mice. Our patch successfully provided ES, generated by photovoltaic energy harvested from the organic solar cell under visible light illumination. In vivo experiment results show that the patch promoted cutaneous wound healing via enhanced host-inductive cell proliferation, cytokine secretion, and protein synthesis which is critical for wound healing process. Unlike the current treatments for wound healing that engage passive healing processes and often are unsuccessful, our wearable photovoltaic patch can stimulate regenerative activities of endogenous cells and actively contribute to the wound healing processes.

Topography‐Guided Control of Local Migratory Behaviors and Protein Expression of Cancer Cells

In vivo cancer cell migration and invasion are directed by biophysical guidance mechanisms such as pre-existing microtracks and basement membrane extracellular matrices. Here, this paper reports the correlation of the local migratory behavior of cancer cells and the biochemical signal expression using the topography that can guide or inhibit cell behaviors. To this end, the local apparent migration and the protein expression level are investigated with respect to the topographical feature size (flat, nanoline, and microline) and orientation (microline, microconcentric, and microradial) with the collectively migrating (A431) and individually migrating (MDA-MB-231 and U-87-MG) cancer cells. The results show that the migration and the protein expression of focal adhesion kinase, rho-associated protein kinase, and extracellular signal-regulated kinase are localized in the periphery of cell colony. Furthermore, the inhibition of migratory behavior at the periphery recues the protein expression, while the guidance of migration enhances the aforementioned protein expression. The results may imply the employ of biophysical inhibitory factors can help to control invasiveness of cancer cells during the progression state.

Therapeutic Angiogenesis via Solar Cell-Facilitated Electrical Stimulation

Cell therapy has been suggested as a treatment modality for ischemic diseases, but the poor survival and engraftment of implanted cells limit its therapeutic efficacy. To overcome such limitation, we used electrical stimulation (ES) derived from a wearable solar cell for inducing angiogenesis in ischemic tissue. ES enhanced the secretion of angiogenic growth factors and the migration of mesenchymal stem cells (MSCs), myoblasts, endothelial progenitor cells, and endothelial cells in vitro. In a mouse ischemic hindlimb model, ES generated by a solar cell and applied to the ischemic region promoted migration of MSCs toward the ischemic site and upregulated expression of angiogenic paracrine factors (vascular endothelial, basic fibroblast, and hepatocyte growth factors; and stromal cell-derived factor-1α). Importantly, solar cell-generated ES promoted the formation of capillaries and arterioles at the ischemic region, attenuated muscle necrosis and fibrosis, and eventually prevented loss of the ischemic limb. Solar cell ES therapy showed higher angiogenic efficacy than conventional MSC therapy. This study shows the feasibility of using solar cell ES as a novel treatment for therapeutic angiogenesis.