Ji Yoon Lee

Podoplanin-Expressing Cells Derived From Bone Marrow Play a Crucial Role in Postnatal Lymphatic Neovascularization

Background— Emerging evidence has suggested a contribution of bone marrow (BM) cells to lymphatic vessel formation; however, the exact phenotype of the cells with lymphatic endothelial progenitor cell function has yet to be identified. Here, we investigate the identity of BM-derived lymphatic endothelial progenitor cells and their role in lymphatic neovascularization. Methods and Results— Culture of BM-mononuclear cells in the presence of vascular endothelial growth factors A and C and endothelial growth factor resulted in expression of lymphatic endothelial cell markers. Among these cells, podoplanin+ cells were isolated by magnetic-activated cell sorting and characterized by fluorescence-activated cell sorter analysis and immunocytochemistry. These podoplanin+ cells highly express markers for lymphatic endothelial cells, hematopoietic lineages, and stem/progenitor cells; on further cultivation, they generate lymphatic endothelial cells. We further confirmed that podoplanin+ cells exist in small numbers in BM and peripheral blood of normal mice but are significantly (15-fold) augmented on lymphangiogenic stimuli such as tumor implantation. Next, to evaluate the potential of podoplanin+ cells for the formation of new lymphatic vessels in vivo, we injected culture-isolated or freshly isolated BM-derived podoplanin+ cells into wound and tumor models. Immunohistochemistry demonstrated that the injected cells were incorporated into the lymphatic vasculature, displayed lymphatic endothelial cell phenotypes, and increased lymphatic vascular density in tissues, suggesting lymphvasculogenesis. Podoplanin+ cells also expressed high levels of lymphangiogenic cytokines and increased proliferation of lymphatic endothelial cells during coculture, suggesting a lymphangiogenic or paracrine role. Conclusions— Our results provide compelling evidence that BM-derived podoplanin+ cells, a previously unrecognized cell type, function as lymphatic endothelial progenitor cells and participate in postnatal lymphatic neovascularization through both lymphvasculogenesis and lymphangiogenesis.

Generation of pure lymphatic endothelial cells from human pluripotent stem cells and their therapeutic effects on wound repair

Human pluripotent stem cells (hPSCs) have emerged as an important source for cell therapy. However, to date, no studies demonstrated generation of purified hPSC-derived lymphatic endothelial cells (LECs) and tested their therapeutic potential in disease models. Here we sought to differentiate hPSCs into the LEC lineage, purify them with LEC markers, and evaluate their therapeutic effects. We found that an OP9-assisted culture system reinforced by addition of VEGF-A, VEGF-C, and EGF most efficiently generated LECs, which were then isolated via FACS-sorting with LYVE-1 and PODOPLANIN. These hPSC-derived LYVE-1+PODOPLANIN+cells showed a pure committed LEC phenotype, formed new lymphatic vessels, and expressed lymphangiogenic factors at high levels. These hPSC-derived LECs enhanced wound healing through lymphangiogenesis and lymphvasculogenesis. Here we report, for the first time, that LECs can be selectively isolated from differentiating hPSCs, and that these cells are potent for lymphatic vessel formation in vivo and wound healing. This system and the purified hPSC-derived LECs can serve as a new platform for studying LEC development as well as for cell therapy.

Diabetic Mesenchymal Stem Cells Are Ineffective for Improving Limb Ischemia Due to Their Impaired Angiogenic Capability.

The purpose of this study was to investigate the effects of diabetes on mesenchymal stem cells (MSCs) in terms of their angiogenic and therapeutic potential for repairing tissue ischemia. We culture-isolated MSCs from streptozotocin-induced diabetic rats (D-MSCs) and compared their proliferation, differentiation, and angiogenic effects with those from normal rats (N-MSCs). The angiogenic effects of MSCs were evaluated by real-time PCR, in vitro tube formation assay, and transplantation of the MSCs into a hindlimb ischemia model followed by laser Doppler perfusion imaging. The number of MSCs derived from diabetic rats was smaller, and their proliferation rate was slower than N-MSCs. Upon induction of differentiation, the osteogenic and angiogenic differentiation of D-MSCs were aberrant compared to N-MSCs. The expression of angiogenic factors was lower in D-MSCs than N-MSCs. D-MSCs cocultured with endothelial cells resulted in decreased tube formation compared to N-MSCs. D-MSCs were ineffective to improve hindlimb ischemia and showed lower capillary density and angiogenic gene expression in ischemic limbs than N-MSCs. D-MSCs have defective proliferation and angiogenic activities and are ineffective for repairing hindlimb ischemia. Newer measures are needed before MSCs can be employed as a source for autologous cell therapy.

Role of bone marrow-derived lymphatic endothelial progenitor cells for lymphatic neovascularization.

The lymphatic vasculature plays a pivotal role in maintaining tissue fluid homeostasis, immune surveillance, and lipid uptake in the gastrointestinal organs. Therefore, impaired function of the lymphatic vessels caused by genetic defects, infection, trauma, or surgery leads to the abnormal accrual of lymph fluid in the tissue and culminates in the swelling of affected tissues, known as lymphedema. Lymphedema causes impaired wound healing, compromised immune defense, and, in rare case, lymphangiosarcoma. Although millions of people suffer from lymphedema worldwide, no effective therapy is currently available. In addition, recent advances in cancer biology have disclosed an indispensable function of the lymphatic vessel in tumor growth and metastasis. Therefore, understanding the detailed mechanisms governing lymphatic vessel formation and function in pathophysiologic conditions is essential to prevent or treat these diseases. We review the developmental processes of the lymphatic vessels and postnatal lymphatic neovascularization, focusing on the role of recently identified bone marrow-derived podoplanin-expressing (podoplanin(+)) cells as lymphatic endothelial progenitor cells.

Angiogenesis in the Transplanted Donor Graft After Living-donor Liver Transplantation

Background There is no direct evidence for the role of angiogenesis in liver regeneration in humans. This study aimed to determine whether angiogenesis is involved in the regeneration of transplanted donor grafts in human living-donor liver transplantation (LDLT) and to examine the impact of donor graft volume on angiogenesis. Methods Clinical data and liver tissue characteristics were analyzed in 4 patients who received adult-to-adult LDLT with dual left lobe grafts from 2 living donors. Liver tissues from transplanted donor grafts were obtained and immunohistochemically examined at 3 to 4 weeks after transplantation using the endothelial marker Ki67+ and CD31+. Results All recipients showed recovery of normal liver function and a significant increase in the volume of engrafted left lobes after transplantation. Immunohistochemistry showed a remarkable increase in Ki67+ single hepatocyte proliferation, implying the role of hepatocytes in liver reconstitution, and a high density of blood vessels and proliferative endothelium, suggesting in vivo angiogenesis. Furthermore, we found that Ki67+ nuclei in CD31+ sinusoidal endothelial cells were higher in recipients with smaller donor grafts than in those with larger donor grafts. Conclusions Our results suggested that angiogenesis is involved in the regeneration of transplanted liver in humans in inverse proportion to the donor graft volume.