Vascularization of tissues is a major challenge of tissue engineering (TE). We hypothesize that blood-derived endothelial progenitor cells (EPCs) have the required proliferative and vasculogenic activity to create vascular networks in vivo. To test this, EPCs isolated from human umbilical cord blood or from adult peripheral blood, and human saphenous vein smooth muscle cells (HSVSMCs) as a source of perivascular cells, were combined in Matrigel and implanted subcutaneously into immunodeficient mice. Evaluation of implants at one week revealed an extensive network of human-specific lumenal structures containing erythrocytes, indicating formation of functional anastomoses with the host vasculature. Quantitative analyses showed the microvessel density was significantly superior to that generated by human dermal microvascular endothelial cells (HDMECs) but similar to that generated by human umbilical vein endothelial cells (HUVECs). We also found that as EPCs were expanded in culture, their morphology, growth kinetics, and proliferative responses toward angiogenic factors progressively resembled those of HDMECs, indicating a process of in vitro maturation. This maturation correlated with a decrease in the degree of vascularization in vivo, which could be compensated for by increasing the number of EPCs seeded into the implants. Our findings strongly support the use of human EPCs to form vascular networks in engineered organs and tissues.

Tissue engineering may offer patients new options when replacement or repair of an organ is needed. However, most tissues will require a microvascular network to supply oxygen and nutrients. One strategy for creating a microvascular network would be promotion of vasculogenesis in situ by seeding vascular progenitor cells within the biopolymeric construct. To pursue this strategy, we isolated CD34(+)/CD133(+) endothelial progenitor cells (EPC) from human umbilical cord blood and expanded the cells ex vivo as EPC-derived endothelial cells (EC). The EPC lost expression of the stem cell marker CD133 but continued to express the endothelial markers KDR/VEGF-R2, VE-cadherin, CD31, von Willebrand factor, and E-selectin. The cells were also shown to mediate calcium-dependent adhesion of HL-60 cells, a human promyelocytic leukemia cell line, providing evidence for a proinflammatory endothelial phenotype. The EPC-derived EC maintained this endothelial phenotype when expanded in roller bottles and subsequently seeded on polyglycolic acid-poly-l-lactic acid (PGA-PLLA) scaffolds, but microvessel formation was not observed. In contrast, EPC-derived EC seeded with human smooth muscle cells formed capillary-like structures throughout the scaffold (76.5 +/- 35 microvessels/mm(2)). These results indicate that 1) EPC-derived EC can be expanded in vitro and seeded on biodegradable scaffolds with preservation of endothelial phenotype and 2) EPC-derived EC seeded with human smooth muscle cells form microvessels on porous PGA-PLLA scaffolds. These properties indicate that EPC may be well suited for creating microvascular networks within tissue-engineered constructs.

Infantile hemangiomas are composed of endothelial cells (ECs), endothelial progenitor cells (EPCs), as well as perivascular and hematopoietic cells. Our hypothesis is that hemangioma-derived EPCs (HemEPCs) differentiate into the mature ECs that comprise the major compartment of the tumor. To test this, we isolated EPCs (CD133 ؉ /Ulex europeus-I ؉ ) and mature ECs (CD133 ؊ /Ulex europeus-I ؉ ) from proliferating hemangiomas and used a previously described property of hemangioma-derived ECs (HemECs), enhanced migratory activity in response to the angiogenesis inhibitor endostatin, to determine if HemEPCs share this abnormal behavior. Umbilical cord bloodderived EPCs (cbEPCs) were analyzed in parallel as a normal control. Our results show that HemEPCs, HemECs, and cbEPCs exhibit increased adhesion, migration, and proliferation in response to endostatin. This angiogenic response to endostatin was consistently expressed by HemEPCs over several weeks in culture, whereas HemECs and cbEPCs shifted toward the mature endothelial response to endostatin. Similar mRNAexpression patterns among HemEPCs, HemECs, and cbEPCs, revealed by microarray analyses, provided further indication of an EPC phenotype. This is the first demonstration that human EPCs, isolated from blood or from a proliferating hemangioma, are stimulated by an angiogenesis inhibitor. These findings suggest that EPCs respond differently from mature ECs when exposed to angiogenic or antiangiogenic signals. IntroductionInfantile hemangioma, the most common tumor of infancy, is characterized by rapid proliferation of the endothelial cells followed by slow spontaneous involution. 1 This transition from the proliferating phase to the involuting phase represents a gradient of cellular activity from unregulated proliferation to apoptosis. The molecular events that control the evolution of hemangioma remain obscure. Both intrinsic and extrinsic anomalies have been suggested to underlie the primary defect. [2][3][4][5][6] Recent studies showing that hemangioma-derived endothelial cells (HemECs) are clonal provide support for an intrinsic defect. 4,6 We and others have identified endothelial progenitor cells (EPCs) in hemangioma tissue and circulating blood of patients with hemangiomas, respectively. 7,8 These findings suggest that a hemangioma may arise from the clonal expansion of an EPC.An angioblastic origin for hemangiomas has been envisioned for over a century. In 1863, Virchow 9 questioned whether hemangiomas represented sequestered embryonic mesoderm. Pack and Miller 10 suggested that hemangiomas arise from the localized growth of angioblastic cells. Similarly, Malan 11 imagined hemangiomas as an activation of dormant angioblasts. Histologic examination of hemangioma ECs reveals an immature phenotype with large nuclei and scant cytoplasm. 12 During the rapid growth phase of hemangiomas, syncytial EC hyperplasia, with and without lumens, is seen. In the involuting phase, hyperplasia diminishes and mature vascular channels with defined lumens become prominent. 1 C...

Ferroptosis is a new form of regulated cell death, which is characterized by the iron-dependent accumulation of lethal lipid peroxides and involved in many critical diseases. Recent reports revealed that cellular energy metabolism activities such as glycolysis, pentose phosphate pathway (PPP), and tricarboxylic acid cycle are involved in the regulation of key ferroptosis markers such as reduced nicotinamide adenine dinucleotide phosphate (NADPH), glutathione (GSH), and reactive oxygen species (ROS), therefore imposing potential regulatory roles in ferroptosis. Remarkably, tumor cells can activate adaptive metabolic responses to inhibit ferroptosis for self-preservation such as the upregulation of glycolysis and PPP. Due to the rapid proliferation of tumor cells and the intensified metabolic rate, tumor energy metabolism has become a target for disrupting the redox homeostasis and induce ferroptosis. Based on these emerging insights, regulatory impact of those-tumor specific metabolic aberrations is systematically characterized, such as rewired glucose metabolism and metabolic compensation through glutamine utilization on ferroptosis and analyzed the underlying molecular mechanisms. Additionally, those ferroptosis-based therapeutic strategies are also discussed by exploiting those metabolic vulnerabilities, which may open up new avenues for tumor treatment in a clinical context.

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Survival of tissue transplants generated in vitro is strongly limited by the slow process of graft vascularization in vivo. A method to enhance graft vascularization is to establish a primitive vascular plexus within the graft prior to transplantation. Endothelial cells (EC) cultured as multicellular spheroids within a collagen matrix form sprouts resembling angiogenesis in vitro. However, osteoblasts integrated into the graft suppress EC sprouting. This inhibition depends on direct cell-cell-interactions and is characteristic of mature ECs isolated from preexisting vessels. In contrast, sprouting of human blood endothelial progenitor cells is not inhibited by osteoblasts, making these cells suitable for tissue engineering of pre-vascularized bone grafts.

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An homologous series of divinylchalcogenophene‐bridged binuclear ruthenium complexes [{(PMe3)3Cl(CO)Ru}2(µ‐CH=CH‐C4H2E‐CH=CH)] (4a–4d, E = O, S, Se, Te) have been synthesised and fully characterised by X‐ray crystallography and various spectroscopic techniques. The single‐crystal X‐ray diffraction results reveal a distinct short/long bond‐length alternation along the polyene‐like hydrocarbon backbone, with geometric constraints imposed by the chalcogenophene leading to an increasing distance between the two metal centres (dRu–Ru) in complexes 4a–4d as the heteroatom in the five‐membered ring is changed from oxygen (9.980 Å in 4a) to tellurium (11.063 Å in 4d). The complexes undergo two sequential one‐electron oxidation processes, the half‐wave potential and separation of which appear to be sensitive to a range of factors, including aromatic stabilisation and re‐organisation energies. Analysis of [4a–4d]n+ (n = 0, 1, 2) by UV/Vis/NIR and IR spectroelectrochemical methods, supported by DFT calculations (n = 0, 1), revealed that the redox character of the complexes is dominated by the polyene‐like backbone with the chalcogenide playing a subtle but influential, structural rather than electronic, role. In the radical cations [4a–4d]+, the charge is rather effectively delocalised over the 10‐atom Ru–[4‐s‐cis‐all‐trans‐(CH=CH)4]–Ru chain, giving rise to a species with spectroscopic properties not dissimilar to oxidised polyaceylene.