Neovascularization Capacity Research Articles

Generation of Directly Reprogrammed Human Endothelial Cells.

Direct reprogramming provides a novel breakthrough for generating functional endothelial cells (ECs) without the need for intermediate stem or progenitor states, offering a promising resource for cardiovascular research and treatment. ETV2 is a key transcription factor that has been identified as a pioneering factor for specifying endothelial lineage. Achieving precise ETV2 induction is essential for effective endothelial reprogramming, and maintaining the reprogrammed cellular phenotype relies on a specific combination of growth factors and small molecules. Thus, we hereby provide a straightforward and comprehensive protocol for generating two distinct types of reprogrammed ECs (rECs) from human dermal fibroblasts (HDFs). Early rECs demonstrate a robust neovascularization property but lack the mature EC phenotype, while late rECs exhibit phenotypical similarity to human postnatal ECs and have a neovascularization capacity similarto early rECs. Both cell types can be derived from human somatic source cells, making them suitable for personalized disease investigations, drug discovery, and disease therapy.

Biomimetic vascularized adipose-derived mesenchymal stem cells bone-periosteum graft enhances angiogenesis and osteogenesis in a male rabbit spine fusion model.

Several artificial bone grafts have been developed but fail to achieve anticipated osteogenesis due to their insufficient neovascularization capacity and periosteum support. This study aimed to develop a vascularized bone-periosteum construct (VBPC) to provide better angiogenesis and osteogenesis for bone regeneration. A total of 24 male New Zealand white rabbits were divided into four groups according to the experimental materials. Allogenic adipose-derived mesenchymal stem cells (AMSCs) were cultured and seeded evenly in the collagen/chitosan sheet to form cell sheet as periosteum. Simultaneously, allogenic AMSCs were seeded onto alginate beads and were cultured to differentiate to endothelial-like cells to form vascularized bone construct (VBC). The cell sheet was wrapped onto VBC to create a vascularized bone-periosteum construct (VBPC). Four different experimental materials - acellular construct, VBC, non-vascularized bone-periosteum construct, and VBPC - were then implanted in bilateral L4-L5 intertransverse space. At 12 weeks post-surgery, the bone-forming capacities were determined by CT, biomechanical testing, histology, and immunohistochemistry staining analyses. At 12 weeks, the VBPC group significantly increased new bone formation volume compared with the other groups. Biomechanical testing demonstrated higher torque strength in the VBPC group. Notably, the haematoxylin and eosin, Masson's trichrome, and immunohistochemistry-stained histological results revealed that VBPC promoted neovascularization and new bone formation in the spine fusion areas. The tissue-engineered VBPC showed great capability in promoting angiogenesis and osteogenesis in vivo. It may provide a novel approach to create a superior blood supply and nutritional environment to overcome the deficits of current artificial bone graft substitutes.

CD133+ endothelial-like stem cells restore neovascularization and promote longevity in progeroid and naturally aged mice

The stem cell theory of aging dictates that a decline in the number and/or function of stem cells causes tissue degeneration and aging; however, it still lacks unequivocal experimental support. Here, using lineage tracing and single-cell transcriptomics, we identify a population of CD133+ bone marrow-derived endothelial-like cells (ELCs) as potential endothelial progenitor cells, which contribute to tubular structures in vitro and neovascularization in vivo. We demonstrate that supplementation with wild-type and young ELCs respectively restores neovascularization and extends lifespan in progeric and naturally aged mice. Mechanistically, we identify an upregulation of farnesyl diphosphate synthase (FDPS) in aged CD133+ ELCs—a key enzyme in isoprenoid biosynthesis. Overexpression of FDPS compromises the neovascularization capacity of CD133+ ELCs, whereas FDPS inhibition by pamidronate enhances neovascularization, improves health measures and extends lifespan in aged mice. These findings highlight stem cell-based strategies for the treatment of progeria and age-related pathologies.

Promoting early neovascularization by allotransplanted adipose-derived Muse cells in an ovine model of acute myocardial infarction.

Recent preclinical studies have demonstrated that bone marrow (BM)-derived Muse cells have a homing mechanism to reach damaged cardiac tissue while also being able to reduce myocardial infarct size and improve cardiac function; however, the potential of BM-Muse cells to foster new blood-vessel formation has not been fully assessed. Up to date, adipose tissue (AT)-derived Muse cells remain to be studied in acute myocardial infarction (AMI). The aim of the present study was to analyze in vitro and in vivo the neovascularization capacity of AT-Muse cells while exploring their biodistribution and differentiation potential in a translational ovine model of AMI. AT-Muse cells were successfully isolated from ovine adipose tissue. In adult sheep, one or more diagonal branches of the left anterior descending coronary artery were permanently ligated for thirty minutes. Sheep were randomized in two groups and treated with intramyocardial injections: Vehicle (PBS, n = 4) and AT-Muse (2x107 AT-Muse cells labeled with PKH26 Red Fluorescent Dye, n = 4). Molecular characterization showed higher expression of angiogenic genes (VEGF, PGF and ANG) and increased number of tube formation in AT-Muse cells group compared to Adipose-derived mesenchymal stromal cells (ASCs) group. At 7 days post-IAM, the AT-Muse group showed significantly more arterioles and capillaries than the Vehicle group. Co-localization of PKH26+ cells with desmin, sarcomeric actin and troponin T implied the differentiation of Muse cells to a cardiac fate; moreover, PKH26+ cells also co-localized with a lectin marker, suggesting a possible differentiation to a vascular lineage. Intramyocardially administered AT-Muse cells displayed a significant neovascularization activity and survival capacity in an ovine model of AMI.

Promoting angiogenesis and diabetic wound healing through delivery of protein transduction domain-BMP2 formulated nanoparticles with hydrogel

Decreased angiogenesis contributes to delayed wound healing in diabetic patients. Recombinant human bone morphogenetic protein-2 (rhBMP2) has also been demonstrated to promote angiogenesis. However, the short half-lives of soluble growth factors, including rhBMP2, limit their use in wound-healing applications. To address this limitation, we propose a novel delivery model using a protein transduction domain (PTD) formulated in a lipid nanoparticle (LNP). We aimed to determine whether a gelatin hydrogel dressing loaded with LNP-formulated PTD-BMP2 (LNP-PTD-BMP2) could enhance the angiogenic function of BMP2 and improve diabetic wound healing. In vitro, compared to the control and rhBMP2, LNP-PTD-BMP2 induced greater tube formation in human umbilical vein endothelial cells and increased the cell recruitment capacity of HaCaT cells. We inflicted large, full-thickness back skin wounds on streptozotocin-induced diabetic mice and applied gelatin hydrogel (GH) cross-linked by microbial transglutaminase containing rhBMP2, LNP-PTD-BMP2, or a control to these wounds. Wounds treated with LNP-PTD-BMP2-loaded GH exhibited enhanced wound closure, increased re-epithelialization rates, and higher collagen deposition than those with other treatments. Moreover, LNP-PTD-BMP2-loaded GH treatment resulted in more CD31- and α-SMA-positive cells, indicating greater neovascularization capacity than rhBMP2-loaded GH or GH treatments alone. Furthermore, in vivo near-infrared fluorescence revealed that LNP-PTD-BMP2 has a longer half-life than rhBMP2 and that BMP2 localizes around wounds. In conclusion, LNP-PTD-BMP2-loaded GH is a viable treatment option for diabetic wounds.

3D-bioprinted vascular scaffold with tunable mechanical properties for simulating and promoting neo-vascularization

Alternative artificial vessels with tissue-matching mechanical and biological performance have been continuously taking great attention in bioengineering. However, it is challenging to take into account both mechanical and biological properties in formulating a hydrogel material. In the current study, a composite hydrogel ink based on geltain-methacryloyl (GelMA) and sodium alginate (SA) was prepared by a two-step polymerization process, and its fast shaping was realized by stabilizing the alginate fraction in calcium ion bath as well as the photo-crosslinking of GelMA. Mechanical properties of the transparent 3D printing GelMA/Gelatin/SA blood vessels were determined by testing their stretching and resilience performance. Based on Von Mise stress simulation using Ansys, strain of the artificial blood vessels reached 147% and the elastic Young’s modulus reached approximately 224 ​kPa in the optimal hydrogel formulation, matching well with capability of enduring certain blood pressure encountered in real tissue. A selective and uniform permeability of hydrogel tubes was presented by using small molecules and human red blood cells, meanwhile excellent hemolysis, cell viability, and proliferation ability were also verified. Based on the results of in vitro assessment and the in vivo transplantation in SD rats, our proposed GelMA/Gelatin/SA vessels, with tissue-matching mechanical properties and their ideal biodegradation behavior, promoted neo-vascularization capacity and showed promising potential in producing an artificial blood vessel.

Accelerated Bone Regeneration by MOF Modified Multifunctional Membranes through Enhancement of Osteogenic and Angiogenic Performance

Owing to the insufficient guidance of new bone formation in orthopedic and craniomaxillofacial surgery, construction of a guided bone regeneration membrane to support vascularized bone regeneration remains a challenge. Herein, an electrospun asymmetric double-layer polycaprolactone/collagen (PCL/Col) membrane modified by metal-organic framework (MOF) crystals is developed. The optimization of the PCL/Col weight ratio (1:1 and 1:1.5) enables the composite membrane with a balanced tensile strength (only fell by 49.9% in wet conditions) and a controlled degradation rate (completely degraded at 12 weeks). The MOF crystals can provide a pH-responsive release of Zn2+ ions. In vitro experiments indicate that the barrier layer functions to prevent the infiltration of fibrous connective tissue. The MOF crystal layer functions to enhance osteogenesis and angiogenesis in vitro. Using a rat calvarial defect model, the MOF crystals exhibit a sign of osteoinductivity along with blood vessel formation after 8 weeks post-surgery. Strikingly, when assessed in a chick chorioallantoic membrane model, the MOF modified membrane demonstrates a significant angiogenic response, which can be envisaged as its outstanding merits over the commercially Col membrane. Therefore, the MOF crystals represent an exciting biomaterial option, with neovascularization capacity for bone tissue engineering and regenerative medicine.

MiR-96 and miR-183 differentially regulate neonatal and adult postinfarct neovascularization.

Following myocardial infarction (MI), the adult heart has minimal regenerative potential. Conversely, the neonatal heart can undergo extensive regeneration, and neovascularization capacity was hypothesized to contribute to this difference. Here, we demonstrate the higher angiogenic potential of neonatal compared with adult mouse cardiac endothelial cells (MCECs) in vitro and use this difference to identify candidate microRNAs (miRs) regulating cardiac angiogenesis after MI. miR expression profiling revealed miR-96 and miR-183 upregulation in adult compared with neonatal MCECs. Their overexpression decreased the angiogenic potential of neonatal MCECs in vitro and prevented scar resolution and neovascularization in neonatal mice after MI. Inversely, their inhibition improved the angiogenic potential of adult MCECs, and miR-96/miR-183–KO mice had increased peri-infarct neovascularization. In silico analyses identified anillin (ANLN) as a direct target of miR-96 and miR-183. In agreement, Anln expression declined following their overexpression and increased after their inhibition in vitro. Moreover, ANLN expression inversely correlated with miR-96 expression and age in cardiac ECs of cardiovascular patients. In vivo, ANLN+ vessels were enriched in the peri-infarct area of miR-96/miR-183–KO mice. These findings identify miR-96 and miR-183 as regulators of neovascularization following MI and miR-regulated genes, such as anillin, as potential therapeutic targets for cardiovascular disease.

Control of Angiogenesis via a VHL/miR-212/132 Axis.

A common feature of tumorigenesis is the upregulation of angiogenesis pathways in order to supply nutrients via the blood for the growing tumor. Understanding how cells promote angiogenesis and how to control these processes pharmaceutically are of great clinical interest. Clear cell renal cell carcinoma (ccRCC) is the most common form of sporadic and inherited kidney cancer which is associated with excess neovascularization. ccRCC is highly associated with biallelic mutations in the von Hippel–Lindau (VHL) tumor suppressor gene. Although upregulation of the miR-212/132 family and disturbed VHL signaling have both been linked with angiogenesis, no evidence of a possible connection between the two has yet been made. We show that miRNA-212/132 levels are increased after loss of functional pVHL, the protein product of the VHL gene, in vivo and in vitro. Furthermore, we show that blocking miRNA-212/132 with anti-miRs can significantly alleviate the excessive vascular branching phenotype characteristic of vhl−/− mutant zebrafish. Moreover, using human umbilical vascular endothelial cells (HUVECs) and an endothelial cell/pericyte coculture system, we observed that VHL knockdown promotes endothelial cells neovascularization capacity in vitro, an effect which can be inhibited by anti-miR-212/132 treatment. Taken together, our results demonstrate an important role for miRNA-212/132 in angiogenesis induced by loss of VHL. Intriguingly, this also presents a possibility for the pharmaceutical manipulation of angiogenesis by modulating levels of MiR212/132.

Leucine-activated nanohybrid biofilm for skin regeneration via improving cell affinity and neovascularization capacity.

The accumulation of skin diseases has increased the need for biomimicking materials with high bioactivity and biosafety for wound healing, where how to improve the cell affinity of the skin regenerative materials as well as their neovascularization capacity is a key factor for rapid regeneration of the injured skin tissue. In the current study, we developed an advanced type of biodegradable nanofibrous biofilm which can attract skin-related cells and accelerate blood vessel formation for skin regeneration. Firstly, bioactive nanohybrids (LEU@LP) were fabricated via in situ doping of the nutrient amino acid leucine (beneficial for fibroblast proliferation and protein synthesis) into LAPONITE® nanodisks (enriched in Mg and Si favorable for vascularization). LEU@LP nanoparticles were then hybridized with a biodegradable polylactide (PLA) nanofibrous mesh via an airbrushing technique, followed by a subsequent ammonia plasma surface treatment to improve PLA's hydrophilicity to increase cell affinity. The resulting hybrid biofilms with skin-biomimicking nanofibrous structural networks can promote cell adhesion, spreading, migration and proliferation of fibroblasts, leading to the ideal skin wound healing (with blood vessel formation and hair follicle regeneration), probably attributed to their better hydrophilicity to promote cell affinity and the capacity of sustainable release of leucine (beneficial for fibroblasts proliferation) and the composition provision (Mg and Si which are beneficial for neovascularization).

ClC-3 Deficiency Impairs the Neovascularization Capacity of Early Endothelial Progenitor Cells by Decreasing CXCR4/JAK-2 Signalling

BackgroundEndothelial progenitor cell (EPC) therapy has been suggested as a major breakthrough in the treatment of ischemic diseases. However, the molecular mechanism that underlies EPC functional regulation is still unclear. MethodsWe examined the angiogenic capacity of EPCs in a hindlimb ischemia model of wild-type and ClC-3 knockout mice. ResultsMice lacking of ClC-3 exhibited reduced blood flow recovery and neovascularization in ischemic muscles 7 and 14 days after hind limb ischemia. Moreover, compared with wild-type EPCs, the hindlimb blood reperfusion in mice receiving ClC-3 knockout EPCs was significantly impaired, accompanied by reduced EPC homing and retention. In vitro, EPCs derived from ClC-3 knockout mice displayed impaired migratory, adhesive, and angiogenic activity. CXC chemokine receptor 4 (CXCR4) expression was significantly reduced in EPC from ClC-3 knockout mice compared with wild-type. Moreover, the expression and phosphorylation of Janus kinase 2 (JAK-2), a downstream signalling of CXCR4, was also reduced in ClC-3 knockout EPC, indicating that CXCR4/JAK-2 signalling is dysregulated by ClC-3 deficiency. Consistent with this assumption, the migratory capacity of wild-type EPCs was attenuated by either CXCR4 antagonist AMD3100 or JAK-2 inhibitor AG490. More importantly, the impaired migratory capacity of ClC-3 knockout EPCs was rescued by overexpression of CXCR4. ConclusionsClC-3 plays a critical role in the angiogenic capacity of EPCs and EPC-mediated neovascularization of ischemic tissues. Disturbance of CXCR4/JAK-2 signalling may contribute to the functional impairment of ClC-3 deficient EPCs. Thus, ClC-3 may be a potential therapeutic target for modulating neovascularization in ischemic diseases.

Superparamagnetic iron oxide nanoparticle-mediated expression of miR-326 inhibits human endometrial carcinoma stem cell growth.

Background: Previously, our group confirmed the presence of a subset of cancer stem cells in the tissues of endometrial carcinoma (ie, human endometrial carcinoma stem cells [HuECSCs]). However, the mechanisms by which microRNAs regulate the growth of HuECSCs remain elusive.Methods: We loaded miR-326 onto superparamagnetic iron oxide nanoparticles (miR-326@SPION) and transfected them into HuECSCs.Results: In the present study, we found that the expression levels of members of the G-protein coupled receptor 91 (GPR91)/signal transducer and activator of transcription 3 (STAT3)/vascular endothelial growth factor (VEGF) pathway were significantly elevated in CD44+/CD133+ HuECSCs. Luciferase reporter assays indicated that the succinate receptor 1 (SUCNR1) gene, also known as the G-protein coupled receptor 91 (GPR91) gene, was one of the potential targets of miR-326. Transmission electron microscopy revealed that the SPIONs could cross the cell membrane and accumulate in the cytoplasm. The overexpression of miR-326 significantly inhibited the proliferation and cell cycle progression of HuECSCs in vitro. MiR-326 overexpression also effectively inhibited the invasion and angiogenic capacities of HuECSCs in the extracellular matrix. Meanwhile, miR-326 overexpression significantly inhibited the tumorigenicity and tumour neovascularization capacity of HuECSCs in nude mice. Both quantitative real-time PCR and Western blotting confirmed that overexpression of miR-326 significantly reduced the expression of members of the GPR91/STAT3/VEGF pathway in HuECSCs, and the activity (level of phosphorylation) of key molecules in this pathway was also reduced.Conclusion: Collectively, we confirmed that SPIONs are highly efficient nanocarriers for nucleic acids, on which the loading of miR-326 inhibited the activation of the GPR91/STAT3/VEGF signaling pathway and significantly attenuated the activity of stem cells in endometrial carcinoma, both in vitro and in vivo.

Sema3E/PlexinD1 signaling inhibits postischemic angiogenesis by regulating endothelial DLL4 and filopodia formation in a rat model of ischemic stroke.

Angiogenesis is a crucial defense response to hypoxia that regulates the process of raising the promise of long-term neurologic recovery during the management of stroke. A high expression of antiangiogenic factors leads to the loss of neovascularization capacity in pathologic conditions. We have previously documented an impairment of the cerebral vessel perfusion and neovascularization in the cortex neighboring the stroke-induced lesion, which was accompanied by an activation of semaphorin 3E (Sema3E)/PlexinD1 after ischemic stroke. In this study, we employed micro-optical sectioning tomography to fully investigate the details of the vascular pattern, including the capillaries. We found that after transient middle cerebral artery occlusion, inhibiting PlexinD1 signaling led to an organized recovery of the vascular network in the ischemic area. We then further explored the possible mechanisms. In vivo, Sema3E substantially decreased dynamic delta-like 4 (DLL4) expression. In cultured brain microvascular endothelial cells, Sema3E down-regulated DLL4 expression via inhibiting Ras-related C3 botulinum toxin substrate 1-induced JNK phosphorylation. At the microcosmic level, Sema3E/PlexinD1 signaling promoted F-actin disassembly and focal adhesion reduction by activating the small guanosine triphosphatase Ras homolog family member J by releasing RhoGEF Tuba from direct binding to PlexinD1, thus mediating endothelial cell motility and filopodia retraction. Our study reveals that Sema3E/PlexinD1 signaling, which suppressed endothelial DLL4 expression, cell motility, and filopodia formation, is expected to be a novel druggable target for angiogenesis during poststroke progression.-Zhou, Y.-F., Chen, A.-Q., Wu, J.-H., Mao, L., Xia, Y.-P., Jin, H.-J., He, Q.-W., Miao, Q. R., Yue, Z.-Y., Liu, X.-L., Huang, M., Li, Y.-N., Hu, B. Sema3E/PlexinD1 signaling inhibits postischemic angiogenesis by regulating endothelial DLL4 and filopodia formation in a rat model of ischemic stroke.

Prevascularized bladder acellular matrix hydrogel/silk fibroin composite scaffolds promote the regeneration of urethra in a rabbit model

Objective: To evaluate the effects of urethral regeneration with prevascularized bladder acellular matrix hydrogel (BAMH)/silk fibroin (SF) composite scaffolds in a rabbit model. Materials and methods: BAMH/SF and collagen Type I hydrogel/SF (CH/SF) scaffolds were prepared and the structure of the scaffolds was assessed using scanning electron microscopy. BAMH/SF, CH/SF and SF scaffolds were incubated in the omentum of male rabbits for two weeks and then harvested for repairing autologous urethral defects. Histological analysis of the incubated scaffolds was performed to evaluate the neovascularization capacity, and the outcomes of urethroplasty were evaluated at one and three months post-operatively. Results: The composited scaffolds were composed of a highly porous BAMH or CH buttressed by compact SF outer layer. The histological analysis of the incubated BAMH/SF revealed a signifcant increase of the neovascularization among three groups after a two-week incubation. At three months, the urethra maintained wide caliber in the BAMH/SF group. Strictures were found in the CH/SF and SF groups. Histologically, at one month, intact and multilayer epithelium occurred in the BAMH/SF group, and one layer epithelium was found in the CH/SF and SF groups. However, there was similar epithelial regeneration in BAMH/SF and CH/SF groups at three months (p > 0.05). Comparisons of smooth muscle content and vessel density among the SF, CH/SF and BAMH/SF revealed a significant increase at each time point (p < 0.05). Conclusion: Our results demonstrate that incubated BAMH/SF promote neovascularization, and prevascularized BAMH/SF promote the regeneration of the urethral epithelium and smooth muscle, which indicates its potential for urethral reconstruction.

Cellular self-assembly into 3D microtissues enhances the angiogenic activity and functional neovascularization capacity of human cardiopoietic stem cells.

While cell therapy has been proposed as next-generation therapy to treat the diseased heart, current strategies display only limited clinical efficacy. Besides the ongoing quest for the ideal cell type, in particular the very low retention rate of single-cell (SC) suspensions after delivery remains a major problem. To improve cellular retention, cellular self-assembly into 3D microtissues (MTs) prior to transplantation has emerged as an encouraging alternative. Importantly, 3D-MTs have also been reported to enhance the angiogenic activity and neovascularization potential of stem cells. Therefore, here using the chorioallantoic membrane (CAM) assay we comprehensively evaluate the impact of cell format (SCs versus 3D-MTs) on the angiogenic potential of human cardiopoietic stem cells, a promising second-generation cell type for cardiac repair. Biodegradable collagen scaffolds were seeded with human cardiopoietic stem cells, either as SCs or as 3D-MTs generated by using a modified hanging drop method. Thereafter, seeded scaffolds were placed on the CAM of living chicken embryos and analyzed for their perfusion capacity in vivo using magnetic resonance imaging assessment which was then linked to a longitudinal histomorphometric ex vivo analysis comprising blood vessel density and characteristics such as shape and size. Cellular self-assembly into 3D-MTs led to a significant increase of vessel density mainly driven by a higher number of neo-capillary formation. In contrast, SC-seeded scaffolds displayed a higher frequency of larger neo-vessels resulting in an overall 1.76-fold higher total vessel area (TVA). Importantly, despite that larger TVA in SC-seeded group, the mean perfusion capacity (MPC) was comparable between groups, therefore suggesting functional superiority together with an enhanced perfusion efficacy of the neo-vessels in 3D-MT-seeded scaffolds. This was further underlined by a 1.64-fold higher perfusion ratio when relating MPC to TVA. Our study shows that cellular self-assembly of human cardiopoietic stem cells into 3D-MTs substantially enhances their overall angiogenic potential and their functional neovascularization capacity. Hence, the concept of 3D-MTs may be considered to increase the therapeutic efficacy of future cell therapy concepts.

SOX17 Regulates Conversion of Human Fibroblasts Into Endothelial Cells and Erythroblasts by Dedifferentiation Into CD34+ Progenitor Cells.

The mechanisms underlying the dedifferentiation and lineage conversion of adult human fibroblasts into functional endothelial cells have not yet been fully defined. Furthermore, it is not known whether fibroblast dedifferentiation recapitulates the generation of multipotent progenitors during embryonic development, which give rise to endothelial and hematopoietic cell lineages. Here we established the role of the developmental transcription factor SOX17 in regulating the bilineage conversion of fibroblasts by the generation of intermediate progenitors. CD34+ progenitors were generated after the dedifferentiation of human adult dermal fibroblasts by overexpression of pluripotency transcription factors. Sorted CD34+ cells were transdifferentiated into induced endothelial cells and induced erythroblasts using lineage-specific growth factors. The therapeutic potential of the generated cells was assessed in an experimental model of myocardial infarction. Induced endothelial cells expressed specific endothelial cell surface markers and also exhibited the capacity for cell proliferation and neovascularization. Induced erythroblasts expressed erythroid surface markers and formed erythroid colonies. Endothelial lineage conversion was dependent on the upregulation of the developmental transcription factor SOX17, whereas suppression of SOX17 instead directed the cells toward an erythroid fate. Implantation of these human bipotential CD34+ progenitors into nonobese diabetic/severe combined immunodeficiency (NOD-SCID) mice resulted in the formation of microvessels derived from human fibroblasts perfused with mouse and human erythrocytes. Endothelial cells generated from human fibroblasts also showed upregulation of telomerase. Cell implantation markedly improved vascularity and cardiac function after myocardial infarction without any evidence of teratoma formation. Dedifferentiation of fibroblasts to intermediate CD34+ progenitors gives rise to endothelial cells and erythroblasts in a SOX17-dependent manner. These findings identify the intermediate CD34+ progenitor state as a critical bifurcation point, which can be tuned to generate functional blood vessels or erythrocytes and salvage ischemic tissue.

Abstract 27: ApoA-I Improves Lymphatic Function Through a Platelet-Dependent Mechanism in Atherosclerotic Mice

Rationale: Lymphatic vessels (LVs) are now recognized as prerequisite players in the modulation of cholesterol removal from the artery wall in experimental conditions of plaque regression, and a particular attention has been brought on the role of the collecting LVs in early atherosclerosis-related lymphatic dysfunction. Whereas recent findings revealed that apoA-I restores the neovascularization capacity of the lymphatic system during tumor necrosis factor-induced inflammation, the effect of apoA-I on collecting LV function during atherosclerosis has not been tested. Objective: In the present study, we address whether and how apoA-I can enhance collecting LV function in atherosclerosis-associated lymphatic dysfunction. Methods and Results: A 6-week systemic treatment with lipid-free apoA-I enhanced lymphatic transport and abrogated collecting lymphatic vessel permeability in atherosclerotic Ldlr –/– mice when compared to control. As injection of apoA-I has been shown to protect wild-type mice against flow restriction-induced thrombosis, and that platelets are identified as key elements in the maintenance of lymphatic vessel integrity via their interaction with lymphatic endothelial cells (LECs), we have tested whether the effects of apoA-I could be mediated through a platelet-dependent mechanism. Our in vivo results show that apoA-I kinetics in lymph reflected that of blood. Ex vivo experiments performed with washed platelets isolated from mouse blood reveal that apoA-I decreased thrombin-induced but not podoplanin-induced platelet aggregation. Whereas this result suggests that apoA-I limits platelet thrombotic potential in blood but not in lymph, we demonstrate that treatment of human LECs with apoA-I increases the adhesion of bridge-like platelets on human LECs. Conclusions: Our results suggest that apoA-I can mediate beneficial effects on lymphatic function by promoting platelet adhesion to the lymphatic endothelium and consequently restore collecting LV integrity. Altogether, we bring forward a new pleiotropic role for apoA-I in lymphatic function and unveil new potential therapeutic targets for the prevention and treatment of atherosclerosis.

Investigating Neovascularization in Rat Decellularized Intestine: An In Vitro Platform for Studying Angiogenesis.

One of the main challenges currently faced by tissue engineers is the loss of tissues postimplantation due to delayed neovascularization. Several strategies are under investigation to create vascularized tissue, but none have yet overcome this problem. In this study, we produced a decellularized natural vascular scaffold from rat intestine to use as an in vitro platform for neovascularization studies for tissue-engineered constructs. Decellularization resulted in almost complete (97%) removal of nuclei and DNA, while collagen, glycosaminoglycan, and laminin content were preserved. Decellularization did, however, result in the loss of elastin and fibronectin. Some proangiogenic factors were retained, as fragments of decellularized intestine were able to stimulate angiogenesis in the chick chorioallantoic membrane assay. We demonstrated that decellularization left perfusable vascular channels intact, and these could be repopulated with human dermal microvascular endothelial cells. Optimization of reendothelialization of the vascular channels showed that this was improved by continuous perfusion of the vasculature and further improved by infusion of human dermal fibroblasts into the intestinal lumen, from where they invaded into the decellularized tissue. Finally we explored the ability of the perfused cells to form new vessels. In the absence of exogenous angiogenic stimuli, Dll4, a marker of endothelial capillary-tip cell activation during sprouting angiogenesis, was absent, indicating that the reformed vasculature was largely quiescent. However, after addition of vascular endothelial growth factor A, Dll4-positive endothelial cells could be detected, demonstrating that this engineered vascular construct maintained its capacity for neovascularization. In summary, we have demonstrated how a natural xenobiotic vasculature can be used as an in vitro model platform to study neovascularization and provide information on factors that are critical for efficient reendothelialization of decellularized tissue.

Significance of endothelial progenitor cells (EPC) for tumorigenesis of head and neck squamous cell carcinoma (HNSCC): possible marker of tumor progression and neovascularization?

Angiogenesis and neovascularisation plays a crucial role for tumorigenesis and tumor progression in head and neck squamous cell carcinoma (HNSCC). The aim of our study was to investigate the neovascularization capacity by endothelial progenitor cells (EPC) in tumor patient as a possible predictor for tumor progression and tumor stage. Therefore, we investigated the cell number and biologic activity by cell migration and colony-forming ability of EPC. Cells were isolated from the peripheral venous blood of 79 patients who suffer HNSCC in different stages of disease. Thirty-three healthy individuals served as the control group. Significantly increased biological activities were reflected by expression of the migration rate (1027±1510) in comparison to the control group (632±269) and the clonal potency measured by colony-forming unit (CFU) (tumor patients (19.7±12.3) vs. control group (10.84±4.8)). To determine whether or not EPC number can be used as a valid prognostic marker for clinical outcome of tumor patients, we furthermore compared a "high EPC-number-subgroup" (HI) with a "low EPC-number-subgroup" (LO) in a Kaplan-Meier survival curve. The HI-subgroup shows herein clearly a worse outcome. Our findings indicate a possible pathway for EPC to play a critical role in the vasculogenesis and consequently in the progression of HNSCC. Our findings could serve as possible predictors for the neovascularisation potential in HNSCC tumor patients.

Apolipoprotein A-I Limits the Negative Effect of Tumor Necrosis Factor on Lymphangiogenesis.

Lymphatic endothelial dysfunction underlies the pathogenesis of many chronic inflammatory disorders. The proinflammatory cytokine tumor necrosis factor (TNF) is known for its role in disrupting the function of the lymphatic vasculature. This study investigates the ability of apolipoprotein (apo) A-I, the principal apolipoprotein of high-density lipoproteins, to preserve the normal function of lymphatic endothelial cells treated with TNF. TNF decreased the ability of lymphatic endothelial cells to form tube-like structures. Preincubation of lymphatic endothelial cells with apoA-I attenuated the TNF-mediated inhibition of tube formation in a concentration-dependent manner. In addition, apoA-I reversed the TNF-mediated suppression of lymphatic endothelial cell migration and lymphatic outgrowth in thoracic duct rings. ApoA-I also abrogated the negative effect of TNF on lymphatic neovascularization in an ATP-binding cassette transporter A1-dependent manner. At the molecular level, this involved downregulation of TNF receptor-1 and the conservation of prospero-related homeobox gene-1 expression, a master regulator of lymphangiogenesis. ApoA-I also re-established the normal phenotype of the lymphatic network in the diaphragms of human TNF transgenic mice. ApoA-I restores the neovascularization capacity of the lymphatic system during TNF-mediated inflammation. This study provides a proof-of-concept that high-density lipoprotein-based therapeutic strategies may attenuate chronic inflammation via its action on lymphatic vasculature.