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Biomedical subjects

Joyce Bischoff

Publications and source records attributed to Joyce Bischoff.

18 recordsLinked to original sources
PubMed2006

Human pulmonary valve progenitor cells exhibit endothelial/mesenchymal plasticity in response to vascular endothelial growth factor-A and transforming growth factor-beta2.

In situ analysis of fetal semilunar valve leaflets has revealed cells coexpressing endothelial and mesenchymal markers along the endothelium, with diminished frequency seen in adult valves. To determine whether such cells are progenitor cells, we isolated clonal populations from human pulmonary valves. The clones expressed endothelial markers but showed potential to further differentiate into endothelium in response to vascular endothelial growth factor (VEGF)-A. When exposed to transforming growth factor (TGF)-beta2, individual clones adopted a mesenchymal phenotype to varying degrees and expressed markers of endothelial to mesenchymal transformation (EMT). Both VEGF- and TGFbeta2-induced phenotypic changes were partially reversible, indicating the plasticity of these cells. When challenged with VEGF or TGFbeta2, a hierarchy of endothelial/mesenchymal potential could be seen among the clonal populations: cells initially closer to an endothelial phenotype showed a strong response to TGFbeta2 that could be inhibited by VEGF, whereas cells closer to a mesenchymal phenotype responded to TGFbeta2 but were resistant to endothelial-inducing effects of VEGF. These findings suggest the presence of bipotential valve progenitor cells with ability to differentiate into either endothelial or interstitial cells of the valve leaflet. Understanding the differentiation potential and function of these cells may be important for understanding heart valve disease and may also be applied to current paradigms for creating tissue-engineered heart valves.

Biomarkers↗
PubMed2006

Endothelial progenitor cells from infantile hemangioma and umbilical cord blood display unique cellular responses to endostatin.

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 blood-derived 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 mRNA-expression 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.

Angiogenesis Inhibitors↗
PubMed2006

Mesenchymal stem cells and adipogenesis in hemangioma involution.

Hemangioma is a benign tumor of infancy whose hallmark is rapid growth during the first year of life followed by slow regression during early childhood. The proliferating phase is characterized by abundant immature endothelial cells, the involuting phase by prominent endothelial-lined vascular channels and endothelial apoptosis, and the involuted phase by few remaining capillary-like vessels surrounded by loose fibrofatty tissue. Nothing is known about the mechanisms that contribute to the adipogenesis during this spontaneous regression. We postulated that mesenchymal stem cells (MSCs) reside in the tumor and preferentially differentiate into adipocytes. To test this hypothesis, we isolated MSCs from 14 proliferating and five involuting hemangiomas by taking advantage of the well known selective adhesion of MSCs to bacteriologic dishes. These hemangioma-derived MSCs (Hem-MSCs) are similar to MSCs obtained from human bone marrow, expressing the cell surface markers SH2 (CD105), SH3, SH4, CD90, CD29, smooth muscle alpha-actin, and CD133 but not the hematopoietic markers CD45 and CD14 or the hematopoietic/endothelial markers CD34, CD31, and kinase insert domain receptor (KDR). Hem-MSCs exhibited multilineage differentiation with robust adipogenic potential that correlated with the proliferating phase. The numbers of adipogenic Hem-MSCs were higher in proliferating-phase than in involuting-phase tumors and higher than in normal infantile skin. Furthermore, Hem-MSCs exhibited a random pattern of X-chromosomal inactivation, indicating that these cells are not clonally derived. In summary, we have identified MSCs as a novel cellular constituent in infantile hemangioma. These MSCs may contribute to the adipogenesis during hemangioma involution.

Adipogenesis↗
PubMed2006

Vascular endothelial growth factor receptor signaling is required for cardiac valve formation in zebrafish.

Vascular endothelial growth factor-receptors (VEGF-Rs) are pivotal regulators of vascular development, but a specific role for these receptors in the formation of heart valves has not been identified. We took advantage of small molecule inhibitors of VEGF-R signaling and showed that blocking VEGF-R signaling with receptor selective tyrosine kinase inhibitors, PTK 787 and AAC 787, from 17-21 hr post-fertilization (hpf) in zebrafish embryos resulted in a functional and structural defect in cardiac valve development. Regurgitation of blood between the two chambers of the heart, as well as a loss of cell-restricted expression of the valve differentiation markers notch 1b and bone morphogenetic protein-4 (bmp-4), was readily apparent in treated embryos. In addition, microangiography revealed a loss of a definitive atrioventricular constriction in treated embryos. Taken together, these data demonstrate a novel function for VEGF-Rs in the endocardial endothelium of the developing cardiac valve.

Animals↗
PubMed2006

Engineering of blood vessels from acellular collagen matrices coated with human endothelial cells.

Small-caliber synthetic grafts used for coronary bypass artery grafting are compromised by thrombogenicity and accelerated intimal thickening, resulting in early graft occlusion. Herein we describe the fabrication and physical properties of small-caliber blood vessels using decellularized porcine aortic segments. These vessels were further coated with human saphenous vein endothelial cells (HSVECs) for future clinical applications. Chemical staining of decellularized vessels showed that they preserved their native matrix architecture, including several collagen layers in between internal and external elastin layers. The burst pressure for the decellularized vessels was higher than 1,000 mmHg. HSVECs, seeded on the luminal side, adhered to the matrix and formed a uniform monolayer. HSVEC-seeded vessels produced prostaglandin I2 and released vasoactive agents in response to the calcium ionophore A23187. These results show that engineered blood vessels coated with the host endothelial cells possess morphologic and functional characteristics of human small-caliber vessels. Tissue-engineered vessels may potentially be useful clinically as vascular grafts.

Animals↗
PubMed2004

Heart valve development: endothelial cell signaling and differentiation.

During the past decade, single gene disruption in mice and large-scale mutagenesis screens in zebrafish have elucidated many fundamental genetic pathways that govern early heart patterning and differentiation. Specifically, a number of genes have been revealed serendipitously to play important and selective roles in cardiac valve development. These initially surprising results have now converged on a finite number of signaling pathways that regulate endothelial proliferation and differentiation in developing and postnatal heart valves. This review highlights the roles of the most well-established ligands and signaling pathways, including VEGF, NFATc1, Notch, Wnt/beta-catenin, BMP/TGF-beta, ErbB, and NF1/Ras. Based on the interactions among and relative timing of these pathways, a signaling network model for heart valve development is proposed.

Animals↗
PubMed2004

E-selectin is required for the antiangiogenic activity of endostatin.

Endostatin, a 20-kDa fragment of collagen XVIII, is a potent angiogenesis inhibitor. E-selectin, an inducible leukocyte adhesion molecule specifically expressed by endothelial cells, has also been implicated in angiogenesis. By using in vivo, ex vivo, and in vitro angiogenic assays, we investigated the functional relationship between endostatin and E-selectin. In corneal micropocket assays, recombinant endostatin administered i.p. by osmotic pump inhibited basic fibroblast growth factor-induced angiogenesis in WT, but not E-selectin-deficient, mice. Similarly, endostatin inhibited vascular endothelial growth factor-stimulated endothelial sprout formation from aortic rings dissected from WT but not from E-selectin-deficient mice. To further explore this apparent requirement for E-selectin in endostatin action, we manipulated E-selectin expression in cultured human endothelial cells. When E-selectin was induced by IL-1beta, or lipopolysaccharide, human umbilical vein endothelial cells and human dermal microvascular endothelial cells each became markedly more sensitive to inhibition by endostatin in a vascular endothelial growth factor-induced cell migration assay. To dissociate E-selectin expression from other consequences of endothelial activation, human umbilical vein endothelial cells were transduced with an adenoviral human E-selectin expression construct; these cells also showed increased sensitivity to endostatin, and this effect required the E-selectin cytoplasmic domain. Taken together, these results indicate that E-selectin is required for the antiangiogenic activity of endostatin in vivo and ex vivo and confers endostatin sensitivity to nonresponsive human endothelial cells in vitro. E-selectin may be a useful predictor and modulator of endostatin efficacy in antiangiogenic therapy.

Angiogenesis Inhibitors↗
PubMed2004

Tissue-engineered microvessels on three-dimensional biodegradable scaffolds using human endothelial progenitor cells.

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.

AC133 Antigen↗
PubMed2003

Endothelial progenitor cells in infantile hemangioma.

Infantile hemangioma is an endothelial tumor that grows rapidly after birth but slowly regresses during early childhood. Initial proliferation of hemangioma is characterized by clonal expansion of endothelial cells (ECs) and neovascularization. Here, we demonstrated mRNA encoding CD133-2, an important marker for endothelial progenitor cells (EPCs), predominantly in proliferating but not involuting or involuted hemangioma. Progenitor cells coexpressing CD133 and CD34 were detected by flow cytometry in 11 of 12 proliferating hemangioma specimens from children 3 to 24 months of age. Furthermore, in 4 proliferating hemangiomas, we showed that 0.14% to 1.6% of CD45(-) nucleated cells were EPCs that coexpressed CD133 and the EC marker KDR. This finding is consistent with the presence of KDR(+) immature ECs in proliferating hemangioma. Our results suggest that EPCs contribute to the early growth of hemangioma. To our knowledge, this is the first study to show direct evidence of EPCs in a human vascular tumor.

AC133 Antigen↗
PubMed2003

Differential expression of CD146 in tissues and endothelial cells derived from infantile haemangioma and normal human skin.

Haemangioma is the most common tumour of endothelial origin, occurring in 4-10% of Caucasian infants. It is characterized by rapid growth during the first year of postnatal life, followed by spontaneous regression from 1 to 7 years of age. The cell surface adhesion molecule CD146 has been identified as an endothelial cell marker. Despite advances in understanding the functional role of CD146 in normal endothelial cells and tumour progression, its expression and a possible role in an endothelial tumour have not been studied. As part of an investigation of endothelial cell alterations in infantile haemangioma, differential expression studies were performed with several known antigens and endothelial cell markers. Using immunohistochemical and flow cytometric analyses, cultured human dermal microvascular endothelial cells isolated from newborn foreskin (HDMEC) were compared with endothelial cells derived from haemangioma tissue (HemECs). In addition, immunohistochemistry was used to compare haemangioma tissues with normal human skin. Unexpectedly, cultured HemECs showed a significantly lower level of CD146 than HDMECs by both flow cytometric analysis and immunofluorescence staining. Using immunohistochemical studies, it was further demonstrated that endothelia in all haemangioma tissues, regardless of the tumour phase, showed negative immunoreactivity for CD146. In contrast, strong positive staining for CD146 was observed in the pericyte-like cells that surround the endothelial layers. These findings are believed to be relevant to the molecular basis of haemangioma. Furthermore, it is possible that antibodies against CD146 may be useful for separating haemangioma-derived endothelial cells from normal endothelial cells and pericytes.

Antigens, CD↗
PubMed2003

Thoracic Surgery Directors Association Award. Bone marrow as a cell source for tissue engineering heart valves.

BACKGROUND: This study was designed to assess the feasibility of using ovine bone marrow-derived mesenchymal stem cells to develop a trileaflet heart valve using a tissue engineering approach. METHODS: Bone marrow was aspirated from the sternum of adult sheep. Cells were isolated using a Ficoll gradient, cultured, and characterized based on immunofluorescent staining and the ability to differentiate down a specific cell lineage. Two million cells per centimeter squared were delivered onto a polyglycolic acid (PGA), poly-4-hydroxybutyrate (P4HB) composite scaffold and cultured for 1 week before being transferred to a pulse duplicator for an additional 2 weeks. The tissue-engineered valves were assessed by histology, scanning electron microscopy, and biomechanical flexure testing. RESULTS: Cells expressed SH2, a marker for mesenchymal stem cells, as well as specific markers of smooth muscle cell lineage including alpha-smooth muscle actin, desmin, and calponin. These cells could be induced to differentiate down an adipocyte lineage confirming they had not fully committed to a specific cell lineage. Preliminary histologic examination showed patchy surface confluency confirmed by scanning electron microscopy, and deep cellular material. Biomechanical flexure testing of the leaflets showed an effective stiffness comparable to normal valve leaflets. CONCLUSIONS: Mesenchymal stem cells can be isolated noninvasively from the sternum of sheep and can adhere to and populate a PGA/P4HB composite scaffold to form "tissue" that has biomechanical properties similar to native heart valve leaflets. Thus, bone marrow may be a potential source of cells for tissue engineering trileaflet heart valves, particularly in children with congenital heart disease.

Animals↗
PubMed2003

Quantitative evaluation of endothelial progenitors and cardiac valve endothelial cells: proliferation and differentiation on poly-glycolic acid/poly-4-hydroxybutyrate scaffold in response to vascular endothelial growth factor and transforming growth factor beta1.

Three-dimensional scaffolds made of bioabsorbable polymeric constituents are currently being tested for use in tissue engineering of various tissues. A composite scaffold of poly-glycolic acid (PGA) non-woven mesh dip-coated in a 1% solution of poly-4-hydroxybutyrate (P4HB) was shown to be suitable as a scaffold for creation of tissue-engineered trileaflet pulmonic valve replacements in sheep [Hoerstrup, S.P., et al., Circulation 102(Suppl. 3), III44, 2000]. However, little is known about how cells seeded on PGA/P4HB respond in vitro to soluble factors supplied in the culture medium. To optimize tissue development in vitro, before implantation, we set out to develop quantitative biochemical assays to measure how cells seeded on PGA/P4HB respond to growth and differentiation factors. Herein we show that ovine aortic valvular endothelial cells and circulating endothelial progenitor cells (EPCs) seeded onto PGA/P4HB proliferate in response to vascular endothelial growth factor and transdifferentiate to a mesenchymal phenotype in response to transforming growth factor beta(1). Transdifferentiation from an endothelial to mesenchymal phenotype is a critical step during embryonic development of cardiac valves. Our results demonstrate that valvular endothelial cells and EPCs isolated from peripheral blood can recapitulate critical developmental steps on PGA/P4HB. These results demonstrate that PGA/P4HB provides a conducive environment for cellular proliferation, differentiation, and tissue development.

Cell Differentiation↗
PubMed2003

Human pulmonary valve endothelial cells express functional adhesion molecules for leukocytes.

BACKGROUND AND AIM OF THE STUDY: Histopathological studies of rejected orthotopic heart transplants suggest that cardiac valve endothelium is spared the inflammatory cell infiltration and tissue damage that occurs in the myocardium. To test whether this apparent protection from leukocyte invasion might be an inherent feature of the valve endothelium, leukocyte adhesion molecule expression and function were analyzed in human pulmonary valve endothelial cells (HPVEC). Use of cultured HPVEC allowed delineation of the potential contribution of functional adhesion molecules from the contribution of hemodynamic forces exerted on the leaflet surface in vivo METHODS AND RESULTS: HPVEC express E-selectin, ICAM-1, and VCAM-1 in response to the inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) similarly to other types of cultured human endothelial cells. In a static cell adhesion assay, E-selectin-mediated adhesion of HL-60 cells, a human promyelocytic leukemia cell line, and U937 cells, a human monocytic cell line, was determined in cells treated with TNF-alpha for 5 h. After 24 h of TNF-alpha, adhesion of U937 cells to HPVEC was mediated primarily by VCAM-1, consistent with the high expression of VCAM-1 and diminished expression of E-selectin at 24 h. CONCLUSION: These results demonstrate that HPVEC express functional leukocyte adhesion molecules in vitro and suggest that cardiac valve endothelium is competent to initiate leukocyte adhesion. Thus, other factors, such as the hemodynamic forces exerted on the valve, may contribute to the apparent protection from inflammatory cell infiltration in vivo.

Adolescent↗
PubMed2002

NFATc1 mediates vascular endothelial growth factor-induced proliferation of human pulmonary valve endothelial cells.

Mice deficient for the transcription factor NFATc1 fail to form pulmonary and aortic valves, a defect reminiscent of some types of congenital human heart disease. We examined the mechanisms by which NFATc1 is activated and translocated to the nucleus in human pulmonary valve endothelial cells to gain a better understanding of its potential role(s) in post-natal valvular repair as well as valve development. Herein we demonstrate that activation of NFATc1 in human pulmonary valve endothelial cells is specific to vascular endothelial growth factor (VEGF) signaling through VEGF receptor 2. VEGF-induced NFATc1 nuclear translocation was inhibited by either cyclosporin A or a calcineurin-specific peptide inhibitor; these findings suggest that VEGF stimulates NFATc1 nuclear import in human pulmonary valve endothelial cells by a calcineurin-dependent mechanism. Importantly, both cyclosporin A and the calcineurin-specific peptide inhibitor reduced VEGF-induced human pulmonary valve endothelial cell proliferation, indicating a functional role for NFATc1 in endothelial growth. In contrast, VEGF-induced proliferation of human dermal microvascular and human umbilical vein endothelial cells was not sensitive to cyclosporin A. Finally, NFATc1 was detected in the endothelium of human pulmonary valve leaflets by immunohistochemistry. These results suggest VEGF-induced NFATc1 activation may be an important mechanism in cardiac valve maintenance and function by enhancing endothelial proliferation.

Adolescent↗
PubMed2002

AC133-2, a novel isoform of human AC133 stem cell antigen.

Human AC133 antigen, also called CD133, was recently identified as a hematopoietic stem cell marker. However, the molecular structure and function of this protein has remained unclear. Here we cloned and identified a novel isoform of AC133, which we named AC133-2. In comparison to the reported AC133 cDNA, which is referred to herein as AC133-1, a small exon of 27 nucleotides is deleted in AC133-2 by alternative mRNA splicing. Similar to the previously characterized AC133 antigen, recombinant AC133-2 expressed in 293 cells was glycosylated and transported to plasma membrane. AC133-2 mRNA was found predominant in a variety of human fetal tissue, adult tissues, and several carcinomas. In contrast, AC133-1 mRNA was more prominent in fetal brain and adult skeletal muscle but was not detected in fetal liver and kidney, adult pancreas, kidney, and placenta, suggesting different roles for the two isoforms in fetal development and mature organ homeostasis. Here, we demonstrate that AC133-2 is the isoform expressed on hematopoietic stem cells derived from fetal liver, bone marrow, and peripheral blood. The results indicate that AC133-2, not AC133-1, has been the cell surface antigen recognized by anti-AC133 monoclonal antibodies that are used for isolation of hematopoietic stem cells. To further investigate its expression in other stem cell populations, we found that AC133-2 co-expressed with beta(1) integrin in the basal layer of human neonatal epidermis. AC133-2(+)/beta(1) integrin(+) cells proliferated and differentiated in culture, which coincided with a loss of AC133-2 and gain in a terminal differentiation marker involucrin. Taken together, these results suggest that AC133-2 is expressed in multiple stem cell niches and may provide a means to isolate specific stem cell subpopulations from human tissues.

AC133 Antigen↗
PubMed2002

Monoclonal expansion of endothelial cells in hemangioma: an intrinsic defect with extrinsic consequences?

Infantile hemangioma is a benign tumor of endothelial cells (ECs) that is well known to pediatricians because of its frequency and sometimes disturbingly rapid growth. The primary defect(s) that cause hemangioma have not yet been elucidated, but recent studies have revealed that hemangiomas are composed of clonal ECs that exhibit abnormal properties in vitro. These studies support the hypothesis that hemangiomas arise when a somatic mutation occurs in a single endothelial progenitor, leading to dysregulated activity of one or more genes that control EC growth. Aberrant endothelial growth may in turn alter patterns of gene expression in nearby cells--in the overlying epidermis, for example--and account for observed extrinsic alterations that may influence hemangiogenesis. Unraveling the cellular and molecular basis of hemangioma is likely to yield critical insights into the mechanisms of EC proliferation and regression that may be applicable to other cardiovascular disorders.

Cell Differentiation↗
PubMedDate not supplied

Genomic imprinting of IGF2 is maintained in infantile hemangioma despite its high level of expression.

Hemangioma, the most common tumor of infancy, is characterized by rapid growth and slow regression. Increased mRNA expression of insulin-like growth factor 2 (IGF2) has been detected in the proliferating phase by cDNA microarray analysis, but the underlying mechanism causing the increase remains unknown. Here, using quantitative real-time polymerase chain reaction (PCR) and immunohistochemistry, we show that IGF2 is highly expressed in both proliferating and involuting phase hemangioma, but is not detectable in other vascular lesions such as pyogenic granuloma, venous malformation, lymphatic malformation, or in normal infant skin. Loss of imprinting of the Igf2 gene has been associated with IGF2 overexpression in a variety of childhood tumors. To determine if loss of imprinting and consequent bi-allelic expression might contribute to the increased expression of IGF2, we examined the genomic imprinting status of Igf2 in 48 individual hemangiomas. We determined allele-specific Igf2 expression using reverse transcriptase-PCR combined with analysis of an Apa I-sensitive restriction fragment length polymorphism. Similar to heterozygous normal skin controls, all 15 informative hemangiomas showed uniform mono-allelic expression of Igf2. Therefore, loss of imprinting is not involved in the increased expression of IGF2 in infantile hemangioma.

Alleles↗