DESCRIPTION (provided by applicant): The shortage of donor organs for transplantation suggests a need to develop engineered tissue transplants. Proper in vitro vascularization, a key prerequisite for the development of functional engineered tissue constructs, would enable adequate mass exchange, gas supply, and functional mediator exchange in high- density tissue cultures. The impact of physical and mechanical factors supporting endothelial differentiation has been investigated, but not in three-dimensional (3D) co-culture models. We propose to address this gap in cellular models and technology model systems, by analyzing neo-vascularization in an organ-like environment in vitro designed to mimic human organogenesis and that can vary physical conditions, such as flow- and pressure changes in the rhythm of the heart rate. In the fetal liver in vivo, angiogenesis occurs in hematopoietic and hepatic tissues that develop together. In our cell model for enabling vascularization in vitro, we therefore propose to investigate second trimester human fetal liver derived endothelial progenitors within fetal parenchymal cells, which contribute to hematopoietic and hepatic tissue vascularization. In the culture technology model, we propose to apply physical forces to control vascular structure formation, shear stress, perfusion flow and pressure changes. Additionally we will investigate the effects of calcium liberating hydroxyapatite scaffolds that mimics natural bone on formation of hematopoietic vascular sinusoids in the stem cell niche. RFP transfection labeled progenitors (hemangioblasts and angioblasts) and non-endothelial fetal liver cells will be cultured in 3D perfusion and the response to various physical-mechanical cues determined. Harvested cells will be analyzed by histology, flow cytometry, and gene expression, and compared to prenatal organ explants and postnatal organ tissues in vivo. The prior labeling of hemangioblasts will allow us to selectively distinguish between original hemangioblasts, endothelial- and non-endothelial cell types. The bioreactor model provides four independent interwoven hollow fiber compartments, enabling 3D perfusion with low gradients by decentral mass exchange and integral oxygenation. This has been proven to support vascularized tissue-like structure formation at high cell densities. We have already demonstrated that our 3D perfusion bioreactors support the spontaneous neo-tissue formation with neo-vascular hepatic structures and functionality in the laboratory and in clinical application for extracorporeal liver support. The innovation of our project is the specific experimental model that mimics the mass exchange in the native organ environment, allowing the fate of labeled fetal vascular progenitors to be studied during tissue formation, depending on different physical conditions. The project outcome will contribute to our understanding of the role of bioengineered supports and physical forces in establishing functional 3D engineered neo-vascular constructs in hematopoietic and hepatic tissues. (End of Abstract)

NARRATIVE The shortage of donor organs for transplantation suggests the need for engineered tissue transplants. The development of functional engineered tissue constructs, however, depends on proper vascularization. We propose to address a gap in model systems for analyzing neo-vascularization by developing a in-vitro organ- like environment capable of mimicking human organogenesis under various physical conditions. We propose to investigate the fate of labeled early human endothelial progenitors in previously developed 3D perfusion bioreactors. These bioreactors provide a specific experimental model that mimics the mass exchange in the native organ environment, while the fate of labeled vascular progenitors can be studied during tissue formation under different physical parameters. Specifically, we can investigate how physical forces that occur in vivo during organogenesis, such as flow and pressure changes, instruct the establishment of functional 3D engineered neo-vascular constructs in hematopoietic and hepatic tissues. In the fetal liver in vivo, angiogenesis occurs in hematopoietic and hepatic tissues that develop together. As a cell model for our studies on enabling vascularization in vitro, we therefore propose to investigate genetically labeled human fetal liver derived endothelial progenitors co-cultured with fetal parenchymal cells, that contribute to hematopoietic- and hepatic tissue vascularization. Success of our proposed studies would have a positive impact on research in angiogenesis, hematology, hepatology, and transplantation medicine. The in vitro tissue culture model can be offered for basic research or pharmacological studies and cell-based transplantation therapy can be further developed. Positive implications for public health would relate to the clinically significant problem of mortality in transplantation medicine.