acase@tulane.edu / An emerging need in the microcirculation research is the development of biomimetic angiogenesis models that recapitulate the complexity of a real tissue. Angiogenesis, defined as the growth of new vessels from pre-existing vessels, involves multiple cell types, such as endothelial and perivascular cells, in a multi-system setting since blood vessel networks are usually accompanied by lymphatic and nervous systems. Therefore, a need exists for a model of angiogenesis from intact microvascular networks that more closely reflects an in vivo scenario for the investigation of underlying mechanisms and the pre-clinical development of therapies. While other approaches have proven useful in identifying mechanistic signaling information, they are often limited in their complexity and capability to mimic physiologically relevant scenarios in one way or another and do not fully recapitulate the in vivo scenario. The first aim of this study was to demonstrate the ability for time-lapse comparisons of microvascular networks in angiogenesis scenarios to investigate the fate of vascular islands and investigate the endothelial cell plasticity. We developed a time-lapse angiogenesis model based on our previously introduced rat mesentery model. We demonstrated that time-lapse rat mesentery culture model is a powerful tool to study multi-cell, multi-system dynamics in microvascular networks. For the second aim of this study, we used the method developed in aim one to establish rat mesentery culture model as a novel anti-angiogenic drug screening tool. Using time-lapse model enabled tissue-specific comparisons before and after drug treatment to investigate its effects on entire microvascular networks. Validation of this method for anti-angiogenic drug testing was demonstrated using known angiogenesis inhibitor. Next, we showcased a potential application of the model for evaluating unknown effects of drug repositioning based on FDA-approved drug combinations. The results demonstrated the ability to identify concentration-dependent effects in an intact network scenario. The objective of the third aim was to showcase the capability of the rat mesentery culture model to study stem cell fate. We developed a protocol to deliver mesenchymal stem cells to mesentery tissues and culture for a period of time in a controlled environment. We confirmed the perivascular location of a subset of stem cells within capillaries, with morphologies resembling pericytes, and expressing pericyte markers. We also demonstrated that tracking stem cells within the microvascular networks is possible using the rat mesentery culture model. Furthermore, we reported a high variability in perivascular incorporation among cells from different donors. This work establishes for the first time, to the best of our knowledge, an ex vivo model to look at microvascular networks before and after growth. We confirmed, for the first time, vascular island incorporation as a new mode of angiogenesis using a novel method for time-lapse imaging of microvascular networks ex vivo. The results also establish this method for drug testing and stem cell tracking in a microvascular setting. / 1 / Mohammad Sadegh Azimi