Central Nervous System (CNS) has been identified as an immunoprivileged site originally due to the lack of lymphatic vasculature. There are intricate vascular network without lymphatic vasculature in the brain and spinal cord during development and in adult. Using the spinal cord vasculature model, we focus on understanding mechanisms by which the spinal cord prevents lymphangiogenesis but not angiogenesis. We have found that supernatant from cultured embryonic spinal cord prevents the differentiation of lymphatic endothelial cells, as well as the migration of lymphatic but not blood endothelial cells. Now we are extensively working to identify neuronal or glial signal(s) that prevent the differentiation and migration of the lymphatic endothelial cells in the CNS. The findings also provide a rational for testing the signal(s) as potent inhibitors of adult and tumor-induced lymphangiogenesis. Stem cells are established in the niche, a unique and specialized microenvironment. Given the importance of the vascular niche for a variety of stem cells, understanding the paracrine signals for stem cell maintenance has become more important. Whole-mount staining approach of the subventricular zone (SVZ) in the lateral ventricle walls of adult brain has revealed that slowly-dividing SVZ cells (adult neural stem cells?) are closely interacted with the local vasculature. Our challenge is to utilize a systematic multi-faceted approach to identify and validate the vascular niche signals involved in maintenance, self-renewal, proliferation and differentiation of neural stem cells. We have also developed a whole-mount imaging approach to examine brain vascular network that associate with neurons and astrocytes as well as neural stem cells. We are now evaluating the physiological relevance of the candidate niche signals in vitro and in vivo.
