On angiogenesis modulation

• During evolution, the transition from unicellular to multicellular organisms required the origin of a transport system capable of interconnecting specialized cells throughout the body of the organism. In higher animals, this route of transportation is the cardiovascular system, which allows gas exchange, and transport of immune cells, hormones, macromolecules, nutrients and waste products. Due to its central role, supporting other organs and tissues, the cardiovascular system forms early during the embryonic development and is the first functional organ of the body. The construction of a vascular system can seem to be trivial (a circuit of patent tubes of various diameters, how complicated can it be?), but it is not. First, the system contains many different cell types that interact with one another. Endothelial cells constitute the actual tube in contact with the blood. Mural cells, either vascular smooth muscle cells around larger vessels, or pericytes in the case of the capillaries, “wrap” the endothelium and exert vasoactive control, provide it with structural support, and instructive molecular cues. Second, many cellular processes including oxygen sensing, proliferation, differentiation, apoptosis, and adhesion are at work when a vascular system is formed, all requiring tight regulation and coordination. Third, different vascular beds have different properties, which need to be established and regulated via cell signaling. For example, compare the difference in permeability of the kidney endothelium with that of the blood- brain barrier. The phenomenon of blood vessel formation from pre-existing ones – angiogenesis – has been known for at least 100 years, and has been implicated in the pathology of many diseases, which in turn has sparked intensive research in the field in recent years. However, despite a tremendous effort to map and master this biological process, it is evident – given the somewhat meager results in the clinic – that more knowledge on how blood vessels are formed is required before effective drugs, inhibiting or stimulating angiogenesis, can be generated. For example, the identities of all genes involved are not known and more important, the principles of angiogenesis, according to which these genes effectuate their respective roles, are still very much in the dark. Herein, I describe work aimed at identifying genes and chemical compounds previously not implicated in angiogenesis, as well as at characterizing the role of angiogenesis modulating genes. Included is: i) how the regulator of G-protein coupled signaling RGS5 was identified as a novel marker for pericytes; ii) how the role of Notch signaling in angiogenesis was characterized, and shown to regulate the number of endothelial tip cells, in turn affecting the density of the resulting vascular plexus; iii) how sixteen genes and twenty-eight compounds modulating angiogenesis were identified, and a role for the serine/threonine (S/T) phosphatases PPP1CA, PPP1CC, and PPP4C was uncovered using – for the first time in vertebrates – a combination of reverse and chemical genetics; and finally iv) how the drug Perhexiline maleate for the treatment of angina pectoris, was identified as an anti-angiogenic compound, using a functional cell-based chemical screen.

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