title: Tipping off endothelial tubes: nitric oxide drives tip cells.
abstract: Angiogenesis, the formation of new blood vessels from pre-existing vessels, is a complex process that warrants cell migration, proliferation, tip cell formation, ring formation, and finally tube formation. Angiogenesis is initiated by a single leader endothelial cell called "tip cell," followed by vessel elongation by "stalk cells." Tip cells are characterized by their long filopodial extensions and expression of vascular endothelial growth factor receptor-2 and endocan. Although nitric oxide (NO) is an important modulator of angiogenesis, its role in angiogenic sprouting and specifically in tip cell formation is poorly understood. The present study tested the role of endothelial nitric oxide synthase (eNOS)/NO/cyclic GMP (cGMP) signaling in tip cell formation. In primary endothelial cell culture, about 40% of the tip cells showed characteristic sub-cellular localization of eNOS toward the anterior progressive end of the tip cells, and eNOS became phosphorylated at serine 1177. Loss of eNOS suppressed tip cell formation. Live cell NO imaging demonstrated approximately 35% more NO in tip cells compared with stalk cells. Tip cells showed increased level of cGMP relative to stalk cells. Further, the dissection of NO downstream signaling using pharmacological inhibitors and inducers indicates that NO uses the sGC/cGMP pathway in tip cells to lead angiogenesis. Taken together, the present study confirms that eNOS/NO/cGMP signaling defines the direction of tip cell migration and thereby initiates new blood vessel formation.
authors.affiliation: AU-KBC Research Centre, MIT Campus of Anna University, Chennai, India.
authors.forename: Mani Krishna
authors.initials: MK
authors.lastname: Priya
authors.forename: Giriraj
authors.initials: G
authors.lastname: Sahu
authors.forename: David R
authors.initials: DR
authors.lastname: Soto-Pantoja
authors.forename: Naga
authors.initials: N
authors.lastname: Goldy
authors.forename: Abaya Meenakshi
authors.initials: AM
authors.lastname: Sundaresan
authors.forename: Vivek
authors.initials: V
authors.lastname: Jadhav
authors.forename: T R
authors.initials: TR
authors.lastname: Barathkumar
authors.forename: Uttara
authors.initials: U
authors.lastname: Saran
authors.forename: B M
authors.initials: BM
authors.lastname: Jaffar Ali
authors.forename: David D
authors.initials: DD
authors.lastname: Roberts
authors.forename: Amal Kanti
authors.initials: AK
authors.lastname: Bera
authors.forename: Suvro
authors.initials: S
authors.lastname: Chatterjee
mesh_terms: D000818:Animals; D002417:Cattle; D002461:Cell Line, Transformed; D002645:Chickens; D006152:Cyclic GMP / Q000378:metabolism; D006801:Humans; D018919:Neovascularization, Physiologic / Q000502:physiology; D009569:Nitric Oxide / Q000502:physiology*; D052250:Nitric Oxide Synthase Type III / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D034741:RNA, Small Interfering / Q000235:genetics; D015854:Up-Regulation
chemical_list: D034741:RNA, Small Interfering; D009569:Nitric Oxide; D052250:Nitric Oxide Synthase Type III; D006152:Cyclic GMP