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(Circulation Research. 2009;105:260.)
© 2009 American Heart Association, Inc.

Cellular Biology

Angiomotin-Like Protein 1 Controls Endothelial Polarity and Junction Stability During Sprouting Angiogenesis

Yujuan Zheng, Simona Vertuani, Staffan Nyström, Stéphane Audebert, Inèz Meijer, Tetyana Tegnebratt, Jean-Paul Borg, Per Uhlén, Arindam Majumdar^*, Lars Holmgren^*

From the Department of Oncology and Pathology (Y.Z., S.V., S.N., I.M., T.T., L.H.), Cancer Centrum Karolinska; and Laboratory of Molecular Neurobiology (P.U.) and Division of Matrix Biology (A.M.), Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Stockholm, Sweden; and Institut National de la Santé et de la Recherche Médicale (S.A., J.-P.B.), U891, Centre de Recherche en Cancérologie de Marseille, Institut Paoli-Calmettes, Univ Méditerranée, Marseille, France.

Correspondence to Lars Holmgren, Department of Oncology and Pathology, Cancer Centrum Karolinska, Karolinska Institutet, SE-17176 Stockholm, Sweden. E-mail lars.holmgren{at}ki.se

Rationale: We have previously shown that angiomotin (Amot) is essential for endothelial cell migration during mouse embryogenesis. However, 5% of Amot knockout mice survived without any detectable vascular defects. Angiomotin-like protein 1 (AmotL1) potentially compensates for the absence of Amot as it is 62% homologous to Amot and exhibits similar expression pattern in endothelial cells.

Objective: Here, we report the identification of a novel isoform of AmotL1 that controls endothelial cell polarization and directional migration.

Methods and Results: Small interfering RNA–mediated silencing of AmotL1 in mouse aortic endothelial cells caused a significant reduction in migration. In confluent mouse pancreatic islet endothelial cells (MS-1), AmotL1 colocalized with Amot to tight junctions. Small interfering RNA knockdown of both Amot and AmotL1 in MS-1 cells exhibited an additive effect on increasing paracellular permeability compared to that of knocking down either Amot or AmotL1, indicating both proteins were required for proper tight junction activity. Moreover, as visualized using high-resolution 2-photon microscopy, the morpholino-mediated knockdown of amotl1 during zebrafish embryogenesis resulted in vascular migratory defect of intersegmental vessels with strikingly decreased junction stability between the stalk cells and the aorta. However, the phenotype was quite distinct from that of amot knockdown which affected polarization of the tip cells of intersegmental vessels. Double knockdown resulted in an additive phenotype of depolarized tip cells with no or decreased connection of the stalk cells to the dorsal aorta.

Conclusions: These results cumulatively validate that Amot and AmotL1 have similar effects on endothelial migration and tight junction formation in vitro. However, in vivo Amot appears to control the polarity of vascular tip cells whereas AmotL1 mainly affects the stability of cell–cell junctions of the stalk cells.

Key Words: AmotL1 • polarity • migration • junction stability • zebrafish