RESUMEN
BACKGROUND: Schlemm's canal (SC) is a large vessel residing in the iridocorneal angle and is required to regulate aqueous humor outflow. Normal SC structure and function is indispensable for maintaining normal intraocular pressure, and elevated intraocular pressure is a risk factor for development of glaucoma. Recent reports have identified a key role of the angiopoietin-Tie2 pathway for SC development and function; however, the role of the orphan receptor Tie1 has not been clarified. METHODS: We used Tie1 knock out mice to study the function of Tie1 in SC development and function. Real-time quantitative polymerase chain reaction and Western blot analyses were used to verify Tie1 deletion. High-resolution microscopy of mouse SC whole mount and cross sections were used to study SC morphology. Measurement of intraocular pressure in live mice was used to study the impact of Tie1 on SC function. RESULTS: Tie1 is highly expressed in both human and mouse SC. Tie1 knock out mice display hypomorphic SC and elevated intraocular pressure as a result of attenuated SC development. CONCLUSIONS: Tie1 is indispensable for SC development and function, supporting it as a novel target for future SC-targeted glaucoma therapies and a candidate gene for glaucoma in humans.
Asunto(s)
Cámara Anterior/enzimología , Cámara Anterior/crecimiento & desarrollo , Endotelio Corneal/enzimología , Receptor TIE-1/metabolismo , Animales , Humor Acuoso/fisiología , Glaucoma/etiología , Humanos , Presión Intraocular/fisiología , Vasos Linfáticos/anomalías , Vasos Linfáticos/enzimología , Vasos Linfáticos/fisiología , Ratones , Ratones Noqueados , Modelos Animales , Receptor TIE-1/deficiencia , Receptor TIE-1/genéticaRESUMEN
Although the response of endothelial cells to the disturbed blood flow in the vicinity of atherosclerotic lesions is known to be distinct from that elicited by nonatherogenic laminar flow, the mechanisms involved are poorly understood. Our initial studies confirmed that expression of the endothelial receptor tyrosine kinase Tie1 was evident at regions of atherogenic flow in mature animals. We therefore hypothesized that Tie1 plays a role in the endothelial response to atherogenic shear stress. Consistent with this, we found that Tie1+/- mice bred to the apoE-deficient background displayed a 35% reduction in atherosclerosis relative to Tie1+/+;Apoe-/- mice. Since deletion of Tie1 results in embryonic lethality secondary to vascular dysfunction, we used conditional and inducible mutagenesis to study the effect of endothelial-specific Tie1 attenuation on atherogenesis in Apoe-/- mice and found a dose-dependent decrease in atherosclerotic lesions. Analysis of primary aortic endothelial cells indicated that atheroprotective laminar flow decreased Tie1 expression in vitro. Attenuation of Tie1 was associated with an increase in eNOS expression and Tie2 phosphorylation. In addition, Tie1 attenuation increased IkBα expression while decreasing ICAM levels. In summary, we have found that shear stress conditions that modulate atherogenic events also regulate Tie1 expression. Therefore, Tie1 may play a novel proinflammatory role in atherosclerosis.
Asunto(s)
Aterosclerosis/prevención & control , Receptor TIE-1/deficiencia , Receptor TIE-1/genética , Animales , Apolipoproteínas E/deficiencia , Apolipoproteínas E/genética , Aterosclerosis/etiología , Aterosclerosis/fisiopatología , Secuencia de Bases , Moléculas de Adhesión Celular/genética , Cartilla de ADN/genética , Modelos Animales de Enfermedad , Células Endoteliales/fisiología , Femenino , Expresión Génica , Hemorreología , Operón Lac , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Ratones Transgénicos , Óxido Nítrico Sintasa de Tipo III/genética , ARN Mensajero/genética , ARN Mensajero/metabolismo , Receptor TIE-1/fisiología , Transducción de Señal , Estrés Mecánico , Quinasas Asociadas a rho/genéticaRESUMEN
OBJECTIVE: Studies of Tie1 gene-targeted embryos have demonstrated loss of blood vessel integrity, but the relevance of Tie1 in lymphatic vasculature development is unknown. We tested the hypothesis that the swelling observed in Tie1 mutant embryos is associated with lymphatic vascular defects. METHODS AND RESULTS: We could extend the survival of the Tie1-deficient embryos in the ICR background, which allowed us to study their lymphatic vessel development. At embryonic day (E) 14.5, the Tie1(-/-) embryos had edema and hemorrhages and began to die. Immunohistochemical analysis revealed that they have abnormal lymph sacs. Tie1(-/-) mutants were swollen already at E12.5 without signs of hemorrhage. Their lymph sacs were abnormally patterned, suggesting that lymphatic malformations precede the blood vascular defects. We generated mice with a conditional Cre/loxP Tie1(neo) locus and found that the homozygous Tie1(neo/neo) hypomorphic embryos survived until E15.5 with lymphatic malformations resembling those seen in the Tie1(-/-) mutants. CONCLUSIONS: Our data show that loss of Tie1 results in lymphatic vascular abnormalities that precede the blood vessel phenotype. These findings indicate that Tie1 is involved in lymphangiogenesis and suggest differential requirements for Tie1 signaling in the two vascular compartments.
Asunto(s)
Células Endoteliales/enzimología , Linfangiogénesis , Vasos Linfáticos/enzimología , Receptor TIE-1/metabolismo , Animales , Edema/enzimología , Edema/fisiopatología , Pérdida del Embrión , Células Endoteliales/patología , Edad Gestacional , Hemorragia/enzimología , Hemorragia/fisiopatología , Homocigoto , Inmunohistoquímica , Linfangiogénesis/genética , Vasos Linfáticos/embriología , Vasos Linfáticos/fisiopatología , Ratones , Ratones Endogámicos ICR , Ratones Noqueados , Fenotipo , Receptor TIE-1/deficiencia , Receptor TIE-1/genéticaRESUMEN
In mammals, the continuous production of hematopoietic cells (HCs) is sustained by a small number of hematopoietic stem cells (HSCs) residing in the bone marrow. Early HSC activity arises in the aorta-gonad mesonephros region, within cells localized to the ventral floor of the major blood vessels, suggesting that the first HSCs may be derived from cells capable of giving rise to the hematopoietic system and to the endothelial cells of the vasculature. TIE1 (TIE) and TIE2 (TEK) are related receptor tyrosine kinases with an embryonic expression pattern in endothelial cells, their precursors, and HCs, suggestive of a role in the divergence and function of both lineages. Indeed, gene targeting approaches have shown that TIE1, TIE2, and ligands for TIE2, the angiopoietins, are essential for vascular development and maintenance. To explore possible roles for these receptors in HCs, we have examined the ability of embryonic cells lacking both TIE1 and TIE2 to contribute to developmental and adult hematopoiesis by generating chimeric animals between normal embryonic cells and cells lacking these receptors. We show here that TIE receptors are not required for differentiation and proliferation of definitive hematopoietic lineages in the embryo and fetus; surprisingly, however, these receptors are specifically required during postnatal bone marrow hematopoiesis.