RESUMEN
RATIONALE: Noonan syndrome (NS) is one of the most frequent genetic disorders. Bleeding problems are among the most common, yet poorly defined complications associated with NS. A lack of consensus on the management of bleeding complications in patients with NS indicates an urgent need for new therapeutic approaches. OBJECTIVE: Bleeding disorders have recently been described in patients with NS harboring mutations of LZTR1 (leucine zipper-like transcription regulator 1), an adaptor for CUL3 (CULLIN3) ubiquitin ligase complex. Here, we assessed the pathobiology of LZTR1-mediated bleeding disorders. METHODS AND RESULTS: Whole-body and vascular specific knockout of Lztr1 results in perinatal lethality due to cardiovascular dysfunction. Lztr1 deletion in blood vessels of adult mice leads to abnormal vascular leakage. We found that defective adherent and tight junctions in Lztr1-depleted endothelial cells are caused by dysregulation of vesicular trafficking. LZTR1 affects the dynamics of fusion and fission of recycling endosomes by controlling ubiquitination of the ESCRT-III (endosomal sorting complex required for transport III) component CHMP1B (charged multivesicular protein 1B), whereas NS-associated LZTR1 mutations diminish CHMP1B ubiquitination. LZTR1-mediated dysregulation of CHMP1B ubiquitination triggers endosomal accumulation and subsequent activation of VEGFR2 (vascular endothelial growth factor receptor 2) and decreases blood levels of soluble VEGFR2 in Lztr1 haploinsufficient mice. Inhibition of VEGFR2 activity by cediranib rescues vascular abnormalities observed in Lztr1 knockout mice Conclusions: Lztr1 deletion phenotypically overlaps with bleeding diathesis observed in patients with NS. ELISA screening of soluble VEGFR2 in the blood of LZTR1-mutated patients with NS may predict both the severity of NS phenotypes and potential responders to anti-VEGF therapy. VEGFR inhibitors could be beneficial for the treatment of bleeding disorders in patients with NS.
Asunto(s)
Vasos Sanguíneos/metabolismo , Endosomas/metabolismo , Células Endoteliales/metabolismo , Hemorragia/metabolismo , Síndrome de Noonan/metabolismo , Factores de Transcripción/metabolismo , Receptor 2 de Factores de Crecimiento Endotelial Vascular/metabolismo , Malformaciones Vasculares/metabolismo , Animales , Vasos Sanguíneos/anomalías , Vasos Sanguíneos/efectos de los fármacos , Carcinoma Pulmonar de Lewis/metabolismo , Carcinoma Pulmonar de Lewis/patología , Modelos Animales de Enfermedad , Complejos de Clasificación Endosomal Requeridos para el Transporte/metabolismo , Endosomas/genética , Endosomas/patología , Células Endoteliales/efectos de los fármacos , Células Endoteliales/patología , Haploinsuficiencia , Células HeLa , Hemorragia/genética , Hemorragia/patología , Hemorragia/prevención & control , Humanos , Linfocinas/genética , Linfocinas/metabolismo , Ratones Endogámicos C57BL , Ratones Noqueados , Neovascularización Patológica , Síndrome de Noonan/tratamiento farmacológico , Síndrome de Noonan/genética , Síndrome de Noonan/patología , Fosforilación , Factor de Crecimiento Derivado de Plaquetas/genética , Factor de Crecimiento Derivado de Plaquetas/metabolismo , Inhibidores de Proteínas Quinasas/farmacología , Transporte de Proteínas , Quinazolinas/farmacología , Transducción de Señal , Factores de Transcripción/deficiencia , Factores de Transcripción/genética , Ubiquitinación , Receptor 2 de Factores de Crecimiento Endotelial Vascular/antagonistas & inhibidores , Receptor 2 de Factores de Crecimiento Endotelial Vascular/genética , Malformaciones Vasculares/tratamiento farmacológico , Malformaciones Vasculares/genética , Malformaciones Vasculares/patologíaRESUMEN
Here we identify a new role for Syndecan (Sdc), the only transmembrane heparan sulphate proteoglycan in Drosophila, in tracheal development. Sdc is required cell autonomously for efficient directed migration and fusion of dorsal branch cells, but not for dorsal branch formation per se. The cytoplasmic domain of Sdc is dispensable, indicating that Sdc does not transduce a signal by itself. Although the branch-specific phenotype of sdc mutants resembles those seen in the absence of Slit/Robo2 signalling, genetic interaction experiments indicate that Sdc also helps to suppress Slit/Robo2 signalling. We conclude that Sdc cell autonomously regulates Slit/Robo2 signalling in tracheal cells to guarantee ordered directional migration and branch fusion.
