The Noonan Syndrome Gene <i>Lztr1</i> Controls Cardiovascular Function by Regulating Vesicular Trafficking.

Abstract

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. 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. Whole-body and vascular specific knockout of <i>Lztr1</i> results in perinatal lethality due to cardiovascular dysfunction. <i>Lztr1</i> deletion in blood vessels of adult mice leads to abnormal vascular leakage. We found that defective adherent and tight junctions in <i>Lztr1</i>-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 <i>LZTR1</i> 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 <i>Lztr1</i> haploinsufficient mice. Inhibition of VEGFR2 activity by cediranib rescues vascular abnormalities observed in <i>Lztr1</i> knockout mice Conclusions: <i>Lztr1</i> deletion phenotypically overlaps with bleeding diathesis observed in patients with NS. ELISA screening of soluble VEGFR2 in the blood of <i>LZTR1</i>-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.