Venous malformation-causative TIE2 mutations mediate an AKT-dependent decrease in PDGFB

Abstract

Mutations in the endothelial cell (EC) tyrosine kinase receptor TIE2 cause inherited and sporadic forms of venous malformation. The recurrent somatic mutation L914F and common germline mutation R849W differ in terms of phosphorylation level, as well as sub-cellular localization and trafficking of the receptor. Previous studies have shed light on certain pathogenic properties of R849W, but the mechanisms of action of L914F are unknown. We used global gene expression profiling to study the effects of L914F on ECs. We found that L914F strongly dysregulates genes involved in vascular development, cell migration and extracellular matrix processing, while R849W has weak effects. We also demonstrate, for the first time, that TIE2-mutant ECs are deficient in the production of PDGFB, both in vitro and ex vivo in patient tissues. This defect is mediated by the chronic, ligand-independent activation of AKT by the mutant receptors. Inadequate secretion of the major mural cell attractant likely plays an important role in the development of abnormal vascular channels, contributing to the characteristic paucity of surrounding vascular smooth muscle cells.

Rapamycin improves TIE2-mutated venous malformation in murine model and human subjects

“…3 in the current study) (15). The L914F mutation, like all other reported VM-causing TIE2 kinase domain substitutions, also elicits TIE2 receptor hyperphosphorylation and enhanced AKT signaling in cultured endothelial cells (30). Sustained endothelial AKT activation caused vascular malformations and increased blood vessel size in a transgenic myristoylated AKT mouse model (35).…”

“…30 and shown in Figure 4), a major effect of the elevated p-TIE2 in HUVEC-TIE2-L914F was strong activation of p-AKT. In TIE2-L914F, we detected increased p-AKT473 and p-AKT308, 38 ± 0.067-fold and 6 ± 0.28-fold higher than in HUVEC-TIE2-WT, respectively ( Figure 5, A and B).…”

Somatic PIK3CA mutations as a driver of sporadic venous malformations

“…ECs, which are key players in the development of vascular malformations, create a pathological niche that involves the mural cell compartment, probably in part as a result of aberrant cytokine secretion ( 12 , 34 ). To test the impact of the PIK3CA activating mutation H1047R on the secretion of angiogenic factors, we performed antibody arrays in our primary ECs carrying wild-type PIK3CA or the H1047R mutation.…”

La rapamycine ouvre l’ère des thérapies ciblées dans les malformations veineuses

“…En soutenue de TIE2 indépendamment de sa liaison à ses ligands. La mutation de TEK la plus fréquemment retrouvée dans les formes familiales est la substitution R849W 6 , alors que dans les formes sporadiques, la mutation la plus fré-quente (correspondant à 77 % des cas) est L914F 7 [5]. In vitro, les mutations de TIE2, exprimées dans des cellules endothéliales (HUVEC, human umbilical vein endothelial cells), entraînent une activation accrue d'Akt et de STAT-1 8 (signal transducer and activator of transcription 1) et une diminution de la production de PDGF-B (platelet-derived growth factor subunit B), un facteur de croissance stimulant la maturation endothéliale par attrait des péricytes autour des cellules endothéliales [6].…”

“…Au niveau moléculaire, la mutation de TIE2 est associée à une augmentation importante de l'activité d'Akt, confirmant le rôle du récepteur dans la stimulation de l'axe PI3K-Akt ( Figure 2B). 6 Substitution d'un tryptophane par une arginine en position 849. 7 Substitution d'une phénylalanine par une leucine en position 914.…”