Inducible Knockdown of Endothelial Protein Tyrosine Phosphatase-1B Promotes Neointima Formation in Obese Mice by Enhancing Endothelial Senescence

Aims: Protein tyrosine phosphatase-1B (PTP1B) is a negative regulator of receptor tyrosine kinase signaling. In this study, we determined the importance of PTP1B expressed in endothelial cells for the vascular response to arterial injury in obesity. Results: Morphometric analysis of vascular lesions generated by 10% ferric chloride (FeCl3) revealed that tamoxifen-inducible endothelial PTP1B deletion (Tie2.ERT2-CrexPTP1B(fl/fl); End.PTP1B knockout, KO) significantly increased neointima formation, and reduced numbers of (endothelial lectin-positive) luminal cells in End.PTP1B-KO mice suggested impaired lesion re-endothelialization. Significantly higher numbers of proliferating cell nuclear antigen (PCNA)-positive proliferating cells as well as smooth muscle actin (SMA)-positive or vascular cell adhesion molecule-1 (VCAM1)-positive activated smooth muscle cells or vimentin-positive myofibroblasts were detected in neointimal lesions of End.PTP1B-KO mice, whereas F4/80-positive macrophage numbers did not differ. Activated receptor tyrosine kinase and transforming growth factor-beta (TGF) signaling and oxidative stress markers were also significantly more abundant in End.PTP1B-KO mouse lesions. Genetic knockdown or pharmacological inhibition of PTP1B in endothelial cells resulted in increased expression of caveolin-1 and oxidative stress, and distinct morphological changes, elevated numbers of senescence-associated beta-galactosidase-positive cells, and increased expression of tumor suppressor protein 53 (p53) or the cell cycle inhibitor cyclin-dependent kinase inhibitor-2A (p16INK4A) suggested senescence, all of which could be attenuated by small interfering RNA (siRNA)-mediated downregulation of caveolin-1. In vitro, senescence could be prevented and impaired re-endothelialization restored by preincubation with the antioxidant Trolox. Innovation: Our results reveal a previously unknown role of PTP1B in endothelial cells and provide mechanistic insights how PTP1B deletion or inhibition may promote endothelial senescence. Conclusion: Absence of PTP1B in endothelial cells impairs re-endothelialization, and the failure to induce smooth muscle cell quiescence or to protect from circulating growth factors may result in neointimal hyperplasia.