Abstract 14421: Hax1 Inhibits Mst1 to Promote Pro-angiogeneic Effects of Cardiac Stem Cells for Myocardial Repair
Background: Our previous study revealed that HCLS-associated protein X-1 (HAX1) could regulate Hippo cascades to enhance the therapeutic effects of sca1+ cardiac stem cells (CSCssca1+) in a mouse model of myocardial infarction (MI). This study is designed to elucidate the mechanism of interaction between HAX1 and Mammalian sterile twenty-like 1 (Mst1), an upstream kinase signal of the Hippo cassette, and determine any enhanced therapeutic effects of HAX1-overexpressing CSCssca1+ (CSCsHAX1) against MI.
Methods and Results: The co-immunoprecipitation and kinase activity assay demonstrated that HAX1 directly interacts with Mst1, which subsequently inhibits further Mst1 activation (as evidenced by the increased ED50 value) (Fig 1A). This inhibitory effect leads to decreased phosphorylation of large tumor suppressor 1 (LATS1) and enhanced nuclear translocation of Yes-associated protein (Yap) in CSCsHAX1 compared with non-encoding DNA sequence-transduced CSCssca1+ (CSCsNull). Interestingly, in vitro analysis using real time-PCR and flow cytometry revealed that VEGF expression levels increased to a greater extent in CSCsHAX1 in response to hypoxia (Fig 1B). This pronounced neovascularization effect was further confirmed in vivo by Von Willebrand factor staining (Fig 1C), when CSCsHAX1 were engrafted into mouse myocardium post ischemic injury. Corresponding echocardiograph assessment revealed that the recovery of cardiac function was significantly improved in CSCsHAX1-treated hearts when compared with CSCsNull group, as indicated by the increased value of ejection fraction (EF) (Fig 1D).
Conclusion: HAX1 can inhibit Mst1 activity through direct interaction with this principle Hippo pathway kinase that consequently promotes Yap nucleus translocation. This leads to the increased expression of VEGF in CSCsHAX1 for myocardial repair and heart performance improvement post MI.
Author Disclosures: W. Cai: None. L. Wang: None. L. Jiang: None. P. Christian: None. M. Xu: None. R.W. Millard: None. Y. Wang: None.
- © 2016 by American Heart Association, Inc.