Angiopoietin-1 protects mesenchymal stem cells against serum deprivation and hypoxia-induced apoptosis through the PI3K/Akt pathway.
OBJECTIVE
The angiopoietin-1 (Ang1)/Tie-2 signaling system not only plays a pivotal role in vessel growth, remodeling, and maturation, but also reduces apoptosis of endothelial cells, neurons, and cardiomyocytes. However, relatively little is known as to whether Ang1 has a protective effect on mesenchymal stem cells (MSC). The aim of the present study was to investigate the protective effect of Ang1/Tie-2 signaling on MSC against serum deprivation and hypoxia-induced apoptosis, and to determine the possible mechanisms.


METHODS
Hoechst 33342 and terminal deoxynucleotidyl transferase-mediated digoxigenin-dUTP nick-end labeling staining were used to assess the apoptosis of MSC. The expression of Tie-2, Akt, Bcl-2, Bax, and cleaved caspase-9 and -3 was detected by Western blot analysis.


RESULTS
This study showed that MSC expressed Tie-2 receptor, and Ang1 induced Tie-2 receptor phosphorylation. The protective effect of Ang1 on MSC was dose-dependent and peaked at 50 microg/L; however, the soluble Tie-2/Fc fusion protein, which acts as an inhibitor by sequestering Ang1, abrogated the anti-apoptotic effect. Ang1 induced Akt phosphorylation, increased the Bcl-2/Bax ratio, and decreased the activation of caspase-9 and -3. All these effects were attenuated by Tie-2/Fc and a phosphatidylinositol 3 kinase (PI3K) inhibitor, wortmannin.


CONCLUSIONS
These results demonstrate that Ang1 can protect MSC against serum deprivation and hypoxia-induced apoptosis; Ang1/Tie-2 signaling and its downstream PI3K/Akt messenger pathway are crucial in the processes leading to MSC survival.
Liu
Xian-bao
XB
Department of Cardiology, Second affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou 310009, China.
Jiang
Jun
J
Gui
Chun
C
Hu
Xin-yang
XY
Xiang
Mei-xiang
MX
Wang
Jian-an
JA
D042683:Angiopoietin-1 / Q000494:pharmacology*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D020169:Caspases / Q000502:physiology; D002470:Cell Survival / Q000187:drug effects; D016895:Culture Media, Serum-Free; D006801:Humans; D000860:Hypoxia / Q000473:pathology / Q000517:prevention & control*; D020287:In Situ Nick-End Labeling; D059630:Mesenchymal Stem Cells / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D051058:Oncogene Protein v-akt / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects*
D042683:Angiopoietin-1; D016895:Culture Media, Serum-Free; D019869:Phosphatidylinositol 3-Kinases; D051058:Oncogene Protein v-akt; D020169:Caspases