β‐arrestin2/miR‐155/ GSK 3β regulates transition of 5′‐azacytizine‐induced Sca‐1‐positive cells to cardiomyocytes

Stem‐cell antigen 1–positive (Sca‐1+) cardiac stem cells ( CSC s), a vital kind of CSC s in humans, promote cardiac repair in vivo and can differentiate to cardiomyocytes with 5′‐azacytizine treatment in vitro . However, the underlying molecular mechanisms are unknown. β‐arrestin2 is an important scaffold protein and highly expressed in the heart. To explore the function of β‐arrestin2 in Sca‐1+ CSC differentiation, we used β‐arrestin2–knockout mice and overexpression strategies. Real‐time PCR revealed that β‐arrestin2 promoted 5′‐azacytizine‐induced Sca‐1+ CSC differentiation in vitro . Because the micro RNA 155 (miR‐155) may regulate β‐arrestin2 expression, we detected its role and relationship with β‐arrestin2 and glycogen synthase kinase 3 ( GSK 3β), another probable target of miR‐155. Real‐time PCR revealed that miR‐155, inhibited by β‐arrestin2, impaired 5′‐azacytizine‐induced Sca‐1+ CSC differentiation. On luciferase report assay, miR‐155 could inhibit the activity of β‐arrestin2 and GSK 3β, which suggests a loop pathway between miR‐155 and β‐arrestin2. Furthermore, β‐arrestin2‐knockout inhibited the activity of GSK 3β. Akt, the upstream inhibitor of GSK 3β, was inhibited in β‐arrestin2‐Knockout mice, so the activity of GSK 3β was regulated by β‐arrestin2 not Akt. We transplanted Sca‐1+ CSC s from β‐arrestin2‐knockout mice to mice with myocardial infarction and found similar protective functions as in wild‐type mice but impaired arterial elastance. Furthermore, low level of β‐arrestin2 agreed with decreased phosphorylation of AKT and increased phophorylation of GSK 3β, similar to in vitro findings. The β‐arrestin2/miR‐155/ GSK 3β pathway may be a new mechanism with implications for treatment of heart disease.