Akt activation in platelets depends on Gi signaling pathways

Area of Science:

• Biochemistry
• Cell Biology
• Hematology

Background:

• The serine-threonine kinase Akt is a key regulator of cell survival, cell cycle, and platelet activation.
• Platelet stimulation by agonists like thrombin leads to Akt activation.
• Thrombin activates multiple G protein signaling pathways, necessitating an investigation into its mechanism of Akt activation.

Purpose of the Study:

• To elucidate the specific G protein signaling pathways involved in thrombin-induced Akt activation in platelets.
• To determine the roles of PAR1, PAR4, P2Y1, and P2Y12 receptors in this activation process.

Main Methods:

• Stimulation of platelets with various agonists (thrombin, PAR1-AP, PAR4-AP) and ADP.
• Assessment of Akt phosphorylation at Thr308 and Ser473.
• Utilized receptor antagonists (AR-C69931MX) and inhibitors (GF 109203X).
• Employed knockout mouse models (Galphaq-deficient, P2Y1-deficient) and clopidogrel treatment.

Main Results:

• Thrombin, PAR1-AP, and PAR4-AP induced Akt phosphorylation and activation, inhibited by P2Y12 antagonist and PKC inhibitor.
• Supplemental Gi or Gz signaling restored Akt phosphorylation.
• Galphaq-deficient platelets showed impaired Akt phosphorylation by thrombin and PAR4-AP.
• ADP induced Akt phosphorylation in Galphaq- and P2Y1-deficient platelets, blocked by P2Y12 antagonist.
• Clopidogrel treatment abolished ADP-induced Akt phosphorylation.

Conclusions:

• Gi signaling pathways are essential for Akt activation in platelets; Gq and G12/13 are not required.
• Secreted ADP acting through Gi signaling pathways plays a critical role in platelet Akt activation.