Defects in secretion, aggregation, and thrombus formation in platelets from mice lacking Akt2

Area of Science:

• Hematology
• Molecular Biology
• Biochemistry

Background:

• Phosphoinositide 3-kinases (PI3Ks) are known to be involved in platelet activation.
• The specific role of Akt, a downstream effector of PI3K, in platelet function remains incompletely defined.

Purpose of the Study:

• To investigate the contribution of Akt isoforms, specifically Akt1 and Akt2, to platelet activation and thrombus formation.
• To elucidate the signaling pathways through which Akt influences platelet responses.

Main Methods:

• Analysis of Akt1 and Akt2 expression in mouse platelets.
• Assessment of platelet aggregation, fibrinogen binding, and granule secretion in Akt2-deficient mice.
• Evaluation of arterial thrombus formation and stability in vivo.
• Investigation of Akt activation pathways in response to different agonists and receptor deletions (Gαq, Gαi2).

Main Results:

• Akt2 is the predominant Akt isoform in mouse platelets.
• Deletion of Akt2 significantly impaired platelet aggregation, fibrinogen binding, and secretion, especially in response to low agonist concentrations via G(q)-coupled receptors.
• Loss of Akt2 compromised arterial thrombus formation and stability in vivo.
• Akt1 deficiency had minimal impact unless Akt2 was also absent.
• Thrombin-induced Akt activation was dependent on Gαq, while ADP-induced activation was dependent on Gαi2.

Conclusions:

• Akt2 is a critical component of PI3K-dependent signaling downstream of G(q)-coupled receptors in platelets.
• Akt2 plays a vital role in promoting thrombus growth and stability, partly by supporting platelet secretion.
• Akt1's role is less significant, becoming apparent primarily in the absence of Akt2.