OC 35.3 - Protein tyrosine phosphatase PTPN22 modulates platelet function and thrombosis

Background: Protein tyrosine phosphatase non-receptor type 22 (PTPN22) is a protein tyrosine phosphatase and negatively regulates T cell signaling. However, whether it is expressed and functions in platelets remains unknown.

Aims: To investigate the expression and role of PTPN22 in platelet function.

Methods: Platelets were isolated from WT or PTPN22-deficient mice to measure platelet aggregation, granule secretion, spreading and clot retraction along with the measurement of tail bleeding time, arterial and venous thrombus formation. In addition, quantitative phosphoproteomic analysis was conducted to indentify the potential target of PTPN22. Moreover, human platelets were treated with PTPN22 inhibitor LTV-1 to measure platelet function.

Results: PTPN22 expression in both human and mouse platelets. Using PTPN22-/- mice, we demonstrated that PTPN22 deficiency significantly shortened tail-bleeding time and accelerated arterial thrombus formation without affecting venous thrombosis and the coagulation factor VIII and IX. Consistently, PTPN22-deficient platelets exhibited enhanced platelet aggregation, spreading and clot retraction. Quantitative phosphoproteomic analysis revealed the significant difference of phosphodiesterase 5A (PDE5A) phosphorylation in PTPN22-deficient platelets compared to wild-type platelets after collagen-related peptide (CRP) stimulation, which was confirmed by increased PDE5A phosphorylation (Ser92) in CRP-treated PTPN22-deficient platelets, concomitant with reduced cGMP level and VASP phosphorylation (Ser157/239). In addition, PTPN22 interacted with phosphorylated PDE5A (Ser92) and dephosphorylated it in activated platelets. Moreover, purified PTPN22 but not mutant form (C227S) possesses intrinsic serine phosphatase activity. Furthermore, inhibition of PTPN22 enhanced human platelet aggregation, spreading, clot retraction and increased PDE5A phosphorylation (Ser92). Finally, PTPN22 expression was significantly reduced in platelets of coronary artery disease patients.

Conclusion(s): In conclusion, our study demonstrates a novel role of PTPN22 in platelet function and arterial thrombosis, identifying new potential targets for future prevention of thrombotic or cardiovascular diseases.