A novel thromboxane A2 receptor D304N variant that abrogates ligand binding in a patient with a bleeding diathesis

Area of Science:

• Hematology
• Molecular Biology
• Genetics

Background:

• Mild mucocutaneous bleeding can indicate underlying platelet dysfunction.
• Thromboxane A(2) receptor (TxA(2)R) plays a crucial role in platelet aggregation and signaling.

Purpose of the Study:

• To investigate the genetic cause of mild mucocutaneous bleeding in a patient with impaired platelet aggregation.
• To characterize the functional impact of a novel TxA(2)R variant.

Main Methods:

• Analyzed platelet aggregation and ATP secretion in response to various agonists.
• Sequenced the TBXA2R gene and identified a heterozygous transversion.
• Expressed the variant D304N TxA(2)R in Chinese hamster ovary-K1 cells to assess receptor function and ligand binding.

Main Results:

• The patient exhibited reduced platelet aggregation and ATP secretion specifically in response to arachidonic acid and a TxA(2)R agonist.
• A heterozygous D304N substitution in the TBXA2R gene was identified.
• The D304N variant TxA(2)R showed loss of function in response to U46619 and significantly reduced binding of the TxA(2)R antagonist.

Conclusions:

• The D304N substitution in TxA(2)R is the cause of clinically significant platelet dysfunction in this patient.
• This variant leads to impaired platelet function through reduced ligand binding.
• The NPXXY motif in transmembrane domain 7 of TxA(2)R is critical for receptor function and ligand interaction in vivo.