Gas6 and TAM Receptors in Mouse Platelets

Growth Arrest Specific-6 (Gas6) is a new vitamin K-dependent protein and is a ligand for TAM receptors, three receptors (Tyro, Axl and Mer) belonging to the receptor tyrosine kinase subfamily. The number of publications concerning the physiological importance of the new vitamin-K dependent proteins, which are not members of the coagulation cascade, is growing. Gas6 has a structural homology to natural anticoagulant of protein S, but has no anticoagulant activity. Some research groups have reported contradictory results concerning the presence of Gas6 and its receptors in mouse platelets. The purpose of this study is to investigate the presence of Gas6 and its receptors in mouse platelets as mRNA and protein levels.

25 specific pathogen-free, 8–10 week old, 25–30 g in weight, race of Balb-C male/female mice were anesthetized under light ether anesthesia and blood samples were taken from their hearts. Total RNAs were isolated from platelets, then mRNAs encoding Gas6 and TAM receptors were detected by Reverse Transcription-Polymerase Chain Reaction (RT-PCR). Protein concentrations of Gas6 and TAM receptors in platelets were measured by ELISA. We were unable to measure the Mer protein level because of the absence of any commercial ELISA kit for mouse Mer.

RT-PCR results indicated the presence of mRNAs encoding to Gas6 and Mer in mouse platelets. However, although RT-PCR reactions were performed at various temperatures and cycles, we could not detect the presence of mRNAs encoding Axl and Tyro. Receptor levels of Axl and Tyro were below the detection limits of the ELISA method. Plasma Gas6 concentration was found to be 26 ng/ml.

We found the presence of mRNAs encoding Gas6 and only receptor Mer in mouse platelets but not Axl and Tyro. Protein Gas6, Axl and Tyro levels were below the detection limits of the ELISA methods. The presence of mRNA is not evidence of protein expression in platelets because they have no DNA. Further studies are required to clarify the presence of Gas6 and TAM receptors in platelets using Real Time PCR, and more sensitive immunological methods, and then, as studies of their effects on mechanisms. Original results from these further studies will provide reliable information as to whether Gas6 and its TAM receptors may be a pharmacological target in thrombosis, hemostasis, restenosis and atherosclerosis.

No relevant conflicts of interest to declare.