Sequence alignment analysis of proteins involved in platelet-endothelial cell interaction identifies molecular incompatibilities between Homo sapiens and Sus scrofa

Abstract

Background: Platelets play a vital role in acute humoral xenograft rejection (AHXR) in pig-to-primate xenotransplantation, presenting as microvascular thrombosis in the graft and/or consumptive coagulopathy in the recipient. Adhesion and aggregation of primate platelets to the activated vascular endothelial cells through sequential binding of ligands on endothelial cells and subendothelial matrix ultimately trigger a complex biological process of prothrombotic signaling cascades. Increasing evidence suggests that the molecular incompatibilities in effector molecules across species may partially contribute to dysregulated microvascular thrombosis in xenografts. 

Method: We selected candidate genes from the NCBI database with keywords: platelet-endothelium interaction，platelet adhension, platelet aggregation, and subendothelial matrix ligands. Pair-wise amino acid alignments were made using the Emboss Needle method. Emboss needle created optimal global alignment of the amino acid sequences of human genes and pig genes using ClustalW2.

Results: Most of the proteins involved in platelet-EC interaction in Homo sapiens share high sequence similarity with their homologues in Sus scrofa. Cytokines that potentially induce endothelial damage (such as CD40L, TNF-α) were highly conserved between Homo sapiens and Sus scrofa. Some endothelium-derived cytokines (such as IL-8, CCL2, CCL5) that can induce platelet activation or enhance aggregation share high sequence similarity between Homo sapiens and sus scrofa.  Some regulators that potentially transduce inhibitory signaling to control platelet activation or complement activation have relatively poor sequence identity between Homo sapiens and Sus scrofa, and some even lack their homologues in Sus scrofa.

Conclusion: The characteristic of sequence similarity of proteins involved in platelet-EC interaction indicated the molecular incompatibilities between humans (Homo sapiens) and pigs (Sus scrofa). This study provides a clue for explanation of excessive platelet activity in pig-to-primate xenotransplantation.