Proteomic and Biochemical profiling of 4.1R deficient red blood cells

Abstract

Eryptosis is a term used to describe the highly regulated homeostatic process of erythrocyte programmed cell death. It mimics apoptosis in nucleated cells in that cell shrinkage and Phosphatidylserine (PS) exposure at the outer membrane leaflet are observed. Recently our group reported that the ligation of a specific synthetic peptide (4N1K), a natural ligand (thrombospondin-1) and a monoclonal antibody (BRIC- 126) which all bind to red cell CD47 glycoprotein (also known as Integrin associated protein) can trigger PS exposure in erythrocytes. We have also demonstrated that several key red cell membrane proteins 4.1R/p55/Glycophorin C (GPC) are involved in the CD47 pathway. This is primarily because we have demonstrated a direct protein-proteininteraction between CD47 and p4.1 and p55. In order to explore these interactions in more depth, we have studied red cells obtained from 4.1R deficient individuals using a combination of differential proteomic profiling and biochemical analysis of the red cell PS-exposure pathways. Interestingly GPC has a interaction with p55 and p4.1Rwhich has been well established. We have used proteomic profiling, use of CD47 ligands to explore PS exposure pathways, protein immunoblotting and flow cytometry on 4.1R deficient red cells in these studies. Our findings have produced significant differences compared with that of normal control age-matched erythrocytes. We show that4.1R deficient RBCs lack, or are significantly deficient in several membrane and membrane skeletal components, and give novel insight into the complexes that 4.1R maintains in the mature RBC. This may suggest it plays a key role in eryptosis, especially pertinent as it is known to have binding sites for PS. Protein immunoblotting showed absence of protein 4.1R and protein p55 confirming earlier studies. Glycophorin C was also diminished and Glycophorin A appeared equal as previously reported. However, previously unreported results included a deficiency of CD44, alterations in CD47 expression, lack of GPC dimerisation, and deficiency of aldolase A. Further we showed that PS exposure is increased in the CD47 pathway (when challenged with CD47 ligands BRIC 126 and 4N1K) in cells lacking protein 4.1R compared with control cells, but decreased in the GPC pathway (when challenged with BRIC 10) in cells lacking protein 4.1R compared with control cells. 4.1R(Madrid) cells were also shown to be resistant to TSP-1 mediated eryptosis. This difference in PS exposure suggests an important regulatory role for 4.1R in both of these apoptotic pathways, and may suggest that CD47-induced PS exposure occurs independently of binding to 4.1R/p55.Studies are ongoing with red cells obtained from a further 4.1R deficient individual (4.1R-/- Lille) and initial analysis is confirms the alterations seen in the 4.R-/- Madrid sample