Making the cut: Protein breakdown in platelets during storage

Proteolysis is an important part of normal cell processes and occurs for many reasons. For example, proteins can be completely broken down to prevent the build up of unnecessary or damaged proteins. In this way, proteolysis works like a shredder and completely destroys unwanted proteins. Proteolysis can also be a controlled and specific process during which the protein is cut at very specific sites. The resulting protein or peptide is shorter but stable and often functional. In this case, proteolysis can be compared to a scissors in skilled hands, carefully tailoring the form and function of specific proteins.

Platelets, red blood cells and plasma prepared by Canadian Blood Services for transfusion contain thousands of different types of proteins. Platelets are important for blood clotting and are often transfused as supportive therapy for cancer patients. Unlike red blood cells and plasma, which can be stored for longer, platelets have a short shelf life of just five days. In part, this is because they must be stored at room temperature, which puts them at greater risk of bacterial contamination. However, this is not the only reason to limit platelet storage time. The function of platelets declines during their short storage time. Known as the platelet storage lesion, this phenomenon is much studied but not yet fully understood. The platelet storage lesion affects everything from platelet shape to the platelet’s ability to metabolize and involves changes in the platelet’s proteins.

In this study, researchers at the University of British Columbia centre for blood research explored platelet storage lesion from a new perspective. They focused on what happens to proteins, and, specifically, which proteins get cut, where they get cut, and how these protein changes might affect protein and platelet function.

• Nearly 3,000 proteins and over 7,500 unique peptides were identified in platelets.
• Over 3,000 N-termini were found. The N-terminus is a physical starting point of a protein or a peptide; its position defines the structural and functional boundaries of a protein and may indicate that the protein or peptide has been cut by proteases.
• Proteins involved in cell structure, metabolism and cell communication were shown to be cut during platelet storage.
• The majority (77 per cent) of the cut proteins produced stable fragments. This suggests that the process is not simply breakdown or degradation of unnecessary proteins, but a regulated, controlled process.
• Experiments with protease blocking drugs showed that metalloproteinases were responsible for much of the proteolysis seen in platelets during storage.

Dr. Anna Prudova is a research associate in Dr. Christopher Overall’s laboratory at the University of British Columbia centre for blood research, Vancouver, BC. Dr. Ulrich Eckhard and Nikolaus Fortelny are a postdoctoral fellow and a graduate student, respectively, in Dr. Overall’s laboratory at the centre for blood research. Dr. Christopher Overall is a professor in the department of oral biological and medical sciences and the department of biochemistry and molecular biology at the University of British Columbia, Vancouver, BC. Dr. Katherine Serrano is a research associate with Canadian Blood Services centre for innovation and a clinical assistant professor at the department of pathology and laboratory medicine at the University of British Columbia. Dr. Dana Devine is the Canadian Blood Services chief medical and scientific officer and a professor in the department of pathology and laboratory medicine at the University of British Columbia.