Proteome and functional decline as platelets age in the circulation

Abstract

Background Platelets circulate in the blood of healthy individuals for approximately 7–10 days regulated by finely balanced processes of production and destruction. As platelets are anucleate we reasoned that their protein composition would change as they age and that this change would be linked to alterations in structure and function. Objective To isolate platelets of different ages from healthy individuals to test the hypothesis that changes in protein content cause alterations in platelet structure and function. Methods Platelets were separated according to thiazole orange fluorescence intensity as a surrogate indicator of mRNA content and so a marker of platelet age and then subjected to proteomics, imaging, and functional assays to produce an in‐depth analysis of platelet composition and function. Results Total protein content was 45 ± 5% lower in old platelets compared to young platelets. Predictive proteomic pathway analysis identified associations with 28 biological processes, notably higher hemostasis in young platelets whilst apoptosis and senescence were higher in old platelets. Further studies confirmed platelet ageing was linked to a decrease in cytoskeletal protein and associated capability to spread and adhere, a reduction in mitochondria number, and lower calcium dynamics and granule secretion. Conclusions Our findings demonstrate changes in protein content are linked to alterations in function as platelets age. This work delineates physical and functional changes in platelets as they age and serves as a base to examine differences associated with altered mean age of platelet populations in conditions such as immune thrombocytopenia and diabetes.

Neutrophil-Derived Protein S100A8/A9 Alters the Platelet Proteome in Acute Myocardial Infarction and Is Associated With Changes in Platelet Reactivity

“…Functional relevance of low levels of platelet protein synthesis is challenged by the fact that platelets lose around half of their total protein content over the course of their circulating life. 43 An alternative source of S100A8 and S100A9 are megakaryocytes. While recent single-cell transcriptomic analysis of primary human megakaryocytes found S100A8 and S100A9 to be differentially expressed in 32 N compared with 4 N megakaryocytes, no increase in these transcripts was seen in megakaryocytes harvested at the time of MI.…”

Comprehensive phenotyping of human platelets by single‐cell cytometry

“…CD31 expression shows large interindividual variation, and high levels correlate with low platelet reactivity to CLEC‐2 and GPVI agonists [34]. Moreover, CD31 and GPVI levels decline as platelets age in the circulation, so these markers may be useful for discriminating young and old platelets [53].…”

Platelet Subtypes in Inflammatory Settings

“…The youngest platelet subtype released into the circulation appears to be more reactive and shows an increased tendency to recruit other platelets and immune cells to the site of injury. The newly formed platelets contain a residual amount of the megakaryocytic messenger RNA (mRNA) that gives them a greater array of functional pathways ( 26 ). As platelets age, the total protein content is degraded or lost without the possibility for replacement leaving old platelets with several biological alterations in function ( 26 ).…”

“…The newly formed platelets contain a residual amount of the megakaryocytic messenger RNA (mRNA) that gives them a greater array of functional pathways ( 26 ). As platelets age, the total protein content is degraded or lost without the possibility for replacement leaving old platelets with several biological alterations in function ( 26 ). Differences related to platelet age propose a young platelet subpopulation that are rapid hemostatic responders and an old platelet population with higher apoptosis and senescence.…”

“…RP is about 2–3 times higher in the BM compared to peripheral blood where they are present for ≤24 h in humans and count for around 12% of the total platelet population in a steady-state ( 45 – 47 ). Platelet aging is linked to a decrease in cytoskeletal protein, lower mitochondria number, as well as lower calcium dynamics and granule secretion ( 26 ). A recent study showed that the total protein content was almost 50% lower in old platelets compared to young platelets ( 26 ).…”