The role of RNA uptake in platelet heterogeneity

Abstract

The role of platelets in regulating vascular homeostasis has expanded beyond mediation of haemostasis and thrombosis. The discovery of platelet RNA and the presence of subpopulations of platelets containing varying amounts of RNA suggest a role for platelet transcripts in vascular function. As the RNA in anucleated platelets is biologically functional and may transfer to other vascular cells, we hypothesised that platelet RNA diminishes over the lifespan of the platelet with diminishing platelet size due to horizontal cellular transfer. The purpose of this study is to determine if platelet RNA variance is the result of horizontal cellular transfer between platelets and other vascular cells. Utilising platelet sorting and RNA sequencing, we found that smaller platelets contained a more diverse set of transcripts than larger platelets. Further investigation using fluorescence imaging, gene expression analyses and in vitro and in vivo modelling revealed that platelets take up RNA from other vascular cells in a complex manner, revealing a dynamic role for platelets in modulating vascular homeostasis through bidirectional RNA transfer. The resultant RNA profile heterogeneity suggests unique functional roles for platelets dependent on size and complexity. This study expands our basic understanding of platelet function and heterogeneity and is the first to evaluate endogenous vascular RNA uptake and its relation to platelet processes. Our findings describe a novel endogenous phenomenon that can help elucidate the platelet's role in these non-thrombotic and haemostatic fields, as well as present potential for diagnostic and therapeutic development.

Biology of Platelet Purinergic Receptors and Implications for Platelet Heterogeneity

“…Human and murine platelets express functional cAMP-increasing P1 receptors A2aAR and A2bAR ( Ledent et al, 1997 ; Yang et al, 2010 ), but are not known to have functional cAMP-inhibiting P1 receptors A1AR and A3AR. It is noteworthy that A1AR mRNA has been detected by qRT-PCR ( Amisten et al, 2008 ) but significant expression was not detected by sequencing in more recent studies ( Rowley et al, 2011 ; Clancy et al, 2017 ). An increased level of intracellular cAMP, in turn, inhibits platelet aggregation/function.…”

“…Human platelets are not a homogeneous population, but vary in size (2–5 μm) and content. RNA sequencing shows that platelets may contain as many as 9500 different transcripts ( Rowley et al, 2011 ; Bray et al, 2013 ; Clancy et al, 2017 ), most of which are prepackaged from the MK. Additionally, platelets uptake transcripts and transcript fragments from circulating cells and the endothelium ( Clancy et al, 2017 ).…”

“…RNA sequencing shows that platelets may contain as many as 9500 different transcripts ( Rowley et al, 2011 ; Bray et al, 2013 ; Clancy et al, 2017 ), most of which are prepackaged from the MK. Additionally, platelets uptake transcripts and transcript fragments from circulating cells and the endothelium ( Clancy et al, 2017 ). The heterogeneous size of platelets ( Thon and Italiano, 2012 ) is hypothesized to be a result of platelets losing their contents into the circulation as they age; hence, large platelets are also referred to as “immature” and small platelets are referred to as “mature” ( Penington and Streatfield, 1975 ; Penington et al, 1976a , b ).…”

“…Studies have shown that large (immature) platelets are highly hemostatically active while small (mature) platelets are less hemostatically functional ( Thompson et al, 1984 ; Guthikonda et al, 2008 ). It is noteworthy that the predominant size of platelets in a healthy individual lies somewhere in between ( Clancy et al, 2017 ). In patients with acute coronary syndrome (developing early stent thrombosis) there is a baseline platelet size increase predicting platelet reactivity ( Huczek et al, 2010 ).…”

Genomics and transcriptomics of megakaryocytes and platelets: Implications for health and disease

“…Platelets are also capable of transferring RNA molecules while in the circulation or interacting with other normal cells 51. Labeled RNA from platelet‐derived particles can be transferred to other immune cells and endothelial cells.…”