The cellular basis of platelet secretion: Emerging structure/function relationships

Abstract

Platelet activation has long been known to be accompanied by secretion from at least three types of compartments. These include dense granules, the major source of small molecules; α-granules, the major protein storage organelle, and lysosomes, the site of acid hydrolase storage. Despite ~60 years of research, there are still many unanswered questions about the cell biology of platelet secretion: e.g., how are these secretory organelles organized to support cargo release and what are the key routes of cargo release, granule to plasma membrane or granule to canalicular system (CS). Moreover, in recent years, increasing evidence points to the platelet being organized for secretion of the contents from other organelles, namely, the dense tubular system (endoplasmic reticulum) and the Golgi apparatus. Conceivably, protein secretion is a wide-spread property of the platelet and its organelles. In this review, we concentrate on the cell biology of the α-granule and its structure/function relationships. We both review the literature and discuss the wide array of 3-dimensional, high resolution structural approaches that have emerged in the last few years. These have begun to reveal new and unanticipated outcomes and some of these are discussed. We are hopeful that the next several years will bring rapid advances to this field that will resolve past controversies and be clinically relevant.

Development of a label‒free nanolc/ms/ms assay for monitoring the changes in the proteomic landscape of thrombin‒activated human platelets

“…[2][3][4][5][6][7][8] Activated platelets undergo vast cytoskeleton, organelles, and secretory protein reorganization accompanied by many posttranslational modifications (PTM). [5][6][7][8][9][10][11][12][13][14] Due to their anucleate nature, platelets have limited protein synthesis, and therefore it is expected that most of the changes encountered at the level of the proteome under different pathophysiological conditions will be determined mostly by changes in protein expression (translational and post-translational regulated), at the level of PTM, proteolysis, or secretion during platelets degranulation processes associated with their activation. [11][12][13][14][15] It is well documented that selected platelet messages are translated into proteins after activation, regulating the inflammatory and hemostatic responses of the platelet.…”

“…[5][6][7][8][9][10][11][12][13][14] Due to their anucleate nature, platelets have limited protein synthesis, and therefore it is expected that most of the changes encountered at the level of the proteome under different pathophysiological conditions will be determined mostly by changes in protein expression (translational and post-translational regulated), at the level of PTM, proteolysis, or secretion during platelets degranulation processes associated with their activation. [11][12][13][14][15] It is well documented that selected platelet messages are translated into proteins after activation, regulating the inflammatory and hemostatic responses of the platelet. [2][3][4][5][6][7][8] Platelets can be affected by many physiological conditions during blood circulation that can ultimately lead to vascular complications initiated by thrombus formation.…”

“…[2][3][4][5][6][7][8] Platelets can be affected by many physiological conditions during blood circulation that can ultimately lead to vascular complications initiated by thrombus formation. [12][13][14][15][16] During activation, release of platelet microparticles can generate various pathophysiological effects, such as initiation and exacerbation of stroke. 16,17 One of the most advanced studies applied to the research of platelets biology under different activation states is the mass spectrometry coupled with profiling of protein changes applied to both resting and activated whole platelet proteomes, or to platelet subproteomes, including the platelet granules (alpha and dense), membrane systems, lipid rafts, and enriched phosphoproteome.…”

“…Research conducted in the last five years acknowledges the identification of 5000-5500 expressed proteins in human platelets, a proteome that is highly similar between different healthy individuals. [10][11][12][13][14][15][16][17][18][19][20][21] Recent emerging analytical technologies coupling the fractionation of the cellular proteome with the multidimensional nano LC/ESI/MS/MS sequencing, together with systems biology approaches empowered by bioinformatics analysis and data mining enabled a revolution in platelet proteomics that led to the development of new, mass spectrometric-based assays for enhanced research of platelet pathophysiology. [15][16][17][18][19][20][21] Consequently, the modern proteomics approaches can reveal: (1) targeted and untargeted quantitative changes in the abundances of thousands of proteins; (2) post-translational modifications; (3) protein-protein interactions networks; (4) subcellular localization, i.e.…”

“…membrane-bound proteins, or secreted proteome in the microvesicles, exosomes, microparticles found in platelets releasates. [13][14][15][16] Using highly sensitive and highly specific mass spectrometers (providing mass accuracy and resolution), and proteome fractionations assays involving denaturant, and reducing one-dimensional or two-dimensional protein electrophoretic systems (1-DE and 2-DE, respectively) followed by protein digestions with multiple enzymes (trypsin, LysC, Glu-C and Asp-N, among others), and further fractionations of peptides by means of orthogonal chromatographic systems, thousands of proteoforms can be characterized from highly pure fractions consisting of only 2x10 8 platelets, purified from small volumes of blood, usually in the range of few milliliters. [20][21][22][23][24][25][26][27][28] Consequently, the future advances in the mass spectrometric profiling of protein expression and their corresponding highly-regulated PTM are expected to allow platelet proteomics to be implemented in many research and clinical laboratories as a reliable tool for characterizing the molecular and cellular pathways that affect platelet homeostasis in healthy and disease states.…”