The life cycle of platelet granules

Abstract

Platelet granules are unique among secretory vesicles in both their content and their life cycle. Platelets contain three major granule types—dense granules, α-granules, and lysosomes—although other granule types have been reported. Dense granules and α-granules are the most well-studied and the most physiologically important. Platelet granules are formed in large, multilobulated cells, termed megakaryocytes, prior to transport into platelets. The biogenesis of dense granules and α-granules involves common but also distinct pathways. Both are formed from the trans-Golgi network and early endosomes and mature in multivesicular bodies, but the formation of dense granules requires trafficking machinery different from that of α-granules. Following formation in the megakaryocyte body, both granule types are transported through and mature in long proplatelet extensions prior to the release of nascent platelets into the bloodstream. Granules remain stored in circulating platelets until platelet activation triggers the exocytosis of their contents. Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins, located on both the granules and target membranes, provide the mechanical energy that enables membrane fusion during both granulogenesis and exocytosis. The function of these core fusion engines is controlled by SNARE regulators, which direct the site, timing, and extent to which these SNAREs interact and consequently the resulting membrane fusion. In this review, we assess new developments in the study of platelet granules, from their generation to their exocytosis.

Hypothermia‐induced activation of the splenic platelet pool as a risk factor for thrombotic disease in a mouse model

“…Upon activation, platelets release various substances from their intracellular granules that contribute to coagulation . For example, plasma PPBP and PF4 reportedly activate coagulation .…”

“…[35][36][37][38] In our splenic tissue analysis, hypothermia enhanced vWF expression in both mRNA and Upon activation, platelets release various substances from their intracellular granules that contribute to coagulation. [39][40][41][42][43][44] For example, plasma PPBP and PF4 reportedly activate coagulation. [45][46][47][48] Although we suspect that these substances were released into the plasma of hypothermic mice, we did not detect significant thrombosis or plasma D-dimer elevation in mice euthanized immediately after the hypothermia treatment.…”

Ultrastructural observations on the platelets of the Arabian oryx (Oryx leucoryx)

“…As in humans, the electron‐dense bodies were the smallest platelet granules. The content of the dense bodies has been described as containing 5‐hydroxytryptamine, non‐metabolic pools of adenine nucleotides and catecholamines and are considered to be storage and secretory organelles for non‐protein molecules that influence haemostasis (King et al, ; Sharda & Flaumenhaft, ).…”

Blood platelet research in autism spectrum disorders: In search of biomarkers

“…Alpha and dense granules are formed in megakaryocytes in the bone marrow prior to their transport into forming platelets . In platelets, granules can release their content following platelet activation.…”

“…Alpha and dense granules are formed in megakaryocytes in the bone marrow prior to their transport into forming platelets. 37 In platelets, granules can release their content following platelet activation. It is known that the BEACH (named after Beige and Chediak-Higashi) domain-containing proteins are important for platelet granule formation and secretion.…”