Dissection of autophagy in human platelets

Banerjee

et al. 2015

Blood

113

Key Points• Autophagy, an essential degradation pathway, is constitutively active in resting platelets and is induced upon platelet activation.• Platelet autophagy is indispensable for hemostasis and thrombus formation.Autophagy is important for maintaining cellular homeostasis, and thus its deficiency is implicated in a broad spectrum of human diseases. Its role in platelet function has only recently been examined. Our biochemical and imaging studies demonstrate that the core autophagy machinery exists in platelets, and that autophagy is constitutively active in resting platelets. Moreover, autophagy is induced upon platelet activation, as indicated by agonist-induced loss of the autophagy marker LC3II. Additional experiments, using inhibitors of platelet activation, proteases, and lysosomal acidification, as well as platelets from knockout mouse strains, show that agonist-induced LC3II loss is a consequence of platelet signaling cascades and requires proteases, acidic compartments, and membrane fusion. To assess the physiological role of platelet autophagy, we generated a mouse strain with a megakaryocyte-and platelet-specific deletion of Atg7, an enzyme required for LC3II production. Ex vivo analysis of platelets from these mice shows modest defects in aggregation and granule cargo packaging. Although these mice have normal platelet numbers and size distributions, they exhibit a robust bleeding diathesis in the tail-bleeding assay and a prolonged occlusion time in the FeCl 3 -induced carotid injury model. Our results demonstrate that autophagy occurs in platelets and is important for hemostasis and thrombosis. (Blood. 2015;126(10):1224-1233 Introduction Autophagy, one of the major degradation pathways in eukaryotes, is important for cellular homeostasis and is implicated in a broad spectrum of human diseases including cancer, neurodegeneration, and cardiovascular diseases.1 There are 3 main types: chaperone-mediated autophagy, 2 microautophagy, 3,4 and the primary form, macroautophagy (referred to hereafter as autophagy).5 Autophagy involves de novo synthesis of double-membraned organelles called autophagosomes that contain cytosolic constituents including damaged organelles (eg, mitochondria) and protein aggregates. Autophagosomes fuse with multivesicular bodies, late endosomes, and lysosomes to form autolysosomes, 6 in which waste elimination, energy production, and recycling of cellular components take place.Autophagosome biogenesis and maturation use several protein complexes. [7][8][9][10] In mammals, cellular signals (eg, starvation) activate the Ulk1 complex (Ulk1, FIP200, Atg13, and Atg101), 11-14 which together with syntaxin 17, 15 localizes Atg14/Atg14L [16][17][18][19] to the endoplasmic reticulum. 15,20 This recruits the Beclin 1-Vps34 core complex (Beclin 1, Vps34, and Vps15) to autophagosome initiation sites and promotes phosphatidylinositol 3-phosphate production for recruitment of additional autophagy pathway components.20,21 Two ubiquitin-like conjugation systems are also important for autoph...

Section: Discussionsupporting

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Section: Autophagy In Hemostasis and Thrombosis 1229mentioning

confidence: 88%

Section: Autophagy In Hemostasis and Thrombosis 1229mentioning

confidence: 99%

Section: Introductionmentioning

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See 3 more Smart Citations

Autophagy is induced upon platelet activation and is essential for hemostasis and thrombosis

Ouseph

Banerjee

et al. 2015

Blood

113

Autophagic regulation of platelet biology

Luo

Jiang

Journal Cellular Physiology

et al. 2019

Platelets, developed from megakaryocytes, are characterized by anucleate and short‐life span hemocyte in mammal vessel. Platelets are very important in the cardiovascular system. Studies indicate the occurrence of autophagy platelets and megakaryocytes. Moreover, abnormal autophagy decreases the number of platelets and suppresses platelet aggregation. In addition, mitophagy, as a kind of selective autophagy, could inhibit platelet aggregation under oxidative stress or hypoxic, whereas promote platelet aggregation after reperfusion. Finally, autophagy regulates hemorrhagic and thrombosis diseases by influencing the number and function of platelets. In this paper, the role of autophagy in platelets and megakaryocytes, as well as coupled with the promotive or inhibitory role of hemorrhagic and thrombosis diseases are elucidated. Therefore, autophagy may be a potentially therapeutic target in modulating the platelet‐related diseases.

Autophagy in Platelets

Banerjee

Methods in Molecular Biology

Ouseph

et al. 2019

Anucleate platelets are produced by fragmentation of megakaryocytes. Platelets circulate in the blood stream for a finite period: Upon vessel injury, they are activated to participate in hemostasis; upon senescence, unused platelets are cleared. Platelet hypofunction leads to bleeding. Conversely, pathogenic platelet activation leads to occlusive events that precipitate strokes and heart attacks. Recently, we and others have shown that autophagy occurs in platelets and is important for platelet production and normal functions including hemostasis and thrombosis. Due to the unique properties of platelets, such as their lack of nuclei and their propensity for activation, methods for studying platelet autophagy must be specifically tailored. Here, we describe useful methods for examining autophagy in both human and mouse platelets.