Chanzu Harry, Lykins Joshua, Wigna-Kumar Subershan, Joshi Smita, Pokrovskaya Irina, Storrie Brian, Pejler Gunnar, Wood Jeremy P, Whiteheart Sidney W
Department of Molecular and Cellular Biochemistry, University of Kentucky College of Medicine, Lexington, KY, USA.
Lexington VA Medical Center, Lexington, KY, USA.
J Thromb Haemost. 2021 Apr;19(4):1082-1095. doi: 10.1111/jth.15243. Epub 2021 Feb 8.
Serglycin (SRGN) is an intragranular, sulfated proteoglycan in hematopoietic cells that affects granule composition and function.
To understand how SRGN affects platelet granule packaging, cargo release, and extra-platelet microenvironments.
Platelets and megakaryocytes from SRGN mice were assayed for secretion kinetics, cargo levels, granule morphology upon activation, and receptor shedding.
Metabolic, SO labeling identified SRGN as a major sulfated macromolecule in megakaryocytes. SRGN colocalized with α-granule markers (platelet factor 4 [PF4], von Willebrand factor [VWF], and P-selectin), but its deletion did not affect α-granule morphology or number. Platelet α-granule composition was altered, with a reduction in basic proteins (pI ≥8; e.g., PF4, SDF-1, angiogenin) and constitutive release of PF4 from SRGN megakaryocytes. P-Selectin, VWF, and fibrinogen were unaffected. Serotonin (5-HT) uptake and β-hexosaminidase (HEXB) were slightly elevated. Thrombin-induced exocytosis of PF4 from platelets was defective; however, release of RANTES/CCL5 was normal and osteopontin secretion was more rapid. Release of 5-HT and HEXB (from dense granules and lysosomes, respectively) were unaffected. Ultrastructural studies showed distinct morphologies in activated platelets. The α-granule lumen of SRGN platelet had a grainy staining pattern, whereas that of wild-type granules had only fibrous material remaining. α-Granule swelling and decondensation were reduced in SRGN platelets. Upon stimulation of platelets, a SRGN/PF4 complex was released in a time- and agonist-dependent manner. Shedding of GPVI from SRGN platelets was modestly enhanced. Shedding of GP1b was unaffected.
The polyanionic proteoglycan SRGN influences α-granule packaging, cargo release, and shedding of platelet membrane proteins.
丝甘酸性蛋白（SRGN）是造血细胞中的一种颗粒内硫酸化蛋白聚糖，可影响颗粒的组成和功能。
了解SRGN如何影响血小板颗粒包装、货物释放及血小板外微环境。
对SRGN小鼠的血小板和巨核细胞进行分泌动力学、货物水平、激活后颗粒形态及受体脱落检测。
代谢性35SO标记确定SRGN为巨核细胞中的主要硫酸化大分子。SRGN与α颗粒标志物（血小板因子4 [PF4]、血管性血友病因子[VWF]和P选择素）共定位，但其缺失不影响α颗粒形态或数量。血小板α颗粒组成发生改变，碱性蛋白（pI≥8；如PF4、SDF-1、血管生成素）减少，且PF4从SRGN巨核细胞中组成性释放。P选择素、VWF和纤维蛋白原未受影响。5-羟色胺（5-HT）摄取和β-N-乙酰氨基己糖苷酶（HEXB）略有升高。凝血酶诱导的血小板PF4胞吐作用存在缺陷；然而，RANTES/CCL5释放正常，骨桥蛋白分泌更快。5-HT和HEXB（分别来自致密颗粒和溶酶体）的释放未受影响。超微结构研究显示激活血小板有不同形态。SRGN血小板的α颗粒腔有颗粒状染色模式，而野生型颗粒的α颗粒腔仅残留纤维状物质。SRGN血小板中α颗粒肿胀和去浓缩减少。刺激血小板后，SRGN/PF4复合物以时间和激动剂依赖的方式释放。SRGN血小板中糖蛋白VI（GPVI）的脱落略有增强。糖蛋白Ib（GP1b）的脱落未受影响。
多阴离子蛋白聚糖SRGN影响α颗粒包装、货物释放及血小板膜蛋白的脱落。
