Semin Thromb Hemost 2024; 50(08): 1187-1190
DOI: 10.1055/s-0044-1787663
Historical Commentary

Platelet Pathophysiology: Unexpected New Research Directions

Alan D. Michelson
1   Division of Hematology/Oncology, Boston Children's Hospital, Dana-Farber Cancer Institute and Harvard Medical School, Boston, Massachusetts
,
Andrew L. Frelinger III
1   Division of Hematology/Oncology, Boston Children's Hospital, Dana-Farber Cancer Institute and Harvard Medical School, Boston, Massachusetts
,
Robin L. Haynes
2   Department of Pathology, Boston Children's Hospital and Harvard Medical School, Boston, Massachusetts
,
Hannah C. Kinney
2   Department of Pathology, Boston Children's Hospital and Harvard Medical School, Boston, Massachusetts
,
Thomas Gremmel
3   Department of Internal Medicine I, Cardiology and Intensive Care Medicine, Landesklinikum Mistelbach-Gänserndorf, Mistelbach, Austria
4   Institute of Cardiovascular Pharmacotherapy and Interventional Cardiology, Karl Landsteiner Society, St. Pölten, Austria
5   Karl Landsteiner University of Health Sciences, Krems, Austria
› Author Affiliations
Funding This article received funding from Eunice Kennedy Shriver National Institute of Child Health and Development Grant P01-HD036379 (to H.C.K.).

We are very honored that our 2016 review of platelet physiology[1] is one of the top three most downloaded papers in Seminars and Thrombosis and Haemostasis from 2014 to 2023. But why study platelet physiology? Because these remarkable little cells play key roles in many important pathophysiological processes, including thrombosis, hemorrhage, inflammation, antimicrobial host defense, wound healing, angiogenesis, and tumor growth and metastasis.[2] In addition to primary disorders of platelet number and function, platelets have a critical role in many other very common diseases, including coronary artery disease, stroke, peripheral vascular disease, and diabetes mellitus.[2] There remain many incompletely understood aspects of platelet physiology and its relationship to diseases, a few examples of which are the role of platelets in innate and adaptive immunity,[3] [4] the genetic basis of thrombocytopenia,[5] the role of platelet activation in coronavirus disease 2019,[6] the role of platelet activation in liver disease,[7] and novel targets for antiplatelet therapy.[8] [9] [10] But science in general, and the study of platelet physiology in particular, can sometimes lead researchers in an unexpected new direction, as will be discussed in this commentary focused on the relationship between platelet function and sudden infant death syndrome (SIDS).

SIDS is defined as the sudden unexpected death of an apparently healthy infant less than 1 year of age that remains unexplained despite a complete autopsy with ancillary testing, examination of the death scene, and review of the clinical history.[11] [12] SIDS is the leading cause of postneonatal mortality in the United States.[13] [14] [15] There are no currently available biomarkers of SIDS in living infants. However, a subset of infants who die of SIDS have abnormalities in the neurotransmitter, serotonin (5-hydroxytryptamine [5-HT]) and the adaptor molecule, 14-3-3 pathways in regions of the brain involved in gasping, response to hypoxia, and arousal ([Fig. 1]).[16] [17] [18] [19] [20] [21]

Zoom Image
Fig. 1 Platelet physiology and neuron physiology involve many of the same molecules and pathways. Previously identified abnormalities in neurons of SIDS subjects are shown in purple. (Adapted from Kinney et al[40].) GP, glycoprotein; SIDS, sudden infant death syndrome; VMAT, vesicular monoamine transporter; 5-HT, 5-hydroxytryptamine.

Serotonin is synthesized in the gut, where it is released primarily after stimulation of enterochromaffin cells.[22] [23] [24] Once 5-HT enters the intestinal vasculature, it is sequestered inside platelets by the 5-HT transporter ([Fig. 1]), and then into dense granules by the vesicular monoamine transporter ([Fig. 1]). Approximately 95% of the 5-HT in blood is carried in platelet-dense granules,[25] and serum contains the secretion products of activated platelets, including their dense granules. Platelet activation leads to secretion of dense granule contents, and the secreted 5-HT binds to the platelet surface 5-HT receptor 5-HT2A ([Fig. 1]), activating signaling pathways that amplify initial platelet activation.[26] [27] [28] Downstream events following 5-HT binding to 5-HT2A include increases in cytosolic calcium and F-actin ([Fig. 1]).

Because (a) approximately 20 to 80% of SIDS deaths are associated with 5-HT receptor (5-HT1A or 5-HT2A/C) binding abnormalities in regions of the brainstem critical in homeostatic regulation,[29] [30] (b) approximately 95% of the 5-HT in blood is carried in platelet-dense granules[25] and serum contains the secretion products of activated platelets (including their dense granules), and (c) blood platelets have similar 5-HT signaling pathways to brain neurons ([Fig. 1]), we hypothesized that SIDS is associated with an alteration in serum 5-HT levels. Indeed, we demonstrated that serum 5-HT, adjusted for postconceptional age, was significantly elevated (95%) in SIDS infants (n = 61) compared with autopsied controls (n = 15; SIDS, 177.2 ± 15.1 [mean ± SE] ng/mL vs. controls, 91.1 ± 30.6 ng/mL; p = 0.014), as determined by ELISA.[31] This increase was validated using high-performance liquid chromatography. Thirty-one percent (19/61) of SIDS cases had 5-HT levels greater than 2 SD above the mean of the controls, thus defining a subset of SIDS cases with elevated 5-HT.[31] There was no association between genotypes of the serotonin transporter promoter region polymorphism and serum 5-HT level. This study demonstrated that SIDS is associated with peripheral abnormalities in the 5-HT pathway, and that high serum 5-HT may serve as a potential forensic biomarker in autopsied SIDS infants with serotonergic defects.[31]

Because (a) brain neurons have 5-HT and 14-3-3 signaling pathways which are abnormal in SIDS ([Fig. 1]) and (b) blood platelets have similar 5-HT and 14-3-3 signaling pathways to neurons ([Fig. 1]), we then hypothesized that SIDS is, at least in part, a multiorgan dysregulation of 5-HT and that platelets may be a peripherally accessible marker for SIDS brain abnormalities. However, before we could address this hypothesis, we needed to overcome some major hurdles. As we recently discussed,[32] direct study of SIDS is inherently difficult due to the infrequent and unexpected nature of the disease, regulatory issues, and logistical and methodological issues surrounding specimen collection and storage. Regulatory issues were addressed by means of a Californian law which identified research on SIDS to be in the public interest and allows samples collected at autopsy to be made available for research.[31] [32] Platelet analysis requires free-flowing, unclotted blood which, somewhat surprisingly, is found at autopsy either because coagulation has not occurred or because fibrinolysis has taken place following postmortem coagulation. Previous studies have reported that platelets in postmortem blood are largely unactivated.[33] We were able to specifically demonstrate the feasibility of measuring platelet pathophysiology in postmortem blood.[32]

We then showed the following in SIDS subjects compared with control cases[32]: (1) increased levels of plasma and intraplatelet 5-HT, (2) decreased levels of platelet 14-3-3ζ protein, (3) decreased levels of the platelet surface adhesion receptor glycoprotein (GP) IX, and (4) in this independent cohort, confirmation of our previous finding[31] of elevated serum 5-HT. Moreover, a correlation was observed between platelet surface GPIX and levels of both serum and plasma 5-HT. Thus, the differences between SIDS and controls in both platelet and brainstem 5-HT and 14-3-3 biomarkers suggest a global dysregulation of these pathways in SIDS.

Unrecognized infection and neuroinflammation may be present in a subset of SIDS[34] and, as we recently reviewed,[32] platelets may represent a link between the periphery and neuroinflammation.[35] [36] [37] [38] In the setting of epilepsy, platelets themselves are reported to directly contribute to neuroinflammation by modulating brain 5-HT.[39] Specifically, platelet degranulation near the blood–brain barrier may directly affect the brain endothelium and factors released by platelets, including 5-HT, may alter neuronal activity.[39] Therefore, the presently reported platelet biomarker abnormalities raise the possibility that platelets in SIDS may also contribute to neuroinflammation.[32]

The presence in SIDS of both platelet and brainstem 5-HT and 14-3-3 abnormalities suggest the potential for platelets to be used as a model system to study 5-HT and 14-3-3 interactions in SIDS.[32] Moreover, platelet and serum biomarkers may aid in the forensic determination of SIDS and, unlike neurons, have the potential to be an easily accessible predictor of SIDS risk in living infants. Thus, the study of platelet physiology[1] can sometimes lead researchers in unexpected and fruitful new directions.



Publication History

Article published online:
18 June 2024

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  • References

  • 1 Gremmel T, Frelinger III AL, Michelson AD. Platelet physiology. Semin Thromb Hemost 2016; 42 (03) 191-204
  • 2 Michelson AD, Cattaneo M, Frelinger AL, Newman PJ. eds. Platelets. 4th ed.. Elsevier; 2019
  • 3 Koupenova M, Livada AC, Morrell CN. Platelet and megakaryocyte roles in innate and adaptive immunity. Circ Res 2022; 130 (02) 288-308
  • 4 Karakas D, Ni H. Unveiling platelets as immune regulatory cells. Circ Res 2024; 134 (08) 987-989
  • 5 Battinelli EM. PEARing into gestational thrombocytopenia. Blood 2024; 143 (15) 1439-1441
  • 6 Sciaudone A, Corkrey H, Humphries F, Koupenova M. Platelets and SARS-CoV-2 during COVID-19: immunity, thrombosis, and beyond. Circ Res 2023; 132 (10) 1272-1289
  • 7 Hofer BS, Brusilovskaya K, Simbrunner B. et al. Decreased platelet activation predicts hepatic decompensation and mortality in patients with cirrhosis. Hepatology 2023; (e-pub ahead of print) DOI: 10.1097/HEP.0000000000000740.
  • 8 Gremmel T, Michelson AD, Frelinger III AL, Bhatt DL. Novel aspects of antiplatelet therapy in cardiovascular disease. Res Pract Thromb Haemost 2018; 2 (03) 439-449
  • 9 Tscharre M, Michelson AD, Gremmel T. Novel antiplatelet agents in cardiovascular disease. J Cardiovasc Pharmacol Ther 2020; 25 (03) 191-200
  • 10 Billiald P, Slater A, Welin M. et al. Targeting platelet GPVI with glenzocimab: a novel mechanism for inhibition. Blood Adv 2023; 7 (07) 1258-1268
  • 11 Willinger M, James LS, Catz C. Defining the sudden infant death syndrome (SIDS): deliberations of an expert panel convened by the National Institute of Child Health and Human Development. Pediatr Pathol 1991; 11 (05) 677-684
  • 12 Goldstein RD, Blair PS, Sens MA. et al; 3rd International Congress on Sudden Infant and Child Death. Inconsistent classification of unexplained sudden deaths in infants and children hinders surveillance, prevention and research: recommendations from The 3rd International Congress on Sudden Infant and Child Death. Forensic Sci Med Pathol 2019; 15 (04) 622-628
  • 13 Centers for Disease Control and Prevention. Sudden Unexpected Infant Death and Sudden Infant Death Syndrome. 2023 Accessed April 12, 2023 at: https://www.cdc.gov/sids/data.htm
  • 14 Matthews TJ, MacDorman MF, Thoma ME. Infant mortality statistics from the 2013 period linked birth/infant death data set. Natl Vital Stat Rep 2015; 64 (09) 1-30
  • 15 Filiano JJ, Kinney HC. A perspective on neuropathologic findings in victims of the sudden infant death syndrome: the triple-risk model. Biol Neonate 1994; 65 (3-4): 194-197
  • 16 Panigrahy A, Filiano J, Sleeper LA. et al. Decreased serotonergic receptor binding in rhombic lip-derived regions of the medulla oblongata in the sudden infant death syndrome. J Neuropathol Exp Neurol 2000; 59 (05) 377-384
  • 17 Kinney HC, Randall LL, Sleeper LA. et al. Serotonergic brainstem abnormalities in Northern Plains Indians with the sudden infant death syndrome. J Neuropathol Exp Neurol 2003; 62 (11) 1178-1191
  • 18 Paterson DS, Trachtenberg FL, Thompson EG. et al. Multiple serotonergic brainstem abnormalities in sudden infant death syndrome. JAMA 2006; 296 (17) 2124-2132
  • 19 Kinney HC, Richerson GB, Dymecki SM, Darnall RA, Nattie EE. The brainstem and serotonin in the sudden infant death syndrome. Annu Rev Pathol 2009; 4: 517-550
  • 20 Broadbelt KG, Rivera KD, Paterson DS. et al. Brainstem deficiency of the 14-3-3 regulator of serotonin synthesis: a proteomics analysis in the sudden infant death syndrome. Mol Cell Proteomics 2012; 11 (01) M111.009530
  • 21 Kinney HC, Haynes RL. The serotonin brainstem hypothesis for the sudden infant death syndrome. J Neuropathol Exp Neurol 2019; 78 (09) 765-779
  • 22 Chen JJ, Li Z, Pan H. et al. Maintenance of serotonin in the intestinal mucosa and ganglia of mice that lack the high-affinity serotonin transporter: abnormal intestinal motility and the expression of cation transporters. J Neurosci 2001; 21 (16) 6348-6361
  • 23 Gershon MD. Review article: serotonin receptors and transporters – roles in normal and abnormal gastrointestinal motility. Aliment Pharmacol Ther 2004; 20 (Suppl. 07) 3-14
  • 24 Gershon MD, Tack J. The serotonin signaling system: from basic understanding to drug development for functional GI disorders. Gastroenterology 2007; 132 (01) 397-414
  • 25 Anderson GM, Feibel FC, Cohen DJ. Determination of serotonin in whole blood, platelet-rich plasma, platelet-poor plasma and plasma ultrafiltrate. Life Sci 1987; 40 (11) 1063-1070
  • 26 Bellido I, Delange L, Gomez-Luque A. The platelet of the patients with ischemic cardiopathy and cardiac valve disease showed a reduction of 8OH-DPAT binding sites. Thromb Res 2008; 121 (04) 555-565
  • 27 Martini C, Trincavelli ML, Tuscano D. et al. Serotonin-mediated phosphorylation of extracellular regulated kinases in platelets of patients with panic disorder versus controls. Neurochem Int 2004; 44 (08) 627-639
  • 28 Nagatomo T, Rashid M, Abul Muntasir H, Komiyama T. Functions of 5-HT2A receptor and its antagonists in the cardiovascular system. Pharmacol Ther 2004; 104 (01) 59-81
  • 29 Kinney HC, Cryan JB, Haynes RL. et al. Dentate gyrus abnormalities in sudden unexplained death in infants: morphological marker of underlying brain vulnerability. Acta Neuropathol 2015; 129 (01) 65-80
  • 30 Cummings KJ, Leiter JC, Trachtenberg FL. et al. Altered 5-HT2A/C receptor binding in the medulla oblongata in the sudden infant death syndrome (SIDS): Part II. age-associated alterations in serotonin receptor binding profiles within medullary nuclei supporting cardiorespiratory homeostasis. J Neuropathol Exp Neurol 2024; 83 (03) 144-160
  • 31 Haynes RL, Frelinger III AL, Giles EK. et al. High serum serotonin in sudden infant death syndrome. Proc Natl Acad Sci U S A 2017; 114 (29) 7695-7700
  • 32 Frelinger III AL, Haynes RL, Goldstein RD. et al. Dysregulation of platelet serotonin, 14-3-3 and GPIX in sudden infant death syndrome. Sci Rep 2024; 14 (01) 11092
  • 33 Thomsen H, Krisch B. The postmortem activation status of platelets. Int J Legal Med 1994; 107 (03) 111-117
  • 34 Ramachandran PS, Okaty BW, Riehs M. et al. Multiomic analysis of neuroinflammation and occult infection in sudden infant death syndrome. JAMA Neurol 2024; 81 (03) 240-247
  • 35 Thornton P, McColl BW, Greenhalgh A, Denes A, Allan SM, Rothwell NJ. Platelet interleukin-1alpha drives cerebrovascular inflammation. Blood 2010; 115 (17) 3632-3639
  • 36 Rawish E, Nording H, Münte T, Langer HF. Platelets as mediators of neuroinflammation and thrombosis. Front Immunol 2020; 11: 548631
  • 37 Rust C, Malan-Muller S, van den Heuvel LL. et al. Platelets bridging the gap between gut dysbiosis and neuroinflammation in stress-linked disorders: a narrative review. J Neuroimmunol 2023; 382: 578155
  • 38 Kopeikina E, Ponomarev ED. The role of platelets in the stimulation of neuronal synaptic plasticity, electric activity, and oxidative phosphorylation: possibilities for new therapy of neurodegenerative diseases. Front Cell Neurosci 2021; 15: 680126
  • 39 Kopeikina E, Dukhinova M, Yung AWY. et al. Platelets promote epileptic seizures by modulating brain serotonin level, enhancing neuronal electric activity, and contributing to neuroinflammation and oxidative stress. Prog Neurobiol 2020; 188: 101783
  • 40 Kinney HC, Broadbelt KG, Haynes RL, Rognum IJ, Paterson DS. The serotonergic anatomy of the developing human medulla oblongata: implications for pediatric disorders of homeostasis. J Chem Neuroanat 2011; 41 (04) 182-199