Heparan sulfates are critical regulators of the inhibitory megakaryocyte-platelet receptor G6b-B

Vögtle, Timo; Sharma, Sumana; Mori, Jun; Nagy, Z.; Semeniak, Daniela; Geer, Mitchell J.; Smith, Christopher W.; Lane, Jordan; Pollack, Scott J.; Lassila, Riitta; Jouppila, Annukka; Barr, Alastair J.; Ogg, D.; Howard, Tina D.; McMiken, H.J.; Warwicker, Juli; Geh, Catherine; Rowlinson, Rachel; Abbott, W. Mark; Schulze, Harald; Wright, Gavin J.; Mazharian, Alexandra; Fütterer, Klaus; Rajesh, Sundaresan; Douglas, Michael E.; Senis, Yotis A.

doi:10.1101/584698

Cited by 4 publications

(5 citation statements)

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“…53 Recent reports have demonstrated that HS chains have an unexpected role as regulators of the platelet receptor G6b-B, which functions to attenuate platelet activation and play key roles in platelet production. 54 Interestingly, overexpression of HPSE in mice promotes megakaryopoiesis, 55 and it is plausible that increased HPSE expression by megakaryocytes could play a direct role in generation of hyperreactive platelets. Apart from the contribution of serglycin to alpha-granule development, PGs remain understudied in the context of platelets and it is plausible that G6b-B interactions with HSPGs at the platelet surface function to restrain inappropriate platelet activation.…”

Section: Discussionmentioning

confidence: 99%

“…Unbiased proteomic analysis of vascular surface molecules altered during the course of murine sepsis indicate that platelet degranulation and extracellular matrix remodeling are the top pair of proteomic changes observed in the vasculature 53 . Recent reports have demonstrated that HS chains have an unexpected role as regulators of the platelet receptor G6b‐B, which functions to attenuate platelet activation and play key roles in platelet production 54 . Interestingly, overexpression of HPSE in mice promotes megakaryopoiesis, 55 and it is plausible that increased HPSE expression by megakaryocytes could play a direct role in generation of hyperreactive platelets.…”

Section: Discussionmentioning

confidence: 99%

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Heparanase expression and activity are increased in platelets during clinical sepsis

Eustes

Campbell

Middleton

et al. 2021

Journal of Thrombosis and Haemostasis

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Background: Heparanase (HPSE) is the only known mammalian enzyme that can degrade heparan sulfate. Heparan sulfate proteoglycans are essential components of the glycocalyx, and maintain physiological barriers between the blood and endothelial cells. HPSE increases during sepsis, which contributes to injurious glyocalyx degradation, loss of endothelial barrier function, and mortality.Objectives: As platelets are one of the most abundant cellular sources of HPSE, we sought to determine whether HPSE expression and activity increases in human platelets during clinical sepsis. We also examined associations between platelet HPSE expression and clinical outcomes.Patients/Methods: Expression and activity of HPSE was determined in platelets isolated from septic patients (n = 59) and, for comparison, sex-matched healthy donors (n = 46) using complementary transcriptomic, proteomic, and functional enzymatic assays. Septic patients were followed for the primary outcome of mortality, and clinical data were captured prospectively for septic patients. Results:The mRNA expression of HPSE was significantly increased in platelets isolated from septic patients. Ribosomal footprint profiling, followed by [S35] methionine labeling assays, demonstrated that HPSE mRNA translation and HPSE protein S U PP O RTI N G I N FO R M ATI O N Additional supporting information may be found online in the Supporting Information section. How to cite this article: Eustes AS, Campbell RA, Middleton EA, et al. Heparanase expression and activity are increased in platelets during clinical sepsis.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Heparanase expression and activity are increased in platelets during clinical sepsis

Eustes

Campbell

Middleton

et al. 2021

Journal of Thrombosis and Haemostasis

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“…The inhibitory immunoreceptor tyrosine‐based inhibition motif (ITIM)‐containing receptor G6b‐B binds the heparan sulfate side‐chains of perlecan in the blood vessel wall and plays a central role in maintaining MKs and platelets in a resting state. ( 5,6 ) Mice and humans with null and loss‐of‐function mutations in the gene coding G6b‐B, namely Mpig6b and MPIG6B , respectively, develop a complex MK and platelet phenotype, characterized by severe macrothrombocytopenia, large clusters of MKs and MK fragments in the bone marrow, extramedullary hematopoiesis, and primary focal MF in the marrow and spleen. ( 5,7,8 ) Whether bone health is affected by the G6b‐B deficiency is not known.…”

Section: Introductionmentioning

confidence: 99%

Severity of Megakaryocyte-Driven Osteosclerosis in Mpig6b-Deficient Mice Is Sex-Linked

Stavnichuk

Tauer

Nagy

et al. 2020

Journal of Bone and Mineral Research

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Patients with chronic myelofibrosis often suffer from osteosclerosis, which is associated with bone pain and may lead to bone marrow failure. The pathogenesis of myelofibrosis is linked to aberrant megakaryocyte development and function. Null and loss‐of‐function mutations in MPIG6B, which codes for the inhibitory heparan sulfate receptor G6b‐B, result in severe macrothrombocytopenia, large megakaryocyte clusters, and focal primary myelofibrosis in mice and humans. We investigated the development of osteosclerosis in Mpig6b null (Mpig6b−/−) mice. Although male and female Mpig6b−/− mice presented with elevated bone marrow megakaryocyte number and macrothrombocytopenia, female Mpig6b−/− mice developed progressive splenomegaly starting at 8 weeks of age. Micro–computed tomography (μCT) of femurs showed that female Mpig6b−/− mice had increased cortical thickness and reduced bone marrow area starting at 8 weeks of age and developed occlusion of the medullary cavity by trabeculae by 16 weeks of age. In contrast, male Mpig6b−/− mice developed only a small number of trabeculae in the medullary cavity at the proximal diaphysis and demonstrated a temporary decrease in bone volume fraction and trabecular thickness at 16 weeks. Ovariectomy of 10‐week‐old female Mpig6b−/− mice prevented the development of medullary cavity osteosclerosis, whereas orchiectomy of male Mpig6b−/− mice did not exacerbate their disease. Importantly, ovariectomized female Mpig6b−/− mice also demonstrated improvement in spleen weight compared to sham‐operated Mpig6b−/− mice, establishing estrogen as a contributing factor to the severity of the megakaryocyte‐driven osteosclerosis. © 2021 American Society for Bone and Mineral Research (ASBMR).

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“…Structural models of the receptor bridging complexes were constructed using a combination of AlphaFold2-generated structural models, the crystal structure of the G6b-B ectodomain bound to the 17.4 antibody (9), and manual modelling in ChimeraX (19). AlphaFold2 (20) was used to generate structural models of full-length receptors platelet glycoprotein VI (Uniprot Q9HCN6), G6b-B (Uniprot O95866) and FcgRIIA (Uniprot P31995), using the colab web interface (https://colab.research.google.com/github/sokrypton/ColabFold/blob/main/AlphaFold2.ipynb).…”

Section: Structural Modelingmentioning

confidence: 99%

G6b-B antibody-based cis-acting platelet receptor inhibitors (CAPRIs) as a new family of anti-thrombotic therapeutics

Mazharian,

Bertin,

Sarkar

et al. 2024

Preprint

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Platelets are highly reactive fragments of megakaryocytes that play a fundamental role in thrombosis and hemostasis. Predictably, all conventional anti-platelet therapies elicit bleeding, raising the question whether the thrombotic activity of platelets can be targeted separately. In this study, we describe a novel approach of inhibiting platelet activation through the use of bispecific single-chain variable fragments (bi-scFvs), termed cis-acting platelet receptor inhibitors (CAPRIs) that harness the immunoreceptor tyrosine-based inhibition motif (ITIM)-containing co-inhibitory receptor G6b-B (G6B) to suppress immunoreceptor tyrosine-based (ITAM)-containing receptor-mediated platelet activation. CAPRI-mediated hetero-clustering of G6B with either the ITAM-containing GPVI-FcR γ-chain complex or FcγRIIA (CD32A) inhibited collagen- or immune complex-induced platelet aggregation. G6B-GPVI CAPRIs strongly and specifically inhibited thrombus formation on collagen under arterial shear, whereas G6B-CD32A CAPRI strongly and specifically inhibited thrombus formation to heparin-induced thrombocytopenia, vaccine-induced thrombotic thrombocytopenia and antiphospholipid syndrome complexes on Von Willebrand Factor-coated surfaces and photochemical-injured endothelial cells under arterial shear. Our findings provide proof-of-concept that CAPRIs are highly effective at inhibiting ITAM receptor-mediated platelet activation, laying the foundation for a novel family of anti-thrombotic therapeutics with potentially improved efficacy and fewer bleeding outcomes compared with current anti-platelet therapies.

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Heparan sulfates are critical regulators of the inhibitory megakaryocyte-platelet receptor G6b-B

Cited by 4 publications

References 73 publications

Heparanase expression and activity are increased in platelets during clinical sepsis

Heparanase expression and activity are increased in platelets during clinical sepsis

Severity of Megakaryocyte-Driven Osteosclerosis in Mpig6b-Deficient Mice Is Sex-Linked

G6b-B antibody-based cis-acting platelet receptor inhibitors (CAPRIs) as a new family of anti-thrombotic therapeutics

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