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GPVI signaling is compromised in newly formed young platelets after acute thrombocytopenia in mice

Shuchi Gupta, Deya Cherpokova, Markus Spindler, Martina Morowski, Markus Bender and Bernhard Nieswandt

Key points

  • Newly formed young platelets produced by megakaryocytes in response to acute thrombocytopenia display a selective GPVI-ITAM signaling defect.

  • This signaling defect protects mice from occlusive arterial thrombus formation.

Abstract

At sites of vascular injury, exposed subendothelial collagens trigger platelet activation and thrombus formation by interacting with the immunoreceptor tyrosine-based activation motif (ITAM)-coupled glycoprotein (GP) VI on the platelet surface. Platelets are derived from the cytoplasm of megakaryocytes (MKs), which extend large proplatelets into bone marrow (BM) sinusoids that are then released into the blood stream where the final platelet sizing and maturation occurs. The mechanisms that prevent activation of MKs and forming proplatelets in the collagen-rich BM environment remain largely elusive. Here we demonstrate that newly formed young platelets (NFYPs) released after antibody-mediated thrombocytopenia in mice display a severe and highly selective signaling defect downstream of GPVI resulting in impaired collagen-dependent activation and thrombus formation in vitro and in vivo. The diminished GPVI signaling in NFYPs was linked to reduced phosphorylation of key downstream signaling proteins, including Syk, LAT and PLCγ2, whereas G protein-coupled receptor and CLEC-2 signaling pathways remained unaffected. This GPVI signaling defect was overcome, once the platelet counts were restored to normal in the circulation. Overall, these results indicate that the GPVI-ITAM signaling machinery in NFYPs after antibody-mediated thrombocytopenia only becomes fully functional in the blood circulation.

  • Submitted August 2, 2017.
  • Accepted December 20, 2017.