Impact of Itga2-Gp6-double collagen receptor deficient mice for bone marrow megakaryocytes and platelets

PLoS One. 2019 Aug 9;14(8):e0216839. doi: 10.1371/journal.pone.0216839. eCollection 2019.

Abstract

The two main collagen receptors on platelets, GPVI and integrin α2β1, play an important role for the recognition of exposed collagen at sites of vessel injury, which leads to platelet activation and subsequently stable thrombus formation. Both receptors are already expressed on megakaryocytes, the platelet forming cells within the bone marrow. Megakaryocytes are in permanent contact with collagen filaments in the marrow cavity and at the basal lamina of sinusoids without obvious preactivation. The role of both collagen receptors for megakaryocyte maturation and thrombopoiesis is still poorly understood. To investigate the function of both collagen receptors, we generated mice that are double deficient for Gp6 and Itga2. Flow cytometric analyses revealed that the deficiency of both receptors had no impact on platelet number and led to the expected lack in GPVI responsiveness. Integrin activation and degranulation ability was comparable to wildtype mice. By immunofluorescence microscopy, we could demonstrate that both wildtype and double-deficient megakaryocytes were overall normally distributed within the bone marrow. We found megakaryocyte count and size to be normal, the localization within the bone marrow, the degree of maturation, as well as their association to sinusoids were also unaltered. However, the contact of megakaryocytes to collagen type I filaments was decreased at sinusoids compared to wildtype mice, while the interaction to type IV collagen was unaffected. Our results imply that GPVI and α2β1 have no influence on the localization of megakaryocytes within the bone marrow, their association to the sinusoids or their maturation. The decreased contact of megakaryocytes to collagen type I might at least partially explain the unaltered platelet phenotype in these mice, since proplatelet formation is mediated by these receptors and their interaction to collagen. It is rather likely that other compensatory signaling pathways and receptors play a role that needs to be elucidated.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blood Platelets / cytology*
  • Gene Deletion*
  • Integrin alpha2beta1 / deficiency*
  • Integrin alpha2beta1 / genetics*
  • Megakaryocytes / cytology*
  • Mice
  • Platelet Membrane Glycoproteins / deficiency*
  • Platelet Membrane Glycoproteins / genetics*
  • Thrombopoiesis / genetics

Substances

  • Integrin alpha2beta1
  • Platelet Membrane Glycoproteins
  • platelet membrane glycoprotein VI

Grants and funding

The study was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Projektnummer 374031971 – TRR 240 to HS. (https://www.dfg.de) The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.