Agbani, E. O. | Search bioRxiv

bioRxiv2021

Platelet generation from circulating megakaryocytes is triggered in the lung vasculature

Platelets, small hemostatic blood cells, are derived from megakaryocytes, although the generation process is not clear. Only small numbers of platelets have been produced in systems outside the body, where bone marrow and lung are proposed as sites of platelet generation. Here we show that perfusion of megakaryocytes ex vivo through the mouse lung vasculature generates very large numbers of platelets, up to 3,000 per megakaryocyte. Despite their large size, megakaryocytes were able repeatedly to passage through the lung vasculature, leading to enucleation and fragmentation to generate platelets intravascularly. Using the ex vivo lung and a novel in vitro microfluidic chamber we determined the contributions of oxygenation, ventilation and endothelial cell health to platelet generation, and showed a critical role for the actin regulator TPM4. One-Sentence SummaryMegakaryocytes form platelets intravascularly in the lung, dependent upon oxygenation, endothelium and megakaryocyte TPM4

physiology↗

bioRxiv2017

Phosphatidylserine Exposure after Vascular Injury-Platelet or Endothelial

BackgroundPlatelets membranes are considered the paramount site for the assembly of tenase and prothrombinase complex and are key players in localising coagulation to wound sites. However, the endothelium is also known to express phosphatidylserine (PS) and support the binding of recombinant FVa/FXa even beyond the site of injury. It thus remains unclear, what cell type play the preeminent role in the cellular control of coagulation after vascular injury.\n\nApproachTo address this question, we utilised a model of haemostasis (full thickness 1mm excisional skin wounds) as well as tissues after injury in laser and ferric chloride models of thrombosis. Damage to the endothelium was assessed by the combined methods of picrosirius red staining, immunofluorescence and electron microscopy. Using multiphoton microscopy, we then compared the spatial distribution of PS on platelets and the endothelium.\n\nResultsPlatelets and detectable PS significantly co-localised compared with similar analysis of endothelial cell and exposed PS on wounded carotids arteries which was not significant. Point injury by laser induced restricted damage of the endothelium which was associated with limited platelets recruitment. In consistence with platelets response after FeCl3 injury, platelets exposed most of the PS detected at the wound edge where skin vessels were transected in our haemostasis model (Correlation Coeff. 0.78 +/- 0.12 vs 0.35 +/- 0.23).\n\nConclusionsWe surmised that data from the different models support a paradigm of graded haemostatic response to vascular injury, in which full platelets response is limited to wound sites exposing the sub-endothelial matrix.

physiology↗