Location is everything when it comes to megakaryocyte function

Abstract

Megakaryocytes (MKs) give rise to platelets, which are blood cells that are essential to prevent hemorrhage. Although the majority of MKs localize to the bone marrow, there is a distinct population of lung-residing MKs (MKL). In this issue of the JCI, Pariser et al. examined gene expression patterns of MKs collected from murine and nonhuman primate bone marrow or lung. This Commentary explores the premise that environmental factors from the lung determine the genetic and phenotypic similarity of MKL to lung dendritic cells, distinguishing MKL from bone marrow MKs. Indeed, while MKL retain the ability to make platelets, they also process and present antigens that activate CD4+ lymphocytes. These data suggest that MKL may play an important role in immune processes beyond platelet production.

Figure 1. Model for MK plasticity.

The lung contains intravascular and extravascular populations of megakaryocytes (MK_L). MK_L that are large, polyploid (average of 16N), and intravascular are ideally positioned to release proplatelets into flowing blood. Extravascular diploid (2N) MK_L resemble lung dendritic cells. The local environment modulates the phenotype of BM MKs (MK_BM) and MK_L. Notably, MK_BM that are transferred into the lungs adopt an MK_L-like phenotype (6). MKs or MK progenitors may continuously migrate between the BM and the lungs.