Relieving DYRK1A repression of MKL1 confers an adult-like phenotype to human infantile megakaryocytes

Abstract

Infantile (fetal and neonatal) megakaryocytes have a distinct phenotype consisting of hyperproliferation, limited morphogenesis, and low platelet production capacity. These properties contribute to clinical problems that include thrombocytopenia in neonates, delayed platelet engraftment in recipients of cord blood stem cell transplants, and inefficient ex vivo platelet production from pluripotent stem cell-derived megakaryocytes.The infantile phenotype results from deficiency of the actin-regulated coactivator, MKL1, which programs cytoskeletal changes driving morphogenesis. As a strategy to complement this molecular defect, we screened pathways with potential to affect MKL1 function and found that Dyrk1a kinase inhibition dramatically enhanced megakaryocyte morphogenesis in vitro and in vivo. Dyrk1 inhibitors rescued enlargement, polyploidization, and thrombopoiesis in human neonatal megakaryocytes. Megakaryocytes derived from induced pluripotent stem cells responded in a similar manner. Progenitors undergoing Dyrk1 inhibition demonstrated filamentous actin assembly, MKL1 nuclear translocation, and modulation of MKL1 target genes. Loss of function studies confirmed MKL1 involvement in this morphogenetic pathway. Ablim2, a stabilizer of filamentous actin, increased with Dyrk1 inhibition, and Ablim2 knockdown abrogated the actin, MKL1, and morphogenetic responses to Dyrk1 inhibition. These results thus delineate a pharmacologically tractable morphogenetic pathway whose manipulation may alleviate clinical problems associated with the limited thrombopoietic capacity of infantile megakaryocytes.

Synergistic roles of DYRK1A and GATA1 in trisomy 21 megakaryopoiesis

“…While significant research has characterized the antiproliferative role of DYRK1A in nonhematopoietic cells ( 19 , 20 , 27 , 46 ), a smaller body of work suggests DYRK1A promotes megakaryopoiesis and cell proliferation ( 16 , 21 ). Retroviral overexpression of Dyrk1a in ex vivo assays using euploid murine bone marrow cells induced an expansion of CD41 + megakaryocytes that was modestly enhanced with Gata1s ( 16 ).…”

“…Our studies reveal that DYRK1A and wtGATA1 synergistically restrain megakaryocyte proliferation, and in the presence of GATA1s mutations, DYRK1A loss unexpectedly exacerbates the expansion of immature megakaryocytes. These findings were surprising since DYRK1A overexpression has been shown to promote murine megakaryocyte expansion, while pharmacologic inhibition enhances maturation of human neonatal megakaryocytes ( 16 , 21 ), underscoring the cell context– and species-specific effects of this HSA21-encoded gene.…”

Baffled‐flow culture system enables the mass production of megakaryocytes from human embryonic stem cells by enhancing mitochondrial function

“…In addition, the development and maturation of MKs were accompanied by other unique changes, including gradually increasing cell size and granularity, which can be assessed based on FSC and SSC/granularity, respectively, using flow cytometry. 25,42 We found that the percentage of HG CD42b + MKs in the DC group was significantly higher than that in the SC group (Figure S4B). Several studies have indicated that platelet-producing human stem cell-derived MKs can be identified and enriched using FV uptake.…”

“…MKs derived from the DC group showed stronger MK‐characteristic gene expression and an increased percentage of β1‐Tubulin + CD42 + cells. In addition, the development and maturation of MKs were accompanied by other unique changes, including gradually increasing cell size and granularity, which can be assessed based on FSC and SSC/granularity, respectively, using flow cytometry 25,42 . We found that the percentage of HG CD42b + MKs in the DC group was significantly higher than that in the SC group (Figure S4B).…”

Over‐expression of Dyrk1A affects bleeding by modulating plasma fibronectin and fibrinogen level in mice

“…It was previously shown that 66% of DS babies have mild to moderate thrombocytopenia 3,4 . Recent results showed that Dyrk1A kinase inhibition enhances platelet production in infantile megakaryocytes, identifying Dyrk1A as a critical morphogenetic brake in megakaryopoiesis 32 . However, another study shows that the frequency of thrombocytopenia is 2.1% and thrombocytosis is much more frequent 33 .…”