WNT9A Is a Conserved Regulator of Hematopoietic Stem and Progenitor Cell Development.

Jenna Richter,Elizabeth Ng,Andrew Elefanty,David Traver,Edouard Stanley,Karl Willert

doi:10.3390/genes9020066

Abstract

Hematopoietic stem cells (HSCs) differentiate into all cell types of the blood and can be used therapeutically to treat hematopoietic cancers and disorders. Despite decades of research, it is not yet possible to derive therapy-grade HSCs from pluripotent precursors. Analysis of HSC development in model organisms has identified some of the molecular cues that are necessary to instruct hematopoiesis in vivo, including Wnt9A, which is required during an early time window in zebrafish development. Although bona fide HSCs cannot be derived in vitro, it is possible to model human hematopoietic progenitor development by differentiating human pluripotent stem cells to hematopoietic cells. Herein, we modulate WNT9A expression during the in vitro differentiation of human embryonic stem cells to hematopoietic progenitor cells and demonstrate that WNT9A also regulates human hematopoietic progenitor cell development in vitro. Overexpression of WNT9A only impacts differentiation to CD34+/CD45+ cells during early time windows and does so in a dose-dependent manner. The cells that receive the Wnt signal—not the cells that secrete WNT9A—differentiate most efficiently to hematopoietic progenitors; this mimics the paracrine action of Wnt9a during in vivo hematopoiesis. Taken together, these data indicate that WNT9A is a conserved regulator of zebrafish and human hematopoietic development.

Highlights

Hematopoietic stem cells (HSCs) give rise to all blood cells
Utilizing the in vitro hematopoietic differentiation system as a model for human hematopoietic development, we show here that (1) Wnt positively regulates the differentiation of human progenitors; (2) WNT9A impacts in vitro human hematopoiesis in a time-dependent manner; (3) WNT9A has a dose-dependent effect on hematopoietic differentiation; (4) in vitro differentiation dynamics in response to WNT9A mimic the paracrine nature of the Wnt9a signal observed in zebrafish
Pluripotent cells progress through mesodermal and endothelial cell fates before a subset is further specified towards hematopoietic progenitor cells (Figure 1A,B); the corresponding time window for the Wnt requirement in vitro is approximately between day two and day four of differentiation, according to the expression of marker genes for mesoderm (BRY, WNT3) and endothelium (CD31/PECAM) (Figure 1B)

Summary

Introduction

Hematopoietic stem cells (HSCs) give rise to all blood cells. This property is exploited for therapeutic use; HSC transplants from bone marrow or peripheral blood are commonly used to treat hematopoietic cancers and disorders [1,2]. Induced pluripotent stem cell technology has made it possible to derive patient-matched pluripotent cells that are theoretically capable of differentiating into. HSCs [3,4,5] These cells represent a potential source of HSCs for each patient in need of a transplant, which would be a significant advancement in the field of regenerative medicine. Current protocols yield hematopoietic cells with limited repopulation capacity, subpar ability to differentiate into all blood lineages, or utilize the enforced expression of hematopoietic transcription factors to induce

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