-Author name in bold denotes the presenting author
-Asterisk * with author name denotes a Non-ASH member
Clinically Relevant Abstract denotes an abstract that is clinically relevant.

PhD Trainee denotes that this is a recommended PHD Trainee Session.

Ticketed Session denotes that this is a ticketed session.

1309 Blood Flow Directs Yap/Taz-Mediated Transcriptional Regulation of Self-Renewal Programs to Control Developmental HSPC Expansion By Mechanical Stimulation of Piezo1

Program: Oral and Poster Abstracts
Session: 501. Hematopoietic Stem and Progenitor Cells and Hematopoiesis: Basic and Translational: Poster I
Hematology Disease Topics & Pathways:
Research, Fundamental Science, Translational Research, bioinformatics, hematopoiesis, metabolism, computational biology, Biological Processes, molecular biology, Technology and Procedures
Saturday, December 9, 2023, 5:30 PM-7:30 PM

Wade W Sugden, PhD1, Zachary LeBlanc1*, Mayuri Tanaka-Yano, PhD1, Ran Jing2*, Maria Gonzalez di Tillio1*, Mohamad Najia, PhD1*, Yang Tang1*, Elizabeth Molnar1*, Stephan George1*, Brittney Love1*, Caroline Kubaczka1*, Nan Liu1*, Nah-Young Shin, PhD1*, Thorsten M. Schlaeger, PhD2*, Edroaldo Lummertz da Rocha, PhD3*, Alan B. Cantor, MD, PhD4, Stuart H Orkin, MD1, Robert Grant Rowe1, Wolfram Goessling, MD, PhD5, George Q. Daley, MD, PhD1 and Trista E. North, PhD6

1Department of Hematology/Oncology, Harvard Medical School/Boston Children's Hospital, Boston, MA
2Harvard Medical School/Boston Children's Hospital, Boston, MA
3Graduate Program of Pharmacology, Federal University of Santa Catarina, Florianopolis, Brazil
4Division of Pediatric Hematology/Oncology, Boston Children's Hospital and Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA
5Brigham and Women's Hospital, Boston, MA
6Stem Cell Program, Boston Children's Hospital, Harvard Medical School, Boston, MA

Hematopoietic stem and progenitor cells (HSPCs) emerge from artery-derived hemogenic endothelium (HE) in the vertebrate embryo during development. This process entails a cellular reprogramming from endothelial to hematopoietic gene signatures driven by the Runx1 transcription factor (TF), which is referred to as the endothelial-to-hematopoietic transition (EHT). A major goal of cellular therapeutics is to derive patient-specific HSPCs from iPSCs for clinical use, yet current differentiation protocols largely fail to recapitulate EHT to produce or expand long-lived multi-potent HSPCs in vitro, suggesting an incomplete understanding of the in vivo regulatory cues. Physical forces of wall shear stress (WSS) and cyclic stretch (CS) produced by hemodynamic blood flow in embryos are one such cue required during EHT to generate HSPCs from HE, however the mechanisms by which these forces are sensed and converted into a “stemness” regulatory module remain undefined.

Our previous work implicated the Hippo pathway TF YAP as essential for the maintenance, but not initiation, of the hematopoietic program in newly specified HE. Here, using scRNA-sequencing of sorted zebrafish trunk endothelial cells to capture all stages of EHT progression, we find that overexpression of YAP drives lipid metabolism, cell cycling, and propagation of a hematopoietic gene regulatory network (GRN) in the earliest specified HE cells. By employing a heat shock-inducible dominant negative YAP zebrafish line, we unmask a latent role for the YAP paralogue TAZ in hematopoiesis, which can promote CD41+ and Flk+/Myb+ HSPC production upon reduced YAP function. YAP and TAZ initiate transcriptional responses downstream of mechanical stimuli and require DNA binding cofactors to regulate target genes. Surprisingly, luciferase assays in HEK293 cells demonstrated a potent synergistic effect of TAZ/RUNX1, but not YAP/RUNX1, in transcriptional regulation at RUNX enhancers.

Finally, by pharmacologic and genetic manipulation, we identify the stretch-gated membrane ion channel Piezo1 as a potent regulator of CS-induced YAP/TAZ mechanotransduction in HE. Stimulation of zebrafish embryos with the Piezo1 small molecule agonist Yoda1 significantly increases HSPC number and YAP target gene expression in a YAP-dependent fashion. A similar modulation of blood and YAP target genes in human iPSC-derived CD34+ HE cells is seen with Yoda1, suggesting that this stretch-Piezo1-YAP axis can be chemically tuned in vitro to enhance HSPC differentiation. These results illuminate molecular details of how YAP/TAZ directs the production of HSPCs from HE in response to mechanical cues, and have broader implications for alternate regulatory effects of mechanically-stimulated Hippo TFs depending on the transcriptional milieu in cell-type specific contexts.

Disclosures: Schlaeger: Megakaryon Inc.: Research Funding. Cantor: Cellarity, Inc.: Consultancy. Daley: Megakaryon Inc.: Research Funding.

*signifies non-member of ASH