2028 - PULSATION IN BLOOD VESSELS STIMULATES MECHANOSENSITIVE AND EPIGENETIC MECHANISMS TO PROMOTE THE BIRTH OF HEMATOPOIETIC STEM CELLS

Abstract

During fetal development, a subset of endothelial cells changes their fate to become HSCs in the aorta-gonad-mesonephros (AGM) region. However, the mechanisms regulating the endothelial-to-hematopoietic transition (EHT) remain largely unknown. Our machine learning and confocal imaging demonstrate that the rhythmic contraction in ventral part of dorsal aorta is concurrent with EHT events. We also found that pulsation-mediated cyclical contraction stretches AGM in circumferential direction. Using serial transplant, limiting dilution, and replating assays, we found that the circumferential stretching of hemogenic endothelial cells or Piezo1 activation yields 3-times higher amounts of Long Term (LT)-HSC formation; which reconstitute to normal multi-lineage adult blood. Using vaccine-challenge, adult globin expression, MPO enzyme activity, immunoglobulins, and T-cell receptor rearrangement analyses, we found that circumferential stretching or Piezo1 activation-derived HSCs reconstitute to functional T and B cells, adult erythrocytes, and myeloid cells. Our Piezo1fl/flxScl-Cre conditional knockout, gene-silencing, & confocal imaging further demonstrate that circumferential stretching of blood vessels activates Piezo1; which enhances epigenetic regulator Dnmt3b expression to stimulate the EHT. Our Cut&Run & MassArray analyses demonstrate that Dnmt3b suppresses endothelial genes during EHT. In conclusion, we found that pulsation-mediated circumferential stretching of AGM stimulates the EHT by Piezo1 activation and Dnmt3b over-expression. This leads to the formation of long-term self-renewing HSCs engrafting upon serial transplantations and reconstituting normal adult blood. To our knowledge, this is the first report demonstrating how biomechanical forces utilize epigenetic machinery to promote cell fate transition as well as a bioreactor to develop and expand LT-HSCs.