# Transient mechanical activation of the Piezo1 channel facilitates ex vivo expansion of hematopoietic stem cells

## TL;DR

This study shows that briefly activating the Piezo1 channel helps expand blood stem cells outside the body, which could improve stem cell therapies.

## Contribution

The novel finding is that transient mechanical activation of Piezo1 using 500-nm polystyrene microspheres enhances functional HSC expansion.

## Key findings

- PS500 microspheres significantly expand mouse and human hematopoietic stem cells ex vivo.
- PS500 activates Piezo1, leading to Ca2+-dependent cytokine expression and STAT3 activation.
- Transient Piezo1 activation is essential for maintaining HSC function during culture.

## Abstract

Achieving long-term ex vivo expansion of functional hematopoietic stem cells (HSCs) is essential for advancing HSC-based clinical therapies. Although mechanosensitive ion channels are known to play key roles in the hematopoietic system, their involvement in HSC expansion remains unclear. Here, we show that Piezo1 is highly expressed in HSCs. Both genetic deletion and prolonged chemical activation of Piezo1 impair cultured HSC function, indicating that transient mechanical activation of Piezo1 is required for maintenance of HSCs in culture. To achieve this, we screened various microspheres and found that PS500 (500-nm polystyrene microspheres) significantly enhanced ex vivo expansion of mouse bone marrow HSCs with long-term repopulating capacity. PS500 also expanded human umbilical cord blood HSCs capable of engraftment in immunodeficient mice. Mechanistically, PS500 activates Piezo1, triggering Ca2+-dependent expression of proliferative cytokines and subsequent STAT3 activation, which support HSC self-renewal and proliferation. Together, these findings show that PS500 enables transient Piezo1 activation and efficient, non-toxic expansion of functional HSCs, offering a promising approach for the generation of transplantable HSCs for clinical use.