# Mesenchymal stromal cells modulate survival and regeneration of human hematopoietic stem cells via PGE2/cAMP signaling

## TL;DR

Mesenchymal stromal cells protect human blood stem cells from radiation damage through a signaling pathway involving PGE2 and cAMP.

## Contribution

The study identifies PGE2/cAMP signaling as a novel mechanism by which mesenchymal stromal cells protect hematopoietic stem cells from genotoxic stress.

## Key findings

- MSC-secreted PGE2 activates cAMP/CREB signaling to protect HSPCs from irradiation-induced apoptosis.
- Pharmacological activation of the cAMP pathway with Forskolin/IBMX preserves HSPC function and self-renewal.
- cAMP agonists reduce pro-apoptotic proteins and stabilize anti-apoptotic proteins in HSPCs.

## Abstract

Ionizing radiation and chemotherapy significantly impair hematopoietic stem and progenitor cell (HSPC) function, increasing the risk of bone marrow failure and secondary malignancies. Mesenchymal stromal cells (MSCs), critical regulators within the hematopoietic niche, maintain HSPC quiescence, self-renewal, survival, and differentiation. However, the specific pro-regenerative signaling pathways activated by MSCs in human HSPCs remain incompletely defined. Here, we show that bone marrow-derived MSCs effectively suppress irradiation-induced apoptosis and preserve the in vivo repopulation capacity of human HSPCs. Transcriptomic analysis of HSPCs revealed a pronounced upregulation of CREB target genes following MSC co-culture, consistent with increased activation of the cAMP/CREB signaling pathway. Mechanistically, MSC-secreted prostaglandin E2 (PGE2) emerged as a key mediator of cAMP induced response in HSPCs. MSC-derived PGE2 preferentially inhibited IR-induced apoptosis in quiescent HSPCs, whereas pharmacological activation of cAMP pathway with Forskolin and IBMX (Forskolin/IBMX) robustly protected both quiescent and cycling HSPCs. Notably, the protective effect of Forskolin/IBMX persisted for up to 72 hours post-irradiation and significantly enhanced HSPC self-renewal. At the molecular level, we revealed reduced pro-apoptotic ASPP1 and PUMA expression, elevated p21 and stabilized anti-apoptotic MCL1 and BCL-XL proteins in human HSPCs treated with cAMP pathway agonists. Overall, our findings highlight the pivotal role of PGE2/cAMP/CREB signaling axis as a central mediator of MSC-mediated protection of human HSPCs under genotoxic stress and identify pharmacological cAMP activation as a promising strategy to protect human HSPCs against DNA damage-induced hematotoxicity.