Mesenchymal Stromal Cells regulate human Hematopoietic Stem Cell survival and regeneration via cAMP/PKA pathway

Ionizing radiation and chemotherapy suppress normal Hematopoietic Stem and Progenitor Cells (HSPCs) function and present an inherent risk of developing bone marrow failure and secondary leukemias. Mesenchymal Stromal Cells (MSCs) constitute an essential HSPC niche component by regulating HSPC quiescence, self-renewal, survival, and differentiation. Yet, the underlying pro-regenerative signaling pathways activated in HSPCs by MSCs remain poorly understood. Here, using co-culture system of bone marrow-derived MSCs and HSPCs we established that irradiated HSPCs co-cultured with MSCs underwent significantly less apoptosis and maintained their in vivo repopulating ability. We reveal that MSCs mediate protection by preserving pro-survival MCL1 protein levels in human HSPCs. Moreover, using unbiased HSPC transcriptomic analysis complemented with ex vivo and in vivo validation studies we discovered that MSCs activate cAMP/PKA/CREB signaling pathway in HSPCs to prevent MCL1 decline and apoptosis onset upon irradiation. Pharmacological activation of cAMP signaling pathway in human HSPCs replicated MSC mediated protection of HSPC functionality. Collectively, our results highlight the role of cAMP/PKA/CREB signaling pathway in MSC-HSPC cross-talk and its critical role in the regulation of survival and self-renewal ability of human HSPCs. Furthermore, we also revealed pharmacological agents that can mitigate radiation-induced hematological sequelae. ### Competing Interest Statement The authors have declared no competing interest.