The role of cell extrinsic Nrf2 in hematopoietic stem cell transplantation with iron overload

Joana REIS1,2, Carolina PEREIRA1,2, Marta LOPES1,2, Maria José TELES1,3, Laura MOSTEO LOPEZ1, Graça PORTO1,4,5, Tiago L DUARTE1, Delfim DUARTE6,7,8

1i3S - Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal
2ICBAS - Instituto de Ciências BIomédias Abel Salazar da Universidade do Porto, Porto, Portugal
3Departamento de Patologica Clínica, Centro Hospitalar Universitário de São João, Porto, Portugal
4Departamento de Patologia Molecular e Imunologia, ICBAS , Porto, Portugal
5Serviço de Hematologia, Centro Hospitalar Universitário de Santo António, Porto, Portugal
6Departamento de Onco-hematologia, Instituto Português de Oncologia do Porto, Porto, Portugal
7Departamento de Biomedicina, Unidade de Bioquímica, Faculdade de Medicina da Universidade do Porto, Porto, Portugal
8Porto Comprehensive Cancer Center, Porto, Portugal

Patients undergoing allogeneic hematopoietic stem cell transplantation (HSCT) often present iron overload (IOL). HSCT patients with high labile plasma iron show increased non-relapse mortality. NRF2 is a master anti-oxidant regulator, protecting against iron toxicity. The role of NRF2 in HSCT is not fully understood. We hypothesize that cell extrinsic NRF2 expression may impact HSCT outcome when IOL is present. To evaluate non-hematopoietic NRF2, we generated BM chimeras using WT, Nrf2-/-, Hamp1-/- and Nrf2-/-Hamp1-/- as recipients where WT BM cells were transplanted. We observed that, unlike single Hamp1-/- or Nrf2-/- recipient mice, Nrf2-/-Hamp1-/- recipients had shorter survival, indicating failure in HSC engraftment. Notably, treatment of Nrf2-/- mice with iron dextran (FeDx) prior to irradiation and transplant recapitulated the phenotype of double-KO mice. Since the liver systemically regulates hematopoiesis and considering that Nrf2 plays a protective role against iron toxicity in the liver, we repeated the experiment with Alb-CreT/+;Nrf2fl/fl recipient mice. The deletion of hepatic Nrf2 had no impact in the survival or success of BM transplant. We next hypothesized that niche cells might be involved. Sorted LepR+ MSCs from FeDx-treated mice showed increased expression of downstream Nrf2 target genes Nqo1, Gclc and Hmox1 while serum CXCL12 remained unaltered, suggesting that another cell type is involved, such as endothelial cells.

These results suggest that Nrf2 is a player in HSCT but the critical cell type and molecular mechanism involved remain unknown. Our work may contribute to improve the success rate of HSCT where the use of Nrf2 agonists might be of interest.