title: Spleen hypoplasia leads to abnormal stress hematopoiesis in mice with loss of Pbx homeoproteins in splenic mesenchyme.
abstract: The spleen plays critical roles in immunity and also provides a permissive microenvironment for hematopoiesis. Previous studies have reported that the TALE-class homeodomain transcription factor Pbx1 is essential in hematopoietic stem and progenitor cells (HSPCs) for stem cell maintenance and progenitor expansion. However, the role of Pbx1 in the hematopoietic niche has not been investigated. Here we explored the effects that genetic perturbation of the splenic mesenchymal niche has on hematopoiesis upon loss of members of the Pbx family of homeoproteins. Splenic mesenchyme-specific inactivation of Pbx1 (SKO) on a Pbx2- or Pbx3-deficient genetic background (DKO) resulted in abnormal development of the spleen, which is dysmorphic and severely hypoplastic. This phenotype, in turn, affected the number of HSPCs in the fetal and adult spleen at steady state, as well as markedly impairing the kinetics of hematopoietic regeneration in adult mice after sub-lethal and lethal myelosuppressive irradiation. Spleens of mice with compound Pyx deficiency 8 days following sublethal irradiation displayed significant downregulation of multiple cytokine-encoding genes, including KitL/SCF, Cxcl12/SDF-1, IL-3, IL-4, GM-CSF/Csf2 IL-10, and Igf-1, compared with controls. KitL/SCF and Cxcl12/SDF-1 were recently shown to play key roles in the splenic niche in response to various haematopoietic stresses such as myeloablation, blood loss, or pregnancy. Our results demonstrate that, in addition to their intrinsic roles in HSPCs, non-cell autonomous functions of Pbx factors within the splenic niche contribute to the regulation of hematopoiesis, at least in part via the control of KitL/SCF and Cxcl12/SDF-1. Furthermore, our study establishes that abnormal spleen development and hypoplasia have deleterious effects on the efficiency of hematopoietic recovery after bone marrow injury.
authors.affiliation: Department of Cell and Developmental Biology, Weill Cornell Medicine, New York, NY, USA.
authors.forename: Rediet
authors.initials: R
authors.lastname: Zewdu
authors.affiliation: Department of Cell and Developmental Biology, Weill Cornell Medicine, New York, NY, USA.|Program in Craniofacial Biology, Department of Orofacial Sciences & Department of Anatomy, University of California San Francisco, San Francisco, CA, USA.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Risolino
authors.affiliation: Department of Cell and Developmental Biology, Weill Cornell Medicine, New York, NY, USA.
authors.forename: Alexandru
authors.initials: A
authors.lastname: Barbulescu
authors.affiliation: Department of Genetic Medicine, Weill Cornell Medicine, New York, NY, USA.
authors.forename: Pradeep
authors.initials: P
authors.lastname: Ramalingam
authors.affiliation: Department of Genetic Medicine, Weill Cornell Medicine, New York, NY, USA.
authors.forename: Jason M
authors.initials: JM
authors.lastname: Butler
authors.affiliation: Department of Cell and Developmental Biology, Weill Cornell Medicine, New York, NY, USA.|Program in Craniofacial Biology, Department of Orofacial Sciences & Department of Anatomy, University of California San Francisco, San Francisco, CA, USA.
authors.forename: Licia
authors.initials: L
authors.lastname: Selleri
mesh_terms: D000818:Animals; D016207:Cytokines / Q000378:metabolism; D006411:Hematopoiesis, Extramedullary; D018398:Homeodomain Proteins / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D013154:Spleen / Q000502:physiology; D013312:Stress, Physiological; D014157:Transcription Factors / Q000502:physiology*
chemical_list: D016207:Cytokines; D018398:Homeodomain Proteins; C481797:Pbx1 protein, mouse; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D014157:Transcription Factors
keywords: Cxcl12/SDF-1; GM-CSF; Nkx2-5+  spleen niche KitL/SCF; Pbx transcription factors; extramedullary hematopoiesis; hematopoietic stem cells; spleen hypoplasia