title: ARAP3 functions in hematopoietic stem cells.
abstract: ARAP3 is a GTPase-activating protein (GAP) that inactivates Arf6 and RhoA small GTPases. ARAP3 deficiency in mice causes a sprouting angiogenic defect resulting in embryonic lethality by E11. Mice with an ARAP3 R302,303A mutation (Arap3KI/KI) that prevents activation by phosphoinositide-3-kinase (PI3K) have a similar angiogenic phenotype, although some animals survive to adulthood. Here, we report that hematopoietic stem cells (HSCs) from rare adult Arap3KI/KI bone marrow are compromised in their ability to reconstitute recipient mice and to self-renew. To elucidate the potential cell-autonomous and non-cell-autonomous roles of ARAP3 in hematopoiesis, we conditionally deleted Arap3 in hematopoietic cells and in several cell types within the HSC niche. Excision of Arap3 in hematopoietic cells using Vav1-Cre does not alter the ability of ARAP3-deficient progenitor cells to proliferate and differentiate in vitro or ARAP3-deficient HSCs to provide multi-lineage reconstitution and to undergo self-renewal in vivo. Thus, our data suggest that ARAP3 does not play a cell-autonomous role in HSPCs. Deletion of Arap3 in osteoblasts and mesenchymal stromal cells using Prx1-Cre resulted in no discernable phenotypes in hematopoietic development or HSC homeostasis in adult mice. In contrast, deletion of Arap3 using vascular endothelial cadherin (VEC or Cdh5)-driven Cre resulted in embryonic lethality, however HSCs from surviving adult mice were largely normal. Reverse transplantations into VEC-driven Arap3 conditional knockout mice revealed no discernable difference in HSC frequencies or function in comparison to control mice. Taken together, our investigation suggests that despite a critical role for ARAP3 in embryonic vascular development, its loss in endothelial cells minimally impacts HSCs in adult bone marrow.
authors.affiliation: Department of Pediatrics, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, United States of America; Division of Hematology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, United States of America.
authors.forename: Yiwen
authors.initials: Y
authors.lastname: Song
authors.affiliation: Division of Hematology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, United States of America.
authors.forename: Jing
authors.initials: J
authors.lastname: Jiang
authors.affiliation: MRC Centre for Inflammation Research, The Queen's Medical Research Institute, The University of Edinburgh, United Kingdom.
authors.forename: Sonja
authors.initials: S
authors.lastname: Vermeren
authors.affiliation: Department of Pediatrics, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, United States of America; Division of Hematology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, United States of America.
authors.forename: Wei
authors.initials: W
authors.lastname: Tong
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D020690:GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D006410:Hematopoiesis; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000235:genetics; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009154:Mutation; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism
chemical_list: C000592378:ARAP3 protein, mouse; D048868:Adaptor Proteins, Signal Transducing; D020690:GTPase-Activating Proteins; D018398:Homeodomain Proteins; C489936:Prrx1 protein, mouse