title: TGF-beta signaling-deficient hematopoietic stem cells have normal self-renewal and regenerative ability in vivo despite increased proliferative capacity in vitro.
abstract: Studies in vitro implicate transforming growth factor beta (TGF-beta) as a key regulator of hematopoiesis with potent inhibitory effects on progenitor and stem cell proliferation. In vivo studies have been hampered by early lethality of knock-out mice for TGF-beta isoforms and the receptors. To directly assess the role of TGF-beta signaling for hematopoiesis and hematopoietic stem cell (HSC) function in vivo, we generated a conditional knock-out model in which a disruption of the TGF-beta type I receptor (T beta RI) gene was induced in adult mice. HSCs from induced mice showed increased proliferation recruitment when cultured as single cells under low stimulatory conditions in vitro, consistent with an inhibitory role of TGF-beta in HSC proliferation. However, induced T beta RI null mice show normal in vivo hematopoiesis with normal numbers and differentiation ability of hematopoietic progenitor cells. Furthermore HSCs from T beta RI null mice exhibit a normal cell cycle distribution and do not differ in their ability long term to repopulate primary and secondary recipient mice following bone marrow transplantation. These findings challenge the classical view that TGF-beta is an essential negative regulator of hematopoietic stem cells under physiologic conditions in vivo.
authors.affiliation: Department of Molecular Medicine and Gene Therapy, Institute of Laboratory Medicine, Lund University Hospital, BMC A12, 221 84 Lund, Sweden. jonas.larsson@molmed.lu.se
authors.forename: Jonas
authors.initials: J
authors.lastname: Larsson
authors.forename: Ulrika
authors.initials: U
authors.lastname: Blank
authors.forename: Hildur
authors.initials: H
authors.lastname: Helgadottir
authors.forename: Jon Mar
authors.initials: JM
authors.lastname: Björnsson
authors.forename: Mats
authors.initials: M
authors.lastname: Ehinger
authors.forename: Marie-José
authors.initials: MJ
authors.lastname: Goumans
authors.forename: Xiaolong
authors.initials: X
authors.lastname: Fan
authors.forename: Per
authors.initials: P
authors.lastname: Levéen
authors.forename: Stefan
authors.initials: S
authors.lastname: Karlsson
mesh_terms: D030201:Activin Receptors, Type I / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D000818:Animals; D016026:Bone Marrow Transplantation; D002453:Cell Cycle; D002454:Cell Differentiation; D002455:Cell Division; D002478:Cells, Cultured; D006410:Hematopoiesis; D006412:Hematopoietic Stem Cells / Q000166:cytology*; D051379:Mice; D018345:Mice, Knockout; D017346:Protein Serine-Threonine Kinases; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction; D016212:Transforming Growth Factor beta / Q000502:physiology*
chemical_list: D018125:Receptors, Transforming Growth Factor beta; D016212:Transforming Growth Factor beta; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I; D000077293:Receptor, Transforming Growth Factor-beta Type I