title: Osteoblastic expansion induced by parathyroid hormone receptor signaling in murine osteocytes is not sufficient to increase hematopoietic stem cells.
abstract: Microenvironmental expansion of hematopoietic stem cells (HSCs) is induced by treatment with parathyroid hormone (PTH) or activation of the PTH receptor (PTH1R) in osteoblastic cells; however, the osteoblastic subset mediating this action of PTH is unknown. Osteocytes are terminally differentiated osteoblasts embedded in mineralized bone matrix but are connected with the BM. Activation of PTH1R in osteocytes increases osteoblastic number and bone mass. To establish whether osteocyte-mediated PTH1R signaling expands HSCs, we studied mice expressing a constitutively active PTH1R in osteocytes (TG mice). Osteoblasts, osteoclasts, and trabecular bone were increased in TG mice without changes in BM phenotypic HSCs or HSC function. TG mice had progressively increased trabecular bone but decreased HSC function. In severely affected TG mice, phenotypic HSCs were decreased in the BM but increased in the spleen. TG osteocytes had no increase in signals associated with microenvironmental HSC support, and the spindle-shaped osteoblastic cells that increased with PTH treatment were not present in TG bones. These findings demonstrate that activation of PTH1R signaling in osteocytes does not expand BM HSCs, which are instead decreased in TG mice. Therefore, osteocytes do not mediate the HSC expansion induced by PTH1R signaling. Further, osteoblastic expansion is not sufficient to increase HSCs.
authors.affiliation: Department of Medicine, Division of Endocrinology, and J. P. Wilmot Cancer Center, University of Rochester School of Medicine, Rochester, NY 14642, USA. laura_calvi@urmc.rochester.edu
authors.forename: Laura M
authors.initials: LM
authors.lastname: Calvi
authors.forename: Olga
authors.initials: O
authors.lastname: Bromberg
authors.forename: Yumie
authors.initials: Y
authors.lastname: Rhee
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Weber
authors.forename: Julianne N P
authors.initials: JN
authors.lastname: Smith
authors.forename: Miles J
authors.initials: MJ
authors.lastname: Basil
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Frisch
authors.forename: Teresita
authors.initials: T
authors.lastname: Bellido
mesh_terms: D000818:Animals; D016723:Bone Remodeling; D005434:Flow Cytometry; D006410:Hematopoiesis / Q000502:physiology; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000378:metabolism; D006801:Humans; D007124:Immunoenzyme Techniques; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation / Q000235:genetics; D010006:Osteoblasts / Q000166:cytology* / Q000378:metabolism; D010011:Osteocytes / Q000166:cytology / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000378:metabolism; D051381:Rats; D044168:Receptor, Parathyroid Hormone, Type 1 / Q000502:physiology*; D015398:Signal Transduction
chemical_list: C473449:PTH1R protein, human; D010281:Parathyroid Hormone; D044168:Receptor, Parathyroid Hormone, Type 1