Retinoic Acid Receptor γ Activity in Mesenchymal Stem Cells Regulates Endochondral Bone, Angiogenesis, and B Lymphopoiesis

• Published in: Journal of bone and mineral research Vol. 33; no. 12; pp. 2202 - 2213
• Main Authors: Green, Alanna C, Rudolph‐Stringer, Victoria, Straszkowski, Lenny, Tjin, Gavin, Crimeen‐Irwin, Blessing, Walia, Mannu, Martin, T John, Sims, Natalie A, Purton, Louise E
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01-12-2018
• Subjects: Angiogenesis; Animals; B-Lymphocytes - metabolism; Bone and Bones - metabolism; Bone Development; Bone growth; Bone marrow; Bone Marrow - blood supply; Bone Marrow - pathology; Bone mass; Cancellous bone; Cancellous Bone - metabolism; Chondrocytes; Clonal deletion; Computed tomography; Cortical bone; Cortical Bone - metabolism; CXCL12 protein; Endochondral bone; Epiphysis; Female; Females; Flow cytometry; Gene deletion; GENETIC ANIMAL MODELS; Hemopoiesis; Lymphocytes B; Lymphopoiesis; Male; Mesenchymal stem cells; Mesenchymal Stem Cells - metabolism; Mesenchyme; Mice, Transgenic; Neovascularization, Physiologic; Organ Size; OSTEOBLASTS; Osteoblasts - metabolism; Osteoclastogenesis; Osteoclasts; Osteoclasts - metabolism; Osteogenesis; OSTEOIMMUNOLOGY; Osteoprogenitor cells; Receptors, Retinoic Acid - metabolism; Retinoic Acid Receptor gamma; Retinoic acid receptors; Stem cell transplantation; Stem cells; STROMAL/STEM CELLS; Tibia - pathology; TISSUE SIGNALING—OTHER (RETINOIC ACID RECEPTOR SIGNALING); Vascularization; TISSUE SIGNALING-OTHER (RETINOIC ACID RECEPTOR SIGNALING); GENETIC ANIMAL MODELS; STROMAL/STEM CELLS; OSTEOIMMUNOLOGY; OSTEOBLASTS
• ISSN: 0884-0431; 1523-4681
• DOI: 10.1002/jbmr.3558

ABSTRACT
Retinoic acid receptor (RAR) signaling regulates bone structure and hematopoiesis through intrinsic and extrinsic mechanisms. This study aimed to establish how early in the osteoblast lineage loss of RARγ (Rarg) disrupts the bone marrow microenvironment. Bone structure was analyzed by micro–computed tomography (μCT) in Rarg–/– mice and mice with Rarg conditional deletion in Osterix‐Cre–targeted osteoblast progenitors or Prrx1‐Cre–targeted mesenchymal stem cells. Rarg–/– tibias exhibited less trabecular and cortical bone and impaired longitudinal and radial growth. The trabecular bone and longitudinal, but not radial, growth defects were recapitulated in Prrx1:RargΔ/Δ mice but not Osx1:RargΔ/Δ mice. Although both male and female Prrx1:RargΔ/Δ mice had low trabecular bone mass, males exhibited increased numbers of trabecular osteoclasts and Prrx1:RargΔ/Δ females had impaired mineral deposition. Both male and female Prrx1:RargΔ/Δ growth plates were narrower than controls and their epiphyses contained hypertrophic chondrocyte islands. Flow cytometry revealed that male Prrx1:RargΔ/Δ bone marrow exhibited elevated pro‐B and pre‐B lymphocyte numbers, accompanied by increased Cxcl12 expression in bone marrow cells. Prrx1:RargΔ/Δ bone marrow also had elevated megakaryocyte‐derived Vegfa expression accompanied by smaller sinusoidal vessels. Thus, RARγ expression by Prrx1‐Cre–targeted cells directly regulates endochondral bone formation and indirectly regulates tibial vascularization. Furthermore, RARγ expression by Prrx1‐Cre–targeted cells extrinsically regulates osteoclastogenesis and B lymphopoiesis in male mice. © 2018 American Society for Bone and Mineral Research.