Pten knockout in mouse preosteoblasts leads to changes in bone turnover and strength

Judith Lorenz; Sandy Richter; Anna S Kirstein; Florentien Kolbig; Michèle Nebe; Marco Schulze; Wieland Kiess; Ingo Spitzbarth; Nora Klöting; Diana Le Duc; Ulrike Baschant; Antje Garten

doi:10.1093/jbmrpl/ziad016

Pten knockout in mouse preosteoblasts leads to changes in bone turnover and strength

JBMR Plus. 2024 Jan 4;8(3):ziad016. doi: 10.1093/jbmrpl/ziad016. eCollection 2024 Feb.

Authors

Affiliations

¹ Pediatric Research Center, Leipzig University, University Hospital for Children and Adolescents, Department for Child and Adolescent Medicine, 04103 Leipzig, Germany.
² Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200 Copenhagen, Denmark.
³ Saxon Incubator for Clinical Translation (SIKT), Leipzig University, 04103 Leipzig, Germany.
⁴ Faculty of Veterinary Medicine, Institute of Veterinary Pathology, Leipzig University, 04103 Leipzig, Germany.
⁵ Helmholtz Institute for Metabolic, Obesity and Vascular Research (HI-MAG) of the Helmholtz Zentrum München, Leipzig University and University Hospital Leipzig, 04103 Leipzig, Germany.
⁶ Institute of Human Genetics, Leipzig University, 04103 Leipzig, Germany.
⁷ Department of Medicine III, Technische Universität Dresden, 01309 Dresden, Germany.

Abstract

Bone development and remodeling are controlled by the phosphoinositide-3-kinase (Pi3k) signaling pathway. We investigated the effects of downregulation of phosphatase and tensin homolog (Pten), a negative regulator of Pi3k signaling, in a mouse model of Pten deficiency in preosteoblasts. We aimed to identify mechanisms that are involved in the regulation of bone turnover and are linked to bone disorders. Femora, tibiae, and bone marrow stromal cells (BMSCs) isolated from mice with a conditional deletion of Pten (Pten cKO) in Osterix/Sp7-expressing osteoprogenitor cells were compared to Cre-negative controls. Bone phenotyping was performed by μCT measurements, bone histomorphometry, quantification of bone turnover markers CTX and procollagen type 1 N propeptide (P1NP), and three-point bending test. Proliferation of BMSCs was measured by counting nuclei and Ki-67-stained cells. In vitro, osteogenic differentiation capacity was determined by ALP staining, as well as by detecting gene expression of osteogenic markers. BMSCs from Pten cKO mice were functionally different from control BMSCs. Osteogenic markers were increased in BMSCs derived from Pten cKO mice, while Pten protein expression was lower and Akt phosphorylation was increased. We detected a higher trabecular bone volume and an altered cortical bone morphology in Pten cKO bones with a progressive decrease in bone and tissue mineral density. Pten cKO bones displayed fewer osteoclasts and more osteoblasts (P = .00095) per trabecular bone surface and a higher trabecular bone formation rate. Biomechanical analysis revealed a significantly higher bone strength (P = .00012 for males) and elasticity of Pten cKO femora. On the cellular level, both proliferation and osteogenic differentiation capacity of Pten cKO BMSCs were significantly increased compared to controls. Our findings suggest that Pten knockout in osteoprogenitor cells increases bone stability and elasticity by increasing trabecular bone mass and leads to increased proliferation and osteogenic differentiation of BMSCs.

Keywords: Pten; bone marrow; osteoprogenitor; osterix; stem cells.