Pleckstrin homology (PH) domain and Leucine Rich Repeat Phosphatase 1 (Phlpp1) Suppresses Parathyroid Hormone Receptor 1 (Pth1r) Expression and Signaling During Bone Growth

Abstract

Endochondral ossification is tightly controlled by a coordinated network of signaling cascades including parathyroid hormone (PTH). Pleckstrin homology (PH) domain and leucine rich repeat phosphatase 1 (Phlpp1) affects endochondral ossification by suppressing chondrocyte proliferation in the growth plate, longitudinal bone growth, and bone mineralization. As such, Phlpp1−/− mice have shorter long bones, thicker growth plates, and proportionally larger growth plate proliferative zones. The goal of this study was to determine how Phlpp1 deficiency affects PTH signaling during bone growth. Transcriptomic analysis revealed greater PTH receptor 1 (Pth1r) expression and enrichment of histone 3 lysine 27 acetylation (H3K27ac) at the Pth1r promoter in Phlpp1‐deficient chondrocytes. PTH (1‐34) enhanced and PTH (7‐34) attenuated cell proliferation, cAMP signaling, cAMP response element‐binding protein (CREB) phosphorylation, and cell metabolic activity in Phlpp1‐inhibited chondrocytes. To understand the role of Pth1r action in the endochondral phenotypes of Phlpp1‐deficient mice, Phlpp1−/− mice were injected with Pth1r ligand PTH (7‐34) daily for the first 4 weeks of life. PTH (7‐34) reversed the abnormal growth plate and long‐bone growth phenotypes of Phlpp1−/− mice but did not rescue deficits in bone mineral density or trabecular number. These results show that elevated Pth1r expression and signaling contributes to increased proliferation in Phlpp1−/− chondrocytes and shorter bones in Phlpp1‐deficient mice. Our data reveal a novel molecular relationship between Phlpp1 and Pth1r in chondrocytes during growth plate development and longitudinal bone growth. © 2021 American Society for Bone and Mineral Research (ASBMR).

Phlpp1 Expression in Osteoblasts Plays a Modest Role in Bone Homeostasis

“…We first assessed expression of PHLPP1 within Phlpp1 cKO Col1a1 mice compared with control littermates via immunohistochemistry (IHC). We confirmed PHLPP1 expression by growth plate chondrocytes as shown by prior reports ( 18 , 29 ) but did not observe loss of PHLPP1 levels within the growth plate of Phlpp1 cKO Col1a1 mice (Fig. 3 ).…”

“…For instance, Phlpp1 inhibits the systemic actions of insulin and reduces survival of β cells within the pancreas, which could indirectly affect skeletal development and degeneration. (30)(31)(32) Prior work also supports that Phlpp1 ablation limits chondrocyte proliferation and endochondral ossification (18,29) but limits articular cartilage and intervertebral disc degeneration. (33,34) Likewise, Phlpp1 deficiency promotes inflammatory responses of immune cells by enhancing STAT1-dependent signaling.…”

Pleckstrin homology (PH) domain and leucine rich repeat phosphatase 1 (Phlpp1) suppresses parathyroid hormone receptor 1 (Pth1r) expression and signaling during bone growth

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A reader of the Journal of Bone and Mineral Research (JBMR ® ) has informed the authors that in the article by Weaver et al, (1) the concentration of PTH(7-34) used in vivo was incorrectly stated in the figure legends. The errors are in legends to Figures 3-5, as well as Supplemental Figures 2, 5, and 6.

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