Deficiency in the phosphatase PHLPP1 suppresses osteoclast-mediated bone resorption and enhances bone formation in mice

Anna M. Mattson, Dana L. Begun, David H.H. Molstad, Margaret A. Meyer, Merry Jo Oursler, Jennifer J Westendorf, Elizabeth Bradley

Research output: Contribution to journalArticle

Abstract

Enhanced osteoclast-mediated bone resorption and diminished formation May promote bone loss. Pleckstrin homology (PH) domain and leucine-rich repeat protein phosphatase 1 (Phlpp1) regulates protein kinase C (PKC) and other proteins in the control of bone mass. Germline Phlpp1 deficiency reduces bone volume, but the mechanisms remain unknown. Here, we found that conditional Phlpp1 deletion in murine osteoclasts increases their numbers, but also enhances bone mass. Despite elevating osteoclasts, Phlpp1 deficiency did not increase serum markers of bone resorption, but elevated serum markers of bone formation. These results suggest that Phlpp1 suppresses osteoclast formation and production of paracrine factors controlling osteoblast activity. Phlpp1 deficiency elevated osteoclast numbers and size in ex vivo osteoclastogenesis assays, accompanied by enhanced expression of proto-oncogene C-Fms (C-Fms) and hyper-responsiveness to macrophage colony-stimulating factor (M-CSF) in bone marrow macrophages. Although Phlpp1 deficiency increased TRAP cell numbers, it suppressed actin-ring formation and bone resorption in these assays. We observed that Phlpp1 deficiency increases activity of PKC, a PKC isoform controlling cell polarity, and that addition of a PKC pseudosubstrate restores osteoclastogenesis and bone resorption of Phlpp1-deficient osteoclasts. Moreover, Phlpp1 deficiency increased expression of the bone-coupling factor collagen triple helix repeat-containing 1 (Cthrc1). Conditioned growth medium derived from Phlpp1-deficient osteoclasts enhanced mineralization of ex vivo osteoblast cultures, an effect that was abrogated by Cthrc1 knockdown. In summary, Phlpp1 critically regulates osteoclast numbers, and Phlpp1 deficiency enhances bone mass despite higher osteoclast numbers because it apparently disrupts PKC activity, cell polarity, and bone resorption and increases secretion of bone-forming Cthrc1.

Original languageEnglish (US)
Pages (from-to)11772-11784
Number of pages13
JournalJournal of Biological Chemistry
Volume294
Issue number31
DOIs
StatePublished - Jan 1 2019

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Protein Phosphatase 1
Osteoclasts
Bone Resorption
Phosphoric Monoester Hydrolases
Osteogenesis
Bone
Protein Kinase C
Bone and Bones
Cell Polarity
Collagen
Osteoblasts
Pleckstrin Homology Domains
leucine-rich repeat proteins
Assays
Biomarkers
Macrophage Colony-Stimulating Factor
Proto-Oncogenes
Macrophages
Conditioned Culture Medium
Cell culture

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

Cite this

Deficiency in the phosphatase PHLPP1 suppresses osteoclast-mediated bone resorption and enhances bone formation in mice. / Mattson, Anna M.; Begun, Dana L.; Molstad, David H.H.; Meyer, Margaret A.; Oursler, Merry Jo; Westendorf, Jennifer J; Bradley, Elizabeth.

In: Journal of Biological Chemistry, Vol. 294, No. 31, 01.01.2019, p. 11772-11784.

Research output: Contribution to journalArticle

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