Ablation of Enpp6 Results in Transient Bone Hypomineralization

Scott Dillon, Karla Suchacki, Shun Neng Hsu, Louise A. Stephen, Rongling Wang, William P. Cawthorn, Alan J. Stewart, Fabio Nudelman, Nicholas M. Morton, Colin Farquharson

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)

Abstract

Biomineralization is a fundamental process key to the development of the skeleton. The phosphatase orphan phosphatase 1 (PHOSPHO1), which likely functions within extracellular matrix vesicles, has emerged as a critical regulator of biomineralization. However, the biochemical pathways that generate intravesicular PHOSPHO1 substrates are currently unknown. We hypothesized that the enzyme ectonucleotide pyrophosphatase/phosphodiesterase 6 (ENPP6) is an upstream source of the PHOSPHO1 substrate. To test this, we characterized skeletal phenotypes of mice homozygous for a targeted deletion of Enpp6 (Enpp6−/−). Micro-computed tomography of the trabecular compartment revealed transient hypomineralization in Enpp6−/− tibias (p < 0.05) that normalized by 12 weeks of age. Whole-bone cortical analysis also revealed significantly hypomineralized proximal bone in 4- but not 12-week-old Enpp6−/− mice (p < 0.05) compared with WT animals. Back-scattered SEM revealed a failure in 4-week-old trabecular bone of mineralization foci to propagate. Static histomorphometry revealed increased osteoid volume (p > 0.01) and osteoid surface (p < 0.05), which recovered by 12 weeks but was not accompanied by changes in osteoblast or osteoclast number. This study is the first to characterize the skeletal phenotype of Enpp6−/− mice, revealing transient hypomineralization in young animals compared with WT controls. These data suggest that ENPP6 is important for bone mineralization and may function upstream of PHOSPHO1 as a novel means of generating its substrates inside matrix vesicles. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.
Original languageEnglish
Article numbere10439
JournalJBMR Plus
Volume5
Issue number2
DOIs
Publication statusPrint publication - Feb 2021
Externally publishedYes

Keywords

  • ECTONUCLEOTIDE PYROPHOSPHATASE/PHOSPHODIESTERASE 6
  • MATRIX MINERALIZATION
  • MATRIX VESICLE
  • ORPHAN PHOSPHATASE 1
  • OSTEOBLAST

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