Vitamin D receptor expression in mature osteoclasts reduces bone loss due to low dietary calcium intake in male mice

Yolandi Starczak; Daniel C Reinke; Kate R Barratt; Patricia K Russell; Michelle V Clarke; Rachel A Davey; Gerald J Atkins; Paul H Anderson

doi:10.1016/j.jsbmb.2021.105857

Vitamin D receptor expression in mature osteoclasts reduces bone loss due to low dietary calcium intake in male mice

J Steroid Biochem Mol Biol. 2021 Jun:210:105857. doi: 10.1016/j.jsbmb.2021.105857. Epub 2021 Feb 26.

Authors

Yolandi Starczak¹, Daniel C Reinke², Kate R Barratt³, Patricia K Russell⁴, Michelle V Clarke⁴, Rachel A Davey⁴, Gerald J Atkins², Paul H Anderson⁵

Affiliations

¹ Clinical and Health Sciences, Health and Biomedical Innovation, University of South Australia, SA, Australia; Centre for Orthopaedic and Trauma Research, Faculty of Health Sciences, The University of Adelaide, SA, Australia.
² Centre for Orthopaedic and Trauma Research, Faculty of Health Sciences, The University of Adelaide, SA, Australia.
³ Clinical and Health Sciences, Health and Biomedical Innovation, University of South Australia, SA, Australia.
⁴ Department of Medicine, Austin Health, The University of Melbourne, Heidelberg, VIC, Australia.
⁵ Clinical and Health Sciences, Health and Biomedical Innovation, University of South Australia, SA, Australia. Electronic address: Paul.Anderson@unisa.edu.au.

PMID: 33647520
DOI: 10.1016/j.jsbmb.2021.105857

Abstract

Mature osteoclasts express the vitamin D receptor (VDR) and are able to respond to active vitamin D (1α, 25-dihydroxyvitamin D₃; 1,25(OH)₂D₃) by regulating cell maturation and activity. However, the in vivo consequences of vitamin D signalling directly within functionally mature osteoclasts is only partially understood. To investigate the in vivo role of VDR in mature osteoclasts, conditional deletion of the VDR under control of the cathepsin K promoter (Ctsk^Cre/Vdr^-/-), was assessed in 6 and 12-week-old mice, either under normal dietary conditions (NormCaP) or when fed a low calcium (0.03 %), low phosphorous (0.08 %) diet (LowCaP). Splenocytes from Ctsk^Cre/Vdr^-/- mice were co-cultured with MLO-Y4 osteocyte-like cells to assess the effect on osteoclastogenesis. Six-week-old Ctsk^Cre/Vdr^-/- mice demonstrated a 10 % decrease in vertebral bone volume (p < 0.05), which was associated with increased osteoclast size (p < 0.05) when compared to Vdr^fl/fl control mice. Control mice fed a LowCaP diet exhibited extensive trabecular bone loss associated with increased osteoclast surface, number and size (p < 0.0001). Interestingly, Ctsk^Cre/Vdr^-/- mice fed a LowCaP diet showed exacerbated loss of bone volume fraction (BV/TV%) and trabecular number (Tb.N), by a further 22 % and 21 %, respectively (p < 0.05), suggesting increased osteoclastic bone resorption activity with the loss of VDR in mature osteoclasts under these conditions. Co-culture of Ctsk^Cre/Vdr^-/- splenocytes with MLO-Y4 cells increased resulting osteoclast numbers 2.5-fold, which were greater in nuclei density and exhibited increased resorption of dentine compared to osteoclasts derived from Vdr^fl/fl splenocyte cultures. These data suggest that in addition to RANKL-mediated osteoclastogenesis, intact VDR signalling is required for the direct regulation of the differentiation and activity of osteoclasts in both in vivo and ex vivo settings.

Keywords: 1α,25-dihydroxyvitamin D(3); Bone resorption; Osteoclastogenesis; Osteoclasts; Vitamin D receptor.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
Bone and Bones / diagnostic imaging
Bone and Bones / physiopathology
Calcium / blood
Calcium, Dietary / pharmacology*
Cathepsin K / genetics
Cathepsin K / metabolism
Coculture Techniques
Male
Mice
Mice, Knockout
Mice, Transgenic
Osteoclasts / cytology
Osteoclasts / drug effects
Osteoclasts / physiology*
Osteogenesis
Osteoporosis / etiology*
Phosphorus / metabolism
Receptors, Calcitriol / genetics*
Receptors, Calcitriol / metabolism
X-Ray Microtomography

Substances

Calcium, Dietary
Receptors, Calcitriol
Vdr protein, mouse
Phosphorus
Cathepsin K
Ctsk protein, mouse
Calcium