Open Access

Extracellular acidification stimulates OGR1 to modify osteoclast differentiation and activity through the Ca2+‑calcineurin‑NFATc1 pathway

  • Authors:
    • Feng-Bo Li
    • Su-Qing Bao
    • Xiao-Lei Sun
    • Jian-Xiong Ma
    • Xin-Long Ma
  • View Affiliations

  • Published online on: December 5, 2024     https://doi.org/10.3892/etm.2024.12778
  • Article Number: 28
  • Copyright: © Li et al. This is an open access article distributed under the terms of Creative Commons Attribution License.

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Abstract

The aim of the present study was to explore the role of ovarian cancer G protein‑coupled receptor 1 (OGR1) in osteoclast differentiation and activity induced by extracellular acid. The impact of extracellular acidification on osteoclasts was investigated. Briefly, osteoclasts were generated from RAW 264.7 cells using 100 ng/ml receptor activator of nuclear factor‑κB ligand in cell culture media at pH 6.8 or 7.4. Tartrate‑resistant acid phosphatase (TRAP) staining and the bone resorption pit assay were used to detect the effects of extracellular acid on the number and absorptive capacity of osteoclasts. Intracellular Ca2+ levels were analyzed using laser scanning confocal microscopy. Reverse transcription‑quantitative PCR was used to detect the expression levels of genes associated with osteoclast formation and bone erosion. The role of OGR1 in the acid‑stimulated formation and bone resorption of osteoclasts was also investigated. The results showed that in the pH 6.8 medium group the number of osteoclasts was 511.2±54.72 and the area of bone absorption was 4,184.88±277.14 µm2; both were significantly higher than those in the pH 7.4 medium group (all P<0.01). Inhibition of OGR1 using copper ion (Cu2+) reduced the number of osteoclasts and the area of bone resorption in the pH 6.8 medium group (all P<0.05). Furthermore, extracellular acid (pH 6.8) was able to induce a transient increase of Ca2+ levels in osteoclasts; however, inhibition of OGR1 using Cu2+ effectively attenuated the acid‑induced increase of Ca2+ in osteoclasts. In addition, the elevation in Ca2+ levels was inhibited when BAPTA, a cytoplasmic Ca2+ chelator with cellular permeability, was added to the cells; however, the extracellular Ca2+‑chelating agent ethylene glycol tetraacetic acid did not inhibit the acid‑stimulated increase in Ca2+. Treatment with the phospholipase C inhibitor U73122 also inhibited the acid‑stimulated increase of Ca2+ in osteoclasts. Furthermore, the mRNA expression levels of TRAP, matrix metalloproteinase‑9, osteoclast‑related receptor, nuclear factor‑activated T cell 1 (NFATc1), cathepsin K and integrin β3 were elevated in the pH 6.8 medium group compared with those in the pH 7.4 medium group (all P<0.05). By contrast, the inhibition of OGR1 using Cu2+ partially reduced the effects of the acidic environment on osteoclast differentiation and activity‑related gene expression (all P<0.05). In addition, the mRNA and protein expression levels of calcineurin were increased in osteoclasts in the pH 6.8 group compared with those in the pH 7.4 group (P<0.05), whereas blocking OGR1 suppressed the expression of acid‑induced calcineurin. The mRNA expression levels of NFATc1 in osteoclasts were also increased in the pH 6.8 medium group compared with those in the pH 7.4 medium group (P<0.05). By contrast, the specific calcineurin inhibitor cyclosporine A significantly inhibited the acid‑induced expression of NFATc1 in osteoclasts. In conclusion, the present study revealed that extracellular acidification may increase osteoclast differentiation and bone resorption activity. Furthermore, OGR1‑mediated Ca2+ elevation could have a crucial role in osteoclasts by regulating the Ca2+‑calcineurin‑NFATc1 signaling pathway and downstream signaling.

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February-2025
Volume 29 Issue 2

Print ISSN: 1792-0981
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Spandidos Publications style
Li F, Bao S, Sun X, Ma J and Ma X: Extracellular acidification stimulates OGR1 to modify osteoclast differentiation and activity through the Ca2+‑calcineurin‑NFATc1 pathway. Exp Ther Med 29: 28, 2025.
APA
Li, F., Bao, S., Sun, X., Ma, J., & Ma, X. (2025). Extracellular acidification stimulates OGR1 to modify osteoclast differentiation and activity through the Ca2+‑calcineurin‑NFATc1 pathway. Experimental and Therapeutic Medicine, 29, 28. https://doi.org/10.3892/etm.2024.12778
MLA
Li, F., Bao, S., Sun, X., Ma, J., Ma, X."Extracellular acidification stimulates OGR1 to modify osteoclast differentiation and activity through the Ca2+‑calcineurin‑NFATc1 pathway". Experimental and Therapeutic Medicine 29.2 (2025): 28.
Chicago
Li, F., Bao, S., Sun, X., Ma, J., Ma, X."Extracellular acidification stimulates OGR1 to modify osteoclast differentiation and activity through the Ca2+‑calcineurin‑NFATc1 pathway". Experimental and Therapeutic Medicine 29, no. 2 (2025): 28. https://doi.org/10.3892/etm.2024.12778