Systemic Inflammation Affects Human Osteocyte-Specific Protein and Cytokine Expression

Calcif Tissue Int. 2016 Jun;98(6):596-608. doi: 10.1007/s00223-016-0116-8. Epub 2016 Feb 18.

Abstract

Bone remodeling can be disturbed in active rheumatoid arthritis (RA), possibly as a result of elevated levels of circulating inflammatory cytokines. Osteocyte-specific proteins and cytokines play a vital role in bone remodeling by orchestrating bone formation and/or bone resorption. Therefore, we aimed to investigate the effect of RA-serum or inflammatory cytokines on expression of human osteocyte-specific proteins and cytokines. Human trabecular bone chips were cultured with RA-serum or inflammatory cytokines for 7-days. Live-dead staining was performed to assess cell viability. Gene expression of osteocyte-specific proteins and cytokines was analyzed by qPCR. Immuno-staining was performed for osteocyte-specific markers. Approximately 60 % of the osteocytes on the bone chips were alive at day-7. Cells in or on the bone chips did express the gene for osteocyte markers SOST, FGF23, DMP1, and MEPE, and the cytokines IL-1β, IL-6, and TNFα at day 0 and 7. Active RA-serum treatment enhanced IL-1β, TNFα, SOST, and DKK1 gene expression. IL-1β treatment enhanced IL-1β, TNFα, IL-6, IL-8, FGF23, and SOST gene expression. TNFα treatment enhanced IL-1β, TNFα, IL-6, IL-8, and FGF23 gene expression. IL-8 treatment enhanced TNFα, IL-8, and FGF23 gene expression. A combination of IL-1β, IL-6, and TNFα treatment synergistically upregulated IL-1β, IL-6, and IL-8 gene expression, as well as enhanced TNFα, OPG, SOST, and FGF23, and inhibited DKK1 gene expression. In conclusion, gene expression of human osteocyte-specific proteins and cytokines was affected by RA-serum, and exogenous recombinant cytokines treatment suggesting that osteocytes could provide a new target to prevent systemic inflammation-induced bone loss in RA.

Keywords: Bone loss; Chemokine; Cytokine; Inflammation; Osteocyte signaling; Rheumatoid arthritis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Arthritis, Rheumatoid / metabolism*
  • Cells, Cultured
  • Cytokines / metabolism*
  • Female
  • Gene Expression
  • Humans
  • Immunohistochemistry
  • Inflammation / metabolism*
  • Male
  • Middle Aged
  • Osteocytes / metabolism*
  • Real-Time Polymerase Chain Reaction

Substances

  • Cytokines