α2-HS-glycoprotein: Expression in chondrocytes and augmentation of alkaline phosphatase and phospholipase A2 activity

F. Yang, Z. Schwartz, L. D. Swain, C. C. Lee, B. H. Bowman, B. D. Boyan

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Abstract

The α2-HS-glycoprotein is a plasma protein synthesized in liver and enriched in bone. The concentration of α2-HS-glycoprotein dynamically changes in various physiological conditions and is highest in bone during growth, suggesting that it is involved in regulation of endochondral ossification. Northern blot analysis demonstrated that mRNA transcripts from growth zone and resting zone costochondral chondrocyte cultures hybridized with α2-HS-glycoprotein cDNA. However, a difference of mRNA transcript size was observed, with chondrocyte mRNA transcripts being 2.2 kb, while mRNA isolated from liver was 1.6 kb. Presence of α2-HS-glycoprotein in cartilage cells was found by immuno-histochemical staining of human fetal epiphyses using anti-human α2-HS-glycoprotein antibody. To understand the role of α2-HS-glycoprotein in cartilage growth, the effects of exogenous α2-HS-glycoprotein were correlated with alkaline phosphatase (ALPase) and phospholipase A2 (PA2) activity in the chondrocyte cultures. Alkaline phosphatase specific activity was stimulated by α2-HS-glycoprotein at concentrations between 0.25 and 1.25μ/mL in the growth zone and resting zone cultures 2.7 and 2.0-fold, respectively. Matrix vesicle PA2 activity was increased only in the growth zone chondrocyte cultures. These results suggested that α2-HS-glycoprotein may contribute to the regulation of the expression of the chondrocyte phenotype. Steady state mRNA levels of ALPase were analyzed in chondrocytes after additions of α2-HS-glycoprotein. The ALPase mRNA levels remained stationary during the stimulation of enzymatic activity, indicating that the effect of α2-HS-glycoprotein upon alkaline phosphatase activity is not at the transcriptional level.

Original languageEnglish (US)
Pages (from-to)7-15
Number of pages9
JournalBone
Volume12
Issue number1
DOIs
StatePublished - 1991

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Keywords

  • Alkaline phosphatase
  • Cartilage
  • Chondrocyte
  • Immunohistochemistry
  • Phospholipase A
  • in vitro
  • α-HS-glycoprotein mRNA

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Physiology
  • Histology

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