Iron excess limits HHIPL-2 gene expression and decreases osteoblastic activity in human MG-63 cells

Osteoporos Int. 2012 Oct;23(10):2435-45. doi: 10.1007/s00198-011-1871-z. Epub 2012 Jan 12.

Abstract

In order to understand mechanisms involved in osteoporosis observed during iron overload diseases, we analyzed the impact of iron on a human osteoblast-like cell line. Iron exposure decreases osteoblast phenotype. HHIPL-2 is an iron-modulated gene which could contribute to these alterations. Our results suggest osteoblast impairment in iron-related osteoporosis.

Introduction: Iron overload may cause osteoporosis. An iron-related decrease in osteoblast activity has been suggested.

Methods: We investigated the effect of iron exposure on human osteoblast cells (MG-63) by analyzing the impact of ferric ammonium citrate (FAC) and iron citrate (FeCi) on the expression of genes involved in iron metabolism or associated with osteoblast phenotype. A transcriptomic analysis was performed to identify iron-modulated genes.

Results: FAC and FeCi exposure modulated cellular iron status with a decrease in TFRC mRNA level and an increase in intracellular ferritin level. FAC increased ROS level and caspase 3 activity. Ferroportin, HFE and TFR2 mRNAs were expressed in MG-63 cells under basal conditions. The level of ferroportin mRNA was increased by iron, whereas HFE mRNA level was decreased. The level of mRNA alpha 1 collagen type I chain, osteocalcin and the transcriptional factor RUNX2 were decreased by iron. Transcriptomic analysis revealed that the mRNA level of HedgeHog Interacting Protein Like-2 (HHIPL-2) gene, encoding an inhibitor of the hedgehog signaling pathway, was decreased in the presence of FAC. Specific inhibition of HHIPL-2 expression decreased osteoblast marker mRNA levels. Purmorphamine, hedgehog pathway activator, increased the mRNA level of GLI1, a target gene for the hedgehog pathway, and decreased osteoblast marker levels. GLI1 mRNA level was increased under iron exposure.

Conclusion: We showed that in human MG-63 cells, iron exposure impacts iron metabolism and osteoblast gene expression. HHIPL-2 gene expression modulation may contribute to these alterations. Our results support a role of osteoblast impairment in iron-related osteoporosis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cation Transport Proteins / biosynthesis
  • Cation Transport Proteins / genetics
  • Cells, Cultured
  • Citric Acid
  • Ferric Compounds / pharmacology
  • Ferrous Compounds / pharmacology
  • Gene Expression Regulation / drug effects
  • Hemochromatosis Protein
  • Histocompatibility Antigens Class I / biosynthesis
  • Histocompatibility Antigens Class I / genetics
  • Humans
  • Iron Overload / genetics
  • Iron Overload / metabolism*
  • Membrane Proteins / biosynthesis
  • Membrane Proteins / genetics
  • Osteoblasts / drug effects
  • Osteoblasts / metabolism*
  • Oxidative Stress / drug effects
  • Phenotype
  • Quaternary Ammonium Compounds / pharmacology

Substances

  • Cation Transport Proteins
  • Ferric Compounds
  • Ferrous Compounds
  • HFE protein, human
  • Hemochromatosis Protein
  • Histocompatibility Antigens Class I
  • Membrane Proteins
  • Quaternary Ammonium Compounds
  • metal transporting protein 1
  • Citric Acid
  • ferrous citrate
  • ferric ammonium citrate