In vivo mechanical loading modulates insulin-like growth factor binding protein-2 gene expression in rat osteocytes

Calcif Tissue Int. 2007 Feb;80(2):137-43. doi: 10.1007/s00223-006-0077-4. Epub 2007 Feb 3.

Abstract

Mechanical stimulation is essential for maintaining skeletal integrity. Mechanosensitive osteocytes are important during the osteogenic response. The growth hormone-insulin-like growth factor (GH-IGF) axis plays a key role during regulation of bone formation and remodeling. Insulin-like growth factor binding proteins (IGFBPs) are able to modulate IGF activity. The aim of this study was to characterize the role of IGFBP-2 in the translation of mechanical stimuli into bone formation locally in rat tibiae. Female Wistar rats were assigned to three groups (n = 5): load, sham, and control. The four-point bending model was used to induce a single period of mechanical loading on the tibial shaft. The effect on IGFBP-2 mRNA expression 6 hours after stimulation was determined with nonradioactive in situ hybridization on decalcified tibial sections. Endogenous IGFBP-2 mRNA was expressed in trabecular and cortical osteoblasts, some trabecular and subendocortical osteocytes, intracortical endothelial cells of blood vessels, and periosteum. Megakaryocytes, macrophages, and myeloid cells also expressed IGFBP-2 mRNA. Loading and sham loading did not affect IGFBP-2 mRNA expression in osteoblasts, bone marrow cells, and chondrocytes. An increase of IGFBP-2 mRNA-positive osteocytes was shown in loaded (1.68-fold) and sham-loaded (1.35-fold) endocortical tibial shaft. In conclusion, 6 hours after a single loading session, the number of IGFBP-2 mRNA-expressing osteocytes at the endosteal side of the shaft and inner lamellae was increased in squeezed and bended tibiae. Mechanical stimulation modulates IGFBP-2 mRNA expression in endocortical osteocytes. We suggest that IGFBP-2 plays a role in the lamellar bone formation process.

MeSH terms

  • Animals
  • Bone Marrow Cells / metabolism
  • Chondrocytes / metabolism
  • Female
  • Gene Expression Regulation*
  • Insulin-Like Growth Factor Binding Protein 2 / genetics*
  • Insulin-Like Growth Factor Binding Protein 2 / metabolism
  • Osteocytes / metabolism*
  • Osteogenesis / genetics
  • RNA, Messenger / metabolism
  • Rats
  • Rats, Wistar
  • Stress, Mechanical
  • Tibia / metabolism
  • Tibia / physiology
  • Weight-Bearing / physiology*

Substances

  • Insulin-Like Growth Factor Binding Protein 2
  • RNA, Messenger