Alendronate inhibits VEGF expression in growth plate chondrocytes by acting on the mevalonate pathway

Abstract

Bisphosphonates decrease chondrocyte turnover at the growth plate and impact bone growth. Likewise vascular endothelial growth factor (VEGF) plays an important role in endochondral bone elongation by influencing chondrocyte turnover at the growth plate. To investigate whether the action of bisphosphonate on the growth plate works through VEGF, VEGF protein expression and isoform transcription in endochondral chondrocytes isolated from growing mice and treated with a clinically used bisphosphonate, alendronate, were assessed. Alendronate at 10microM and 100microM concentrations decreased secreted VEGF protein expression but not cell associated protein. Bisphosphonates are known to inhibit the mevalonate intracellular signaling pathway used by VEGF. Addition of the mevalonate pathway intermediates farnesol (FOH) and geranylgeraniol (GGOH) interacted with the low concentration of alendronate to further decrease secreted VEGF protein whereas FOH partially restored VEGF protein secretion when combined with the high alendronate. Similar to the protein data, the addition of alendronate decreased VEGF mRNA isoforms. VEGF mRNA levels were rescued by the GGOH mevalonate pathway intermediate at the low alendronate dose whereas neither intermediate consistently restored the VEGF mRNA levels at the high alendronate dose. Thus, the bisphophonate alendronate impairs growth plate chondrocyte turnover by down-regulating the secreted forms of VEGF mRNA and protein by inhibiting the mevalonate pathway.

Keywords: VEGF; bisphosphonate.; chondrocyte.

Fig. (1)

VEGF transcript isoform changes in endochondral chondrocytes treated with 10 µM (A) or 100 µM (B) alendronate for 24 hours. VEGF n-fold transcription changes for each isoform were calibrated relative to ITS +IGF-I control. Gray bars are ITS+IGF-I control, red bars are alendronate treated cells, green bars are alendronate plus 10µM FOH, and blue bars are alendronate plus 10µM GGOH. All values are expressed as least square means ± SEM. Within an individual VEGF isoform, bars labeled with different letters are significantly different from one another (p < 0.01).