Acidic pH environments increase the expression of cathepsin B in osteoblasts: The significance of ER stress in bone physiology

Abstract

Hypoxia, inflammation, and acidity occur after bone fracture. To simplify the fracture model, we tested the effects of acidity in osteoblasts. We tested three osteoblast cell lines, MG63, MC3T3E1, and HOS cells, with MG63 cells showing much higher sensitivity to acidic pH. In physiologically acidic surroundings, pH 7.2, the endoplasmic reticulum stress response was measured through the expression of unfolded protein response proteins. Acidic surroundings time-dependently increased IL-6 secretion. Cathepsin B, a marker of the inflammation and angiogenic processes that occur after bone fracture, also increased. Thus, acidity can cause ER stress, increase IL-6, and increases cathepsin B expression in osteoblasts.

Keywords::

• Bone fracture
• osteoblasts
• acidic pH
• cathepsin B
• IL-6

Acknowledgments

This work was supported by a research grant from the Korea Research Foundation (2005-015-E00210; 2007-314-C00234).

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.