Glucose-dependent regulation of osteoclast H+-ATPase expression:: Potential role of p38 MAP-kinase

Bone resorption is glucose concentration dependent. Mechanisms regulating glucose-dependent increases in bone resorption have not been identified. Glucose activates p38 MAP-kinase in other cells and since MAP kinases activate transcription factors, we hypothesized that glucose-stimulated bone resorption may be modulated by increased expression of the vacuolar H+-ATPase. Glucose activates osteoclast p38 MAP-kinase in a time and concentration-dependent manner as determined by Western analysis with phospho-specific p38 antibody while total p38 levels are unchanged. The K-0.5 for glucose-dependent activation of p38 MAP-kinase is similar to7 mM, activation is maximal at 30 min and is elevated but returning to basal levels by 60 min. The concentration-dependent increase in H+-ATPase expression was confirmed by Northern analysis. The specific inhibitor of p38 MAP-kinase, SB203580, inhibited glucose transport in osteoclasts, as well as glucose concentration-dependent increases in bone resorption and expression of H+-ATPase A and B subunits. Glucose had no effect on calmodulin expression levels that are regulated in response to other environmental changes. The glucose-stimulated increase in H--ATPase mRNA expression is a specific response to glucose since glucose has little effect on G3PDH mRNA levels. We conclude that glucose regulates osteoclast H--ATPase expression by a mechanism likely to involve p38 MAP-kinase.