Osteoclast Precursors Display Dynamic Metabolic Shifts toward Accelerated Glucose Metabolism at an Early Stage of RANKL-Stimulated Osteoclast Differentiation

Abstract

Mature osteoclasts have an increased citric acid cycle and mitochondrial respiration to generate high ATP production and ultimately lead to bone resorption. However, changes in metabolic pathways during osteoclast differentiation have not been fully illustrated. We report that glycolysis and oxidative phosphorylation characterized by glucose and oxygen consumption as well as lactate production were increased during receptor activator of nuclear factor-ĸB ligand (RANKL)-induced osteoclastogenesis from RAW264.7 and bone marrow-derived macrophage cells. Cell proliferation and differentiation varied according to glucose concentrations (0 to 100 mM). Maximal cell growth occurred at 20 mM glucose concentration and differentiation occurred at 5 mM concentration. Despite the similar growth rates exhibited when cultured cells were exposed to either 5 mM or 40 mM glucose, their differentiation was markedly decreased in high glucose concentrations. This finding suggests the possibility that osteoclastogenesis could be regulated by changes in metabolic substrate concentrations. To further address the effect of metabolic shift on osteoclastogenesis, we exposed cultured cells to pyruvate, which is capable of promoting mitochondrial respiration. Treatment of pyruvate synergistically increased osteoclastogenesis through the activation of RANKL-stimulated signals (ERK and JNK). We also found that osteoclastogenesis was retarded by blocking ATP production with either the inhibitors of mitochondrial complexes, such as rotenone and antimycin A, or the inhibitor of ATP synthase, oligomycin. Taken together, these results indicate that glucose metabolism during osteoclast differentiation is accelerated and that a metabolic shift towards mitochondrial respiration allows high ATP production and induces enhanced osteoclast differentiation.

Delayed bone regeneration and low bone mass in a rat model of insulin-resistant type 2 diabetes mellitus is due to impaired osteoblast function

“…We did not observe altered osteoclast functions ex vivo, in contrast to other reports, which suggested that a diabetic microenvironment tends to inhibit osteoclast differentiation and function (30,16,29,4,12). However, none of these studies used an in vivo model of rats with type 2 diabetes mellitus.…”

AMP-activated protein kinase pathway and bone metabolism

“…It could also be an indication for the skeleton to instigate the appropriate bone remodeling response associated either with augmentation of energy-producing processes or decreased energycosting processes. Changes in metabolic pathways indeed occur during bone cell differentiation and function to allow high ATP generation for bone matrix production and mineralization, as well as for bone resorption (Komarova et al 2000, Kim et al 2007. The potential role of AMPK in the regulation of bone homeostasis is shown in Fig.…”

Cytosolic proteome profiling of monocytes for male osteoporosis

“…For example, glycolysis, a metabolic pathway, occurs in the monocytic cytosol, giving rise to adenosine triphosphate (ATP) as one of the main energy sources for cellular differentiation and migration [15]. Cytosolic proteins for biosynthetic substrates and metabolic enzymes for energy generation are increasingly expressed during the receptor activator of nuclear factor kappa-B ligand (RANKL)-stimulated osteoclastogenesis [16]. Importantly, proteins in monocytes may have specific functional roles depending on distinct subcellular localizations.…”