DNA methyltransferase 3a regulates osteoclast differentiation by coupling to an S-adenosylmethionine–producing metabolic pathway

Abstract

Metabolic reprogramming occurs in response to the cellular environment to mediate differentiation, but the fundamental mechanisms linking metabolic processes to differentiation programs remain to be elucidated. During osteoclast differentiation, a shift toward more oxidative metabolic processes occurs. In this study we identified the de novo DNA methyltransferase 3a (Dnmt3a) as a transcription factor that couples these metabolic changes to osteoclast differentiation. We also found that receptor activator of nuclear factor-κB ligand (RANKL), an essential cytokine for osteoclastogenesis, induces this metabolic shift towards oxidative metabolism, which is accompanied by an increase in S-adenosylmethionine (SAM) production. We found that SAM-mediated DNA methylation by Dnmt3a regulates osteoclastogenesis via epigenetic repression of anti-osteoclastogenic genes. The importance of Dnmt3a in bone homeostasis was underscored by the observations that Dnmt3a-deficient osteoclast precursor cells do not differentiate efficiently into osteoclasts and that mice with an osteoclast-specific deficiency in Dnmt3a have elevated bone mass due to a smaller number of osteoclasts. Furthermore, inhibition of DNA methylation by theaflavin-3,3'-digallate abrogated bone loss in models of osteoporosis. Thus, this study reveals the role of epigenetic processes in the regulation of cellular metabolism and differentiation, which may provide the molecular basis for a new therapeutic strategy for a variety of bone disorders.

MYC-dependent oxidative metabolism regulates osteoclastogenesis via nuclear receptor ERRα

“…Moreover, the basal OCR was greatly increased by the ectopic expression of MYC ( Figure 3G). Consistent with previous reports (7,16), perturbation of metabolic pathways such as glutaminolysis, glycolysis, and oxidative phosphorylation using specific inhibitors severely abrogated osteoclast differentiation (Supplemental Figure 10), implicating the significance of metabolic reprogramming in osteoclastogenesis. Collectively, these results indicate that MYC is a crucial regulator of RANKL-activated mitochondrial respiration that supports an increased energy demand during osteoclast differentiation.…”

“…Taken together, these results suggest that ing the essential role of MYC in meeting energy and anabolic demands during osteoclast differentiation. In previous studies, increased oxidative phosphorylation has been partially mediated by increased mitochondrial biogenesis orchestrated by PGC1β (18) and is accompanied by an increase in S-adenosylmethionine (SAM) production (16). We have observed that the effect of MYC on oxidative phosphorylation is independent of mitochondrial biogenesis and that the overexpression of MYC is unable to regulate PGC1β expression, which suggests the uncoupling of PGC1β from oxidative phosphorylation in osteoclastogenesis.…”

“…Accordingly, metabolic genes involved in oxidative phosphorylation, which are highly induced in MYC WT OCPs upon RANKL stimulation, were suppressed in MYC ΔM OCPs ( Figure 3C). Recent studies show that a metabolic shift toward oxidative processes during osteoclast differentiation provides metabolites (15)(16)(17), although key upstream modulators that induce oxidative metabolic reprogramming in osteoclastogenesis are not yet clarified. To directly test whether MYC mediates the RANKL-induced shift toward mitochondrial respiration, we performed an extracellular flux analysis 2 days after RANKL stimulation (Figure 3, D and E, and Supplemental Figure 9).…”

“…We have shown, for the first time to our knowledge, a tight association between oxidative phosphorylation and the MYC/ERRα pathway during osteoclastogenesis. Emerging evidence has indicated that the induction of anabolic metabolic pathways by RANKL is important for osteoclastogenesis (7,(14)(15)(16)(17), but the mechanisms by which these pathways are induced and their relationship to the NFATc1 program have not been clearly identified. We determined that ERRα deficiency results not only in defective oxidative phosphorylation but also in compromised bone resorption, without affecting RANKL-induced NFATc1 expression.…”

“…Metabolic adaptation to meet increased energy demand is required to undergo osteoclast differentiation (7,(14)(15)(16)(17). Recent studies have shown that several factors such as peroxisome proliferator-activated receptor γ coactivator 1β (PGC1β), PPARγ, and estrogen receptor-related receptor α (ERRα) govern key metabolic processes by transcriptionally regulating distinct metabolic genes during osteoclast differentiation as part of bone remodeling (18)(19)(20)(21).…”