Dataset Information

Suppression of AMP-activated protein kinase reverses osteoprotegerin-induced inhibition of osteoclast differentiation by reducing autophagy.

ABSTRACT:

Objectives

Osteoclasts (OC) are unique terminally differentiated cells whose primary function is bone resorption. We previously showed that osteoprotegerin (OPG) inhibits OC differentiation in vitro by enhancing autophagy via the adenosine monophosphate-activated protein kinase (AMPK)/mTOR/p70S6K signalling pathway in vitro. Here, we aimed to elucidate the mechanism of AMPK mediated autophagy to regulate OPG-mediated inhibition of OC differentiation and identify potential therapeutic targets associated with bone loss.

Materials and methods

We used the AMPK activator AICAR to determine the relationship between AMPK activation and OC differentiation, and studied the role of AMPK-mediated autophagy in OPG-mediated inhibition of OC differentiation by using autophagy inhibitors or AMPK knockdown.

Results

AMP-activated protein kinase activation caused LC3II accumulation and weakened OC differentiation activity. In contrast, inactivation of autophagy by 3-methyladenine or Bafilomycin A1 could attenuate OPG-mediated inhibition of OC differentiation via the AMPK/mTOR/p70S6K signalling pathway. Furthermore, the AMPK inhibitor compound C and knockdown of AMPK impaired OPG-mediated inhibition of OC differentiation by inducing autophagy.

Conclusions

These results demonstrated that the AMPK signalling pathway functions as a critical regulator in the OPG-mediated inhibition of OC differentiation, by inducing autophagy. Our results provide a basis for future bone-related studies on the AMPK signalling pathway.

SUBMITTER: Tong X

PROVIDER: S-EPMC6985670 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:AIMS:The abundance of beta 3-adrenergic receptors (?3-ARs) is upregulated in diseased human myocardium. We previously showed that cardiac-specific expression of ?3-AR inhibits the hypertrophic response to neurohormonal stimulation. Here, we further analysed signalling pathways involved in the anti-hypertrophic effect of ?3-AR. METHODS AND RESULTS:In vitro hypertrophic responses to phenylephrine (PE) were analysed in neonatal rat ventricular myocytes (NRVM) infected with a recombinant adenovirus expressing the human ?3-AR (AdVh?3). We confirmed results in mice with cardiomyocyte-specific moderate expression of human ?3-AR (?3-TG) and wild-type (WT) littermates submitted to thoracic transverse aortic constriction (TAC) for 9 weeks. We observed a colocalization of ?3-AR with the AMP-activated protein kinase (AMPK) both in neonatal rat and in adult mouse cardiomyocytes. Treatment of NRVM with PE induced hypertrophy and a decrease in phosphorylation of Thr172-AMPK (/2, P = 0.0487) and phosphorylation of Ser79-acetyl-CoA carboxylase (ACC) (/2.6, P = 0.0317), inducing an increase in phosphorylated Ser235/236 S6 protein (×2.5, P = 0.0367) known to be involved in protein synthesis. These effects were reproduced by TAC in WT mice but restored to basal levels in ?3-AR expressing cells/mice. siRNA targeting of AMPK partly abrogated the anti-hypertrophic effect of ?3-AR in response to PE in NRVM. Concomitant with hypertrophy, autophagy was decreased by PE, as measured by microtubule-associated protein 1 light chain 3 (LC3)-II/LC3-I ratio (/2.6, P = 0.0010) and p62 abundance (×3, P = 0.0016) in NRVM or by TAC in WT mice (LC3-II/LC3-I ratio: /5.4, P = 0.0159), but preserved in human ?3-AR expressing cells and mice, together with reduced hypertrophy. CONCLUSIONS:Cardiac-specific moderate expression of ?3-AR inhibits the hypertrophic response in part through AMPK activation followed by inhibition of protein synthesis and preservation of autophagy. Activation of the cardiac ?3-AR pathway may provide future therapeutic avenues for the modulation of hypertrophic remodelling.