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ERK inhibits osteoclast differentiation in RAW 264.7 cells through the osteoprotegerin-mediated autophagy

Soo-Young Shin1, In-Soon Kang2, Chaekyun Kim1

  • 1Laboratory of Leukocyte Signaling Research, Department of Pharmacology, College of Medicine, Inha University, Incheon 22212, Republic of Korea; BK21, Program in Biomedical Science and Engineering, Inha University, Incheon 22212, Republic of Korea.

Bone
|February 13, 2025
PubMed

Insights

Extracellular signal-regulated kinase (ERK) pathway impacts osteoclast (OC) differentiation differently in various cells. In RAW 264.7 cells, ERK inhibition promotes OC differentiation by reducing osteoprotegerin and autophagy.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Bone Biology

Background:

  • Osteoclasts (OCs) are crucial for bone resorption, originating from monocytes/macrophages.
  • The extracellular signal-regulated kinase (ERK) pathway influences cell proliferation, differentiation, and survival, including OCs.
  • ERK's precise role in OC differentiation requires further elucidation due to cell-type-specific effects.

Purpose of the Study:

  • To investigate the differential effects of ERK inhibition on OC differentiation in bone marrow-derived macrophages (BMMs) and RAW 264.7 cells.
  • To elucidate the underlying molecular mechanisms by which ERK regulates OC differentiation in RAW 264.7 cells.
  • To explore the interplay between ERK, osteoprotegerin (OPG), and autophagy in OC differentiation.

Main Methods:

  • Treatment of BMMs and RAW 264.7 cells with ERK inhibitors.
  • ERK downregulation using small interfering RNA (siRNA) in RAW 264.7 cells.
  • Analysis of OC-specific markers, transcription factors, OPG expression, and autophagy-related proteins (LC3-II, p62).
  • Investigation of the Akt/mammalian target of the rapamycin (mTOR) and unc-51-like autophagy activating kinase 1 (ULK1) signaling pathways.

Main Results:

  • ERK inhibitors reduced BMM proliferation but decreased OC differentiation in BMMs while increasing it in RAW 264.7 cells.
  • ERK downregulation in RAW 264.7 cells enhanced OC differentiation and expression of key OC markers.
  • ERK inhibition in RAW 264.7 cells decreased OPG expression and autophagy (via Akt/mTOR activation and ULK1 inhibition), promoting OC formation.
  • OPG knockdown mimicked the effects of ERK inhibition on autophagy.

Conclusions:

  • ERK plays a complex, cell-dependent role in regulating OC differentiation.
  • In RAW 264.7 cells, ERK negatively regulates OC differentiation by suppressing OPG expression and autophagy.
  • Targeting the ERK pathway may offer novel therapeutic strategies for bone disorders characterized by aberrant OC activity.
Keywords:
AutophagyERKOsteoclastOsteoprotegerinRAW 264.7 cells

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