miR-135b expression downregulates Ppm1e to activate AMPK signaling and protect osteoblastic cells from dexamethasone

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Osteoblast (bone-forming cell) dysfunction contributes to various bone diseases.
• Dexamethasone (Dex) is a glucocorticoid that can induce osteoblast apoptosis.
• AMP-activated protein kinase (AMPK) activation shows potential for protecting osteoblasts from Dex-induced damage.

Purpose of the Study:

• To investigate the role of microRNA-135b (miR-135b) in protecting osteoblasts from Dex.
• To elucidate the mechanism by which miR-135b exerts its protective effects, focusing on AMPK activation and Ppm1e regulation.

Main Methods:

• Utilized human osteoblastic cell lines (OB-6, hFOB1.19).
• Employed forced miR-135b expression and shRNA-mediated knockdown of Ppm1e.
• Assessed AMPK signaling activation, Ppm1e levels, NADPH activity, and oxidative stress markers.
• Investigated the necessity of AMPK in miR-135b-mediated protection.

Main Results:

• Forced miR-135b expression downregulated Ppm1e and activated AMPK signaling in osteoblastic cells.
• miR-135b protected osteoblastic cells from Dex-induced damage, an effect mimicked by Ppm1e knockdown.
• miR-135b-induced protection was dependent on AMPK activation and involved increased NADPH activity and reduced oxidative stress.
• Elevated miR-135b levels correlated with Ppm1e downregulation and AMPK activation in human necrotic femoral head tissues.

Conclusions:

• miR-135b protects osteoblastic cells from Dex-induced injury by downregulating Ppm1e, leading to AMPK activation.
• The miR-135b/Ppm1e/AMPK axis represents a novel therapeutic target for conditions involving osteoblast damage and glucocorticoid toxicity.