A new superoxide-generating oxidase in murine osteoclasts

Area of Science:

• Biochemistry
• Cell Biology
• Bone Physiology

Background:

• Superoxide production by osteoclasts is essential for bone resorption.
• NADPH oxidase is implicated in osteoclast superoxide generation, with p91 as a key subunit.
• Osteoclasts from p91 knockout mice exhibit normal superoxide production, suggesting an alternative oxidase.

Purpose of the Study:

• To identify alternative NADPH oxidase subunits in osteoclasts.
• To investigate the role of Nox 4 in osteoclastic superoxide production and bone resorption.
• To explain the functional osteoclast activity in the absence of p91.

Main Methods:

• Cloning and characterization of the Nox 4 NADPH oxidase subunit.
• Assessment of Nox 4 expression and activity in osteoclasts.
• Inhibition of Nox 4 using antisense oligonucleotides.
• Measurement of superoxide production and resorption pit formation.

Main Results:

• A novel NADPH oxidase subunit, Nox 4, was cloned and found to share 58% amino acid similarity with p91.
• Nox 4 is expressed and active in osteoclasts.
• Antisense oligonucleotides targeting Nox 4 significantly reduced osteoclastic superoxide generation and resorption.
• Nox 4-containing oxidase complexes were functional in p91 knockout osteoclasts, maintaining normal resorptive activity.

Conclusions:

• Nox 4 is a functional NADPH oxidase subunit in osteoclasts.
• Nox 4 plays a critical role in osteoclastic bone resorption.
• Nox 4 activity explains the sustained superoxide production and bone resorption in p91-deficient osteoclasts.