Caspase-2 modulates osteoclastogenesis through down-regulating oxidative stress

Area of Science:

• Cell Biology
• Bone Biology
• Biochemistry

Background:

• Caspase-2 (Casp-2) deficiency in mice leads to osteopenia and elevated osteoclast numbers.
• Osteoclastogenesis, the process of osteoclast formation, is crucial for bone remodeling.
• Oxidative stress, particularly mitochondrial reactive oxygen species (ROS), impacts late-stage osteoclast differentiation.

Purpose of the Study:

• To investigate the role of Caspase-2 (Casp-2) in osteoclast differentiation and its regulation of oxidative stress.
• To determine the effect of Casp-2 loss on macrophage-to-osteoclast differentiation and osteoclast function.

Main Methods:

• siRNA-mediated knockdown of Casp-2 in osteoclast precursors.
• Osteoclast differentiation assays using bone marrow macrophage (BMM) precursors from Casp2(-/-) mice.
• Measurement of tartrate-resistant acid phosphatase (TRAP) activity, osteoclast size, and nuclearity.
• Analysis of total and mitochondrial ROS levels, and expression of antioxidant enzymes (catalase, SOD2) and transcription factors (FoxO3a).

Main Results:

• Casp-2 protein levels decrease during macrophage differentiation into osteoclasts.
• Casp-2 knockdown or deficiency significantly increases osteoclast numbers, size, and TRAP activity.
• Loss of Casp-2 enhances precursor fusion and NFATc1 auto-amplification during later stages of differentiation.
• Casp2(-/-) BMM precursors exhibit elevated total and mitochondrial ROS, with reduced FoxO3a and antioxidant enzyme expression.

Conclusions:

• Caspase-2 (Casp-2) plays a novel inhibitory role in osteoclast differentiation.
• The loss of Casp-2 leads to increased osteoclastogenesis, mediated by elevated oxidative stress, particularly mitochondrial ROS.
• Casp-2 acts as a modulator of ROS production and osteoclast differentiation, impacting bone homeostasis.