Mechanisms of mitochondrial reactive oxygen species action in bone mesenchymal cells

Area of Science:

• Biochemistry
• Cell Biology
• Gerontology

Background:

• Aging-associated bone loss is linked to mitochondrial reactive oxygen species (ROS), reduced NAD+, and cellular senescence.
• The precise in vivo mechanisms by which ROS contribute to bone loss remain incompletely understood.

Purpose of the Study:

• To investigate the role of mitochondrial ROS in bone aging by genetically deleting the mitochondrial antioxidant enzyme Sod2 in osteoblast lineage cells.
• To elucidate the impact of ROS on cellular senescence, NAD+ levels, and bone metabolism.

Main Methods:

• Generation of Sod2 conditional knockout mice (Sod2^ΔOsx1) in osteoblast lineage cells.
• Assessment of bone mass, mitochondrial function, NAD+ levels, and cellular senescence markers.
• Single-cell RNA-sequencing analysis of bone mesenchymal cells to identify affected signaling pathways.

Main Results:

• Sod2^ΔOsx1 mice exhibited low bone mass, impaired mitochondrial respiration, and reduced NAD+ levels.
• NAD+ precursor administration improved mitochondrial function in vitro but did not rescue bone mass in vivo.
• ROS did not significantly affect senescence markers but disrupted parathyroid hormone signaling, iron metabolism, and proteostasis in bone mesenchymal cells.

Conclusions:

• Mitochondrial ROS contribute to age-related bone loss through mechanisms beyond cellular senescence, including disruption of key metabolic and signaling pathways.
• Combined therapeutic strategies targeting mitochondrial ROS, senescent cells, and NAD+ levels may be effective in combating osteoporosis.