Tissue hyperoxygenation promotes oxidative metabolism in motor unit

Area of Science:

• Physiology
• Neuroscience
• Molecular Biology

Background:

• Mutant hemoglobin (Hb) variants with lowered O2 affinity can increase oxygen availability in peripheral tissues.
• Understanding the long-term effects of altered oxygen transport on the neuromuscular system is crucial.

Purpose of the Study:

• To investigate the chronic in vivo impact of low-affinity Hb variants on the neuromuscular system using a mouse model.
• To assess adaptations in energy metabolism within the neuron-muscle motor unit.

Main Methods:

• Utilized a mouse model with two low-affinity Hb variants (Titusville and Presbyterian).
• Evaluated voluntary running ability and analyzed muscle fiber type and mitochondrial enzyme activity (succinate dehydrogenase - SDH).
• Examined mitochondrial oxidative enzyme activity and electron microscopic (EM) density in spinal ventral horn motoneurons.

Main Results:

• Mutant mice exhibited significantly increased voluntary running ability compared to wild-type littermates.
• Tibialis anterior (TA) muscles showed a shift from glycolytic to oxidative fibers with upregulated SDH activity.
• Spinal motoneurons innervating TA muscles displayed heightened mitochondrial oxidative enzyme activity and increased EM mitochondrial density.

Conclusions:

• Low oxygen affinity hemoglobin adaptation leads to enhanced energy metabolism in the neuron-muscle motor unit.
• Increased mitochondrial activity in both muscle and motoneurons promotes overall motor unit function.
• Tissue hyperoxygenation due to low O2 affinity Hb variants drives adaptive changes in the neuromuscular system.