Respiratory pathology in the Optn^-/- mouse model of Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis (ALS) is a devastating neurodegenerative disorder that results in death due to respiratory failure. Many genetic defects are associated with ALS; one such defect is a mutation in the gene encoding optineurin (OPTN). Using an optineurin null mouse (Optn^-/-), we sought to characterize the impact of optineurin deficiency on respiratory neurodegeneration. Respiratory function was assessed at 6 and 12 mo of age using whole body plethysmography at baseline during normoxia (FiO₂: 0.21; N₂ balance) and during a respiratory challenge with hypoxia and hypercapnia (FiCO₂: 0.07, FiO₂: 0.10; N₂ balance). Histological analyses to assess motor neuron viability and respiratory nerve integrity were performed in the medulla, cervical spinal cord, hypoglossal nerve, and phrenic nerve. Minute ventilation, peak inspiratory flow, and peak expiratory flow are significantly reduced during a respiratory challenge in 6 mo Optn^-/-mice. By 12 mo, tidal volume is also significantly reduced in Optn^-/- mice. Furthermore, 12mo Optn^-/- mice exhibit hypoglossal motor neuron loss, phrenic and hypoglossal dysmyelination, and accumulated mitochondria in the hypoglossal nerve axons. Overall, these data indicate that Optn^-/- mice display neurodegenerative respiratory dysfunction and are a useful model to study the impact of novel therapies on respiratory function for optineurin-deficient ALS patients.