Mouse model of Leigh Syndrome reveals swallow-breathing discoordination rescued by chronic hypoxia
Authors: Huff Alyssa , Amarante Marlusa , Oliveira Luiz , Ramirez Jan Marino , Kalume Franck 
Published: May 2023

Leigh Syndrome is a severe neurometabolic disorder and the most common form of mitochondrial disorder in the pediatric population. It has been linked to loss of function mutations in Ndufs4, the gene that codes for a subunit of the mitochondrial complex I. First signs of early-onset Leigh Syndrome (LS) include difficulty swallowing (dysphagia), suckling and feeding. These symptoms result in an inability to grow and gain weight, leading to a failure to thrive. Mice lacking Ndufs4 globally, constitutes as an excellent model of LS, mimicking several core symptoms of the disease in humans including seizures, ataxia, hypotonia, rigidity, weight loss, and failure to thrive. In our previous work, we demonstrated that excitatory and inhibitory neurons drive distinct phenotypes in the mouse model. Knock out (KO) of Ndufs4 in mice, specifically in glutamatergic ( Vglut2) neurons, reproduces motor dysfunctions associated with LS. Whereas KO of the gene in GABAergic neurons primarily lead to epilepsy. Here we uncovered that KO of Ndufs4 gene, specifically in the Vglut2 neurons, mimics swallow dysfunction seen in LS. Using freely breathing urethane anesthetized adult Vglut2/Ndufs4 KO mice, swallow was evoked by injection of water into the oral cavity. Swallow and respiratory activity was measured via monopolar suction electrodes of the hypoglossal (XII) and vagus (X) nerves as well as bipolar electromyogram (EMG) of the submental, laryngeal complex and costal diaphragm muscles. Post-hoc histological analysis of swallow and breathing related medullary areas was performed using IBA-1 for microglia and TMEM119 for macrophage analysis. This protocol was performed in Vglut2/Ndufs4 KO mice 1) exposed to room air and 2) exposed to 11% oxygen for 6 months. We found, mice exposed to chronic hypoxia (CH) no longer presented with symptoms such as: ataxia, hunched posture, unbalanced, clasping, weight loss, as seen in mice exposed to room air (RA). CH mice lived significantly longer than RA mice (225 ±6, 111±19, p= 0.000). CH mice weighed significantly more than RA mice (26 ±2g, 19±2g, p= 0.000). We also saw a discoordination in swallowing and breathing in RA mice with 1) swallows occurring during inspiration, 2) various abnormal swallow related phenotypes, 3) swallow induced apneas for more than 30s, and 4) variable reset of the respiratory rhythm. CH mice showed no evidence of the former disturbances, indicating CH rescues swallow-breathing coordination. CH exposure also suppressed inflammatory reaction in respiratory and swallow centers such as PiCo and NTS. This study gives first insights into possible mechanisms of LS and treatment for dysphagia in LS.

F32 HL160102-01, P01 HL090554, R01 HL126523, R01 HL144801, R01 HL151389, R01 NIH/NS 102796

This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.