Abstracts

Rationale:
Leigh Syndrome (LS), is a devastating neurodegenerative disorder due to mitochondrial dysfunction. Symptoms typically present during childhood and rapidly progress, leading to death before 3 years of age. LS is associated with nuclear and mitochondrial genetic mutations in NDUFS4, the gene that encodes NADH-ubiquinone iron-sulfur protein 4 of complex I in the mitochondrial electron transport chain. Mice carrying global or conditional knockout (KO) of Ndufs4, are well established models of LS. They exhibit several key features of the disease in humans including respiratory dysfunction, seizures, and premature death. Our recent studies have shown that excitatory and inhibitory neurons participate in the mechanisms of two distinct types of premature death in LS mice. Deletion of Ndufs4 in glutamatergic neurons led to progressive movement disorders, respiratory dysfunction and premature death. In contrast, KO of Ndufs4 in GABAergic neurons led to seizures of increasing severity and SUDEP. In this study, we investigated the responsiveness of the respiratory system to compromising gas conditions in search of markers for premature death susceptibility in LS mice.
Method:
Mice with Ndufs4 selectively deleted in either GABAergic neurons (Gad2 KO) or in glutamatergic neurons (Vglut2 KO) and controls were generated by crossing Ndufs4 floxed mice with Gad2Cre or Vglut2Cre mice, respectively. Mice of each genotype underwent gas challenge tests at 3 disease stages. They were placed in a plethysmography chamber and allowed to acclimate in air, for at least 10 minutes. Respiratory function was recorded at baseline and during exposure to hypercapnia (10 min. in 5% CO2), hypoxia (5 min. in 5% CO2/10% O2) and anoxia (5 min. of 5% CO2).
Results:
Respiratory parameters of mutant mice compared to controls revealed the following. During the early stage of disease, Vglut2 KO mice exhibited a moderate, but not statistically significant, increase in baseline tidal volume and minute ventilation. In contrast, Gad2 KO mice had a slight, not statistically significant, decrease of the same parameters. Following the gas challenges, Vglut2 mutants responded similarly to controls, whereas Gad2 mutants showed enhanced response in tidal volume and minute ventilation. In the mid-stage of the disease, Vglut2 KO mice had increased baseline minute ventilation, whereas Gad2 KO mice had similar measures as controls. Gas challenges showed blunted respiratory response in Vglut2 KOs, but the opposite response in Gad2 KOs. In the late disease stage, baseline tidal volume and minute ventilation were mildly suppressed in Vglut2 KO mice, but not in Gad2 KO mice. Following gas challenges, Vglut2 KOs had a suppressed response while Gad2 KOs responded slightly better.
Conclusion:
These findings indicate that baseline and gas challenge-induced respiratory dysfunctions are reliable markers of risk for non-SUDEP fatality, not SUDEP, in our LS mice.
Funding:
:This study is supported by funding from National Institutes of Health, USA (1R01NS102796, FK)