PDE4D Inhibition with GEBR32A stimulates Schwann cell differentiation and improves the funcional outcome in models for charcot marie tooth disease 1A

Abstract

Introduction: 2-oxyglutarate dehydrogenase (OGDH) is an E1 component of α-ketoglutarate dehydrogenase complex (α-KGDH) that plays a pivotal role in the Krebs cycle metabolism. Biallelic variants in OGDH have been reported to cause OGDH deficiency (OGDHD; OMIM: # 203740), an early-onset neurodevelopmental and mitochon-drial disorder. However, whether monoallelic OGDH variants could lead to dominant effects in humans had not been known. Methods:. Results: In this study, we identified de novo OGDH c. 1909C>T (p.-Arg637Trp), heterozygous c.162T>G (p.Ser54Arg) and heterozygous c.512A>G (p. Lys171Arg) variants by whole-exome sequencing (WES) in individuals exhibiting late-onset neurological phenotypes, including peripheral neuropathy, cerebellar ataxia and bilateral optic atrophy. Blood analysis for the individual with the p.Arg637Trp variant did not reveal ketogenosis, however lactate levels were increased in CSF. In patient lymphoblasts, OGDH protein levels did not appear altered, both in whole-cell lysate and in the mitochondrial fraction, compared to familial controls. Analysis of the enzyme activity showed reduced enzyme activity in patient cells. Analysis of the cellular mitochondrial functioning in patient-derived fibroblasts revealed defects in mito-chondrial respiration. To determine whether the monoallelic OGDH variants act as dominant-negative mutations, we generated Drosoph-ila models harboring UAS-dOgdh (p.Arg639Trp) and UAS-dOgdh (p.-Thr58Arg) mutations, homologous to the human variants. We found that ubiquitous expression of dOgdh (p.Arg639Trp) or dOgdh (p.-Thr58Arg) did not result in developmental lethality, but to locomotion defects in aged flies, confirming the human phenotype. Conclusions: These findings indicate that both variants act as document-negative mutations, consistent with the observed clinical manifestations in individuals carrying these monoallelic OGDH variants. Our data suggest that monoallelic OGDH variants disrupt α-KGDH function, thereby causing a late-onset neuropathy phenotype in patients.