Rationale: Somatic pathogenic
SLC35A2 variants are found in ~50% of patient brain tissue with mild malformations of cortical development with oligodendroglial hyperplasia (MOGHE). MOGHE is a newly recognized brain pathology identified in some patients who undergo surgery for the treatment of medically intractable focal epilepsy. It is characterized by heterotopic neurons, clusters of oligodendrocytes, and hypomyelination in white matter. In MOGHE, oligodendrocytes carry the highest allelic fraction of
SLC35A2 somatic variants contributing to its loss-of-function (LOF).
SLC35A2 encodes a transmembrane transporter in the Golgi Apparatus, responsible for shuttling galactose for N-linked glycosylation. While the relationship between LOF
SLC35A2 and MOGHE is tested in human tissue samples, an animal model is necessary to characterize the impact of LOF
SLC35A2 on oligodendrocytes and its role in intrinsic epileptogenicity of MOGHE lesions.
Methods: We utilized Cre-LoxP to generate an oligodendrocyte-specific deletion of
SLC35A2 in mice. Mice were produced carrying loxP sites on exon 3 of
SLC35A2. We bred floxed female mice to male Olig2-Cre to generate an oligodendrocyte-specific knockout. Littermates without Olig2-cre were considered as controls. To characterize the molecular phenotype at weaning age (PND21), we utilized immunohistochemistry. Genotypes were confirmed by PCR. To assess behavioral phenotypes, a 28-point neurological examination was conducted. We measured initial length and weight at PND21, with subsequent weekly assessments to monitor differences between genotypes.
Results: We successfully generated heterozygous and hemizygous-
SLC35A2 knockout mice with Olig2-Cre expression. All fourteen male/female were hetero/hemizygous for the
SLC35A2 -floxed allele, and half of both litters were positive for the Olig2-cre (referred to as “cKO”). Six cKO mice (7.3 ± 0.79) were smaller than the eight controls (9.8 ± 1.39) in weight (g). Overall, there were fewer Olig2+ cells in the corpus callosum in cKO mice compared to controls. CNPase, a marker of myelinating oligodendrocytes, revealed patchy myelination in the cortex and fimbria of the hippocampus. Male cKO mice that survived past weaning age (PND21) suffered from severe ataxia and consistently scored high on the 28-point neurological exam (n=4) indicating motor deficits. Interestingly, female cKO do not seem to exhibit the same observable traits as male cKO
SLC35A2 mice.
Conclusions: In this study, we generated a conditional knockout
SLC35A2 mouse model in oligodendrocytes. We demonstrated a reduction of Olig2-positive cells in the white matter of the mouse brain. We observed hypomyelination throughout the cortex and fimbria of the hippocampus. Lastly, we found severe ataxia and differences in weight of male cKO mice. Ongoing molecular and behavioral studies using this mouse model will contribute to the understanding of SLC35A2 in oligodendrocytes and their role in MOGHE-induced epileptogenicity.
Funding: The Cleveland Clinic Epilepsy Center internally funded this project.