Authors :
Presenting Author: Noriyuki Shinagawa, BS – The Research Institute at Nationwide Children's Hospital
James Anderson, BS – The Research Institute at Nationwide Children's Hospital
Kaiwen Wu, n/a – The Research Institute at Nationwide Children's Hospital
Lauren Mashburn-Warren, PhD – The Research Institute at Nationwide Children's Hospital
June Yoon, PhD – The Research Institute at Nationwide Children's Hospital
Tracy Bedrosian, PhD – Nationwide Children's Hospital
Rationale:
The SLC35A2 gene located on the X chromosome encodes a UDP-galactose transporter that localizes to the endoplasmic reticulum and Golgi body. Recently, somatic variants in SLC35A2 have been implicated as a prominent cause of mild malformation of cortical development with oligodendroglial hyperplasia in epilepsy (MOGHE), a histopathological entity associated with drug-resistant epilepsy. The development of detrimental phenotypes is believed to be caused by defects in glycosylation, specifically in the incorporation of galactose into the glycan chains of various molecules necessary for cell adhesion and signaling; however, the exact mechanisms leading to disease remain unknown. Seizures associated with SLC35A2 deficiency tend to respond poorly to anti-seizure medication due to their drug-resistant nature. For MOGHE patients experiencing drug-resistant seizures, the standard treatment remains surgical resection of the epileptic focus. Although some patients respond well to surgery, surgical resection carries the risk of damaging vital areas of the brain and cannot be performed when the epileptic focus coincides with a region of high functional importance. Therefore, there is a critical need for an effective medical treatment for seizures caused by SLC35A2 variants.
Methods:
Our lab previously developed a novel mouse model in which Emx1-mediated Cre recombinase expression knocks out Slc35a2 in forebrain neural progenitors. These mice recapitulate the phenotypes seen in patients with mosaic SLC35A2 deficiency, including seizures, neuronal migration deficits, and an increased density of OLIG2-positive cells. As Slc35a2 loss-of-function was sufficient to cause seizures and MOGHE-like phenotypes in mice, we hypothesized that gene replacement would be successful in rescuing these phenotypes. We designed recombinant adeno-associated viral vectors (AAVs) containing a functional copy of Slc35a2 and mCherry reporter expressed under the chicken beta actin (CBA) promoter and packaged in an AAV8 capsid. We injected these AAVs into the lateral ventricles of postnatal day 0 mice.
Results:
Efficient transduction of neurons and glial cells in the cerebral cortex was confirmed in situ through mCherry immunofluorescence analysis. Gene expression of Slc35a2 measured through RT-qPCR demonstrates a significant rescue in mice treated with AAVs containing Slc35a2-mCherry compared to those treated with AAVs encoding mCherry only. Conditional knockout male mice injected with the treatment AAV have significantly improved survival compared to their littermates injected with the control vector. In addition, treated males show a dose-dependent rescue in their weight profiles, with weights in the group injected with the highest dose tracking with those of wildtype mice.
Conclusions:
Although much more work establishing the safety and efficacy of gene replacement therapies for disease caused by SLC35A2 variants is currently ongoing, the data demonstrate the potential for Slc35a2 gene replacement to rescue phenotypes in SLC35A2-deficient mice.
Funding: NIH‐NINDS (R01NS129784)