Authors :
Divyalakshmi Soundararajan, MS – Columbia Vagelos College of Physicians & Surgeons
Emi Kouyama-Suzuki, PhD – Shinshu University School of Medicine
Nina Levy, PhD – Technion Israel Institute of Technology
Yoshinori Shirai, PhD – Shinshu University School of Medicine
Yonat Israel, BS – Technion Faculty of Medicine
Li Suyao, MSc – Shinshu University School of Medicine
Weichen Zang, MSc – Shinshu University School of Medicine
Gabriel Jimenez, BS – Columbia University Vagelos College of Physicians & Surgeons
Aaron Lowenkamp, BS – Technion Faculty of Medicine
Shaun Orth, BS – Technion Faculty of Medicine
Niguse Garoma, MSc – Technion Faculty of Medicine
Leah Avi-Isaac, BS – Technion Faculty of Medicine
Yisrael Weiss, BS – Technion Faculty of Medicine
Joseph Zarowin, BS – Technion Faculty of Medicine
Veronika Borisov, PhD – Technion Faculty of Medicine
Shmuel Halpert, MD – Technion Faculty of Medicine
Wayne Frankel, PhD – Columbia University Vagelos College of Physicians & Surgeons
Tristan Sands, MD, PhD – Columbia University Vagelos College of Physicians & Surgeons
Katsuhiko Tabuchi, MD PHD – Shinshu University School of Medicine
Presenting Author: Andrew Levy, MD – Technion Faculty of Medicine, Technion Israel Institute of Techology Haifa, Israel
Rationale:
The IQSEC2 protein is a guanine exchange factor for Arf6. Pathological mutations in the X-linked IQSEC2 gene, occurring in 1000 children, are associated with drug resistant epilepsy, severe intellectual disability and autism. Approximately 80% of all mutations are premature termination codons predicted to result in no IQSEC2 protein being produced (Class 1 mutations). Class 2 mutations are missense mutations in one of seven functional domains of IQSEC2 altering IQSEC2 functional activity. The rationale for this study was to investigate if an AAV containing the human IQSEC2 gene could rescue IQSEC2 disease in mice with class I or class II IQSEC2 mutations. We sought to increase the reliability and confidence in these findings by conducting these studies in several independent laboratories. Methods:
These studies were carried out at Columbia University, Shinshu University and the Technion and approved by their respective IACUCs. The characterization of the IQSEC2 mutant mouse models developed by the three groups have been published.1-4 Two of the models were IQSEC2 knockouts [ Phe860Serfs*8 and Ser254*] and two were human class II mutations [A350V and S1474Qfs*133]. The AAV used in all studies (IQSEC2 #40) had a neuron specific mini promoter, the human full length ORF for IQSEC2 and a synthetic polyadenylation site. AAV was injected directly to the brain. Phenotypes, previously shown to be different between IQSEC2 mutant and wild type littermates, were assessed after AAV treatment: weight gain, seizure threshold using ECT, social behavior interactions using the three chamber paradigm (social preference test and social novelty preference test) and vocalizations by a male test mouse induced by a female mouse. Results:
In laboratories at Columbia and Shinshu working with the two different knockout models IQSEC2 AAV #40 was found to rescue abnormal phenotypes. At Columbia, delayed growth in mutant mice was significantly improved (p for interaction genotype and virus < 0.0001, n >20) and the seizure threshold was normalized in the mutant mice. At Shinshu, abnormal social behaviors in the mutant mice were rescued (p< 0.05, n >15 mice in each group for social preference and social novel preference). However, at the Technion this AAV was not able to rescue abnormal phenotypes (seizures and vocalizations assessed in males exposed to a female stimulus) in mice with either A350V or S1474Q*fs133 mutations. Conclusions:
AAV IQSEC2 40 rescued abnormal phenotypes in IQSEC2 knockout mice which do not produce the IQSEC2 protein. We propose that this AAV may be appropriate for a proof of concept study in children with class I IQSEC2 mutations.
References.
1. Sah et al. doi:10.1016/j.nbd.2020.104758
2. Mehta et al. doi:10.3390/cells10102724
3. Rogers et al. doi:10.3389/fnmol.2019.00043
4. Israel et al. doi:10.3390/biom15050635 Funding:
US-Israel Binational Science Foundation # 2023012 (TS and APL); Israel Science Foundation # 591/23 (APL); NIH R01NS031348 (TS); Grant-in-Aid for Transformative Research Areas (A) 23H04227 (KT).