A research group led by Researcher Yuji Nakamura, Associate Professor Issei Shimada, Professor Yoichi Kato, and Professor Shinji Saitoh of the Graduate School of Medical Sciences at Nagoya City University (NCU), together with Designated Professor Norio Ozaki and Designated Lecturer Yuko Arioka of the Nagoya University Graduate School of Medicine and researchers of the University of Tokyo, Kyoto University, and Kumamoto University conducted international research in collaboration with 12 countries. The research group announced that they have clarified the pathogenic mechanisms of pediatric intractable neurological diseases using cerebral organoids and discovered a gene responsible for decreased human neural stem cell counts. This was achieved by combining genetic analysis with a three-dimensional culture model. These findings are expected to contribute to the development of new therapeutic methods and were published in the international journal Brain on July 31.
Many rare diseases in children are difficult to diagnose, and the discovery of causative genes for these diseases and clarification of their effects are known to be difficult even with whole-transcriptome analysis. In this study, the research group analyzed the genes of patients with intractable neurological diseases associated with developmental and degenerative epileptic−dyskinetic encephalopathy, which are difficult to diagnose, and identified mutations in the PNPLA8 gene, a member of the phospholipase A2 family of phospholipid-hydrolyzing enzymes.
In response, the group generated a three-dimensional brain culture model (cerebral organoid model) from iPS cells and investigated the effects of loss of function of the PNPLA8 gene. The results showed that loss of PNPLA8 gene function reduces the number of human-specific neural stem cells, resulting in a smaller brain size. The loss of PNPLA8 gene function was associated with a continuum ranging from mild to severe forms, with the severe form presenting with microcephaly due to the lack of wrinkles in the brain and the mild form presenting with symptoms such as difficulty walking. PNPLA8 was identified as a gene responsible for developmental and degenerative epileptic−dyskinetic encephalopathy (DDEDE).
By generating cerebral organoids from iPS cells lacking the PNPLA8 gene and iPS cells derived from patients with DDEDE, the research group also found that the number of human-specific neural stem cells, called outer radial glia cells, was reduced and neurogenesis was decreased in patients with DDEDE. Moreover, large-scale transcriptomic and lipidomic analyses revealed that abnormal phospholipid metabolism may prevent normal neural stem cells differentiation and affect neurogenesis. The research group also confirmed that the addition of deficient phospholipids restored the number of human-specific neural stem cells. Moving forward, the research group aims at shedding light further on the mechanisms and develop therapeutic means by combining their model with various animal models.
Saitoh said, "Because the disease described in this paper is extremely rare, the study was an international collaborative study by 63 researchers from 12 countries to enroll sufficient patients. Functional analysis was also performed in collaboration with eight universities in Japan. We realized that international collaboration is essential for research on rare genetic diseases, and we also strongly felt that collaboration with highly skilled researchers is essential for high-level research."
Journal Information
Publication: Brain
Title: Biallelic null variants in PNPLA8 cause microcephaly by reducing the number of basal radial glia
DOI: 10.1093/brain/awae185
This article has been translated by JST with permission from The Science News Ltd. (https://sci-news.co.jp/). Unauthorized reproduction of the article and photographs is prohibited.