An international research group led by Professor Toru Takumi (Senior Visiting Scientist, RIKEN Center for Biosystems Dynamics Research) and researcher Chia-wen Lin from the Graduate School of Medicine at Kobe University has shown that idiopathic autism*1 is caused by epigenetics*2 hematopoietic cell abnormalities during fetal development, leading to immune dysregulation in the brain and gut. The study results revealed that in autism, there are immune abnormalities that can be seen in the brain and gut.
It is hoped that further classification of autism pathophysiology will lead to the creation of new treatment strategies for autism and other neurodevelopmental disorders.*3.
The results of this research will be published in Molecular psychiatry Monday, May 2, 2022 (1:00 a.m. BST).
- In BTBR mice*4an animal model of autism, we have identified HDAC1*5 such as etiology of immune abnormalities by single-cell RNA-seq*6 GA analysis*7 blood cells.
- Single-cell RNA-seq analysis of the yolk sac*8 hematopoietic cells also identified HDAC1 as the etiology of microglia*9 developmental abnormalities.
- Regulating HDAC activity at the fetal stage ameliorated brain inflammation and immune dysregulation in BTBR mice.
- We found that changes in the gut environment, particularly the immune system, lead to abnormalities in the gut microbiota*ten of BTBR mice.
Autism (autism spectrum disorder) is a neurodevelopmental disorder that remains largely unexplored despite the rapid increase in the number of patients. Immune abnormalities, now thought to be the cause of many diseases, also play an important role in the development of autism. Cerebral inflammation and disturbances of the peripheral immune system are frequently observed in autistic patients. Moreover, immune abnormalities are accompanied by abnormalities of the intestinal microbiota, which would also be involved in the pathogenesis of the disease via the brain-gut axis.*11. However, the essential mechanisms underlying these immune abnormalities remain to be elucidated.
Given the critical developmental stages of immune insults and the significant involvement of the immune system in the development of autism, the research team hypothesized that a common etiology underlies widespread immune dysregulation and originates from different types of progenitor cells. The analysis focused on hematopoietic cells from which immune cells are derived, as well as the yolk sac (YS) and aorta-gonad-mesonephros (AGM), which are involved in hematopoiesis at the stage fetal. These findings search for a common ancestor of inflammation in the brain and peripheral immune system abnormalities. In this study, BTBR mice were used as an idiopathic model for autism.
Single-cell RNA sequencing (sc-RNA seq) of BTBR mice traced the origin of immune abnormalities back to the embryonic yolk sac (YS) and aorta-gonad-mesonephros (AGM) stages and identified where macrophages (microglia) and peripheral immune cells differentiate. Definitive hematopoiesis*12 in YS and AGM, single-cell level analysis has successfully identified pathological mechanisms at the molecular level in rare progenitor cells at early stages of development. Namely, we found a common mechanism of transcriptional regulation via HDAC1, a histone deacetylase, underlying these pathologies (Figures 1 and 2).
We have also shown that manipulating epigenetic mechanisms during specific developmental stages can restore immune abnormalities in brain and peripheral tissues. Namely, we identified histone deacetylase HDAC1 as a common mechanism. Administration of this histone inhibitors (sodium butyrate or romidepsin) at the fetal stage in BTBR mice suppressed elevated inflammatory cytokines*13 and microglial activation (Figure 3).
We further demonstrated that dysregulated immunity can determine gut dysbiosis of specific patterns in autistic mouse models, making potential biomarkers of Treg and gut dysbiosis a means to categorize the immunosupregulated ASD subtype.
From the above, it is clear that the abnormalities of the brain and peripheral organs (such as the intestines) seen in autism are caused by epigenetic abnormalities in the hematopoietic stem cell lineage, the ancestor of immune cells. (Figure 4).
Our findings not only provide the missing piece to solve the long-standing puzzle of systemic immune dysregulation in autism, but also suggest the role of epigenetic disruption as a common etiology among different risk factor models of autism. environmental. Moreover, to develop precision medicine for ASDs in the future, subtyping ASDs based on the mechanism of pathogenesis is a key first step to resolve the heterogeneity of ASDs and open a new avenue for treatment. of ASDs.
*1 Idiopathic Autism: Autism is considered a multifactorial disorder that can be caused by genetic and environmental factors. It is understood that genetic factors such as genetic and genomic abnormalities can cause autism, but there are still many cases of autism whose cause is unknown. Autism whose cause cannot be determined (including environmental factors) is called idiopathic autism.
*2 Epigenetics: The study of patterns of inheritance that affect the functioning of genes but do not involve alterations in DNA sequence. Even though the information in the genome remains the same, biological mechanisms such as DNA methylation and chemical modification of histone proteins can alter gene expression.
*3 Neurodevelopmental Disorder：Previously called developmental disorders, it is a disorder that occurs in connection with a functional problem of the brain.
*4 BTBR mice:A type of cogenic mouse. From the analysis of the systemic behavior of this line of mice, it has been reported that the behavior of the BTBR mouse is closest to autistic behavior. Hence, it is known as the idiopathic autistic mouse model.
*5 HDAC1:Histone deacetylase 1 regulates gene expression by modifying histone proteins.
*6 single cell RNA-seq:The invention relates to a method for in-depth study of the qualitative and quantitative aspects of all mRNAs present in individual cells using a next-generation sequencer. By combining this with statistical analysis methods such as dimension reduction, it is possible to classify cells based on their gene expression and estimate cellular state. Additionally, performing pseudo-temporal command analysis based on changes in gene expression profile allows for the representation of fibers in the cellular state that accompanies development.
*7 AGM:The aorta-gonad-mesonephros (AGM) region is a hematopoietic site within the fetus (i.e. where the cellular components of fetal blood are formed).
*8 Yolk sac:During pregnancy, the sac, which is a membrane that surrounds the egg yolk, is also a hematopoietic site (primary hematopoiesis).
*9 Microglia: A type of central nervous system glial cell responsible for the central immune system. Microglia are also called the resident macrophages of the central nervous system. Unlike other glial cells (such as astrocytes and oligodendrocytes), microglia arise from precursor cells derived from the yolk sac.
*10 Intestinal microbiota: clusters of bacteria in the intestine, also called intestinal flora. Recent advances in research using a next-generation sequencer to analyze the metagenome of gut bacteria have shown links to various disorders, including autism.
*11 Brain-gut axis: The relationship between the brain and the gut, also called the brain-gut connection. Two-way communication occurs between the brain and the gut through mediums such as the autonomic nervous system and humoral factors (eg, hormones and cytokines). Recently, this two-way communication system between the gut microbiota (microbiota) and the brain has received a lot of attention.
*12 Definitive hematopoiesis: During the fetal period, hematopoiesis begins in the yolk sac with primary hematopoiesis, then secondary hematopoiesis occurs in the AGM region. Subsequent hematopoiesis during the fetal period occurs in the liver and finally in the bone marrow. Hematopoiesis continues throughout a person’s life with the bone marrow as the primary site for this process.
*13 Inflammatory Cytokine：A signaling molecule secreted by immune cells, it causes inflammation.
This research was funded by sources such as those listed below:
- The following grants from the Japan Society for the Promotion of Science (JSPS): Grant-in-Aid for Scientific Research (S).
- Strategic Research Program for Brain Science of Japan Agency for Medical Research and Development
- Takeda Science Foundation Fellowship.
“A common epigenetic mechanism across different cellular origins underlies systemic immune dysregulation in an idiopathic autistic mouse model”
Chia-Wen Lin, Dian E Septyaningtrias, Hsu-Wen Chao, Mikiko Konda, Koji Atarashi, Kozue Takeshita, Kota Tamada, Jun Nomura, Yohei Sasagawa, Kaori Tanaka, Itoshi Nikaido, Kenya Honda, Thomas J McHugh, Toru Takumi