Summary: Researchers made significant strides in understanding autism spectrum disorder’s genetic underpinnings. By studying mice with a frameshift mutation in the KMT2C gene, they observed behavioral and cognitive impairments resembling ASD symptoms.
Through extensive molecular analyses, they discovered an unexpected increase in the expression of genes linked to ASD risk due to KMT2C haploinsufficiency, implicating indirect effects on gene expression. Remarkably, treatment with the drug vafidemstat showed promise in correcting these abnormalities, suggesting a potential therapeutic approach for ASD and similar conditions.
Key Facts:
- Researchers found that a frameshift mutation in the KMT2C gene, leading to haploinsufficiency, models ASD-like symptoms in mice, including reduced sociality and cognitive impairments.
- Contrary to expectations, KMT2C haploinsufficiency resulted in increased expression of ASD-associated genes, indicating an indirect mechanism of transcriptomic dysregulation.
- Vafidemstat treatment ameliorated social deficits and normalized gene expression in mutant mice, pointing to a promising therapeutic pathway for ASD.
Source: Juntendo University
Autism spectrum disorder (ASD) encompasses neurodevelopmental conditions where patients display repetitive behavior and impaired sociality. Genetic factors have been shown to influence the development of ASD.
Additionally, recent studies have shown that the genes involved in chromatin modification and gene transcription are involved in the pathogenesis of ASD.
Among the many genes implicated in this process, the gene KMT2C (lysine methyltransferase 2c), which codes for a catalytic unit of H3K4 (histone H3 lysine 4) methyltransferase complex, has been identified to be associated with the development of autism and other neurodevelopmental disorders.
Previous studies have shown that haploinsufficiency (a condition where, of the two copies of the gene, only one remains functional) of KMT2C is a risk factor for ASD and other neurodevelopmental disorders. However, the molecular mechanism through which the loss-of-function mutation in KMT2C leads to these conditions remains unclear.
To address this knowledge gap, researchers from Juntendo University, RIKEN, and the University of Tokyo in Japan aimed to provide answers to these questions in a benchmark study published in the journal Molecular Psychiatry on 26 March 2024. The research team included Professor Tadafumi Kato from the Department of Psychiatry and Behavioral Science at Juntendo University Graduate School of Medicine, Dr. Takumi Nakamura and Dr. Atsushi Takata from the RIKEN Center for Brain Science, and Professor Takashi Tsuboi from Graduate School of Arts and Sciences, The University of Tokyo.
To get to the bottom of KMT2C’s role in ASD pathogenesis, the team developed and analyzed genetically engineered strain mice (Kmt2c+/fs) having a frameshift mutation that models the KMT2C haploinsufficiency.
They then performed various behavioral analyses, in which they observed that the mutant mice exhibited lower sociality, inflexibility, auditory hypersensitivity, and cognitive impairments, which are all ASD-related symptoms.
Next, they performed transcriptomic and epigenetic profiling to understand the basis of the molecular changes observed in the mutant mice. What they discovered was remarkable: the genes associated with increased ASD risk showed higher expression in these mutant mice.
Dr. Takata exclaims, “This was somewhat unexpected. KMT2C mediates H3K4 methylation, which is thought to activate gene expression, and thereby KMT2C haploinsufficiency was expected to cause reduced expression of target genes.”
To gain mechanistic insights into their finding, the researchers carried out chromatin immunoprecipitation, a technique to determine the location on the DNA where the protein interacts with it.
They found an overlap between KMT2C and the differentially expressed genes exhibiting reduced expression, suggesting that KMT2C haploinsufficiency leads to ASD-related transcriptomic changes through an indirect effect on gene expression.
Further, to identify the cell types that contribute more to the pathological changes seen in the mutant mice, the researchers performed single-cell RNA sequencing of newborn mice brains. They observed that the altered genes associated with ASD risk were predominant in undifferentiated radial glial cells.
However, a gross change in the cell composition was not observed, implying that the transcriptomic dysregulation does not severely impact cell fate.
Finally, the researchers tested the effects of vafidemstat, a brain penetrant inhibitor of LSD1 (lysine-specific histone demethylase 1A), that could ameliorate histone methylation abnormalities.
They found that vafidemstat improved the social deficits in the mutant mice and had an exceptional rescuing effect by changing the expression levels of the differentially expressed genes to their normal expression level. This finding showed that vafidemstat is a valid drug for mutant mice and can potentially help restore the normal transcriptomic state.
What sets this discovery apart is that it challenges the commonly held belief that ASD disability may not be cured and demonstrates the efficacy of vafidemstat in improving ASD-like phenotypes.
The results open doors to future research to strengthen the foundation for the pharmacologic treatment of ASD and other neurodevelopmental disorders. Prof. Kato concludes, “Our research shows that drugs similar to vafidemstat may be generalizable to multiple categories of psychiatric disorders.”
About this genetics and autism research news
Author: Yoshitaka Nakashima
Source: Juntendo University
Contact: Yoshitaka Nakashima – Juntendo University
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Transcriptomic dysregulation and autistic-like behaviors in Kmt2c haploinsufficient mice rescued by an LSD1 inhibitor” by Tadafumi Kato et al. Molecular Psychiatry
Abstract
Transcriptomic dysregulation and autistic-like behaviors in Kmt2c haploinsufficient mice rescued by an LSD1 inhibitor
Recent studies have consistently demonstrated that the regulation of chromatin and gene transcription plays a pivotal role in the pathogenesis of neurodevelopmental disorders.
Among many genes involved in these pathways, KMT2C, encoding one of the six known histone H3 lysine 4 (H3K4) methyltransferases in humans and rodents, was identified as a gene whose heterozygous loss-of-function variants are causally associated with autism spectrum disorder (ASD) and the Kleefstra syndrome phenotypic spectrum.
However, little is known about how KMT2C haploinsufficiency causes neurodevelopmental deficits and how these conditions can be treated.
To address this, we developed and analyzed genetically engineered mice with a heterozygous frameshift mutation of Kmt2c (Kmt2c+/fs mice) as a disease model with high etiological validity. In a series of behavioral analyses, the mutant mice exhibit autistic-like behaviors such as impairments in sociality, flexibility, and working memory, demonstrating their face validity as an ASD model.
To investigate the molecular basis of the observed abnormalities, we performed a transcriptomic analysis of their bulk adult brains and found that ASD risk genes were specifically enriched in the upregulated differentially expressed genes (DEGs), whereas KMT2C peaks detected by ChIP-seq were significantly co-localized with the downregulated genes, suggesting an important role of putative indirect effects of Kmt2c haploinsufficiency.
We further performed single-cell RNA sequencing of newborn mouse brains to obtain cell type-resolved insights at an earlier stage.
By integrating findings from ASD exome sequencing, genome-wide association, and postmortem brain studies to characterize DEGs in each cell cluster, we found strong ASD-associated transcriptomic changes in radial glia and immature neurons with no obvious bias toward upregulated or downregulated DEGs. On the other hand, there was no significant gross change in the cellular composition.
Lastly, we explored potential therapeutic agents and demonstrate that vafidemstat, a lysine-specific histone demethylase 1 (LSD1) inhibitor that was effective in other models of neuropsychiatric/neurodevelopmental disorders, ameliorates impairments in sociality but not working memory in adult Kmt2c+/fs mice.
Intriguingly, the administration of vafidemstat was shown to alter the vast majority of DEGs in the direction to normalize the transcriptomic abnormalities in the mutant mice (94.3 and 82.5% of the significant upregulated and downregulated DEGs, respectively, P < 2.2 × 10−16, binomial test), which could be the molecular mechanism underlying the behavioral rescuing.
In summary, our study expands the repertoire of ASD models with high etiological and face validity, elucidates the cell-type resolved molecular alterations due to Kmt2c haploinsufficiency, and demonstrates the efficacy of an LSD1 inhibitor that might be generalizable to multiple categories of psychiatric disorders along with a better understanding of its presumed mechanisms of action.
