Scientists around the world are trying to better understand mental health and brain disorders such as autism, schizophrenia, and Alzheimer’s disease.
Over the past few decades, researchers have discovered that genes, brain chemicals, and the way brain cells communicate with each other all play important roles in these conditions. Even with these advances, many questions remain unanswered. One mystery involves a little-known protein called IDO2.
IDO2 is an enzyme found in the brain and other parts of the body. It takes part in a natural process called the tryptophan-kynurenine pathway. Tryptophan is a nutrient that people get from foods such as eggs, milk, cheese, meat, fish, and nuts.
The body uses tryptophan to make many important substances that affect sleep, mood, immunity, and brain function.
Scientists have known for some time that changes in this pathway are linked to several mental health conditions, including depression, schizophrenia, and autism spectrum disorder. However, the exact role of IDO2 has remained largely unknown.
To investigate this question, a team of researchers from Fujita Health University in Japan, led by Associate Professor Yasuko Yamamoto, carried out a series of experiments using specially bred mice that did not have the IDO2 gene.
These animals are called IDO2 knock-out mice. By comparing them with normal mice, the scientists hoped to understand what happens when this enzyme is missing.
The researchers quickly noticed that the mice behaved differently. The animals had difficulty adapting to new environments and often showed repetitive behaviors, such as grooming themselves over and over again.
They also seemed less interested in exploring their surroundings. These patterns of behavior resemble some of the characteristics often seen in people with autism spectrum disorder.
The mice also had problems with social interaction. They did not easily learn from other mice and appeared less interested in social activities. Difficulties with social communication and social learning are important features of autism, so these findings caught the attention of the researchers.
The team then examined the brains of the mice to understand why these changes had occurred. They found that removing IDO2 changed the balance of chemicals inside the brain. In particular, it affected dopamine, an important chemical messenger that helps control motivation, emotions, learning, movement, and the brain’s reward system.
The changes were especially noticeable in two brain regions called the striatum and the amygdala, which play important roles in emotions, behavior, and social responses.
One of the most important discoveries involved a molecule called brain-derived neurotrophic factor, or BDNF. BDNF acts like a support system for brain cells. It helps nerve cells grow, survive, and form strong connections with each other.
Healthy levels of BDNF are important for learning, memory, and normal brain development. The mice without IDO2 had much lower levels of BDNF, suggesting that the development of their brain connections had been disrupted.
When the scientists examined brain cells under a microscope, they found more immature connections between nerve cells. These underdeveloped connections may have prevented brain cells from communicating properly and could help explain the unusual behaviors seen in the animals.
The researchers also studied microglia, which are special cells that act as the brain’s maintenance and cleaning crew. Normally, microglia help remove damaged cells and trim away extra connections between neurons during development.
In the IDO2-deficient mice, however, these cells became more aggressive and shifted into a different state. This change may have created a less healthy environment for brain development and normal behavior.
The scientists then carried out another experiment and restored IDO2 activity in the mice. Remarkably, many of the animals’ behaviors improved.
They adapted better to new situations, showed less repetitive behavior, and became more social. This result suggests that IDO2 plays an important role in keeping the brain’s chemical systems balanced and supporting healthy behavior.
To explore whether these findings might also be relevant to people, the researchers analyzed brain samples from 309 individuals with autism spectrum disorder. In one case, involving a 16-year-old girl, they found a mutation in the IDO2 gene.
Although this single case does not prove that IDO2 causes autism, it provides an important clue that the enzyme may contribute to some cases of the condition.
The findings offer a new direction for understanding how autism develops and how changes in brain chemistry and brain connections may contribute to symptoms. The research also raises the possibility that one day scientists may be able to develop new treatments that target IDO2 or related pathways in the brain.
In addition, researchers are continuing to study many other ways to support people with autism, including therapies that improve social skills, programs involving animals such as cats and dogs to reduce anxiety, and nutritional approaches that may promote brain health.
The study, titled ‘Indoleamine 2,3-dioxygenase 2 deficiency associates with autism-like behavior via dopaminergic neuronal dysfunction,’ was published in The FEBS Journal in late 2023.
Although much more work is needed, this study provides an important piece of the puzzle and brings scientists one step closer to understanding the complex biology of autism and other brain disorders.
As researchers continue to uncover how proteins such as IDO2 shape brain development, there is growing hope that future discoveries could lead to earlier diagnosis and better treatments for people living with these conditions.
If you care about autism, please read studies about a new cause of autism, and cats may help decrease anxiety for kids with autism.
For more information about health, please see recent studies about vitamin D that may hold the clue to more autism, and results showing strange eating habits may signal autism.
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