Depression is one of the most common and serious mental health conditions in the world.
According to global health estimates, more than 280 million people are affected by depression.
The condition can deeply impact daily life, relationships, work, and physical health.
People with depression may feel overwhelming sadness, lose interest in activities they once enjoyed, struggle with sleep problems, feel exhausted all the time, or withdraw from family and friends. In severe cases, depression can increase the risk of self-harm and suicide.
Although depression is very common, scientists still do not fully understand exactly how it develops inside the brain.
For many years, most antidepressant medications have focused on chemicals called neurotransmitters, especially serotonin.
These medicines can help many patients, but they do not work well for everyone. Researchers estimate that only about half of patients experience strong improvement from current antidepressants. Some people also experience side effects such as nausea, anxiety, headaches, or sleep problems.
Because of these limitations, scientists around the world are searching for completely new ways to understand and treat depression. Now, researchers from the Institute for Basic Science, also known as IBS, have discovered a new biological pathway that may help explain how depression develops.
The study was led by scientists C. Justin Lee and Boyoung Lee and published in the journal Science Advances. Their findings suggest that stress can change important sugar-related structures inside the brain, which may contribute directly to depression.
At first, sugar chains in the brain may sound unusual or unimportant, but they actually play a major role in how cells function. The researchers focused on a process called glycosylation. This is a natural process where sugar chains attach to proteins and help control how those proteins behave.
Glycosylation is already known to be important in diseases such as cancer and Alzheimer’s disease. However, scientists are only beginning to understand how it may affect mental health conditions.
To study the problem, the research team used mice exposed to chronic stress. Scientists often use chronic stress models because long-term stress is one of the strongest known risk factors for depression in humans.
The researchers carefully examined proteins and sugar-chain changes in nine different brain regions. They discovered that stress caused major changes in sugar structures, especially in a part of the brain called the prefrontal cortex.
The prefrontal cortex is extremely important for emotional control, decision-making, social behavior, and thinking. Many previous studies have already linked this area of the brain to depression and anxiety disorders.
One of the most important discoveries involved a process called sialylation. This process adds a special molecule called sialic acid to the ends of sugar chains. Sialic acid helps stabilize proteins and allows brain cells to function properly.
The scientists found that stressed mice had much lower levels of an enzyme called St3gal1, which is responsible for helping this process happen. In other words, stress appeared to disrupt the brain’s normal sugar-related protein regulation system.
To understand whether this enzyme directly affects depression, the researchers performed two major experiments.
First, they lowered St3gal1 levels in healthy mice that had not been exposed to stress. Surprisingly, these mice began showing behaviors linked to depression and anxiety even though they had not experienced chronic stress.
They became less motivated, showed more signs of emotional distress, and behaved similarly to stressed animals.
Next, the researchers increased St3gal1 levels in mice that had been exposed to chronic stress. These mice showed fewer depressive behaviors and appeared emotionally healthier than stressed mice with lower enzyme levels.
These experiments strongly suggested that the enzyme plays a direct role in regulating mood and depressive symptoms.
The researchers then looked deeper into what was happening inside the brain cells. They discovered that lower St3gal1 levels weakened communication between nerve cells.
One important protein affected by this process was neurexin 2, also called NRXN2. This protein helps nerve cells form stable connections with each other. When NRXN2 became unstable, communication between brain cells became disrupted, especially in systems involved in emotional regulation.
The scientists believe this chain of events may help explain how chronic stress eventually changes brain function and contributes to depression.
Researcher Boyoung Lee explained that the study provides one of the clearest links so far between sugar-chain regulation in the brain and depression. The findings may eventually lead to completely new ways of diagnosing and treating mental illness.
Instead of only targeting neurotransmitters like serotonin, future treatments might focus on protecting or repairing these sugar-related pathways inside brain cells.
Director C. Justin Lee also said the discovery may have implications beyond depression. Similar biological pathways may be involved in other mental health conditions, including post-traumatic stress disorder, often called PTSD, and schizophrenia.
The findings are especially important because stress-related mental health disorders continue to rise around the world. Many experts believe modern lifestyles, social pressures, loneliness, economic stress, and trauma are contributing to increasing rates of depression and anxiety.
Although much more research is still needed before new treatments become available, the study opens an exciting new direction for mental health science. It suggests that tiny sugar-related processes inside brain cells may play a much bigger role in emotional health than previously understood.
For millions of people living with depression, the research offers new hope that future treatments may become more effective, more personalized, and possibly safer than current medications.
If you care about mental health, please read studies about how dairy foods may influence depression risk, and 6 foods you can eat to improve mental health.
For more mental health information, please see recent studies about top foods to tame your stress, and Omega-3 fats may help reduce depression.
The study was published in Science Advances.
