IL-6 may drive inflammation in neuropsychiatric disorders.

Neuropsychiatric disorders are the leading cause of disability among people living in the United States, accounting for nearly 20 percent of all years of life lost to disability and premature death. Evidence suggests that brain inflammation is a key player in neuropsychiatric disorders, the effects of which may be bidirectional. A recent study identified potential links between inflammation and structural alterations in regions of the brain implicated in neuropsychiatric disorders.

The brains of people with neuropsychiatric disorders exhibit a range of abnormal structural alterations, but researchers don’t fully understand what drives these abnormalities. One possible player is interleukin-6 (IL-6), a cytokine that can cross the blood-brain barrier, increasing the barrier’s permeability and promoting brain inflammation. In turn, this inflammation can impair synaptic pruning, a natural process that occurs in the brain between early childhood and adulthood and eliminates extra synapses. Inappropriate synaptic pruning is associated with some neuropsychiatric disorders, including schizophrenia and autism.

The investigators searched for evidence of potential causality in the association between inflammatory cytokines and altered brain structure using Mendelian randomization, a research method that provides evidence of links between modifiable risk factors and disease based on genetic variants within a population. Using data from more than 20,000 adults enrolled in the UK Biobank study, the researchers looked for associations between genetic variants that influence levels of interleukin-6 (IL-6, a pro-inflammatory cytokine), as well as other inflammatory factors. and changes in gray matter volume in specific areas of the brain. They also examined postmortem brain tissue to assess gene expression in the brain areas of interest.

They found that genes that influence the production of pro-inflammatory molecules, especially IL-6, are strongly linked with brain structure in the temporal and frontal regions of the brain, areas of the brain commonly implicated in neuropsychiatric disorders. The postmortem analyses revealed that the overproduction of these pro-inflammatory genes is associated with disorders such as epilepsy, cognitive disorder, schizophrenia, psychotic disorder, and autism spectrum disorder.

These findings suggest that pro-inflammatory pathways, especially those associated with IL-6, are essential for normal brain structural development and IL-6 elevation may drive structural alterations implicated in neuropsychiatric disorders. Evidence suggests that heat stress reduces symptoms associated with depression, a type of neuropsychiatric disorder. Learn about a clinical trial that is investigating the benefits of heat stress in this episode featuring Dr. Ashley Mason.

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