HMN 2026: How Chloride ions do more than help neurons fire—they may also help control how genes are expressed

Chloride ions, best known for helping cells maintain fluid balance and electrical stability, may also play a more direct role in regulating brain development than previously thought. In a new study, published in the journal Science Signaling, scientists have found that the ions can alter the activity of a key RNA-processing enzyme, resulting in severe neurodevelopmental disorders.

Researchers at the Biosciences National Laboratory in Campinas, Brazil found that chloride ions interact with a critical region of an enzyme called DDX3X, interfering with its ability to unwind RNA. The unspooling of RNA, the team underscored, is an essential step in gene expression.

“Chloride homeostasis is pivotal during neurodevelopment and in multiple processes in mature neurons, and its disruption is implicated in several neurodevelopmental disorders,” writes Dr. Ivan Rosa e Silva, lead author of the new research.

“Given that chloride plays key roles in multiple aspects of brain development and function, and that DDX3X is an important protein during neurodevelopment,” Rosa e Silva continued, “we sought to investigate the effects of chloride on DDX3X stability and enzymatic activity.”

Chloride’s unexpected role

DDX3X belongs to a class of enzymes known as RNA helicases, which separate double-stranded RNA into single strands so that genetic information can be read and used by the cell. The protein is also involved in the formation of stress granules, temporary structures that cells assemble under adverse conditions.

The researchers show that chloride ions bind directly to the RNA-binding region of DDX3X, dampening its enzymatic activity. This suggests that fluctuations in chloride levels inside cells—long known to influence neuronal signaling—may also regulate RNA metabolism.

The team also examined how changes in chloride concentration affect the behavior of DDX3X inside cells. In a human neuroblastoma cell line, reducing intracellular chloride levels triggered the formation of large stress granules containing the enzyme.

Stress granules are thought to help cells cope with environmental or metabolic duress by temporarily halting certain aspects of RNA processing. The findings suggest that chloride shifts could influence when and how these structures form.

A mutation alters regulation

The study also offers insight into how mutations in DDX3X may contribute to disease. Indeed, a specific mutation, known as R326H, has been tied to a severe X-linked neurodevelopmental disorder called DDX3X syndrome. The researchers found that this mutation reduced the ability of chloride ions to regulate DDX3X, potentially disrupting normal control of RNA processing.

That loss of regulation can have downstream effects during brain development, when precise control of gene expression is crucial.

Chloride ions are already known to play a central role in neurons, where they help govern electrical signaling and synaptic activity. Disruptions in chloride balance have been associated with conditions such as epilepsy, autism spectrum disorders, and fragile X syndrome.

The new findings suggest that chloride may influence these processes not only through electrical signaling, but also by directly modulating proteins involved in RNA regulation.

Implications for brain development

Although the findings come from experiments in cultured cells in the laboratory, they suggest a new way to think about how ionic changes in neurons might influence gene expression and brain development.

“Chloride homeostasis modulates fundamental biological functions across all tissues by regulating the charge balance in cells,” Rosa e Silva explained in the research paper.

He underscores that chloride ions help maintain osmotic equilibrium and volume control within cells. Shifts in chloride ion concentrations are also important in the development, function, and excitation of neurons and synapses.

The study adds to a growing body of evidence that ions, long viewed as simple regulators of cellular balance, may also act as signaling molecules in their own right by shaping fundamental processes inside cells.

Additional research will be needed to determine precisely how chloride-dependent regulation of DDX3X operates in the brain and whether it can be targeted therapeutically, Rosa e Silva and colleagues note in the study.

“Further investigation into the biology of DDX3X regulation by chloride ions during neurodevelopment may be a promising area for future therapeutic interventions,” Rosa e Silva concludes.

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