Ali Rifat

This study reflects the dedication of a great team over many years. I am sincerely thankful to my co-first author Tom Bickel, to our PI Christian Madry and to all collaborators who brought their expertise and care to this work.

Read the full story here: www.science.org/doi/10.1126/...

In summary, we could show that CLIC1 regulates microglial morphodynamics and inflammation across species, through a non-canonical, ion channel independent mechanism. Given its high enrichment in microglia, CLIC1 could be a potential target to contain neuroinflammation.

Finally, we asked whether these mechanisms translate to human microglia. Using a mouse model with xenotransplanted human microglia and human brain tissue, we confirmed that CLIC1 regulates microglial morphodynamics and inflammatory signaling across species.

CLIC1 turned out to influence not only process motility but also inflammation. Inhibiting CLIC1 strongly reduced NLRP3-dependent release of IL-1β. This function was again incompatible with CLIC1 acting as a Cl⁻ channel and was instead governed by its conserved enzymatic activity.

If not as an ion channel, how does CLIC1 control motility and ramification? CLIC1 can also exist in a soluble cytosolic form. In this state, it interacts with actin and ERM family proteins, and likely serves as a scaffold protein that links the cytoskeleton to the plasma membrane.

To test if CLIC1 acts as a Cl⁻ channel, we repeated our experiments in Cl⁻-free solutions. Surprisingly, depleting Cl⁻ did not alter the effect of CLIC1 blockade on motility and ramification. So, contrary to its name, CLIC1 does not act as a Cl⁻ channel to regulate this.

To confirm this genetically, we analyzed a constitutive and a microglia-specific CLIC1 knockout mouse. In both cases, microglia showed reduced process ramification and impaired motility, closely matching the pharmacological phenotype.

To test wheter our initial effects could be explained by CLIC1, we blocked it using the small molecule IAA94 and an anti-CLIC1 antibody. The result was clear: CLIC1 blockade reduced microglial ramification and process motility, thereby reducing the surveillance of the brain.

To identify candidate genes, we turned to scRNA sequencing, and found one gene prominently standing out: CLIC1, which encodes the Chloride Intracellular Channel 1. It was highly expressed in both mouse and human microglia but barely detectable in other brain cells.

In our experiments, broad-spectrum Cl⁻ channel blockers profoundly impaired microglial motility and process ramification. Yet patch-clamp recordings revealed no tonic Cl⁻ conductance in the plasma membrane. We considered two options: either a nonspecific drug effect or an intracellular Cl⁻ channel.

Microglia are the brain’s most dynamic cells, constantly extending and retracting their processes to monitor the parenchyma and respond to potential danger with inflammatory signaling.

Our new study in @ScienceAdvances @science.org explores how these functions are regulated.

The chloride intracellular channel 1 (CLIC1) is essential for microglial morphodynamics and neuroinflammation CLIC1 regulates surveillance, morphology, and interleukin release in mouse and human brain microglia.

Very interesting paper in Science Advances by the Madry lab showing that the chloride channel Clic1 regulates morphodynamics and surveillance of #microglia via ERM proteins. These functions are chloride independent. www.science.org/doi/10.1126/...