Clozapine-induced human microglial exosomes impair neurites and cognition

Clozapine is the most effective treatment for treatment-resistant schizophrenia but has been linked to cognitive impairment and brain volume reductions. The potential mechanisms underlying these effects remain unclear. Microglial exosomes, which carry microRNAs (miRNAs) and other cargo, act as immune-neuron communication vectors capable of modulating neuronal function and cognition.

We compared cognitive performance and inflammatory markers across clozapine-treated individuals, haloperidol-treated individuals, and healthy controls. Human microglial cells were treated with clozapine and assessed for phenotypic changes and exosome production. Exosomes from control and clozapine-treated microglia were applied to neuroblastoma cells and primary murine cortical neurons to assess neurite outgrowth and brain-derived neurotrophic factor (BDNF) expression. C. elegans were exposed to exosomes and evaluated for lifespan, healthspan markers, and cognitive function via olfactory associative learning assays. Exosomal miRNA cargo was characterized by small RNA sequencing.

Clozapine-treated individuals exhibited elevated systemic inflammatory markers and lower cognitive performance compared with healthy controls. Clozapine altered microglial morphology, reduced proliferation and migration, and significantly increased exosome production. Small RNA sequencing identified six dysregulated miRNAs in clozapine-induced microglial exosomes, including upregulation of miR-34a-5p. Exposure of neurons to clozapine-induced exosomes reduced neurite length, branch points, and BDNF expression. In C. elegans, clozapine-induced exosomes reduced lifespan and severely impaired learning and short-term memory.

These findings identify a neuroimmune exosomal pathway through which clozapine-exposed microglia can impair neuronal structure and cognition, associated with dysregulated miRNA cargo. This work provides a framework linking microglial immune signalling, extracellular vesicle biology, and cognitive vulnerability during clozapine exposure.