A puzzling part of anorexia nervosa (AN) is the maladaptive response to negative energy balance, i.e., maintained starvation and low body weight. Large-scale genetic studies suggest AN is correlated with several metabolic and anthropometric traits, and genetic variants being enriched in microglia. Hypothalamic circuits are fundamental regulators of energy balance, and emerging evidence indicates that interactions between hypothalamic neurons and microglia are central to this energy homeostasis. We hypothesize that a genetic vulnerability in AN results in dysfunction of hypothalamic microglia.

We generated fibroblast-derived induced pluripotent stem cells from AN patients and healthy controls (HC), and differentiated them into microglia, hypothalamic and cortical neurons. Synaptosomes isolated from the neurons were fed to microglia, assessing their phagocytic capacity. Additionally, we performed spatial transcriptomic profiling of hypothalamic microglia in anx/anx and wild-type mice.

AN-derived microglia exhibited significantly reduced phagocytosis of hypothalamic synaptosomes compared to HC, while no difference in phagocytic capacity was observed with cortical synaptosomes, indicating selective aberrant synaptic engulfment of hypothalamic circuits in AN patients. Spatial transcriptomics of hypothalamic microglia revealed differentially expressed genes centered around synaptic pruning in the anorectic anx/anx mouse.

Taken together, our findings suggest that aberrant microglia-driven synaptic pruning of hypothalamic neurons contributes to the maintained negative energy balance in AN.