Adolescent social isolation decreases colonic goblet cells and impairs spatial cognition through the reduction of cystine

Negative experiences during adolescence, such as social isolation (SI), bullying, and abuse, increase the risk of psychiatric diseases in adulthood. However, the pathogenesis of psychiatric diseases induced by these factors remain poorly understood. In adolescents, stress affects the intestinal homeostasis in the gut-brain axis. This study determined whether adolescent SI induces behavioral abnormalities by disrupting colonic function. Adolescent mice exposed to SI exhibit spatial cognitive deficits and microglial activation in the hippocampus (HIP). SI decreased the differentiation of mucin-producing goblet cells, which was accompanied by alterations in the composition of the gut microbiota, particularly the depletion of mucin-feeding bacteria. Treatment with rebamipide, which promotes goblet cell differentiation in the colon, attenuated SI-induced spatial cognitive deficits and microglial activation in the HIP and decreased cystine, a downstream metabolite of homocysteine. Treatment with cystine ameliorated SI-induced spatial cognitive deficits and increased microglial C-C motif chemokine ligand 7 (CCL7) levels in the HIP. Inhibition of CCL7 receptors by antagonists of CC motif chemokine receptors 2 (CCR2) and 3 (CCR3) in the HIP prevented spatial cognitive deficits induced by SI. Infusion of CCL7 into the HIP following microglial ablation with clodronate liposome induced spatial cognitive deficits. These findings suggest that adolescent SI decreases serum cystine levels by damaging the colonic goblet cells, resulting in spatial cognitive deficits by triggering microglial activation in the HIP. Our results indicate that increased CCL7 expression in hippocampal microglia may contribute to spatial cognitive deficits by activating CCR2 and CCR3.