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bioRxiv2023

Environmental enrichment and physical exercise prevent stress-induced behavioral and blood-brain barrier alterations via Fgf2

Chronic stress can promote loss of blood-brain barrier (BBB) integrity leading to passage of circulating inflammatory mediators in mood-regulating brain areas and establishment of depressive behaviors. Conversely, neurovascular adaptations favoring resilience to stress exposure remain undetermined. Here, we report that environmental enrichment dampens stress-induced loss of endothelial tight junction protein Claudin-5 (Cldn5) along with anxiety- and depression-like behaviors in mice via an increase in fibroblast growth factor 2 (Fgf2). Treatment of mouse and human endothelial cells with Fgf2 preceding an immune challenge with the proinflammatory cytokine TNF, elevated after chronic stress and in depression, reduces BBB dysfunction, and altered cell signaling. Coping with voluntary physical exercise also protects the BBB from stress deleterious effects by increasing Fgf2 preventing Cldn5 loss, exacerbated inflammation, and social avoidance. Circulating FGF2 level is linked with depression severity and symptomatology in humans supporting involvement of this growth factor in mood disorders and stress-induced BBB changes.

neuroscience↗

bioRxiv2022

Chronic stress exposure alters the gut barrier: sex-specific effects on microbiota and jejunum tight junctions

Major depressive disorder (MDD) is the leading cause of disability worldwide. However, 30-50% of patients are unresponsive to commonly prescribed antidepressants, highlighting untapped causal biological mechanisms. Dysfunction in the microbiota-gut-brain axis, the bidirectional communications between the central nervous system and gastrointestinal tract that are modulated by gut microorganisms, has been implicated in MDD pathogenesis. Exposure to chronic stress disrupts blood-brain barrier integrity, still, little is known about intestinal barrier function in these conditions particularly for the small intestine where most food and drug absorption takes place. Thus, here we investigate how chronic social or variable stress, two mouse models of depression, impact the jejunum (JEJ) intestinal barrier in males and females. Mice were subjected to stress paradigms followed by analysis of gene expression profiles of intestinal barrier-related targets, fecal microbial composition, and blood-based markers. Altered microbial populations as well as changes in gene expression of JEJ tight junctions were observed depending on the type and duration of stress, with sex-specific effects. We took advantage of machine learning to characterize in detail morphological tight junction properties identifying a cluster of ruffled junctions in stressed animals. Junctional ruffling is associated with inflammation, so we evaluated if LPS injection recapitulates stress-induced changes in the JEJ and observed profound sex differences. Finally, LPS-binding protein (LBP), a marker of gut barrier leakiness, was associated with stress vulnerability in mice and translational value was confirmed on blood samples from women with MDD. Our results provide evidence that chronic stress disrupts intestinal barrier homeostasis in conjunction with the manifestation of depressive-like behaviors in a sex-specific manner in mice and possibly, human depression.

neuroscience↗