Circadian chaos: the role of bile acids in chronic stress-induced insomnia

Chronic stress is a major risk factor for insomnia, yet the molecular mechanisms linking stress-induced gut dysbiosis and bile acid (BA) metabolism to circadian disruption remain poorly understood. A rat model of chronic unpredictable mild stress combined with modified multiple platform sleep deprivation was established. Sleep-wake patterns were assessed by PiezoSleep monitoring. Anxiety- and depression-like behaviors were evaluated using the open field test, elevated plus maze, and tail suspension test. Spatial memory was tested with the Morris water maze. Gut microbiota was profiled via 16S rRNA sequencing. Serum total BAs were measured by enzymatic cycling, and hypothalamic BA metabolites were quantified by targeted UPLC-MS/MS. The BA sequestrant cholestyramine was administered to evaluate therapeutic effects. To test BA sufficiency, a separate cohort received oral deoxycholic acid (DCA) for three days with subsequent sleep and molecular assessments. Model rats showed marked sleep loss, a reversed day/night sleep ratio, anxiety- and depression-like behaviors, and cognitive deficits. Their gut microbiota exhibited reduced Firmicutes along with increased Bacteroidetes and Proteobacteria . Serum total BAs and hypothalamic levels of deoxycholic acid were significantly elevated. This was accompanied by upregulation of TGR5, ERK, and CK1ε, depletion of nuclear PER2, and disrupted the rhythmic secretion of Clock and Bmal1 . Cholestyramine lowered BA loads, restored PER2 nuclear localization, normalized the rhythmic gene expression of Clock and Bmal1 , and reversed all behavioral and sleep abnormalities. Importantly, DCA alone phenocopied the core sleep, molecular, and circadian disturbances observed in the model rats. BA overload, especially DCA, drives circadian and sleep disturbances via the hypothalamic TGR5-ERK-CK1ε-PER2 pathway. BA sequestering represents a promising strategy for treating insomnia with comorbid negative emotional states.