A strong bidirectional link between metabolic and psychiatric disorders exists; yet, the molecular basis underlying this interaction remains unresolved. Here we explored the role of the brown adipose tissue (BAT) as modulatory interface, focusing on the involvement of uncoupling protein 1 (UCP-1), a key metabolic regulator highly expressed in BAT, in the control of emotional behavior. Male and female constitutive UCP-1 knock-out (KO) mice were used to investigate the consequences of UCP-1 deficiency on anxiety-related and depression-related behaviors under mild thermogenic (23°C) and thermoneutral (29°C) conditions. UCP-1 KO mice displayed a selective enhancement of anxiety-related behavior exclusively under thermogenic conditions, but not at thermoneutrality. Neural and endocrine stress mediators were not affected in UCP-1 KO mice, which showed an activation of the integrated stress response alongside enhanced fibroblast-growth factor-21 (FGF-21) levels. However, viral-mediated overexpression of FGF-21 did not phenocopy the behavioral alterations of UCP-1 KO mice and blocking FGF-21 activity did not rescue the anxiogenic phenotype of UCP-1 KO mice. No effects of surgical removal of the intrascapular BAT on anxiety-like behavior or FGF-21 levels were observed in either UCP-1 KO or WT mice. We provide evidence for a novel role of UCP-1 in the regulation of emotions that manifests as inhibitory constraint on anxiety-related behavior, exclusively under thermogenic conditions. We propose this function of UCP-1 to be independent of its activity in the BAT and likely mediated through a central role of UCP-1 in brain regions with converging involvement in energy and emotional control.SIGNIFICANCE STATEMENT In this first description of a temperature-dependent phenotype of emotional behavior, we propose uncoupling protein-1 (UCP-1), the key component of the thermogenic function of the brown adipose tissue, as molecular break controlling anxiety-related behavior in mice. We suggest the involvement of UCP-1 in fear regulation to be mediated through its expression in brain regions with converging roles in energy and emotional control. These data are important and relevant in light of the largely unexplored bidirectional link between metabolic and psychiatric disorders, which has the potential for providing insight into novel therapeutic strategies for the management of both conditions.
Keywords: anxiety; brown adipose tissue; fear; mouse behavior; uncoupling protein 1.
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