The Role of TCF7L2 in Regulating Energy Metabolism in Thalamocortical Circuitry and its Broader Impact on Social Behavior
Psychiatric and metabolic disorders often co-occur. While shared genetic factors and cellular dysfunctions are implicated, the underlying molecular mechanisms remain poorly understood. TCF7L2, a risk gene for type 2 diabetes and autism spectrum disorder, is highly expressed in the thalamus--a brain region extensively interconnected with the cortex, playing a key role in sensory processing, motor control, and behavioral regulation. Given its known role as a transcription factor regulating systemic energy metabolism, we explored its potential contribution to brain metabolism and behavior. To this end, we used a conditional knockout model with postnatal TCF7L2 loss in the thalamus and partial deficiency in the pancreas. Tcf7l2 knockout mice exhibited social deficits and reduced motor habituation. In parallel, they also developed systemic glucose intolerance, modelling the psychiatric-metabolic comorbidity. Thalamic depletion of TCF7L2 resulted in elevated inhibitory phosphorylation of the pyruvate dehydrogenase --an enzymatic gatekeeper for pyruvate utilization in energy production--in the thalamus and cortex. This was accompanied by altered thalamic and cortical metabolism, characterized by reduced efficiency of pyruvate oxidation alongside enhanced oxidation of fatty acids and ketone bodies. Notably, a ketogenic diet alleviated metabolic dysregulation in the brain and normalized some social behaviors in knockout mice. These findings suggest that impaired energy metabolism in the thalamocortical circuitry may represent one of the pathogenic mechanisms underlying neuropsychiatric symptoms.