Genetic Activation of mTORC1 Signaling Worsens Neurocognitive Outcome after Traumatic Brain Injury

Abstract

Although the mechanisms that contribute to the development of traumatic brain injury (TBI)-related deficits are not fully understood, it has been proposed that altered energy utilization may be a contributing factor. The tuberous sclerosis complex, a heterodimer composed of hamartin/Tsc-1 and tuberin/Tsc-2, is a critical regulatory node that integrates nutritional and growth signals to govern energy using processes by regulating the activity of mechanistic Target of Rapamycin complex 1 (mTORC1). mTORC1 activation results in enhanced protein synthesis, an energy consuming process. We show that mice that have a heterozygous deletion of Tsc2 exhibit elevated basal mTORC1 activity in the cortex and the hippocampus while still exhibiting normal motor and neurocognitive functions. In addition, a mild closed head injury (mCHI) that did not activate mTORC1 in wild-type mice resulted in a further increase in mTORC1 activity in Tsc2^+/KO mice above the level of activity observed in uninjured Tsc2^+/KO mice. This enhanced level of increased mTORC1 activity was associated with worsened cognitive function as assessed using the Morris water maze and context discrimination tasks. These results suggest that there is a threshold of increased mTORC1 activity after a TBI that is detrimental to neurobehavioral performance, and interventions to inhibit excessive mTORC1 activation may be beneficial to neurocognitive outcome.