A Farnesyltransferase Inhibitor Restores Cognitive Deficits in Tsc2(+/–) Mice through Inhibition of Rheb1

Tuberous sclerosis complex (TSC) is caused by mutations inTsc1orTsc2, whose gene products inhibit the small G-protein Rheb1. Rheb1 activates mTORC1, which may cause refractory epilepsy, intellectual disability, and autism. The mTORC1 inhibitors have been used for TSC patients with intractable epilepsy. However, its effectiveness for cognitive symptoms remains unclear. We found a new signaling pathway for synapse formation through Rheb1 activation, but not mTORC1. Here, we show that treatment with the farnesyltransferase inhibitor lonafarnib increased unfarnesylated (inactive) Rheb1 levels and restored synaptic abnormalities in culturedTsc2+/−neurons, whereas rapamycin did not enhance spine synapse formation. Lonafarnib treatment also restored the plasticity-related Arc (activity-regulated cytoskeleton-associated protein) expression in culturedTsc2+/−neurons. Lonafarnib action was partly dependent on the Rheb1 reduction with syntenin. Oral administration of lonafarnib increased unfarnesylated protein levels without affecting mTORC1 and MAP (mitogen-activated protein (MAP)) kinase signaling, and restored dendritic spine morphology in the hippocampi of maleTsc2+/−mice. In addition, lonafarnib treatment ameliorated contextual memory impairments and restored memory-related Arc expression in maleTsc2+/−micein vivo. HeterozygousRheb1knockout in maleTsc2+/−mice reproduced the results observed with pharmacological treatment. These results suggest that the Rheb1 activation may be responsible for synaptic abnormalities and memory impairments inTsc2+/−mice, and its inhibition by lonafarnib could provide insight into potential treatment options for TSC-associated neuropsychiatric disorders.SIGNIFICANCE STATEMENTTuberous sclerosis complex (TSC) is an autosomal-dominant disease that causes neuropsychiatric symptoms, including intractable epilepsy, intellectual disability (ID) and autism. No pharmacological treatment for ID has been reported so far. To develop a pharmacological treatment for ID, we investigated the mechanism of TSC and found that Rheb1 activation is responsible for synaptic abnormalities in TSC neurons. To inhibit Rheb1 function, we used the farnesyltransferase inhibitor lonafarnib, because farnesylation of Rheb1 is required for its activation. Lonafarnib treatment increased inactive Rheb1 and recovered proper synapse formation and plasticity-related Arc (activity-regulated cytoskeleton-associated protein) expression in TSC neurons. Furthermore,in vivolonafarnib treatment restored contextual memory and Arc induction in TSC mice. Together, Rheb1 inhibition by lonafarnib could provide insight into potential treatments for TSC-associated ID.