mTORC1 signaling in Parkinson disease and L-DOPA-induced dyskinesia: A sensitized matter

Parkinson's disease is caused by the progressive loss of dopamine innervation to the basal ganglia and is commonly treated with the dopamine precursor, L-DOPA. Prolonged administration of L-DOPA results in the development of severe motor complications, or dyskinesia, which seriously hamper its clinical use. Recent evidence indicates that L-DOPA-induced dyskinesia (LID) is associated with persistent activation of the mammalian target of rapamycin complex 1 (mTORC1) in the medium spiny neurons (MSNs) of the striatum, the main component of the basal ganglia. This phenomenon is secondary to the development of a strong sensitization at the level of dopamine D1 receptors, which are abundantly expressed in a subset of MSNs. Such sensitization confers to dopaminergic drugs (including L-DOPA) the ability to activate the extracellular signal-regulated protein kinases 1/2, which, in turn promote mTORC1 signaling. Using a mouse model of LID, we recently showed that administration of the allosteric mTORC1 inhibitor, rapamycin, reduces dyskinesia. This finding is discussed with respect to underlying mechanisms and potential significance for the development of future therapeutic interventions.