D1/D5 inverse agonists restore the normal excitability of striatal cholinergic interneurons in dyskinesia

CECILIA TUBERT; PAZ, RODRIGO MANUEL; STAHL, AGOSTINA MONICA; LORENA RELA; MURER, MARIO GUSTAVO

Congreso; FALAN; 2022

Striatal cholinergic interneurons (SCIN) are the main source of striatal ACh. In Parkinson´s disease (PD), dopaminergic neurons that innervate the striatum degenerate, leading to a relative increase of cholinergic function that contributes to the generation of PD symptoms (Barbeau A, 1962, C Med Ass J). The gold standard therapy for PD is levodopa (L-dopa) administration, but prolonged treatment may result in adverse effects like dyskinesia (Kalia LV & Lang AE, 2015, Lancet). This highlights the need for the development of alternative therapies for patients with advanced PD. Previously, we found that SCIN are hyperexcitable in a mouse model of PD as a result of a reduction in a current mediated by Kv1.3 channels, which is not explained by reduced channel expression (Tubert C et al., 2016, Cell rep). Contrary to expectations, in a recent study we report that L-dopa administration at doses that induce dyskinesia not only does not revert the hyperexcitability observed in SCIN of parkinsonian mice but instead exacerbates the already increased excitability of these cells through an undetermined mechanisms likely involving stimulation of the D1/D5 receptors in SCIN (Paz RM et al., 2021, Mov dis). Our aim is to identify these mechanisms. Because this enhanced hyperexcitability is observed in the off L-dopa medication condition, 24 hs after the end of a chronic L-dopa treatment, we hypothesize that physiologic activation of D1/D5 receptors results in a reduction of Kv1.3 current and a consequent increase in excitability, and that an alteration in D1/D5 signaling contributes to the enhancement of hyperexcitability observed in the off L-dopa medication condition. With ex-vivo electrophysiological recordings and classic pharmacology, we found that, in physiological conditions, activation of D1/D5 receptors increases SCIN excitability by reducing Kv1.3 current through a signaling pathway involving cAMP and Erk1/2 kinase. Moreover, in parkinsonian and dyskinetic mice, antagonizing cAMP signaling in SCIN restores a normal excitability. Finally, our results suggest that the cAMP pathway overactivity is due to an increased ligand-independent activity of D1/D5 receptors that entails an increased cAMP production followed by a reduction in Kv1.3 current, and that reducing their ligand-independent activity with D1/D5 inverse agonists restore SCIN’s normal physiology. Our work unravels a signaling pathway involved in the dysregulation of membrane currents causing SCIN hiperexcitability in parkinsonian mice treated with L-dopa. These changes persist during off-medication periods due to tonic mechanisms that can be acutely reversed by pharmacological interventions. Thus, targeting the D5-cAMP-ERK1/2 signaling pathway selectively in SCIN may have therapeutic effects in duskinesia by restoring the normal SCIN function.