Persistent increase in olfactory type G-protein alpha subunit levels may underlie D1 receptor functional hypersensitivity in Parkinson disease.
Although L-dopa remains the most effective treatment of Parkinson disease, its long-term administration is hampered by the appearance of dyskinesia. Hypersensitivity of dopamine D1 receptors in the striatum has been suggested to contribute to the genesis of these delayed adverse effects. However, D1 receptor amounts are unchanged in Parkinson disease, suggesting alterations of downstream effectors. In rodents, striatal D1 receptors activate adenylyl cyclase through olfactory type G-protein alpha subunit (Galphaolf) and G-protein gamma 7 subunit (Ggamma7). We found that Galphaolf was enriched in human basal ganglia and was markedly diminished in the putamen of patients with Huntington disease, in relation with the degeneration of medium spiny neurons. In contrast, in the putamen of patients with Parkinson disease, Galphaolf and Ggamma7 levels were both significantly increased. In the rat, the degeneration of dopamine neurons augmented Galphaolf levels in the striatal neurons, specifically at the plasma membrane, an effect accounting for the increase of D1 response on cAMP production in dopamine-depleted striatum. In lesioned rats, Galphaolf levels were normalized by a 3 week treatment with l-dopa or a D1 agonist but not with aD2-D3 agonist, supporting a Galphaolf regulation by D1 receptor usage. In contrast, the increases of Galphaolf levels in patients were not affected by the duration of l-dopa treatment but correlated with duration of disease. In conclusion, our results revealed in the parkinsonian putamen a prolonged elevation of Galphaolf levels that may lead to a persistent D1 receptor hypersensitivity and contribute to the genesis of long-term complications of L-dopa.
Corvol
Jean-Christophe
JC
Institut National de la Santé et de la Recherche Médicale-Université Pierre et Marie Curie Unité 536, Institut du Fer à Moulin, 75005 Paris, France. jean-christophe.corvol@psl.ap-hop-paris.fr
Muriel
Marie-Paule
MP
Valjent
Emmanuel
E
Féger
Jean
J
Hanoun
Naïma
N
Girault
Jean-Antoine
JA
Hirsch
Etienne C
EC
Hervé
Denis
D
D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D000978:Antiparkinson Agents / Q000494:pharmacology; D003342:Corpus Striatum / Q000378:metabolism / Q000473:pathology; D005260:Female; D044385:GTP-Binding Protein alpha Subunits / Q000378:metabolism*; D006801:Humans; D007980:Levodopa / Q000494:pharmacology; D008297:Male; D008875:Middle Aged; D016627:Oxidopamine / Q000494:pharmacology; D010300:Parkinson Disease / Q000378:metabolism* / Q000473:pathology; D011699:Putamen / Q000378:metabolism* / Q000473:pathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017447:Receptors, Dopamine D1 / Q000378:metabolism*; D013565:Sympatholytics / Q000494:pharmacology
D000978:Antiparkinson Agents; D044385:GTP-Binding Protein alpha Subunits; D017447:Receptors, Dopamine D1; D013565:Sympatholytics; D007980:Levodopa; D016627:Oxidopamine