Apomorphine Modulates FGF-2 Expression In Astrocytes And Promotes Survival Of Dopaminergic Neurons

Parkinson's disease is a common movement disorder characterized by selectiveand progressive loss of nigral dopaminergic (DA) neurons. Although currently there isno cure for this devastating disease, several therapies provide effective relief from thesymptoms. Apomorphine (APO), a mixed D1/D2 dopamine receptor agonist, has beenknown to preferentially control excessive apoptotic rates and reduce excess nitroxide(NO), therefore functioning as a potent antioxidant and affecting DA function. Toaddress novel mechanisms underlying the neuroprotective action of APO, our researchprojects demonstrate that APO stimulates synthesis of neurotrophic factors in astrocytes,thereby effectively preventing midbrain dopaminergic neuron loss.Here we showed that astrocytic FGF-2 expression was robustly induced inresponse to APO in a dose-and time-dependent manner. Conversely, S-APO did notalter FGF-2 levels. APO treatment resulted in export of high molecular weight forms ofFGF-2 to the cytoplasm from the nucleus and increased extracellular release of FGF-2.This APO-induced effect was correlated with activation of D1 and D2 receptors, as itcould be either mimicked by dopamine receptor agonists or partially blocked byantagonists. Activation of the D1 receptor preferentially increased PKA activity, whilstactivation of the D2 receptor only promoted phosphorylation of MAPK. Using RT-PCRand western blot analysis, we first found RGS2 and 5 were expressed in striatalastrocytes. Exposed with APO, RGS2 mRNA decreased by 100% at 30 min. RGS5mRNA was a little more sensitive to APO stimulation and vanished at 10 min. Twohours later mRNA returned to the basal levels. Treatment with APO, RGS2 proteincould be translocated to the membrane from the nucleus. The percentage of astrocytes inwhich nuclear RGS2 protein was rich decreased, while the percentage of glia in whichmore RGS2 protein was transported to the membrane increased 2 times. APO failed toinduce FGF-2 upregulation in astrocytes transfected with pEGFP-RGS2.In this study we characterized SKF83959, a selective agonist for the PI-linkedD1 liked DAR, stimulated IP3 hydrolysis and increased intracellular Ca2+. Via thismolecular mechanism, SKF83959 induced FGF-2 biosynthesis and secretion inastrocytes, thereby promoting survival of TH positive neurons. SKF83959 could notaffect the activity of adenylyl cyclase stimulated by D1 agonist, SKF38393. cAMP/PKAand MEK/MAPK signaling cascades were independent signal transduction pathways.Our chemical modification was to change -OH-, bonded to benzene rings, into-CH3COO-and -CH3O-, yielding two derivant, Z-MF1 and Z-MF2. These two smallchemical compounds also could upregulate FGF-2 expression in astrocytic culture.