Nuclear receptor Nurr1 agonists enhance its dual functions and improve behavioral deficits in an animal model of Parkinson’s disease

Abstract

Parkinson's disease (PD), primarily caused by selective degeneration of midbrain dopamine (mDA) neurons, is the most prevalent movement disorder, affecting 1-2% of the global population over the age of 65. Currently available pharmacological treatments are largely symptomatic and lose their efficacy over time with accompanying severe side effects such as dyskinesia. Thus, there is an unmet clinical need to develop mechanism-based and/or diseasemodifying treatments. Based on the unique dual role of the nuclear orphan receptor Nurr1 for development and maintenance of mDA neurons and their protection from inflammation-induced death, we hypothesize that Nurr1 can be a molecular target for neuroprotective therapeutic development for PD. Here we show successful identification of Nurr1 agonists sharing an identical chemical scaffold, 4-amino-7-chloroquinoline, suggesting a critical structure-activity relationship. In particular, we found that two antimalarial drugs, amodiaquine and chloroquine stimulate the transcriptional function of Nurr1 through physical interaction with its ligand binding domain (LBD). Remarkably, these compounds were able to enhance the contrasting dual functions of Nurr1 by further increasing transcriptional activation of mDA-specific genes and further enhancing transrepression of neurotoxic proinflammatory gene expression in microglia. Importantly, these compounds significantly improved behavioral deficits in 6-hydroxydopamine lesioned rat model of PD without any detectable signs of dyskinesia-like behavior. These findings offer proof of principle that small molecules targeting the Nurr1 LBD can be used as a mechanismbased and neuroprotective strategy for PD.P D is primarily caused by selective degeneration of midbrain dopamine (mDA) neurons and is the most prevalent movement disorder, affecting 1-2% of the global population over the age of 65 (1-3). Currently available pharmacological treatments [e.g., L-3,4-dihydroxyphenylalanine (L-DOPA)] are largely symptomatic and lose their efficacy over time, with accompanying severe side effects such as dyskinesia. Thus, there is an unmet clinical need to develop mechanism-based and/or disease-modifying treatments (2, 3).During the last two decades, many intrinsic signals and extrinsic transcription factors have been identified to play critical roles for mDA neuron development (4-6). In particular, development of mDA neurons is dependent on two major signaling molecules, Sonic hedgehog (Shh) and wingless-type MMTV integration site family, member 1 (Wnt1), and their downstream factors. These two critical pathways (i.e., Shh-FoxA2 and Wnt1-Lmx1a) merge to control the expression of the orphan nuclear receptor related 1 protein (Nurr1) (7), suggesting that Nurr1 is a key regulator of mDA neurons. Indeed, Nurr1 [also known as nuclear receptor subfamily 4, group A, member 2 (NR4A2)] is essential not only for development (8-10) but also for maintenance of mDA neurons in adult brains (11). In addition, a recent study demonstrated that Nurr1 plays critical roles ...

Daphnane and Phorbol Diterpenes, Anti-neuroinflammatory Compounds with Nurr1 Activation from the Roots and Stems of <i>Daphne genkwa</i>

“…Horse serum, penicillin, streptomycin, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) were purchased from Invitrogen (Carlsbad, CA, U.S.A. Nurr1 Assay Nurr1 activity was measured as previously reported. 14) In brief, SK-N-BE(2)-C human neuroblastoma cells were maintained in DMEM supplemented with 10% FBS. All culture media contained 100 units/mL penicillin and 100 µg/mL streptomycin.…”

“…14) In brief, BV-2 cells, a microglial-like mouse cell line, were maintained in six-well culture plates (Corning Costar, Corning, NY, U.S.A.) at a density of 1.0×10 5 cells/ well in DMEM supplemented with 10% FBS heat-inactivated at 56°C for 30 min, 2 mM L-glutamine, and 1X Pen-Strep (Invitrogen). To begin the experiment, BV-2 cells were washed with DMEM and treated with LPS (1 µg/mL) in the presence or absence of test compounds.…”

“…Indeed, small-molecule Nurr1 agonists such as amodiaquine have been reported to improve behavioral deficits in animal models of PD. 14) During screening for Nurr1 activators from Korean medicinal plants, we previously reported that a methanol extract of the stem and root portions of Daphne genkwa SIEBOLD et ZUCC. (Thymelaeaceae) and daphnane-type diterpenes, yuanhuacin (1) and genkwanine N, had Nurr1-activating activity as well as neuroprotective effects in an animal model of PD.…”

Toward neuroprotective treatments of Parkinson’s disease

“…11 and 12). In particular, we recently identified three compounds from a Food and Drug Administration-approved drug library: that is, two antimalarial drugs, amodiaquine (AQ) and chloroquine (CQ), and a painrelieving drug (glafenine), which all share the 4-amino-7-chloroquinoline scaffold, strongly supporting a structure-activity relationship (20). These compounds appear to directly bind to Nurr1's LBD, as determined by surface plasmon resonance assays, fluorescence-quenching analysis, radioligand-binding assay using [ 3 H]-CQ, and NMR.…”

“…These compounds appear to directly bind to Nurr1's LBD, as determined by surface plasmon resonance assays, fluorescence-quenching analysis, radioligand-binding assay using [ 3 H]-CQ, and NMR. Notably, AQ and CQ enhanced Nurr1's contrasting functions stimulating expression of mDAspecific proteins (e.g., TH expression), repression of microglial activation, and neurotoxic cytokine gene expression, resulting in significant neuroprotective effects in a 6-OHDA-lesioned rat model of PD without any sign of dyskinesia-like side effects (20). Thus, it will be of great interest to address whether small molecules that directly activate Nurr1 and Nurr1:RXRα can exhibit a synergistic effect for neuroprotection of mDA neurons.…”