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. 2018 Apr;15(2):459-469.
doi: 10.1007/s13311-018-0603-x.

Cannabinoid CB1 and CB2 Receptors, and Monoacylglycerol Lipase Gene Expression Alterations in the Basal Ganglia of Patients With Parkinson's Disease

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Free PMC article

Cannabinoid CB1 and CB2 Receptors, and Monoacylglycerol Lipase Gene Expression Alterations in the Basal Ganglia of Patients With Parkinson's Disease

Francisco Navarrete et al. Neurotherapeutics. .
Free PMC article

Abstract

Previous studies suggest that the endocannabinoid system plays an important role in the neuropathological basis of Parkinson's disease (PD). This study was designed to detect potential alterations in the cannabinoid receptors CB1 (CB1r) and CB2 (A isoform, CB2Ar), and in monoacylglycerol lipase (MAGL) gene expression in the substantia nigra (SN) and putamen (PUT) of patients with PD. Immunohistochemical studies were performed to identify precise CB2r cellular localization in the SN of control and PD patients. To ensure the validity and reliability of gene expression data, the RNA integrity number (RIN) was calculated. CB1r, CB2Ar, and MAGL gene expressions were evaluated by real-time polymerase chain reaction (real-time PCR) using Taqman assays. Immunohistochemical experiments with in situ proximity ligation assay (PLA) were used to detect the precise cellular localization of CB2r in neurons, astrocytes, and/or microglia. All RIN values from control and PD postmortem brain samples were > 6. CB1r gene expression was unchanged in the SN but significantly higher in the PUT of patients with PD. CB2Ar gene expression was significantly increased (4-fold) in the SN but decreased in the PUT, whereas MAGL gene expression was decreased in the SN and increased in the PUT. Immunohistochemical analyses revealed that CB2r co-localize with astrocytes but not with neurons or microglial cells in the SN. The results of the present study suggest that CB1r, CB2r, and MAGL are closely related to the neuropathological processes of PD. Therefore, the pharmacological modulation of these targets could represent a new potential therapeutic tool for the management of PD.

Keywords: Basal ganglia; CB1 and CB2 receptor; Gene expression; Immunohistochemistry; MAGL; Parkinson’s disease.

Figures

Fig. 1
Fig. 1
Total RNA integrity number (RIN) evaluation in the substantia nigra (SN) and putamen (PUT) of healthy controls (n = 16 and n = 23, respectively) and patients with Parkinson’s disease (n = 25 and n = 28, respectively). (A, B) Representative electropherogram images of mean RIN values from SN and PUT brain regions, respectively. (C) RIN values summary table; gray boxes contain global mean values
Fig. 2
Fig. 2
Cannabinoid CB1 receptor (CB1r), cannabinoid CB2 receptor A isoform (CB2Ar), and monoacylglycerol lipase (MAGL) gene expression analyses by real-time polymerase chain reaction (real-time PCR). Gene expression in patients with Parkinson’s disease (PD) is expressed relative to healthy controls. Data are expressed as mean ± SEM of 2–ΔΔCt. CB1r, CB2Ar, and MAGL gene expression in the substantia nigra (SN) (A, C, and E, respectively) and PUT (B, D, and F, respectively). *Significantly different (p < 0.05) from controls
Fig. 3
Fig. 3
Localization of cannabinoid CB2 receptor (CB2r) in the substantia nigra (SN) pars compacta. Dopaminergic neurons were identified by tyrosine hydroxylase (TH) immunostain and color-coded in blue. Astrocytes were evidenced following glial fibrillary acidic protein (GFAP) immunostain and are shown in green. The observed glial reaction was far more intense in brains from patients with Parkinson’s disease (PD) than in the corresponding control samples. Furthermore, the presence of CB2r (as assessed with the proximity ligation assay (PLA) stain, illustrated in red) was mostly seen in pericellular astrocytical processes surrounding TH+ neuronal somata. It seems clear that the intensity of CB2r immunostaining was always higher in samples coming from PD brains. The presence of self-fluorescent neuromelanin pigment was often observed in the cytoplasm of TH+ neurons. Scale bar is 10 μm in all panels
Fig. 4
Fig. 4
Localization of the cannabinoid CB2 receptor (CB2r) in the substantia nigra (SN) pars compacta. Dopaminergic neurons were identified by tyrosine hydroxylase (TH) immunostain and color-coded in blue. Microglial cells were evidenced following ionized calcium-binding adapter molecule 1 (Iba1) immunostain and color-coded in green (arrows), whereas the proximity ligation assay (PLA) stain was done to elucidate the presence of CB2r (red channel). CB2r was abundantly found in extracellular locations other than dopaminergic and microglial cells. Scale bar is 10 μm in all panels. LB = Lewy body

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