Elsevier

Neurobiology of Disease

Volume 49, January 2013, Pages 159-168
Neurobiology of Disease

Lack of CCR5 modifies glial phenotypes and population of the nigral dopaminergic neurons, but not MPTP-induced dopaminergic neurodegeneration

https://doi.org/10.1016/j.nbd.2012.08.001Get rights and content

Abstract

Constitutive expression of C–C chemokine receptor (CCR) 5 has been detected in astrocytes, microglia and neurons, but its physiological roles in the central nervous system are obscure. The bidirectional interactions between neuron and glial cells through CCR5 and its ligands were thought to be crucial for maintaining normal neuronal activities. No study has described function of CCR5 in the dopaminergic neurodegeneration in Parkinson's disease. In order to examine effects of CCR5 on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic neurodegeneration, we employed CCR5 wild type (WT) and knockout (KO) mice. Immunostainings for tyrosine hydroxylase (TH) exhibited that CCR5 KO mice had lower number of TH-positive neurons even in the absence of MPTP. Difference in MPTP (15 mg/kg × 4 times, 2 hr interval)-mediated loss of TH-positive neurons was subtle between CCR5 WT and KO mice, but there was larger dopamine depletion, behavioral impairments and microglial activation in CCR5 deficient mice. Intriguingly, CCR5 KO brains contained higher immunoreactivity for monoamine oxidase (MAO) B which was mainly localized within astrocytes. In agreement with upregulation of MAO B, concentration of MPP + was higher in the substantia nigra and striatum of CCR5 KO mice after MPTP injection. We found remarkable activation of p38 MAPK in CCR5 deficient mice, which positively regulates MAO B expression. These results indicate that CCR5 deficiency modifies the nigrostriatal dopaminergic neuronal system and bidirectional interaction between neurons and glial cells via CCR5 might be important for dopaminergic neuronal survival.

Highlights

► We examined effects of CCR5 deficiency on the dopamine neuron via MPTP animal model. ► CCR5 deletion led to loss of nigral dopamine neurons and microglial activation. ► Monoamine oxidase B was elevated in astrocytes of CCR5 null mice. ► MPTP neurotoxicity was more severe in CCR5 knockout mice. ► We report importance of cross talk between glia and neurons via CCR5.

Introduction

Parkinson's disease (PD) is the third most prevalent neurodegenerative disease after Alzheimer's disease and dementia with Lewy body disease (Smeyne and Jackson-Lewis, 2005). The neurodegenerative disorder is pathologically characterized by dopaminergic neurodegeneration in the substantia nigra and consequent depletion of dopamine in the striatum. Until now, specific underlying mechanisms by which the dopaminergic neurons are degenerated in PD brains remain to be elucidated.

The 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD model has been extensively used since the system recapitulates several cardinal features of PD including dopaminergic neuronal loss in the substantia nigra, depletion of dopamine level in the striatum and impairment in locomotor activity. MPTP-mediated dopaminergic neurotoxicity is elicited by 1-methyl-4-phenyl pyridium (MPP +), an active neurotoxic metabolite of MPTP which is mainly produced by monoamine oxidase (MAO) B in astrocytes (Youdim et al., 2006). Once MPP + is released from astrocytes, the chemical is taken up by dopaminergic neurons through the dopamine transporter (DAT) leading to the neuronal death. MAO B is a key player in MPTP neurotoxicity as administration of deprenyl, a selective MAO B inhibitor prevents MPTP-induced dopaminergic neurotoxicity (Heikkila et al., 1985, Langston et al., 1984). Evidence showed astroglial activation and increased MAO B activity with aging (Alper et al., 1999). In addition, MAO B activity is elevated in astrocytes around beta-amyloid-positive plaques (Gulyas et al., 2011). These findings suggest that rise in MAO B activity might be related to pathogenesis of neurodegenerative diseases. A recent study showed that overexpression of MAO B in astrocytes causes dopaminergic neurodegeneration (Mallajosyula et al., 2008). In the study, they showed that overexpressed MAO B elevated production of membrane permeant H2O2 which could oxidize dopamine within dopaminergic neurons. This was accompanied by mitochondrial complex I dysfunction and increased mitochondrial superoxide resulting in dopaminergic neuronal death.

Chemokines and their corresponding receptors are broadly expressed in the central nervous system and regulate glial and neuronal cell functions (Asensio and Campbell, 1999). Emerging evidence indicates that chemokine receptors are involved in neuronal death and hence neurodegenerative diseases (Cartier et al., 2005). Among various chemokine receptors, CC chemokine receptor 5 (CCR5) is stimulated by three β-chemokines: CCL3/macrophage inflammatory protein-1a (MIP 1α), CCL4/MIP-1β and CCL5. Constitutive CCR5 expression has been detected in astrocytes, microglia and neurons (Sorce et al., 2011). Although roles of CCR5 in the central nervous system are obscure, bidirectional interactions between neuron and glial cells through CCR5 and its ligands are thought to be crucial for maintaining normal neuronal activities. In support, RANTES attenuated inflammatory response of microglia after motor neuron injury via CCR5, and demise of motor neurons was accelerated in CCR5 null mice (Gamo et al., 2008). Moreover, CCR5 deficient mice seemed to be vulnerable to ischemic injury (Sorce et al., 2010). In the study, ischemic brain injury was induced by occlusion of the middle artery, and resultant motor deficit and infarction were worse in CCR5 knockout (KO) mice than wild type (WT) mice.

We have shown astroglial activation in the brains of CCR5 knockout (KO) mice, which might be mediated by compensatory increase in CCL2-mediated signaling (Lee et al., 2009). CCL2 could activate microglia and astrocytes resulting in activation of p38 mitogen-activated protein kinase (MAPK) (McMahon and Malcangio, 2009), which might upregulate MAO B expression (De Zutter and Davis, 2001, Wong et al., 2002). We hypothesized that CCR5 deficiency might be related to astroglial activation and concurrent increase in MAO B activity. Here, we show that CCR5 KO mice have lower number of the nigral dopaminergic neurons, and worse MPTP-mediated impairments in the nigrostriatal dopaminergic system than WT mice.

Section snippets

Animals and MPTP treatment

CCR5 KO mice on the C57BL6/J background were purchased from the Jackson Laboratory (Bar Harbor, ME, USA). CCR5 KO mice had no overt developmental abnormalities. We bred CCR5 KO mice with C57BL6/J mice to obtain CCR5 heterozygous mice. Then, male and female CCR5 heterozygous mice were bred to generate CCR5 WT and KO mice. Genotypes of mice were confirmed by polymerase chain reaction. Detection of CCR5 WT allele was achieved by using primers 5′-CAGGCAACAGAGACTCTTGG-3′ (oIMR6916) and

Dopaminergic neurodegeneration in the nigrostriatal pathway

We evaluated MPTP-neurotoxicity using immunohistochemical stainings for TH. There were abundant TH-positive neurons in the substantia nigra of CCR5 KO and WT mice (Fig. 1A). However, our unexpected finding was that naive CCR5 KO mice had lower number of TH-positive neurons throughout the substantia nigra than CCR5 WT mice. This observation was verified by stereological counting for dopaminergic neurons in the substantia nigra. In agreement with the observation, there was a decrease in density

Discussion

Apart from chemotactic activity, chemokines mediate neuron–glia bidirectional communication in physiological and pathological conditions through their receptors. Chemokines are also involved in development of the nervous system (Westmoreland et al., 2002). CCR5 is one of the most studied chemokine receptors since it has been discovered that HIV infects T-cells through the chemokine receptor (Dean et al., 1996, Wu et al., 2002). However, few studies have described its role in dopaminergic

Conclusions

We demonstrated that there was a decrease in the number of TH-positive neurons of CCR5 KO mice compared with CCR5 WT. This observation was accompanied by microglial activation and increased MAO B expression in the substantia nigra of CCR5 null mice. Furthermore, the number of the dopaminergic neurons, striatal dopamine level and locomotor activity were lower in CCR5 KO mice in comparison to CCR5 WT mice. These results might be partially attributable to elevated MAO B expression in the nigra of

Acknowledgment

This work was supported by the National Research Foundation Grant (MRC, 2010‐0029480), Priority Research Center Program (2011‐0031403), and the Regional Core Research Program (Chungbuk BIT research-oriented University Consortium) funded by the Ministry of Education, Science and Technology of Korea. This work was also supported by the Korean Health Technology R&D Project (A101836) funded by Ministry of Health, Welfare and Family Affairs of Korea. We disclose that there is no conflict of interest.

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