Constitutive neuronal expression of CCR2 chemokine receptor and its colocalization with neurotransmitters in normal rat brain: Functional effect of MCP‐1/CCL2 on calcium mobilization in primary cultured neurons

Abstract

Chemokines and their receptors are well described in the immune system, where they promote cell migration and activation. In the central nervous system, chemokine has been implicated in neuroinflammatory processes. However, an increasing number of evidence suggests that they have regulatory functions in the normal nervous system, where they could participate in cell communication. In this work, using a semiquantitative immunohistochemistry approach, we provide the first neuroanatomical mapping of constitutive neuronal CCR2 localization. Neuronal expression of CCR2 was observed in the anterior olfactory nucleus, cerebral cortex, hippocampal formation, caudate putamen, globus pallidus, supraoptic and paraventricular hypothalamic nuclei, amygdala, substantia nigra, ventral tegmental area, and in the brainstem and cerebellum. These data are largely in accordance with results obtained using quantitative autoradiography with [(125)I]MCP-1/CCL2 and RT-PCR CCR2 mRNA analysis. Furthermore, using dual fluorescent immunohistochemistry we studied the chemical phenotype of labeled neurons and demonstrated the coexistence of CCR2 with classical neurotransmitters. Indeed, localization of CCR2 immunostaining is observed in dopaminergic neurons in the substantia nigra pars compacta and in the ventral tegmental area as well as in cholinergic neurons in the substantia innominata and caudate putamen. Finally, we show that the preferential CCR2 ligand, MCP-1/CCL2, elicits Ca(2+) transients in primary cultured neurons from various rat brain regions including the cortex, hippocampus, hypothalamus, and mesencephalon. In conclusion, the constitutive neuronal CCR2 expression in selective brain structures suggests that this receptor could be involved in neuronal communication and possibly associated with cholinergic and dopaminergic neurotransmission and related disorders.

The chemokine CCL2 activates p38 mitogen-activated protein kinase pathway in cultured rat hippocampal cells

“…It has previously been reported that CCR2 is expressed on several types of neurons such as human fetal neurons and NT2.N cells (Coughlan et al, 2000) and spinal cord neurons (Gosselin et al, 2005), and that it is constitutively expressed in several regions of the adult rat brain including hippocampus (Banisadr et al, 2005b). The expression of CCR2 has also been reported previously for astrocytes (Andjelkovic et al, 2002;Rezaie et al, 2002).…”

“…Recent studies show that CCL2 and its receptor CCR2 are expressed in the normal hippocampus and that the levels of expression increase during neuroinflammatory conditions associated with CNS injury and disease (Banisadr et al, 2005a;Banisadr et al, 2005b;Galasso et al, 2000;Kalehua et al, 2004;Little et al, 2002;Sakurai-Yamashita et al, 2006;Sheehan et al, 2007;Szaflarski et al, 1998). These results implicate a role for CCL2 in the hippocampus, particularly during neuroinflammatory conditions.…”

“…A similar result was reported for spinal cord cultures (Gosselin et al, 2005) The functional consequence of CCR2 expression in the hippocampus and CCL2 activation of the p38 MAPK pathway remain to be determined. Few studies on the effects of CCL2 on hippocampal neurons have appeared, although one report showed that CCL2 can induce Ca 2+ transients in cultured neurons from several brain regions including the hippocampus (Banisadr et al, 2005b). CCL2 has also been reported to alter neuronal excitability and Ca 2+ signaling in cerebellar neurons (van Gassen et al, 2005) and to reduce inhibitory responses mediated by GABA receptors in spinal cord neurons (Gosselin et al, 2005).…”

“…The hippocampal cultures contain both neurons and glial cells and both cell types have been reported to express CCR2 (Banisadr et al, 2005b). Therefore, both cell types could contribute to the increase in the level of p-p38 MAPK produced by CCL2 exposure.…”

Role of CCR2 in Inflammatory Conditions of the Central Nervous System

“…23 Similarly, an immunohistochemical study of rat brain observed neuronal expression of CCR2 in various regions such as cerebral cortex, hippocampus, caudate putamen, and substantia nigra. 24 Furthermore, CCR2 colocalizes with dopaminergic neurons in the substantia nigra pars compacta and ventral tegmental area, as well as cholinergic neurons in substantia innominata and caudate putamen, suggesting potential neuronal modulating roles of CCR2. 24 Examinations using receptor radiography identified regions of CCL2 binding sites similar to CCR2 receptors identified using immunohistochemistry.…”