Ž . European Journal of Pharmacology 374 1999 309–313 www.elsevier.nlrlocaterejphar Short communication ž / Functional expression of the fractalkine CX C receptor and its 3 regulation by lipopolysaccharide in rat microglia Erik W.G.M. Boddeke a, ) , Inge Meigel b , Stefan Frentzel b , Knut Biber a , Li Q. Renn c , Peter Gebicke-Harter c ¨ a Department of Medical Physiology, UniÕersity of Groningen, Bloemsingel 10, 9712 KZ Groningen, Netherlands b NoÕartis Pharma, NS Research, CH4002 Basel, Switzerland c Department of Psychiatry, UniÕersity of Freiburg, 79104 Freiburg, Germany Received 19 April 1999; accepted 22 April 1999 Abstract Functional expression of CX CR1, a recently discovered receptor for the chemokine fractalkine, was investigated in cultured rat 3 Ž . microglia. Reverse transcriptase polymerase chain reaction PCR experiments show abundant expression of fractalkine receptor mRNA in microglia. mRNA expression of fractalkine was undetectable in astrocytes and microglia but was very strong in cortical neurons. Ž . Incubation of microglia with lipopolysaccharide 100 ngrml transiently suppressed expression of fractalkine receptor mRNA. Ž y10 y8 . Fractalkine induced a concentration-dependent 10 –10 M and, at high concentrations, oscillatory mobilization of intracellular Ca 2q in microglia The concentration–response curve of fractalkine was shifted to the right after 12 h incubation with lipopolysaccharide. It is concluded that treatment with endotoxin downregulates expression of fractalkine receptor mRNA in rat microglia and suppresses the functional response to fractalkine. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Fractalkine; CX C receptor; Lipopolysaccharide 3 1 1. Introduction Chemokines are small proteins that stimulate migration Ž . of leukocytes and mediate inflammation Baggiolini, 1998 . These proteins are classified according to characteristic Ž . cystein signature motifs into subgroups Baggiolini, 1998 . Recently, a chemokine bearing a new CX C cystein motif 3 Ž . has been cloned Bazan et al., 1997; Pan et al., 1997 . This chemokine, named fractalkine, displays potent chemo- attractant activity for T cells and monocytes and is of Ž . non-haemopoietic origin Bazan et al., 1997 . Fractalkine seems to be produced by endothelial cells and also by neurons and occurs as a cell surface-bound as well as a cleaved protein. Recently, the orphan receptors V28 and RBS11 have been characterized as the human and rat receptors for fractalkine, respectively, and have been renamed CX CR1 3 ) Corresponding author. Tel.: q31-50-363-2701; Fax: q31-50-363- 2751; E-mail: h.w.g.m.boddeke@med.rug.nl Ž . Imai et al., 1997; Jiang et al., 1998 . The fractalkine receptor is a seven transmembrane-spanning G protein- coupled receptor expressed in leukocytes. Its signal trans- duction presumably plays a role in their migration and adhesion. Both fractalkine and its receptor are constitutively ex- pressed in human and rat brain, suggesting a physiological role of this chemokine in the nervous system. Recently, expression of fractalkine has been observed predominantly in neurons, whereas its receptor was primarily detectable Ž in microglia cells and not in neurons Nishiyori et al., . 1998 . Accordingly, it has been suggested that fractalkine acts as a paracrine signaling molecule from neuron to Ž . microglia Harrison et al., 1998; Nishiyori et al., 1998 . In this respect, the expression of fractalkine receptor mRNA may be regulated and thus involved in recruitment of leukocytes and microglia during neuroinflammation. In- deed an increase in fractalkine receptor mRNA in the facial nucleus has been observed after lesion of the rat Ž . facial nerve Harrison et al., 1998 . This increase, how- ever, may be due to an increased number of activated microglia migrating into the lesion-area. 0014-2999r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0014-2999 99 00307-6