C5a, but not C3a, increases VEGF secretion in ARPE-19 human retinal pigment epithelial cells.

PURPOSE: We examined the potential for the pro-inflammatory complement proteins C5a and C3a to increase VEGF expression in ARPE-19 cells. MATERIALS AND METHODS: Expression of complement receptors in ARPE-19 cells was evaluated by RT-PCR. VEGF secretion from ARPE-19 cells treated with C5a or C3a was determined by ELISA. RESULTS: C5a and C3a receptor, but not C5L2, were detected in human eye tissue and ARPE-19 cells. C5a, but not C3a, treatment increased VEGF secretion from ARPE-19 cells, an effect inhibited by the C5aR antagonist, NDT 9513727. CONCLUSIONS: C5a receptor mediates increased VEGF secretion from ARPE-19 cells, suggesting a role for the C5a receptor in the pathogenesis of macular degeneration.

Molecular characterization of the gerbil C5a receptor and identification of a transmembrane domain V amino acid that is crucial for small molecule antagonist interaction.

Anaphylatoxin C5a is a potent inflammatory mediator associated with pathogenesis and progression of several inflammation-associated disorders. Small molecule C5a receptor (C5aR) antagonist development is hampered by species-specific receptor biology and the associated inability to use standard rat and mouse in vivo models. Gerbil is one rodent species reportedly responsive to small molecule C5aR antagonists with human C5aR affinity. We report the identification of the gerbil C5aR cDNA using a degenerate primer PCR cloning strategy. The nucleotide sequence revealed an open reading frame encoding a 347-amino acid protein. The cloned receptor (expressed in Sf9 cells) bound recombinant human C5a with nanomolar affinity. Alignment of the gerbil C5aR sequence with those from other species showed that a Trp residue in transmembrane domain V is the only transmembrane domain amino acid unique to small molecule C5aR antagonist-responsive species (i.e. gerbil, human, and non-human primate). Site-directed mutagenesis was used to generate human and mouse C5aRs with a residue exchange of this Trp residue. Mutation of Trp to Leu in human C5aR completely eliminated small molecule antagonist-receptor interaction. In contrast, mutation of Leu to Trp in mouse C5aR enabled small molecule antagonist-receptor interaction. This crucial Trp residue is located deeper within transmembrane domain V than residues reportedly involved in C5a- and cyclic peptide C5a antagonist-receptor interaction, suggesting a novel interaction site(s) for small molecule antagonists. These data provide insight into the basis for small molecule antagonist species selectivity and further define sites critical for C5aR activation and function.

Excitatory monocyte chemoattractant protein-1 signaling is up-regulated in sensory neurons after chronic compression of the dorsal root ganglion.

Neuronal hyperexcitability in both injured and adjacent uninjured neurons is associated with states of chronic injury and pain and is likely subject to neuroinflammatory processes. Chronic inflammatory responses are largely orchestrated by chemokines. One chemokine, monocyte chemoattractant protein-1 (MCP-1), in the presence of its cognate receptor, the beta chemokine receptor 2 (CCR2), produces neural activity in dissociated neuronal cultures of neonatal dorsal root ganglion (DRG) neurons. Using a neuropathic pain model, chronic compression of the DRG (CCD), we compared anatomically separate populations of noncompressed lumbar DRG (L3/L6) with compressed lumbar DRG (L4/L5) for changes in the gene expression of CCR2. In situ hybridization revealed that CCR2 mRNA was up-regulated in neurons and nonneuronal cells present in both compressed L4/L5 and ipsilateral noncompressed L3/L6 DRGs at postoperative day 5 (POD5). The total percentages of compressed and noncompressed neurons exhibiting CCR2 mRNA transcripts in L3, L5, and L6 DRG were 33 +/- 3.5%, 49 +/- 6.2%, and 41 +/- 5.6%, respectively, and included cell bodies of small, medium, and large size. In addition, the preferred CCR2 ligand, MCP-1, was up-regulated by POD5 in both compressed L4/L5 and noncompressed L3/L6 DRG neurons. Application of MCP-1 to the cell bodies of the intact formerly compressed DRG in vitro produced potent excitatory effects not observed in control ganglia. MCP-1/CCR2 signaling is directly involved with a chronic compression injury and may contribute to associated neuronal hyperexcitability and neuropathic pain.