Chemokine CCL2 induces apoptosis in cortex following traumatic brain injury

The chemokine C-C motif ligand 2 (CCL2) is an important mediator of neuroinflammation. Released in response to acute injury, ischemia, and neurodegenerative disease, CCL2 binds primarily to the G-protein-coupled chemokine C-C motif receptor 2 (CCR2) to recruit inflammatory cells to sites of tissue damage. Inflammation is thought to have both beneficial and deleterious consequences following traumatic brain injury (TBI), so we investigated CCL2-CCR2 signaling during the post-TBI period to assess possible neurodegenerative and protective actions. Local TBI in adult rat cortex was induced by Feeney's weight-drop method, and the expression of CCL2 and CCR2 in the tissue around the contusion site was measured by real-time quantitative PCR. Both CCL2 and CCR2 mRNA levels were increased markedly for at least 10 days after injury, peaking on day 3. The CCL2 protein was mainly co-localized with the astroglial marker glial fibrillary acidic protein and CCR2 protein with the neuronal nuclear marker NeuN as revealed by double immunofluorescence staining. A selective CCR2 antagonist, RS504393, reduced TUNEL staining, a marker of apoptosis, and improved performance in the Morris water maze 3 days post-TBI, suggesting that CCL2-CCR2 signaling has deleterious effects on neuronal survival and learning. Targeting the CCL2-CCR2 pathway may provide a novel therapeutic approach for the treatment of TBI.