Chemokine receptors CCR5 and CXCR4 are new therapeutic targets for brain recovery following Traumatic Brain Injury

Aim: Chemokine receptor CCR5 was recently found to be a negative modulator of learning and memory. Its inhibition improved outcome after stroke and TBI. To better understand its role after TBI, we investigated the effect of reduced CCR5 signaling as a neuroprotective strategy, and the temporal changes of CCR5 expression after TBI in different brain cell types in order to establish therapeutic strategy.Methods: To silence CCR5 expression, injections of ccr5 shRNA or dsred shRNA (control) into the CA1 and CA3 regions of the hippocampus were made two weeks prior to induction of closed head injury in mice. Mice were then followed for 30 days and sacrificed at different time points to assess lesion area, inflammatory components of the glial response (immunohistochemistry), cytokine levels (ELISA array) and ERK phosphorylation (Western blot). Flow cytometry analysis (FACS) was performed to study post injury temporal changes of CCR5 and CXCR4 expression on cortical and hippocampal cell populations (neurons, astrocytes, microglia). Phosphorylation of NR1 subuint of NMDAR (Western blot) and CREB (immunohistochemistry) were also assessed.Results: ccr5 shRNA mice displayed reduced lesion area, dynamic alterations in the levels of inflammation-related CCR5 ligands and cytokines, and higher levels of p-ERK. ccr5 shRNA also reduced astrocytosis activation in the lesioned and sub-lesioned cortex. FACS analysis revealed an increase of cortical CCR5 and CXCR4 expression in CD11b positive cells, astrocytes and neurons, especially apparent on cells expressing both receptors at 3 and 11 days post injury. At day 3 post injury the lowest levels of p-NR1 and p-CREB were found, suggesting this time point as critical for future therapeutic implications.