CX3C chemokine receptor 1 deficiency modulates microglia morphology but does not affect lesion size and short-term deficits after experimental stroke

The fractalkine/CX3C chemokine receptor 1 (CX3CR1) pathway has been identified to play an essential role in the chemotaxis of microglia, leukocyte trafficking and microglia/macrophage recruitment. It has also been shown to be important in the regulation of the inflammatory response in the early phase after experimental stroke. The present study was performed to investigate if CX3CR1 deficiency affects microglia during the first 14 days with consequences for tissue damage after experimental stroke. CX3CR1 deficiency significantly increased the number of intersections of GFP positive microglia in the proximal peri-infarct area at 2, 7 and 14 days following tMCAO compared to heterozygous and wildtype littermates. In addition, the length of microglial branches increased until day 7 in CX3CR1 knockout mice while the presence of a functional CX3CR1 allele resulted in a gradual reduction of their length following tMCAO. After stroke, wildtype, heterozygous and CX3CR1 deficient mice did not show differences in the composite neuroscore and assessment of infarct volumes from CX3CR1 wildtype, heterozygous and deficient mice revealed no differences between the genotypes 7 and 14 days after stroke. Results demonstrate that CX3CR1 deficiency affects the morphology of GFP positive microglia located in the proximal peri-infarct region during the first 14 days after tMCAO. Our data also indicate that CX3CR1 deficiency does not affect definite infarct volumes. Modulation of the CX3CR1 pathway may have implication for microglia function contributing to mechanisms of tissue reorganization in the post-ischemic brain.