Molecular and Cellular Identification of the Immune Response in Peripheral Ganglia Following Nerve Injury
Jon P. Niemi1, Jane A. Lindborg1, Madeline A. Howarth1,2, Kevin W. Liu1, Deepti Mahajan1, Christian Z. Moore1, Richard E. Zigmond1,
1Department of Neurosciences, Case Western Reserve University, Cleveland OH, ,2Hathaway Brown School, Shaker Heights OH.
Neuroinflammation accompanies neural trauma and most neurological diseases. Axotomy in the peripheral nervous system leads to dramatic changes in the injured neuron; the cell body expresses a distinct set of genes known as regeneration-asso¬ci-a¬ted genes, the distal axonal segments degenerate and their debris is cleared, and the axons in the proximal segment form growth cones and extend neurites. These processes are orchestrated in part by immune and other non-neuronal cells. Macro-phage accumulation in peripheral ganglia play an integral role in supporting regeneration. We have explored the molecular and cellular components of the injury-induced immune response within these ganglia. Adult male wild type (WT) and Ccr2 -/- mice were subjected to a unilateral transection of the sciatic nerve and axotomy of the superior cervical ganglion (SCG). Antibody arrays were used to determine the expression of chemokines and cytokines in the dorsal root ganglia (DRG) and SCG. Flow cytometry and immunohistochemistry were utilized to identify the cellular composition of the injury-induced immune response within ganglia. Chemokine expression in the ganglia differed 48 h after nerve injury with a large increase in macrophage inflammatory protein-1γ in the SCG but not in the DRG, while CCL2 was highly expressed in both ganglia. Differences between WT and Ccr2 -/- mice were also observed with increased MCP-5 expression in Ccr2 -/- DRG and SCG. Diminished macrophage accumulation in the DRG and SCG of Ccr2 -/- mice was found compared to WT ganglia 7 d after nerve injury. Interestingly, neutrophils were found in the SCG but not in the DRG. Cytokine expression, measured 7 d after injury, differed between ganglion type and genotype. Macrophage activation was assayed by colabeling ganglia with the anti-inflammatory marker CD206 and the macrophage marker CD68, and an almost complete colocalization of the two markers was found in both ganglia. Thus, both molecular and cellular differences in the nerve injury-induced immune response was found between DRG and SCG and between WT and Ccr2 -/- mice. (Supported by NS095017).