CHL1-Deficient and Wild-Type Male Mice do Not Differ in Locomotor Recovery from Spinal Cord Injury.

CHL1 is a close homolog of L1, a cell adhesion molecule that plays major roles in neural and tumor cell functions. We had found that young adult female mice deficient in CHL1 recovered better than their wild-type female littermates after thoracic Spinal Cord Injury (SCI). This observation was surprising, because CHL1 increases neurite outgrowth in vitro. Injury of adult mouse central and peripheral nervous systems upregulate CHL1 expression in neurons and astrocytes, consistent with CHL1's pro-active, homophilic interaction between CHL1 surface molecules in wild-type mice. After SCI, CHL1 expression was observed to increase in the glial scar, areas of axonal regrowth and remodeling of neural circuits. These observations were made only in females, and we therefore sought to analyze SCI in CHL1-deficient male mice. We now show that CHL1-deficient males did not recover better or worse than their male wild-type littermates. Primary and secondary lesion volumes were similar in the two genotypes, as seen in female mice which were studied in parallel with male mice. Assessment of peripheral leukocytes showed a significant increase in numbers of blood neutrophils at 24 h after SCI in males, but not in females. Lymphocyte numbers in mutant males increased slightly, but numbers of lymphocytes or monocytes did not differ significantly between males or females. These results indicate that CHL1-deficient males and females differ in the number of neutrophils but not lymphocytes or monocytes, suggesting that the difference between males and females is unlikely due to differences in leukocytes.