Abstracts

The hyaluronan receptor CD44 is a transmembrane glycoprotein which is mainly expressed by immune and endothelial cells. CD44 is involved in adhesion, matrix organization, lymphocyte trafficking and activation of inflammatory genes. In the brain CD44 expression is normally very limited but can be upregulated after injury. Our initial microarray experiments revealed CD44 upregulation in the mouse pilcarpine model. Here we study the localization of CD44 during epileptogenesis.
The pilocarpine mouse epilepsy model was used with CF1 mice as described in Borges et al. 2003 (Exp. Neurol. in press). Briefly, after pilocarpine-induced status epilepticus 4-5 mice were sacrificed at 1, 3, 10 and 31 days. All mice sacrificed at 31 d displayed spontaneous seizures. Paraffin-embedded brain sections were immunostained with two anti-CD44 antibodies, Km114 and Im7, which showed identical staining patterns.
For rats the lithium/pilocarpine model was used and sections were stained with the anti-CD44 antibody, Ox49 (all antibodies from Pharmingen). Mossy fiber sprouting was assessed by immunostaining for neuropeptide Y.
In normal mouse brain CD44 expression was below our detection threshold, but CD44 positive leukocytes/granulocytes appeared in damaged thalamic nuclei at 1 d and in the hippocampus at 3 d after status epilepticus. Moreover, CD44 immunoreactivity was observed at 3 d in the hippocampal neuropil, with the strongest labelling in the stratum lacunosum moleculare and the inner third of the dentate inner molecular layer, which at 31 d displayed NPY-positive sprouted mossy fibers (supragranular layer). The CD44 expression in the hippocampal neuropil including the stratum lacunosum moleculare persisted up to 31 d, but CD44 disappeared in the supragranular layer after 10 d. Thus, CD44 expression in the supragranular layer precedes mossy fiber sprouting, which was found earliest at 10 d.
In untreated rat brains, light CD44 staining was found in the stratum lacunosum moleculare and the pia.Ten to eighteen days after status epilepticus the CD44 expression pattern of rat hippocampus resembled the pattern of the 3 d mice. CD44 was found in the neuropil with strongest immunoreactivity in stratum lacunosum moleculare and the supragranular layer. No evidence for mossy fiber sprouting was found at 18 d. We are currently examining rats at later time points for CD44 and NPY expression.
In both rodent epilepsy models CD44 was found in the neuropil of the damaged hippocampus with highest expression in stratum lacunosum moleculare and the dentate supragranular layer, where it preceded mossy fiber sprouting. CD44 expression after status epilepticus-induced brain damage might play a role in tissue repair by regulating the formation of new extracellular matrix in injured areas. Furthermore, by influencing interactions between cell membranes and matrix CD44 could potentially be involved in axonal outgrowth, such as mossy fiber sprouting.
[Supported by: Epilepsy Foundation, NINDS]