Focal Cerebral Ischemia Induces Expression of Glutaminyl Cyclase along with Downstream Molecular and Cellular Inflammatory Responses

Glutaminyl cyclase (QC) and its isoenzyme (isoQC) catalyze the formation of N-terminal pyroglutamate (pGlu) from glutamine on a number of neuropeptides, peptide hormones and chemokines. Chemokines of the C-C ligand (CCL) motif family are known to contribute to inflammation in neurodegenerative conditions. Here, we used a model of transient focal cerebral ischemia to explore functional, cellular and molecular responses to ischemia in mice lacking genes for QC, isoQC and their substrate CCL2. Mice of the different genotypes were evaluated for functional consequences of stroke, infarct volume, activation of glia cells, and for QC, isoQC and CCL2 expression. The number of QC-immunoreactive, but not of isoQC-immunoreactive, neurons increased robustly in the infarct area at 24 and 72 h after ischemia. In parallel, immunohistochemical signals for the QC substrate CCL2 increased from 24 to 72 h after ischemia induction without differences between genotypes analyzed. The increase in CCL2 was accompanied by morphological activation of Iba1-immunoreactive microglia and recruitment of MHC-II-positive cells at 72 h after ischemia. Among other chemokines quantified in the brain tissue, CCL17 showed higher concentrations at 72 h compared to 24 h after ischemia. Collectively, these data suggest a critical role for QC in inflammatory processes in the stroke-affected brain.