Enzymatic regulation of CCL2 bioactivity in neuroinflammation
Molecular Biology and Physiology of Neurons and Glial Cells
Molecular and Cellular Neurology and Neuropathology
Final Report Abstract
The present proposal focused on the regulation of neuroinflammatory effects mediated by the C-C motif chemokine CCL2. We hypothesized that the biological activity of CCL2 is tuned by enzyme-catalyzed post-translational modification. On the one hand, N-terminal CCL2 truncation by dipeptidyl peptidase IV/CD26 (DP4) initiates further proteolytical degradation and abolishes its biological activity. On the other hand, N-terminal pyroglutamate modification catalyzed by the glutaminyl cyclases QC and/or isoQC protects CCL2 from proteolytical degradation and increases its biological activity. Thus, we considered the tandem of the QC/isoQC and DP4 enzymes as pro- and anti-inflammatory molecular check-points in neuroinflammation, as they may specifically modulate CCL2 activity and the functional outcome in neuroinflammatory conditions in vivo. We exemplified these regulated enzymatic actions in brain disease by specifically investigating (i) the regulation of expression of QC/isoQC and DP4 and generation of CCL2 in brain as well as the activation of local microglia and infiltrating peripheral monocytes in an inflammatory stroke mouse model, (ii) the consequences of QC/isoQC and DP4 ablation in knock-out mice on the above markers and on the functional outcome such as infarct size and neurological deficits in the ischemia model, (iii) the mechanisms and kinetics of microglia and monocyte recruitment by CCL2. The results obtained show particularly (to i): Reduced DP4 immunoreactivity in the infarct area and a specific up-regulation of QC, but not of its sister enzyme isoQC in the infarct area that is accompanied by increased CCL2 levels, activation of microglia and infiltration of peripheral, MHC-II-positive immune cells into the infarct region. (to ii): The absence of the enzymes QC and isoQC on the one hand, and of DP4 on the other hand in the respective knock-out mice did not show the postulated opposing effects on CCL2 and functional parameters. However, in QC-KO and in isoQC-KO mice, the levels of CCL2 were only half as high as in wild type mice and the number of activated microglia and infiltrated MHC-II-positive cells was also lower than in wild type mice. We conclude, (iii) that the underlying mechanisms of the regulation of CCL2 bioactivity are more multifaceted than previously thought. There are, however, strong effects of reduced QC/isoQC activity in the knock-out mice on CCL2 levels and the cellular immune response.
Publications
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Tricellulin, α-Catenin and Microfibrillar-Associated Protein 5 Exhibit Concomitantly Altered Immunosignals along with Vascular, Extracellular and Cytoskeletal Elements after Experimental Focal Cerebral Ischemia. International Journal of Molecular Sciences, 24(15), 11893.
Höfling, Corinna; Roßner, Steffen; Flachmeyer, Bianca; Krueger, Martin; Härtig, Wolfgang & Michalski, Dominik
