Mouse strain and brain region‐specific expression of the glutaminyl cyclases QC and isoQC

Abstract

Glutaminyl cyclases (QCs) catalyze the formation of pyroglutamate (pGlu) from glutamine precursors at the N-terminus of a number of peptide hormones, neuropeptides and chemokines. This post-translational modification stabilizes these peptides, protects them from proteolytical degradation or is important for their biological activity. However, QC is also involved in a pathogenic pGlu modification of peptides accumulating in protein aggregation disorders such as Alzheimer's disease and familial Danish and familial British dementia. Its isoenzyme (isoQC) was shown to contribute to aspects of inflammation by pGlu-modifying and thereby stabilizing the monocyte chemoattractant protein CCL2. For the generation of respective animal models and for pharmacological treatment studies the characterization of the mouse strain and brain region-specific expression of QC and isoQC is indispensible. In order to address this issue, we used enzymatic activity assays and specific antibodies to detect both QC variants by immunohistochemistry in nine different mouse strains. Comparing different brain regions, the highest enzymatic QC/isoQC activity was detected in ventral brain, followed by cortex and hippocampus. Immunohistochemical stainings revealed that QC/isoQC activity in cortex mostly arises from isoQC expression. For most brain regions, the highest QC/isoQC activity was detected in C3H and FVB mice, whereas low QC/isoQC activity was present in CD1, SJL and C57 mice. Quantification of QC- and isoQC-immunoreactive cells by unbiased stereology revealed a higher abundance of isoQC- than of QC-immunoreactive neurons in Edinger-Westphal nucleus and in substantia nigra. In the locus coeruleus, however, there were comparable densities of QC- and of isoQC-immunoreactive neurons. These observations are of considerable importance with regard to the selection of appropriate mouse strains for the study of QC/isoQC relevance in mouse models of neurodegeneration and neuroinflammation and for the testing of therapeutical interventions in these models.

Immunohistochemical Evidence from APP-Transgenic Mice for Glutaminyl Cyclase as Drug Target to Diminish pE-Abeta Formation

“…In agreement with our recent study [ 30 ], the rat anti-hAPP antibody 1D1 only labeled neurons in hAPP-transgenic Tg2576 mice, but not in wild type littermates ( Figure 2 A). Similarly, in QC knock-out mice, no neuronal labeling was generated by the goat anti-mouse QC antiserum ( Figure 2 B), and the staining pattern in wild type mice corresponded to the one obtained by the rabbit anti-QC antiserum 1301, which has been used in several preceding studies [ 19 , 20 , 28 , 29 , 31 ]. Furthermore, dot blot analysis of unmodified Abeta and pE-Abeta peptides spotted onto nitrocellulose membranes revealed the detection of pE-Abeta, but not of full length Abeta, by the J8 monoclonal antibody ( Figure 2 C).…”

“…Using the rabbit anti-QC antiserum 1301, tested to be specific in QC knock-out mouse brain [ 28 , 29 ], we observed robust QC expression in the hypothalamic nuclei, where physiological QC substrates reside. Additionally, a subpopulation of neocortical and of GABAergic interneurons in the mouse hippocampus displays QC immunoreactivity [ 28 ].…”

The Development of Small Molecule Inhibitors of Glutaminyl Cyclase and Isoglutaminyl Cyclase for Alzheimer's Disease

“…Furthermore, h‐isoQC is a golgi resident enzyme while h‐QC is uniformly distributed in the cell. Both h‐isoQC and h‐QC catalyze some common substrates but they also have distinct substrates . It has been demonstrated that CCL2 (Monocyte chemoattractant protein 1) is a specific substrate for h‐isoQC but not for h‐QC .…”

Natural Products from Microalgae with Potential against Alzheimer’s Disease: Sulfolipids Are Potent Glutaminyl Cyclase Inhibitors

“…A direct correlation between the overexpression of QC and the vulnerability of neuronal populations could be described [24]. Inhibition of QCs may have therapeutic potential to treat disorders associated with protein aggregation and (neuro) inflammation and thus might be regarded as a therapeutic approach in the treatment of AD [25]. …”