Post-proline cleaving enzyme in human cerebrospinal fluid from control patients and parkinsonian patients

New tricks of prolyl oligopeptidase inhibitors - A common drug therapy for several neurodegenerative diseases

Changes in prolyl oligopeptidase (PREP) expression levels, protein distribution, and activity correlate with aging and are reported in many neurodegenerative conditions. Together with decreased neuropeptide levels observed in aging and neurodegeneration, and PREP's ability to cleave only small peptides, PREP was identified as a druggable target. Known PREP non-enzymatic functions were disregarded or attributed to PREP enzymatic activity, and several potent small molecule PREP inhibitors were developed during early stages of PREP research. These showed a lot of potential but with variable results in experimental memory models, however, the initial excitement was short-lived and all of the clinical trials were discontinued in either Phase I or II clinical trials for unknown reasons. Recently, PREP's ability to form protein-protein interactions, alter cell proliferation and autophagy has gained more attention than earlier recognized catalytical activity. Of new findings, particularly the aggregation of alpha-synuclein (aSyn) that is seen in the presence of PREP is especially interesting because PREP inhibitors are capable of altering aSyn-PREP interaction in a manner that reduces the aSyn dimerization process. Therefore, it is possible that PREP inhibitors that are altering interactions could have different characteristics than those aimed for strong inhibition of catalytic activity. Moreover, PREP co-localization with aSyn, tau, and amyloid-beta hints to PREP's possible role not only in the synucleinopathies but in other neurodegenerative diseases as well. This commentary will focus on less well-acknowledged non-enzymatic functions of PREP that may provide a better approach for the development of PREP inhibitors for the treatment of neurodegenerative disorders.

Alzheimer-associated cerebrospinal fluid fragments of neurogranin are generated by Calpain-1 and prolyl endopeptidase

Background

Neurogranin (Ng) is a small 7.6 kDa postsynaptic protein that has been detected at elevated concentrations in cerebrospinal fluid (CSF) of patients with Alzheimer’s disease (AD), both as a full-length molecule and as fragments from its C-terminal half. Ng is involved in postsynaptic calcium (Ca) signal transduction and memory formation via binding to calmodulin in a Ca-dependent manner. The mechanism of Ng secretion from neurons to CSF is currently unknown, but enzymatic cleavage of Ng may be of relevance. Therefore, the aim of the study was to identify the enzymes responsible for the cleavage of Ng, yielding the Ng fragment pattern of C-terminal fragments detectable and increased in CSF of AD patients.

Methods

Fluorigenic quenched FRET probes containing sequences of Ng were utilized to identify Ng cleaving activities among enzymes known to have increased activity in AD and in chromatographically fractionated mouse brain extracts.

Results

Human Calpain-1 and prolyl endopeptidase were identified as the candidate enzymes involved in the formation of endogenous Ng peptides present in CSF, cleaving mainly in the central region of Ng, and between amino acids 75_76 in the Ng sequence, respectively. The cleavage by Calpain-1 affects the IQ domain of Ng, which may deactivate or change the function of Ng in Ca²⁺/calmodulin -dependent signaling for synaptic plasticity. While shorter Ng fragments were readily cleaved in vitro by prolyl endopeptidase, the efficiency of cleavage on larger Ng fragments was much lower.

Conclusions

Calpain-1 and prolyl endopeptidase cleave Ng in the IQ domain and near the C-terminus, respectively, yielding specific fragments of Ng in CSF. These fragments may give clues to the roles of increased activities of these enzymes in the pathophysiology of AD, and provide possible targets for pharmacologic intervention.

Electronic supplementary material

The online version of this article (10.1186/s13024-018-0279-z) contains supplementary material, which is available to authorized users.

Prolyl oligopeptidase and dipeptidyl peptidase II/dipeptidyl peptidase IV ratio in the cerebrospinal fluid in Parkinson's disease: historical overview and future prospects

Prolyl oligopeptidase (also named prolyl endopeptidase; PREP) hydrolyzes the Pro-Xaa bonds of biologically active oligopeptides on their carboxyl side. In 1987, we detected PREP activity in human cerebrospinal fluid (CSF) using highly sensitive liquid chromatography-fluorometry with succinyl-Gly-Pro-4-methyl-coumarin amide as a new synthetic substrate, and found a marked decrease in its activity in the cerebrospinal fluid (CSF) from patients with Parkinson's disease (PD) as compared with its level in control patients without neurological diseases. In 2013, Hannula et al. found co-localization of PREP with α-synuclein in the postmortem PD brain. Several recent studies also suggest that the level of PREP in the brain of PD patients may be related to dopamine (DA) cell death via promotion of α-synuclein oligomerization and that inhibitors of PREP may play a neuroprotective role in PD. Although the relationship between another family of prolyl oligopeptidase enzymes, dipeptidyl peptidase II (DPP II) and dipeptidyl peptidase IV (DPP IV), and α-synuclein in the PD brain is not yet clear, we found that the DPP II activity/DPP IV activity ratio in the CSF was significantly increased in PD patients. This review discusses the possibility of PREP as well as the DPP II/DPP IV ratio in the CSF as potential biomarkers of PD.

Cerebrospinal fluid biochemical studies in patients with Parkinson's disease: toward a potential search for biomarkers for this disease

The blood-brain barrier supplies brain tissues with nutrients and filters certain compounds from the brain back to the bloodstream. In several neurodegenerative diseases, including Parkinson's disease (PD), there are disruptions of the blood-brain barrier. Cerebrospinal fluid (CSF) has been widely investigated in PD and in other parkinsonian syndromes with the aim of establishing useful biomarkers for an accurate differential diagnosis among these syndromes. This review article summarizes the studies reported on CSF levels of many potential biomarkers of PD. The most consistent findings are: (a) the possible role of CSF urate on the progression of the disease; (b) the possible relations of CSF total tau and phosphotau protein with the progression of PD and with the preservation of cognitive function in PD patients; (c) the possible value of CSF beta-amyloid 1-42 as a useful marker of further cognitive decline in PD patients, and (d) the potential usefulness of CSF neurofilament (NFL) protein levels in the differential diagnosis between PD and other parkinsonian syndromes. Future multicentric, longitudinal, prospective studies with long-term follow-up and neuropathological confirmation would be useful in establishing appropriate biomarkers for PD.

Prolyl oligopeptidase stimulates the aggregation of alpha-synuclein

Despite its thorough enzymological and biochemical characterization the exact function of prolyl oligopeptidase (PO, E.C. 3.4.21.26) remains unclear. The positive effect of PO inhibitors on learning and memory in animal models for amnesia, enzyme activity measurements in patient samples and (neuro)peptide degradation studies link the enzyme with neurodegenerative disorders. The brain protein alpha-synuclein currently attracts much attention because of its proposed role in the pathology of Parkinson's disease. A fundamental question concerns how the essentially disordered protein is transformed into the highly organized fibrils that are found in Lewy bodies, the hallmarks of Parkinson's disease. Using gel electrophoresis and MALDI TOF/TOF mass spectrometry we investigated the possibility of alpha-synuclein as a PO substrate. We found that in vitro incubation of the protein with PO did not result in truncation of full-length alpha-synuclein. Surprisingly, however, we found an acceleration of the aggregation process of alpha-synuclein using turbidity measurements that was reversed by specific inhibitors of PO enzymatic activity. If PO displays this activity also in vivo, PO inhibitors might have an effect on neurodegenerative disorders through a decrease in the aggregation of alpha-synuclein.

A prolyl oligopeptidase inhibitor, Z-Pro-Prolinal, inhibits glyceraldehyde-3-phosphate dehydrogenase translocation and production of reactive oxygen species in CV1-P cells exposed to 6-hydroxydopamine

We studied the ability of prolyl oligopeptidase (POP) inhibitors, Z-Pro-Prolinal and JTP-4819, to prevent translocation of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and formation of reactive oxygen species (ROS), in 6-hydroxydopamine (6-OHDA) and cytosine arabinoside (Ara-C) treated monkey fibroblast (CV1-P) and human neuroblastoma (SH-SY5Y) cells. The cells were pretreated with POP inhibitors (30 min) before addition of toxicants. GAPDH was analyzed by Western hybridization, ROS by fluorescent 2'7'-dichlorodihydro-fluorescein diacetate, and viability by the MTT method. Both toxicants induced GAPDH translocation to the particulate fraction (mitochondria and nuclei). Z-Pro-Prolinal was able to inhibit the translocation in 6-OHDA-exposed CV1-P cells. In SH-SY5Y cells and in JTP-4819 pretreated cells, no prevention of translocation was seen. However, the intensity of GAPDH in cytosolic fraction increased. Both inhibitors blocked 6-OHDA-induced ROS-production to the control level in CV1-P but, not in SH-SY5Y cells, without affecting their viability. In conclusion, POP inhibitors are able to prevent certain cell stress related factors such as ROS production or GAPDH translocation.

Suggested functions for prolyl oligopeptidase: a puzzling paradox

Prolyl oligopeptidase (PO, E.C. 3.4.21.26) is a post-proline cleaving enzyme with endopeptidase activity towards peptides not longer than 30 amino acids. It has been purified and characterized from various mammalian and bacterial sources, but despite its thorough enzymological and structural characterization, the exact function of PO remains obscure. Many investigations have addressed the physiological role of this enzyme, mainly by the use of specific PO inhibitors, activity measurements in clinical samples and (neuro)peptide degradation studies. From the combined results emerges a puzzling paradox: how can an intracellular, cytoplasmatic oligopeptidase affect not only the amount of extracellular neuropeptides but also signal transduction and secretion? This report provides a review of the literature on the suggested functions for PO, highlighting possible pitfalls and contradictions.

Two peptidase activities decrease in treated bipolar disorder not schizophrenic patients

BACKGROUND

Inhibition of prolyl oligopeptidase (PO) in primary neuronal cultures has been shown to reverse the effect of the common mood-stabilizers lithium, valproic acid and carbamazepine. In clinical studies, abnormal plasma PO activity has been associated with bipolar disorder (BD) and schizophrenia. However, this association is complicated by the discovery in bovine plasma of a Z-Pro-prolinal-insensitive peptidase (ZIP), a novel enzyme that cleaves the same substrate as PO.

METHODS

We developed an assay to distinguish between ZIP and PO and measured both activities in plasma from 48 BD and 50 schizophrenic patients undergoing treatment and compared them with 50 control subjects.

RESULTS

ZIP activity is restricted to blood plasma, whereas PO activity is present in the cytosol of lymphocytes, but can also be detected in blood plasma. Significant decreases in their plasma activities were found between treated BD (p = 0.007 and 0.03 respectively) but not schizophrenic (p > 0.05) patients and controls.

CONCLUSIONS

We have found that the enzyme activity previously reported as plasma PO actually comprises two enzymes, PO and ZIP. This study shows a statistically significant decrease of both enzymes in BD patients undergoing lithium treatment. No statistically significant change in PO or ZIP activity is observed in schizophrenic patients.

Pharmacology of long-term potentiation. A model for learning reviewed

Long-term potentiation is widely used as a model for memory formation. Recently, much information concerning this topic like the involvement of protein kinase C, arachidonic acid and N-methyl-D-aspartate receptors has been reported. In this review recent discoveries concerning long-term potentiation and the pharmacological implications for the development of cognition-enhancing drugs are discussed.