Axonal transport of puromycin-sensitive aminopeptidase in rat sciatic nerves

Rapid imaging of lung cancer using a red fluorescent probe to detect dipeptidyl peptidase 4 and puromycin-sensitive aminopeptidase activities

Rapid identification of lung-cancer micro-lesions is becoming increasingly important to improve the outcome of surgery by accurately defining the tumor/normal tissue margins and detecting tiny tumors, especially for patients with low lung function and early-stage cancer. The purpose of this study is to select and validate the best red fluorescent probe for rapid diagnosis of lung cancer by screening a library of 400 red fluorescent probes based on 2-methyl silicon rhodamine (2MeSiR) as the fluorescent scaffold, as well as to identify the target enzymes that activate the selected probe, and to confirm their expression in cancer cells. The selected probe, glutamine-alanine-2-methyl silicon rhodamine (QA-2MeSiR), showed 96.3% sensitivity and 85.2% specificity for visualization of lung cancer in surgically resected specimens within 10 min. In order to further reduce the background fluorescence while retaining the same side-chain structure, we modified QA-2MeSiR to obtain glutamine-alanine-2-methoxy silicon rhodamine (QA-2OMeSiR). This probe rapidly visualized even borderline lesions. Dipeptidyl peptidase 4 and puromycin-sensitive aminopeptidase were identified as enzymes mediating the cleavage and consequent fluorescence activation of QA-2OMeSiR, and it was confirmed that both enzymes are expressed in lung cancer. QA-2OMeSiR is a promising candidate for clinical application.

Synovial fluid peptidase activity as a biomarker for knee osteoarthritis clinical progression

AIMS

To analyze the potential role of synovial fluid peptidase activity as a measure of disease burden and predictive biomarker of progression in knee osteoarthritis (KOA).

METHODS

A cross-sectional study of 39 patients (women 71.8%, men 28.2%; mean age of 72.03 years (SD 1.15) with advanced KOA (Ahlbäck grade ≥ 3 and clinical indications for arthrocentesis) recruited through the (Orthopaedic Department at the Complejo Asistencial Universitario de León, Spain (CAULE)), measuring synovial fluid levels of puromycin-sensitive aminopeptidase (PSA), neutral aminopeptidase (NAP), aminopeptidase B (APB), prolyl endopeptidase (PEP), aspartate aminopeptidase (ASP), glutamyl aminopeptidase (GLU) and pyroglutamyl aminopeptidase (PGAP).

RESULTS

Synovial fluid peptidase activity varied significantly as a function of clinical signs, with differences in levels of PEP (p = 0.020), ASP (p < 0.001), and PGAP (p = 0. 003) associated with knee locking, PEP (p = 0.006), ASP (p = 0.001), GLU (p = 0.037), and PGAP (p = 0.000) with knee failure, and PEP (p = 0.006), ASP (p = 0.001), GLU (p = 0.037), and PGAP (p < 0.001) with knee effusion. Further, patients with the greatest functional impairment had significantly higher levels of APB (p = 0.005), PEP (p = 0.005), ASP (p = 0.006), GLU (p = 0.020), and PGAP (p < 0.001) activity, though not of NAP or PSA, indicating local alterations in the renin-angiotensin system. A binary logistic regression model showed that PSA was protective (p = 0.005; Exp (B) 0.949), whereas PEP (p = 0.005) and GLU were risk factors (p = 0.012).

CONCLUSION

These results suggest synovial fluid peptidase activity could play a role as a measure of disease burden and predictive biomarker of progression in KOA. Cite this article: Bone Joint Res 2020;9(11):789-797.

Planarian homolog of puromycin-sensitive aminopeptidase DjPsa is required for brain regeneration

Puromycin-sensitive aminopeptidase (PSA) belongs to the M1 zinc metallopeptidase family. PSA is the most abundant aminopeptidase in the brain and plays a role in the metabolism of neuropeptides including those involved in neurodegeneration. A cDNA DjPsa was identified from the planarian Dugesia japonica cDNA library. It contains a 639-bp open reading frame corresponding to a deduced protein of 212 amino acids. Whole mount in situ hybridization revealed that DjPsa is expressed in the brain and ventral nerve cords of intact and regenerating animals and demonstrates a tissue and stage-specific expression pattern of DjPsa in developing embryos and larvae. Knocking down DjPsa gene expression with RNA interference during planarian regeneration inhibits the brain reformation completely. The results suggest that DjPsa is required for planarian brain regeneration.

Axonal transport of neprilysin in rat sciatic nerves

Axonal transport of neprilysin, a putative neuropeptide degrading-enzyme, was examined in the proximal, middle, and distal segments of rat sciatic nerves using a double ligation technique. Neprilysin activity was significantly increased not only in the proximal segment but also in the distal segment 12-120 h after ligation, and the maximal neprilysin activity was found in the proximal and distal segments at 96 and 72 h, respectively. Western blot analysis of neprilysin showed that its immunoreactivities in the proximal and distal segments were 2.8- and 2.4-fold higher than that in the middle segment, indicating that neprilysin is transported by anterograde and retrograde axonal flow. These observations suggest that neprilysin may be involved in the metabolism of neuropeptides in nerve terminals or synaptic clefts.

Bestatin inhibits cell growth, cell division, and spore cell differentiation in Dictyostelium discoideum

Bestatin methyl ester (BME) is an inhibitor of Zn(2+)-binding aminopeptidases that inhibits cell proliferation and induces apoptosis in normal and cancer cells. We have used Dictyostelium as a model organism to study the effects of BME. Only two Zn(2+)-binding aminopeptidases have been identified in Dictyostelium to date, puromycin-sensitive aminopeptidase A and B (PsaA and PsaB). PSA from other organisms is known to regulate cell division and differentiation. Here we show that PsaA is differentially expressed throughout growth and development of Dictyostelium, and its expression is regulated by developmental morphogens. We present evidence that BME specifically interacts with PsaA and inhibits its aminopeptidase activity. Treatment of cells with BME inhibited the rate of cell growth and the frequency of cell division in growing cells and inhibited spore cell differentiation during late development. Overexpression of PsaA-GFP (where GFP is green fluorescent protein) also inhibited spore cell differentiation but did not affect growth. Using chimeras, we have identified that nuclear versus cytoplasmic localization of PsaA affects the choice between stalk or spore cell differentiation pathway. Cells that overexpressed PsaA-GFP (primarily nuclear) differentiated into stalk cells, while cells that overexpressed PsaAΔNLS2-GFP (cytoplasmic) differentiated into spores. In conclusion, we have identified that BME inhibits cell growth, division, and differentiation in Dictyostelium likely through inhibition of PsaA.

Dictyostelium puromycin-sensitive aminopeptidase A is a nucleoplasmic nucleomorphin-binding protein that relocates to the cytoplasm during mitosis

Nucleomorphin (NumA1) is a nucleolar/nucleoplasmic protein linked to cell cycle in Dictyostelium. It interacts with puromycin-sensitive aminopeptidase A (PsaA) which in other organisms is a Zn(2+)-metallopeptidase thought to be involved in cell cycle progression and is involved in several human diseases. Here, we have shown that Dictyostelium PsaA contains domains characteristic of the M1 family of Zn(2+)-metallopeptidases: a GAMEN motif and a Zn(2+)-binding domain. PsaA colocalized with NumA1 in the nucleoplasm in vegetative cells and was also present to a lesser extent in the cytoplasm. The same localization pattern was observed in cells from slugs, however, in fruiting bodies PsaA was only detected in spore nuclei. During mitosis PsaA redistributed mainly throughout the cytoplasm. It possesses a functional nuclear localization signal ((680)RKRF(683)) necessary for nuclear entry. To our knowledge, this is the first nuclear localization signal identified in a Psa from any organism. Treatment with Ca(2+) chelators or calmodulin antagonists indicated that neither Ca(2+) nor calmodulin is involved in PsaA localization. These results are interpreted in terms of the inter-relationship between NumA1 and PsaA in cell function in Dictyostelium.

Human dipeptidyl peptidase III acts as a post-proline-cleaving enzyme on endomorphins

Dipeptidyl peptidase III (DPP III) is a zinc exopeptidase with an implied role in the mammalian pain-modulatory system owing to its high affinity for enkephalins and localisation in the superficial laminae of the spinal cord dorsal horn. Our study revealed that this human enzyme hydrolyses opioid peptides belonging to three new groups, endomorphins, hemorphins and exorphins. The enzymatic hydrolysis products of endomorphin-1 were separated and quantified by capillary electrophoresis and the kinetic parameters were determined for human DPP III and rat DPP IV. Both peptidases cleave endomorphin-1 at comparable rates, with liberation of the N-terminal Tyr-Pro. This is the first evidence of DPP III acting as an endomorphin-cleaving enzyme.

Neuropeptidases

Neuropeptides are neurotransmitters and modulators distributed in the central nervous system (CNS) and peripheral nervous system. Their abnormalities cause neurological and mental diseases. Neuropeptidases are enzymes crucial for the biosynthesis and biodegradation of neuropeptides. We here focus on the peptidases involved in the metabolism of the well-studied opioid peptides. Bioactive enkephalins are formed from propeptides by processing enzymes—prohormone thiol protease, prohormone convertase 1 and 2 (PC 1 and 2), carboxypeptidase H/E, and Arg/Lys aminopeptidase. After they exert their biological effects, enkephalins are likely to be inactivated by degrading enzymes—angiotensin-converting enzyme (ACE), aminopeptidase N (APN), puromycin-sensitive aminopeptidase (PSA), and endopeptidase 24.11. Recently, a neuron-specific aminopeptidase (NAP), which was a putative enkephalin-inactivating enzyme at the synapses, was found. Neuropeptidases are useful drug targets and their inhibitors can be therapeutic. Synthetic anti-enkephalinases and anti-aminopeptidases are being developed. They are potent analgesics but have fewer side effects than the opiates.

Axonal transports of tripeptidyl peptidase II in rat sciatic nerves

Axonal transport of tripeptidyl peptidase II, a putative cholecystokinin inactivating serine peptidase, was examined in the proximal, middle, and distal segments of rat sciatic nerves using a double ligation technique. Enzyme activity significantly increased not only in the proximal segment but also in the distal segment 12-72h after ligation, and the maximal enzyme activity was found in the proximal and distal segments at 72h. Western blot analysis of tripeptidyl peptidase II showed that its immunoreactivities in the proximal and distal segments were 3.1- and 1.7-fold higher than that in the middle segment. The immunohistochemical analysis of the segments also showed an increase in immunoreactive tripeptidyl peptidase II level in the proximal and distal segments in comparison with that in the middle segment, indicating that tripeptidyl peptidase II is transported by anterograde and retrograde axonal flow. The results suggest that tripeptidyl peptidase II may be involved in the metabolism of neuropeptides in nerve terminals or synaptic clefts.

Demonstration of puromycin-sensitive alanyl aminopeptidase in Alzheimer disease brain

Puromycin-sensitive alanyl aminopeptidase (PSA, EC 3.4.11.14) is a member of the ubiquitous aminopeptidase family, which cleaves N-terminal amino acids from proteins. PSA is suggested to function as a trimming protease in the MHC class I pathway, which is activated in brains of Alzheimer disease (AD). We examined the immunohistochemical localization of PSA in brains of AD and control cases using a rabbit anti-PSA. In the control cases, the antiserum revealed staining in a few glial cells and blood vessels. In AD brain, however, intensely stained cells were found richly in the cerebral cortex. Double immunofluorescence studies confirmed that PSA-positive cells were reactive microglia. Such PSA-positive reactive microglia tended to locate in and around senile plaques and were sometimes observed to associate with neurons containing neurofibillary tangles. The present result indicates that reactive microglia express PSA-immunoreactive molecules, probably in association with the pathological conditions of AD.

Anterograde axonal transport of endopeptidase 24.15 in rat sciatic nerves

Axonal transport of endopeptidase 24.15 (EP24.15), a putative neuropeptide degrading-enzyme, was examined in the proximal, middle, and distal segments of rat sciatic nerves using a double ligation technique. At 48h after ligation, a significant amount of the axonal transport of EP24.15 activity was found in the proximal segment, while axonal transport of deamidase activity, a lysosomal enzyme, increased in both proximal and distal segments. Western blot analysis of EP24.15 showed that EP24.15 immunoreactivity in the proximal segment was 1.8-fold higher than that in the middle segment. The immunohistochemical analysis of the segments also showed an increase in the immunoreactive EP24.15 in the proximal segment in comparison with that in the middle segment. In the distal segment, no axonal transport of EP24.15 was found in all methods examined, indicating that EP24.15 is mainly transported by an anterograde axonal flow. These observations suggest that EP24.15 may be involved in the metabolism of neuropeptides in nerve terminals or synaptic clefts.