Anterograde axonal transport of peptidylglycine alpha-amidating monooxygenase in rat sciatic nerves

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.

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.

Changes in the levels of neuropeptides and their metabolizing enzymes in the brain regions of nucleus basalis magnocellularis-lesioned rats

The regulation mechanism of the interrelation between neuropeptides and their metabolizing enzymes in in vivo tissues is still not clear. In the present report, we attempted to measure the levels of neuropeptides and their enzymes in the frontal cortex, hippocampus, and striatum of the rat that had been bilaterally lesioned by the infusion of ibotenic acid or amyloid beta-peptide 25 - 35 (Abeta25 - 35) into the nucleus basalis magnocellularis. In the drug-treated rats, at two weeks after the infusion, the decrease of somatostatin-like immunoreactivity (SS-LI) and the increase of cholecystokinin-8S-LI were found in some brain regions relative to vehicle-treated rats. The immunoreactivities of endopeptidase 24.15 and puromycin-sensitive aminopeptidase and the leucine aminopeptidase- and aminopeptidase B-like enzyme activities did not change in the three brain regions, suggesting that the levels of those peptide-degrading enzymes do not correlate with the changes of the neuropeptide levels. The decrease of subtilisin-like proprotein convertase (SPC)-like enzyme activity was found in the hippocampus of the Abeta25 - 35-treated rats. The SS mRNA level decreased in the hippocampus in parallel with decreases in the SS-LI level and SPC-like enzyme activity. The present data indicate that some of the neuropeptide-processing enzymes may contribute to the control of neuropeptide levels.

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.

Effect of monensin on the levels of tachykinins and their processing enzyme activity in rat dorsal root ganglia

Th effect of monensin, which inhibits trans-Golgi function, on the levels of tachykinins and their processing enzyme activity was examined in organ-cultured rat dorsal root ganglia (DRG). Using an enzyme immunoassay method, we measured neurokinin A and substance P immunoreactivity in the DRG cultured for 72 h with and without 0.1 microM monensin. Both tachykinins were reduced in the DRG treated with monensin. Treatment with monensin also reduced the activity of carboxypeptidase E, which is one of the proteolytic processing enzymes of neuropeptides. These data suggest that proteolytic processing enzymes may in part modulate the biological activity of neuropeptides within a trans-Golgi apparatus.

Axonal transport of puromycin-sensitive aminopeptidase in rat sciatic nerves

Axonal transport of puromycin-sensitive aminopeptidase (PSA), a putative neuropeptide degrading-enzyme which removes amino acid residues from the amino-terminal of neuropeptides, was examined in the proximal, middle, and distal segments of rat sciatic nerves using a double-ligation technique. The soluble fraction of each segment was partially purified by MonoQ column chromatography, and showed two peaks of aminopeptidase activity. One of the aminopeptidases was PSA. At 48 h after the ligations, a significant amount of the axonal transport of PSA activity was found in the proximal segment. Western blot analysis of the segments also showed that immunoreactive PSA in the proximal segment was 2.1-fold higher than that in the middle segment. Furthermore, the immunohistochemical analysis of the segments showed an increase of the immunoreactive PSA in the proximal segment in comparison with the enzyme in the distal segment, indicating that PSA is mainly transported by anterograde axonal flow. These results suggest that PSA plays a role in the metabolism of neuropeptides in nerve terminals or synaptic clefts.

Anterograde axonal transport of Boc-Arg-Val-Arg-Arg-MCA hydrolyzing enzyme in rat sciatic nerves: cleavage occurs between basic residues

Axonal transport of Boc-Arg-Val-Arg-Arg-MCA hydrolyzing enzyme activity was studied in rat sciatic nerves from 12 to 120 h after double ligations. The anterograde axonal transport increased and peaked 72 h after ligation. The optimum pH for Boc-Arg-Val-Arg-Arg-MCA hydrolyzing enzyme activity was 6.5 to 6.9 and did not require Ca(2+) for the activity. Two molecular forms with enzyme activity were identified by size-exclusion chromatography and the molecular masses of the two enzymes were estimated to be 98 and 52 kDa. Two enzyme activities were strongly inhibited by Hg(2+), Cu(2+) and trypsin inhibitors such as TLCK, antipain and leupeptin. It cleaved the substrate, Boc-Arg-Val-Arg-Arg-MCA, between the dibasic sequence Arg-Arg, and needed a support of aminopeptidase B-like enzyme activity for the liberation of 7-amino-4-methylcoumarin. These results suggest that the enzyme is transported in rat sciatic nerves and involved in the post-translational processing of precursor proteins under the anterograde axonal transport. But there is absolutely no evidence for a role in precursor processing and such a putative role is purely speculative.

Axonal transports of Boc-Gly-Arg-Arg-MCA hydrolysing enzyme in rat sciatic nerves

Study on neural axon transport is a very useful method to find a neuron-specific protease. In the present study, the enzyme activity (release of 7-amino-4-methyl-coumarin from t-butyloxycarbonyl-glycyl-L-arginyl-L-arginine-4-methylcoumaryl-7-amide) was measured in the proximal, middle, and distal segments between 12 and 120 h after double ligations of rat sciatic nerves to find precursor processing enzyme specific for pair of basic amino acid residue. The enzyme activity was significantly increased not only in the proximal but also in the distal segments 12-120 h after the ligation, and the maximal enzyme activity was found in both segments at 72 h. The enzyme activity eluted by anion exchange chromatography of the proximal segment showed at least three peaks, and was slightly higher than the activity of the distal one. The activity in the middle segment was very low in comparison with the activity in the proximal and distal segments. These data indicate that some of the enzymes specific for pair of basic amino acid residue are transported by both anterograde and retrograde axonal flow, and may undergo a neuron-specific processing.

Highly sensitive high-performance liquid chromatography-fluorimetric assay method for carboxypeptidase H activity

A rapid and sensitive high-performance liquid chromatographic (HPLC)-fluorimetric assay method has been developed for the determination of carboxypeptidase H activity based on the measurement of N-(5-dimethyl-aminonaphthalene-1-sulfonyl)glycine (dansyl-Gly) formed enzymatically from dansyl-Gly-L-Lys or dansyl-Gly-L-Arg. Dansyl-Gly is eluted faster than the substrates with an N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (Hepes) buffer at pH 7.0 containing methanol, but eluted slower with an acidic buffer at pH 4.6. The new HPLC method separates the product and substrate in less than 5 min using an elution buffer at pH 7.0 containing 60% methanol. Using this method carboxypeptidase H activity has been detected in rat sciatic nerves. This HPLC method facilitates the assay of carboxypeptidase H activity in the enzyme samples from various tissues.

Differences in the distribution of cytochrome b561 and synaptophysin in dog splenic nerve: a biochemical and immunocytochemical study

Compared with neurons of the CNS, the organization of the peripheral adrenergic axon and nerve terminal is more complex because two types of neurotransmitter-containing vesicles, i.e., large (LDVs) and small dense-core vesicles, coexist with the axonal reticulum (AR) and the well-characterized small synaptic vesicles. The AR, which is still poorly examined, is assumed to play some role in neurosecretion. We have studied the subcellular localization of noradrenaline, cytochrome b561, and synaptophysin in control and ligated dog splenic nerve using both biochemical and ultrastructural approaches. Noradrenaline and cytochrome b561 coaccumulated proximal to a ligation, whereas distally only the latter was found. Despite a codistribution with noradrenaline at high densities in sucrose gradients, synaptophysin did not accumulate on either side of the ligation. At the ultrastructural level, cytochrome b561 immunoreactivity was found on LDVs and AR elements, both accumulating proximal to the ligation. Distally, the multivesicular bodies (MVBs), immunolabeled for cytochrome b561, account for the retrograde transport of LDVs and AR membranes retrieved at the nerve terminal. No synaptophysin immunoreactivity could be detected on LDVs, AR, or MVBs. The results obtained from the ligation experiments together with the ultrastructural data clearly illustrate that synaptophysin is absent from LDVs and AR elements in adrenergic axons.

Secretion of peptidylglycine alpha-amidating monooxygenase (PAM) from rat salivary glands

Peptidylglycine alpha-amidating monooxygenase (PAM) is a regulating enzyme to synthesize the biologically active hormones having carboxy-terminal amide. In the present study we investigated secretion of the enzyme from rat saliva. Property of PAM in the saliva was similar to that in the submandibular gland. Both enzymes showed similar pH optimum at 5.0 and optimal ascorbic acid concentration at 2.5 mM. But molecular size of PAM in the saliva was 75 kDa in the gel permeation chromatography on Superose 12 column, while the size in the submandibular gland was 25 kDa. After the treatment with trypsin, PAM in the saliva was converted to a small size molecule, which is similar to the size in rat submandibular gland. These and other data indicate that a native molecular size of PAM is secreted into saliva and plays some physiological roles.

Immunohistochemical study of cholecystokinin peptide in rat spinal motoneurons

With the aid of indirect immunofluorescence histochemistry and sequence specific antibodies a possible localization of cholecystokinin (CCK) peptide in spinal motoneurons has been analyzed. To increase peptide levels, the sciatic nerve was ligated, and the area around the ligation was studied 24 hours later. For comparison, antisera raised against calcitonin gene-related peptide (CGRP) and substance P were employed. With CCK specific antisera (directed to the N-terminal portion of CCK-8 or the midportion of CCK-33) accumulation of peptide-like immunoreactivity (LI) was observed in large, dilated axonal swellings proximal to, but at some distance from, the ligature. Such accumulations were also observed with C-terminally directed CCK antiserum, but in addition numerous axons of smaller diameter extending up to the ligation contained this type of immunoreactivity. The latter antiserum is thought to cross-react with CGRP. In fact, this staining pattern was indistinguishable from the one seen after incubation with CGRP antiserum. In contrast substance P-LI could not be seen in the larger dilated axons but only in large numbers of thinner fibers close to the ligation. Double staining experiments revealed that the large dilations contained both CGRP- and CCK-specific LI. Distal to the ligation CGRP- and substance P- but no specific CCK-LI could be observed. The present findings support the view that CCK mRNA in spinal motoneurons is translated into CCK peptide, at least after axotomy, and that the peptide is transported into the motoneuron axon. However, compared to CGRP the CCK levels are presumably low, and the functional role of CCK peptide in motoneurons remains to be established.