Distribution of prolyl oligopeptidase in the mouse whole-body sections and peripheral tissues

Abstract

Prolyl oligopeptidase (POP) is a serine endopeptidase that hydrolyses proline-containing peptides shorter than 30-mer, including
many bioactive peptides. The distribution of POP in the brain has been studied but little is known about the distribution
of peripheral POP. We used immunohistochemistry to localize POP in mouse whole-body sections and at the cellular level in
peripheral tissues. Furthermore, we used a POP activity assay to reveal the associations between POP protein and its enzymatic
activity. The highest POP protein densities were found in brain, kidney, testis and thymus, but in the liver the amounts of
POP protein were small. There were remarkable differences between the distribution of POP protein and activity. The highest
POP activities were found in the liver and testis while kidney had the lowest activity. In peripheral tissues, POP was present
in various cell types both in the cytoplasm and nucleus of the cells, in contrast to the brain where no nuclear localization
was detected. These findings support the proposed role of POP in cell proliferation in peripheral tissues. The dissociation
of the distribution of POP protein and its enzymatic activity points to nonhydrolytic functions of POP and to strict endogenous
regulation of POP activity.