Immunolocalization of tripeptidyl peptidase II, a cholecystokinin-inactivating enzyme, in rat brain

• Published in: Neuroscience 1999-02, Vol.88 (4), p.1225-1240
• Main Authors: Facchinetti, P, Rose, C, Rostaing, Ph, Triller, A, Schwartz, J.-C
• Format: Article
• Language: English
• Subjects: Aminopeptidases; Animals; Brain - enzymology; Brain - ultrastructure; Cholecystokinin - antagonists & inhibitors; cholecystokinin octapeptide; Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; EC 3.4.14.10; electron microscope immunolocalization; Immunohistochemistry; light microscope immunolocalization; Male; Microscopy, Electron; Rats; Rats, Wistar; satiety; Serine Endopeptidases - metabolism; serine proteases; Tissue Distribution - physiology
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/S0306-4522(98)00257-7

Tripeptidyl peptidase II (EC 3.4.14.10) is a serine peptidase apparently involved in the inactivation of cholecystokinin octapeptide [Rose C. et al. (1996) Nature 380, 403–409]. We have compared its distribution with that of cholecystokinin in rat brain, using a polyclonal antibody raised against a highly purified preparation for immunohistochemistry at the photon and electron microscope levels. Tripeptidyl peptidase II-like immunoreactivity was mostly detected in neurons, and also in ependymal cells and choroid plexuses, localizations consistent with a possible participation of the peptidase in the inactivation of cholecystokinin circulating in the cerebrospinal fluid. Immunoreactivity was mostly detected in cell bodies, large processes and, to a lesser extent, axons of various neuronal populations. Their localizations, relative to that of cholecystokinin terminals, appears to define three distinct situations. The first corresponds to neurons with high immunoreactivity in areas containing cholecystokinin terminals, as in the cerebral cortex or hippocampal formation, where pyramidal cell bodies and processes surrounded by cholecystokinin axons were immunoreactive. A similar situation was encountered in many other areas, namely along the pathways through which cholecystokinin controls satiety, i.e. in sensory vagal neurons, the nucleus tractus solitarius and hypothalamic nuclei. The second situation corresponds to cholecystokinin neuronal populations containing tripeptidyl peptidase II-like immunoreactivity, as in neurons of the supraoptic or paraventricular nuclei, axons in the median eminence or nigral neurons. In both these situations, localization of tripeptidyl peptidase II-like immunoreactivity is consistent with a role in cholecystokinin inactivation. The third situation corresponds to areas with mismatches, such as the cerebellum, a region devoid of cholecystokinin, but in which Purkinje cells displayed high tripeptidyl peptidase II-like immunoreactivity, possibly related to a role in the inactivation of neuropeptides other than cholecystokinin. Also, some areas with cholecystokinin terminals, e.g., the molecular layer of the cerebral cortex, were devoid of tripeptidyl peptidase II-like immunoreactivity, suggesting that processes other than cleavage by tripeptidyl peptidase II may be involved in cholecystokinin inactivation. Tripeptidyl peptidase II-like immunoreactivity was also detected at the ultrastructural level in the cerebral cortex and hypot