Distribution and intraneuronal trafficking of a novel member of the chromogranin family, NESP55, in the rat peripheral nervous system

Abstract

NESP55 (neuroendocrine secretory protein of M r 55 000) is a novel member of the chromogranin family. In the present study, we have investigated the distribution, axonal transport and proteolytic processing of NESP55 in the peripheral nervous system. The amount of NESP55 immunoreactivity in adrenal gland was more than 240 times higher than that in the vas deferens. Double or triple immunostaining demonstrated that NESP55 immunoreactivity was highly co-localized with tyrosine hydroxylase immunoreactivity in bundles of thin axons and postganglionic sympathetic neurons; that NESP55 immunoreactivity also co-existed with vesicular acetylcholine transporter immunoreactivity in large-sized axons in sciatic nerves, and that NESP55 immunoreactivity overlapped with calcitonin gene-related peptide immunoreactivity in some large-sized axons, but NESP55 immunoreactivity was not detected in sensory neurons. Strong NESP55 immunoreactivity was found in cell bodies and axons, but it was not detectable in any terminal region by immunohistochemistry. In crush-operated sciatic nerves, NESP55 immunoreactivity could be found as early as 1 h after operation, and accumulated amounts increased substantially with time. However, NESP55 immunoreactivity was only observed in axons proximal to the crush, but none or very little distal to the crush, which was consistent with the data from radioimmunoassay. Finally, extracts of the normal and crushed sciatic nerve and vas deferens were subjected to high-performance liquid chromatography followed by radioimmunoassay. The results indicate that NESP55 is processed slowly to small peptides (GAIPIRRH) during axonal transport. NESP55 immunoreactivity was only detected in axons proximal to the crush. The data in the present study indicate that NESP55 immunoreactivity is widely distributed in adrenergic, cholinergic, and peptidergic neurons, but not in sensory neurons, and that this peptide is anterogradely, but not retrogradely, transported with fast axonal transport and slowly processed to smaller peptides during axonal transport in the peripheral nervous system.