Serpinin in the rat eye

Abstract

Purpose: To investigate the distribution of the novel chromogranin A-derived neuropeptide serpinin in the rat eye.

Methods: The molecular form of serpinin-immunoreactivity detected by a highly specific antiserum was evaluated both by western blot analysis and reversed phase-HPLC with subsequent ELISA in the rat trigeminal ganglion (TG) and retina and the presence and distribution of the peptide was explored in the rat TG and eye by immunofluorescence.

Results: There was no band in western blots in the rat TG but two weak bands at 30 and 50 kDa in the retina. Only free serpinin but no (pGlu)-serpinin and no serpinin-RRG were detected by RP-HPLC in the rat TG and retina. Numerous small- and medium-sized cells contained serpinin-immunoreactivity in the rat TG and full colocalization with substance P was evident with a more widespread expression of serpinin. Immunoreactivity was present in nerves in the corneal, limbal, irideal, ciliary and choroidal/scleral stroma, sphincter and dilator muscle and around vessels and colocalisation with substance P has been shown in nerves at the limbus, irideal and choroidal stroma. In the retina, immunoreactivity was found in the innermost part and colocalisation was present with GFAP.

Conclusions: Serpinin is a constituent of the sensory innervation of the rat eye. There is indirect evidence that chromogranin A is proteolytically processed already at the site of synthesis in the TG and a widespread but moderate innervation of the eye by free serpinin exists which is typical for neuropeptides. In the retina, serpinin is expressed atypically in glia.