Histochemical evidence for wide expression of the metalloendopeptidase nardilysin in human brain neurons

Nardilysin is a metalloendopeptidase that in vitro cleaves peptides such as dynorphin-A, somatostatin-28, α-neoendorphin and glucagon at the N-terminus of arginine and lysine residues in dibasic moieties. The enzyme is highly expressed in many endocrine tissues. Nardilysin has also been found in the brain. Previously, we have detected that nardilysin interacts with brain-specific proteins, i.e. p42IP4/centaurin-α1 [Stricker R, Chow KM, Walther D, Hanck T, Hersh LB, Reiser G (2006) Interaction of the brain specific protein p42IP4/centaurin-α1 with the peptidase nardilysin is regulated by the cognate ligands of p42IP4, PtdIns(3,4,5)P3 and Ins(1,3,4,5)P4, with stereospecificity. J Neurochem 98:343-354]. However, very little is known about the distribution of nardilysin in the brain. The aim of the present study was to reveal its regional distribution and cellular localization in developing and adult human brain. Using immunohistochemistry and Western blot analysis we demonstrate that the enzyme is widely, but unevenly, expressed in the human brain. We found high staining intensity in the hypothalamus, neocortex and brain stem nuclei. The cellular localization is almost exclusively confined to neurons. In pre- and perinatal human brain cortex, most neurons express the enzyme. In cortical neurons nardilysin protein was found to be partially co-localized with parvalbumin but not calretinin. No co-expression was seen with somatostatin-28 immunoreactivity. A considerable overlap was revealed between p42IP4 and nardilysin. Our data support the hypothesis that nardilysin might possibly play a role in brain development, whereas its putative function in brain peptide metabolism remains to be clarified further.