We have previously described the localisation of the novel obesity peptide, neuropeptide W (NPW), and its receptor GPR7, in rat brain (Singh et al., 2004). In humans, NPW also binds to GPR8, not yet detected in rats and mice (Shimomura et al., 2002). Using antisera to the peptide and its target receptors, the distribution of this novel transmitter system was determined in human peripheral tissues.

Acetone fixed sections (30µm) of fresh frozen human tissue (left ventricle, lung, kidney and left internal mammary artery) were blocked for 1 hr with 5% swine serum. Sections were incubated with 1:200 dilution of rabbit anti-NPW antisera (Phoenix Pharmaceuticals Inc., CA, U.S.A) for 24 hrs at 4^oC. Binding of the primary antisera to the peptide was visualised using the peroxidase anti-peroxidase method. Tissues in which NPW-like immunoreactivity (LI) was detected were then examined for receptor distribution with either the human GPR7_(178-194) or GPR8_(25-45) antisera (Lifespan Biosciences Inc.) at 1:50 dilution.

In human kidney, intense NPW-LI (Figure 1A) was visualised in the glomeruli of the renal cortex while faint staining was also observed within small diameter renal vessels. Specific staining was not detected in renal tubules or the medullary rays. Furthermore, NPW-LI was visualised in the endocardial endothelium cells as well as in the endothelium of both intramyocardial vessels and the left internal mammary artery. Immunoreactive NPW staining was not detected within any cell type in human lung.

Figure 1: Presence of NPW-LI (A) in the glomeruli of the renal cortex and GPR7-LI (B) and GPR8-LI (C) detected in renal tubules of the renal medulla. Scale bar = 200 µm.

As intense NPW-LI was observed in human kidney, sections of the renal system were examined for NPW receptor staining. In the renal medulla, intense and abundant GPR7-LI (Figure 1B) was detected within the renal tubules but not in the medullary rays. GPR8-LI (Figure 1C) was also observed in renal tubules of the medulla but was discretely distributed in comparison to GPR7-LI. Immunoreactivity for both GPR7 and GPR8 was not detected in the renal cortex or renal vessels.

We believe this to be the first evidence of identification of NPW and its receptor in human tissues. The presence of receptor and peptide in the kidney suggests a potential role for this novel transmitter in renal function. Furthermore, the observed NPW-LI in the endothelium of the left internal mammary artery and presence of NPW in the glomeruli might imply NPW to be a circulating peptide.

Shimomura et al., (2002). J Biol Chem; 277, 35826-35832
Singh et al., (2004). http://www.pa2online.org/Vol1Issue3abst016P.html