Abstract
Purpose: :
The recently discovered peptide apelin has been demonstrated to be the endogenous ligand for an orphan G protein–coupled receptor – APJ. Apelin derives from a 77–amino–acid precursor, preproapelin, which through post translational modification is processed to its biologically active forms, with amino acid sequences containing either 13 or 36 residues. Apelin and its receptor are widely expressed in the tissues of the human body including the cardiovascular and the central nervous system. Along with the broad tissue distribution of apelin/APJ, the studies have demonstrated important physiological functions in the cardiovascular system, as well as in the regulation of body fluid homeostasis, food intake and endocrine axis. The aim was to investigate the expression and localisation of apelin– and its receptor APJ within the anatomical structures of the human eye by immunohistochemistry.
Methods: :
Posterior poles of human donor eyes (including sclera, choroid and retina) were formalin–fixed and embedded in paraffin. Thin sections were cut and stained against apelin–36 and apelin receptor APJ. Staining was visualized using the HRP–DAB method.
Results: :
The presence of Apelin–36 immunoreactivity was detected in RPE cells. The expression of apelin receptor APJ was also detected in the RPE cells, as well as in the bipolar ganglion cells of the retina.
Conclusions: :
As far as we know this is the first report about the expression and localisation of the APJ receptor and its ligand apelin within the posterior segment of the human eye. Having in mind the emerging role of apelin in the biology of different cell types (neurons, pancreatic cells, endothelium, adipocytes and other), this finding is opening the intriguing question about the role of the apelin pathway in the physiology of the human retinal pigment epithelium and its possible involvement in pathological processes has to be enrolled.
Keywords: retinal pigment epithelium • immunohistochemistry • retina