Expression of nephrin by human pancreatic islet endothelial cells

Aims/hypothesis: The islet microcirculation has morphological characteristics resembling those of renal glomeruli. Transcription of the nephrin gene, a highly specific barrier protein of the slit diaphragm of podocyte foot processes, has been reported in the pancreas, although its cellular localisation and function remain to be defined. In this study, we purified and characterised microvascular endothelial cells (MECs) isolated from human islets and investigated the expression and distribution of nephrin on these cells. Methods: Human islet MECs were extracted and purified using anti-CD105-coated immunomagnetic beads and their endothelial characteristics were confirmed by expression of classical endothelial markers and basal high-level expression of intercellular adhesion molecule-1 and TNF-alpha-inducible vascular cell adhesion molecule-1. Nephrin expression was assessed by immunofluorescence, flow cytometric analysis and western blotting on cell lysates, as well as by RT-PCR. Results: Immunofluorescence studies detected nephrin in a fine, punctate, diffuse pattern on cultured islet MECs, and also in human pancreatic islet sections. In both cases nephrin colocalised with endothelial markers. TNF-alpha treatment induced a marked reduction and redistribution of the protein in one or multiple aggregates. Nephrin expression was confirmed by flow cytometry, western blotting and RT-PCR studies. In contrast, nephrin could not be detected at the protein or mRNA level in human macro- and microvascular cells from other sites. Conclusions/interpretation: Nephrin is expressed at protein and mRNA levels in islet microendothelium, supporting the hypothesis that islet MECs exhibit distinctive morphological characteristics that indicate functional specialisation of potential pathophysiological importance.