Heterogeneous vascular endothelial growth factor (VEGF) isoform mRNA and receptor mRNA expression in human glomeruli, and the identification of VEGF(148) mRNA, a novel truncated splice variant

Vascular endothelial growth factor (VEGF) mediates increased vascular perme ability and endothelial mitogenesis, and may orchestrate normal glomerular permselectivity and proteinuria. Distinct isoforms result from differential gene splicing. VEGF binds to two cell surface tyrosine-kinase receptors, K DR (kinase domain region) and Flt-I (fms-like tyrosine kinase-I). The latte r also exists in a soluble form (sFlt), which is inhibitory. We have studie d patterns of VEGF-isoform and VEGF-receptor expression in isolated single normal human glomeruli. mRNA from 190 glomeruli (from 20 individuals) was h arvested on to magnetic beads, and nested reverse transcription-PCR was per formed using primers for the VEGF isoforms and VEGF receptors. Simultaneous nested reverse transcription-PCR for CD45 was conducted in order to exclud e leucocyte contamination. Unexpected products were isolated, cloned and se quenced. Multiple patterns of glomerular VEGF mRWA isoform expression were identified. Most frequently (58%), all three common forms were expressed. V EGF(189) (i.e. 189-amino-acid form of VEGF) was expressed in 63%, VEGF(165) in 85% and VEGF(121) in 84% of glomeruli. Two unexpected PCR products were also identified: 18% of glomeruli expressed VEGF(145), and 27% of glomerul i expressed a new truncated VEGF splice variant, VEGF(148), lacking exon 6, the terminal part of exon 7 and exon 8. Multiple patterns of VEGF-receptor expression were also identified, the most common being expression of all t hree isoforms (28%). Overall, KDR was seen in 59% of glomeruli, Flt-I in 45 % and sFlt in 57%. Thus the expression of VEGF within normal glomeruli is c omplex and variable, with inter- and intra-individual variation. Furthermor e, sFlt appears to be the co-dominant form of VEGF receptor expressed withi n glomeruli, suggesting that, in healthy individuals, a degree of VEGF auto regulation is the norm. The physiological importance of VEGF(148) remains t o be confirmed.