Background We studied expression levels of genes encoding the two isoforms of Flk-1 and the effect on these of an intravitreal injection of triamcinolone acetonide (IVTA), in diabetic rat retinas.
Methods The right eyes of both streptozotocin-induced diabetic and non-diabetic rats received triamcinolone treatment, while the left eyes were sham-treated, thereby providing 4 treatment groups. Three pairs of PCR primers were designed to specifically amplify the total, long and truncated isoforms of rat Flk-1 mRNA. Gene transcriptional levels of the two isoforms were evaluated using quantitative polymerase chain reaction (real time RT-PCR). To detect the gene activities, standard efficiency standard curves were set up for each of the candidate isoforms.
Results The transcripts level of the long form Flk-1 is about 4.3 times higher than the level of the short form in the sham-treated normal rat retinas The expression of the total, long and short form of Flk-1 was up regulated by 1.5, 1.8 and 0.7 fold respectively in sham-treated diabetic retinas compared with the sham-treated non-diabetic retinas. IVTA inhibited the expression of the total, long and short forms of Flk-1 by 1.2, 2.0 and 0.3 fold respectively in the IVTA-treated diabetic compared to sham-treated retinas. There was no statistically significant difference in the expression of the total and short form of Flk-1 in IVTA treated diabetic/ non diabetic retinas compared with the sham treated diabetic/non diabetic retinas.
Conclusion The long form of Flk-1 is the predominant mediator of VEGF-A in the pathogenesis of DR, and can be significantly inhibited by IVTA treatment. The short form, which cannot be phosphorylated, does not appear to contribute to the pathogenesis of DR. Further research is warranted to establish whether the truncated form of Flk-1 can be used clinically as a dominant negative inhibitor of the effects of Vascular Endothelial Growth Factor. |
