Two Isoforms of Flk-1 Transcripts in Early Diabetic Rat Retinas

Abstract

Background: We studied the expression levels of genes encoding the two isoforms of fetal liver kinase-1 (Flk-1) and the effect of intravitreal injection of triamcinolone acetonide (IVTA) in diabetic rat retinas on the isoforms.

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 four treatment groups. Three pairs of polymerase chain reaction (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 PCR 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 with 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 diabetic retinopathy (DR) and can be significantly inhibited by the 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 (VEGF).

Keywords::

• Triamcinolone Acetonide
• Diabetic Retinopathy
• Isoforms of Flk-1
• Gene transcript
• VEGFA signalling

ACKNOWLEDGMENT

Dr. Xinyuan Zhang is supported by “The University of Sydney− China Scholarship Council” scholarship.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.