Expression of stromal cell-derived factor 1 is increased in the retina of experimental diabetic rats

Abstract

To investigate the expression of stromal cell-derived factor 1 (SDF-1) in retina of experimental diabetic rats. Thirty four healthy male Wistar rats of six to eight weeks old were chosen and divided randomly into 3 groups: normal control (CON, n = 8), diabetes mellitus 2 months (DM2M, n = 14) and 3 months (DM3M, n = 12). Diabetes was induced by a single intraperitoneal injection of streptozotocin (STZ) (60 mg/kg). At the end point, immunochemistry and digital photomicrography analysis were employed to localize and quantitate the expression of SDF-1 in the retinas. The ratios of integrated optical density (IOD) to area of interest (AOI) were calculated to evaluate the intensities of positive staining. Values of z and t, as well as P value of each, were determined by Wilcoxon-Mann-Whitney test and Student's t-test, respectively. Immunofluorescent double-staining was used to indicate the co-expression of SDF-1 and hypoxia-inducible factor-1 (HIF-1), a pivotal transcription factor activated by hypoxia. The SDF-1 mRNA of the retina from DM2M (n = 4) and CON (n = 2) was detected by real-time RT-PCR. Copies of SDF-1 mRNA were then adjusted by the copies of beta-actin mRNA in each sample. Differences between groups were compared by a Student's t test. Positive immunohistochemical staining for SDF-1 was found in each group, most of which located in the inner part of the retina, especially at the inner nuclear layer (INL) and ganglion cell layer (GCL). The inter-quartile range of IOD/AOI of SDF-1 was between 0.6 x 10(-2) to 1.5 x 10(-2) in diabetic group, and 1.1 x 10(-3) to 2.4 x 10(-3) in control group (z = -3.359, P < 0.001). There was no significant difference between DM2M and DM3M (t = 0.952, P > 0.05). Co-expression of SDF-1 and HIF-1 was found in some cells in the inner part of the retina of diabetic rats. Copies of SDF-1 mRNA in DM2M were 2.3 x 10(-4) +/- 1.2 x 10(-4), and those in CON were 2.9 x 10(-4) +/- 1.0 x 10(-4). The ratios of them to beta-actin were 3.3 x 10(-2) +/- 8.5 x 10(-3) for DM2M and 1.7 x 10(-2) +/- 5.7 x 10(-3) for CON (t = 2.33, P < 0.05). Possibly promoted by HIF-1, expression of SDF-1 is increased in the retinas of diabetic rats, which may play an important role in the mechanism of diabetic retinopathy.