Abstract
Purpose :
Ischemia/Reperfusion (I/R) models retinal vein occlusion of diabetic retinopathy causing severe damage to the retina and retinal ganglion cell (RGC) loss. We previously showed that a-Melanocyte Stimulating Hormone (a-MSH) promotes RGC survival after I/R. There is a potential to use a-MSH agonists that are significantly more stable than native a-MSH. Therefore, we assayed some a-MSH analogs with different melanocortin receptor (MC) affinities for RGC protection following I/R
Methods :
Ischemia (I) was induced in the eyes of naive C57BL/6j mice by cannulation of the anterior chamber. The IOP was raised to 90 mmHg for 60 minutes. The cannula was removed, and IOP returned to normal for reperfusion (R). After the I/R procedure, mice were given two anterior chamber injections of either PBS or 1ng of a-MSH or a-MSH-analog on day 1 and day 5. The analogs were Peptide 1 (P1), PL-8177 an MC1r agonist; P2, MT-II an MC1r and MC3r agonist; P3, PL-9588 an MC1r and MC5r agonist; and P4, PG-901 an MC5r agonist but MC3r antagonist. There were 5 mice in each group. On the seventh day, the retinas were processed for H&E staining, IHC for GFAP, Iba1, and Tuj1. The number of hematoxylin-stained nuclei and Tuj1-stained cells were counted by sample-blinded analysis
Results :
The H&E staining showed that the I/R caused deformation of the retina in untreated and P4-treated eyes, but not with a-MSH, P1, P2, and P3-treated eyes. The total number of hematoxylin-stained nuclei (nuclei/mm) in the uninjured retina was 99±2.0 (mean±SEM) with significantly lower counts in untreated (71±2.2), P2 (82±3.8), and P4 (73±4.4) treated eyes, and not statistically different from counts of eyes treated with a-MSH (87±4.1), P1 (91±4.3), or P3 (94±2.7). The Tuj1 staining in the GCL demonstrated that the decrease in hematoxylin-stained nuclei was the loss of RGC. The number of Tuj1+ RGC in the uninjured retina was 58±4.5 with a significant decrease in untreated (31±2.8), P2 (44±1.3), and P4 (33±2.1) treated eyes and no statistical difference in the retinas of a-MSH (52±1.8), P1 (49±2.1), and P3 (48±2.7) treated eyes. Similar treatment effects were seen for GFAP expression and Iba1+ microglia cell density was significantly lower in I/R retinas treated with peptides that are MC1r agonists
Conclusions :
Agonizing the MC1r is necessary for melanocortin-mediated maintenance of retinal structure and survival of RGCs in eyes with I/R
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.