May 01, 2020
Abnormal activation of signaling pathways related to angiogenesis, inflammation and oxidative stress has been implicated in the pathophysiology of retinopathy of prematurity (ROP), a leading cause of blindness in preterm infants.
Therapies for ROP include laser ablation of avascular retina and anti-vascular endothelial growth factor agents. However, "these therapies have side effects, and even with adequate treatment, visual acuity can be impaired. Targeted therapies with a lower side effect profile are needed," says Gavin W. Roddy, M.D., Ph.D., with Ophthalmology at Mayo Clinic in Rochester, Minnesota.
Stanniocalcin-1 (STC-1) is a multifunctional protein that is upregulated by cellular stresses. STC-1 is cytoprotective in neurons, photoreceptors and retinal ganglion cells; it also reduces intraocular pressure, oxidative stress and inflammation.
Dr. Roddy and fellow researchers Lauren A. Dalvin, M.D., and Michael P. Fautsch, Ph.D., also with Ophthalmology at Mayo Clinic's campus in Rochester, Minnesota, hypothesized that STC-1 might be a stress response protein capable of decreasing inflammatory and oxidative stress underlying ROP.
The research team evaluated STC-1 gene and protein expression in the Sprague-Dawley rat oxygen-induced retinopathy (OIR) model that is most similar to human ROP. After inducing OIR in wild-type and Stc-1(-/-) mice, the researchers isolated retinas and evaluated them for avascular and neovascular areas on retinal flat mounts.
Researchers performed a quantitative real-time polymerase chain reaction (PCR) to quantify gene expression and assayed the vascular endothelial growth factor (VEGF) by enzyme-linked immunosorbent assay (ELISA) in media obtained from induced pluripotent stem cell-derived retinal pigment epithelial (iPS-RPE) human cells after treatment with recombinant STC-1. Key findings from the study include:
- To determine whether STC-1 was upregulated in OIR, researchers quantified STC-1 in retina of rats subjected to OIR compared with room air controls. Compared with controls, OIR rat pups showed significantly increased expression of STC-1 mRNA at P17 (P < 0.01) and P20 (P = 0.02). This finding corresponded with the significant increase in STC-1 protein levels at P18 by Western blot, which was confirmed by densitometry.
- To determine whether STC-1 upregulation was pathological or protective, the researchers subjected Stc-1(-/-) and wild-type mice to OIR. Stc-1(-/-) mice subjected to OIR had increased avascular (15.2 ± 2.5% versus 20.2 ± 2.4%, P = 0.02) and neovascular (8.8 ± 3.7% versus 14.3 ± 2.7%, P < 0.05) areas at P17 compared with wild-type mice.
- To examine differential gene expression between wild-type and Stc-1(-/-) OIR mice, the research team selected known upregulated genes in the mouse OIR model at P17 as markers of disease induction. "Of particular note, VEGF-A was upregulated in Stc-1(-/-) versus wild-type controls (P = 0.03)," says Dr. Fautsch.
- To determine whether STC-1 had a direct effect on VEGF production, researchers selected iPS-RPE cells that produce VEGF in standard culture conditions. Treatment with STC-1 significantly reduced VEGF concentration in iPS-RPE conditioned media at 24 hours (P = 0.01).
The role of STC-1 in the OIR stress response
"We have shown that STC-1 is induced by OIR at the gene and protein level, adding OIR to the list of cellular stresses that induce STC-1 expression," says Dr. Roddy. "Our data suggest STC-1 is a regulator of OIR severity in part due to its effect on VEGF production. Reduction in both avascular and neovascular retina in the presence of STC-1 could be related to a combined effect of neuroprotective and anti-VEGF properties.
"This study, which was published in Current Eye Research in 2020, adds ROP to the list of disease models with worse outcomes in the absence of STC-1," says Dr. Dalvin. "Further studies are needed, however, to evaluate the therapeutic potential of STC-1 in ROP and other retinal vascular disorders."
For more information
Dalvin LA, et al. Stanniocalcin-1 is a modifier of oxygen-induced retinopathy severity. Current Eye Research. 2020;45:46.