Abstract
Purpose :
There is increasing evidence to support a vascular role in the pathophysiology of glaucoma with one element possibly involving insufficient or erratic blood supply to the proximal optic nerve and retina. The α1 subunit of soluble guanylate cyclase (GC1), an enzyme involved in a major pathway of blood flow regulation, has been implicated through human GWAS studies with glaucoma incidence. Because aged GC1 knockout mice exhibit characteristics common to glaucoma, we sought to investigate whether GC1 signaling affected retinal morphology and integrity of the neurovascular unit, which could contribute to the neurodegeneration observed in the model.
Methods :
Age-matched 3- or 15-month GC1-/- and WT mice were utilized throughout the study. Using immunohistological staining and fluorescein angiography, we assessed retinal vasculature and astrocytic morphology. We implemented the REAVER analysis tool to quantify multiple blood vessel properties such as length, density, and diameter. We also manually quantified the length of higher-order branches. Custom written code was also used to quantify regional density of GFAP across wholemount retinas as well as assess radial complexity of the GFAP distribution through Scholl analysis.
Results :
Aged GC1-/- mice exhibit peripheral retinal vessel dilation compared to WT (33.1 ± 6.1 µm vs. 28.4 ± 6.3 µm diameter; p = 0.015) as well as an increased frequency of shorter capillary branches (p<0.001). There is evidence of blood-retinal-barrier (BRB) breakdown and vessel leakage in aged GC1-/- mice that is absent in age-matched WT mice. GC1-/- mice show aberrant isolectin-B4 staining in a debris-like pattern and increased leakage of fluorescein into the retina by fundus imaging. Retinal vessel compromise coincided with an abnormal morphological astrocyte phenotype; focal regions of GC1-/- retina exhibit a highly disorganized distribution of astrocytes, with areas of dense “matted” astrocytic networks surrounding major blood vessels as well as increased global GFAP-positive density across the retina.
Conclusions :
Together our results indicate that dysfunctional GC1-cGMP signaling leads to alterations in retinal vessel and astrocyte morphology with age, which may lead to interruption of blood flow to exacerbate or trigger neurodegeneration. Our results suggest that functional cGMP signaling is important for maintaining the BRB and retinal astrocyte morphology.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.