Description
Purpose
Biallelic mutations in ARHGEF18 cause adult-onset retinal degeneration, but its retinal function is unknown. Arhgef18/p114RhoGEF is a RhoA exchange factor that regulates the mechanical stability of epithelial cell–cell adhesions. We therefore hypothesized that it supports retinal integrity by stabilizing cell–cell adhesion in specific retinal cell types. We investigated the localization of Arhgef18/p114RhoGEF in the retina and the consequences of genetic knockouts in different retinal cells.
Methods
Arhgef18 in mice was deleted in Müller glial cells using a Pdgfra-Cre driver and in endothelial cells using Tie2-Cre. Retinal structure and function were assessed by SD-OCT, fundus imaging, fluorescein angiography, ERG, and histology. Outer limiting membrane (OLM) integrity and retinal degeneration were evaluated by immunofluorescence and TUNEL assays. Mechanistic studies were performed in cultured human Müller glia (MIO-M1A) using siRNA-mediated ARHGEF18 depletion combined with assays to identify deregulated signaling mechanisms and metabolic dysfunction.
Results
Arhgef18/p114RhoGEF associated with the retinal OLM, colocalizing with ZO-1 and p120-catenin. Müller cell–specific knockout led to OLM disruption and progressive vision loss by P60. Although retinas initially formed normally, retinal rosettes appeared by P8 and were followed by OLM dissociation, retinal thinning, and vascular leakage. ARHGEF18/p114RhoGEF depletion in cultured Müller cells confirmed disruption of junctional recruitment of OLM proteins. The depletion also activated NF-κB and β-catenin signaling, as well as the multifunctional kinase TBK1, while reducing mitochondrial activity. TBK1 inhibition or metabolic support with nicotinamide attenuated NF-κB and β-catenin signaling and restored mitochondrial function.
Conclusions
Arhgef18/p114RhoGEF is a novel component of the OLM required for junctional stability and photoreceptor survival. Our results also identify a druggable pathway that may be exploited to treat ARHGEF18-related and, possibly, other OLM-associated retinal degenerations.
Lay Abstract
The retina is a delicate layer at the back of the eye that is essential for vision. In some people, inherited genetic changes can cause the retina to gradually deteriorate, leading to vision loss. However, for many of these conditions, the underlying mechanisms are still unclear. Our research focuses on a protein called ARHGEF18, which has recently been linked to adult-onset retinal degeneration.
We found that ARHGEF18 plays a key role in maintaining the structure of the retina by supporting a barrier known as the outer limiting membrane. This structure helps keep retinal cells properly organised and functioning. Using mouse models, we showed that loss of this protein disrupts retinal structure early in life, eventually leading to progressive damage and vision impairment.
At the cellular level, we discovered that reduced ARHGEF18 affects how retinal support cells interact, activates harmful inflammatory signals, and impairs energy production within cells. Encouragingly, we identified potential ways to counteract these effects. By targeting specific signalling pathways or boosting cellular metabolism, we were able to restore some cellular functions in laboratory models.
These findings provide new insight into how retinal degeneration develops and highlight promising targets for future treatments to protect vision.
| Lay Title | A Protective Protein in the Eye: New Insights into Retinal Degeneration and Treatment Opportunities |
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| Role | Postdoctoral Researcher |