Congratulations to Dr. Cristian Ildefonso on the publication of “The Transcription Factor RelA is Required for Microglia Stress Responses,” which appears in the June 2025 issue of Investigative Ophthalmology & Visual Science.
Abstract
Purpose : RelA (p65), a key NF-kB transcription factor, drives pro-inflammatory gene expression. Inhibiting RelA via AAV gene delivery slowed retinal degeneration in the RPESod2cKO model of geographic atrophy. The underlying mechanisms remain unclear, but RelA inhibition reduced microglial migration to the RPE and decreased pro-inflammatory gene expression. We hypothesize that microglial activity during stress depends on RelA. This study examines whether RelA/p65 activation in retinal microglia is critical to retinal stress or degeneration effects.
Methods : The role of RelA in retinal microglia was studied using a tamoxifen-inducible mouse model (Cx3cr1CreERT2:RelAfl/fl, or microgliaRelAcKO) and RelAfl/fl control mice. Mice received a 75 mg/kg tamoxifen injection for five days, followed by a 30-day washout to eliminate Cx3cr1+ phagocytes. Deletion of RelA was confirmed with GFP-labeled cells. Morphological changes were assessed through retinal immunofluorescence and flow cytometry using GFP and CD11b antibodies. The effects on the retina were evaluated using ERG, OCT, and fundus imaging, while endotoxin-induced vitreous infiltration was measured to assess microglia stress responses.
Results : Our immunofluorescence and flow cytometry analyses revealed that the Cre-dependent deletion of RelA occurs in less than 10% of retinal microglia. Surprisingly, the microglia-specific deletion of RelA does not adversely affect retinal function or morphology. We observed no differences in the a- or b-wave responses or retinal thickness between the microgliaRelAcKO and RelA+ mice. Even after an endotoxin challenge, RelA-negative microglia maintained a more ramified structure. However, there was no impact on immune cell recruitment or the enlargement of retinal vessels between genotypes.
Conclusions : Our research indicates that RelA is found in a specific subset of microglia, and its absence does not seem to impact retinal health or the response to bacterial infections. Interestingly, microglia lacking RelA maintain a surveying morphology even under stressful conditions, such as exposure to endotoxins. Future studies will delve into whether the deletion of RelA affects other microglial subpopulations and examine the genomic profile of RelA-expressing microglia. In summary, inhibiting RelA in retinal microglia appears safe, suggesting its primary role is managing stress responses.