Abstract
Purpose :
The R345W mutation in EFEMP1 (a.k.a. fibulin-3, F3) causes a rare macular dystrophy (Malattia Leventinese/Doyne Honeycomb Retinal Dystrophy, ML/DHRD) resembling an early onset form of age-related macular degeneration (AMD). Studies have demonstrated that R345W knockin mice form basal laminar deposits (BLamDs) and they have also implicated complement activation as a key pathway in disease progression. Yet little additional information on these mice exists. Herein, we sought to thoroughly characterize the R345W EFEMP1 knockin mice with respect to any molecular or physiological differences vs. wild-type mice with the hope of identifying and eventually targeting new pathways for disease intervention.
Methods :
Homozygous R345W knockin mice on the C57BL/6 background (and their littermate controls) were aged up to 20 months prior to analysis. Anterior physiology was measured by in vivo confocal microscopy, rebound tonometer and slit lamp. In vivo retinal structure was evaluated by OCT (also by blue AF), and TEM, histology, and RPE flat mounts post euthanasia. Retinal function was assessed by ERG (scotopic [a,b,c-wave], photopic [a-, b-wave]). Molecular evaluation was achieved using IHC and qPCR.
Results :
No increase in corneal haze or stromal thickness were observed, contrasting our findings in EFEMP1 knockout mice. Slit lamp and IOP assessment were unremarkable in mutant mice. Total retinal thickness (by OCT) was not significantly different between groups (16 mo), while retinal AF was slightly, but significantly increased in mutant mice. Aged R345W mice (16 mo) formed canonical, thick, continuous BLamDs, consistent with previous observations. Histologically, aged R345W mice (16 mo) appeared to be more prone to photoreceptor/RPE disorganization/disruptions including RPE whorls. Yet, remarkably, no differences in any ERG functional readings were detected in R345W mice (up to 20 mo). At the molecular level, we detected significant increases in C3, casp1, Il1b and Nlrp3 (qPCR) in mutant RPE/choroid (18 mo) and increased staining for Nlrp3 and Iba1 in posterior sections (IHC).
Conclusions :
The R345W mice develop ultrastructural defects (BLamDs), disrupted photoreceptor/RPE organization and increased retinal autofluorescence. Molecularly, inflammasome activation may be a triggering event in ML/DHRD. Pharmacological or genetic targeting of Nlrp3 or Casp1 may alter the course of this AMD-like disease.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.