cGAS Drives Noncanonical-Inflammasome Activation in Age-Related Macular Degeneration

Geographic atrophy is a blinding form of age-related macular degeneration characterized by retinal pigmented epithelium (RPE) death; the RPE also exhibits DICER1 deficiency, resultant accumulation of endogenous Alu-retroelement RNA, and NLRP3-inflammasome activation. How the inflammasome is activated in this untreatable disease is largely unknown. Here we demonstrate that RPE degeneration in human-cell-culture and mouse models is driven by a noncanonical-inflammasome pathway that activates caspase-4 (caspase-11 in mice) and caspase-1, and requires cyclic GMP-AMP synthase (cGAS)-dependent interferon-β production and gasdermin D-dependent interleukin-18 secretion. Decreased DICER1 levels or Alu-RNA accumulation triggers cytosolic escape of mitochondrial DNA, which engages cGAS. Moreover, caspase-4, gasdermin D, interferon-β, and cGAS levels were elevated in the RPE in human eyes with geographic atrophy. Collectively, these data highlight an unexpected role of cGAS in responding to mobile-element transcripts, reveal cGAS-driven interferon signaling as a conduit for mitochondrial-damage-induced inflammasome activation, expand the immune-sensing repertoire of cGAS and caspase-4 to noninfectious human disease, and identify new potential targets for treatment of a major cause of blindness

Topographic distribution of choriocapillaris flow deficits in healthy eyes.

PURPOSE:To evaluate the topographic distribution of the choriocapillaris (CC) flow deficits in a population of healthy subjects. METHODS:Using a swept-source optical-coherence tomography angiography (SS-OCTA) device, two repeated volume 6 x 6 mm and 3 x 3 mm scans were acquired in healthy subjects at the Doheny-UCLA Eye Centers. The en-face CC angiogram was binarized and analyzed for percentage of flow deficits (FD%) using a grid of progressive, concentric rings covering a circular area with a diameter of 2.5 mm (in the 3 x 3 mm scans) and 5 mm (in the 6 x 6 mm scans). The FD% for each ring was plotted against the distance from the fovea. The linear trendline of the resulting curve was analyzed and the slope (m) and intercept (q) were computed. RESULTS:Seventy-five eyes of 75 subjects were enrolled and divided into three subgroups based on age (year ranges: 21-40, 41-60 and 61-80). For the entire cohort and within each subgroup, there was a significant association between distance from the fovea and FD% in both 3X3 mm and 6X6 mm scans, with flow deficits increasing with closer proximity to the foveal center. Age was a significant predictor for both m and q for both scan patterns, with older subjects showing a steeper slope. CONCLUSIONS:In SS-OCTA images, the topographic distribution of CC flow deficits varies with distance from the fovea and age. In particular, the FD% tends to decrease from the fovea towards the periphery, with a steeper decline with advancing age. These normal trends may need to be accounted for in future studies of the CC in disease

Quantification of Anterior Chamber Cells in Children With Uveitis Using Anterior Segment Optical Coherence Tomography

PurposeTo evaluate the feasibility of anterior segment optical coherence tomography (AS-OCT) for measuring anterior chamber (AC) cells in children with uveitis and to compare different AS-OCT acquisition modes.DesignValidity and reliability analysis.MethodsWe enrolled children younger than 18 years who had uveitis involving the anterior segment and children without eye disease as controls. All underwent clinical grading of AC cells. AC images of each eye were obtained using the Optovue Avanti RTVue XR AS-OCT. Two acquisition modes were used: a single cross-sectional line scan and an 8-line radial scan in an asterisk pattern. Two independent, masked graders counted cells manually on AS-OCT images. Rater agreement was assessed using intraclass correlation (ICC).ResultsIncluded were 30 children (59 eyes) with uveitis (median age 13.0 years, range 3-17 years) and 20 control children (40 eyes, median age 10.5 years, range 4-17 years). The number of eyes assigned each clinical grade of cells were as follows: none, 32 (54%); 0.5+, 12 (20.3%); 1+, 5 (8.5%); 2+, 8 (13.6%); 3+, 2 (3.4%). ICC of graders for line and radial scan protocols were 0.87 and 0.90. There was no significant difference between acquisition modes for pooled grader results (95% CI for difference: -0.04 to 0.14). ICC of cell counts between line and radial scan protocols was 0.85 (95% CI: 0.69-0.90). No control eyes had cells on AS-OCT images.ConclusionsQuantification of AC cell in children with uveitis is feasible with AS-OCT and has excellent reliability between different graders and acquisition modes

Alu complementary DNA is enriched in atrophic macular degeneration and triggers retinal pigmented epithelium toxicity via cytosolic innate immunity

Long interspersed nuclear element-1 (L1)–mediated reverse transcription (RT) of Alu RNA into cytoplasmic Alu complementary DNA (cDNA) has been implicated in retinal pigmented epithelium (RPE) degeneration. The mechanism of Alu cDNA–induced cytotoxicity and its relevance to human disease are unknown. Here we report that Alu cDNA is highly enriched in the RPE of human eyes with geographic atrophy, an untreatable form of age-related macular degeneration. We demonstrate that the DNA sensor cGAS engages Alu cDNA to induce cytosolic mitochondrial DNA escape, which amplifies cGAS activation, triggering RPE degeneration via the inflammasome. The L1-extinct rice rat was resistant to Alu RNA–induced Alu cDNA synthesis and RPE degeneration, which were enabled upon L1-RT overexpression. Nucleoside RT inhibitors (NRTIs), which inhibit both L1-RT and inflammasome activity, and NRTI derivatives (Kamuvudines) that inhibit inflammasome, but not RT, both block Alu cDNA toxicity, identifying inflammasome activation as the terminal effector of RPE degeneration