A Model for Mast Cell Involvement in Geographic Atrophy

Abstract

Purpose : Mast cells (MCs) are effector cells of innate immunity that reside in choroid. We have previously demonstrated that MCs are elevated in number and in number of degranulated MCs in geographic atrophy (GA) choroid (Bhutto et al, B.J.O.. 2016) and MC tryptase is present in Bruchs membrane (BrMb) in GA subjects (McLeod et al, IOVS, 2017). The purpose of this study was to develop a rat model to demonstrate the functional significance of MC degranulation in choroid and determine whether GA-like changes occur after MC degranulation.

Methods : A hydrogel with 48/80 (a snake venom-like compound) or blank hydrogel was injected subconjunctivally in Sprague-Dawley rats. Rats were sacrificed 6 and 10 weeks after surgery. MCs were stained with nonspecific esterase (NSE), retinal pigment epithelial cells (RPE) labeled with RPE65 in whole mount choroids, and retinal and choroidal area determined in cryosections stained with picrosirius red. An antibody against the IL33 receptor (TPP-44) was administered intravitreally (12 ug in 3 ul/eye) each week to determine if it could prevent MC degranulation and its effect, which was assessed at 6 weeks post implantation.

Results : Choroidal MC degranulation was apparent at one week post implantation of 48/80 but not in blank hydrogel eyes. The choroid was edematous at 1 and 2 weeks post implantation and then the edema subsided in subsequent weeks. By 6 weeks, there was significant loss of RPE in eyes with 48/80 compared to blank hydrogel (p<0.005). The areas of retina and choroid in cryosections were similar in both groups at 6 weeks post implantation but reduction in retinal and choroidal areas was significant at 10 weeks post implantation in 48/80 eyes compared to blank hydrogel or to eyes at 6 weeks after implantation (p<0.05). TPP-44 significantly inhibited RPE loss at the 6 weeks time point (p<0.005 respectively).

Conclusions : Inducing MC degranulation in rat choroid in a slow release fashion resulted in loss of RPE at 6 weeks post implantation and significantly reduced retinal and choroidal areas by 10 weeks. Pharmacological blockade of the MC IL33 receptor reduced RPE loss at 6 weeks. Therefore, inhibiting MC degranulation prevented RPE loss, a phenotypic characteristic of GA.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.