Metallothionein is activated specifically in Müller cells in response to retinal stress

Abstract

Purpose : Metallothionein 1 (MT1) is a metal transporter and antioxidative protein that is essential in maintaining cellular physiological and redox balance. While the oxidative stress-related neuroprotective effect of the MT1 in central nervous system disorders has been investigated, the role of MT1 in the retina is still not clear.

Methods : Macular explants and peripheral retinal explants from four human donors were exposed to intense light stress (32k lux, left eye) or dim light (5 lux, right eye of the same donor). We first used single-cell RNA sequencing technology to compare the different transcription profiles of different types of retinal cells in the human macula and peripheral retina in response to photic stress. We identified one of the top differentially expressed genes, MT1, expressed more in the peripheral-dominant Müller cells in response to stress than the Müller cells that dominate the macula. We explored further the expression pattern of MT1 in the macula and temporal mid-periphery. We stained the MT1 protein together with the Müller cell-specific marker, cellular retinaldehyde–binding protein (CRALBP). We also assessed the topographic protein expression of MT1 in retinal punches (2mm diameter) from the macula, including the fovea, to the periphery by Western blot. The changes of MT1 expression in Müller cells in response to retinal stress was explored further in a mouse model of subretinal neovascularization, the JR5558 mouse. To understand the protective roles of MT1 in Müller cells, we used siRNA to knock down the MT1 in human primary Müller cells in vitro and evaluate their response to photic stress. The viability of huPMCs with or without knockdown under photic stress was assessed by an AlamarBlue viability assay and LDH cell toxicity assay.

Results : The MT1 protein was specifically expressed in Müller cells and expressed more in the peripheral retina than the macula. The peripheral Müller cells upregulated their MT1 transcription levels in response to stress much more than the macular Müller cells. MT1 expression was also activated in the JR5558 mouse. MT1 knockdown in vitro significantly reduced the viability and increased cell cytotoxicity of human primary Müller cells under stress.

Conclusions : Increased levels of MT1 in Müller cells may protect the peripheral retina and help explain why the macula is more prone to develop certain degenerative conditions than the peripheral retina.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.