Potential role of zinc dyshomeostasis in matrix metalloproteinase-2 and-9 activation and photoreceptor cell death in experimental retinal detachment

Abstract

PURPOSE. We investigated whether zinc dyshomeostasis, a known mechanism of cell death in acute brain injury, contributes to the activation of matrix metalloproteinases (MMPs) and photoreceptor cell death in experimental retinal detachment (RD). METHODS. RD was induced in mice by subretinal injection of 1:1 mixture of balanced salt solution and 1% sodium hyaluronate. On days 1 and 3 post RD, eyeballs were sectioned and examined for cell death (TUNEL staining), the degree of hypoxic insult (Hypoxyprobe staining), free zinc levels (TFL-Zn staining), and MMP-2 and-9 activity (gelatin zymography). In addition, we examined whether modulating extracellular zinc concentration or MMP activation in subretinal fluid affected photoreceptor cell death in RD. These changes were further examined in primary retinal cell and photoreceptor-derived cell (661W) cultures. RESULTS. Photoreceptor cell death peaked on day 3 post RD. Intracellular zinc markedly decreased on day 1 post RD, and subsequently accumulated on day 3. MMP-2 and-9 activity showed a concurrent increase in detached retinas. Detached retinas stained with Hypoxyprobe showed strongly positive cells, especially in the photoreceptor layer. Subretinal injection of a zinc-chelator (CaEDTA) or MMP inhibitor (GM6001, minocycline) at the time of RD significantly attenuated photoreceptor cell death in RD. Similar findings were confirmed in oxygen-glucose–deprived or zinc-exposed cell cultures. CONCLUSIONS. Upon RD, hypoxic retinal cells in deep layers underwent zinc dyshomeostasis, MMP activation, and ultimately death. These findings provide new insight into the possible mechanism of photoreceptor death in RD, and as such may prove useful in crafting protective measures for photoreceptor cells.