metallothionein and Retinal-Degeneration

Retinal photoreceptor damage is a common feature of ophthalmic disorders, such as age-related macular degeneration and retinitis pigmentosa. Oxidative stress has a key role in these diseases. Metallothioneins (MTs) are a family of cysteine-rich proteins, and various physiologic functions have been reported, including protection against metal toxicity and antioxidative potency. We investigated the functional role of MT-III in light-induced retinal damage.. The expression of retinal MT-I, -II, and -III mRNA was evaluated by real-time reverse-transcription PCR in retina exposed to light. Retinal damage in MT-deficient mice was induced by exposure to white light at 16,000 lux for 3 hours after dark adaptation. Photoreceptor damage was evaluated histologically by measuring the thickness of the outer nuclear layer (ONL) 5 days after light exposure and by electroretinogram recording. In an in vitro experiment, the MT-III siRNAs were tested for their effects on light-induced mouse photoreceptor cell (661W) damage.. The mRNAs of the MTs were increased significantly in murine retina after light exposure. The ONL in the MT-III-deficient mice was remarkably thinner compared to light-exposed wild-type (WT) mice, and a- and b-wave amplitudes were decreased; the damage induced in MT-I/-II-deficient mice was comparable to that observed in WT mice. MT-III knockdown by siRNA in 661W exacerbated the cell damage and increased the production of reactive oxygen species in response to light exposure.. These findings suggested that MT-III can help protect against light-induced retinal damage compared to MT-I/II. Some of these effects may be exerted by its antioxidative potency.

Topics: Animals; Cell Culture Techniques; Disease Models, Animal; Disease Progression; Electroretinography; Female; Gene Expression Regulation; Light; Male; Metallothionein; Metallothionein 3; Mice; Nerve Tissue Proteins; Oxidative Stress; Radiation Injuries, Experimental; Reactive Oxygen Species; Retina; Retinal Degeneration; RNA, Messenger

Metallothioneins (MTs) in the brain and retina are believed to bind metals and reduce free radicals, thereby protecting neurons from oxidative damage. This study was undertaken to investigate whether retinal photoreceptor (PR) cells lacking MTs are more susceptible to hyperbaric oxygen (HBO)-induced cell death in vivo.. Wild-type (WT) and MT-knockout (MT-KO) mice lacking metallothionein (MT)-1 and MT-2 were exposed to three atmospheres of 100% oxygen for 3 hours, 3 times per week for 1, 3, or 5 weeks. The control animals were not exposed. Histologic analysis of PR viability was performed by counting rows of nuclei in the outer nuclear layer (ONL). Ultrastructure studies verified PR damage.. HBO exposure produced a major loss of PR cells in the central retinas of WT and MT-KO mice, with no effect on the peripheral retina even at the longest (5 weeks) exposures. The degree of PR damage and cell death increased with duration of HBO exposure. One week of HBO exposure was insufficient to cause PR death, but tissue damage was observed in the inner and outer segments. At 3 weeks, the rows of PR nuclei in the central retina were significantly reduced by 38% in WT and 28% in MT-KO animals. At 5 weeks, PR loss was identical in WT (34%) and MT-KO (34%) animals and was comparable to that in WT at 3 weeks.. The data suggest that MT-1 and -2 alone are not sufficient for protecting PRs against HBO-induced cell death. The selective degeneration of central PRs may provide clues to mechanisms of oxidative damage in retinal disease.

Topics: Animals; Cell Death; Cell Nucleus; Cell Survival; Disease Susceptibility; Hyperbaric Oxygenation; Metallothionein; Mice; Mice, Knockout; Photoreceptor Cells; Retinal Degeneration

Oxidative stress plays a role in human age-related macular degeneration and in the light damage model of retinal degeneration. Metallothionein (MT), an antioxidant, has been reported to protect retinal pigment epithelial cells against apoptosis and oxidative stress. The purpose of this study was to evaluate changes in MT expression level and retinal localization following light damage. To accomplish this, Balb/c mice were exposed to cool white fluorescent light (10,000 lx) for 7 hr. In three independent experiments, at several intervals after the light injury, retinal MTs were studied at the protein level by immunohistochemistry (IHC) and Western analysis, and at the mRNA level by quantitative PCR with isoform-specific primers. Western analysis and IHC indicated an increase in metallothionein protein following light damage. MT localized to the retinal pigment epithelium and several layers of neural retina. Quantitative PCR identified the expression of MT I-III isoforms, not the MT IV isoform in the mouse retina, and, following light damage, showed increased expression of retinal MT-I and MT-II mRNAs by 8- and 22-fold, respectively. Increased expression of the antioxidant MT in the light damaged mouse retina suggests that upregulation of MT is an important acute retinal response to photo-oxidative stress.

Topics: Animals; Light; Male; Metallothionein; Mice; Mice, Inbred BALB C; Oxidative Stress; Polymerase Chain Reaction; Radiation Injuries, Experimental; Retina; Retinal Degeneration; RNA, Messenger; Up-Regulation