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Expression of antioxidant protective proteins in the rat retina during prenatal and postnatal development
1Department of Microbiology and Immunology, University of South Carolina School of Medicine, Columbia 29208, USA.
Insights
Premature rat retinas lack key antioxidant defenses like heme oxygenase-1 and catalase at birth, increasing vulnerability to oxidative stress. This study reveals crucial insights into retinopathy of prematurity development.
Area of Science:
- Ophthalmology
- Neonatology
- Molecular Biology
Background:
- Retinopathy of prematurity (ROP) involves impaired retinal capillary growth.
- Cyclic oxygen exposure in premature infants can trigger neovascularization and retinal detachment.
- ROP's sensitivity to oxidative stress is linked to insufficient antioxidant proteins.
Purpose of the Study:
- To investigate the expression patterns of antioxidant protein mRNAs in developing rat retinas.
- To determine if premature retinas have reduced antioxidant defenses at birth.
Main Methods:
- In situ hybridization and RT-PCR with Southern blot analysis were used.
- Antioxidant mRNA expression (heme oxygenase-1, metallothionein, superoxide dismutase, catalase) was measured.
- Retinas were analyzed from embryonic day 16 to postnatal day 4.
Main Results:
- Superoxide dismutase mRNA levels remained constant.
- Metallothionein mRNA decreased significantly around birth.
- Catalase and heme oxygenase-1 mRNA levels were low until birth, with catalase increasing postnatally.
Conclusions:
- Rat retinas exhibit distinct developmental patterns for antioxidant mRNAs.
- Low expression of heme oxygenase-1 and catalase mRNAs near birth suggests diminished antioxidant capacity.
- Premature rats, and likely humans, may be born with inadequate antioxidant defenses, predisposing them to ROP.
Purpose:
In retinopathy of prematurity, capillary growth in the retina is attenuated. Subsequent cyclic elevation of oxygen levels leads to renewed capillary growth that may eventually result in retinal detachment. It is hypothesized that the sensitivity of the premature retina to oxidative shock results from the absence of antioxidant protective proteins.
Methods:
The expression of heme oxygenase-1, metallothionein, superoxide dismutase, and catalase mRNAs was measured in retinas of rats from 6 days before birth to 4 days after birth using in situ hybridization and semiquantitative reverse transcription-polymerase chain reaction with Southern blot analysis.
Results:
Superoxide dismutase mRNA was expressed to a similar extent at all time points. Metallothionein mRNA expression, which was high at embryonic days (E) 16 and 18, decreased to low levels by the time of birth and remained low at least until 4 days after birth. Catalase mRNA expression was low until birth and increased until at least postnatal day 4. Heme oxygenase-1 mRNA showed low expression at E16 and E18, increased before birth, and then diminished.
Conclusions:
Four antioxidant protein mRNAs showed very different patterns of expression in the rat retina. Two of these proteins, heme oxygenase-1 and catalase, were expressed at relatively low levels until approximately the time of birth. The former is important in protection against heme-mediated generation of reactive oxygen species, whereas the latter protects against hydrogen peroxide-generated damage. As a result of the low expression of these mRNAs, and presumably the proteins encoded by them, the premature rat (and probably the premature human) is likely to be born without a full complement of antioxidant defenses.