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Biochemical characterization of retinal protein and phospholipid synthesis in mice exposed transplacentally to
1Laboratory of Retinal Cell and Molecular Biology, National Eye Institute, Bethesda, Md 20892.
Abstract:
Transplacental exposure to the DNA alkylating agent N-methyl-N-nitrosourea on day 16 of gestation in CD-1 albino mice induces a degeneration of the retina, the severity of which depends upon the dosage level of the drug. A 1 mg kg-1 dose provokes a progressive retinal degeneration in the offspring which begins at about 4-6 weeks of age and is characterized by gradual thinning of the retinal layers. A 15 mg kg-1 dosage of MNU provokes severe retinal dysplasia characterized morphologically by rosettes in the outer nuclear layer and loss of rod outer segments (ROS). In the present biochemical experiments, retinal protein synthesis was examined in mice 2-, 4-, and 6 weeks of age exposed to 1 mg kg-1 MNU and 2- and 5 weeks of age exposed to 15 mg kg-1 MNU. Phospholipid synthesis was examined in mice 2-, 4-, 6- and 12 weeks of age exposed to 1 mg kg-1 MNU and at 2 weeks in mice exposed to 15 mg kg-1 MNU. Retinas were incubated for 2 hr at 37 degrees C in media supplemented with either [3H]leucine for protein synthesis studies or [3H]glycerol for phospholipid synthesis experiments. Aliquots of crude ROS and the retinal debris were taken for protein determination, scintillation counting, SDS-PAGE separation of labeled opsin, phosphorus determination and TLC separation of phospholipids. Results indicated that mice exposed to 1 mg kg-1 MNU did not differ significantly from age-matched controls in these measurements, whereas mice exposed to 15 mg kg-1 MNU were significantly different from controls. These results suggest that even as early as 2 weeks of age protein and lipid metabolism are adversely affected in mice exposed to the higher dose of the alkylating agent at a critical time in retinal development, but general protein and lipid synthesis is not affected in animals exposed to 1 mg kg-1 MNU at least up to 12 weeks of age. These studies suggest further investigation of more subtle derangement in the retinal function in animals exposed to low levels of MNU.
Insights
High-dose N-methyl-N-nitrosourea (MNU) exposure in pregnant mice causes severe retinal dysplasia in offspring. Lower MNU doses did not significantly impact retinal protein or phospholipid synthesis.
Area of Science:
- Neuroscience
- Toxicology
- Developmental Biology
Background:
- Transplacental exposure to DNA alkylating agents can impact fetal development.
- N-methyl-N-nitrosourea (MNU) is a known DNA alkylating agent with teratogenic potential.
- Retinal development is a sensitive period for environmental insults.
Purpose of the Study:
- To investigate the biochemical effects of transplacental N-methyl-N-nitrosourea (MNU) exposure on retinal development in mice.
- To determine the dose-dependent impact of MNU on retinal protein and phospholipid synthesis.
- To assess the long-term consequences of early-life MNU exposure on retinal biochemistry.
Main Methods:
- CD-1 albino mice were exposed transplacentally to 1 mg/kg or 15 mg/kg MNU on day 16 of gestation.
- Retinal protein and phospholipid synthesis were measured at various ages post-exposure using radiolabeled precursors ([3H]leucine and [3H]glycerol).
- Biochemical analyses included protein determination, scintillation counting, SDS-PAGE, phosphorus determination, and thin-layer chromatography (TLC).
Main Results:
- Mice exposed to 15 mg/kg MNU exhibited significant alterations in retinal protein and phospholipid metabolism as early as 2 weeks of age.
- Exposure to 1 mg/kg MNU did not result in significant differences in retinal protein or phospholipid synthesis compared to controls up to 12 weeks of age.
- Morphological changes, including retinal dysplasia and loss of rod outer segments, were observed at the higher MNU dose.
Conclusions:
- High-dose MNU exposure during gestation severely disrupts retinal biochemical pathways, affecting protein and lipid metabolism.
- Low-dose MNU exposure did not elicit significant biochemical changes in retinal protein or lipid synthesis, suggesting a threshold effect.
- Further research is warranted to explore subtle functional deficits in retinal function following low-level MNU exposure.