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Microperoxisomes in retinal pigment epithelium
Abstract:
Microperoxisomes were found to be abundant in the retinal pigment epithelium of the human, rhesus monkey, mice, rats, domestic fowl, and frog by ultrastructural histochemistry. They were rare in other cells of the retina and choroid. These organelles had a granular matrix, ranged in diameter from 0.15 mum to 0.30 mum, and were bound by a single tripartite membrane which often maintained slender connections with the smooth endoplasmic reticulum and other microperoxisomes. They exhibited a positive reaction (electron opaque product) following incubation in diaminobenzidine and H2O2 for the demonstration of the peroxidatic activity of catalase (Novikoff et al., J. Histochem. Cytochem. 20: 1006, 1972). The reaction was inhibited by: (1) aminotriazole; (2) dichlorophenol-indophenol; (3) preheating at 95 degrees C.; or (4) elimination of H2O2. Microperoxisomes, like the well-known peroxisomes (microbodies) of liver cells have been inplicated in various aspects of lipid metabolism and the detoxification of H2O2. We demonstrated for the first time that microperoxisomes respond to drug-induced changes in lipid metabolism, as previously shown for peroxisomes. Nafenopin is a recently utilized drug which greatly decreases serum lipids, increases hepatic catalase activity, and induces an increased size and number of hepatic peroxisomes. Black, beige, albino, and obese mutant mice of the C57BL/6J strain treated with nafenopin for several weeks showed a two- to threefold increase in the number of microperoxisomes in the retinal pigment epithelium. Microperoxisomes of the retinal pigment epithelium may be involved in the transport, storage, and rapid turnover of lipids associated with the maintenance of photoreceptor outer segment disc membranes.
Insights
Microperoxisomes are abundant in the retinal pigment epithelium and respond to drug-induced lipid changes. These organelles may play a role in lipid metabolism and photoreceptor health.
Area of Science:
- Cell Biology
- Histochemistry
- Ophthalmology
Background:
- Microperoxisomes are organelles found in various cell types.
- They are similar to peroxisomes and implicated in lipid metabolism and hydrogen peroxide detoxification.
- Their presence and function in the retinal pigment epithelium (RPE) are not fully understood.
Purpose of the Study:
- To investigate the presence and characteristics of microperoxisomes in the RPE.
- To determine if RPE microperoxisomes respond to drug-induced changes in lipid metabolism.
- To explore the potential role of RPE microperoxisomes in photoreceptor maintenance.
Main Methods:
- Ultrastructural histochemistry was used to identify and characterize microperoxisomes in the RPE of multiple species.
- Diaminobenzidine and hydrogen peroxide incubation demonstrated peroxidatic activity of catalase.
- Mice were treated with nafenopin, a drug known to affect lipid metabolism and hepatic peroxisomes, to observe changes in RPE microperoxisomes.
Main Results:
- Microperoxisomes were abundant in the RPE of humans, monkeys, mice, rats, fowl, and frogs, but rare elsewhere in the retina and choroid.
- These organelles exhibited catalase activity and were connected to the smooth endoplasmic reticulum.
- Nafenopin treatment led to a two- to threefold increase in RPE microperoxisome number in mice.
Conclusions:
- Microperoxisomes are a significant organelle in the RPE across various species.
- RPE microperoxisomes respond to drug-induced alterations in lipid metabolism, similar to hepatic peroxisomes.
- These findings suggest a role for RPE microperoxisomes in lipid transport, storage, and turnover, crucial for photoreceptor outer segment disc membranes.