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Proteoglycan synthesis by chicken corneal explants
K Nakazawa1, T Isomura, S Shimoeda
1Section of Radiochemistry, Faculty of Pharmacy, Meijo University, Nagoya.
Insights
Corneal explants reveal that stromal tissue is rich in keratan sulfate proteoglycan and chondroitin sulfate/dermatan sulfate proteoglycan. Tissue interactions are crucial for proteoglycan synthesis in the cornea.
Area of Science:
- Ophthalmology
- Biochemistry
- Extracellular Matrix Biology
Background:
- Proteoglycans are essential components of the corneal extracellular matrix, playing vital roles in maintaining corneal structure and function.
- Keratan sulfate proteoglycans (KSPG) and chondroitin sulfate proteoglycans (CSPG) are the major proteoglycans found in the corneal stroma.
- Understanding the synthesis and regulation of corneal proteoglycans is crucial for addressing corneal diseases.
Purpose of the Study:
- To investigate the synthesis and distribution of proteoglycans in different corneal tissues.
- To explore the role of tissue interactions in proteoglycan synthesis within the cornea.
- To compare the catabolism and elimination of different glycosaminoglycan species in isolated corneal tissues.
Main Methods:
- Corneal explants from 3-day-old chicks were cultured in vitro with [35S]sulfate and [3H]glucosamine.
- Constituent tissues (stroma, epithelium, endothelium, corneo-scleral rim) were dissected and analyzed for proteoglycan incorporation.
- Individual tissues were also cultured separately to assess the impact of tissue interactions on proteoglycan synthesis.
Main Results:
- Stromal tissue showed the highest incorporation of 35S, with KSPG and CSPG as predominant proteoglycans.
- Heparan sulfate proteoglycan was the major proteoglycan in epithelial tissue.
- Isolated tissue cultures demonstrated decreased proteoglycan synthesis, suggesting intercellular interactions are important.
- Keratan sulfate species appeared to be more readily catabolized and eliminated from isolated stromal tissue compared to CSPG.
Conclusions:
- Corneal constituent tissues interact to facilitate proteoglycan synthesis.
- Keratan sulfate proteoglycans may be more susceptible to degradation when the corneal stroma is not supported by surrounding tissues.
- These findings contribute to understanding corneal matrix homeostasis and potential therapeutic targets for corneal diseases.
Abstract:
Corneal explants with scleral rims were freshly prepared from 3-day-old hatched chicks, cultured in vitro for 5 h in the presence of [35S]sulfate and [3H]glucosamine, then the constituent tissues (stroma, epithelium, endothelium, and corneo-scleral rim) were dissected from the explants. Incorporation of 35S activity into stromal tissue was the highest among the constituent tissues (54% of the total). Two predominant proteoglycans were identified in the stromal fraction: keratan sulfate proteoglycan and chondroitin sulfate/dermatan sulfate proteoglycan. Whereas heparan sulfate proteoglycan was found in epithelial tissue as the major proteoglycan therein, it was a minor component in the other tissues. In contrast, most of the 35S-labeled material in the culture medium was the sulfated glycoprotein, which was probably synthesized and secreted by epithelial cells. When each constituent tissue was separately cultured in the presence of radioactive precursors, incorporation of radioactivities into each tissue decreased markedly compared with those into the respective tissues obtained by dissection after culture of the whole cornea with scleral rim. This suggests that corneal constituent tissues interact with each other for proteoglycan synthesis. But the glycosaminoglycan compositions of stromal proteoglycans synthesized in stroma cultured alone and in stroma from the cultured cornea with scleral rim were similar to each other; the two major glycosaminoglycans were chondroitin sulfate/dermatan sulfate and keratan sulfate. In contrast, when stromal tissue was cultured alone, most of the 35S-labeled material in the culture medium was keratan sulfate proteoglycan and free keratan sulfate chain, suggesting that keratan sulfate species are catabolized and eliminated more readily from collagen lamina than chondroitin sulfate/dermatan sulfate species, unless the corneal stroma is surrounded with other tissues. Whereas keratan sulfate was not detected in epithelium cultured alone, a small amount of it was found in endothelium cultured alone.