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Expression of small leucine-rich proteoglycans during experimental fungal keratitis
Xiaoyong Yuan1, Xia Hua, Kirk R Wilhelmus
1Sid W. Richardson Ocular Microbiology Laboratory, Cullen Eye Institute, Department of Ophthalmology, Baylor College of Medicine, Houston, TX, USA.
Purpose:
To investigate the expression of members of the small leucine-rich proteoglycan family and related leucine-rich repeat proteins during the inception and progression of experimental keratomycosis.
Methods:
Scarified corneas of BALB/c mice were topically inoculated with Candida albicans and monitored daily over 1 week for corneal opacification. A murine gene microarray compared infected corneas to controls 1 day postinoculation (PI). Real-time reverse transcriptase polymerase chain reaction determined small leucine-rich proteoglycan gene levels in infected and mock-infected corneas at 1, 3, and 7 days PI and in normal corneas. Immunostaining localized keratocan protein in murine corneas.
Results:
Eyes with C. albicans keratitis rapidly developed corneal inflammation with opacification. Microarray showed that genes for biglycan, asporin, lumican, fibromodulin, osteomodulin, keratocan, osteoglycin, and chondroadherin were significantly (P < 0.01) downregulated more than 2-fold at the onset of fungal keratitis. By real-time reverse transcriptase polymerase chain reaction, the gene encoding keratocan was initially downregulated 137-fold and remained downregulated 2.5-fold at 1 week. Genes coding for lumican, osteomodulin, and fibromodulin were downregulated 4- to 9-fold 1 day after fungal inoculation and returned to normal levels by 3 days PI. Immunofluorescence demonstrated that keratocan was present throughout the corneal stroma of normal mice and mock-infected controls but was markedly less during early fungal keratitis.
Conclusions:
Transcriptional levels of keratocan and other proteoglycans decrease during the initial stages of C. albicans keratitis. Alterations in the stromal extracellular matrix may contribute to the acute inflammatory response of corneal infection.
Insights
Small leucine-rich proteoglycans, including keratocan, are downregulated during experimental Candida albicans keratitis. This suggests extracellular matrix alterations may drive the inflammatory response in fungal corneal infections.
Area of Science:
- Ophthalmology
- Mycology
- Molecular Biology
Background:
- The corneal extracellular matrix (ECM) plays a crucial role in maintaining corneal integrity and clarity.
- Small leucine-rich proteoglycans (SLRPs) are key components of the ECM, influencing tissue organization and cell behavior.
- Fungal keratitis, particularly Candida albicans keratitis, is a significant cause of visual impairment, and its pathogenesis involves complex host-pathogen interactions.
Purpose of the Study:
- To investigate the expression patterns of SLRPs and related leucine-rich repeat proteins during the development and progression of experimental fungal keratitis.
- To determine the impact of Candida albicans infection on the transcriptional levels of specific proteoglycans in the cornea.
Main Methods:
- Experimental fungal keratitis was induced in BALB/c mice by topical inoculation with Candida albicans.
- Gene expression analysis was performed using murine gene microarrays and real-time reverse transcriptase polymerase chain reaction (RT-PCR) at various time points post-inoculation.
- Immunohistochemistry was employed to localize keratocan protein expression in infected and control corneas.
Main Results:
- Candida albicans keratitis rapidly induced corneal opacification and inflammation.
- Microarray analysis revealed significant downregulation ( > 2-fold, P < 0.01) of multiple SLRP genes, including biglycan, asporin, lumican, fibromodulin, osteomodulin, keratocan, osteoglycin, and chondroadherin, at the onset of infection.
- RT-PCR confirmed a substantial initial downregulation of keratocan (137-fold), with persistent downregulation at 1 week.
- Immunofluorescence showed reduced keratocan protein levels in the corneal stroma during early fungal keratitis.
Conclusions:
- Transcriptional levels of keratocan and other SLRPs are significantly decreased during the early stages of Candida albicans keratitis.
- These observed alterations in corneal stromal ECM composition may contribute to the acute inflammatory response during fungal infection.
- Understanding these molecular changes could offer insights into therapeutic strategies for fungal keratitis.
