Microbial modulation of proteoglycan and glycosaminoglycan biosynthesis in a three-dimensional corneal epithelium...

Recently, a three-dimensional in vitro corneal epithelium model, designated QobuR, was developed. This model aims to reproduce the complex cellular interactions observed in vivo and to provide an alternative to animal models for toxicity testing and ophthalmic drug development. However, the corneal epithelium, like other exposed epithelia, is continuously exposed to microorganisms present on the ocular surface, although the existence and extent of a stable corneal microbiota remain areas of ongoing investigation. Nonetheless, microbial exposure may exert a significant influence on its physiology. During microbial interaction with epithelial surfaces, cell-surface proteoglycans and glycosaminoglycans act as key mediators, and this interaction can induce changes in their biosynthesis and structure. As these molecules function as specific receptors for numerous ligands and regulate essential cellular processes, their interaction with the microbiota may contribute to the maintenance of tissue homeostasis.

In this study, we analyzed the transcriptional profiles of genes involved in PG and GAG biosynthesis in the QobuR model following controlled co-culture with individual bacterial species and with a mixed microbial consortium designed to represent the ocular surface microbiota. Expression changes were assessed by qRT-PCR and complemented by immunohistochemical analysis.

Distinct bacterial species induced specific patterns of gene expression, predominantly affecting enzymes involved in late-stage sulfation of heparan sulfate and chondroitin sulfate chains. Exposure to the microbial consortium resulted in broader and more complex transcriptional modulation, incorporating most changes observed in individual conditions while introducing additional alterations. Notably, the transcriptional profile of microbiota-exposed QobuR showed increased similarity to donor-derived corneal epithelium. These observations were supported by immunohistochemical analyses.

These findings demonstrate that corneal epithelial cells exhibit dynamic transcriptional responses to microbial exposure under controlled in vitro conditions. The results highlight the relevance of incorporating host-microbe interaction components into three-dimensional epithelial models, while also emphasizing that the interpretation of these responses should consider the experimental framework and the current uncertainties regarding the composition and the functional role of the ocular surface microbiota.