Differential Expression of Proteoglycans by Corneal Stromal Cells in Keratoconus

Keratoconus is a heterogeneous disease associated with a range of pathologies, including disorders that involve proteoglycans (PGs). Some PG alterations, mainly in keratan sulfate (KS), occur in keratoconus. In this article, we studied the differential expression of the genes encoding PGs in cells isolated from keratoconus patients and healthy controls, as well as in corneal sections.

Human central corneal tissue was obtained from cadaver donors and patients undergoing penetrating keratoplasty surgery. A transcriptomic approach was used, employing quantitative PCR, to analyze both the expression of the enzymes involved in glycosaminoglycan (GAG) biosynthesis and the PG core proteins. The expressions of the differentially expressed core proteins and of the GAG chains were also analyzed by immunocytochemistry in the cultured cells, as well as by immunohistochemistry in corneal sections.

The mRNA levels of most major matrix PG mRNAs in the cultured keratoconic stromal cells decreased except collagen XVIII, which increased. At keratocyte surfaces, some heparan sulfate PGs were down-regulated. With respect to GAGs, there were changes in gene expression for the polymerization of the GAG chains, mainly KS and chondroitin sulfate, and in the modification of the saccharidic chains, pointing to an alteration of the sulfation patterns of all GAG species.

Most of the PG core proteins underwent significant changes in cultured keratoconic cells and corneas. With regard to GAG chains, the polymerization of the chains and their chemical modification was modified in way that depended on the specific type of GAG involved.