Abstract
Purpose: :
The matrix metalloproteinases (MMPs) are a family of peptidase enzymes responsible for the degradation of various extracellular matrix components, including collagen, gelatin, laminin, fibronectin and proteoglycan. These enzymes are involved in tissue remodeling and during normal cellular events are down regulated by their endogenic inhibitors. Tissue inhibitors of metalloproteinases (TIMPs) are capable of inhibiting the activities of all known matrix metalloproteinases and thus play a key role in maintaining the balance between synthesis and degradation of basic extracellular matrix components in the normal cornea. However, under pathological conditions, disruption of this balance may appear due to the increased expression of MMPs or decreased expression of TIMPs. Purpose of this study was to investigate whether changes in expression of MMPs and TIMPs might contribute to immoderate proteolytic activity of MMPs in corneas damaged by UV rays.
Methods: :
In the first group of rabbits the corneas were irradiated with UVA lamp (365 nm, once a day during 4 days, a dose per day 1.01 J/cm2), in the second group with UVB lamp (312 nm, once a day during 4 days, a dose per day 1.01 J/cm2). Normal corneas served as controls. MMPs (type 1, 2, 7, 8, 9) and TIMPs (type 1, 2, 3, 4) were examined in cryostat sections immunohistochemically using polyclonal goat primary antibodies. The densitometric measurements of the immunohistochemical staining for MMPs and TIMPs were performed using image analysis software KS400 from Carl Zeiss. For statistical analysis a one-way ANOVA test with Bonferroni’s multiple comparison post-test was employed.
Results: :
Results of immunohistochemical examination showed that UVA rays did not change expression of MMPs and TIMPs studied in corneal epithelium. In contrast, UVB rays induced overexpression of MMPs and significantly decreased expression of TIMPs in corneal epithelial cells.
Conclusions: :
Comparing the effect of the same doses of UVA and UVB rays on the normal rabbit cornea, UVB/not UVA rays evoked the increased expression of MMPs and the decreased expression of TIMPs in the corneal epithelium. Even if further studies are necessary, our results indicate that insufficient inhibition of MMPs due to the decreased presence of TIMPs in corneas irradiated by UVB rays may lead to excessive proteolysis of corneal proteins.
Keywords: cornea: epithelium • cornea: basic science