UVB-mediated down-regulation of proteasome in cultured human primary pterygium fibroblasts

Abstract

BackgroundPterygium is a condition characterized by epithelial overgrowth of the cornea, inflammatory cell infiltration and an abnormal extracellular matrix accumulation. Chronic UV exposure is considered as a pathogenic factor of this disease. Proteasome is an intracellular multi-subunit protease complex that degrades intracellular proteins. Among proteasome subunits the β5 (PSMB5), bearing chymotrypsin-like activity. It is considered as the main proteasome subunit and its expression is mediated by Nrf2-ARE pathway in many cell types. This study investigates the expression of PSMB5 in pterygium and the effect of UVB irradiation on its expression and activity in pterygium fibroblasts.MethodsNormal conjunctival and pterygium specimens were obtained from the bulbar conjunctiva of patients undergoing cataract surgery and from patients with pterygium undergoing surgical removal of primary tissue, respectively. Fibroblasts were isolated upon treatment of specimens with clostridium collagenase. The expression of PSMB5 and Nrf2 in tissues and cells was ascertained by RT-PCR analysis and western blotting. Cell survival was measured by the MTT method and the proteasome chymotrypsin-like activity was determined by fluorometry.ResultsRT-PCR analysis showed that the expression of PSMB5 was significantly lower in pterygium than in normal conjunctiva. The expression of PSMB5 was mediated by the Nrf2/ARE pathway as indicated by using the Nrf2 activator Oltipraz. The expression of PSMB5 and Nrf2 by pterygium fibroblasts was suppressed in a dose dependent manner following UVB radiation of 0–50 mJ/cm2 doses. The expression of PSMB5, but not of Nrf2, remained at almost the control levels, when UVB exposure was performed after pre-incubation of cells with the src kinases inhibitor PP2. UVB irradiation had very low deleterious effect on fibroblasts survival, while it did not affect the proteasome chymotrypsin-like activity.ConclusionIn pterygium fibroblasts, UVB exposure leads to down-regulation of Nrf2/ARE-mediated PSMB5 gene expression, in which src kinases may be implicated. This effect may be partially responsible for the lower expression of PSMB5 detected in pterygium as compared to normal conjunctiva.

Conjunctival Autograft versus Combined Amniotic Membrane and Mini-Simple Limbal Epithelial Transplant for Primary Pterygium Excision

“…Pterygium is postulated to occur due to localized dysfunction of nasal limbal stem cells consequential to exposure to UVB light. [ 18 ] This theory forms the basis of the incorporation of limbal stem cells in the surgical treatment of pterygium. Of all the techniques described in literature, [ 3 , 4 ][ 5 ][ 6 ] CAG modality has been found to be associated with the lowest recurrence rate.…”

A novel role for Livin in the response to ultraviolet�B radiation and pterygium development

“…A number of studies have demonstrated that UV exposure is a factor precipitating the development of pterygium (3,21,32,33). Histological examination has confirmed that elastic connective tissue lesions and severely damaged areas of the Bowman membrane indicate direct damage caused by solar radiation or indirect damage due to excessive proteolytic activity (3,21).…”

Comparison Of Conjunctival Autograft And Combined Amniotic Membrane Mini-Simple Limbal Epithelial Transplantion After Primary Pterygium Excision

“…Pterygium occurs primarily due to local de ciency of limbal stem cells(LSCD)secondary to exposure to UV type B(UVB) light 18 . The basic difference between the primary and recurrent pterygium is that the body of the former is free from the underlying structures whereas that of the latter is rmly adherent to the underlying tissues namely episclera and sclera.This is primarily the reason one has to be extremely careful and diligent in the surgical treatment of pterygium to avoid complications and nancial implications .…”