Hyperexpression of LDL Receptors in Human Pterygium

Abstract

Abstract: : Purpose:: to evaluate the expression of LDL receptors (LDL-R) and hydroxy-methyl glutaryl coenzyme A reductase (HMGCoA-R) activity in primary pterygium. Methods:: specimens from four eyes with primary pterygium and four eyes with normal conjunctiva were obtained at time of surgery. RT-PCR analysis. Total RNA was isolated from cells using the guanidine isothiocyanate phenol-chloroform extraction method. Integrity of RNA was evaluated by agarose gel electrophoresis, and RNA yield was quantified spectrophotometrically and A260/A280 ratios determined. Equal amounts of total RNA (1 mg) were reverse transcribed into cDNA using the random hexamer method. cDNA was subsequently amplified by the polymerase chain reaction (PCR) in the presence of specific primers according to the instructions provided by the manufacturer (GeneAmp RNA PCR Kit, Perkin-Elmer Cetus). The overall procedure was standardized by expressing the amount of PCR product for each target mRNA relative to the amount of product formed for b -actin. Since a low yield of PCR products is often obtained when cDNA segments are coamplified with an internal standard gene in the same tube, the relative levels of gene expression were determined by comparing the PCR products of the target cDNA and b -actin gene processed in separate tubes. Results: increased expression of LDL-R and HMGCoA-R was found in pterygia with respect to both adjacent normal conjunctiva and normal controls. Conclusions: An increase in the number of LDL-R as well as an increase in HMGCoA-R activity, the rate limiting enzyme of the intracellular cholesterol synthesis, have been widely reported in a number of proliferating tissues, including tumoral tissues. Our results suggest that: 1) pterygium is a disorder of abnormal growth rather than a degenerative process; 2) cholesterol metabolism may play a role directly or indirectly in the process of endothelial proliferation observed in pterygium. In addition, 3) the increased expression of LDL receptor could imply the possibility to use photodynamic therapy with verteporfin for the treatment of pterygium.

Keywords: Pterygium • cornea: basic science • gene/expression