Small leucine rich repeat proteoglycans (SLRPs) in the human sclera: identification of abundant levels of PRELP.

PURPOSE The small leucine rich proteoglycan (SLRP) family is made up of several members which are thought to guide matrix assembly and organization through protein:protein and/or protein:carbohydrate interactions. In order to better characterize the composition of the scleral extracellular matrix, gene and protein expression of several members of the SLRP family were evaluated in the human sclera from donors aged 2-93 years of age. METHODS Semi-quantitative and quantitative RT-PCR analyses were performed on RNA isolated from human donor sclera using primers for decorin, fibromodulin, PRELP (proline arginine rich end leucine-rich protein), biglycan, chondroadherin, and lumican. Additionally, the protein expression and distribution of the SLRP family member, PRELP, was determined in the human sclera through western blot detection and immunohistochemistry. RESULTS Semi-quantitative and quantitative PCR analysis showed that all six SLRPs were expressed in the human sclera, with PRELP exhibiting the highest steady state mRNA levels, relative to that of the other SLRPs (p<0.001, ANOVA). Further analysis of PRELP in the human sclera by western blot analysis indicated that PRELP contained a 45 kDa core protein with short unsulfated keratan sulfate side chains and appeared in greatest abundance in sclera during the fourth decade of life. CONCLUSIONS These results suggest that several SLRP proteoglycans are expressed in the human sclera and provide the first description of the PRELP protein in the human sclera. The relative abundance of PRELP mRNA and protein in the human sclera, and the observed age-related variation in scleral PRELP expression suggests that PRELP may play a critical role in regulating the biomechanical properties of scleral extracellular matrix.