Investigation of the relationship between clusterin genetic polymorphisms and clusterin level of tear and aqueous humor in pseudoexfoliation syndrome and glaucoma

Pseudoexfoliation syndrome (PES) is an age-related systemic disorder of extracellular matrix characterized by the presence of fibrillar deposits in both ocular tissues and many internal organs. Glaucoma that occurs due to pseudoexfoliation is called pseudoexfoliative glaucoma (PEG) and can cause blindness if it is not treated. Therefore, in order to find potential factors causing PEG and PES diseases, and the identification of PES patients who are at risk of developing PEG is of great importance. Clusterin protein prevents the stress-induced precipitation and aggregation of misfolded proteins under cellular stress conditions. Clusterin expression is induced in cellular stress conditions such as heat shock and oxidative stress. Despite the formation of misfolded proteins due to the oxidative environment in the anterior chamber of the eye in PES patients, clusterin expression level is unexpectedly low in aqueous humor of PEG and PES patients. Genetic polymorphisms may be one of the factors causing low clusterin expression. This study aimed to investigate the association of clusterin genetic polymorphisms and clusterin protein levels of aqueous humor and tears in PEG and PES risk. The genotyping of clusterin genetic polymorphisms from whole blood samples of 213 PEG patients, 214 PES patients and 215 control individuals was performed by PCR-RFLP and real-time PCR methods. Clusterin and total protein concentrations of aqueous humor samples of 12 PEG patients, 17 PES patients, 22 controls and of tear samples of 80 PEG patients, 81 PES patients and 80 controls were analyzed by ELISA and Bradford methods. All samples were obtained from University of Health Sciences, Faculty of Medicine, Gülhane Training and Research Hospital, Ophthalmology Unit, Ankara, Turkey. This study shows that being male significantly increased PEG risk by ~2-fold. TT genotype in clusterin rs11136000 C/T, rs1532278 C/T and rs2279590 C/T is ~3-fold protective and AA genotype in rs3087554 A/G is ~2.4-fold protective against PEG disease. According to combined genotype analysis, having CC genotype in clusterin rs11136000 C/T, rs1532278 C/T and rs2279590 C/T and having AG genotype in rs3087554 A/G seems to be distinctive for PEG and PES diseases. Clusterin and total protein concentration in aqueous humor samples and total protein concentration in tear samples were significantly higher in PEG patients than PES patients and controls. To the best of our knowledge, this study is the first investigation of clusterin levels in tears and of clusterin levels in aqueous humor in Turkish population. Clusterin rs1532278 C/T, clusterin rs3087554 A/G and clusterin rs2279590 C/T are studied for the first time in PEG and PES risk, in Turkish population and in Turkish population for PEG and PES risk, respectively. These results can be confirmed in the future by further studies on these issues and a parameter to be used as a biomarker can be developed. In this respect, this study is a project that contributes to Biomedical Engineering and prepares background for diagnostic and therapeutic tools that will be developed in the future. Keywords: Pseudoexfoliation, Glaucoma, Clusterin, rs11136000 C/T, rs3087554 A/G, rs1532278 C/T, rs2279590 C/T, Genotype, Polymorphism, Aqueous humor, Tear.