Expression And Significance Of Human Telomerase Reverse Transcriptase In Lens Epithelial Cells Of Age-related Cataract

Background and PurposeAge-related cataract is also called senile cataract. It is a leading cause of loss of vision throughout the world with aging its morbidity rate goes higher. So far there is no clear understanding on the etiology and pathogenesis of age-related cataract.Telomeres are the repetitive nucleotide sequences at the ends of eukaryotic chromosomes. Telomeres length decurtate accompanying per cell division and eventually cells become senescent. Telomerase is a ribouncleoprotein complex that can catalyze and synthesis telomeric sequences, preventing cells take place procedure death because of telomeres exhaustion. Telomerase activity is considered to have a close correlation with cancer development, cell immortalization, proliferation and senescent. There are 3 subunits composing of telomerase, among of total human telomerase reverse transcriptase (hTERT) is presumed to correlate telomerase activity significantly.Colitz found telomerase activity expressed in experimental animals' lens epithelial cells (LEC) recently and speculated that telomerase activity was a reaction to oxidative damage, proliferation or other factors. But there were few researches about telomerase's expression in human LEC and the relationship between telomeraseand age-related cataract.Our experiment evaluated the expression of hTERT and the index which can reflex cell proliferation state well-proliferation cell nuclear antigen (PCNA) in different types of age-related cataract and normal LEC and the index which can reflex cell proliferation state well- proliferation cell nuclear antigen (PCNA), to discuss their meanings and interrelation. We also observed the ultrastructural change of age-related cataract LEC by transmission electron microscope.Materials and Methods100 specimens of human age-related cataract lens anterior capsules were obstained which include 35 cortial cataract, 35 nuclear cataract and 30 subcapsular cataract. The control were 15 cases of normal LEC. We observed 6 age-related cataract LEC's ultrastructural change comparing with 2 normal LEC.Results1. expression of hTERT protein: the positive immunostaining rate in age-related cataract was 79%(79/100), in which weak, moderate and strong positive staining was 16, 26, 37, respectively; the positive immunostaining rate in normal lens was 40%(6/15),in which weak and moderate positive staining was 4, 2, respectively. Comparing the staining rate and intensity of age-related cataract and normal lens, respectively, there were all significant differences(P<0.05).2. expression of hTERTmRNA: the positive staining rate in age-related cataract was71%(71/100), in which weak, moderate and strong positive staining was 10, 29, 32, respectively; the positive staining rate in normal lens was 33.33 %(5/15),in which weak and moderate positive staining was 3, 2, respectively. Comparing the staining rate and intensity of age-related cataract and normal lens, respectively, there were all significant differences(F<0.05).3. There were no statistic significances of the positive rate and staining intensity of hTERT in three types of senile cataracts(P>0.05).4. The expression of hTERT on protein level was in coincidence with that on mRNA level.5. expression of PCNA in three types of age-related cataract: the positive staining rate in cortial cataract was 11.43%(4/35), in which weak and moderate positive staining was 3, 1, respectively; the positive staining rate in nuclear cataract was 31.43%(ll/35), in which weak , moderate and strong positive staining was 4, 6,1, respectively; the positive staining rate in subcapsular cataract was 10%(3/30), in which weak and moderate positive staining was 2, 1, respectively. Comparing the staining rate of three types of age-related cataract, there was significant difference(P <0.05). Comparing the staining intensity of three types of age-related cataract,, there was not significant difference(P>0.05).6. Spearman rank correlation analysis of staining intensity of hTERT and PCNA in age-related cataract and normal lens was made. There was no correlation in staining intensity between hTERT and PCNA(rs=-0.800, P>0.05).Conclusions1. Telomerase activity expressed in human LEC.2. There were oncosis cells besides apoptotic cells in LEC.3. Telomerase in normal LEC may function in avoiding DNA damage, telomeres length shorten by oxidative stress and ultraviolet light exposure, thereby preventing cell senescent and death while supported the viewpoint that LEC belong to stem cells.4. Elevated telomerase activity in age-related cataract LEC did not correlate with increased proliferation in LEC; instead, it was a response to DNA damage, telomeres length shorten by oxidative stress , ultraviolet light exposure or other unidentified factors. When the damage built up to such a degree that elevated telomerase activity couldn't prevent telomeres length shorten or also exist alternative telomeres length mechanism, LEC became senescent, apoptosis or oncosis.5. Immunochemistry and in situ hybridization can take place telomeric repeat amplification protocol (TRAP) to detect telomerase activity.