Epigenetic changes of the Klotho gene in age-related cataracts

To determine the mRNA and protein expression, and methylation levels of the Klotho in lens epithelial cells (LECs) of normal transparent lenses and age-related cataracts (ARCs), and to explore the role of epigenetic changes of the Klotho gene in regulating the development of ARCs.

A total of 90 subjects were divided into three groups: a young adult group with normal transparent lenses aging from18 to30 years, a middle-aged group with ARC aging from 40 to 49 years, and an elderly group with ARC aging from 67 to 85 years. The LECs were collected through curvilinear capsulorhexis. The mRNA expression of the Klotho gene was determined using the reverse transcription polymerase chain reaction (RT-PCR). Protein expression of the Klotho gene in LECs was detected using immunohistochemical (IHC) staining. The methylation specific polymerase chain reaction (MSP) was used to detect the methylation level of the target gene.

Decreased mRNA expression of the Klotho gene was reversely correlated with age. IHC results showed that the Klotho was mainly expressed in the cell membrane and cytoplasm of LECs. It was strongly positive in the young adult group (100.0%), with even distribution; weakly positive in the middle-aged group (36.7%), with expression distributed 4-5 mm away from the center of the anterior lens capsule; and negative in the elderly group (0.0%). MSP results showed that the Klotho gene was highly methylated in the elderly group (93.3%) and weakly methylated (56.7%) in the middle-aged group, but barely methylated in the young adult group (3.3%).

Klotho were positively expressed in the LECs of normal individuals at the mRNA and protein level. Its promoter showed increased methylation as age increased, resulting in Klotho gene silencing as well as down-regulated expression or no expression of the Klotho protein. These epigenetic changes could affect the biological activities of LECs, which provided the basis for further studies of the association between the Klotho gene and ARC.