Introduction:
Circular RNA (circRNA) is considered to be a vital regulator of disease progression, including age-related cataract (ARC). However, the molecular mechanism of circHIPK3 in ARC progression has not been fully elucidated.

Material and methods:
The expression levels of circHIPK3, miR-499a-5p and E2F transcription factor 3 (E2F3) were measured by quantitative real-time PCR. Cell counting kit 8 assay and flow cytometry were performed to detect cell viability and apoptosis, respectively. Western blot analysis was employed to test the protein levels of apoptosis-related markers and E2F3. Biotin-labeled RNA pull-down assay was used to select miRNAs that could be targeted by circHIPK3, and dual-luciferase reporter assay was performed to confirm the interaction between miR-499a-5p and circHIPK3 or E2F3.

Results:
CircHIPK3 is a stable circRNA that is significantly under-expressed in the anterior lens capsule tissues of ARC patients. Knockdown of circHIPK3 suppressed SRA01/04 cell viability and accelerated apoptosis. Moreover, miR-499a-5p could be targeted by circHIPK3, and its inhibitor reversed the effect of circHIPK3 silencing on cell viability and apoptosis. Furthermore, E2F3 was a target of miR-499a-5p, and its overexpression reversed the effect of miR-499a-5p on the viability and apoptosis of SRA01/04 cells. In addition, circHIPK3 positively regulated E2F3 expression by sponging miR-499a-5p.

Conclusions:
CircHIPK3 knockdown inhibited viability and enhanced apoptosis of lens epithelial cells to promote ARC progression by regulating miR-499a-5p/E2F3 axis.