SIRT6 enhances telomerase activity to protect against DNA damage and senescence in hypertrophic ligamentum flavum cells from lumbar spinal stenosis patients

Lumbar spinal stenosis (LSS) is a condition wherein patients exhibit age-related fibrosis, elastin-to-collagen ratio reductions, and ligamentum flavum hypertrophy. This study was designed to assess the relationship between SIRT6 and telomerase activity in hypertrophic ligamentum flavum (LFH) cells from LSS patients. We observed significant reductions in SIRT6, TPP1, and POT1 protein levels as well as increases in telomerase reverse transcriptase (TERT) levels and telomerase activity in LFH tissues relative to non- hypertrophic ligamentum flavum (LFN) tissues. When SIRT6 was overexpressed in these LFH cells, this was associated with significant increases in telomerase activity and a significant reduction in fibrosis-related protein expression. These effects were reversed, however, when telomerase activity was inactivated by hTERT knockdown in these same cells. SIRT6 overexpression was further found to reduce the frequency of senescence-associated β-galactosidase (SA-β-Gal)-positive LFH cells and to decrease p16, MMP3, and L1 mRNA levels and telomere dysfunction-induced foci (TIFs) in LFH cells. In contrast, hTERT knockdown-induced telomerase inactivation eliminated these SIRT6-dependent effects. Overall, our results indicate that SIRT6 functions as a key protective factor that prevents cellular senescence and telomere dysfunction in ligamentum flavum cells, with this effect being at least partially attributable to SIRT6-dependent telomerase activation.