The existence of senescent cells in conjunctival epithelium from elderly individuals

The ocular surface microenvironment changes with aging. However, it remains unclear if cellular senescence influences the ocular surface. We investigated the presence of p16^INK4a-expressing senescent cells in healthy human conjunctiva.

Clinical and experimental.

Healthy conjunctival tissue samples were obtained from middle-aged and elderly subjects. RT-qPCR was performed to assess the expression of senescence markers CDKN2A (p16^INK4a) and CDKN1A (p21^CIP1/WAF1) and immunostaining was performed to examine the expression of the senescence marker p16^INK4a, stem cell markers Ki67 and p63, tight-junction marker ZO-1.

Our study involved 19 conjunctival tissue samples (10 elderly and 9 middle-aged), mean age [elderly: 75.8 ± 3.7 years (72–81), middle-aged: 52.7 ± 7 years (38–59)], sex (elderly: 3 men, 7 women; middle-aged: 3 men, 6 women). The expression of p16^INK4a was significantly increased at the RNA level in the elderly compared to middle-aged (p < 0.05). Positivity rate of p16^INK4a was significantly elevated in the elderly (15.0 ± 7.8%) compared to middle-aged (0.2 ± 0.6%) (p < 0.05). Positivity rate of Ki67and p63 was significantly reduced in the elderly (1.7 ± 1.7% and 16.5 ± 9.5%) compared to middle-aged (3.9 ± 1.8% and 24.7 ± 5.7%) (p < 0.05). ZO-1 expression was reduced in tissue samples showing p16^INK4a-positivity but retained in tissue samples in which p16^INK4a was undetectable.

Senescent cells accumulate with age in the conjunctival epithelium, accompanied by a decrease in Ki67, p63 and ZO-1 expressing cells.