Expression of p53 in normal sun-exposed and protected skin (type IV-V) in different decades of age

The checkpoint protein p53, which is activated by DNA damage, is involved in the decision whether the cells should stop replication and proceed to repair their DNA or die by apoptosis. We evaluate the expression of p53 and the number of apoptotic cells in normal sun-exposed (face) and protected (abdomen) skin in Egyptians between 6 and 77 years of age. The degree of p53 expression in facial skin significantly increases from a score of 1.5 +/- 1.5 (mean +/- SEM) in the 1st decade to 4.8 +/- 0.3 in the 8th decade (p = 0.02), while no significant changes are detected in the protected skin (p = 0.1). Overall, the level of expression is significantly higher in sun-exposed facial skin than in abdominal skin (p = 0.007). However, p53 expression versus age is significantly higher in the facial skin of older age groups in both males (p = 0.003) and females (p = 0.02). The pattern of staining was found to be dispersed (wild-type) in the majority (97.3%) of biopsies from sun-exposed skin and in all biopsies from non-exposed skin. The expression of wild-type p53 in type IV-V skin therefore correlates with both site and age of the individual. In contrast, the number of apoptotic cells significantly decreases with advancing age in sun-exposed skin (p = 0.005). Increased age-associated expression of p53 in sun-exposed skin, but not in protected areas of skin, is found to reflect an accumulation of the wild-type protein, as judged by the staining pattern. The decrease in apoptotic cells with age may suggest the accumulation of senescent cells in the skin and their relative resistance to apoptosis. Such alteration in the proliferation/apoptosis balance could play a role in tumorigenesis.