Mitochondrial common deletion mutation and extrinsic skin ageing in German and Japanese women

The mitochondrial common deletion (CD) mutation is induced by oxidative stress. One main source of oxidative stress is the error-prone process of the respiratory chain located in the mitochondria. Another important source is the exposure to environmental factors, which further induces oxidative stress in the cells. For human skin, the primary damaging environmental factor is ultraviolet (UV) radiation, which is able to induce CD mutations and the characteristic extrinsic skin ageing signs. Traditionally, levels of UV exposure differ between German and Japanese populations, as tanned skin represents beauty and health in Western cultures, whereas photo-protected skin is considered ideal in Asia. We hypothesize that (i) this cultural-related UV exposure pattern might be reflected by CD concentrations in environmentally exposed skin and (ii) CD concentrations in environmentally exposed areas might be associated with the manifestation of extrinsic skin ageing. In this study, we determined the concentration of CD in skin from the neck (environmentally exposed area) and the buttock (environmentally protected area) of 22 German and 46 Japanese women between 30 and 70 years of age. We evaluated skin ageing signs by a validated clinical score, and exposure to environmental factors, such as UV exposure and smoking, was assessed using a questionnaire-based interview. Higher levels of CD were detected in neck skin than in buttock skin in both German and Japanese women. CD also increased with age in the neck skin. German women had higher CD concentrations in the neck skin than Japanese women. The CD concentrations in the buttock skin samples were similar in both populations. These findings suggest higher environmental UV exposure resulted in higher levels of CD in the skin of German women compared with Japanese women. However, only in Japanese women were the signs of extrinsic skin ageing associated with higher CD concentrations in the neck skin, in agreement with the hypothesis (ii). In German women, we did not find this latter association, which might be due to reaching a maximum level of CD, beyond which cells undergo negative selection and are lost to the population samples. In conclusion, under some conditions, there seems to be an association between the CD mutation concentration and extrinsic skin ageing, but this may be modified by cellular and tissue processes which affect the sampling rate for CD mutation concentrations and prevent a statistical association with extrinsic skin ageing.