Protein alterations produced in the very heart of cells themselves over time irreversibly damage cells, and ultimately tissue. Glyoxalase (GO) is one natural and powerful damage prevention system in the body, and according to new experiments by researchers at UPMC-Sorbonne Université and Dior Science, this system exists in skin cells. GLO consists of two intracellular enzymes, glyoxalase 1 (GLO1) and glyoxalase 2 (GLO2), both of which work in tandem to detoxify certain harmful dicarbonyl products produced as a result of everyday metabolism and exposure to other oxidative stressors, such ultraviolet rays from the Sun and pollution.
The new result shows that the modification produced, in particular, by the dicarbonyl compounds glyoxal (GO) and methylglyoxal (MGO) in the presence or not of oxygen reactive species (ROS) in skin not only affects extracellular, structural, proteins, such as elastin and collagen, but also intracellular ones. GLO detects and neutralises GO and MGO, as soon as they are produced and thus prevents them attacking cells and cell components such as DNA and proteins.
The system affords protection in a two-punch process: first by GLO1 and then by GLO2. The enzymes produce molecules, such as glycolate (for the glyoxal), which are not toxic.
The researchers, led by Carine Nizard of Dior Science and Isabelle Petropoulos of the UPMC, are the first to discover that the GLO system is located in the keratinocytes of the human epidermis (the cells that are responsible for tissue renewal) and the fibroblasts of the dermis (the layer that is found just above subcutaneous tissue). GLO appears to weaken with time, however, and becomes less effective. This weakening is unfortunately accelerated when skin is exposed to UV rays.
Finding out where GLO enzymes are located in skin
To understand why this happens, the researchers decided to find out where the GLO enzymes were located in young versus aged or photo-exposed human skin samples. They did this using a technique called immunohistochemical staining. In their experiments, Nizard, Petropoulos and doctoral student Sabrina Radjei stained cross-sections of their samples with anti-human antibodies that bind to either GLO1 or GLO2.
The researchers obtained their samples from biopsies of old and young human skin isolated from abdominal skin surgery. The old skin samples were obtained from donors with an average age of 63.2 +/- 1.6 years, and the young ones from donors with an average of 27.5 +/- 1.7 years. They also studied normal human adult epidermal keratinocytes (NHEK) from 26 and 65-year-old donors. These cells were subjected to replicative senescence – that is, they were aged artificially so that they were no longer able to proliferate and showed signs (specific biomarkers) of ageing. Finally, they looked at sun-exposed skin cells (taken from the forearm) and sun-protected skin cells (from the upper inner arm). Again, these samples were obtained from biopsies.
GLO expression and activity
They found that, in all the samples, GLO1 is mostly located in the basal layer of the epidermis (where stem cells are found), while GLO2 is located in the upper layer keratinocytes. Although overall GLO expression is not modified in dermal fibroblasts as they age, the activity and expression of GLO1 does decrease. These changes mean that the GLO system cannot do its job properly as skin ages, and damaged proteins build up in cells. This protein build-up also occurs in photo-aged old skin samples, but not as much in non-photo-exposed young ones.
In contrast, in the basal layer of the epidermis, where GLO1 is strongly expressed, the level of damaged proteins does not increase – in either the old or young skin samples. This means that the GLO system appears to protect progenitor cells against damage.
“We have known for a long time that exposure to UV rays accelerates skin ageing by increasing the production of ROS, altering DNA and oxidizing proteins,” explain Nizard and Petropoulos. “In our new work, we found no obvious difference in GLO1 expression in the sun-exposed versus sun-protected skin samples. However, what we did find was that, in the old skin samples, there was a huge accumulation of glycated proteins when this skin was photo-exposed, mainly in the dermis, but also in the epidermis. The GLO2 enzyme, for its part, was less expressed in sun-exposed compared to sun-protected epidermis in both the young and old skin samples,” they say.
These results show that UV rays can alter the way glyoxalase protects keratinocytes. So, could protecting glyoxalase itself for as long as possible using simple measures (such as using sunscreen) or indeed boosting its activity when, or even before, it starts to slow down (using targeted, technologically active ingredients that could topically applied) help keep skin younger for longer?
The experiments performed in this study
The skin slices studied were obtained from LVMH Recherche Laboratories’ Hélios R&D facility in Saint Jean de Braye near Orléans. The experiments were performed at the UPMC, in the UMR 8256 Biological Adaptation and Ageing Lab.
Reference: Experimental Dermatology, 2016, 25 475-494 / doi: 10.1111/exd.12995