A study conducted at the Center for Research on Redox Processes in Biomedicine (Redoxoma) helps to understand the damage caused by type A ultraviolet radiation (UVA) – the main component of sunlight – to the most abundant type of skin cell, the keratinocyte.
To do the investigation, the researchers exposed a lineage of keratinocytes to a single, low dose of UVA light, equivalent to 20 minutes of sun exposure. Another control culture was maintained under the same experimental conditions, however, in the dark, so that the differences between them could be compared later by means of a proteomic analysis, that is, of the set of proteins present in the cells.
This approach was combined with an artificial intelligence technique known as machine learning, which also allowed us to map the reorganization of proteins in cells in response to UVA light. The results were described in two articles published in Scientific Reports and iScience.
“Basically, in one of the studies, we did a more classical proteomics, to look at changes in proteins. In the other, we analyzed changes in the subcellular distribution of these proteins, that is, changes that have more to do with localization. We noticed that changes in abundance of the proteome were linked to keratinocyte senescence, which is a process closely related to cellular aging and which will lead to a pro-inflammatory phenotype. When we focused on the short term, for the effects that occurred right after radiation, we mainly saw mitochondrial damage [à organela que produz energia para a célula]”, says Hellen Paula Valerio, first author of the articles and researcher at the Butantan Institute.
The investigation was carried out during Valerio’s doctorate, with the support of a Fapesp grant and guidance from Paolo Di Mascio and Graziella Eliza Ronsein, both professors at the Institute of Chemistry at the University of São Paulo (IQ-USP) and members of Redoxoma, a of Research, Innovation and Dissemination (CEPID) of Fapesp.
Senescence
The experiment with the keratinocyte lines showed that UVA radiation induces senescence signals in these cells. And as the researchers explain, senescent cells do not multiply.
According to Valerio, there is evidence that aged tissues have greater amounts of senescent cells than young tissues. Furthermore, evidence suggests that if senescence is reversed, tissue can rejuvenate.
To observe changes in protein levels, the researchers used an approach based on shotgun proteomics, which, because of its higher resolution, can identify even the least abundant molecules in the sample. The cells were irradiated and, 24 hours later, the proteins were extracted and analyzed by mass spectrometry – a method that makes it possible to discriminate substances in biological samples according to molecular mass –, always in comparison with non-irradiated control cells.
It was possible to observe that UVA light promoted a great modification in the set of proteins (proteome) of keratinocytes. The researchers found a greater abundance of antioxidant enzymes and inflammatory mediators. An increase in the level of p16 protein was also observed – important for cell cycle control and involved in senescence. Subsequent biochemical assays confirmed the proteomic data.
In another test, a lineage of skin cells known as HaCaT, considered pre-tumorigenic, was irradiated, and in this case, no signs of senescence were observed.
Another interesting result was that irradiated primary keratinocytes secreted molecules that produced effects in non-irradiated HaCaT cells. That is, they induced oxidative stress in neighboring cells and activated the immune system in pre-tumor keratinocytes (the HaCaT cells).
“This is a very complex thing. We are seeing the exchange of signals between neighboring cells. Then comes the question of working with a single cell in culture or starting to ‘make’ tissues, that is, co-culture of cells”, comments Di Mascio.
According to the researchers, these observations offer insights into the cellular mechanisms by which UVA light causes skin aging.
* With information from the Redoxoma Press Office.
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