TESTING
Skin response to microorganisms Based on these encouraging results, we sought to increase our knowledge of bacterial-host interactions by analysing the expression of other biomarkers associated with the infectious context. To do so, we selected 93 genes for their
key role in three processes related to bacterial infection, namely inflammation, innate immunity response, and skin barrier structure and homeostasis. To measure and compare the simultaneous expression of these 93 genes, we amplified retro-transcripted RNA extracted from RHE colonized or not by C. acnes using a microplate-based quantitative PCR system known as TaqMan Low Density Array (TLDA). After statistical analysis of the results obtained
with this technology, we observed an upregulation of several genes involved in inflammation and immune defences (Figure 4). In parallel, we also observed changes in the expression of some genes involved in the structure and homeostasis of the skin barrier (also Figure 4), confirming a response of the tissue to the presence of a C. acnes phylotype IA1 strain.
Conclusions In conclusion, this work described a new 3D in vitro skin model allowing the study of interactions between C. acnes and the epidermis. As detailed here, we were able to colonize RHE using a C. acnes phylotype IA1 strain. With IA1 phylotype being clearly predominant
in acne-prone skin, it reinforces the interest of this model for the study of anti-acne molecules.
37
Non-colonised RHE
RHE colonised with C. acnes
Figure 2: Reconstructed human epidermis (RHE) morphology analysis. Hemalun/Eosin staining of paraffin-embedded RHE colonised or not with a strain of Cutibacterium acnes
The colonization of RHE in a lipid environment promoted not only the bacterial growth, but also the induction of an infectious context in the colonized tissue. As demonstrated by colony counting, the
bacteria showed 2-logs positive growth on the stratum corneum of RHE in three days. The addition of a growth inhibitor confirmed these observations, allowing the inhibitor to be used as a reference to compare the performance of potential anti-acne molecules. In the last part of this work, we also
demonstrated that the presence of C. acnes induces a variation in the expression of various cell biomarkers. The TLDA technology described here is routinely used in our laboratory to measure and compare the simultaneous expression of a large number of genes in cells subjected to different conditions.
All the 93 biomarkers analysed here are of
great importance for the study of the effect of dermo-cosmetic compounds. They are therefore compiled in a proprietary TLDA that we have named ‘Skin Response to Microorganisms’, to be used to evaluate the effect of an ingredient to interfere on bacteria-host interactions. This powerful transcriptomic tool is therefore an important step in understanding the mechanism of action of innovative compounds that target the skin microflora. The subsequent quantification of the corresponding proteins by ELISA or immunostaining assays would provide interesting additional data for claim objectivation. The completion of the in vitro 3D model described here allows us to study both the survival of a microorganism on the surface of the epidermis, and the responses of the skin to the presence of this microorganism.
www.personalcaremagazine.com
June 2022 PERSONAL CARE
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