Does MicroRNA Have Applications In Skincare Formulations?

The Nobel Assembly at Karolinska Institutes in Stockholm, Sweden awarded the 2024 Nobel Prize in Physiology or Medicine to Victor Ambros and Gary Ruvkun for their major discovery in the field of epigenetics. The researchers were honored for the discovery of MicroRNA (mi-RNA) and its role in post-transcriptional gene regulation. 

What is miRNA, and why is it so important?

DNA and RNA Defined

We all know that DNA is a cell’s blueprint. It contains all the instructions for the cell to function. We also know that every cell in our body contains the same DNA and yet, liver cells, epidermal cells, muscle cells, neurons, lymphocytes, etc. have different structure and make different proteins. Why? During embryonic development, cells specialize and express different genes. 

Indeed, “DNA makes RNA makes proteins,” is molecular biology dogma. In years past, the heated question was, “what part of DNA makes what RNA?” Then enzymes called DNA-dependent RNA polymerases were discovered. These enzymes bind to well-defined sites on DNA, called promoters and synthetize RNA, complementary to the DNA sequence downstream, called messenger RNA (mRNA). mRNA binds to the ribosomes and dictates the synthesis of the protein for which it code, according to the genetic code. One amino acid being sequentially incorporated in the nascent protein per every triplet of nucleotides in the mRNA. Many genes are always expressed and are called “constitutive.” Others, called “inducible,” are expressed only either in the absence of “repressors” that sterically hinder the binding of the RNA polymerases to DNA, or in the presence of transcription factors, that modify the specificity of binding. They are produced because of a change in the environmental conditions (e.g. heat shock mRNAs are made only under thermic or oxidative stress), because of a viral infection or because of a pro-inflammatory event. It was later understood that mutations in the promoters or chemical modifications of the DNA, such as the methylation of cytosines, can modulate gene expression, too.

The actual synthesis of proteins, on the other hand, was the object of detailed analyses. The “translation,” that is interplay of the ribosomes with mRNA and tRNA and the different elongation factors, was elucidated but was never considered as a possible target for natural or artificial interventions aimed at modulating gene expression. The observations reported in the 1970s and 1980s^1,2 that RNA complementary to a messenger could shut down the synthesis of the protein coded for by the mRNA itself, both in vitro and in vivo, were considered intellectual curiosities. This “complementary RNA” was called “antisense” RNA and it was understood that by binding to the complementary messenger it generated a steric hindrance impeding the ribosomes to do their job in translating the mRNA into a protein.

A New Role for RNA

The worm C. elegans is about 1 millimeter long and is carefully studied, among other reasons, because its development follows a very strict schedule as well as because it is a convenient model to study aging. The strict schedule of development can be altered by mutations. Ambros and Ruvkun studied two mutant strains of worms, lin-4 and lin-14, that somehow had alterations in the timing of the activation of the genetic programs during development. Ambros and Ruvkun knew each other well since they did their postdoctoral training in the same laboratory and were now independent scientists at University of Massachusetts Medical School and Harvard University.

Ambros showed that the gene lin-4 somehow blocked the activity of gene lin-14, and that the gene lin-4 produced a very short RNA molecule (slightly more than 20 nucleotides) devoid of the capacity to code for proteins. Ruvkun demonstrated that lin-4 did not repress the synthesis of mRNA from lin-14 and that the inhibition of protein production occurred at a later stage…perhaps during the translation process? Ambros and Ruvkun compared their results: the very short RNA from lin-4 was complementary to a stretch of the lin-14 mRNA and lin-4 turns off the expression of lin-14 by binding to its mRNA, thus blocking the production of the lin-14 protein.

As noted in the press release from the Karolinska Institutes: A new principle of gene regulation, mediated by a previously unknown type of RNA, microRNA, had been discovered! The results were published in 1993 in two articles in the journal Cell.^3,4

After that, scientists uncovered more than one thousand genes for different microRNAs in human cells. We now believe that regulation of gene expression by microRNAs is ubiquitous in higher organisms. In 1998, small interfering RNA (siRNA) were found in plants. They are produced via complex molecular mechanisms and bind to mRNA, provoking its degradation by specific RNA-digesting enzymes. 

What about Skincare?

siRNA and miRNA can hinder the expression of genes having complementary sequences either by provoking the degradation of a given mRNA (for siRNA and miRNA) or the inhibition/retardation of the translation of the messenger RNA (for miRNA).

In the treatment of diseases, siRNA and miRNA have a major advantage over pharmacological xenobiotics and monoclonal antibody drugs because they work by Watson–Crick base pairing with mRNA, whereas medicines and monoclonal antibodies must recognize the tertiary structure of the proteins they target. Therefore, the diseases that are not treatable by xenobiotics and monoclonal antibodies can theoretically be treated by RNA interference because any gene of interest can be targeted by siRNA and miRNA.

In this spirit, several recent papers indicate possible ways of application of siRNA and miRNA to cosmetic problems.^5,6 The main difficulty presented by the topical application of products containing interfering RNAs resides in the fact that RNAs can be easily degraded by RNase or other degrading enzymes resident in the stratum corneum or harbored by the skin microbiome. One way to prevent degradation of the therapeutic oligoneucleotides, is to chemically modify the RNA by adding a phosphorothioate linkage to the backbones. However, the phosphorothioate modification can be proinflammatory. So, it might be best to encapsulate the interfering RNAs in liposomes, hoping that topically applied liposomes penetrate the stratum corneum and reach the appropriate cells in the epidermis. It would be a problem if an interfering RNA meant to target the mRNA of keratinocytes were to enter a melanocyte, wouldn’t it?

References:

1. Pestka S, Daugherty BL, Jung V, Hotta K, Pestka RK. Anti-mRNA: specific inhibition of translation of single mRNA molecules. Proc Natl Acad Sci U S A. 1984 Dec;81(23):7525-8. doi: 10.1073/pnas.81.23.7525. PMID: 6438637; PMCID: PMC392179.
2. Paterson BM, Roberts BE, Kuff EL. Structural gene identification and mapping by DNA-mRNA hybrid-arrested cell-free translation. Proc Natl Acad Sci U S A. 1977 Oct;74(10):4370-4. doi: 10.1073/pnas.74.10.4370. PMID: 270678; PMCID: PMC431943.
3. Lee RC, Feinbaum RL, Ambros V. The C. elegans heterochronic gene lin-4 encodes small RNAs with antisense complementarity to lin-14. Cell. 1993;75(5):843-854. doi:10.1016/0092-8674(93)90529-y
4. Wightman B, Ha I, Ruvkun G. Posttranscriptional regulation of the heterochronic gene lin-14 by lin-4 mediates temporal pattern formation in C. elegans. Cell. 1993;75(5):855-862. doi:10.1016/0092-8674(93)90530-4
5. Pingjing Zhang et al Use of small RNA as antiaging cosmeceuticals. J. Cosmet. Sci 2013, 64, 455-468
6. Chang, Y. T., Huang, T. H., Alalaiwe, A., Hwang, E., & Fang, J. Y. (2023). Small interfering RNA-based nanotherapeutics for treating skin-related diseases. Expert Opinion on Drug Delivery, 20(6), 757–772. https://doi.org/10.1080/17425247.2023.2206646

Paolo Giacomoni, PhD

Insight Analysis Consulting

paologiac@gmail.com
516-769-6904

Paolo Giacomoni acts as an independent consultant to the skin care industry. He served as Executive Director of Research at Estée Lauder and was Head of the Department of Biology with L’Oréal. He has built a record of achievements through research on DNA damage and metabolic impairment induced by UV radiation as well as on the positive effects of vitamins and antioxidants. He has authored more than 100 peer-reviewed publications and has more than 20 patents. He is presently Head of R&D with L.RAPHAEL—The science of beauty—Geneva, Switzerland.