Cracking the code on skin and oral mucosa

The UCD Charles Derma Seminar series recently heard a talk by Prof Inês Sequeira on regeneration, immunity, and cancer

The Charles Institute, Ireland’s national dermatology research and education centre, hosts a range of guest speakers who cover a variety of topics ranging from skin cancer to psoriasis, among others. The series, which is currently sponsored by Johnson & Johnson, is designed to provide expert advice from a range of distinguished national and international experts in their respective fields and is chaired by Prof Desmond Tobin, Full Professor of Dermatological Science at UCD School of Medicine and Director of the Charles Institute of Dermatology. The seminars are broadcast to attendees with a special interest in dermatology and cutaneous science in other locations, who access the talks remotely via an audio-visual link.

Attendees heard a presentation from Prof Inês Sequeira, Associate Professor at Queen Mary University of London and Deputy Research Director at the Institute of Dentistry in the UK. At the time of her appearance at the UCD Charles Seminar Series, Prof Sequeira was also due to join the NOVA Institute for Biomedical Systems Biology in Lisbon, Portugal, as Group Leader and Vice-Director for Research.

Prof Sequeira has dedicated her career to improving understanding of skin and oral epithelia homeostasis, wound healing, and cancer. She brought her expert knowledge to the Charles Institute with a talk titled, ‘Decoding skin and oral mucosa: Insights into regeneration, immunity, and cancer through spatial and single-cell omics’.

Prof Sequeira and her team focus their work on the scarless potential of oral mucosa in comparison to skin, as well as looking into the heterogeneity and clonal evolution of oral cancer. In an effort to decode this oral mucosa versus skin conundrum, Prof Sequeira uses 3D in vitro and in vivo models and cutting-edge computational tools, and single-cell and spatial omics to dissect the molecular and cellular heterogeneity of oral tissues, in both disease and health.

Scarless healing

Unlike skin, the oral mucosa can repair itself rapidly, and without scarring. Prof Sequeira explained that it is important to understand the mysteries behind this type of scarless healing. She and her team are dedicated to understanding how the immune system plays a vital role in both wound healing and cancer, she said.

The way the immune system supports healthy repair and shapes immune tolerance in the mouth and skin are central to the team’s research, and state-of-the-art tools in single-cell and spatial genomics proteomics and advanced tissue models help in this work. This allows the team to map how cells communicate with each other during disease and also in the healing process. The goal is to translate the results into practical skin repair and therapy options, she said, and understanding how the immune system is disrupted in cancer and other diseases is a key objective.

In her talk, Prof Sequeira covered a wide range of topics relating to oral tissue diversity and hair follicle stem cells, and she provided an overview of the evolution of her research. She discussed the interactions between epithelial cells, immune cells, and fibroblasts and the skin, oral, and thymus areas. She also provided an overview of the organisation of hair follicle anagen stem cells. She said: “Hair follicle stem cells display conveyor belt-like dynamics. Hair growth is fuelled by the germinative layer cells that become more transcriptionally committed distally and this is not as restricted as previously thought, so there is plasticity.”

Prof Sequeira also spoke briefly about oral fibroblasts and oral tissue diversity in multiple functional niches, such as labial and buccal mucosae, major and minor salivary glands, gingiva, tongue, and hard and soft palate, and tonsils. Her team is also involved in the Human Cell Atlas project, specifically the human oral and craniofacial Human Cell Atlas. The purpose, she said, is to create a comprehensive reference map for all human cells as a basis for understanding human health and diagnosing, monitoring and treating disease.

“The next steps are to compare different developmental stages and different ages and expand to a cross-tissues comparison,” she said. “We need to know how fibroblasts-immune cell-keratinocyte crosstalk is regulated and deregulated in disease and this requires in vitro and in vivo validation.”

Thymus gland

Prof Sequeira and her team are assessing the role of keratin-76 (Krt76), a type II intermediate filament protein that contributes to the structural integrity of epithelial cells, which is expressed in the supra-basal layers of stratified epithelia in humans and mice in the palate, tongue, buccal mucosa, skin, thymus, and squamous stomach areas.

She pointed out that loss of Krt76 therein contributes to skin T-cell infiltration, and loss of thymic Krt76 leads to reduced T-cell negative selection. “You have a thymic epithelial cell, let’s call it TEC,” she told the attendees.

“These TECs present the tissue self-antigen to the T-cells in the thymus. If the T-cell has a weak affinity, they survive, they’re okay to go into the periphery. If it has a very strong affinity, they are going to recognise the antigens in the body, so ‘let’s kill them, otherwise they cause an autoimmune disease’. If by any chance you lose a tissue self-antigen (TSA), T-cells are never presented with this antigen, and therefore these auto-reactive T-cells survive. They lack what is called a negative selection, and then they go into the periphery, eventually leading into an autoimmune disease.”

Prof Sequeira outlined an important study that directly links keratin Krt76 with T-cell tolerance, presenting a novel role for thymus keratins in the development of skin immunopathologies. She said: “We showed that Krt76 is necessary for CorneoTEC differentiation, and for the expression of skin-specific TSAs in the thymus, and establishment of immune tolerance in the periphery….”

“Have you ever thought of looking into a skin disease from a thymic angle? That’s what I would love to discuss more and consider possible collaborations where we could actually look at this disease from a different angle and try to decouple the mutation in the skin from the organ of T-cell development, the thymus.”

Her take-home message was that “tissues are both more diverse and more similar than we imagined”, she said.

“Every tissue is a mosaic of unexpected cellular diversity, yet fundamental biological mechanisms create surprising connections across tissue types. Using multiomics technologies in our labs, we have really been able to define both the boundaries and bridges in tissue biology.”

Skin vs oral microenvironment

Each UCD Charles Institute seminar is followed by an informative clinical discussion and Q&A, which is moderated by Prof Tobin. In these, participants in-person and online have the opportunity to raise questions and offer input.

Following the presentation, Prof Tobin touched on the topic of saliva, and its relationship with oral mucosa and overall health.

“What exactly is saliva, and how does it differ from plasma, or exudate from burns?” he asked Prof Sequeira, “and has anybody done proteomics on saliva?”

“Yes, and some teams that are part of the Oral and Craniofacial Human Cell atlas have also done single-cell analysis on saliva samples,” said Prof Sequeira. “But we also have all these peptides and the anti-inflammatory role of saliva, and all of the bacteria that are present too.”

Prof Tobin pointed out that one of his students is studying the comparisons between burns exudate and plasma, in the context of pro- or anti-wound healing. Prof Tobin added: “We are finding some really interesting differences between plasma and exudate, which is a mix between plasma and something else, from the skin. So saliva is something similar to an interstitial fluid perhaps, but also coming into that is the mucosal protein repertoire, and bacteria. It would be interesting [to study] across different diseases, dental conditions, and so on, to see whether saliva is disturbed.”

Prof Sequeira responded: “We are working on a project that compares the microbiomes of the skin of patients, with their oral mucosa and saliva…. I think it would be really interesting to also compare that with liquid from burn blisters.”