The epidermis is more than a passive outer covering. It is a continuously renewing tissue that forms a barrier against microbes, chemicals, dehydration and mechanical damage. Its cells must coordinate proliferation, differentiation, adhesion and repair to maintain this barrier throughout life. With age, however, the epidermis becomes less efficient at regenerating and healing wounds. The skin also develops a chronic inflammatory background often described as “inflammaging.” Unlike the intense, short-lived inflammation caused by an infection or injury, inflammaging is persistent and relatively subtle. Over time, it can interfere with tissue maintenance and contribute to functional decline. The new study suggests that the problem is not simply an excess of inflammatory signals, but also a change in the way epidermal cells interpret and amplify those signals.

At the centre of the mechanism are BMAL1 and YAP, two proteins with apparently different biological identities. BMAL1 is widely known as a core component of the circadian clock, the molecular timing system that helps cells coordinate activities across the 24-hour day. YAP, or yes-associated protein, is part of the Hippo signalling pathway and helps cells respond to mechanical forces, tissue architecture and changes in their surroundings. In the epidermis, the researchers found that BMAL1 and YAP work together independently of daily circadian rhythms. In adult skin, this partnership helps preserve epidermal identity and supports the proper operation of skin cells. Their interaction therefore represents a form of transcriptional control: the proteins influence which genes are switched on by occupying regulatory regions of DNA.

Ageing appears to redirect this cellular machinery. As skin becomes physically stiffer and inflammatory signals accumulate, BMAL1 and YAP increasingly concentrate at regulatory regions associated with inflammation. These regions function as genomic control points, including enhancers and promoters that determine the activity of nearby genes. By occupying them together, the two proteins can increase the transcription of inflammatory programmes in epidermal cells. The result is not merely a response to inflammation arriving from elsewhere in the tissue. The epidermis itself becomes an active amplifier, converting environmental and immune cues into a stronger and more sustained genetic response. This shift helps explain how mechanisms that normally preserve tissue homeostasis can acquire a damaging role during ageing.

The study also connects this pathway to interleukin-17, or IL-17, a cytokine previously implicated by the same laboratory in age-related skin deterioration. IL-17 is produced by immune cells located in the dermis, the layer beneath the epidermis, and acts as a communication signal between the immune system and skin cells. In their earlier work, published in 2023, the researchers reported that temporarily blocking IL-17 in mice reduced persistent inflammation and delayed some features associated with skin ageing. The new findings trace the signal further downstream. According to the experiments, IL-17 contributes to the activation of YAP in epidermal cells, linking an immune-derived message to changes in the transcriptional machinery of the skin’s outer layer.

When the researchers blocked IL-17 in aged mice, activity associated with YAP declined, as did the expression of the inflammatory genes examined in the study. This result supports a model in which immune cells in the dermis release IL-17, epidermal cells respond by activating YAP, and YAP then works with BMAL1 at inflammatory gene-control regions. Age-related changes in tissue stiffness may reinforce the same response by increasing mechanical signals that favour YAP activity. Together, these inputs could create a feedback loop: inflammation alters the cellular environment, the altered environment activates transcriptional regulators, and those regulators drive genes that sustain inflammation. Such a loop would help account for the persistence of inflammaging even when no acute injury or infection is present.

The findings are significant because they place mechanical biology, circadian proteins and immune signalling within a single framework for skin ageing. BMAL1’s involvement is particularly notable because its best-known role is regulating daily biological rhythms. In this context, however, the protein’s partnership with YAP appears to operate outside the timing function traditionally associated with the circadian clock. The work suggests that proteins can retain their molecular identity while participating in different regulatory tasks depending on the age and condition of a tissue. It also highlights the importance of chromatin context—the organisation and accessibility of DNA—in determining whether a protein supports normal cell function or promotes disease-associated gene expression.

The researchers supported their mouse experiments with analyses of human skin data, strengthening the relevance of the mechanism to human ageing while not proving that the pathway operates identically in every person. Most of the experimental evidence came from aged mouse skin, where the investigators could manipulate IL-17 and observe changes in YAP-associated activity and inflammatory gene expression. Human data provided an additional indication that the molecular relationships identified in mice are present in human tissue. As with any preclinical study, further research will be required to determine how strongly the pathway contributes to age-related skin changes in people, how it varies between individuals, and whether it is involved in specific disorders such as chronic inflammatory skin diseases or skin cancer.

The discovery also raises an important therapeutic challenge. Suppressing inflammation in ageing skin might appear beneficial, but IL-17, YAP and BMAL1 all perform essential functions. IL-17 contributes to host defence, YAP helps tissues respond to mechanical conditions and injury, and BMAL1 is central to cellular timing and physiological regulation. Blocking these pathways broadly could therefore impair wound healing, barrier maintenance or protection against infection. The most promising future strategies may need to target the age-dependent interaction between the proteins, their recruitment to inflammatory regions of DNA, or the abnormal combination of immune and mechanical signals that activates them. Any intervention would need to reduce chronic amplification without disabling the normal repair and defence programmes of the epidermis.

“Our results show that, during ageing, mechanisms that normally maintain epidermal homeostasis change function and begin to amplify inflammation,” says Salvador Aznar Benitah, an ICREA researcher and head of the Stem Cells and Cancer laboratory at IRB Barcelona. First author Júlia Bonjoch describes the work as the next step after the laboratory’s 2023 identification of IL-17 as a key signal in skin ageing: “Now we have discovered how epidermal cells respond to that signal and amplify inflammation.” Researchers from the Max Planck Institute for Molecular Biomedicine in Münster, Germany, also contributed to the study. Funders included the European Research Council, the Government of Spain, the Generalitat de Catalunya, Fundació La Marató de TV3, the Fondation Bettencourt Schueller, the Spanish Association Against Cancer and Worldwide Cancer Research.

News Publication Date: 19 August 2026

Web References: https://doi.org/10.1038/s43587-026-01192-1

References: Nature Aging, DOI: 10.1038/s43587-026-01192-1

Keywords: skin ageing, chronic inflammation, inflammaging, epidermis, BMAL1, YAP, IL-17, circadian clock, Hippo signalling pathway, skin regeneration, tissue stiffness, epidermal homeostasis, molecular biology, immunology

Psoriasis, traditionally viewed through the lens of aberrant immune activation and keratinocyte proliferation, has long challenged scientists due to its multifaceted etiology. Historically, much emphasis was placed on T cell-mediated responses as the primary drivers of disease pathology. However, this recent investigation pivots the spotlight towards innate immune effectors—specifically NK cells—and their interaction with epidermal cells, mediated through the expression of MHC-II molecules. This novel axis reveals previously uncharted territories in psoriasis pathogenesis.

At the molecular heart of this mechanism lies the expression of MHC class II molecules on epidermal keratinocytes, a feature not typically associated with these cells under homeostatic conditions. The study demonstrates that during psoriatic inflammation, keratinocytes aberrantly upregulate MHC-II, effectively transforming them into atypical antigen-presenting cells. This upregulation serves as a beacon that recruits circulating NK cells to the epidermis, a process that has been meticulously delineated using sophisticated in vivo and in vitro models reflective of human disease.

The recruited NK cells, upon engagement with MHC-II-expressing keratinocytes, undergo activation that culminates in the secretion of cytotoxic mediators triggering pyroptotic cell death within the epidermis. Unlike apoptosis, pyroptosis is characterized by the formation of membrane pores, cellular swelling, and the release of pro-inflammatory cytokines such as IL-1β and IL-18. This cascade amplifies local inflammation, recruiting additional immune cells and exacerbating the psoriatic lesions, creating a feedback loop that sustains and escalates the disease state.

Mechanistically, the interaction between NK cells and keratinocytes hinges on receptor-ligand crosstalk facilitated by MHC-II molecules, which, in this context, appear to act beyond classic antigen presentation roles. The study uncovers that NK cell activation is contingent upon direct recognition of these MHC-II molecules, highlighting a noncanonical pathway wherein NK cells modulate keratinocyte fate through targeted pyroptosis. This insight challenges long-established immunological dogma and opens avenues for exploring NK cell behavior in other inflammatory skin diseases.

Translated from bench to bedside, these findings possess profound therapeutic implications. Targeting the MHC-II mediated recruitment of NK cells or intercepting the pyroptotic signaling cascade could ameliorate psoriatic inflammation, offering a precision medicine approach. Current psoriasis therapies largely focus on systemic immunosuppression or biologics directed at cytokines such as TNF-α and IL-17; however, this study advocates for a paradigm shift by tuning innate immunity at the epidermal interface.

Further, the identification of pyroptosis as a critical effector mechanism in keratinocyte demise underscores the broader significance of inflammatory cell death pathways in skin disease. It beckons the exploration of selective inhibitors of pyroptotic components such as gasdermin D, caspase-1, and inflammasome complexes, which might serve as novel pharmacological targets. Such interventions could diminish inflammatory amplification without broadly suppressing immune competence.

This research also exemplifies the complex cellular heterogeneity within psoriatic lesions, spotlighting keratinocytes not merely as passive victims of immune attack but as active participants in immune modulation. Their transformation into MHC-II-expressing entities suggests plasticity and adaptability in response to inflammatory cues, revolutionizing the way epidermal responses are conceptualized in chronic dermatoses.

Technical rigor was a hallmark of this study, employing cutting-edge techniques including single-cell RNA sequencing to delineate expression profiles of MHC-II and pyroptosis-related genes in keratinocytes. Coupled with high-resolution imaging and functional assays, the comprehensive approach furnished incontrovertible evidence linking epidermal MHC-II expression to NK cell-mediated pyroptosis, thus cementing this axis as a cornerstone in psoriasis pathobiology.

Moreover, animal models genetically engineered to abrogate MHC-II expression on keratinocytes exhibited markedly reduced NK cell infiltration and attenuated psoriatic pathology, reinforcing causality. This genetic evidence substantiates the mechanistic hypothesis, elevating the translational potential of targeting this pathway in human patients.

Significantly, the temporal dynamics of NK cell recruitment and subsequent pyroptosis induction appear tightly regulated and disease-stage dependent, suggesting potential windows for therapeutic intervention that could preempt irreversible skin damage. Understanding these kinetics further facilitates the design of treatment modalities that are both effective and minimally disruptive to normal skin homeostasis.

The study also invites reconsideration of NK cells’ roles beyond cytotoxicity, suggesting their function as regulatory sentinels shaping epidermal integrity through controlled cell death pathways. This dualistic role exemplifies the delicate balance of immune surveillance and tissue homeostasis, a balance disrupted in psoriatic disease states.

In addition, the data propose that aberrant epidermal MHC-II expression may serve as a biomarker for disease activity or severity in psoriasis, enabling clinicians to stratify patients and tailor interventions more precisely. This biomarker potential, combined with emerging therapeutic targets, gestures towards a future where personalized medicine optimally manages this chronic condition.

While illuminating, the findings also raise pivotal questions regarding the upstream signals inducing MHC-II expression on keratinocytes and the broader immunological milieu influencing NK cell behavior. Decoding these triggers will be essential to fully manipulate this pathway therapeutically and to understand its relevance across diverse inflammatory skin disorders.

Ultimately, this study by Yi, Yu, Wang and colleagues constitutes a watershed moment in psoriasis research, integrating molecular immunology, cell biology, and translational medicine. By delineating the epidermal MHC-II–NK cell–pyroptosis axis, it lays a robust foundation for innovative treatment strategies aimed at restoring skin integrity by modulating innate immune interactions.

As the prevalence of psoriasis continues to rise globally, unraveling such intricate cellular dialogues provides an invaluable beacon of hope. Future research inspired by these findings promises not only to refine therapeutic approaches but also to deepen our overarching grasp of skin immunology’s complexities, paving the way for breakthroughs that extend beyond psoriasis to other inflammatory and autoimmune conditions.

Subject of Research:
The study investigates the role of epidermal MHC class II molecules in mediating NK cell recruitment and triggering pyroptosis in keratinocytes, contributing to the pathogenesis of psoriasis.

Article Title:
Epidermal MHC-II-mediated NK cell recruitment triggers keratinocyte pyroptosis, facilitating pathogenesis of psoriasis.

Article References:
Yi, X., Yu, P., Wang, J. et al. Epidermal MHC-II-mediated NK cell recruitment triggers keratinocyte pyroptosis, facilitating pathogenesis of psoriasis. Exp Mol Med (2026). https://doi.org/10.1038/s12276-026-01717-z

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DOI:
https://doi.org/10.1038/s12276-026-01717-z