Single-Cell and Spatial Transcriptomic Analysis of Human Skin Delineates Intercellular Communication and Pathogenic Cells

Unraveling the Functional Heterogeneity of Human Skin at Single-Cell Resolution

The skin consists of several cell populations, including epithelial, immune, and stromal cells. Recently, there has been a significant increase in single-cell RNA-sequencing studies, contributing to the development of a consensus Human Skin Cell Atlas. The aim is to understand skin biology better and identify potential therapeutic targets. The present review utilized previously published single-cell RNA-sequencing datasets to explore human skin's cellular and functional heterogeneity. Additionally, it summarizes the functional significance of newly identified cell subpopulations in processes such as wound healing and aging.

Skin in the game: a review of single-cell and spatial transcriptomics in dermatological research

Single-cell RNA sequencing (scRNA-seq) and spatial transcriptomics (ST) are two emerging research technologies that uniquely characterize gene expression microenvironments on a cellular or subcellular level. The skin, a clinically accessible tissue composed of diverse, essential cell populations, serves as an ideal target for these high-resolution investigative approaches. Using these tools, researchers are assembling a compendium of data and discoveries in healthy skin as well as a range of dermatologic pathophysiologies, including atopic dermatitis, psoriasis, and cutaneous malignancies. The ongoing advancement of single-cell approaches, coupled with anticipated decreases in cost with increased adoption, will reshape dermatologic research, profoundly influencing disease characterization, prognosis, and ultimately clinical practice.

Type 1 innate lymphoid cells: a biomarker and therapeutic candidate in sarcoidosis

Sarcoidosis is an inflammatory disease characterized by immune cell-rich granulomas that form in multiple organs. In this issue of the JCI, Sati and colleagues used scRNA-seq and spatial transcriptomics of skin samples from patients with sarcoidosis and non-sarcoidosis granulomatous disease to identify upregulation of a stromal-immune CXCL12/CXCR4 axis and accumulation of type 1 innate lymphoid cells (ILC1s) in sarcoidosis. The accumulation of ILC1s in skin and blood was specific to patients with sarcoidosis and not observed in other granulomatous diseases. The authors used a mouse model of lung granuloma to show that ILCs contribute to granuloma formation and that blockade of CXCR4 reduced the formation of granulomas, providing a proof of concept that sarcoidosis may be treated by CXCR4 blockade to prevent the progression of disease in patients. These results suggest ILC1s could serve as a diagnostic biomarker in sarcoidosis and a potential therapeutic target.

Analysis of intracellular communication reveals consistent gene changes associated with early-stage acne skin

A comprehensive understanding of the intricate cellular and molecular changes governing the complex interactions between cells within acne lesions is currently lacking. Herein, we analyzed early papules from six subjects with active acne vulgaris, utilizing single-cell and high-resolution spatial RNA sequencing. We observed significant changes in signaling pathways across seven different cell types when comparing lesional skin samples (LSS) to healthy skin samples (HSS). Using CellChat, we constructed an atlas of signaling pathways for the HSS, identifying key signal distributions and cell-specific genes within individual clusters. Further, our comparative analysis revealed changes in 49 signaling pathways across all cell clusters in the LSS- 4 exhibited decreased activity, whereas 45 were upregulated, suggesting that acne significantly alters cellular dynamics. We identified ten molecules, including GRN, IL-13RA1 and SDC1 that were consistently altered in all donors. Subsequently, we focused on the function of GRN and IL-13RA1 in TREM2 macrophages and keratinocytes as these cells participate in inflammation and hyperkeratinization in the early stages of acne development. We evaluated their function in TREM2 macrophages and the HaCaT cell line. We found that GRN increased the expression of proinflammatory cytokines and chemokines, including IL-18, CCL5, and CXCL2 in TREM2 macrophages. Additionally, the activation of IL-13RA1 by IL-13 in HaCaT cells promoted the dysregulation of genes associated with hyperkeratinization, including KRT17, KRT16, and FLG. These findings suggest that modulating the GRN-SORT1 and IL-13-IL-13RA1 signaling pathways could be a promising approach for developing new acne treatments.

Analysis of Intracellular Communication Reveals Consistent Gene Changes Associated with Early-Stage Acne Skin

A comprehensive understanding of the intricate cellular and molecular changes governing the complex interactions between cells within acne lesions is currently lacking. Herein, we analyzed early papules from six subjects with active acne vulgaris, utilizing single-cell and high-resolution spatial RNA sequencing. We observed significant changes in signaling pathways across seven different cell types when comparing lesional skin samples (LSS) to healthy skin samples (HSS). Using CellChat, we constructed an atlas of signaling pathways for the HSS, identifying key signal distributions and cell-specific genes within individual clusters. Further, our comparative analysis revealed changes in 49 signaling pathways across all cell clusters in the LSS- 4 exhibited decreased activity, whereas 45 were upregulated, suggesting that acne significantly alters cellular dynamics. We identified ten molecules, including GRN, IL-13RA1 and SDC1 that were consistently altered in all donors. Subsequently, we focused on the function of GRN and IL-13RA1 in TREM2 macrophages and keratinocytes as these cells participate in inflammation and hyperkeratinization in the early stages of acne development. We evaluated their function in TREM2 macrophages and the HaCaT cell line. We found that GRN increased the expression of proinflammatory cytokines and chemokines, including IL-18, CCL5, and CXCL2 in TREM2 macrophages. Additionally, the activation of IL-13RA1 by IL-13 in HaCaT cells promoted the dysregulation of genes associated with hyperkeratinization, including KRT17, KRT16, and FLG. These findings suggest that modulating the GRN-SORT1 and IL-13-IL-13RA1 signaling pathways could be a promising approach for developing new acne treatments.

Unveiling the mechanisms of trichloroethylene hypersensitivity syndrome: Exploring the role of connexin 43 gap junctions in severe skin damage

Trichloroethylene (TCE), extensively used as an organic solvent in various industrial applications, has been identified as a causative factor in inducing hypersensitivity syndrome (THS). Currently, there is no specific treatment for THS, and most patients experience serious adverse outcomes due to extensive skin damage leading to severe infection. However, the pathogenesis of THS-associated skin damage remains unclear. This study aims to elucidate the mechanism underlying skin damage from the perspective of intercellular communication and gap junctions in THS. Our results verified that hyperactivation of connexin43 gap junctions, caused by the aberrantly elevated expression of connexin43, triggers a bystander effect that promotes apoptosis and inflammation in THS via the TNF-TNFRSF1B and mitochondria-associated pathways. Additionally, we identified the gap junction inhibitor Carbenoxolone disodium (CBX) as a promising agent for the treatment of skin damage in THS. CBX protects against inflammatory cell infiltration in the skin and decreases immune cell imbalance in the peripheral blood of THS mice. Furthermore, CBX reduces connexin43 expression, apoptosis and inflammation in THS mice. The study reveals new insights into the mechanisms underlying TCE-induced skin damage, offering a potential treatment strategy for the development of effective therapies targeting severe dermatitis induced by chemical exposure.

Hurdles in translating science from lab to market in delivery systems for Cosmetics: An industrial perspective

In recent decades, a sweeping technological wave has reshaped the global economic landscape. Fueled by the unceasing forces of digital innovation and venture capital investment, this transformative machine has left a significant mark across numerous economic sectors. More recently, the emergence of 'deep tech' start-ups, focusing on areas such as artificial intelligence, nanotechnology, and biotechnology, has infused a fresh wave of innovation into various sectors, including the pharmaceutical and cosmetic industry. This review explores the significance of innovation within the cosmetics sector, with a particular emphasis on delivery systems. It assesses the crucial process of bridging the gap between research and the market, particularly in the translation of nanotechnology into tangible real-world applications. With the rise of nanotechnology-based beauty ingredients, we can anticipate groundbreaking advancements that promise to surpass consumer expectations, ushering in a new era of unparalleled innovation in beauty products.