A Roadmap for a Consensus Human Skin Cell Atlas and Single-Cell Data Standardization

Single-cell technologies have become essential to driving discovery in both basic and translational investigative dermatology. Despite the multitude of available datasets, a central reference atlas of normal human skin, which can serve as a reference resource for skin cell types, cell states, and their molecular signatures, is still lacking. For any such atlas to receive broad acceptance, participation by many investigators during atlas construction is an essential prerequisite. As part of the Human Cell Atlas project, we have assembled a Skin Biological Network to build a consensus Human Skin Cell Atlas and outline a roadmap toward that goal. We define the drivers of skin diversity to be considered when selecting sequencing datasets for the atlas and list practical hurdles during skin sampling that can result in data gaps and impede comprehensive representation and technical considerations for tissue processing and computational analysis, the accounting for which should minimize biases in cell type enrichments and exclusions and decrease batch effects. By outlining our goals for Atlas 1.0, we discuss how it will uncover new aspects of skin biology.

IRX5 promotes DNA damage repair and activation of hair follicle stem cells

The molecular mechanisms allowing hair follicles to periodically activate their stem cells (HFSCs) are incompletely characterized. Here, we identify the transcription factor IRX5 as a promoter of HFSC activation. Irx5-/- mice have delayed anagen onset, with increased DNA damage and diminished HFSC proliferation. Open chromatin regions form near cell cycle progression and DNA damage repair genes in Irx5-/- HFSCs. DNA damage repair factor BRCA1 is an IRX5 downstream target. Inhibition of FGF kinase signaling partially rescues the anagen delay in Irx5-/- mice, suggesting that the Irx5-/- HFSC quiescent phenotype is partly due to failure to suppress Fgf18 expression. Interfollicular epidermal stem cells also show decreased proliferation and increased DNA damage in Irx5-/-mice. Consistent with a role for IRX5 as a promoter of DNA damage repair, we find that IRX genes are upregulated in many cancer types and that there is a correlation between IRX5 and BRCA1 expression in breast cancer.

Differential cell composition and split epidermal differentiation in human palm, sole, and hip skin

Palmoplantar skin is structurally and functionally unique, but the transcriptional programs driving this specialization are unclear. Here, we use bulk and single-cell RNA sequencing of human palm, sole, and hip skin to describe the distinguishing characteristics of palmoplantar and non-palmoplantar skin while also uncovering differences between palmar and plantar sites. Our approach reveals an altered immune environment in palmoplantar skin, with downregulation of diverse immunological processes and decreased immune cell populations. Further, we identify specific fibroblast populations that appear to orchestrate key differences in cell-cell communication in palm, sole, and hip. Dedicated keratinocyte analysis highlights major differences in basal cell fraction among the three sites and demonstrates the existence of two spinous keratinocyte populations constituting parallel, site-selective epidermal differentiation trajectories. In summary, this deep characterization of highly adapted palmoplantar skin contributes key insights into the fundamental biology of human skin and provides a valuable data resource for further investigation.

Biogeographic and disease-specific alterations in epidermal lipid composition and single cell analysis of acral keratinocytes

The epidermis is the outermost layer of skin. Here, we used targeted lipid profiling to characterize the biogeographic alterations of human epidermal lipids across 12 anatomically distinct body sites, and we used single-cell RNA-Seq to compare keratinocyte gene expression at acral and nonacral sites. We demonstrate that acral skin has low expression of EOS acyl-ceramides and the genes involved in their synthesis, as well as low expression of genes involved in filaggrin and keratin citrullination (PADI1 and PADI3) and corneodesmosome degradation, changes that are consistent with increased corneocyte retention. Several overarching principles governing epidermal lipid expression were also noted. For example, there was a strong negative correlation between the expression of 18-carbon and 22-carbon sphingoid base ceramides. Disease-specific alterations in epidermal lipid gene expression and their corresponding alterations to the epidermal lipidome were characterized. Lipid biomarkers with diagnostic utility for inflammatory and precancerous conditions were identified, and a 2-analyte diagnostic model of psoriasis was constructed using a step-forward algorithm. Finally, gene coexpression analysis revealed a strong connection between lipid and immune gene expression. This work highlights (a) mechanisms by which the epidermis is uniquely adapted for the specific environmental insults encountered at different body surfaces and (b) how inflammation-associated alterations in gene expression affect the epidermal lipidome.

Validation of a pseudo-3D phantom for radiobiological treatment plan verifications

Performing realistic and reliable in vitro biological dose verification with good resolution for a complex treatment plan remains a challenge in particle beam therapy. Here, a new 3D bio-phantom consisting of 96-well plates containing cells embedded into Matrigel matrix was investigated as an alternative tool for biological dose verification. Feasibility tests include cell growth in the Matrigel as well as film dosimetric experiments that rule out the appearance of field inhomogeneities due to the presence of the well plate irregular structure. The response of CHO-K1 cells in Matrigel to radiation was studied by obtaining survival curves following x-ray and monoenergetic ¹²C ion irradiation, which showed increased radioresistance of 3D cell cultures in Matrigel as compared to a monolayer. Finally, as a proof of concept, a ¹²C treatment plan was optimized using in-house treatment planning system TRiP98 for uniform cell survival in a rectangular volume and employed to irradiate the 3D phantom. Cell survival distribution in the Matrigel-based phantom was analyzed and compared to cell survival in a reference setup using cell monolayers. Results of both methods were in good agreement and followed the TRiP98 calculation. Therefore, we conclude that this 3D bio-phantom can be a suitable, accurate alternative tool for verifying the biological effect calculated by treatment planning systems, which could be applied to test novel treatment planning approaches involving multiple fields, multiple ion modalities, complex geometries, or unconventional optimization strategies.

Oxygen beams for therapy: advanced biological treatment planning and experimental verification

Nowadays there is a rising interest towards exploiting new therapeutical beams beyond carbon ions and protons. In particular, [Formula: see text]O ions are being widely discussed due to their increased LET distribution. In this contribution, we report on the first experimental verification of biologically optimized treatment plans, accounting for different biological effects, generated with the TRiP98 planning system with [Formula: see text]O beams, performed at HIT and GSI. This implies the measurements of 3D profiles of absorbed dose as well as several biological measurements. The latter includes the measurements of relative biological effectiveness along the range of linear energy transfer values from  ≈20 up to  ≈750 keV μ [Formula: see text], oxygen enhancement ratio values and the verification of the kill-painting approach, to overcome hypoxia, with a phantom imitating an unevenly oxygenated target. With the present implementation, our treatment planning system is able to perform a comparative analysis of different ions, according to any given condition of the target. For the particular cases of low target oxygenation, [Formula: see text]O ions demonstrate a higher peak-to-entrance dose ratio for the same cell killing in the target region compared to [Formula: see text]C ions. Based on this phenomenon, we performed a short computational analysis to reveal the potential range of treatment plans, where [Formula: see text]O can benefit over lighter modalities. It emerges that for more hypoxic target regions (partial oxygen pressure of  ≈0.15% or lower) and relatively low doses (≈4 Gy or lower) the choice of [Formula: see text]O over [Formula: see text]C or [Formula: see text]He may be justified.

Development of a porcine animal model for urethral stricture repair using autologous urothelial cells

OBJECTIVE

To present a versatile large animal model for endoscopic stricture repair using autologous urothelial cells.

MATERIALS AND METHODS

12 male minipigs were used. An artificial stricture model was established using suture-ligation, thermo-coagulation and internal urethrotomy. A vesicostomy served for urinary diversion. Stricture formation was confirmed radiologically and histologically. Autologous urothelial cells were harvested from bladder washings, cultivated and labeled. Internal urethrotomy was done in all, and the cultivated cells were injected into the urethrotomy wound. All animals were sacrificed after 4 or 8 weeks. Immunohistology was done to confirm the presence of autologous urothelial cells within the reconstituted urethra.

RESULTS

Stricture formation was verified with all three methods. Histologically, no significant differences in the severity of stricture development could be observed with regard to the method used. The autologous urothelial cells in the area of the urethrotomy could be detected in the urothelium and the corpus spongiosum until 8 weeks after re-implantation.

CONCLUSIONS

We created a reliable and reproducible porcine model for artificial urethral strictures. Autologous urothelial cells can be implanted into an artificial stricture after urethrotomy. These cells retain their epithelial phenotype and are integrated in the resident urothelium. Further comparative studies are needed to ultimately determine a superior efficacy of this novel approach.

[Course and treatment of osteomyelitis in childhood (author's transl)]

In the years 1955-1972 132 children with osteomyelitis were treated in the Pediatric, Surgical and Orthopedic Department of the university of Kiel. There was no increase in the incidence of osteomyelitis during this period. Acute hematogenous osteomyelitis was diagnosed in 111 children, chronic hematogenous osteomyelitis in 11 children, traumatic and postoperative osteomyelitis in 10 children. Secondary chronic osteomyelitis occurred in 1 patient. Mainly staphylococci (in 90%) were the pathogenic bacteria, whereas haemophilus, pseudomonas, streptococci group A, E. coli and mixed infections occurred less frequently. In 17 of 111 patients with acute hematogenous osteomyelitis there were no roentgenological changes. Bacteriological investigations of blood and pus, and the antistaphylolysin reaction (repeated in the course of the disease) were helpful to establish the diagnosis in many cases. 107 of 111 patients with acute hematogenous osteomyelitis were cured (8 patients with defects). 4 children died in septic shock or because of complications (meningitis, pleural empyema, pneumonia). Bactericidal antibiotics in high dosage (penicillins, gentamicin) were superior to bacteriostatic antibiotics. Additional surgical treatment was necessary in 49 of 111 patients with acute hematogenous osteomyelitis. Recommendations for antibiotic therapy of osteomyelitis are given.