Quantitative morphometric analysis of intrinsic and extrinsic skin ageing in individuals with Fitzpatrick skin types II-III.

Skin ageing is an intricate physiological process affected by intrinsic and extrinsic factors. There is a demand to understand how the skin changes with age and photoexposure in individuals with Fitzpatrick skin types I-III due to accelerated photoageing and the risk of cutaneous malignancies. To assess the structural impact of intrinsic and extrinsic ageing, we analysed 14 skin parameters from the photoprotected buttock and photoexposed dorsal forearm of young and ageing females with Fitzpatrick skin types II-III (n = 20) using histomorphic techniques. Whilst the minimum viable epidermis (Emin ) remained constant (Q > 0.05), the maximum viable epidermis (Emax ) was decreased by both age and photoexposure (Q ≤ 0.05), which suggests that differences in epidermal thickness are attributed to changes in the dermal-epidermal junction (DEJ). Changes in Emax were not affected by epidermal cell proliferation. For the first time, we investigated the basal keratinocyte morphology with age and photoexposure. Basal keratinocytes had an increased cell size, cellular height and a more columnar phenotype in photoexposed sites of young and ageing individuals (Q ≤ 0.05), however no significant differences were observed with age. Some of the most striking changes were observed in the DEJ, and a decrease in the interdigitation index was observed with both age and photoexposure (Q ≤ 0.001), accompanied by a decreased height of rête ridges and dermal papilla. Interestingly, young photoexposed skin was comparable to ageing skin across many parameters, and we hypothesise that this is due to accelerated photoageing. This study highlights the importance of skin care education and photoprotection from an early age.

The microfollicle: a model of the human hair follicle for in vitro studies.

Access to complex in vitro models that recapitulate the unique markers and cell-cell interactions of the hair follicle is rather limited. Creation of scalable, affordable, and relevant in vitro systems which can provide predictive screens of cosmetic ingredients and therapeutic actives for hair health would be highly valued. In this study, we explore the features of the microfollicle, a human hair follicle organoid model based on the spatio-temporally defined co-culture of primary cells. The microfollicle provides a 3D differentiation platform for outer root sheath keratinocytes, dermal papilla fibroblasts, and melanocytes, via epidermal-mesenchymal-neuroectodermal cross-talk. For assay applications, microfollicle cultures were adapted to 96-well plates suitable for medium-throughput testing up to 21 days, and characterized for their spatial and lineage markers. The microfollicles showed hair-specific keratin expression in both early and late stages of cultivation. The gene expression profile of microfollicles was also compared with human clinical biopsy samples in response to the benchmark hair-growth compound, minoxidil. The gene expression changes in microfollicles showed up to 75% overlap with the corresponding gene expression signature observed in the clinical study. Based on our results, the cultivation of the microfollicle appears to be a practical tool for generating testable insights for hair follicle development and offers a complex model for pre-clinical substance testing.

Mouse hair cycle expression dynamics modeled as coupled mesenchymal and epithelial oscillators.

The hair cycle is a dynamic process where follicles repeatedly move through phases of growth, retraction, and relative quiescence. This process is an example of temporal and spatial biological complexity. Understanding of the hair cycle and its regulation would shed light on many other complex systems relevant to biological and medical research. Currently, a systematic characterization of gene expression and summarization within the context of a mathematical model is not yet available. Given the cyclic nature of the hair cycle, we felt it was important to consider a subset of genes with periodic expression. To this end, we combined several mathematical approaches with high-throughput, whole mouse skin, mRNA expression data to characterize aspects of the dynamics and the possible cell populations corresponding to potentially periodic patterns. In particular two gene clusters, demonstrating properties of out-of-phase synchronized expression, were identified. A mean field, phase coupled oscillator model was shown to quantitatively recapitulate the synchronization observed in the data. Furthermore, we found only one configuration of positive-negative coupling to be dynamically stable, which provided insight on general features of the regulation. Subsequent bifurcation analysis was able to identify and describe alternate states based on perturbation of system parameters. A 2-population mixture model and cell type enrichment was used to associate the two gene clusters to features of background mesenchymal populations and rapidly expanding follicular epithelial cells. Distinct timing and localization of expression was also shown by RNA and protein imaging for representative genes. Taken together, the evidence suggests that synchronization between expanding epithelial and background mesenchymal cells may be maintained, in part, by inhibitory regulation, and potential mediators of this regulation were identified. Furthermore, the model suggests that impairing this negative regulation will drive a bifurcation which may represent transition into a pathological state such as hair miniaturization.