Metallomic profiling and imaging for understanding skin and scalp biology

Micronutrients such as manganese, iron, copper, and zinc are essential for healthy skin. Although skin contains mainly keratinocytes, about a tenth of the cells are specialized: e.g. melanocytes, Langerhans cells or inflammatory cells. Langerhans cells form tight junctions with keratinocytes, are absent under zinc deficiency, and together with the stratum corneum are important for epidermal barrier function. The relative significance of these metal ions for the different cell types is unknown. Major advances in mass spectrometric techniques now allow imaging the distribution of metal ions in tissues and cells. It established that metal ions are not randomly distributed but rather follow cell-specific functions. For different skin cells such metal profiles are essentially unknown. Metal ions are involved in lipid biosynthesis, which is of direct relevance to processes such as barrier disruption in ageing skin or dandruff in scalp.

1. Quantitative metal imaging in the epidermis. Metal profiling in the different cell types will be conducted using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). The work will utilise immuno-cytochemistry of skin sections to identify cell types and subsequent LA-ICP-MS on adjacent sections for the quantification of metal ions at the cellular level. A correlative light electron microscopy approach will be used to determine which cells have metal-rich vesicles and whether the Birbeck granules in Langerhans cells store metal ions for a potential role in metal ion secretion. Subcellular studies will utilise electron microscopy at King's Centre for Ultrastructural Imaging, as well as draw upon expertise from collaborators at the Francis Crick EM facility. Outcome: identification of cell-specific metal profiles throughout skin.
2. Metal effects on keratinocytes and the immune system. Cell culture models will be used to investigate the effect of metal ion -depletion on the transcriptome of a range of isolated skin cell types, including keratinocytes and immune cells. Co-cultures will study the paracrine effects metal depletion. Ex-vivo skin grown in media depleted by specific metal ions as a model of nutritional micronutrient deficiencies will be separated into unique cell populations by flow cytometry for qPCR of proteins involved in metal homeostasis. This will be correlated with single-cell ICP-MS, measuring metal concentrations in individual cell types. Integration of the datasets will enable a better understanding of the importance of each metal ion throughout different skin cell types. Outcome: identification of metal homeostasis proteins and interactions between skin cell types.
3. Metal effects on the lipidome. Lipidomic analysis of cell lysates, 3D skin models and/or skin/scalp explants grown in metal-depleted media and with topically applied metal ions will be carried out by UPLC-MS/MS to correlate changes due to metal ions with the synthesis of barrier-relevant lipids. Outcome: identification of the role metal ions play in controlling the production of skin lipids.