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Content archived on 2024-05-29

The Role of Calcium and pH in Epidermal physiology and disease: Ionic Homeostasis observed through Fluorescence lifetime imaging


Epidermis displays two unique and characteristic electrolytic gradients: First, calcium (Ca2+), which regulates cell-physiologic processes including cell adhesion, growth, differentiation, and apoptosis, has a steep gradient towards the stratum granulosum (SG) which controls lamellar body (LB) secretion, and thereby permeability barrier function. Second, an acidic pH of the stratum corneum (SC), the functional endpoint in epidermal differentiation, is also required for normal permeability barrier function and regulates desquamation.

The activity of acidic, lysosomal type, lipid processing enzymes, required to fully establish the barrier to the external environment, and the proteases involved in desquamation depend on this pH-gradient. To form and/or maintain such differential ionic concentrations, epithelial tissues generally express tight junctions. To better understand the role of ion-fluxes, changes in ionic gradients, and the functional significance of such localization patterns within the epidermis and S C, we pioneered the use of Fluorescence Lifetime Imaging Microscopy (FLIM), applied to ex-vivo biopsies of intact skin for pH and Ca2+ measurements.

Through this proposal we will:
1) generate a detailed map of Ca2+ and pH gradients and localizations in human epidermis using FLIM, as current concepts are largely based on outdated methodology and studies in rodent skin.
2) We will ascertain the relationship and (co-) regulation of these ionic gradients, and
3) whether tight junctions play a role in establishing and/or maintaining the differential concentrations and localization of these ions.
4) We will assess alterations in ionic distribution that both accompany and could contribute to disease expression, and how these changes are disease related; e.g. changes of epidermal Ca2+ are known for chronic diseases as psoriasis and Hailey-Hailey, and divergent changes in SC pH occur in ichthyoses, inflammatory dermatoses, aged and neonatal skin.

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