Alteration of Dermal Elastic Fibers During Calcifying Dermatosis: Structural Study Using Multiphoton Microscopy

The spectrum of pathologies accompanied by tissue mineral deposits is wide. In dermatology, several pathologies are associated with calcium mineral deposits, such as calciphylaxis and pseudoxanthoma elasticum (PXE). However, few studies have been carried out on the chemical characteristics of these deposits, their implication on the pathophysiology and their consequences. This motivated our two previous studies on the characterization of skin mineral deposits during calciphylaxis and sarcoidosis. We have shown that these deposits were most often composed of carbapatite and preferentially localized to elastic fibers. Most calcifying dermatoses are preceded by an inflammatory skin condition. Some authors suspect the digestion of elastin by metalloproteinase (MMP) of the extracellular matrix, thus creating nucleation nuclei favoring phosphocalcic deposits. We thus wish to study the structural alteration of dermal elastic fibers during calcifying dermatoses using multiphoton microscopy, a tool available at the Laboratoire d'Optique et Biosciences (LOB) at the Ecole Polytechnique. Multiphoton microscopy presents several contrast modes that can be used in parallel and without marking. This makes it possible to identify constituent elements of tissues without the use of artificially added fluorescent dyes or proteins, for example fibrillar collagen by the so-called "SHG" contrast and elastin by its intrinsic fluorescence. It is then possible to deeply image an intact tissue, without staining, by specifically visualizing its various components. Used in several studies on the skin, including the LOB, multiphoton microscopy has shown its interest in the characterization of dermal fibers, in particular elastin and collagen fibers, but also in the structural study of these and of their possible alteration. It has thus been applied to the study of skin aging, but also of pathologies leading to degeneration of elastic fibers (PXE) or collagen (Marfan syndrome). The main objective