Nanomechanical tests in the diagnostics of genodermatoses
Our aim was to apply novel nanomechanical tests to investigate the biophysical properties of collagen VII anchoring fibrils in skin sections in a healthy control and in two recessive dystrophic epidermolysis bullosa (RDEB) patients. One patient was diagnosed with localized RDEB and the other with generalized severe RDEB.
Sections of skin biopsies from patient and control were investigated with atomic force microscopy (AFM) combined with fluorescence imaging. In the localized RDEB patient and healthy control, the anchoring fibrils were first immunostained, identified and scanned using AFM. In the generalized severe RDEB patient (no collagen VII staining), the dermal surface of the basement membrane zone (BMZ) adjacent to bulla formation was scanned. Nanoindentation was used to obtain force-volume maps and to characterize local viscoelasticity. Force-displacement curves were fitted with the Hertz model to calculate the local Young modulus.
The control skin specimen could be partitioned into high-, intermediate- and low-Young-modulus areas that correspond to the dermis, BMZ and the epidermis, respectively. Remarkably, the dermis was stiffer than the epidermis by an order of magnitude. The region with intermediate Young modulus could not be clearly identified in the severe RDEB samples, whereas there was an apparent difference in the distribution of Young’s modulus between healthy control and RDEB loc patient considering the BMZ areas.
The healthy skin may thus be seen as a highly compliant epidermis woven onto a stiff dermis. Hence, collagen VII plays an important role in coupling the mechanically distinct epidermis and dermis. The applied biophysical measurements enabled us to obtain clinically relevant data and may be used in the future to evaluate protein or gene therapies in RDEB patients.
Balázs Mayer1, Pálma Silló1, Mercédesz Mazán1, Dóra Haluszka2, Miklós Z. Kellermayer2, Sarolta Kárpáti1
1Department of Dermatology, Venerology and Dermatooncology, 2Department of Biophysics and Radiation Biology, Faculty of Medicine, Semmelweis University, Budapest, Hungary