Integrating animal models and in vitro tissue models to elucidate the role of desmosomal proteins in diseases

Abstract

Desmosomes are intercellular junctions that provide tissues with structural stability. These junctions might also act as signaling centers that transmit environmental clues to the cell, thereby affecting cell differentiation, migration, and proliferation. The importance of desmosomes is underscored by devastating skin and heart diseases caused by mutations in desmosomal genes. Recent observations suggest that abnormal desmosomal protein expression might indirectly contribute to skin disorders previously not linked to these proteins. For example, it has been postulated that reduced desmosomal protein expression occurs in patients affected by Ankyloblepharon-ectodermal defects-cleft lip/palate syndrome (AEC), a skin fragility disorder caused by mutations in the transcription factor TP63. Currently, it is not clear how these changes in desmosomal gene expression contribute to AEC. We will discuss new approaches that combine in vitro and in vivo models to elucidate the role of desmosomal gene deregulation in human skin diseases such as AEC.

Figure 1

Desmosomal structure and composition. (A) Electron micrograph of a desmosome from mouse epidermis. The arrows demarcate the positions of the plasma membranes of neighboring cells. The brackets indicate the location of the cytoplasmic plaques. (B) Schematic representation of the proteins that assemble into desmosomes. Note that the transmembrane components (DSG and DSC) connect on the cytoplasmic surface of the desmosome with the plaque proteins (JUP, DSP and PKP) which in turn link to the intermediate filament (IF) cytoskeleton.

Figure 2

Clinical presentation of AEC patients. Scalp and palmar erosions on two patients affected by AEC. Patient images provided by the National Foundation for Ectodermal Dysplasias (NFED).

Figure 3

Focal downregulation of DSP and DSC3 expression in non-lesional skin of an AEC patient. (A,B) Normal human skin and (C, D) skin of an AEC patient. The dashed line demarcates the epidermal–dermal junction. The arrowheads in panels (C) and (D) point to areas of normal DSP and DSC3 staining, respectively, while the arrows indicate area in which expression of either DSC3 or DSP is significantly downregulated.

Figure 4

Generating in vitro tissue models using iPSC-derived keratinocytes. (A) iPSC-derived keratinocytes were generated following a protocol similar to a previously published procedure (Itoh et al., 2011). (B) iPSC-derived keratinocytes express keratin 14 (KRT14) and desmoglein 1/2 (DSG1/2). Note that these cells also express other epithelial markers, such as keratin 5, TP63, and α6β4 integrin (data not shown). (C) in vitro skin equivalent generated from human iPSC-derived keratinocytes on an artificial surface. Note that the epithelium stratified with a notable granular and cornified layer. Parakeratosis (retention of nuclei in the stratum corneum) occurs occasionally in in vitro skin equivalents. (D) Staining of the skin equivalent shown in (C) with an antibody for desmocollin 3 (DSC3). Note that these iPSC-derived skin equivalents also express other epithelial markers such as KRT5/14, KRT1/10, and loricrin (data not shown). The dotted line demarcates the junction between stratified epithelium and the artificial matrix on which the cells are growing.