Laminin 332 Is Indispensable for Homeostatic Epidermal Differentiation Programs.

The skin epidermis is attached to the underlying dermis by a laminin 332 (Lm332)-rich basement membrane. Consequently, loss of Lm332 leads to the severe blistering disorder epidermolysis bullosa junctionalis in humans and animals. Owing to the indispensable role of Lm332 in keratinocyte adhesion in vivo, the severity of the disease has limited research into other functions of the protein. We have conditionally disrupted Lm332 expression in basal keratinocytes of adult mice. Although blisters develop along the interfollicular epidermis, hair follicle basal cells provide sufficient anchorage of the epidermis to the dermis, making inducible deletion of the Lama3 gene compatible with life. Loss of Lm332 promoted the thickening of the epidermis and exaggerated desquamation. Global RNA expression analysis revealed major changes in the expression of keratins, cornified envelope proteins, and cellular stress markers. These modifications of the keratinocyte genetic program are accompanied by changes in cell shape and disorganization of the actin cytoskeleton. These data indicate that loss of Lm332-mediated progenitor cell adhesion alters cell fate and disturbs epidermal homeostasis.