Colocalization of multiple laminin isoforms predominantly beneath hemidesmosomes in the upper lamina densa of the epidermal basement membrane

Multiple laminin isoforms including laminins 5 ({alpha}3 ß3 {gamma}2), 6 ({alpha}3 ß1 {gamma}1), 10 ({alpha}5 ß1 {gamma}1), and possibly laminins 7 ({alpha}3 ß2 {gamma}1) and 11 ({alpha}5 ß2 {gamma}1) are present in the epidermal basement membrane. However, only the precise epidermal ultrastructural localization of laminin 5 ({alpha}3 ß3 {gamma}2) has been elucidated. We therefore determined the precise expression and ultrastructural localization of the {alpha}5, ß1, ß2, and {gamma}1 chains in the epidermis. The expression of laminin chains in skin samples was analyzed from patients with epidermolysis bullosa (EB, n=15) that harbor defects in specific hemidesmosome (HD)-associated components. The expression of the {alpha}5, ß1, and {gamma}1 chains (present in laminins 10/11) and ß2 chain (laminins 7/11) was unaffected in all intact (unseparated) skin of EB patients including Herlitz junctional EB with laminin-5 defects (n=6). In the basement membrane of human epidermis, the {alpha}5, ß1, ß2, and {gamma}1 chains were expressed but also localized to the dermal vessels. Immunogold electron microscopy of normal human epidermis localized the {alpha}5, ß1, ß2, and {gamma}1 chains to the upper lamina densa, with between 84% and 92% of labeling restricted to beneath the HDs, similar to laminin 5 (n≥200 gold particles per sample, sample number n=4) but distinct from collagen IV labeling (with only 63% labeling beneath HDs,