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Colocalization of Multiple Laminin Isoforms Predominantly beneath Hemidesmosomes in the Upper Lamina Densa of the Epidermal Basement Membrane

James R. McMillan, Masashi Akiyama, Hideki Nakamura and Hiroshi Shimizu

Creative Research Initiative Sousei (JRM) and Department of Dermatology, Graduate School of Medicine (JRM,MA,HN,HS), Hokkaido University, Sapporo, Japan

Correspondence to: James R. McMillan, MSc, PhD, Department of Dermatology, Hokkaido University Graduate School of Medicine, Kita-ku, Sapporo, 060-8638, Japan. E-mail: jrm57{at}med.hokudai.ac.jp

Multiple laminin isoforms including laminins 5 (3 ß3 2), 6 (3 ß1 1), 10 (5 ß1 1), and possibly laminins 7 (3 ß2 1) and 11 (5 ß2 1) are present in the epidermal basement membrane. However, only the precise epidermal ultrastructural localization of laminin 5 (3 ß3 2) has been elucidated. We therefore determined the precise expression and ultrastructural localization of the 5, ß1, ß2, and 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 5, ß1, and 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 5, ß1, ß2, and 1 chains were expressed but also localized to the dermal vessels. Immunogold electron microscopy of normal human epidermis localized the 5, ß1, ß2, and 1 chains to the upper lamina densa, with between 84% and 92% of labeling restricted to beneath the HDs, similar to laminin 5 (n200 gold particles per sample, sample number n=4) but distinct from collagen IV labeling (with only 63% labeling beneath HDs, p<0.001). Taken together, the majority of the 5ß1/ß21 laminin chains are located beneath HDs. This suggests that laminin-10-associated chains have specific functions or molecular interactions beneath HDs in the epidermal basement membrane. (J Histochem Cytochem 54:109–118, 2006)

Key Words: anchoring filament • epidermal basement membrane • hemidesmosome • immunoelectron microscopy • laminin 5 • laminin 10

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