Presence of Laminin α5 Chain and Lack of Laminin α1 Chain during Human Muscle Development and in Muscular Dystrophies*

There is currently a great interest in identifying laminin isoforms expressed in developing and regenerating skeletal muscle. Laminin α1 has been reported to localize to human fetal muscle and to be induced in muscular dystrophies based on immunohistochemistry with the monoclonal antibody 4C7, suggested to recognize the human laminin α1 chain. Nevertheless, there seems to be no expression of laminin α1 protein or mRNA in developing or dystrophic mouse skeletal muscle fibers. To address the discrepancy between the results obtained in developing and dystrophic human and mouse muscle we expressed the E3 domain of human laminin α1 chain as a recombinant protein and made antibodies specific for human laminin α1 chain (anti-hLN-α1G4/G5). We also made antibodies to the human laminin α5 chain purified from placenta. In the present report we show that hLN-α1G4/G5 antibodies react with a 400-kDa laminin α1 chain and that 4C7 reacts with a 380-kDa laminin α5 chain. Immunohistochemistry with the hLN-α1G4/G5 antibody and 4C7 revealed that the two antibodies stained human kidney, developing and dystrophic muscle in distinct patterns. Our data indicate that the previously reported expression patterns in developing, adult, and dystrophic human muscle tissues with 4C7 should be re-interpreted as an expression of laminin α5 chain. Our data are also consistent with earlier work in mouse, indicating that laminin α1 is largely an epithelial laminin chain not present in developing or dystrophic muscle fibers.