Presence of laminin alpha 5 chain and lack of laminin alpha 1 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 alpha 1 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 alpha 1 chain. Nevertheless, there seems to be no expression of laminin alpha 1 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 alpha 1 chain as a recombinant protein and made antibodies specific for human laminin alpha 1 chain (anti-hLN-alpha 1G4/G5). We also made antibodies to the human laminin alpha 5 chain purified from placenta. In the present report we show that hLN-alpha 1G4/G5 antibodies react with a 400-kDa laminin alpha 1 chain and that 4C7 reacts with a 380-kDa laminin alpha 5 chain. Immunohistochemistry with the hLN-alpha 1G4/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 alpha 5 chain. Our data are also consistent with earlier work in mouse, indicating that laminin alpha 1 is largely an epithelial laminin chain not present in developing or dystrophic muscle fibers.