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Daniel Kjellgren, Lars-Eric Thornell, Ismo Virtanen, Fatima Pedrosa-Domellöf; Laminin Isoforms in Human Extraocular Muscles. Invest. Ophthalmol. Vis. Sci. 2004;45(12):4233-4239. doi: 10.1167/iovs.04-0456.
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purpose. To determine the laminin isoform composition of the basement membranes (BMs) in the human extraocular muscles (EOMs) and relate it to the fact that EOMs are spared in laminin α2-chain–deficient congenital muscular dystrophy.
methods. Samples from adult human EOMs and limb muscle were processed for immunocytochemistry, with monoclonal antibodies against laminin chains (Ln) α1 to -5, β1 and -2, and γ1. Neuromuscular junctions (NMJs) were identified with acetylcholinesterase reaction. The capillary density was measured in sections stained with anti-Lnα5.
results. The extrasynaptic BM of the EOM muscle fibers contained Lnα2, -β1, -β2, and -γ1, and, in contrast to limb muscle, it also contained Lnα4 and -α5, to some extent. The distinct laminin composition of the EOMs was confirmed by the presence of Lutheran protein, an α5-chain–specific receptor not found in limb muscle. At the NMJs, there was increased expression of Lnα4 and expression of Lnα2, -α5, -β1, -β2, and -γ1 was also maintained. The capillary density was very high (1050 ± 190 capillaries/mm2) in the EOMs and significantly (P < 0.05) higher in the orbital (1170 ± 180 capillaries/mm2) than in the global (930 ± 110 capillaries/mm2) layer.
conclusions. The human EOMs showed important differences in laminin isoform composition and capillary density when compared with human limb muscle and muscles of other species. The presence of additional laminin isoforms other than laminin-2 in the BM of the extrasynaptic sarcolemma could partly explain the sparing of the EOMs in Lnα2-deficient congenital muscular dystrophy.
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