Laminin isoforms in human extraocular muscles.
OBJECTIVE
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 alpha2-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) alpha1 to -5, beta1 and -2, and gamma1. Neuromuscular junctions (NMJs) were identified with acetylcholinesterase reaction. The capillary density was measured in sections stained with anti-Lnalpha5.


RESULTS
The extrasynaptic BM of the EOM muscle fibers contained Lnalpha2, -beta1, -beta2, and -gamma1, and, in contrast to limb muscle, it also contained Lnalpha4 and -alpha5, to some extent. The distinct laminin composition of the EOMs was confirmed by the presence of Lutheran protein, an alpha5-chain-specific receptor not found in limb muscle. At the NMJs, there was increased expression of Lnalpha4 and expression of Lnalpha2, -alpha5, -beta1, -beta2, and -gamma1 was also maintained. The capillary density was very high (1050 +/- 190 capillaries/mm(2)) in the EOMs and significantly (P < 0.05) higher in the orbital (1170 +/- 180 capillaries/mm(2)) than in the global (930 +/- 110 capillaries/mm(2)) 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 Lnalpha2-deficient congenital muscular dystrophy.
Kjellgren
Daniel
D
Department of Clinical Science, Section of Ophthalmology, University of Umeå, Umeå, Sweden.
Thornell
Lars-Eric
LE
Virtanen
Ismo
I
Pedrosa-Domellöf
Fatima
F
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001485:Basement Membrane / Q000378:metabolism; D002196:Capillaries / Q000033:anatomy & histology; D005121:Extremities; D006651:Histocytochemistry; D006801:Humans; D007150:Immunohistochemistry; D007231:Infant, Newborn; D007797:Laminin / Q000378:metabolism*; D008875:Middle Aged; D018485:Muscle Fibers, Skeletal / Q000378:metabolism; D018482:Muscle, Skeletal / Q000098:blood supply / Q000378:metabolism; D009801:Oculomotor Muscles / Q000098:blood supply / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D017474:Receptors, Laminin / Q000378:metabolism; D012508:Sarcolemma / Q000378:metabolism; D014018:Tissue Distribution
D007797:Laminin; D020033:Protein Isoforms; D017474:Receptors, Laminin