Expression of laminin alpha 1, alpha 2, alpha 4, and alpha 5 chains, fibronectin, and tenascin-C in skeletal muscle of dystrophic 129ReJ dy/dy mice

The dy/dy mouse is an animal model for human merosin-negative congenital mu scular dystrophy (CMD), which has been reported to have reduced or no expre ssion of the basement membrane protein laminin alpha 2. We here investigate various myogenic and nonmyogenic tissues of mature dy/dy and control 129Re J mice histologically and for laminin alpha 2 expression. In addition, expr ession patterns of laminin alpha 1, alpha 2, alpha 4, and alpha 5 chains, t he interstitial proteins fibronectin and tenascin-C, and the adhesion molec ules VCAM-1, ICAM-1, and alpha 4 integrin were characterized in skeletal mu scle of 1- and 7-day and mature (>6 weeks old) dy/dy and control 129ReJ mic e. The laminin alpha 2 chain remained detectable in myogenic tissues of dy/ dy mice by immunofluorescence using two different monoclonal antibodies and by Northern blot analysis. However, laminin alpha 2 expression was signifi cantly reduced or not detectable in nonmyogenic tissues of dy/dy mice, incl uding skin, lung, kidney, brain, thymus, and eye. Focal lesions were observ ed in mature skeletal muscle only, characterized by necrotic tissue, isolat ed VCAM-1- and ICAM-1-positive cells indicative of inflammatory processes, and regenerating muscle fibers surrounded by intense tenascin-C and fibrone ctin expression. In contrast to studies on human CMD muscle, laminin alpha 1 was not detectable in either dy/dy or control skeletal muscle using immun ofluorescence or Northern blot analysis. Immunofluorescence localized lamin in alpha 4 to basement membranes of blood vessels, the endoneurium of the i ntramuscular nerves, and the neuromuscular junction in skeletal muscle of 1 - and 7-day-old dy/dy and control mice. In mature muscle, laminin alpha 4 e xpression shifted to the perineurium of intramuscular nerves in both dy/dy and control mice. Furthermore, strong upregulation of laminin alpha 4 in th e basement membranes of blood vessels, the perineurium of intramuscular ner ves, and of isolated regenerating muscle fibers in the dy/dy mice was appar ent. Investigation of 1-day-old animals revealed expression of laminin alph a 5 in skeletal muscle fiber basement membranes of dy/dy but not control an imals. This difference between dy/dy and control animals was no longer appa rent at 7 days after birth, indicating a temporary shift in expression patt ern of laminin alpha 5 in dy/dy animals. Analysis of the extracellular matr ix components of 1- and 7-day-old dy/dy and control skeletal muscle reveale d an early onset of the dystrophy, even before histopathological features o f the disease were evident. Our data confirm the absence of laminin alpha 1 chain in myogenic tissues of both dy/dy and control mice and suggest compe nsation for reduced laminin alpha 2 in dy/dy skeletal muscle by laminin alp ha 4 and, in early development, also laminin alpha 5. These results have si gnificant ramifications in the diagnosis of human merosin-negative CMD. (C) 1999 Academic Press.