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Enhanced expression of the alpha 7 beta 1 integrin reduces muscular dystrophy and restores viability in dystrophic mice.

Burkin DJ, Wallace GQ, Nicol KJ, Kaufman DJ, Kaufman SJ - J. Cell Biol. (2001)

Bottom Line: Therefore, the molecular continuity between the extracellular matrix and cell cytoskeleton is essential for the structural and functional integrity of skeletal muscle.Concomitant with the increase in the alpha 7 chain, its heterodimeric partner, beta 1D, was also increased in the transgenic animals.This suggests that enhanced expression of the alpha 7 beta 1 integrin may provide a novel approach to treat DMD and other muscle diseases that arise due to defects in the dystrophin glycoprotein complex.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell and Structural Biology, University of Illinois, Urbana, Illinois 61801, USA.

ABSTRACT
Muscle fibers attach to laminin in the basal lamina using two distinct mechanisms: the dystrophin glycoprotein complex and the alpha 7 beta 1 integrin. Defects in these linkage systems result in Duchenne muscular dystrophy (DMD), alpha 2 laminin congenital muscular dystrophy, sarcoglycan-related muscular dystrophy, and alpha 7 integrin congenital muscular dystrophy. Therefore, the molecular continuity between the extracellular matrix and cell cytoskeleton is essential for the structural and functional integrity of skeletal muscle. To test whether the alpha 7 beta 1 integrin can compensate for the absence of dystrophin, we expressed the rat alpha 7 chain in mdx/utr(-/-) mice that lack both dystrophin and utrophin. These mice develop a severe muscular dystrophy highly akin to that in DMD, and they also die prematurely. Using the muscle creatine kinase promoter, expression of the alpha 7BX2 integrin chain was increased 2.0-2.3-fold in mdx/utr(-/-) mice. Concomitant with the increase in the alpha 7 chain, its heterodimeric partner, beta 1D, was also increased in the transgenic animals. Transgenic expression of the alpha 7BX2 chain in the mdx/utr(-/-) mice extended their longevity by threefold, reduced kyphosis and the development of muscle disease, and maintained mobility and the structure of the neuromuscular junction. Thus, bolstering alpha 7 beta 1 integrin-mediated association of muscle cells with the extracellular matrix alleviates many of the symptoms of disease observed in mdx/utr(-/-) mice and compensates for the absence of the dystrophin- and utrophin-mediated linkage systems. This suggests that enhanced expression of the alpha 7 beta 1 integrin may provide a novel approach to treat DMD and other muscle diseases that arise due to defects in the dystrophin glycoprotein complex. A video that contrasts kyphosis, gait, joint contractures, and mobility in mdx/utr(-/-) and alpha 7BX2-mdx/utr(-/-) mice can be accessed at http://www.jcb.org/cgi/content/full/152/6/1207.

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Histology of hindlimbs from 10-wk-old wild-type, mdx, mdx/utr−/−, and α7BX2-mdx/utr−/− mice. Hematoxylin and eosin (H & E) staining reveals abundant central nuclei in mdx, mdx/utr−/−, and α7BX2-mdx/utr−/− mice. Mononuclear cell infiltration (arrows) and expression of fMyHC are extensive in the mdx/utr−/− mice, but are reduced in the α7BX2-mdx/utr−/− transgenic animals, indicating less degeneration and more stable regeneration in these mice.
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Figure 7: Histology of hindlimbs from 10-wk-old wild-type, mdx, mdx/utr−/−, and α7BX2-mdx/utr−/− mice. Hematoxylin and eosin (H & E) staining reveals abundant central nuclei in mdx, mdx/utr−/−, and α7BX2-mdx/utr−/− mice. Mononuclear cell infiltration (arrows) and expression of fMyHC are extensive in the mdx/utr−/− mice, but are reduced in the α7BX2-mdx/utr−/− transgenic animals, indicating less degeneration and more stable regeneration in these mice.

Mentions: Nuclei are normally localized along the periphery of myofibers, whereas in regenerating muscle nuclei are centrally located (DiMario et al. 1991). Regeneration is also accompanied by a transient reversion to expression of fetal isoforms of myosin heavy chain (fMyHC) (Matsuda et al. 1983; Saad et al. 1987). Hindlimb sections from 5-, 8-, and 10-wk-old wild-type, mdx, mdx/utr−/−, and α7BX2-mdx/utr−/− mice were stained with hematoxylin and eosin to determine the extent of mononuclear infiltration and centrally located nuclei (Fig. 7 and Table ). Immunofluorescence of fMyHC was also determined. Degeneration and regeneration that are characteristic of muscle disease occur earlier in mdx/utr−/− animals compared with mdx mice (Fig. 7 and Table ). These results are consistent with the earlier onset of necrosis and cell infiltration reported previously in these animals (Deconinck et al. 1997b; Grady et al. 1997b). The occurrence of central nuclei in α7BX2-mdx/utr−/− mice was similar to that in mdx/utr−/− mice, indicating that enhanced expression of the integrin does not prevent early degeneration and regeneration. Likewise, fMyHC expression was most extensive at 5 wk in the mdx/utr−/− and α7BX2-mdx/utr−/− mice. In contrast, mdx mice exhibited very little fMyHC at 5 wk. At 8 wk, fMyHC was elevated in mdx mice, and at 10 wk it was reduced, indicating that a cycle of degeneration and regeneration was followed by stabilization. The shift from the β1A to β1D chain supports this conclusion. At all ages examined, the extent of fMyHC expression in the α7BX2-mdx/utr−/− animals was intermediate between that found in the mdx and mdx/utr−/− animals. In the 8- and 10-wk-old transgenic mdx/utr−/− mice, fMyHC expression approached that in mdx mice (Fig. 7). This decreased expression of fMyHC in α7BX2-mdx/utr−/− mice paralleled the greater integrity of tissue seen in the 8- and 10-wk-old transgenic animals compared with the mdx/utr (−/−) mice. The extensive mononuclear cell infiltration observed in the mdx/utr−/− mice (89–97% positive fields) was also partially reduced in the α7BX2-mdx/utr−/− animals (Fig. 7). The percentage of fields with cell infiltration was reduced approximately 17 and 19% in 5- and 8-wk-old transgenic versus nontransgenic mdx/utr−/− mice, respectively. This represents a minimal estimate since the areas of cell infiltration were considerably larger in the nontransgenic animals (Fig. 7). Thus, enhanced expression of the α7β1 integrin does not alter the initial degenerative cycle, but once regeneration has taken place, the additional integrin appears to stabilize muscle integrity, reducing muscle pathology.


Enhanced expression of the alpha 7 beta 1 integrin reduces muscular dystrophy and restores viability in dystrophic mice.

Burkin DJ, Wallace GQ, Nicol KJ, Kaufman DJ, Kaufman SJ - J. Cell Biol. (2001)

Histology of hindlimbs from 10-wk-old wild-type, mdx, mdx/utr−/−, and α7BX2-mdx/utr−/− mice. Hematoxylin and eosin (H & E) staining reveals abundant central nuclei in mdx, mdx/utr−/−, and α7BX2-mdx/utr−/− mice. Mononuclear cell infiltration (arrows) and expression of fMyHC are extensive in the mdx/utr−/− mice, but are reduced in the α7BX2-mdx/utr−/− transgenic animals, indicating less degeneration and more stable regeneration in these mice.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2199213&req=5

Figure 7: Histology of hindlimbs from 10-wk-old wild-type, mdx, mdx/utr−/−, and α7BX2-mdx/utr−/− mice. Hematoxylin and eosin (H & E) staining reveals abundant central nuclei in mdx, mdx/utr−/−, and α7BX2-mdx/utr−/− mice. Mononuclear cell infiltration (arrows) and expression of fMyHC are extensive in the mdx/utr−/− mice, but are reduced in the α7BX2-mdx/utr−/− transgenic animals, indicating less degeneration and more stable regeneration in these mice.
Mentions: Nuclei are normally localized along the periphery of myofibers, whereas in regenerating muscle nuclei are centrally located (DiMario et al. 1991). Regeneration is also accompanied by a transient reversion to expression of fetal isoforms of myosin heavy chain (fMyHC) (Matsuda et al. 1983; Saad et al. 1987). Hindlimb sections from 5-, 8-, and 10-wk-old wild-type, mdx, mdx/utr−/−, and α7BX2-mdx/utr−/− mice were stained with hematoxylin and eosin to determine the extent of mononuclear infiltration and centrally located nuclei (Fig. 7 and Table ). Immunofluorescence of fMyHC was also determined. Degeneration and regeneration that are characteristic of muscle disease occur earlier in mdx/utr−/− animals compared with mdx mice (Fig. 7 and Table ). These results are consistent with the earlier onset of necrosis and cell infiltration reported previously in these animals (Deconinck et al. 1997b; Grady et al. 1997b). The occurrence of central nuclei in α7BX2-mdx/utr−/− mice was similar to that in mdx/utr−/− mice, indicating that enhanced expression of the integrin does not prevent early degeneration and regeneration. Likewise, fMyHC expression was most extensive at 5 wk in the mdx/utr−/− and α7BX2-mdx/utr−/− mice. In contrast, mdx mice exhibited very little fMyHC at 5 wk. At 8 wk, fMyHC was elevated in mdx mice, and at 10 wk it was reduced, indicating that a cycle of degeneration and regeneration was followed by stabilization. The shift from the β1A to β1D chain supports this conclusion. At all ages examined, the extent of fMyHC expression in the α7BX2-mdx/utr−/− animals was intermediate between that found in the mdx and mdx/utr−/− animals. In the 8- and 10-wk-old transgenic mdx/utr−/− mice, fMyHC expression approached that in mdx mice (Fig. 7). This decreased expression of fMyHC in α7BX2-mdx/utr−/− mice paralleled the greater integrity of tissue seen in the 8- and 10-wk-old transgenic animals compared with the mdx/utr (−/−) mice. The extensive mononuclear cell infiltration observed in the mdx/utr−/− mice (89–97% positive fields) was also partially reduced in the α7BX2-mdx/utr−/− animals (Fig. 7). The percentage of fields with cell infiltration was reduced approximately 17 and 19% in 5- and 8-wk-old transgenic versus nontransgenic mdx/utr−/− mice, respectively. This represents a minimal estimate since the areas of cell infiltration were considerably larger in the nontransgenic animals (Fig. 7). Thus, enhanced expression of the α7β1 integrin does not alter the initial degenerative cycle, but once regeneration has taken place, the additional integrin appears to stabilize muscle integrity, reducing muscle pathology.

Bottom Line: Therefore, the molecular continuity between the extracellular matrix and cell cytoskeleton is essential for the structural and functional integrity of skeletal muscle.Concomitant with the increase in the alpha 7 chain, its heterodimeric partner, beta 1D, was also increased in the transgenic animals.This suggests that enhanced expression of the alpha 7 beta 1 integrin may provide a novel approach to treat DMD and other muscle diseases that arise due to defects in the dystrophin glycoprotein complex.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell and Structural Biology, University of Illinois, Urbana, Illinois 61801, USA.

ABSTRACT
Muscle fibers attach to laminin in the basal lamina using two distinct mechanisms: the dystrophin glycoprotein complex and the alpha 7 beta 1 integrin. Defects in these linkage systems result in Duchenne muscular dystrophy (DMD), alpha 2 laminin congenital muscular dystrophy, sarcoglycan-related muscular dystrophy, and alpha 7 integrin congenital muscular dystrophy. Therefore, the molecular continuity between the extracellular matrix and cell cytoskeleton is essential for the structural and functional integrity of skeletal muscle. To test whether the alpha 7 beta 1 integrin can compensate for the absence of dystrophin, we expressed the rat alpha 7 chain in mdx/utr(-/-) mice that lack both dystrophin and utrophin. These mice develop a severe muscular dystrophy highly akin to that in DMD, and they also die prematurely. Using the muscle creatine kinase promoter, expression of the alpha 7BX2 integrin chain was increased 2.0-2.3-fold in mdx/utr(-/-) mice. Concomitant with the increase in the alpha 7 chain, its heterodimeric partner, beta 1D, was also increased in the transgenic animals. Transgenic expression of the alpha 7BX2 chain in the mdx/utr(-/-) mice extended their longevity by threefold, reduced kyphosis and the development of muscle disease, and maintained mobility and the structure of the neuromuscular junction. Thus, bolstering alpha 7 beta 1 integrin-mediated association of muscle cells with the extracellular matrix alleviates many of the symptoms of disease observed in mdx/utr(-/-) mice and compensates for the absence of the dystrophin- and utrophin-mediated linkage systems. This suggests that enhanced expression of the alpha 7 beta 1 integrin may provide a novel approach to treat DMD and other muscle diseases that arise due to defects in the dystrophin glycoprotein complex. A video that contrasts kyphosis, gait, joint contractures, and mobility in mdx/utr(-/-) and alpha 7BX2-mdx/utr(-/-) mice can be accessed at http://www.jcb.org/cgi/content/full/152/6/1207.

Show MeSH
Related in: MedlinePlus