A chronic inflammatory response dominates the skeletal muscle molecular signature in dystrophin-deficient mdx mice

Abstract

Mutations in dystrophin cause Duchenne muscular dystrophy (DMD), but absent dystrophin does not invariably cause necrosis in all muscles, life stages and species. Using DNA microarray, we established a molecular signature of dystrophinopathy in the mdx mouse, with evidence that secondary mechanisms are key contributors to pathogenesis. We used variability controls, adequate replicates and stringent analytic tools, including significance analysis of microarrays to estimate and manage false positive rates. In leg muscle, we identified 242 differentially expressed genes, >75% of which have not been previously reported as altered in human or animal dystrophies. Data provide evidence for coordinated activity of numerous components of a chronic inflammatory response, including cytokine and chemokine signaling, leukocyte adhesion and diapedesis, invasive cell type-specific markers, and complement system activation. Selective chemokine upregulation was confirmed by RT-PCR and immunoblot, and may be a key determinant of the nature of the inflammatory response in dystrophic muscle. Up-regulation of secreted phosphoprotein 1 (minopontin, osteopontin) mRNA and protein in dystrophic muscle identified a novel linkage between inflammatory cells and repair processes. Extracellular matrix genes were up-regulated in mdx to levels similar to those in DMD. Since, unlike DMD, mdx exhibits little fibrosis, data suggest that collagen regulation at post-transcriptional stages mediates extensive fibrosis in DMD. Taken together, these data identify a relatively neglected aspect of DMD, suggest new treatment avenues, and highlight the value of genome-wide profiling in study of complex disease processes.

Comparative transcriptome analysis of muscular dystrophy models Largemyd, Dmdmdx/Largemyd and Dmdmdx: what makes them different?

“…Several transcriptome studies in Dmd mdx mouse were published in the last years, [12][13][14][15][16][17][18][19][20] but no studies in Large myd − / − nor in Dmd mdx /Large myd − / − were performed. 9 In Dmd mdx , similar data to the observed in our study were described by Boer et al 14 and Porter et al 17,21 Using an Affymetrix chip of about 12 000 genes/EST, Boer et al 14 identified 58 DEGs in Dmd mdx limb muscles, from which 49 were unregulated while only 9 were downregulated.…”

“…Osteopontin stimulates myoblasts proliferation 40 and was described as an inflammatory player in dystrophic muscle. 16,41 Recently, it was reported that after a lesion, osteopontin expression is induced and promotes muscle inflammation, necrosis and regeneration, acting as an important factor to muscle remodeling. 40 The overexpression of Spp1 can be related to the intense degeneration and subsequent regeneration present in the muscle at this age.…”

“…The expression profiling of medial gastrocnemius of Dmd mdx mice revealed that most induced genes belongs to immune response and inflammation. 20 Porter et al 16 found 242 DEGs in the Dmd mdx gastrocnemius, of which 29.8% were classified as inflammatory genes, determining a chronic inflammatory response. Similar results were reported also by other authors.…”

AAV-based shRNA silencing of NF-κB ameliorates muscle pathologies in mdx mice

“…Necrosis presents from the age of 1 month as a consequence of the pathological degeneration and regeneration in mdx muscles; 33 hence, we treated mdx mice at the ages of 1 and 4 months to test the therapeutic effects in mdx muscle at different stages of inflammation. The successful anti-inflammatory effect of AAV-mediated p65-shRNA in adult mdx muscle provides a potential therapeutic approach for DMD.…”

Soluble TNF-α receptor secretion from healthy or dystrophic mice after AAV6-mediated muscle gene transfer

“…Accordingly, DNA microarray experiments conducted on skeletal muscles isolated from 8-week-old dystrophic mdx mice showed that 30% of the 242 identified, differentially expressed genes are related to inflammation. 2 Tumor necrosis factor-a (TNF-a) is one of the proinflammatory cytokines that has a role in muscular dystrophy. Indeed, the plasma levels of TNF-a have been found to be increased in DMD patients.…”