Sangeeta Khanna

Persistent over-expression of specific CC class chemokines correlates with macrophage and T-cell recruitment in mdx skeletal muscle

Prior studies and the efficacy of immunotherapies provide evidence that inflammation is mechanistic in pathogenesis of Duchenne muscular dystrophy. To identify putative pro-inflammatory mechanisms, we evaluated chemokine gene/protein expression patterns in skeletal muscle of mdx mice. By DNA microarray, reverse transcription-polymerase chain reaction, quantitative polymerase chain reaction, and immunoblotting, convergent evidence established the induction of six distinct CC class chemokine ligands in adult MDX: CCL2/MCP-1, CCL5/RANTES, CCL6/mu C10, CCL7/MCP-3, CCL8/MCP-2, and CCL9/MIP-1gamma. CCL receptors, CCR2, CCR1, and CCR5, also showed increased expression in mdx muscle. CCL2 and CCL6 were localized to both monocular cells and muscle fibers, suggesting that dystrophic muscle may contribute toward chemotaxis. Temporal patterns of CCL2 and CCL6 showed early induction and maintained expression in mdx limb muscle. These data raise the possibility that chemokine signaling pathways coordinate a spatially and temporally discrete immune response that may contribute toward muscular dystrophy. The chemokine pro-inflammatory pathways described here in mdx may represent new targets for treatment of Duchenne muscular dystrophy.

Comprehensive expression profiling by muscle tissue class and identification of the molecular niche of extraocular muscle

Muscle tissue is an elegant model for biologic integration of structure with function and is frequently affected by a variety of inherited diseases. Traditional muscle classes‐‐skeletal, cardiac, and smooth‐‐share basic aspects of contractile and energetics mechanisms but also have distinctive role‐specific adaptations. We used large‐scale oligonucleotide microarrays to broaden knowledge of the adaptive expression patterns underlying muscle tissue differences and to identify transcript subsets that are most likely to represent candidate disease genes. Using stringent analysis criteria, we found ≥95 transcripts, which were preferentially expressed by each muscle class and were validated by inclusion of known muscle class‐specific and inherited disease‐related genes. Differentially expressed transcripts not previously identified as class‐specific extend understanding of muscle class transcriptomes and may represent novel muscle‐specific disease genes. We also analyzed the expression profile of extraocular muscle, which is divergent from other skeletal muscles, in the broader context of all major muscle classes. Data show that the extraocular muscle phenotype results from the combination of tissue‐specific transcripts, novel expression levels of skeletal muscle transcripts, and partial sharing of gene expression patterns with cardiac and smooth muscle. These, and additional proteomic data, establish that extraocular muscle does not constitute a distinctive muscle class but that it does occupy a novel niche within the skeletal muscle class.

Conservation of Synapse-Signaling Pathways at the Extraocular Muscle Neuromuscular Junction

The cell and molecular biology of extraocular muscle (EOM) is distinct from other skeletal muscles.1,2 Novel aspects of the innervation pattern of EOM include: high motoneuron discharge rates, presence of multiply innervated muscle fiber types in the adult, retention of embryonic acetylcholine receptor isoforms at some neuromuscular junctions (NMJs), absence of significant postjunctional membrane foldings at most NMJs, and sensitivity of EOM to neuromuscular transmission disorders (myasthenia gravis) and distinct response to botulinum toxin. The formation and maturation of the NMJ require a series of inductive interactions between axon and muscle fiber. These interactions culminate in the juxtaposition of a highly specialized nerve terminal with an elaborate postsynaptic apparatus.3,4 The sarcolemmal DGC and its associated proteins are central in this process of synapse formation and stabilization.5,6 The central hypothesis of this work was that the unique phenotype, and functional properties, of EOM may require muscle group-specific adaptations to organize and maintain the NMJ. Therefore, the signaling and sarcolemmal organization at the NMJ may differ between EOM singly (SIF) and multiply innervated fiber types (MIF) and between EOM and other skeletal muscles.