Abstract
Limb-girdle muscular dystrophy type 2A (LGMD2A) is a recessive genetic disorder caused by mutations in calpain 3 (CAPN3). Calpain 3 plays different roles in muscular cells, but little is known about its functions or in vivo substrates. The aim of this study was to identify the genes showing an altered expression in LGMD2A patients and the possible pathways they are implicated in. Ten muscle samples from LGMD2A patients with in which molecular diagnosis was ascertained were investigated using array technology to analyze gene expression profiling as compared to ten normal muscle samples. Upregulated genes were mostly those related to extracellular matrix (different collagens), cell adhesion (fibronectin), muscle development (myosins and melusin) and signal transduction. It is therefore suggested that different proteins located or participating in the costameric region are implicated in processes regulated by calpain 3 during skeletal muscle development. Genes participating in the ubiquitin proteasome degradation pathway were found to be deregulated in LGMD2A patients, suggesting that regulation of this pathway may be under the control of calpain 3 activity. As frizzled-related protein (FRZB) is upregulated in LGMD2A muscle samples, it could be hypothesized that β-catenin regulation is also altered at the Wnt signaling pathway, leading to an incorrect myogenesis. Conversely, expression of most transcription factor genes was downregulated (MYC, FOS and EGR1). Finally, the upregulation of IL-32 and immunoglobulin genes may induce the eosinophil chemoattraction explaining the inflammatory findings observed in presymptomatic stages. The obtained results try to shed some light on identification of novel therapeutic targets for limb-girdle muscular dystrophies.
Highlights
Limb-girdle muscular dystrophy type 2A (LGMD2A) is a recessive genetic disorder caused by mutations in calpain 3 (CAPN3), a muscle-specific, calcium-dependent cystein protease
92 were significantly overexpressed and 64 showed a reduced expression in LGMD2A patients compared to the unaffected controls
Principal component analysis (PCA) grouped together on the one hand patient samples and on the other hand control samples and a greater variability was seen among controls due to the heterogeneity of this group (Figure 1)
Summary
Limb-girdle muscular dystrophy type 2A (LGMD2A) is a recessive genetic disorder caused by mutations in calpain 3 (CAPN3), a muscle-specific, calcium-dependent cystein protease. Calpain 3 structure is similar to that of the ubiquitous calpains 1 and 2, but calpain 3 has specific regions (NS, IS1, and IS2) that confer it special characteristics such as autocatalytic and nuclear translocation capacity. Calpain 3 has a certain role in direct and indirect regulation of conventional calpains by proteolytic degradation of calpains and calpastatin respectively [2]. It may be involved in muscle contraction due to its link to titin and to its regulation by calcium [3,4,5,6,7]
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