O-GlcNAcylation, an original modulator of contractile activity in striated muscle.

There is growing evidence that O-linked N-acetyl-D-glucosaminylation, more simply termed O-GlcNAcylation or O-GlcNAc, is a post-translational modification involved in many cellular processes from transcription to modulation of protein properties. O-GlcNAc is a dynamic and reversible glycosylation and therefore quite similar to the phosphorylation/dephosphorylation process, with which O-GlcNAc can interplay. Since O-GlcNAc serves as a glucose sensor by the way of hexosamine biosynthesis pathway, this glycosylation is often associated with glucose toxicity and development of insulin resistance. In this way, O-GlcNAc could be involved in muscle pathological consequences of diabetes. Nevertheless, in regards of several studies performed in healthy striated muscles, O-GlcNAc seems to exert protective effects against different types of injuries. Recent new insights suggest a key implication of O-GlcNAc in skeletal and cardiac muscles contractile activity, in particular by O-GlcNAc modification of motor as well as regulating contractile proteins. While evidence linked O-GlcNAc to the regulation of calcium activation properties, its exact role remains to be defined as well as the existence of potential interference with phosphorylation. The better understanding of the exact function of OGlcNAc in this physiological process could contribute to the determination of newly markers of skeletal dysfunctions.

Proteomic analysis in cardiovascular diseases.

1. Cardiovascular diseases are a major cause of morbidity and mortality in western countries. The molecular mechanisms responsible for heart dysfunction are still largely unknown, except in cases of genetic defects or alteration of genes and proteins. 2. The publication of genome sequences from humans and other species has demonstrated the complexity of biology, including the finding that one gene does not encode for only one protein but for several, due to mRNA splicing and post-translational modifications. 3. Proteomic analysis can provide an overall understanding of changes in the levels of protein expression. Differential proteomics is a powerful tool for improving our understanding of integrated biochemical responses. The main techniques used are two-dimensional electrophoresis (2D-gel) and Surface-Enhanced Laser Desorption/Ionization Time of Flight (SELDI-TOF) to separate proteins associated with mass spectrometry. Bioinformatic tools make it possible to compare protein profiles obtained from diverse biological samples. 4. The combination of these approaches has proved to be particularly interesting for studying cardiovascular diseases and thereby improving our understanding of the mechanisms involved and identifying new biochemical factors and biomarkers involved in these diseases.

Childhood spinal muscular atrophy induces alterations in contractile and regulatory protein isoform expressions.

AIMS: Although modifications of the survival motor neurone gene are responsible for most spinal muscular atrophy (SMA) cases, the molecular pathophysiology and the muscular target proteins involved are still unknown. The aim of this study was to compare the expression of contractile and regulatory protein isoforms in quadriceps muscles from SMA children with age-matched control quadriceps. METHODS: The isoform patterns of myosin heavy chains (MHC), troponin subunits (T, C and I) and tropomyosin were determined by immunoblotting, reverse transcription-polymerase chain reaction and mass spectrometry analyses. Depending on the disease severity, their expression levels were followed in specific variants of SMA populations (types I, II and III), with comparison with age-matched control muscles. RESULTS: The isoform transitions in SMA muscles were different from the fast-to-faster transitions occurring in normal muscles from children aged 1 month to 5 years old. Moreover, the expression of the neonatal MHC isoform was not repressed in SMA muscles. CONCLUSIONS: The presence of the neonatal MHC isoform in SMA muscles indicates an alteration of the phenotype in these diseased muscles. It is strongly suggested that MHC and troponin T proteins may be good markers for the SMA pathology.