Molecular Profile of the Evolution of Inclusion Body Myositis

Sporadic inclusion body myositis (sIBM) is a myopathy that usually does not become apparent before the age of 50 to 60. The disease is characterized by a progressive weakening of the muscles, including the finger flexors of the hand and proximal leg muscles. Swallowing problems are often observed. Muscular biopsy also reveals a combination of inflammatory, mitochondrial and myodegenerative signs. What triggers the disease has not yet been established, although two hypotheses are currently being explored: auto-immune and degeneration etiologies. Histological inflammatory hallmarks, the presence of sIMB-specific antibodies and the concomitance of other autoimmune pathologies point to the autoimmune hypothesis. On the other hand, immunosuppressive drugs only have a positive effect in a limited number of cases. The degenerative hypothesis is supported by the presence of rimmed vacuoles and protein aggregates (inclusion bodies) in the myocytes. The presence of mitochondrial anomalies can enhance protein aggregation that in turn can worsen mitochondrial changes.

Many genetic studies have been carried out to assess a potential genetic link in the sIBM. However, only connections to a number of HLA alleles and haplotypes have been found. In the present study, the investigators propose to evaluate gene expression in the muscular tissue by high-throughput RNA-sequencing (RNA-seq) in order to increase our knowledge of the sIMB pathophysiology. The RNA-seq technique can not only identify transcripted genes in a given tissue, but also discover unreported alternate or new transcripts, including long non-coding RNAs (lncRNAs). Indeed, lncRNAs play an important role in regulating gene networks, in particular in contributing to the setup and maintenance of epigenetic marks. The RNAseq approach will allow the investigators to assess the perturbations in the gene expression profiles and lncRNAs involved in the onset of the disease, by comparing the profiles obtained from patients at various stages of the disease and control subjects.

This study aims at assessing the gene expression in the muscles of patients suffering from sporadic Inclusion Body Myositis (sIBM) at various stages of the disease, by comparison with muscles of control subject. The investigators use the RNA-seq technique to analyze the gene expression levels and potential alternate transcripts, including long non-coding RNAs (lncRNAs), in muscle tissue samples. The gene expression profiles will point to the genes of interest that can then become the object of future studies, in which epigenetic changes of these genes will be explored further. The value of those possible biomarkers will be assessed. The investigators will also evaluate the correlation between the gene expression profile, the degree of functional impairment, the histological picture and the presence or absence of autoantibodies.

The study is interventional with no immediate benefits to the patient. RNAseq will be performed in both a group of sIBM patients (at early and late stages) and a group of control subjects.

Patients suffering from sIMB will be recruited on the basis of the ENMC 2011 diagnostic criteria. Predominant inflammatory changes (T-cell inflammatory infiltrate, expression of HLA class I antigens) without a degenerative affection (rimmed vacuoles, endomysial fibrosis, protein accumulation) will allow for a classification in the "early sIMB" group. Muscle biopsies of control subjects are part of a proprietary collection of the Neurology Department declared to the Nice University Hospital administration; they are selected from biopsies devoid of anomalies among subjects matching the ages of the sIMB patients. A physical examination and a venipuncture will be performed on patients in order to assess the absence or presence of anti-cN-1A antibodies, a new marker of sIMB. Control subjects will undergo a physical exam and a creatine kinase dosage. Tissue muscle has been collected beforehand in the frame of the routine diagnostic procedure for both patients and control subjects.

Expression profiles will be obtained by RNAseq from 15 muscle biopsies. Three groups of samples will be compared: 5 from early-stage sIMB patients, 5 from late-stage sIMB patients and 5 from control subjects.

In addition to known expression modifications of genes involved in the inflammatory response, in particular at early stages of the sIMB, or of genes involved in autophagy processes, at late stages of the disease where muscle degeneration is advanced, this study will allow identifying lncRNA potentially involved in the sIMB. Inasmuch as lncRNA are crucial for the regulation of cell differentiation and ageing processes at the epigenetic level, this pilot study will make possible to identify a group of genes of particular relevance, thus enabling further research on epigenetic regulation. Furthermore, a delayed gene expression, as is the case with lncRNA in early-stage sIMB patients, compared to lncRNA in late-stages disease patients, may prove a biomarker for evolution, and serve as a beneficial tool for monitoring sIMB in therapeutic trials to come.