miRNA expression profiling of thymus samples from myasthenia gravis patients

Autoimmune myasthenia gravis (MG) is characterized by thymic abnormalities such as hyperplasia and thymoma. Thymus plays an important role in self-tolerance and is involved in initiation and progression of the disease. A large proportion of MG patient show the presence of ectopic germinal centers (GC) in thymus that are absent in normal individuals. However, the exact mechanism how this change in thymus morphology is triggered and if this is related to pathophysiology of the disease remains unknown. In this study we have compared the mRNA profile of thymus samples obtained during a clinical trial (Thymectomy Trial in Non-Thymomatous Myasthenia Gravis Patients Receiving Prednisone Therapy. ClinicalTrials.gov Identifier: NCT00294658). We have compared the miRNA profile of thymus samples that have distinct germinal centers with those that lack them using Affymetrix miRNA array 4.0 to identify the differentially expressed genes with in the two groups. Sixteen frozen tissue samples collected during MGTX trial were cryo-sectioned and were stained with haematoxylin and eosin to examine morphological features and presence of germinal centers. The H and E sections were evaluated by two blinded observers and graded depending on presence (Grades 1-4) or absence of germinal centers (Grade 0). Total RNA including small RNA was isolated from the remaining tissue using mirVana miRNA isolation kit. The RNA samples were processed and applied to Affymetrix miRNA array 4.0. Array data was normalized, batch corrected and analyzed (1-way ANOVA) using Partek Genomics Suite program.