ANALYSIS OF EXPRESSION OF GENES OF THE PROTEASOME SYSTEM ALLOWS THE DEFINITION OF A MOLECULAR INFLAMMATORY PROFILE IN PATIENTS WITH AUTOIMMUNE MYOPATHIES

Background: Idiopathic inflammatory myopathies, including polymyositis (PM), dermatomyositis (DM) and inclusion body myositis (IBM), are diseases with still unknown etiology, probably of autoimmune nature. In PM, expression of some components of the proteasome system is altered. This is a crucial catalytic system involved in immune regulation, cell cycle and apoptosis. A simultaneous analysis of all constitutive and inducible catalytic proteasome subunits in inflammatory and non-inflammatory myopathies that allows for a comprehensive overview has not been done yet. Objectives: To analyse gene expression of components of the proteasome system in muscle samples from patients with inflammatory myophaties (PM, DM, IBM), and from control patients with non-inflammatory disorders (e.g. mitochondrial myopathy, deficiency of myoadenylat desaminase). Methods: Inflammation degree was estimated in histological stainings. RNA from muscle biopsies was used for relative quantification of gene expression by real time PCR. Seven genes of the proteasome system, including the three constitutive catalytic beta subunits b1 (Delta), b2 (Z), b5 (MB1), their corresponding inducible ones b1i (LMP2), b2i (MECL), b5i (LMP7) and one constitutive, non-catalytic alpha subunit (a3), were measured in triplicates by comparison with the house keeping genes beta actin, GAPDH and HPRT. Results were calculated with the delta-Ct method. Statistic analysis was done using non-parametric Mann-Whitney test, P<0.005 was considered as significant. Ratios were calculated using values of expression of corresponding constitutive/inducible subunits. Results: In inflammatory myopathies, DM patients showed the strongest significant differences in the expression of all constitutive and inducible proteasome subunits when compared to non-inflammatory controls, while IBM patients showed a significant decrease in expression of constitutive subunits; PM patients showed differences only in Delta and LMP7. In general, gene expression of constitutive proteasome subunits was significantly higher than of inducible ones, especially for Delta/LMP2 and MB1/LMP7. Notably, the magnitude of this relation calculated as ratio of expression of corresponding constitutive/inducible subunits varied constantly between inflammatory, weak inflammatory and non-inflammatory states. In detail, ratios of expression for Delta/LMP2 varied from 34:1 in non-inflammatory to 9:1 in weak inflammatory and to 3:1 in inflammatory cases; for MB1/LMP7 it was 17:1, 4:1 and 1.5:1, while for Z/MECL it was 2:1, 3:1 and 2:1, respectively. Conclusion: Our results show that gene expression of Delta/LMP2 and MB1/LMP7 proteasome subunits is altered in inflammatory myopathies. Further implications of these alterations for the disease, including expression at protein level, should be analysed. Calculation of proteasome subunits expression ratios allowed a clear differentiation between non-, weak- or inflammatory states in the analyzed myopathies and therefore, could be a useful tool for monitoring of disease development. Disclosure of Interest: None declaredCitation: Annals of the Rheumatic Diseases, volume 68, supplement 3, year 2009, page 466Session: Scleroderma, myositis and related syndromes (Poster Presentations )