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Several BMPs and TNF superfamily molecules together with Runx2 are differently expressed in the peripheral blood of arthritic patients

Background: The network of bone-regulatory cytokines and growth factors affects osteoblast differentiation and activity, thus controlling bone destruction and reparative process. The gene of critical importance in the regulation of bone formation is runt-related transcription factor 2 (Runx2), essential for the expression of the osteoblast-specific gene osteocalcin and osteoblast differentiation. Therefore, the aim of our study was to test if the systemic expression of various bone-regulatory factors including TNF superfamily and BMP family members correlate with the expression of osteoblast differentiation gene Runx2 in different forms of arthritis, depending of the disease activity, applied therapy, arthritis subtype and other clinical parameters. Methods. Three major forms of chronic joint diseases are classified in clinical practice: osteoarthritis (OA), rheumatoid arthritis (RA) and spondyloarthritis (SpA) that includes ankylosing spondylitis (AS), psoriatic arthritis (PA), reactive arthritis, etc. In our study, blood samples were collected from healthy controls (Ctrl ; n = 25, age range 24-61) and RA patients (n = 49, age range 27-57), OA patients (n = 17, age range 45-79) and SpA patients, either with AS (n = 27, age range 32-46) or PA (n = 23, age range 34- 52), after the informed consent. RNA was extracted from PBMCs, amplified by quantitative PCR, and expressed as the relative amounts of RNA for target genes normalized to GPDH. Gene expression values were correlated with the clinical parameters of arthritis. The receiver operating characteristic (ROC) curve analysis was used to determine the efficacy of analyzed genes to discriminate between different types of arthritis and control group. Results. Several of tested immunomodulatory and bone-inducing molecules as well as osteoblast differentiation gene Runx2 were differentially expressed in arthritic patients compared with healthy controls. The greatest difference was found for RA and OA patients that had decreased expression of BMP-4, FasL, LIGHT, TRAIL and Runx2, and OA patients had decreased expression of BMP-6 as well (p<0.05, Kruskal- Wallis followed by Mann-Whitey test). In addition, AS patients had increased expression of Runx2 and PA patients had decreased expression of TRAIL. Negative correlation was found for BMP-4, FasL and Runx2 expression with several disease activity parameters in RA patients (Larsen score, DAS28, physician assessment of disease activity, patient assessment of pain) and positive correlation was found for BMP-4 expression with the disease parameters in PA patients (BASDAI, patient assessment of pain and disease activity). Difference was also found for the tested molecules depending on the response to therapy and type of the applied therapy. ROC curve analysis confirmed the clinical importance of several gene expression values to discriminate between arthritic and normal samples and potential usefulness as diagnostic molecular markers, including BMP-4, FasL, LIGHT and Runx2 for RA and Runx2 for AS patients. Conclusions. Since the modulation of inflammatory and destructive pathways may not be sufficient to achieve restoration of joint function, it is clinically very important to establish the molecular biomarkers, such as Runx2 and BMPs, that would indicate the restoration of bone metabolism homeostasis and stimulation of tissue repair. In addition, correlation between gene expression values and disease parameters observed in our study may be helpful to assess effectiveness of novel therapeutic approached aimed to modulate systemic expression of immunoregulatory and apoptotic factors.

BONE MORPHOGENETIC PROTEINS; TUMOR-NECROSIS FACTORS; RUNX2; GENE EXPRESSION; BLOOD CELLS; ARTHRITIS

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