The Function Of SLPI In Ossification Of Ankylosing Spondylitis And Factors Associated With Severe Hip Involvement

BackgroundAs a major subtype of spondyloarthrities, ankylosing spondylitis’ main clinical features include inflammatory back pain, occurring at an early age, involvement of sacroiliac joint, joint axis, large joints of limbs (lower limbs), enthesitis, and other organ involvement (anterior uveitis, psoriasis, a chronic inflammatory bowel disease). As AS progresses, it eventually leads to ankylosis of joint and spine. Epidemiological studies show, the prevalence rate of AS is about 0.11-0.37% in China. Among all the AS population, more than 20% of patients have hip joint involvement, and 47-90% of them have bilateral hip involvement. At present, the pathogenesis of AS is still unclear, but studies suggest that there is a certain correlation between AS and genetic, immune, infection factors and environment. Unlike other rheumatic arthritis (RA), the natural history of AS is divided into two stages:inflammatory damage and new bone formation. When AS progresses to ankylosis of spine and joint, it also will bring great influence to AS patients’life, work. Therefore, in order to early diagnose and treat AS, the study of the pathogenesis of AS is of great significance.Treatment of AS includes physical therapy, drug therapy, operation therapy. For the medical treatment of AS, the main purpose is to inhibit the inflammatory symptoms. But studies have shown that the inhibition of inflammation could not prevent the progress of ossification. When the spine and joint of AS patients progress to ankylosis, surgical treatment is the only effective treatment. Therefore, study of the mechanism of the abnormal bone ossification in AS, is extremely important for the pathogenesis and effective treatment of AS.ObjectiveThrough selecting the ligaments of hip joint of AS patients and controls, we firstly conducted an Affymetrix gene chip technology for screening differentially expressed genes. Based on the results of gene chip, we combined it with analysis of relevant literature and selected gene which may be involved in the regulation of ligament ossification as the research direction. Then we validated the expression of the selected gene through the mRNA and protein levels of ligament tissue, and the protein levels of plasma. We also verified the effect of the selected gene on human osteosarcoma cell line Saos2 cell by detecting the expression of relevant bone indexes (include ALP, OCN). Finally, combined with the clinical data of AS patients database, we conducted statistical analysis of correlation between the expression level of selected gene and sex, disease duration, disease activity, severity index. Through all the experiment above we carried out a preliminary exploration of the role of selected gene in AS.For AS patients with hip involvement, we collected general information and related clinical evaluation. We evaluated the severity of the hip involvement through BASRI-hip. Then we conducted single factor analysis and multivariate ordinal regression to explore the related risk factors of severe hip involvement in AS patients.MethodsThrough selecting hip joint ligaments of 3 AS patients and 3 normal controls for gene chip screen, we obtained 697 different genes, of which 311 genes were up-regulated,386 genes were down-regulated. Among all the up-regulated genes, we found that SLPI was up-regulated by 2.88 times (p<0.05). Followed by randomly selecting the hip joint ligament tissue and blood samples from AS database, we conducted experiements like RT-PCR, Western-blot, ELISA detection, and the results showed that the expression of SLPI in AS patients, both the blood and joint ligament, was higher than the control group and the difference had statistical significance (p<0.05). Expression levels of osteogenic related indicators (ALP, OCN) were significantly higher in Saos2 cells cultured with SLPI than those of control group. Through the correlation analysis, the plasma SLPI level was correlated with the disease severity condition, BASFI score.We recruited 256 AS patients with different degrees of hip involvement. Through BASRI-hip,107 AS patients were classified as minimal hip disease,73 and 76 as moderate and severe hip involvement, respectively. The single factor analysis and multivariate regression analysis showed that, age of onset, delay in diagnosis, Sacroiliitis score, bilateral hip involvement,severity of the spine involvement were related to the severe hip involvement.ConclusionIn summary, the results of this study showed that by gene chip we could see abnormal expression of multiple genes in ligament tissue of patients with AS, some of them might be involved in inflammation, ossification processes through multiple signal pathways. SLPI was significantly higher expressed in the ligament tissue and plasma in AS patients. Cell experiments also showed that SLPI could increase the expression level of osteogenic related indicators (ALP, OCN) in Saos2 cells. SLPI also correlated with the clinical features (BASFI score index). Preliminary research of SLPI provides a theortical basis for the early diagnosis, treatment of AS.For AS patients, early diagnosis and intervention, have an important significance for the prevention of severe impairement and ankylosis of hip joint.