Microarray analysis of gene expression in the subacromial bursa in patients with rotator cuff disease (SS-74)

Abstract

The role of the subacromial bursa in the pathogenesis of rotator cuff disease is controversial. Initial histologic studies suggested that the bursa was a reparative tissue and was important in rotator cuff healing and repair. More recent reports have suggested that the subacromial bursa is an inflammatory membrane that can lead to shoulder pain through stimulation of afferent nerve endings and their products. The potential role of inflammatory cytokines and proteases in this process remain undefined. The present investigations were undertaken to determine the gene expression pattern of cells in the subacromial bursa in patients with rotator cuff disease. Materials and Methods: Following an IRB approved protocol, subacromial bursa biopsies were obtained intraoperatively from patients undergoing shoulder surgery and analyzed for the expression of cytokines and matrix metalloproteases (MMP). Analysis was performed for two primary rotator cuff repairs, two patients with revision rotator cuff repairs, and one patient undergoing surgery for shoulder instability was used as control. RNA was extracted from the samples using the RNeasy Fibrous Tissue Mini Kit and stored at −70°C. Complementary DNA-array hybridization was done using GE Array Q Series Kits for inflammatory cytokine/receptor genes. The arrays were hybridized with Biotin-dUTP labeled cDNA probes. Images of the bursal specimens were obtained by chemiluminescent detection on x-ray films. Data analysis and normalization was accomplished using ScanAlyze and GE ARRAY Analyzer software. Results: Matrix metalloproteinases (MMP-2, MMP-14, MMP-26, MT1-MMP) and tissue inhibitor of metalloproteinase (TIMP-1, TIMP-2, and TIMP-3) displayed increased expression in the subacromial bursa in both primary and revision rotator cuff repairs, though to a greater degree in revision repair samples. Tumor necrosis factor alpha and its receptor (TNFRSF1A) were slightly increased in subacromial bursa specimens with rotator cuff disease. While the receptors for IL-1B (IL-1R1) and IL-6 (IL-6ST) were increased in rotator cuff disease, IL-1B and IL-6 themselves were not increased. Members of the small inducible cytokine subfamily (SCYA2, SCYA5, SCYC2, SCYE1) genes were all increased in patients with rotator cuff disease. While these results represent trends in gene expression relative to controls, statistical significance could not be determined due to the small numbers of specimens. Discussion: While inflammation in the subacromial bursa has been proposed as the mechanism leading to pain in patients with rotator cuff disease, the exact roles of cytokines and other proteins during this inflammatory process are currently unknown. In these initial studies, gene expression as demonstrated by microarray analysis of cytokines (TNF, IL-1, SCY) and metalloproteases (MMP-2, TIMP) were found to be increased in patients with rotator cuff disease as compared to control. These data provide initial indication that cytokines and metalloproteases play an important role in the pathology of subacromial bursitis. Further investigation will emphasize the isolation and characterization of these genes.