The Research On The Molecular Mechanism Of Idiopathic Orbital Inflammatory Pseudotumor

Idiopathic Orbital Inflammatory Pseudotumor (IOIP) is an inflammatory pseudotumor (IPT) in the orbit of unknown etiology. It is a common eye disease, accounting for 7.1%-12.3%. Fibrosis is the important pathological changes of IOIP. IOIPs are not formally diagnosed until the excised mass is examined by histological and immunohistochemical staining. Due to the lack of well-defined pathogenic mechanism and diagnostic markers, diagnosis and treatment of the disease remain a big challenge.In this study, eleven IOIP tissue samples were obtained from patients at surgical resection, and four normal tissues were collected as controls. Total RNA was extracted and gene expression profiles of both diseased and normal tissues were analyzed with human oligonucleotide microarrays representing 32,050 well-characterized human genes. The expression patterns of selected genes were further confirmed by Real Time RT-PCR. Microarray analysis identified 744 genes differentially expressed in IOIP and non-IOIP samples with at least 21.5-fold changes and P value < 0.005, including 512 down-regulated and 192 up-regulated genes in IOIPs. Principal component analysis (PCA) and hierarchical clustering of microarray data successfully distinguished the IOIP group and the non-IOIP control group. Compared to the non-IOIP, T cell marker (CD₃ and CD₄₅), B cell marker (CD₂₀ and CD₇₉) and a great deal of genes related to T and B cell proliferation and activation (SYK, CD₂₀, LAT, SPIB, LCK, HCST?CD₇₂) were up-regulated in IOIPs. It is suggested that IOIP is a polyclonal disease mainly of T and B cell proliferation and the pathway of PI₃K and NF-?B and inflammation factors were activated in IOIPs.Epstein-Barr virus infection, which causes plenty of lymphocytes infiltration, has also been proposed to be the etiology of IOIPs, however, the relationship between EBV infection and the development of IOIP has not been validated. Hierarchical clustering of microarray data successfully distinguished the IOIP group and the non-IOIP control group. The EBI2 gene, usually activated by EBV, was significantly up-regulated in IOIP group (max=11.7 folds in the microarray data, P=0.00029). EBV-DNA was detected in 9/10 (90%) of the IOIP tissue, 0/4 of the non-IOIP group. It is indicated that EBV infection is the primary reason of IOIP pathogensis.Fibrosis is one of the important pathological changes in IOIPs, the main reason of fibrosis is the accumulation of ECM (Extracellular Matrix). The metabolism of ECM is regulated by MMPs (Matrix Metalloproteinase) and their inhibitors (Tissue Inhibitors of Metalloproteinase). MMPs promote ECM degradation while TIMPs induce the fibrosis by inhibiting MMPs function. TIMP1 is the major factor in TIMPs. In this study, TIMP1 was activated in 5/11 tissue samples in microarray, indicating that TIMP1 is related to the fibrosis in IOIP. TIMP1-shRNA vector was successfully constructed and the gene expression of TIMP1 was suppressed efficiently using RNAi, the protein related to fibrosis was also detected reduced.In conclusion, EBV is a primary etiological factor and the EBI2 gene may serve as a molecular marker for IOIP. These results show that the present clinical diagnosis and therapeutic schedule need modified. Considering EBV is the main pathogenic factor of NPC and about 13.1?29.0% of NPC patients accompany with eye symptoms. As a common disease in eye is associated with EBV, IOIP may be the early stage of the NPC. The research on IOIP may give a clue on the mechanism of carcinogenesis of EBV.