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The application of inflammation-regulated therapeutic gene expression in arthritis conditions increases the efficiency of gene therapy by self-limiting the transgene. Incidentally, constitutive overexpression of transgenes typically leads to detrimental effects in disease conditions; therefore, regulation of expression is warranted. We undertook this study to validate a new gene therapy approach using a cell culture-based inflammation model and a novel self-limiting, inflammation-responsive promoter construct.
We designed a self-limiting promoter construct that expresses an antiinflammatory gene (interleukin-4 [IL-4]) only in the presence of inflammation. Our construct featured a truncated promoter sequence of cyclooxygenase 2 (COX-2) upstream of the IL-4 gene. We triggered inflammation in vitro in articular chondrocytes by applying the inflammatory cytokines IL-1beta and tumor necrosis factor alpha (TNFalpha) together exogenously, and we studied the extent of IL-4 expression and its effect on the inflammatory cascade.
Using articular chondrocytes, we showed that our COX-2 promoter construct expressed IL-4 only in the presence of IL-1beta and TNFalpha. IL-4 expressed in the presence of IL-1beta and TNFalpha down-regulated a series of inflammation mediators, prostaglandins, and matrix metalloproteinases.
The use of this construct for the expression of antiinflammatory genes allows production of a therapeutic gene product that is controlled by the severity of the disease. The effectiveness of this promoter construct for combating inflammation makes it a suitable candidate for the development of a new local gene therapy strategy for the treatment of osteoarthritis, in which IL-1beta and TNFalpha trigger a signal cascade that elevates COX-2 levels.