Complexity of determining cause and effect in vivo after antisense gene therapy

Injuries to joint tissues are major clinical problems occurring with significant frequency and resulting in the formation of scar tissue or in some tissues with no healing at all. Such scar tissue has compromised biomechanical integrity, which leads to impaired function, increased risk of reinjury, induction of remodeling in other joint tissues and increases the risk of diseases such as ostheoarthritis. Development of new therapies, such as gene therapy, to enhance repair could have a significant impact on quality of life for patients. The well-characterized rabbit medial collateral ligament injury model was used to transiently modulate the expression of specific molecules during early stages of healing. The small matrix proteoglycan decorin, known to influence matrix assembly and to bind and growth factors, was targeted in vivo using decorin-specific antisense oligodeoxynucleotides and Hemagglutinating Virus of Japan-Liposome method. After 4 weeks of healing, scar tissue was assessed after antisense exposure by reverse transcription polymerase chain reaction, Western Blot analysis, light and transmission electron microscopy, and biomechanically for low and high load behavior. Ligament scar messenger ribonucleic acid and protein levels for decorin decreased and collagen fibril diameter size increased after antisense treatment. Creep and stress at failure improved after antisense treatment indicating a functional improvement in the scar tissue. However, messenger ribonucleic acid levels for multiple genes were affected by the decorin-specific antisense treatment and therefore all of the observed improvements in the scar tissue cannot be directly ascribed to depressing decorin levels.