Targeted knockout of TNF-α by injection of lentivirus-mediated siRNA into the subacromial bursa for the treatment of subacromial bursitis in rats

Subacromial bursitis (SAB) is the major source of pain in rotator cuff disease. Although multiple investigations have provided support for the role of inflammatory cytokines in SAB, few have focussed on the use these cytokines in the treatment of SAB. The aim of the present study was to observe the therapeutic efficacy of lentivirus-mediated RNA interference (RNAi) on carrageenan-induced SAB by injecting lentivirus-tumor necrosis factor (TNF)-alpha-RNAi expressing TNF-alpha small interfering (si) RNA. Using screened siRNA segments, an siRNA was designed. A lentivirus vector expressing siRNA was established and packed as lentivirus particles. A lentivirus that expressed the negative sequence was used as a lentivirus-negative control (NC). The carrageenan-induced SAB model was established in 32 male Sprague-Dawley rats. The modeled rats were randomly assigned to four groups: Lentivirus-RNAi treatment group, lentivirus-NC group, SAB group and phosphate-buffered saline (PBS) blank control group. The lentivirus was injected (1x10(7) transducing units) into the subacromial bursa of the rats in the lentivirus-RNAi group and lentivirus-NC group, whereas 100 mu l PBS was injected at the same site in the SAB group and the PBS blank control group. At 5 weeks following injection, the animals were sacrificed and venous blood was obtained. The effect of TNF-alpha interference and the expression of inflammatory cytokines were determined by reverse transcription-quantitative polymerase chain reaction, western blotting, hematoxylin and eosin staining, Van Gieson's staining and immunofluorescence. The expression of TNF-alpha was decreased in the lentivirus-TNF-alpha-RNAi group compared with that in the SAB group. Morphological observations revealed that the number of inflammatory cells were reduced and damage to tendon fibers was attenuated in this group, suggesting that the downregulation of the protein expression levels of TNF-alpha-associated nuclear factor-kappa B, matrix metalloproteinase (MMP) 1, MMP9, cyclooxygenase (COX)-1 and COX-2 may exert a therapeutic effect on inflammation of the SAB caused by rheumatoid arthritis. It was also found that the expression of stromal cell-derived growth factor-1 was down-regulated in the lentivirus-TNF-alpha-RNAi group. Therefore, the present study demonstrated that lentivirus-mediated TNF-alpha RNAi effectively inhibited the inflammatory response in SAB, and that injection of a lentivirus vector into the affected region is an effective way of achieving RNAi in vivo.