Abstract
Baculovirus has emerged as a novel gene delivery vector and holds great promise for the genetic modification of mesenchymal stem cells (MSCs). It is known that adult human bone marrow-derived MSCs (hMSCs) express high levels of toll-like receptors (TLRs) 3 and 4. However, it remains unclear regarding how virus infection modulates any TLR pathway in MSCs. In this study, we uncovered that baculovirus transduction upregulated the transcription of TLR3 and many associated genes in hMSCs, as detected by microarray and RT² Profiler™ PCR Array experiments. Flow cytometry and immunofluorescence labeling/confocal microscopy analyses further confirmed the stimulated expression of TLR3 molecules. Moreover, baculovirus transduction of hMSCs led to the activation of signaling molecules downstream of TLR3 pathway, including Toll/IL-1 receptor domain-containing adapter inducing IFN-beta (TRIF), nuclear factor kappaB (NF-kappaB), and IFN-regulatory factor 3 (IRF3). Activation of TLR3 triggered the secretion of interleukin 6 (IL-6) and IL-8, yet small interfering RNAs (siRNA) directed against TLR3 greatly suppressed the IL-6 and IL-8 secretion as a result of baculovirus transduction. Furthermore, baculovirus transduction induced more potent IL-6 and IL-8 secretion in passage 13 MSCs than passage 9 MSCs, which is the result of the different expression levels of TLR3 and NF-kappaB between MSCs of those two passages. This study, for the first time, explored the responses of MSCs to virus transduction and confirmed that baculovirus-transduction of human MSCs elicited TLR3 signaling pathway.