Li-Yu Sung

Simultaneous induction of autophagy and toll-like receptor signaling pathways by graphene oxide

Graphene oxide (GO) nanosheets have sparked growing interests in biological and medical applications. This study examined how macrophage, the primary immune cell type engaging microbes, responded to GO treatment. We uncovered that incubation of macrophage cell RAW264.7 with GO elicited autophagy in a concentration-dependent manner, as evidenced by the appearance of autophagic vacuoles and activation of autophagic marker proteins. Such GO-induced autophagy was observed in various cell lines and in macrophage treated with GO of different sizes. Strikingly, GO treatment of macrophage provoked the toll-like receptor (TLR) signaling cascades and triggered ensuing cytokine responses. Molecular analysis identified that TLR4 and TLR9 and their downstream signaling mediators MyD88, TRAF6 and NF-κB played pivotal roles in the GO-induced inflammatory responses. By silencing individual genes in the signaling pathway, we further unveiled that the GO-induced autophagy was modulated by TLR4, TLR9 and was dependent on downstream adaptor proteins MyD88, TRIF and TRAF6. Altogether, we demonstrated that GO treatment of cells simultaneously triggers autophagy and TLR4/TLR9-regulated inflammatory responses, and the autophagy was at least partly regulated by the TLRs pathway. This study thus suggests a mechanism by which cells respond to nanomaterials and underscores the importance of future safety evaluation of nanomaterials.

Baculovirus as a new gene delivery vector for stem cell engineering and bone tissue engineering

Baculovirus has emerged as a novel vector for in vitro and in vivo gene delivery due to its low cytotoxicity and non-replication nature in mammalian cells, but the applications of baculovirus in the genetic modification of human mesenchymal stem cells (hMSCs) and tissue engineering are yet to be reported. In this study, we genetically engineered hMSCs with a baculovirus (Bac-CB) expressing bone morphogenetic protein-2 (BMP-2). Bac-CB transduction of hMSCs at a multiplicity of infection of 40 triggered effective differentiation of hMSCs into osteoblasts. Supertransduction at day 6 after initial transduction enhanced the BMP-2 expression and further accelerated the in vitro osteogenesis, as confirmed by alkaline phosphatase assay, Alizarin red staining and reverse transcription-polymerase chain reaction analysis of osteoblastic genes. Implantation of the supertransduced cells at ectopic sites in the nude mice resulted in efficient cell differentiation into osteoblasts at week 2 and induced progressive mineralization and partial bone formation at week 6, as confirmed by hematoxylin and eosin, immunohistochemical and Alizarin red staining. These data collectively demonstrated, for the first time, the potential of baculovirus in hMSCs engineering and implicated its use in bone tissue engineering.

Osteogenic differentiation of adipose-derived stem cells and calvarial defect repair using baculovirus-mediated co-expression of BMP-2 and miR-148b

Repair of large calvarial bony defect remains a challenge for orthopedic surgeons. Since microRNAs (miRNAs) modulate the osteogenesis of osteoprogenitor cells, we aimed to engineer human adipose-derived stem cells (hASCs), a promising cell source for bone engineering, with miRNA-expressing baculovirus vectors. We constructed 4 baculoviruses each expressing 1 human miRNA (miR-26a, miR-29b, miR-148b, miR-196a) and verified that the miRNA-expressing baculovirus vectors augmented hASCs osteogenesis. Among these 4 miRNAs, miR-148b and miR-196a exerted more potent osteoinductive effects than miR-26a and miR-29b. Furthermore, we unveiled that co-transduction of hASCs with miR-148b-expressing and bone morphogenetic protein 2 (BMP-2)-expressing baculovirus vectors enhanced and prolonged BMP-2 expression, and synergistically promoted the in vitro osteogenic differentiation of hASCs. Implantation of the hASCs co-expressing BMP-2/miR-148b into critical-size (4 mm in diameter) calvarial bone defects in nude mice accelerated and potentiated the bone healing and remodeling, filling ≈94% of defect area and ≈89% of defect volume with native calvaria-like flat bone in 12 weeks, as judged from micro computed tomography, histology and immunohistochemical staining. Altogether, this study confirmed the feasibility of combining miRNA and growth factor expression for synergistic stimulation of in vitro osteogenesis and in vivo calvarial bone healing.

The repair of osteochondral defects using baculovirus-mediated gene transfer with de-differentiated chondrocytes in bioreactor culture

Baculovirus has emerged as a promising gene delivery vector. Hereby de-differentiated rabbit chondrocytes were transduced ex vivo with a recombinant baculovirus expressing BMP-2 (Bac-CB), seeded to scaffolds and cultured statically for 1 day (Bac-w0 group) or in a rotating-shaft bioreactor (RSB) for 1 week (Bac-w1 group) or 3 weeks (Bac-w3 group). Mock-transduced constructs were cultured statically for 1 day to serve as the control (Mock-w0 group). We unraveled that Bac-CB transduction and increasing culture time in the RSB yielded more mature cartilaginous constructs in vitro. Eight weeks after implanting into the rabbit osteochondral defects, Mock-w0 constructs failed to repair the lesion while Bac-w0 constructs resulted in augmented, yet incomplete, repair. Bac-w1 constructs yielded neocartilage layers rich in glycosaminoglycans and collagen II, but the integration between the graft and host cartilages was not complete. In contrast, Bac-w3 constructs led to the regeneration of hyaline cartilages as characterized by cartilage-like appearance, improved integration, chondrocytes clustered in lacunae, smooth and homogeneous matrix rich in collagen II and glycosaminoglycans but deficient in collagen I. In conclusion, combining baculovirus-modified de-differentiated chondrocytes and RSB culture creates constructs that repair osteochondral defects, and in vitro culture time dictates the construct maturation and subsequent in vivo repair.

Augmented healing of critical-size calvarial defects by baculovirus-engineered MSCs that persistently express growth factors.

Repair of large calvarial bony defects remains clinically challenging because successful spontaneous calvarial re-ossification rarely occurs. Although bone marrow-derived mesenchymal stem cells (BMSCs) genetically engineered with baculovirus (BV) for transient expression of osteogenic/angiogenic factors hold promise for bone engineering, we hypothesized that calvarial bone healing necessitates prolonged growth factor expression. Therefore, we employed a hybrid BV vector system whereby one BV expressed FLP while the other harbored the BMP2 (or VEGF) cassette flanked by Frt sequences. Transduction of rabbit BMSCs with the FLP/Frt-based BV vector led to FLP-mediated episome formation, which not only extended the BMP2/VEGF expression beyond 28 days but augmented the BMSCs osteogenesis. After allotransplantation into rabbits, X-ray, PET/CT, μCT and histological analyses demonstrated that the sustained BMP2/VEGF expression remarkably ameliorated the angiogenesis and regeneration of critical-size (8 mm) calvarial defects, when compared with the group implanted with BMSCs transiently expressing BMP2/VEGF. The prolonged expression by BMSCs accelerated the bone remodeling and regenerated the bone through the natural intramembranous pathway, filling ≈83% of the area and ≈63% of the volume in 12 weeks. These data implicated the potential of the hybrid BV vector to engineer BMSCs for sustained BMP2/VEGF expression and the repair of critical-size calvarial defects.

Combination of baculovirus-expressed BMP-2 and rotating-shaft bioreactor culture synergistically enhances cartilage formation

Baculovirus is an emerging gene delivery vector, thanks to a number of unique advantages. Herein, we genetically modified the rabbit articular chondrocytes with a recombinant baculovirus (Bac-CB) encoding bone morphogenetic protein-2 (BMP-2), which conferred high level BMP-2 expression and triggered the re-differentiation of dedifferentiated third passage (P3) chondrocytes in the monolayer culture. The transduced and mock-transduced P3 cells were seeded into porous scaffolds and cultured in either the dishes or the rotating-shaft bioreactor (RSB), a novel bioreactor imparting a dynamic, two-phase culture environment. Neither mock-transduced constructs in the RSB culture nor the Bac-CB-transduced constructs in the static culture grew into uniform cartilaginous tissues. Only the Bac-CB-transduced constructs cultured in the RSB for 3 weeks resulted in cartilaginous tissues with hyaline appearance, uniform cell distribution, cartilage-specific gene expression and considerably enhanced cartilage-specific extracellular matrix deposition, as determined by histological staining, reverse transcription-PCR analyses and biochemical assays. This is the first study demonstrating that combination of baculovirus-mediated growth factor expression and RSB culture synergistically enhanced in vitro creation of cartilaginous tissues from dedifferentiated chondrocytes. Since baculovirus transduction is generally considered safe, this approach represents a viable alternative to stimulate the formation of engineered cartilage in a more cost-effective way than the growth factor supplementation.

The use of ASCs engineered to express BMP2 or TGF-β3 within scaffold constructs to promote calvarial bone repair.

Calvarial bone healing is difficult and grafts comprising adipose-derived stem cells (ASCs) and PLGA (poly(lactic-co-glycolic acid)) scaffolds barely heal rabbit calvarial defects. Although calvarial bone forms via intramembranous ossification without cartilage templates, it was suggested that chondrocytes/cartilages promote calvarial healing, thus we hypothesized that inducing ASCs chondrogenesis and endochondral ossification involving cartilage formation can improve calvarial healing. To evaluate this hypothesis and selectively induce osteogenesis/chondrogenesis, rabbit ASCs were engineered to express the potent osteogenic (BMP2) or chondrogenic (TGF-β3) factor, seeded into either apatite-coated PLGA or gelatin sponge scaffolds, and allotransplanted into critical-size calvarial defects. Among the 4 ASCs/scaffold constructs, gelatin constructs elicited in vitro chondrogenesis, in vivo osteogenic metabolism and calvarial healing more effectively than apatite-coated PLGA, regardless of BMP2 or TGF-β3 expression. The BMP2-expressing ASCs/gelatin triggered better bone healing than TGF-β3-expressing ASCs/gelatin, filling ≈ 86% of the defect area and ≈ 61% of the volume at week 12. The healing proceeded via endochondral ossification, instead of intramembranous pathway, as evidenced by the formation of cartilage that underwent osteogenesis and hypertrophy. These data demonstrated ossification pathway switching and significantly augmented calvarial healing by the BMP2-expressing ASCs/gelatin constructs, and underscored the importance of growth factor/scaffold combinations on the healing efficacy and pathway.

Baculovirus as a gene delivery vector for cartilage and bone tissue engineering.

Baculovirus is an effective vector for gene delivery into various mammalian cells, including chondrocytes and mesenchymal stem cells, and has been employed for diverse applications. By gene delivery and expression of the growth factor, recombinant baculovirus has been shown to modulate the differentiation state of the cells and stimulates the production of extracellular matrix and tissue formation, hence repairing the damaged cartilage and bone in vivo. This article reviews the studies pertaining to the applications of baculovirus-mediated gene delivery in cartilage and bone tissue engineering and discusses recent progress, future applications and potential hurdles.

Efficient gene delivery into cell lines and stem cells using baculovirus

Baculovirus is a promising vector for transducing numerous types of mammalian cells. We have developed hybrid baculovirus vectors and protocols for the efficient transduction of a variety of cell lines, primary cells and stem cells, including bone marrow–derived mesenchymal stem cells (BMSCs) and adipose-derived stem cells (ASCs). The hybrid vector enables intracellular minicircle formation and prolongs transgene expression. The advantages of this transduction protocol are that baculovirus supernatant alone needs to be added to cells growing in medium, and transduction occurs after only 4–6 h of incubation at room temperature (25 °C) with gentle shaking. The entire procedure, from virus generation to transduction, can be completed within 4 weeks. Compared with other transduction procedures, this protocol is simple and can confer efficiencies >95% for many cell types. This protocol has potential applications in tissue regeneration, as transduced cells continue to express transgenes after implantation. For example, transduction of rabbit ASCs (rASCs) with growth factor–encoding hybrid baculovirus vectors, as described as an example application in this protocol, enables robust and sustained growth factor expression, stimulates stem cell differentiation and augments tissue regeneration after implantation.

CRISPR-Cas9 for the genome engineering of cyanobacteria and succinate production

Cyanobacteria hold promise as a cell factory for producing biofuels and bio-derived chemicals, but genome engineering of cyanobacteria such as Synechococcus elongatus PCC 7942 poses challenges because of their oligoploidy nature and long-term instability of the introduced gene. CRISPR-Cas9 is a newly developed RNA-guided genome editing system, yet its application for cyanobacteria engineering has yet to be reported. Here we demonstrated that CRISPR-Cas9 system can effectively trigger programmable double strand break (DSB) at the chromosome of PCC 7942 and provoke cell death. With the co-transformation of template plasmid harboring the gene cassette and flanking homology arms, CRISPR-Cas9-mediated DSB enabled precise gene integration, ameliorated the homologous recombination efficiency and allowed the use of lower amount of template DNA and shorter homology arms. The CRISPR-Cas9-induced cell death imposed selective pressure and enhanced the chance of concomitant integration of gene cassettes into all chromosomes of PCC 7942, hence accelerating the process of obtaining homogeneous and stable recombinant strains. We further explored the feasibility of engineering cyanobacteria by CRISPR-Cas9-assisted simultaneous glgc knock-out and gltA/ppc knock-in, which improved the succinate titer to 435.0±35.0μg/L, an ≈11-fold increase when compared with that of the wild-type cells. These data altogether justify the use of CRISPR-Cas9 for genome engineering and manipulation of metabolic pathways in cyanobacteria.