Zheng Qixin

Molecular tissue engineering: Concepts, status and challenge

Tissue engineering has confronted many difficulties mainly as follows: 1) How to modulate the adherence, proliferation, and oriented differentiation of seed cells, especially that of stemcells. 2) Massive preparation and sustained controllable delivery of tissue inducing factors or plasmid DNA, such as growth factors, angiogenesis stimulators, and so on. 3) Development of “intelligent biomimetic materials” as extracellular matrix with a good superficial and structural compatibility as well as biological activity to stimulate predictable, controllable and desirable responses under defined conditions. Molecular biology is currently one of the most exciting fields of research across life sciences, and the advances in it also bring a bright future for tissue engineering to overcome these difficulties. In recent years, tissue engineering benefits a lot from molecular biology. Only a comprehensive understanding of the involved ingredients of tissue engineering (cells tissue inducing factors, genes, biomaterials) and the subtle relationships between them at molecular level can lead to a successful manipulation of reparative processes and a better biological substitute. Molecular tissue engineering, the offspring of the tissue engineering and molecular biology, has gained an increasing importance in recent years. It offers the promise of not simply replacing tissue, but improving the restoration. The studies presented in this article put forward this new concept for the first time and provide an insight into the basic principles, status and challenges of this emerging technology.

Expression of Transforming Growth Factor β1 in Mesenchymal Stem Cells: Potential Utility in Molecular Tissue Engineering for Osteochondral Repair

SummaryThe feasibility of using gene therapy to treat full-thickness articular cartilage defects was investigated with respect to the transfection and expression of exogenous transforming growth factor (TGF)-β1 genes in bone marrow-derived mesenchymal stem cells (MSCs)in vitro. The full-length rat TGF-β1 cDNA was transfected to MSCs mediated by lipofectamine and then selected with G418, a synthetic neomycin analog. The transient and stable expression of TGF-β1 by MSCs was detected by using immunohistochemical staining. The lipofectamine-mediated gene therapy efficiently transfected MSCsin vitro with the TGF-β1 gene causing a marked up-regulation in TGF-β1 expression as compared with the vector-transfected control groups, and the increased expression persisted for at least 4 weeks after selected with G418. It was suggested that bone marrow-derived MSCs were susceptible toin vitro lipofectamine mediated TGF-β1 gene transfer and that transgene expression persisted for at least 4 weeks. Having successfully combined the existing techniques of tissue engineering with the novel possibilities offered by modern gene transfer technology, an innovative concept, i.e. molecular tissue engineering, are put forward for the first time. As a new branch of tissue engineering, it represents both a new area and an important trend in research. Using this technique, we have a new powerful tool with which: (1) to modify the functional biology of articular tissue repair along defined pathways of growth and differentiation and (2) to affect a better repair of full-thickness articular cartilage defects that occur as a result of injury and osteoarthritis.

Molecular tissue engineering: Applications for modulation of mesenchymal stem cells proliferation by transforming growth factor β1 gene transfer

SummaryThe effect of transforming growth factor β1 (TGF-β1) gene transfection on the proliferation of bone marrow-derived mesenchymal stem cells (MSCs) and the mechanism was investigated to provide basis for accelerating articular cartilage repairing using molecular tissue engineering technology. TGF-β1 gene at different doses was transduced into the rat bone marrow-derived MSCs to examine the effects of TGF-β1 gene transfection on MSCs DNA synthesis, cell cycle kinetics and the expression of proliferating cell nuclear antigen (PCNA). The results showed that 3 μl lipofectaminemediated 1 μg TGF-β1 gene transfection could effectively promote the proliferation of MSCs best; Under this condition (DNA/Lipofectamine= 1μg/3μl) flow cytometry and immunohistochemical analyses revealed a significant increase in the3H incorporation, DNA content in S phase and the expression of PCNA. Transfection of gene encoding TGF-β1 could induce the cells at G0/G1 phase to S1 phase, modulate the replication of DNA through the enhancement of the PCNA expression, increase the content of DNA at S1 phase and promote the proliferation of MSCs. This new molecular tissue engineering approach could be of potential benefit to enhance the repair of damaged articular cartilage, especially those caused by degenerative joint diseases.

Isolation, Culture and Identification of Neural Stem Cells in New-born Rats

SummaryThe cortexes were obtained from new-born rats and dissociated to single cells by triturating. The cells were cultured in neural stem cell (NSC) culture medium (DMEM supplemented with bFGF, EGF and B27) and formed primary neurospheres after 7 days. Single cells dissociated from neurosphere were cultured in 96-well plates and formed single-cell cloning neurosphere 7 days later. The primary and single-cell cloning neurospheres were both positive for the immunofluorescent staining of nestin and were identified as NSC. It was proved that NSC can be expandedin vitro and provide seed cells for neural tissue engineering.

A RGD-containing oligopeptide (K)16GRGDSPC: a novel vector for integrin-mediated targeted gene delivery.

A 23 amino acid, bifunctional integrin-targeted synthetic oligopeptide was evaluated for ex vivo gene delivery to rabbit bone marrow stromal cells (BMSCs). Synthesis of the peptide (K)16GRGDSPC was performed on a solid-phase batch peptide synthesizer. BMSCs were transfected with plasmid DNA coding for luciferase by (K)16GRGDSPC and the transfection efficiency was assayed. The influences of chloroquine and polyethyleneimine on the transfection efficiency were also examined. The target specificity of (K)16GRGDSPC to mediate exogenous gene into BMSCs was analyzed using cell attachment test and gene delivery inhibition test. The results showed that the transfection efficiency of the oligopeptide vector was lower than that of Lipofectamine. But in the presence of endosomal buffer chloroquine or endosomal disrupting agent polyethyleneimine, the transfection efficiency of the vector was greatly enhanced. In addition, RGD-containing peptides inhibited BMSCs’ attachment to the 96-well plates pretreated with fibronectin or vitronectin and significantly decreased the transfection efficiency of the oligopeptide vector. These studies demonstrated that oligopeptide (K)16GRGDSPC was an ideal novel targeted non-viral gene delivery vector, which was easy to be synthesized, high efficient and low cytotoxicity. The vector could effectively deliver exogenous gene into rat BMSCs.

Wild-type Smad3 gene enhances the osteoblastic differentiation of rat bone marrow-derived mesenchymal stem cells in vitro.

SummaryThis study examined the effect of wild-type Smad3 gene on the osteoblastic differentiation of rat bone marrow-derived mesenchymal stem cellsin vitro. Bone marrow-derived mesenchymal stem cells (MSCs) were stably transfected with the complexes of pcDNA3. 0-Myc-Smad3 or pcDNA3. 0-Myc-Smad3ΔC and Lipofectamine reagent. Immunofluorescence staining was performed to evaluate the c-Myc signal in MSCs. The cell proliferation was detected by MTT method. To clarify the osteoblastic characteristics in stably transfected MSCs, alkaline phosphatase (ALP) mRNA and core binding factor α1 (Cbfa1) mRNA were investigated by RT-PCR, and ALP activity and mineralization were examined by p-nitrophenolphosphate method and alizarin red staining respectively. PD98059, a specific inhibitor of the ERK signaling pathway, was used to determine the role of ERK in Smad3-MSCs osteoblastic differentiation. c-Myc signal was detected in Smad3-MSCs and Smad3 ΔC-MSCs. The proliferation of Smad3-MSCs was slower than that of Smad3 ΔC-MSCs or V-MSCs. The relative levels of ALP mRNA and Cbfal mRNA in Smad3-MSCs, as well as ALP activity and mineralization, were markedly higher than those in Smad3 ΔC-MSCs or V-MSCs. Although ALP activity and mineralization were slightly lower in Smad3-MSCs treated with PD98059 than in those without PD98059 treatment, no significant difference was found between them (P>0.05). It is concluded that the wild-type Smad3 gene, which is a crucial component promoting bone formation, can inhibit the proliferation of MSCs and enhance the osteoblastic differentiation of uncommitted MSCs and the maturation of committed MSCs independent of the ERK signaling pathway.

Influence of exogenous TGFβ1 on the expression of Smad2 and Smad3 in rat bone marrow-derived mesenchymal stem cells

SummaryThe expression of Smad2 and Smad3 and the influence of exogenous transforming growth factorβ1 (TGFβ1) on them in rat bone marrow-derived mesenchymal stem cells (MSCs) cultured in vitro were investigated. The effects of different concentrations of TGFβ1 on cell proliferation and ALP activity were detected by MTT and PNPP in, MSCs respectively. The expression of Smad2 and Smad3 and the influence of exogenous TGFβ1 on them were also examined by immunocytochemistry and Western blot assays. The exogenous TGFβ1 induced a dose-dependent decrease in cell proliferation and a dose-dependent increase, in ALP activity, which plateaued at 5 ng/ml. Smad2 and Smad3 proteins were detected only in the cytoplasm in the absence of TGFβ1 and TGFβ1 could stimulate the translocation of them from the cytoplasm to the nucleus. The total amount of Smad2 protein remained unchanged before and after TGFβ1 treatment (P>0.05). The expression levels of Smad3 remained unchanged after 3 h and 6 h treatment (P>0.05), but decreased markedly after 24 h treatment (P<0.05). It was concluded that TGFβ1 is a latent osteoinductive factor involved in osteoblastic differentiation. Both Samd2 and Samd3 mediate TGFβ1 signaling as downstream mediators in MSCs. The biological output of TGFβ1 triggering the osteoblastic differentiation could be entirely determined by Smad3 in MSCs.

Biodegradation of Absorbable Hydroxyapatite/Poly-DL-lactide Composites in Different Environment

To develop a new generation of absorbable fracture fixation devices with enhanced biocompatibility, the biodegradation mechanism and its influence on the cellular response at the tissue/implant interface of hydroxyapatite/poly-DL-lactide (HA/PDLIA) composites were investigated in vitro and in vivo. HA/PDLIA rods were immersed in phosphate-buffered saline, or implanted in muscle and bony tissue for 52 weeks. Scanning electron microscopic and histological studies were done. The degradation rate was the slowest in vitro, slower in muscle tissue and fast in bone. In vitro, the composites degraded heterogeneously and a hollow structure was formed. In bone, the limited clearing capacity leads to the accumulation of oligomeric debris, which contribute totally to the autocatalytic effect. So, the fastest degradation and intense tissue response were seen. In muscle tissue, oligomeric debris migrated into vicinal fibers over a long distance from the original implant cavity and the tissue reactions were, however, quite moderate. For the same size organic/inorganic composite, the environment where it was placed is the major factor in determining its biodegradation process and cellular reaction. In living tissue, factors such as cells, enzymes and mechanical stress have an obvious influence on the biodegradation and biological process at the tissue/implant interface. The biocompatibility of the HA/PDLIA composites is enhanced with the incorporating of the resorbable HA microparticles.

Surface modification of biomimetic PLGA-(ASP-PEG) matrix with RGD-containing peptide: a new non-viral vector for gene transfer and tissue engineering

RGD-containing peptide (K16-GRGDSPC), characterized as non-viral gene vectors, was fabricated to modify the surface of PLGA-[ASP-PEG] matrix, which offered the foundation for gene transfer with porous matrix of gene activated later. Peptide was synthesized and matrix was executed into chips A, B and chip C. Chip C was regarded as control. Chips A and B were reacted with cross-linker. Then chip A was reacted with peptide. MS and HPLC were used to detect the MW and purity of peptide. Sulphur, existing on the surface of biomaterials, was detected by XPS. The purity of un-reacted peptide in residual solution was detected by a spectrophotometer. HPLC shows that the peptide purity was 94%–95%, and MS shows that the MW was 2 741.3307. XPS reveals that the binding energy of sulphur was 164 eV and the ratio of carbon to sulphur (C/S) was 99.746:0.1014 in reacted chip A. The binding energy of sulphur in reacted chip B was 164 eV and 162 eV, C/S was 99.574:0.4255, and there was no sulphur in chip C. Peptide was manufactured and linked to the surface of biomimetic and 3-D matrix, which offered the possibilities for gene transfer and tissue engineering with this new kind of non-viral gene vector.

Treatment of floating knee injury in children.

SummaryThe necessity and superiority of the surgical operation on children with floating knee injury and the fracture union and complications were investigated. Twenty-eight children with floating knee injury were subjected to open reduction and internal fixation or external fixator. The patients were followed up for 18 months to 7 years. The curative effectiveness was scored by Karlstrom criteria. The results showed that no nonunion or deformity was found. The affected limb was 1.2 cm to 1.5 cm longer in 2 cases, 0.8 to 1.2 cm shorter in 3 cases than the contralateral. No severe dysfunction of knee joint occurred. The excellent-good rate was 92.8% and the curative rate 71.4% respectively. So for children whose age is older than 5 years, its a good way to treat the fractures of femur and tibia with open reduction and internal fixation or external fixator. The method can be advantageous for the nursing care, early function recovery, shortening of the hospital stay and avoidance of severe complications.