Mathematical modelling of tissue-engineered angiogenesis

We present a mathematical model for the vascularisation of a porous scaffold following implantation in vivo. The model is given as a set of coupled non-linear ordinary differential equations (ODEs) which describe the evolution in time of the amounts of the different tissue constituents inside the scaffold. Bifurcation analyses reveal how the extent of scaffold vascularisation changes as a function of the parameter values. For example, it is shown how the loss of seeded cells arising from slow infiltration of vascular tissue can be overcome using a prevascularisation strategy consisting of seeding the scaffold with vascular cells. Using certain assumptions it is shown how the system can be simplified to one which is partially tractable and for which some analysis is given. Limited comparison is also given of the model solutions with experimental data from the chick chorioallantoic membrane (CAM) assay.     

In vitro analysis of integrin expression in stem cells from bone marrow and cord blood during chondrogenic differentiation

The use of adult mesenchymal stem cells (MSC) in cartilage tissue engineering has been implemented in the field of regenerative medicine and offers new perspectives in the generation of transplants for reconstructive surgery. The extracellular matrix (ECM) plays a key role in modulating function and phenotype of the embedded cells and contains the integrins as adhesion receptors mediating cell-cell and cell-matrix interactions. In our study, characteristic changes in integrin expression during the course of chondrogenic differentiation of MSC from bone marrow and foetal cord blood were compared. MSC were isolated from bone marrow biopsies and cord blood. During cell culture, chondrogenic differentiation was performed. The expression of integrins and their signalling components were analysed with microarray and immunohistochemistry in freshly isolated MSC and after chondrogenic differentiation. The fibronectin-receptor (integrin a5b1) was expressed by undifferentiated MSC, expression rose during chondrogenic differentiation in both types of MSC. The components of the vitronectin/osteopontin-receptors (avb5) were not expressed by freshly isolated MSC, expression rose with ongoing differentiation. Receptors for collagens (a1b1, a2b1, a3b1) were weakly expressed by undifferentiated MSC and were activated during differentiation. As intracellular signalling components integrin linked kinase (ILK) and CD47 showed increasing expression with ongoing differentiation. For all integrins, no significant differences could be found in the two types of MSC. Integrin-mediated signalling seems to play an important role in the generation and maintenance of the chondrocytic phenotype during chondrogenic differentiation. Especially the receptors for fibronectin, vitronectin, osteopontin and collagens might be involved in the generation of the ECM. Intracellularly, their signals might be transduced by ILK and CD47. To fully harness the potential of these cells, future studies should be directed to ascertain their cellular and molecular characteristics for optimal identification, isolation and expansion.     

Lincomycin,rational selection of high producing strain and improved fermentation by amino acids supplementation

Based on the report that the introduction of the biosynthetic precursor of lincomycin, propylproline, could increase the production of lincomycin (Bruce et al. in US Patent 3,753,859, 1973), a mutant strain pro10–20, with resistance of feedback suppression of proline (an analog of propylproline) was thus selected and lincomycin production increased by 10%. The addition of three amino acids (l-proline, l-tyrosine, l-alanine) which are the precursors of propylproline to the fermentation medium was found to enhance the accumulation of l-dopa through different pathways and was favorable to lincomycin biosynthesis. The production of lincomycin was increased by 23, 10, 13%, respectively, with the addition of 0.05 g L⁻¹ l-proline at 60 h, 0.005 g L⁻¹ l-tyrosine and 0.1 g L⁻¹ l-alanine directly in the medium.     

微生物脂肪酶蛋白质工程*

微生物脂肪酶催化的化学反应具有严格的立体选择性、位点选择性等专一性,催化活性高而副反应少,催化反应不需要辅助因子等特点,因此广泛应用于工农业生产中的诸多领域。利用蛋白质工程技术,提高微生物脂肪酶的特异性、活性和稳定性,对提高微生物脂肪酶制剂产品的市场竞争能力,扩大微生物脂肪酶的应用领域,具有重要的意义。综述了蛋白质工程技术在微生物脂肪酶改性方面的应用现状、存在问题及前景。     

重组基因工程菌在不对称还原羰基化合物中的应用

手性醇是药物合成的重要手性砌块,利用生物催化剂不对称还原羰基化合物是手性醇制备的重要方法。介绍了生物催化还原羰基化合物的反应原理及特点,综述了重组基因工程菌的构建及其在不对称还原羰基化合物中的应用情况,展望了今后研究发展的方向。     

Metabolic engineering based on systems biology for chemicals production

Microorganisms have been the main sources for the production of chemicals. Production of chemicals requires the development of low-cost and higher-yield processes. Towards this goal, microbial strains with higher levels of production should be first considered. Metabolic engineering has been used extensively over the past two to three decades to increase production of these chemicals. Advances in omics technology and computational simulation are allowing us to perform metabolic engineering at the systems level. By combining the results of omics analyses and computational simulation, systems biology allows us to understand cellular physiology and characteristics, which can subsequently be used for designing strategies. Here, we review the current status of metabolic engineering based on systems biology for chemical production and discuss future prospects.     

A novel method for the generation of reaggregated organotypic cultures that permits juxtaposition of defined cell populations

Cellular reaggregation methods have been used to generate in vitro organotypic cultures as a means to elucidate the cellular and molecular requirements of organogenesis. However, reproducibility from experiment to experiment has remained problematic and furthermore, current protocols do not support reaggregation of many important tissues. Here, using the thymus as a model organ, we present a novel reaggregation method termed “compaction reaggregation” that offers improved kinetics of reaggregation and greatly improved efficiency. Using compaction reaggregation we have been able to reaggregate the aorta‐gonad‐ mesonephros region, a tissue that previously proved refractory to commonly used reaggregation methods, enabling the study of hematopoietic stem cell emergence and expansion. Additionally, compaction reaggregation permits the juxtaposition of different cell layers within the aggregated structure thus providing the means to study inductive interactions between different cell populations in vitro. genesis 47:346–351, 2009. © 2009 Wiley‐Liss, Inc.     

An alginate hydrogel matrix for the localised delivery of a fibroblast/keratinocyte co-culture

There is significant interest in the development of tissue-engineered skin analogues, which replace both the dermal and the epidermal layer, without the use of animal or human derived products such as collagen or de-epidermalised dermis. In this study, we proposed that alginate hydrogel could be used to encapsulate fibroblasts and that keratinocytes could be cultured on the surface to form a bilayered structure, which could be used to deliver the co-culture to a wound bed, initially providing wound closure and eventually expediting the healing process. Encapsulation of fibroblasts in 2 and 5% w/v alginate hydrogel effectively inhibited their proliferation, whilst maintaining cell viability allowing keratinocytes to grow uninhibited by fibroblast overgrowth to produce a stratified epidermal layer. It was shown that the alginate degradation process was not influenced by the presence of fibroblasts within the hydrogel and that lowering the alginate concentration from 5 to 2% w/v increased the rate of degradation. Fibroblasts released from the scaffold were able to secrete extracellular matrix (ECM) and thus should replace the degrading scaffold with normal ECM following application to the wound site. These findings demonstrate that alginate hydrogel may be an effective delivery vehicle and scaffold for the healing of full-thickness skin wounds.