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Employment of fibroblasts for gene transfer: applications for grafting into the central nervous system.

Genetic modification of primary skin fibroblasts offers a new approach to the focal delivery of deficient transmitter-specific enzymes (e.g., TH) or trophic substances (e.g., NGF) to the damaged or diseased CNS. Although fibroblasts are unable to provide anatomical corrections to defective neural connectivity, they can serve as biological pumps for the enzymes and growth factors in vivo. The capability of genetically engineered cells to ameliorate disease phenotypes in animal models of CNS disorders may ultimately results in the restoration of function. At this time, primary skin fibroblasts appear to be a convenient cellular population for the application of gene transfer and intracerebral grafting for the animal model of Parkinson's disease. It is now important for future investigations to provide data concerning the long-term stable expression of the transgene product (e.g., TH) following intracerebral implantation, as well as determining optimal conditions for the survival of primary cells grafted into the nervous system.

Animals↗

Mechanically engineered hydrogel scaffolds for axonal growth and angiogenesis after transplantation in spinal cord injury.

OBJECT: Spinal cord injury (SCI) is a complex pathological entity, the treatment of which requires a multipronged approach. One way to integrate different therapeutic strategies for SCI is to develop implantable scaffolds that can deliver therapies in a synergistic manner. Many investigators have developed implantable "bridges," but an important property of such scaffolds--that is, mechanical compatibility with host tissues--has been neglected. In this study, the authors evaluated the results of implanting a mechanically matched hydrogel-based scaffold to treat SCI. METHODS: A nonbiodegradable hydrogel, poly(2-hydroxyethylmethacrylate) (PHEMA), was engineered using thermally initiated free radical solution polymerization. Two groups of 12 adult Sprague-Dawley rats underwent partial cervical hemisection injury followed by implantation of either PHEMA or PHEMA soaked in 1 microg of brain-derived neurotrophic factor (BDNF). Four rats from each group were killed 1, 2, or 4 weeks after induction of the injury. Immunofluorescence staining was performed to determine the presence of scarring, cellular inflammatory responses, gliosis, angiogenesis, and axonal growth in and around the implanted scaffolds. CONCLUSIONS: The implanted PHEMA with 85% water content had a compressive modulus of 3 to 4 kPa, which matched the spinal cord. Implanted PHEMA elicited modest cellular inflammatory responses that disappeared by 4 weeks and minimal scarring was noted around the matrix. Considerable angiogenesis was observed in PHEMA, and PHEMA soaked in BDNF promoted axonal penetration into the gel. The authors conclude that mechanically engineered PHEMA is well accepted by host tissues and might be used as a platform for sustained drug delivery to promote axonal growth and functional recovery after SCI.

Animals↗

Bone tissue engineering by gene delivery.

Recombinant human bone morphogenetic protein-2 and -7 were recently granted United States Food and Drug Administration approval for select clinical applications in bone repair. While significant progress has been made in the delivery of recombinant osteogenic factor to promote bone healing, the short half-life and instability of the protein requires the delivery of milligram quantities of factor or multiple dosages. The potential of gene therapy for bone regeneration is the delivery of physiological levels of therapeutic protein using natural cellular mechanisms. Experimental investigations have demonstrated this approach uses lower dosages of factor to yield bone healing equivalent to that achieved via the administration of recombinant factor or use of bone grafts. The current states of gene delivery for bone tissue engineering applications and challenges to be met are presented in this review. Over the past couple of years, studies have continued to examine the delivery of the osteogenic factor bone morphogenetic protein using gene therapies. The importance of angiogenesis to bone formation has prompted the development of vascular endothelial growth factor gene expression systems for bone regeneration. Viral vectors, in combination with allograft bone, have been investigated to improve existing surgical care. Newly constructed vectors with reduced immunogenicity and regulated gene expression systems provide a greater degree of control over the timing and level of gene expression. Several advances have allowed bone tissue engineering by gene delivery to advance beyond serving as a potential treatment for isolated bone defects and fractures to a gene therapy approach for the treatment of genetic based bone diseases, such as osteogenesis imperfecta.

Animals↗

Co-culture of osteoblasts and chondrocytes modulates cellular differentiation in vitro.

Biological integration of cartilage grafts with subchondral bone remains a significant clinical challenge. We hypothesize that interaction between osteoblasts and chondrocytes is important in regenerating the osteochondral interface on tissue-engineered osteochondral grafts. We describe here a sequential co-culturing model which permits cell-cell contact and paracrine interaction between osteoblast and chondrocytes in 3-D culture. This model was used to determine the effects of co-culture on the phenotypic maintenance of osteoblasts and chondrocytes. It was found that while chondrocytes synthesized a type II collagen and glycosaminoglycan (GAG) matrix, GAG deposition was significantly lower in co-culture. Alkaline phosphatase activity was maintained in osteoblasts, but cell-mediated mineralization in co-culture was markedly lower compared to osteoblast controls. These results collectively suggest that interactions between osteoblasts and chondrocytes modulate cell phenotypes, and the importance of these interactions on osteochondral interface regeneration will be explored in future studies.

Animals↗

Interaction of aggregated native and mutant IgE receptors with the cellular skeleton.

When aggregated, cell surface proteins become resistant to solubilization by detergents, presumably because of aggregation-induced or -stabilized interactions between the membrane protein and the cytoskeleton or plasma membrane skeleton. We genetically engineered variants of the tetrameric high-affinity receptor for IgE (Fc epsilon RI) to identify a site on its alpha, beta, or gamma chains that mediates such putative interactions. Using flow cytofluorometry, we studied rat basophilic leukemia cells, transiently transfected COS cells, and stably transfected P815 cells bearing wild-type and mutated receptors. We observed that (i) solubilization was markedly dependent on the degree of aggregation, the extent varying somewhat with the cell type and, particularly at lower levels of aggregation, with the time after addition of detergent; (ii) truncation of no single cytoplasmic domain of the alpha, beta, or gamma chains ablated the insolubilization effect; and (iii) incomplete receptors were also efficiently insolubilized by aggregation. Thus receptors consisting only of alpha and gamma chains, a "receptor" consisting of only the ectodomain of the alpha chain attached to the plasma membrane by a glycosyl-phosphatidyl inositol anchor, and "receptors" consisting only of minimally modified gamma chains were resistant to solubilization after aggregation. We conclude that no unique subunit or domain of Fc epsilon RI mediates the insolubilization phenomenon. Our results support a model in which the bridging of membrane proteins leads to their becoming nonspecifically enmeshed in a network of membrane skeletal proteins on either the outside and/or the inside of the membrane so that dissolution of the lipid bilayer becomes irrelevant.

Animals↗

Molecularly engineered PEG hydrogels: a novel model system for proteolytically mediated cell migration.

Model systems mimicking the extracellular matrix (ECM) have greatly helped in quantifying cell migration in three dimensions and elucidated the molecular determinants of cellular motility in morphogenesis, regeneration, and disease progression. Here we tested the suitability of proteolytically degradable synthetic poly(ethylene glycol) (PEG)-based hydrogels as an ECM model system for cell migration research and compared this designer matrix with the two well-established ECM mimetics fibrin and collagen. Three-dimensional migration of dermal fibroblasts was quantified by time-lapse microscopy and automated single-cell tracking. A broadband matrix metalloproteinase (MMP) inhibitor and tumor necrosis factor-alpha, a potent MMP-inducer in fibroblasts, were used to alter MMP regulation. We demonstrate a high sensitivity of migration in synthetic networks to both MMP modulators: inhibition led to an almost complete suppression of migration in PEG hydrogels, whereas MMP upregulation increased the fraction of migrating cells significantly. Conversely, migration in collagen and fibrin proved to be less sensitive to the above MMP modulators, as their fibrillar architecture allowed for MMP-independent migration through preexisting pores. The possibility of molecularly recapitulating key functions of the natural extracellular microenvironment and the improved protease sensitivity makes PEG hydrogels an interesting model system that allows correlation between protease activity and cell migration.

Biocompatible Materials↗

[A study of injectable autologous tissue engineering cartilage].

OBJECTIVE: To study the regeneration of injectable autologous cartilage in New Zealand rabbits model. METHODS: Chondrocytes were harvested from auricle of New Zealand rabbits. The cells were mixed with sodium alginate (SA) and temperature dependent synthetic hydrogel (TDSH) to generate final cellular density of 50 x 10(9)/L, and then the chondrocytes-SA and chondrocytes-TDSH composites were injected into the dorsal subcutaneous tissue of New Zealand rabbits with form of autologous cells grafts respectively. The specimen and histology were observed in the process of cartilage fabrication in 4, 8, 12 weeks. RESULTS: Four weeks after injection, the hard knobbles were formed subcutaneously. Eight and twelve weeks after injection, the knobbles was much harder and showed the appearance of cartilage. In histological analysis, the immature cartilage can be observed after 4 weeks. In the eight and twelve weeks, the mature cartilage was formed and showed strong GAG positive expressed by safranine-O. CONCLUSIONS: Neocartilage could be regenerated through injection of alginate and synthetic hydrogel mixed with chondrocytes. Using tissue-engineering methods, Injectable cartilage may have great potential of clinical use in the future.

Animals↗

Microdiesel: Escherichia coli engineered for fuel production.

Biodiesel is an alternative energy source and a substitute for petroleum-based diesel fuel. It is produced from renewable biomass by transesterification of triacylglycerols from plant oils, yielding monoalkyl esters of long-chain fatty acids with short-chain alcohols such as fatty acid methyl esters and fatty acid ethyl esters (FAEEs). Despite numerous environmental benefits, a broader use of biodiesel is hampered by the extensive acreage required for sufficient production of oilseed crops. Therefore, processes are urgently needed to enable biodiesel production from more readily available bulk plant materials like sugars or cellulose. Toward this goal, the authors established biosynthesis of biodiesel-adequate FAEEs, referred to as Microdiesel, in metabolically engineered Escherichia coli. This was achieved by heterologous expression in E. coli of the Zymomonas mobilis pyruvate decarboxylase and alcohol dehydrogenase and the unspecific acyltransferase from Acinetobacter baylyi strain ADP1. By this approach, ethanol formation was combined with subsequent esterification of the ethanol with the acyl moieties of coenzyme A thioesters of fatty acids if the cells were cultivated under aerobic conditions in the presence of glucose and oleic acid. Ethyl oleate was the major constituent of these FAEEs, with minor amounts of ethyl palmitate and ethyl palmitoleate. FAEE concentrations of 1.28 g l(-1) and a FAEE content of the cells of 26 % of the cellular dry mass were achieved by fed-batch fermentation using renewable carbon sources. This novel approach might pave the way for industrial production of biodiesel equivalents from renewable resources by employing engineered micro-organisms, enabling a broader use of biodiesel-like fuels in the future.

Alcohols↗

Engineering mammalian cell factories for improved recombinant monoclonal antibody production: lessons from nature?

In this review we consider how cell specific recombinant monoclonal antibody (Mab) production by engineered mammalian cells can be improved. Whilst it is generally recognized that Mab production is limited post-transcriptionally at folding and assembly reactions, genetic engineering strategies based on overexpression of individual chaperones or foldases in mammalian cells have not reliably increased cell specific Mab production. Given that recent studies have established that chaperones and foldases themselves exist in a large multiprotein complex, which may coordinate the sequential processing of Mabs, we propose that global expansion of all components of the secretory pathway will likely be necessary to generically improve recombinant Mab production by mammalian cells. In this context, what can be learnt from nature? Important recent studies have delineated some of the main cellular pathways involved in the differentiation of B-cells into nature's own high level Mab producers, plasma cells. This is achieved by a dramatic re-programming of cellular function where the coordinated expansion of metabolic and secretory machinery precedes Ig production, then is maintained by induction of a key intracellular signaling pathway, the unfolded protein response (UPR). Here we review genetic engineering strategies to increase cell specific production rate and discuss whether manipulation of intracellular signaling systems such as the UPR will provide a novel means to engineer mammalian cells for high level recombinant Mab production.

Animals↗

Cellular senescence, epigenetic switches and c-Myc.

In response to hyperproliferative signaling elicited by transforming oncogenes some normal human cells can enter replicative senescence as a tumor defense mechanism. We recently found that human fibroblasts or endothelial cells with genetically-engineered reduction of proto-oncogene c-Myc expression switched with an increased frequency to a senescent state by a telomere-independent mechanism involving the polycomb group repressor Bmi-1 and the cyclin-dependent kinase inhibitor p16(INK4a). The same regulatory circuit was triggered upon exposure to mild oxidative stress. These findings point to the existence of a mechanism for monitoring hypoproliferative signaling, whose function may be to limit the proliferation and accretion of physiologically compromised cells. This mechanism may be another example of antagonistic pleiotropy leading to organismal aging.

Cell Cycle↗

Development of the human umbilical vein scaffold for cardiovascular tissue engineering applications.

Biologic function and the mechanical performance of vascular grafting materials are important predictors of graft patency. As such, "functional" materials that improve biologic integration and function have become increasingly sought after. An important alternative to synthetic materials is the use of biomaterials derived from ex vivo tissues that retain significant biologic and mechanical function. Unfortunately, inconsistent mechanical properties that result from tedious, time consuming, manual dissection methods have reduced the potential usefulness of many of these materials. We describe the preparation of the human umbilical vein (HUV) for use as an acellular, three-dimensional, vascular scaffold using a novel, automated dissection methodology. The goal of this investigation was to determine the effectiveness of the autodissection methodology to yield an ex vivo biomaterial with improved uniformity and reduced variance. Mechanical properties, including burst pressure, compliance, uniaxial tension testing, and suture holding capacity, were assessed to determine the suitability of the HUV scaffold for vascular tissue engineering applications. The automated methodology results in a tubular scaffold with significantly reduced sample to sample variation, requiring significantly less time to excise the vein from the umbilical cord than manual dissection methods. Short-term analysis of the interactions between primary human vascular smooth muscle cells and fibroblasts HUV scaffold have shown an excellent potential for cellular integration by native cellular remodeling processes. Our work has shown that the HUV scaffold is mechanically sound, uniform, and maintains its biphasic stress-strain relationship throughout tissue processing. By maintaining the mechanical properties of the native blood vessels, in concert with promising cellular interactions, the HUV scaffold may lead to improved grafts for vascular reconstructive surgeries.

Humans↗

Controlling messenger RNA stability in bacteria: strategies for engineering gene expression.

Recent advances in the understanding of prokaryotic gene expression have led scientists to look beyond traditional promoter control for new methods of regulating gene expression. A promising, new technique centers on controlling the stability of messenger RNA. To exploit the potential of mRNA stability for gene expression control, it is important to understand the mechanisms of prokaryotic mRNA decay as well as the cellular factors that can be used to enhance bacterial gene expression through mRNA stabilization. Factors involved in controlling prokaryotic mRNA stability such as nucleases, secondary structures, translation influences, and transcription effects are discussed and analyzed within the context of three prevailing mRNA decay theories. Several strategies for manipulating mRNA stability in genetically-engineered cells are developed from these discussions and presented as a future direction in gene expression control. In the near future, it should be possible to use these strategies to control mRNA stability in such applications as pharmaceutical protein production and metabolic pathway design.

Bacteria↗

The independent role of cyclic flexure in the early in vitro development of an engineered heart valve tissue.

Tissue engineered heart valves (TEHV) are being investigated as an alternative to current non-viable prosthetic valves and valved conduits. Studies suggest that pulse duplicator bioreactors can stimulate TEHV development. In the current study, a model system was used to determine if cyclic flexure, a major mode of heart valve deformation, has independent effects on TEHV cell and extracellular matrix (ECM) development. Ovine vascular smooth muscle cells (SMC) were seeded for 30 h onto strips of non-woven 50:50 polyglycolic acid (PGA) and poly-L-lactic acid (PLLA) scaffold. After 4 days of incubation, SMC-seeded and unseeded scaffolds were either maintained under static conditions (static group), or subjected to unidirectional cyclic three-point flexure at a physiological frequency and amplitude in a bioreactor (flex group) for 3 weeks. After seeding or incubation, the effective stiffness (E) was measured, with SMC-seeded scaffolds further characterized by DNA, collagen, sulfated glycosaminoglycan (S-GAG), and elastin content, as well as by histology. The seeding period was over 90% efficient, with a significant accumulation of S-GAG, no significant change in E, and no collagen detected. Following 3 weeks of incubation, unseeded scaffolds exhibited no significant change in E in the flex or static groups. In contrast, E of SMC-seeded scaffolds increased 429% in the flex group (p<0.01) and 351% in the static group (p<0.01), with a trend of increased E, a 63% increase in collagen (p<0.05), increased vimentin expression, and a more homogenous transmural cell distribution in the flex versus static group. Moreover, a positive linear relationship (r2=0.996) was found between the mean E and mean collagen concentration. These results show that cyclic flexure can have independent effects on TEHV cell and ECM development, and may be useful in predicting the mechanical properties of TEHV constructed using novel scaffold materials.

Animals↗

The effect of collagen-targeting platelet-derived growth factor on cellularization and vascularization of collagen scaffolds.

Platelet-derived growth factor BB (PDGF-BB) was an important inductive factor during wound healing, but the lack of efficient delivery system limited its clinical application. Here, a peptide of seven amino acids was firstly utilized to engineer PDGF-BB to construct a collagen-targeting system. This peptide functioned as collagen-binding domain (CBD) to specially target the PDGF-BB to the collagen and restrict its diffusion. In our study, in vitro activity assay showed that the CBD-fused PDGF (CBD-PDGF) and native PDGF (NAT-PDGF) possessed similar activity to stimulate the human fibroblast proliferation. As expected, this peptide promoted the binding of PDGF to collagen scaffolds, and CBD-PDGF caused more cells to proliferate on the collagen gel than NAT-PDGF when the same amounts of PDGF were added. In the in vivo experiment, CBD-PDGF-loaded collagen scaffolds were uniformly cellularized and vascularized compared to that of NAT-PDGF-loaded scaffolds. Our study demonstrated that the CBD targeted PDGF to the collagen scaffold to exert its functions, and it suggested this could be an effective system for targeting tissue regeneration and wound repair.

Animals↗

Directions in cardiovascular tissue engineering.

The generation of tissue replacements or supplements for diseased tissue within the cardiovascular system has been the target of recent tissue engineering efforts. While clinically applicable methodologies remain to be achieved, important foundational experimentation has been performed in recent years to begin the move toward engineered tissue replacement therapy. Inadequacies of current valve, vessel, and other heart prostheses are reviewed briefly, followed by the discussion of selected progress in the supplementation or replacement of each cardiovascular component with tissue constructs. Topics addressed include the endothelialization of bio-prosthetic valves and synthetic vascular grafts, the generation of tissue valve leaflets and vascular conduits, the genetic manipulation of endothelial cells with implications for graft endothelialization, and cardiomyoplasty achieved through cellular and genetic means.

Animals↗

Olfactory ensheathing cells: characteristics, genetic engineering, and therapeutic potential.

Injured neurons in the mammalian central nervous system (CNS) do not normally regenerate their axons after injury. Neurotrauma to the CNS usually results in axonal damage and subsequent loss of communication between neuronal networks, causing long-term functional deficits. For CNS regeneration, repair strategies need to be developed that promote regrowth of lesioned axon projections and restoration of neuronal connectivity. After spinal cord injury (SCI), cystic cavitations are often found, particularly in the later stages, due to the loss of neural tissue at the original impact site. Ultimately, for the promotion of axonal regrowth in these situations, some form of transplantation will be required to provide lesioned axons with a supportive substrate along which they can extend. Here, we review the use of olfactory ensheathing cells: their location and role in the olfactory system, their use as cellular transplants in SCI paradigms, alone or in combination with gene therapy, and the unique properties of these cells that may give them a potential advantage over other cellular transplants.

Animals↗

Diverse roles of K(ATP) channels learned from Kir6.2 genetically engineered mice.

The regulation of insulin secretion from pancreatic beta-cells depends critically on the activities of their plasma membrane ion channels. ATP-sensitive K+ channels (K(ATP) channels) are present in many cells and regulate a variety of cellular functions by coupling cell metabolism with membrane potential. The activity of the K(ATP) channels in pancreatic beta-cells is regulated by changes in the ATP and ADP concentrations (ATP/ADP ratio) caused by glucose metabolism. Thus, the K(ATP) channels are the ATP and ADP sensors in the regulation of glucose-induced insulin secretion. K(ATP) channels are also the target of sulfonylureas, which are widely used in the treatment of type 2 diabetes. Molecular cloning of the two subunits of the pancreatic beta-cell K(ATP) channel, Kir6.2 (an inward rectifier K+ channel member) and SUR1 (a receptor for sulfonylureas), has provided great insight into its structure and function. Kir6.2 subunits form the K+ ion-permeable pore and primarily confer inhibition of the channels by ATP, while SUR1 subunits confer activation of the channels by MgADP and K+ channel openers, such as diazoxide, as well as inhibition by sulfonylureas. The SUR1 subunits also enhance the sensitivity of the channels to ATP. To determine the physiological roles of K(ATP) channels directly, we have generated two kinds of genetically engineered mice: mice expressing a dominant-negative form of Kir6.2 specifically in the pancreatic beta-cells (Kir6.2G132S Tg mice) and mice lacking Kir6.2 (Kir6.2 knockout mice). Studies of these mice elucidated various roles of the K(ATP) channels in endocrine pancreatic function: 1) the K(ATP) channels are the major determinant of the resting membrane potential of pancreatic beta-cells, 2) both glucose- and sulfonylurea-induced membrane depolarization of beta-cells require closure of the K(ATP) channels, 3) both glucose- and sulfonylurea-induced rises in intracellular calcium concentration in beta-cells require closure of the K(ATP) channels, 4) both glucose- and sulfonylurea-induced insulin secretions are mediated principally by the K(ATP) channel-dependent pathway, 5) the K(ATP) channels are important for beta-cell survival and architecture of the islets, 6) the K(ATP) channels are important in the differentiation of islet cells, and 7) the K(ATP) channels in glucose-responsive cells generally participate in coupling glucose sensing with cell excitability. Interestingly, despite the severe defect in glucose-induced insulin secretion, Kir6.2 knockout mice show only a very mild impairment in glucose tolerance. However, when the knockout mice become obese with age, they develop fasting hyperglycemia and glucose intolerance, while neither fasting hyperglycemia nor glucose intolerance is evident in the aged knockout mice without obesity, suggesting that both the genetic defect in glucose-induced insulin secretion and the acquired insulin resistance due to environmental factors are necessary to develop diabetes in Kir6.2 knockout mice. Thus, Kir6.2G132S Tg mice and Kir6.2 knockout mice provide a model of type 2 diabetes and clarify the various roles of K(ATP) channels in endocrine pancreatic function.

Adenosine Triphosphate↗

Influence of growth factors on tissue-engineered pediatric elastic cartilage.

OBJECTIVE: To investigate the influence of growth factors on tissue-engineered pediatric human elastic cartilage relative to potential clinical application. DESIGN: Controlled study. SUBJECTS: Eleven children ranging in age from 5 to 15 years provided auricular elastic cartilage specimens measuring approximately 1 x 1 x 0.2 cm and weighing approximately 100 mg. INTERVENTIONS: Three million chondrocytes were plated into 4 groups of Ham F-12 culture medium: group 1, Ham F-12 culture medium only; no growth factors (control group); group 2, Ham F-12 culture medium and basic fibroblast growth factor; group 3, Ham F-12 culture medium and transforming growth actor beta; and group 4, Ham F-12 culture medium and a combination of both growth factors. At 3 weeks, the cells were harvested and mixed with a copolymer gel of polyethylene glycol and polypropylene oxide (Pluronic F-127). The cell solution was injected subcutaneously into athymic mice. The constructs were harvested at up to 22 weeks of in vivo culture and histologically analyzed. RESULTS: The average number of cells generated in vitro was as follows: group 1, 12 million; group 2, 40 million; group 3, 7 million; and group 4, 35 million. Group 2 in vivo gross specimens were the largest and heaviest. Histologically, the control group and the basic fibroblast growth factor group (groups 1 and 2) exhibited characteristics compatible with normal auricular cartilage; groups 3 and 4 demonstrated cellular disorganization and moderate to severe fibrous tissue infiltration. CONCLUSIONS: Basic fibroblast growth factor demonstrates the greatest positive influence on the in vitro and in vivo growth of engineered pediatric human auricular cartilage. The results suggest that basic fibroblast growth factor has the potential for clinical application in which a goal will be to generate a large volume of tissue-engineered cartilage from a small donor specimen in a short period of time and of a quality similar to native human elastic cartilage.

Adolescent↗