The effect of the controlled release of nerve growth factor from collagen gel on the efficiency of neural cell culture

Calming the Nerves via the Immune Instructive Physiochemical Properties of Self-Assembling Peptide Hydrogels

Current therapies for the devastating damage caused by traumatic brain injuries (TBI) are limited. This is in part due to poor drug efficacy to modulate neuroinflammation, angiogenesis and/or promoting neuroprotection and is the combined result of challenges in getting drugs across the blood brain barrier, in a targeted approach. The negative impact of the injured extracellular matrix (ECM) has been identified as a factor in restricting post-injury plasticity of residual neurons and is shown to reduce the functional integration of grafted cells. Therefore, new strategies are needed to manipulate the extracellular environment at the subacute phase to enhance brain regeneration. In this review, potential strategies are to be discussed for the treatment of TBI by using self-assembling peptide (SAP) hydrogels, fabricated via the rational design of supramolecular peptide scaffolds, as an artificial ECM which under the appropriate conditions yields a supramolecular hydrogel. Sequence selection of the peptides allows the tuning of these hydrogels' physical and biochemical properties such as charge, hydrophobicity, cell adhesiveness, stiffness, factor presentation, degradation profile and responsiveness to (external) stimuli. This review aims to facilitate the development of more intelligent biomaterials in the future to satisfy the parameters, requirements, and opportunities for the effective treatment of TBI.

Promising application of a novel biomaterial, light chain of silk fibroin combined with NT3, in repairment of rat sciatic nerve defect injury

Autologous nerve transplantation is the gold standard for treating peripheral nerve defects, but it is associated with defects such as insufficient donor and secondary injury. Artificial nerve guidance conduits (NGCs) are now considered promising alternatives for bridging long nerve gaps, although exploring new biomaterials to construct NGCs remains challenging. Silk fibroin (SF) has good biocompatibility and can self-assemble in aqueous solutions¹. However, the lack of proximal neurotrophic factors after nerve injury is a major concern, leading to incomplete nerve regeneration. In this study, NT-3, a neurotrophin that promotes neuronal survival and differentiation, was bound to the light chain of silk fibroin (FIBL) in two ways: one was directly bound to FIBL (FIBL-NT3) and the other was a polypeptides-linker (FIBL-Linker-NT3). The design aimed to take advantage of silk fiber's character of self-assembly of heavy-light chains and test whether a flexible linker with NT3 molecule is easy to be a NT3 dimer, the active form. In vitro studies indicated that FIBL-Linker-NT3 combined with SF membranes promoted axon growth in adult rat dorsal root ganglion (DRG) neurons. Then we tested if FIBL-Linker-NT3 could self-assemble with the SF heavy chain (SFH). DTT (Dithiothreitol) was used to break the disulfide bonds between the SF light and heavy chains, and the light-chain protein was removed via dialysis. SFH was assembled using FIBL-Linker-NT3, as evidenced by the western blotting results that showed a high molecular band corresponding to SFH-FIBL-Linker-NT3. Chitosan scaffolds have been identified to provide a suitable microenvironment, so a chitosan/SF-FIBL-Linker-NT3 conduit was also constructed. Nerve transplantation of this conduit was evaluated in vivo in a rat sciatic nerve defect model. Immunohistochemical assays showed that the chitosan/SF-FIBL-Linker-NT3 group was superior to the chitosan/PBS, SF, PBS + FIBL-Linker-NT3 groups in nerve regeneration. In addition, the chitosan/SF-FIBL-Linker-NT3 conduit-transplanted group exhibited better recovery in terms of neurite length, sciatic functional index value, sensitivity to heat, time on the rotarod, wet weight ratio, cross-sectional area, compound muscle action potential, number of myelin layers, and myelin thickness in the nerve. Taking together, our study identified that FIBL-Linker-NT3 could promote axonal growth and regeneration in vivo and in vitro and is a promising candidate biomaterial for artificial NGCs.

SARS-CoV-2 and tissue damage: current insights and biomaterial-based therapeutic strategies

The effect of SARS-CoV-2 infection on humanity has gained worldwide attention and importance due to the rapid transmission, lack of treatment options and high mortality rate of the virus. While scientists across the world are searching for vaccines/drugs that can control the spread of the virus and/or reduce the risks associated with infection, patients infected with SARS-CoV-2 have been reported to have tissue/organ damage. With most tissues/organs having limited regenerative potential, interventions that prevent further damage or facilitate healing would be helpful. In the past few decades, biomaterials have gained prominence in the field of tissue engineering, in view of their major role in the regenerative process. Here we describe the effect of SARS-CoV-2 on multiple tissues/organs, and provide evidence for the positive role of biomaterials in aiding tissue repair. These findings are further extrapolated to explore their prospects as a therapeutic platform to address the tissue/organ damage that is frequently observed during this viral outbreak. This study suggests that the biomaterial-based approach could be an effective strategy for regenerating tissues/organs damaged by SARS-CoV-2.

Aligned collagen scaffold combination with human spinal cord-derived neural stem cells to improve spinal cord injury repair

Neural stem/progenitor cell (NSPC)-based spinal cord injury (SCI) therapy is expected to bridge the lesion site by transplanting exogenous NSPCs for replacement of lost cells. The transplanted NSPCs produce a microenvironment conducive to neuronal regeneration, and ultimately, functional recovery. Although both human fetal brain- and spinal cord- derived NSPCs (hbNSPCs and hscNSPCs, respectively) have been used for SCI repair, it remains unclear whether hscNSPCs are a more appropriate stem cell source for transplantation than hbNSPCs. Therefore, in this study, we transplanted hbNSPCs or hscNSPCs into rats with complete transection SCI to monitor their differences in SCI treatment. An aligned collagen sponge scaffold (ACSS) was used here for cell retention. Aligned biomaterial scaffolds provide a support platform and favorable morphology for cell growth and differentiation, and guide axial axonal extension. The ACSS fabricated by our group has been previously reported to improve spinal cord repair by promoting neuronal regeneration and remyelination. Compared with the hbNSPC-ACSS, the hscNSPC-ACSS effectively promoted long-term cell survival and neuronal differentiation and improved the SCI microenvironment by reducing inflammation and glial scar formation. Furthermore, the transplanted hscNSPC-ACSS improved recovery of locomotor functions. Therefore, hscNSPCs appear to be a superior cell source to hbNSPCs for SCI cell therapy with greater potential clinical applications.

PC12 Cell Line: Cell Types, Coating of Culture Vessels, Differentiation and Other Culture Conditions

The PC12 cell line is one of the most commonly used in neuroscience research, including studies on neurotoxicity, neuroprotection, neurosecretion, neuroinflammation, and synaptogenesis. Two types of this line are available in the ATCC collection: traditional PC12 cells grown in suspension and well-attached adherent phenotype. PC12 cells grown in suspension tend to aggregate and adhere poorly to non-coated surfaces. Therefore, it is necessary to modify the surface of culture vessels. This paper aims to characterise the use of two distinct variants of PC12 cells as well as describe their differentiation and neuronal outgrowth with diverse NGF concentrations (rat or human origin) on various surfaces. In our study, we evaluated cell morphology, neurite length, density and outgrowth (measured spectrofluorimetrically), and expression of neuronal biomarkers (doublecortin and NeuN). We found that the collagen coating was the most versatile method of surface modification for both cell lines. For adherent cells, the coating was definitely less important, and the poly-d-lysine surface was as good as collagen. We also demonstrated that the concentration of NGF is of great importance for the degree of differentiation of cells. For suspension cells, we achieved the best neuronal characteristics (length and density of neurites) after 14 days of incubation with 100 ng/mL NGF (change every 48 h), while for adherent cells after 3-5 days, after which they began to proliferate. In the PC12 cell line, doublecortin (DCX) expression in the cytoplasm and NeuN in the cell nucleus were found. In turn, in the PC12 Adh line, DCX was not expressed, and NeuN expression was located in the entire cell (both in the nucleus and cytoplasm). Only the traditional PC12 line grown in suspension after differentiation with NGF should be used for neurobiological studies, especially until the role of the NeuN protein, whose expression has also been noted in the cytoplasm of adherent cells, is well understood.

Schwann Cells Enhance Penetration of Regenerated Axons into Three-Dimensional Microchannels

Nerve regeneration after injury requires proper axon alignment to bridge the lesion site and myelination to achieve functional recovery. Transplanted scaffolds with aligned channels, have been shown to induce axon growth to some extent. However, the penetration of axons into the microchannels remain a challenge, influencing the functional recovery of regenerated nerves. We previously demonstrated that the size of microchannels exerts significant impact on Schwann cells (SCs) migration. Here we demonstrate that migration of SCs promotes, significantly, the dorsal root ganglion (DRG) neurons to extend axons into three-dimensional channels and form aligned fascicular-like axon tracts. Moreover, the migrating SCs attach and wrap around the aligned axons of DRG neurons in the microchannels and initiate myelination. The SCs release growth factors that provide chemotactic signals to the regenerating axons, similar to the response achieved with nerve growth factor (NGF), but with the additional capability of promoting myelination, thereby demonstrating the beneficial effects of including SCs over NGF alone in enhancing axon penetration and myelination in three-dimensional microchannels.

Preparation of NGF encapsulated chitosan nanoparticles and its evaluation on neuronal differentiation potentiality of canine mesenchymal stem cells

Sustained and controlled release of neurotrophic factors in target tissue through nanomaterial based delivery system could be a better strategy for nerve tissue regeneration. The present study aims to prepare the nerve growth factor (NGF) encapsulated chitosan nanoparticles (NGF-CNPs) and its evaluation on neuronal differentiation potentiality of canine bone marrow derived mesenchymal stem cells (cBM-MSCs). The NGF-CNPs were prepared by ionotropic gelation method with tripolyphosphate (TPP) as an ionic cross-linking agent. Observations on physiochemical properties displayed the size of nanoparticles as 80-90 nm with positive zeta potential as well as an ionic interaction between NGF and nanoparticle. NGF loading efficiency was found to be 61% while its sustained release was observed by an in vitro release kinetics study. These nanoparticles were found to be cytocompatible to cBM-MSCs when supplemented at a concentration upto 4 mg/ml in culture media. The NGF-CNP supplemented culture media was able to transdifferentiate the preinduced cBM-MSCs into neurons in a better way than unbound NGF supplementation. Further, it was also noticed that NGF-CNPs were able to transdifferentiate cBM-MSCs without any chemical based preinduction. In conclusion, our findings propose that NGF-CNPs are capable of releasing bioactive NGF with the ability to transdifferentiate mesenchymal stem cells into neurons, suggesting its potential future application in nerve tissue regeneration.

Heparin/collagen encapsulating nerve growth factor multilayers coated aligned PLLA nanofibrous scaffolds for nerve tissue engineering

Biomimicing topological structure of natural nerve tissue to direct axon growth and controlling sustained release of moderate neurotrophic factors are extremely propitious to the functional recovery of damaged nervous systems. In this study, the heparin/collagen encapsulating nerve growth factor (NGF) multilayers were coated onto the aligned poly-L-lactide (PLLA) nanofibrous scaffolds via a layer-by-layer (LbL) self-assembly technique to combine biomolecular signals, and physical guidance cues for peripheral nerve regeneration. Scanning electronic microscopy (SEM) revealed that the surface of aligned PLLA nanofibrous scaffolds coated with heparin/collagen multilayers became rougher and appeared some net-like filaments and protuberances in comparison with PLLA nanofibrous scaffolds. The heparin/collagen multilayers did not destroy the alignment of nanofibers. X-ray photoelectron spectroscopy and water contact angles displayed that heparin and collagen were successfully coated onto the aligned PLLA nanofibrous scaffolds and improved its hydrophilicity. Three-dimensional (3 D) confocal microscopy images further demonstrated that collagen, heparin, and NGF were not only coated onto the surface of aligned PLLA nanofibrous scaffolds but also permeated into the inner of scaffolds. Moreover, NGF presented a sustained release for 2 weeks from aligned nanofibrous scaffolds coated with 5.5 bilayers or above and remained good bioactivity. The heparin/collagen encapsulating NGF multilayers coated aligned nanofibrous scaffolds, in particular 5.5 bilayers or above, was more beneficial to Schwann cells (SCs) proliferation and PC12 cells differentiation as well as the SC cytoskeleton and neurite growth along the direction of nanofibrous alignment compared to the aligned PLLA nanofibrous scaffolds. This novel scaffolds combining sustained release of bioactive NGF and aligned nanofibrous topography presented an excellent potential in peripheral nerve regeneration. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1900-1910, 2017.

Effect of controlled release of brain-derived neurotrophic factor and neurotrophin-3 from collagen gel on neural stem cells

This study aimed to examine the effect of controlled release of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) from collagen gel on rat neural stem cells (NSCs). With three groups of collagen gel, BDNF/collagen gel, and NT-3/collagen gel as controls, BDNF and NT-3 were tested in the BDNF-NT-3/collagen gel group at different time points. The enzyme-linked immunosorbent assay results showed that BDNF and NT-3 were steadily released from collagen gels for 10 days. The cell viability test and the bromodeoxyuridine incorporation assay showed that BDNF-NT-3/collagen gel supported the survival and proliferation of NSCs. The results also showed that the length of processes was markedly longer and differentiation percentage from NSCs into neurons was much higher in the BDNF-NT-3/collagen gel group than those in the collagen gel, BDNF/collagen gel, and NT-3/collagen gel groups. These findings suggest that BDNF-NT-3/collagen gel could significantly improve the ability of NSCs proliferation and differentiation.

Fabrication of Nerve Growth Factor Encapsulated Aligned Poly(ε-Caprolactone) Nanofibers and Their Assessment as a Potential Neural Tissue Engineering Scaffold

Peripheral nerve injury is a serious clinical problem to be solved. There has been no breakthrough so far and neural tissue engineering offers a promising approach to promote the regeneration of peripheral neural injuries. In this study, emulsion electrospinning technique was introduced as a flexible and promising technique for the fabrication of random (R) and aligned (A) Poly(ε-caprolactone) (PCL)-Nerve Growth Factor (NGF)&Bovine Serum Albumin (BSA) nanofibrous scaffolds [(R/A)-PCL-NGF&BSA], where NGF and BSA were encapsulated in the core while PCL form the shell. Random and aligned pure PCL, PCL-BSA, and PCL-NGF nanofibers were also produced for comparison. The scaffolds were characterized by Field Emission Scanning Electron Microscopy (FESEM) and water contact angle test. Release study showed that, with the addition of stabilizer BSA, a sustained release of NGF from emulsion electrospun PCL nanofibers was observed over 28 days. [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt; MTS] assay revealed that (R/A)-PCL-NGF and (R/A)-PCL-NGF&BSA scaffolds favored cell growth and showed no cytotoxicity to PC12 cells. Laser scanning confocal microscope images exhibited that the A-PCL-NGF&BSA scaffold increased the length of neurites and directed neurites extension along the fiber axis, indicating that the A-PCL-NGF&BSA scaffold has a potential for guiding nerve tissue growth and promoting nerve regeneration.

Growth and differentiation of neural stem cells in a three-dimensional collagen gel scaffold

Collagen protein is an ideal scaffold material for the transplantation of neural stem cells. In this study, rat neural stem cells were seeded into a three-dimensional collagen gel scaffold, with suspension cultured neural stem cells being used as a control group. Neural stem cells, which were cultured in medium containing epidermal growth factor and basic fibroblast growth factor, actively expanded and formed neurospheres in both culture groups. In serum-free medium conditions, the processes extended from neurospheres in the collagen gel group were much longer than those in the suspension culture group. Immunofluorescence staining showed that neurospheres cultured in collagen gels were stained positive for nestin and differentiated cells were stained positive for the neuronal marker βIII-tubulin, the astrocytic marker glial fibrillary acidic protein and the oligodendrocytic marker 2’,3’-cyclic nucleotide 3’-phosphodiesterase. Compared with neurospheres cultured in suspension, the differentiation potential of neural stem cells cultured in collagen gels increased, with the formation of neurons at an early stage. Our results show that the three-dimensional collagen gel culture system is superior to suspension culture in the proliferation, differentiation and process outgrowth of neural stem cells.

Fabrication of barium- and strontium-doped silica/titania hollow nanoparticles and their synergetic effects on promoting neuronal differentiation by activating ERK and p38 pathways

Pristine, barium-doped, and strontium-doped hollow nanoparticles (p-HNPs, Ba-HNP, and Sr-HNP; HNPs) are prepared by sonication-mediated etching and redeposition (SMER) method and alkali-earth-metal hydroxide solution treatment. The HNPs are investigated to facilitate synergetic neuronal differentiation through alkali-earth-metal doping and in conjunction with nerve growth factor (NGF). PC12 cells are used as model cells for neuronal differentiation. The differentiation efficiency is improved in the presence of the HNPs+NGF, and the neurite length is in the order of Sr-HNP+NGF > Ba-HNP+NGF > p-HNP+NGF > NGF. Silica/titania have increasing effect on both differentiation efficiency and neurite length, and doped barium/strontium influences additional elongation of the average neurite length. Take advantage of hollow structure, NGF is encapsulated into HNPs, and they are further applied for directly inducing differentiation. The maximum differentiation efficiency is 67% in presence of the NGF-encapsulated Sr-HNP, which was 1.3 times higher than previous research. Furthermore, the neurite length is also 2.7 times higher than MnO2 decorated poly(3,4-ethylenedioxythiophene) nanoellipsoids. Ba- and Sr-HNP may offer a possibility for novel application of metal-hybrid nanomaterials for cell differentiation, and can be expanded to other cellular applications.

Improving protein delivery of fibroblast growth factor-2 from bacterial inclusion bodies used as cell culture substrates

Bacterial inclusion bodies (IBs) have recently been used to generate biocompatible cell culture interfaces, with diverse effects on cultured cells such as cell adhesion enhancement, stimulation of cell growth or induction of mesenchymal stem cell differentiation. Additionally, novel applications of IBs as sustained protein delivery systems with potential applications in regenerative medicine have been successfully explored. In this scenario, with IBs gaining significance in the biomedical field, the fine tuning of this functional biomaterial is crucial. In this work, the effect of temperature on fibroblast growth factor-2 (FGF-2) IB production and performance has been evaluated. FGF-2 was overexpressed in Escherichia coli at 25 and 37 °C, producing IBs with differences in size, particle structure and biological activity. Cell culture topographies made with FGF-2 IBs biofabricated at 25 °C showed higher levels of biological activity as well as a looser supramolecular structure, enabling a higher protein release from the particles. In addition, the controlled use of FGF-2 protein particles enabled the generation of functional topographies with multiple biological activities being effective on diverse cell types.

Effects of controlled release of brain-derived neurotrophic factor from collagen gel on rat neural stem cells

This study aimed to determine the effects of the controlled release of brain-derived neurotrophic factor (BDNF) from collagen gel on rat neural stem cells (NSCs). With two groups of daily addition of BDNF and collagen gel without BDNF as controls, BDNF was tested using ELISA at different time points. In the BDNF-collagen gel group, BDNF was steadily released from gels for 10 days. The cell viability test and the bromodeoxyuridine incorporation assay showed that the BDNF-collagen gel supported the survival and proliferation of NSCs. Compared with controls, the length of processes was markedly longer and the differentiation percentage from NSCs into neurons was much higher in the BDNF-collagen gel group (P<0.05). These findings suggest that BDNF-collagen gel can significantly reduce the amount of BDNF required for the culture of NSCs and increase the differentiation percentage from NSCs into neurons.

A nanostructured bacterial bioscaffold for the sustained bottom-up delivery of protein drugs

AIMS

Bacterial inclusion bodies (IBs) are protein-based, amyloidal nanomaterials that mechanically stimulate mammalian cell proliferation upon surface decoration. However, their biological performance as potentially functional scaffolds in mammalian cell culture still needs to be explored.

MATERIALS & METHODS

Using fluorescent proteins, we demonstrate significant membrane penetration of surface-attached IBs and a corresponding intracellular bioavailability of the protein material.

RESULTS

When IBs are formed by protein drugs, such as the intracellular acting human chaperone Hsp70 or the extracellular/intracellular acting human FGF-2, IB components intervene on top-growing cells, namely by rescuing them from chemically induced apoptosis or by stimulating cell division under serum starvation, respectively. Protein release from IBs seems to mechanistically mimic the sustained secretion of protein hormones from amyloid-like secretory granules in higher organisms.

CONCLUSION

We propose bacterial IBs as biomimetic nanostructured scaffolds (bioscaffolds) suitable for tissue engineering that, while acting as adhesive materials, partially disintegrate for the slow release of their biologically active building blocks. The bottom-up delivery of protein drugs mediated by bioscaffolds offers a highly promising platform for emerging applications in regenerative medicine.

Transplantation of cord blood mesenchymal stem cells as spheroids enhances vascularization

Despite promising results from the therapeutic use of stem cells for treating ischemic diseases, the poor survival of cells transplanted into ischemic regions is one of the major problems that undermine the efficacy of stem cell therapy. Cord blood mononuclear cells (CBMNCs) are an alternative source of mesenchymal stem cells (MSCs) without disadvantages, such as the painful and invasive harvesting procedure, of MSCs derived from bone marrow or adipose tissue. In the present study, we investigated whether the angiogenic efficacy of cord blood mesenchymal stem cells (CBMSCs) can be enhanced by grafting as spheroids in a mouse hindlimb ischemia model. Human CBMSC (hCBMSC) spheroids were prepared by using the hanging-drop method. Mouse hindlimb ischemia was induced by excising the femoral artery and its branches. After surgery, the animals were divided into no-treatment, dissociated hCBMSC, and spheroid hCBMSC groups (n=8 per group) and received corresponding hCBMSC treatments. After surgery, the ischemic hindlimbs were monitored for 4 weeks, and then, the ischemic hindlimb muscles were harvested for histological analysis. Apoptotic signaling, angiogenesis-related signal pathways, and blood vessel formation were investigated in vitro and/or in vivo. The transplantation of hCBMSCs as spheroids into mouse ischemic hindlimbs significantly improved the survival of the transplanted cells by suppressing apoptotic signaling while activating antiapoptotic signaling. Furthermore, the transplantation of hCBMSCs as spheroids significantly increased the number of microvessels and smooth muscle α-actin-positive vessels in the ischemic limbs of mice, and attenuated limb loss and necrosis. Human CBMNC can be considered an alternative source of MSC, and spheroid-based hCBMSC delivery can be considered a simple and effective strategy for enhancing the therapeutic efficacy of hCBMSCs.

Thick collagen-based 3D matrices including growth factors to induce neurite outgrowth

Designing synthetic microenvironments for cellular investigations is a very active area of research at the crossroads of cell biology and materials science. The present work describes the design and functionalization of a three-dimensional (3D) culture support dedicated to the study of neurite outgrowth from neural cells. It is based on a dense self-assembled collagen matrix stabilized by 100-nm-wide interconnected native fibrils without chemical crosslinking. The matrices were made suitable for cell manipulation and direct observation in confocal microscopy by anchoring them to traditional glass supports with a calibrated thickness of ∼50μm. The matrix composition can be readily adapted to specific neural cell types, notably by incorporating appropriate neurotrophic growth factors. Both PC-12 and SH-SY5Y lines respond to growth factors (nerve growth factor and brain-derived neurotrophic factor, respectively) impregnated and slowly released from the support. Significant neurite outgrowth is reported for a large proportion of cells, up to 66% for PC12 and 49% for SH-SY5Y. It is also shown that both growth factors can be chemically conjugated (EDC/NHS) throughout the matrix and yield similar proportions of cells with longer neurites (61% and 52%, respectively). Finally, neurite outgrowth was observed over several tens of microns within the 3D matrix, with both diffusing and immobilized growth factors.

The protection of MSCs from apoptosis in nerve regeneration by TGFβ1 through reducing inflammation and promoting VEGF-dependent angiogenesis

Our previous report demonstrated that autologous adipose-derived mesenchymal stem cells (ADSCs) combined with xenogeneic acellular nerve matrix (XANM) can support the regeneration of defective nerves. Although ADSCs had the potential to replace Schwann cells in engineered-tissue nerves, apoptosis easily obstructed the ability to treat serious nerve injury in the host, such as a >50-mm-long nerve defect. In the present study, we found that, in combination with transforming growth factor β1 (TGFβ1), an ADSCs-XANM graft was sufficient to support the regeneration of a 50-mm sciatic nerve defect, which was not achieved using an ADSCs-XANM graft alone. Based on this finding, we further investigated how TGFβ1 coordinated with ADSCs to enhance nerve regeneration. In vitro, cell culture experiments demonstrated that TGFβ1 did not have a direct effect on ADSC proliferation, apoptosis, the cell cycle, or neural differentiation. The expression of VEGF, however, was significantly increased in ADSCs cultured with TGFβ1. In vivo, fluorescence labeling experiments demonstrated that the survival of transplanted ADSCs inoculated with XANM-TGFβ1 was higher than with XANM. Further study showed that TGFβ1 was capable of impairing the host immune response that was trigged by transplanted XANM. Additionally, we discovered that XANM-ADSCs in immunodeficient mice had apoptosis rates similar to XANM-ADSCs-TGFβ1 over a short time course (7 days). Once we blocked VEGF with a neutralizing antibody, the protective effect of TGFβ1 was impaired over a long time course (28 days). These results suggested that TGFβ1 was capable of enhancing the regenerative capacity of an XANM-ADSCs graft, mainly by protecting transplanted ADSCs from apoptosis. This effect was achieved in part through decreasing inflammation and promoting VEGF-dependent angiogenesis.

Modeling neural differentiation on micropatterned substrates coated with neural matrix components

Topographical and biochemical characteristics of the substrate are critical for neuronal differentiation including axonal outgrowth and regeneration of neural circuits in vivo. Contact stimuli and signaling molecules allow neurons to develop and stabilize synaptic contacts. Here we present the development, characterization and functional validation of a new polymeric support able to induce neuronal differentiation in both PC12 cell line and adult primary skin-derived precursor cells (SKPs) in vitro. By combining a photolithographic technique with use of neural extracellular matrix (ECM) as a substrate, a biocompatible and efficient microenvironment for neuronal differentiation was developed.

Bioadhesiveness and efficient mechanotransduction stimuli synergistically provided by bacterial inclusion bodies as scaffolds for tissue engineering

BACKGROUND

Bacterial inclusion bodies (IBs), mechanically stable, submicron protein particles of 50-500 nm dramatically favor mammalian cell spread when used for substrate surface decoration. The mechanisms supporting fast colonization of IB-modified surfaces have not yet been identified.

RESULTS

This study provides evidence of mechanotransduction-mediated stimulation of mammalian cell proliferation on IB-decorated surfaces, as observed by the enhanced phosphorylation of the signal-regulated protein kinase and by the dramatic emission of filopodia in the presence of IBs. Interestingly, the results also show that IBs are highly bioadhesive materials, and that mammalian cell expansion on IBs is synergistically supported by both enhanced adhesion and mechanical stimulation of cell division.

DISCUSSION

The extent in which these events influence cell growth depends on the particular cell line response but it is also determined by the genetic background of the IB-producing bacteria, thus opening exciting possibilities for the fine tailoring of protein nanoparticle features that are relevant in tissue engineering.

Endostatin binds nerve growth factor and thereby inhibits neurite outgrowth and neuronal migration in-vitro

Endostatin (ES), the C-terminal fragment of collagen XVIII known for its anti-angiogenic properties, is associated with neurological diseases in mammals. In this study, we investigated the effect of ES on nerve growth factor (NGF)-induced neuronal differentiation, migration, neuritogenesis, and neurite extension. ES partially inhibited PC12 cell differentiation and cerebellar granule cell migration. In addition, neurite outgrowth was inhibited in a concentration-dependent manner. This effect was also matrix-dependent, as we observed better inhibition on PC12 cells grown on collagen compared to laminin matrices. Furthermore, we observed partial NGF depletion by collagen and ES, but not by laminin suggesting that NGF-matrix interactions may be important for promoting neuritogenesis, competitive inhibition by ES or low affinity matrix impairs PC12 differentiation and neurite outgrowth. Finally, using a biosensor technique, we demonstrated a direct interaction between NGF and ES suggesting the mechanism of action of ES may involve NGF sequestration. In conclusion, our study demonstrates the inhibitory effect of ES on different steps of neurogenesis including cell differentiation and migration and neuritogenesis by NGF sequestration. Such sequestration may compromise brain repair following injury, but also may play important role in axon finding as well as a potent therapeutical target in diseases involving abnormal elevated neurotrophic growth factor levels. Taken together, this study raises the consideration of ES as a double-edge sword that carries both deleterious and putative therapeutical effects.

Measurements of movement and diffusion coefficients of single cells on polymeric surface from image analysis

Time-lapse digital images were taken every 30 s of PC12 cells cultured on polystyrene dishes, collagen-coated dishes and poly(L-lysine)-coated dishes in high-serum medium, low-serum medium and neurite outgrowth factor (NGF)-containing medium to investigate their diffusion coefficients (i.e., self-diffusion coefficients), D and specific movement (i.e., specific frequent movement) using image analysis and Fast Fourier Transform (FFT) analysis. D for these cells was found to fluctuate as a function of time, D varying between 0 and 0.08 microm(2)/s. The trend observed upon examination of average D values was: D in high-serum medium > or = D in low-serum medium > or = D in NGF-containing medium. Image analysis and FFT analysis of single cells cultured on polymeric dishes in these three media did not have any specific frequency of cell movement between 0 and 0.0167 Hz. The high diffusion coefficient and high amplitude of power spectra of PC12 cells in high-serum medium might be attributed to the high energy necessary for their continual suppression of the mitogen-activated protein kinase (MAPK) cascade and for them to maintain their undifferentiated state.

Biomaterials for Brain Tissue Engineering

Neurological disorders such as traumatic brain injuries or stroke result in neuronal loss and disruption of the brain parenchyma. Current treatment strategies are limited in that they can only mitigate the degeneration process or alleviate the symptoms but do not reverse the condition. In contrast, regenerative cell-based therapies offer long-term hope for many patients. Bioactive scaffolds are likely to reinforce the success of cell replacement therapies by providing a microenvironment that facilitates the survival, proliferation, differentiation, and connectivity of transplanted and/or endogenous cells. This Review outlines various biomaterials (including hydrogels, self-assembling peptides, and electrospun nanofibres) that have been investigated for the repair of brain tissue, and discusses strategies for the immobilization of biomolecules. An overview of the potential clinical applications of such scaffolds in neurodegenerative diseases is also provided.

The effect of neurotrophin-3/chitosan carriers on the proliferation and differentiation of neural stem cells

In this study, the behavior of neural stem cells from the newborn rat spinal cord was compared at neurosphere level after the addition of neurotrophin-3 (NT-3) once or daily, blank chitosan carriers, or NT-3-chitosan carriers respectively. We found that NT-3 enhanced the viability and differentiation of neural stem cells, but as NT-3 has an extremely short half-life at 37 degrees C, in order to maintain the NT-3-mediated proliferation and differentiation effects on neural stem cells, NT-3 needed to be added to the medium every 24 h. However, NT-3-chitosan carriers dramatically increase the differentiation percentage of neural stem cells into neurons, which includes GABAergic and as cholinergic neurons. Although blank chitosan carriers also showed good biocompatibility to the neural stem cells, they induced the differentiation of these cells into neurons at a much lower percentage than the daily addition of NT-3 or the NT-3-chitosan carriers. Our results suggest that NT-3-chitosan carriers may not only maintain the viability of neural stem cells and increase their differentiation percentage into neurons, but also reduce the amount of NT-3 required for the survival and differentiation of these cells. These results may provide an experimental basis for the maximum replacement of dead neurons by neural stem cell transplant after spinal cord injury (SCI).

Applications and Degradation of Proteins Used as Tissue Engineering Materials

This article provides an up-to-date review on the applications of natural polymers, i.e., proteins, as materials for tissue engineering. Proteins are one of the important candidates for tissue engineering materials based on their superior biocompatibility, biodegradation, bioresorbability, and so on. However, their inferior mechanical properties limit their broad application. Currently-available proteins for application in tissue engineering or drug delivery systems, such as fibrin, collagen, zein, silk fibroin, keratin, casein and albumin, and the biodegradation of tissue-engineered substitutes based on proteins are presented. Techniques of scaffold fabrication are also mentioned. Problems and future possibilities for development of protein-based tissue-engineered substitutes are also introduced in this review.

Enhanced nerve growth factor efficiency in neural cell culture by immobilization on the culture substrate

Nerve growth factor (NGF) immobilization on a culture substrate may dramatically reduce the amount of NGF required for pheochromocytoma (PC12) cell culture. Coverslips on which NGF had been immobilized, or with NGF added to the culture medium daily, were used to culture PC12 cells. We examined the effects of adding 5, 10, or 100 ng of NGF to cultures daily, and compared them to the effects of immobilizing 5, 10, or 100 ng of NGF on culture substrates in a single dose. Cultures with 10 or 5 ng NGF added daily showed dramatically decreased cell viability, mitochondrial metabolic activity, and neuronal differentiation compared to cultures with 100 ng NGF added daily, while also exhibiting increased apoptosis. In contrast, a single dose of 100 ng immobilized NGF yielded results similar to 100 ng NGF added daily (total: 300 ng over 3 days), and 10 or 5 ng immobilized NGF showed far better results than 10 or 5 ng NGF added daily. These results demonstrate that NGF immobilization can dramatically reduce the amount of NGF required in neuronal cell culture.