Evaluation of osteoblast differentiation and function when cultured on mesoporous bioactive glass adsorbed with testosterone

Mesoporous bioactive glass (MBG), a kind of porous materials with great osteoconductive and osteoinductive ability, shows promising application in bone tissue engineering due to its high specific surface area, orderly channel structure, and large pore volume. Here we reported that the proliferation, differentiation, and mineralization were promoted in MC3T3-E1 cells cultured on MBG which adsorbed with testosterone (MBG/T). We found that transcriptional activity of Runx2 which is a critical transcription factor is increased in MC3T3-E1 cells cultured on MBG/T. Intriguingly, we observed that ERK phosphorylation was enhanced in MC3T3-E1 cells cultured on MBG/T. We showed that activated Runx2 in MC3T3-E1 cells cultured on MBG/T is through Erk1/2 phosphorylation. Consistent with this result, we also found that the expression of osteoblastic marker genes were increased. Therefore, we concluded that osteoblast differentiation and mineralization was enhanced after cells cultured on MBG/T through Erk1/2-activated Runx2 pathway. Our findings provided that MBG/T is a potential material in the process of bone repair.

Function and mechanism of mesoporous bioactive glass adsorbed epidermal growth factor for accelerating bone tissue regeneration

Mesoporous bioactive glass (MBG) has been demonstrated to play a vital role in bone tissue engineering due to its bioactivity, biocompatibility, and osteoinduction properties. Here, we report that MBG grafted with an amino group (MBG-NH₂) and MBG-NH₂ adsorbed epidermal growth factor (EGF) (MBG-NH₂/EGF) sustained-release EGF, and MBG-NH2/EGF could accelerate osteoblast differentiation and mineralization in MC3T3-E1 cells. We found that MBG-NH₂ could promote bone-like deposit formation and Ca deposition in vitro. Intriguingly, we observed that MBG-NH₂/EGF enhanced MC3T3-E1 cell adhesion. We also showed that extracellular signal-regulated kinase 1/2 (ERK1/2) was phosphorylated when MC3T3-E1 cells were cultured on MBG-NH₂/EGF. Interestingly, the transcription factor Runx2, important for osteoblast differentiation, was also activated when MC3T3-E1 cells were cultured on MBG-NH₂/EGF. We showed that MC3T3-E1 cells cultured on MBG-NH₂/EGF activating Runx2 was through ERK1/2 phosphorylation. Consistent with this survey, we observed that MC3T3-E1 cells cultured on MBG-NH₂/EGF accelerated osteoblastic marker gene expressions, including osteopontin (Opn) and osteocalcin (Ocn). Taken together, we conclude that the osteoblast differentiation and mineralization were accelerated in MC3T3-E1 cells cultured on MBG-NH₂/EGF through ERK-activated Runx2 pathway. These findings support the idea that MBG-NH₂/EGF is a potential biomaterial for bone tissue repair in bone defect-related diseases.

The Effects of Different Factors on the Behavior of Neural Stem Cells

The repair of central nervous system (CNS) injury has been a worldwide problem in the biomedical field. How to reduce the damage to the CNS and promote the reconstruction of the damaged nervous system structure and function recovery has always been the concern of nerve tissue engineering. Multiple differentiation potentials of neural stem cell (NSC) determine the application value for the repair of the CNS injury. Thus, how to regulate the behavior of NSCs becomes the key to treating the CNS injury. So far, a large number of researchers have devoted themselves to searching for a better way to regulate the behavior of NSCs. This paper summarizes the effects of different factors on the behavior of NSCs in the past 10 years, especially on the proliferation and differentiation of NSCs. The final purpose of this review is to provide a more detailed theoretical basis for the clinical repair of the CNS injury by nerve tissue engineering.

The mechanism of a chitosan-collagen composite film used as biomaterial support for MC3T3-E1 cell differentiation

Natural composite biomaterials are good structural supports for bone cells to regenerate lost bone. Here, we report that a chitosan-collagen composite film accelerated osteoblast proliferation, differentiation and matrix mineralization in MC3T3-E1 cells. Intriguingly, we observed that the film enhanced the phosphorylation of Erk1/2. We showed that the chitosan-collagen composite film increased the transcriptional activity of Runx2, which is an important factor regulating osteoblast differentiation downstream of phosphorylated Erk1/2. Consistent with this observation, we found that the chitosan-collagen composite film increased the expression of osteoblastic marker genes, including Type I Collagen and Runx2 in MC3T3-E1 cells. We conclude that this film promoted osteoblast differentiation and matrix mineralization through an Erk1/2-activated Runx2 pathway. Our findings provide new evidence that chitosan-collagen composites are promising biomaterials for bone tissue engineering in bone defect-related diseases.

Role of Biopolymer in Nacre Heated in Nitrogen Atmosphere

Nacre is one of the most attractive biological materials for its superior mechanical property which is mainly due to the “brick-mortar” microstructure. Nacre samples are heated in N2 atmosphere at 200°C, 400°C and 600°C, separately. The microstructures of the fresh and heated samples are characterized by SEM and XRD, and the three-point bending strengths of these samples are tested by universal mechanical testing machine. TG-DSC curves are performed on the fresh nacre and the demineralized one. The results show that biopolymer plays important roles in maintaining the microstructure, toughening mechanism and the phase transformation of aragonite.

Three-Point Bending Fracture Behaviors of Bamboo

Bamboo is a typical natural building material, which is longitudinally reinforced by robust fibers. This present paper focuses on the three-point bending fracture behavior of bamboo across and along fiber lengths with dense fiber layer upward and downward. The three-point bending strength of bamboo across the fibers is about ten times higher than that along the bamboo fibers, and the value of three-point bending strength with dense fiber layer downward is higher than that with dense fiber layer upward. Based on the microstructure of the fracture surfaces and the loading curves, different fracture processes are concluded to explain the anisotropy of bamboo.

The effect of topology of chitosan biomaterials on the differentiation and proliferation of neural stem cells

Neural stem cells (NSCs) are capable of self-renewal and differentiation into three principle central nervous system cell types under specific local microenvironments. Chitosan films (Chi-F), chitosan porous scaffolds (Chi-PS) and chitosan multimicrotubule conduits (Chi-MC) were used to investigate their effects on the differentiation and proliferation of NSCs isolated from the cortices of fetal rats. In the presence of 10% fetal bovine serum most NSCs cultured on Chi-F differentiated into astrocytes, NSCs cultured on Chi-MC showed a significant increase in neuronal differentiation, while Chi-PS somewhat promoted NSCs to differentiate into neurons. However, in serum-free medium with 20 ng ml(-1) basic fibroblast growth factor NSCs cultured on Chi-F showed the greatest proliferation, NSCs cultured on Chi-MC showed moderate cell proliferation, but NSCs cultured on Chi-PS exhibited the least cell proliferation. These observations indicate that chitosan topology can play an important role in regulating differentiation and proliferation of NSCs and raise the possibility of the utilization of chitosan in various structural biomaterials in neural tissue engineering.

Synergistic effect of neural stem cells and olfactory ensheathing cells on repair of adult rat spinal cord injury

Spinal cord injury (SCI) is a common clinical disease that places a heavy burden on families and society. Cellular therapy provides a method of giving a supplement of cells lost in the injury and promoting functional recovery after SCI. Neural stem cells (NSCs) and olfactory ensheathing cells (OECs) are two most promising cell types. NSCs have the potential of differentiating into neurons and glial cells, and OECs could help the axons of neurons pass through the glial scar to promote functional recovery. NSCs were isolated from the cortices of fetal rats on days 12-14 of embryonic development and OECs were isolated from the olfactory bulbs of adult rats. In vitro coculture studies demonstrated OECs could promote NSCs to differentiate into neurons. Four groups of rats that had been 3/4 spinal cord transectioned at T9 were injected with DMEM/F12 solution, NSCs, OECs, and NSCs + OECs, respectively, 7 days post-SCI. Twelve weeks postoperation, the hindlimb locomotor function of rats in the cotransplantation group was significantly improved compared with that in the other three groups. Histological observation and immunohistochemical staining of NF-200 both showed new nerve fibers across the injured region. Cotransplantation of NSCs and OECs might have a synergistic effect on promoting neural regeneration and improving the recovery of locomotion function. Cotransplantation of NSCs and OECs was better than a single graft of either NSCs or OECs. These findings have provided a new way of thinking in the treatment of SCI.

Preparation of cross-linked carboxymethyl chitosan for repairing sciatic nerve injury in rats

A successful nerve regeneration process was achieved with nerve repair tubes made up of 1-ethyl-3(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) cross-linked carboxymethyl chitosan (CM-chitosan) with improved biodegradability. Chitosan has a very slow degradation rate, while the EDC cross-linked CM-chitosan tubes degraded to 30% of original weight during 8 weeks of incubation in lysozyme solution. In vitro cell culture indicated that the CM-chitosan films presented no cytotoxicity to Schwann cells. From in vivo studies using a 10 mm rat sciatic nerve defect model investigated by histomorphometry analysis, the average diameter of the fibers and the average thickness of myelin sheath in the CM-chitosan tubes were 3.7 +/- 0.33 and 0.33 +/- 0.04 mum, respectively, which demonstrated equivalence to nerve autografts (the current "gold" standard); furthermore, the average fiber density in the CM-chitosan tubes was 20.5 x 10(3)/mm(2), which was similar to that of autografts (21 x 10(3)/mm(2)) and significantly higher than that of common chitosan tubes (15.3 x 10(3)/mm(2)).

Surface characterization and cytocompatibility of three chitosan/polycation composite membranes for guided bone regeneration

Guided bone regeneration is a promising surgical procedure for reconstructing bone defects. In this study, three chitosan/polycation composite membranes for guided bone regeneration are produced by blending chitosan with poly-L-lysine, polyethyleneimine, and poly-L-ornithine. For all composite membranes, the surface characteristics including surface topography, chemistry, and wettability are examined by atomic force microscopy, X-ray photoelectron spectroscopy, and contact angle assay. Their cytocompatibility is also evaluated with MC3T3-E1 osteoblast-like cells at cell, protein, and gene levels through cell biology assays, western blot, and RT-PCR analysis. On chitosan/poly-L-lysine composite membrane, MC3T3-E1 cells present well-developed cytoskeletal organization and significantly higher adhesion, proliferation, and differentiation than those on chitosan and the other two composite membranes. Furthermore, MC3T3-E1 cells on chitosan/poly-L-lysine membrane exhibit increased phosphorylation levels of focal adhesion kinase and extracellular signal-regulated kinase 1/2, and achieve an enhanced mRNA expression of fibronectin, Runx 2, RhoA, integrin alpha 5, and integrin beta1. From our results, we conclude that chitosan/ poly-L-lysine composite membrane possesses improved cytocompatibility with osteoblasts when compared to chitosan and holds potential for guided bone regeneration in the near future.

Controlling the degradation of covalently cross-linked carboxymethyl chitosan utilizing bimodal molecular weight distribution

Degradability is often a critical property of materials utilized in tissue engineering. Although chitosan, a naturally derived polysaccharide, is an attractive material due to its biocompatibility and ability to form scaffolds, its slow and uncontrollable rate of degradation can be an undesirable feature. In this study, we characterize chitosan derivatives formed using a combination of carboxymethylation and a bimodal molecular weight distribution. Specifically, chitosan is carboxymethylated to a theoretical extent of approximately 30% as described in our previous work, in which carboxyl groups possessing negative charges are created at a physiological pH. Carboxymethyl chitosan is used to form films and constructs by varying the ratio of high to low molecular weight (MW) while maintaining the mechanical properties of the polymer. The rate of degradation is found to be dependent upon both the carboxymethylation and the ratio of high to low MW polymer, as determined by dry weight loss in lysozyme solution in PBS. Subsequently, biocompatibility is examined to determine the effects of these modifications upon Neuro-2a cells cultured on these films. Neuro-2a cells adhere and proliferate on the modified films at a comparable rate to those cultured on unmodified films. This data indicates that these chitosan derivatives exhibit tunable degradation rates and result in a promising material system for neural tissue engineering.

Surface Properties of Chitosan Films Modified with Polycations and Their Effects on the Behavior of PC12 Cells

A series of composite films were prepared by blending chitosan with three polycations, poly(L-lysine), polyethyleneimine, and poly-L-ornithine, in specific blend proportions. The surface properties of the composite films, including surface topography, chemistry, and wettability, were examined by atomic force microscopy, X-ray photoelectron spectroscopy, and contact angle assay, respectively. For all composite films, blending with different polycations produced different nanoscaled surface topographical features (particles, granules, fibers, and islands) in addition to inducing changes in surface chemistry and wettability. PC12 cells were cultured on these composite films to evaluate the effects of surface properties on cell behavior. The PC12 cell behavior was holistically affected by surface topography, chemistry, and wettability; the cells also displayed responses to surface topography. On the surfaces with fiber topographic features, the PC12 cells exhibited significantly higher levels of adhesion, proliferation, and differentiation when compared to particle, granule, or island dominant surfaces. It appears that the surface topography of chitosan and chitosan-derived materials may play an important role in regulating nerve cell behavior and that topographic modification can be utilized for the applications of chitosan and chitosan-derived materials in nerve or other tissue regeneration.

A comprehensive library of histone mutants identifies nucleosomal residues required for H3K4 methylation

Methylation of histone 3 lysine 4 (H3K4) by yeast Set1-COMPASS requires prior monoubiquitination of histone H2B. To define whether other residues within the histones are also required for H3K4 methylation, we systematically generated a complete library of the alanine substitutions of all of the residues of the four core histones in Saccharomyces cerevisiae. From this study we discovered that 18 residues within the four histones are essential for viability on complete growth media. We also identified several cis-regulatory residues on the histone H3 N-terminal tail, including histone H3 lysine 14 (H3K14), which are required for normal levels of H3K4 trimethylation. Several previously uncharacterized trans-regulatory residues on histones H2A and H2B form a patch on nucleosomes and are required for methylation mediated by COMPASS. This library will be a valuable tool for defining the role of histone residues in processes requiring chromatin.