Staurosporine-induced apoptosis in cultured chick embryonic neurons is reduced by polyethylenimine of low molecular weight used as a coating substrate

Preparation of cell-culturing glass surfaces that release branched polyethyleneimine triggered by thiol-disulfide exchange

To develop a chemical stimulus-responsive substrate for culturing cells, polyethyleneimine (PEI) having a pyridyl disulfide moiety was attached via disulfide linkages to a glass coverslip modified with a silane coupling agent having a thiol group. The surface modification was confirmed by X-ray photoelectron spectroscopy and zeta potential analysis. The obtained surface exhibited sufficiently high cell adhesiveness. Zeta potential measurements revealed that the PEI derivatives were released from the surface through thiol-disulfide exchange when the modified glass coverslip was immersed in a neutral pH buffer containing cysteine. The cell viability assay demonstrated that this chemical stimulus was substantially nontoxic to 293T cells. Because PEI is a widely used transfection reagent, this functional glass coverslip would be potentially useful as an experimental platform for reverse transfection.

Low molecular weight polyethylenimine cross-linked by 2-hydroxypropyl-gamma-cyclodextrin coupled to peptide targeting HER2 as a gene delivery vector

Gene delivery is one of the critical steps for gene therapy. Non-viral vectors have many advantages but suffered from low gene transfection efficiency. Here, in order to develop new polymeric gene vectors with low cytotoxicity and high gene transfection efficiency, we synthesized a cationic polymer composed of low molecular weight polyethylenimine (PEI) of molecular weight of 600 Da cross-linked by 2-hydroxypropyl-gamma-cyclodextrin (HP gamma-CD) and then coupled to MC-10 oligopeptide containing a sequence of Met-Ala-Arg-Ala-Lys-Glu. The oligopeptide can target to HER2, the human epidermal growth factor receptor 2, which is often over expressed in many breast and ovary cancers. The new gene vector was expected to be able to target delivery of genes to HER2 positive cancer cells for gene therapy. The new gene vector was composed of chemically bonded HP gamma-CD, PEI (600 Da), and MC-10 peptide at a molar ratio of 1:3.3:1.2. The gene vector could condense plasmid DNA at an N/P ratio of 6 or above. The particle size of HP gamma-CD-PEI-P/DNA complexes at N/P ratios 40 was around 170-200 nm, with zeta potential of about 20 mV. The gene vector showed very low cytotoxicity, strong targeting specificity to HER2 receptor, and high efficiency of delivering DNA to target cells in vitro and in vivo with the reporter genes. The delivery of therapeutic IFN-alpha gene mediated by the new gene vector and the therapeutic efficiency were also studied in mice animal model. The animal study results showed that the new gene vector HP gamma-CD-PEI-P significantly enhanced the anti-tumor effect on tumor-bearing nude mice as compared to PEI (25 kDa), HP gamma-CD-PEI, and other controls, indicating that this new polymeric gene vector is a potential candidate for cancer gene therapy.

A novel co-polymer based on hydroxypropyl alpha-cyclodextrin conjugated to low molecular weight polyethylenimine as an in vitro gene delivery vector

A novel co-polymer based on 2-hydroxypropyl-alpha-cyclodextrin cross-linked by low molecular weight polyethylenimine was synthesized as a gene delivery vector. The copolymer could bind and condense DNA tightly. It showed lower cytotoxicity than PEI 25kDa in SK-BR-3 cells. Transfection efficiency was increased over 5.5-fold higher than PEI 25 kDa in SK-BR-3 cells in complete serum medium. It is a potential candidate vector for gene therapy.

Recombinant collagen for animal product-free dextran microcarriers

Manufacturers of vaccines and other biologicals are under increasing pressure from regulatory agencies to develop production methods that are completely animal-component-free. In order to comply with this demand, alternative cell culture substrates to those now on the market, primarily collagen or gelatin, must be found. In this paper, we have tested a number of possible substitutes including recombinant collagen, a 100-kDa recombinant gelatin fragment and a peptide derived from a cell-binding region of type I collagen. The small 15-amino acid peptide did not support attachment of human fibroblasts in monolayer culture. The 100-kDa gelatin fragment supported cell attachment in monolayer culture, but was significantly less active than intact porcine gelatin. Recombinant type I collagen was as successful in promoting cell attachment as native collagen, and both were more effective than porcine gelatin. Based on these data, dextran microspheres were treated with the same attachment proteins--porcine gelatin, native collagen, or recombinant collagen. The same trends were observed as in monolayer culture. Concentrations of the recombinant collagen (as well as native collagen) supported cell attachment on dextran microspheres at concentrations as low as 0.01 microg/cm(2). Treatment of the dextran with a low level of polyethylenimine, a cationic moiety, further enhanced attachment when used in conjunction with the low concentration of recombinant collagen. Where there was increased cell attachment, increased proliferation followed. We are confident, based on these findings, that a fully recombinant substitute could replace gelatin in current microcarrier preparations without losing the cell growth benefits provided by the native protein.

Inhibition of monocyte adhesion on brain-derived endothelial cells by NF-kappaB decoy/polyethylenimine complexes

BACKGROUND

The nuclear factor (NF)-kappaB plays a key role in inflammatory reactions of the endothelium by controlling the expression of surface-adhesion molecules and other inflammatory mediators, which facilitate the attachment of monocytes and lymphocytes to the endothelial surface. We investigated the inhibition of monocyte adhesion by NF-kappaB transcription factor decoys complexed with polyethylenimines (PEIs) of different molecular weights and structures (800, 25, and 2.7 kDa PEI).

METHODS

Formation, size and stability of the PEI/decoy complexes were investigated by polyacrylamide gel electrophoresis and photon correlation spectroscopy. The efficiency of the complexes was studied in a cell adhesion assay using the murine brain-derived endothelial cell line bEnd5, activated with lipopolysaccharide as inflammatory model. U-937 monocytes were fluorescently labeled with BCECF-AM to permit quantitative measurement of adhesion. Expression of endothelial cell adhesion molecules was determined at the mRNA level by RT-PCR and at the protein level by ELISA.

RESULTS

Depending on the N/P ratio, decoys formed complexes of <200 nm in size with all PEIs, which were stable against degradation by nucleases and dissociation by albumin. Treatment of bEnd5 and U-937 cells with NF-kappaB decoys complexed with 25 and 2.7 kDa PEI reduced the number of adherent U-937 cells and decreased the levels of ICAM-1 and VCAM-1 mRNA and protein. The effects were specific, time-dependent and increased with higher N/P ratios of complexes and lower cytotoxicity of polymers. In contrast, the efficiency of the 800 kDa PEI was much lower compared to the other polymers.

CONCLUSIONS

Complexes of NF-kappaB decoy and PEIs effectively inhibited the adherence of monocytes on endothelial cells, which could be a promising strategy for the treatment of inflammatory diseases.

Apoptosis mediated by p53 in rat neural AF5 cells following treatment with hydrogen peroxide and staurosporine

AF5 neural cells derived from fetal rat mesencephalic tissue were immortalized with a truncated SV40 LT vector lacking the p53-inactivating domain to maintain long-term cultures with a p53-responsive phenotype. This study examined p53 function in producing programmed cell death in propagating AF5 neural cells after exposure to hydrogen peroxide (H2O2) and the kinase inhibitor staurosporine (STSP). Concentration-dependent exposure of AF5 cells to 0-800 mM H2O2 and STSP at 0-1000 nM revealed increasing cytotoxicity from MTS cell viability assays. Apoptosis occurred at 400 mM H2O2 as evidenced by subG1 DNA and Annexin V flow cytometry analyses and cellular immunofluorescence staining with propidium iodide, anti-Annexin V and DAPI. DNA fragmentation, caspase-3/7 activity and cytochrome c release into cytosol also confirmed H2O2-mediated apoptotic events. p53 protein levels were increased over 24 h by H2O2 in a coordinated fashion with mdm2 expression. p53 activation by H2O2 was evidenced by elevated Ser15 phosphorylation, increased luciferase p53 reporter activity and upregulation of the downstream p53 targets p21(waf1) and apoptotic proteins, bax, Noxa and PUMA. STSP exposure produced apoptosis demonstrated by DNA fragmentation, caspase-3/7 activity, cytochrome c release and over 24 h was accompanied by sustained increase in p53 and Ser15 phosphorylation, rise in p21(waf1) and bax and a transient increase in p53 reporter activity but without Annexin V binding. These findings demonstrate that AF5 cells undergo apoptosis in response to H2O2-mediated oxidative stress and signal pathway disruption by STSP that therefore would be useful in studies related to p53-dependent neuronal cell death and neurodegeneration.

Optimized protocols for the simultaneous preparation of primary neuronal cultures of the neocortex, hippocampus and cerebellum from individual newborn (P0.5) C57Bl/6J mice

Knockout mouse models allow preparation of primary neuronal cultures from distinct brain regions in order to investigate the underlying neuronal pathomechanisms of human metabolic diseases associated with severe, regionally distinct brain pathologies (e.g. Zellweger syndrome, the most severe form of a peroxisomal biogenesis disorder). However, homozygous mouse pups with Zellweger syndrome usually die shortly after birth. Therefore, in this study, we established optimized protocols for the simultaneous preparation and cultivation of serum-free primary neuronal cultures from distinct brain regions (medial neocortex, hippocampus and cerebellum) from individual newborn (P0.5) C57Bl/6J mice. For each of the three types of neuronal cultures, we have optimized the isolation procedures and cultivation conditions including coating substrates, enzyme digestion, mode of trituration, seeding density and composition of the culture medium. As indicated by indirect immunofluorescence using antibodies against NeuN, GFAP and CNPase, the purity of the distinct neuronal cultures was high. The percentage of oligodendrocytes was less than 1% in all neuronal cultures. Only 5% astrocytes were present in cortical, 7% in hippocampal and 10% in cerebellar cultures. Cytosine arabinofuranoside (AraC) treatment reduced the percentage of astrocytes only significantly in hippocampal cultures, however, increased the percentage of apoptotic neurons in hippocampal and cortical cultures.

Spinal cord molecular profiling provides a better understanding of amyotrophic lateral sclerosis pathogenesis

Research efforts in amyotrophic lateral sclerosis (ALS) have not yet provided a comprehensive explanation of the disease pathogenesis, which is emerging as a complex interaction between multiple factors. Gene expression studies traditionally based on single mRNA specie analysis have recently progressed to allow entire transcriptional profiles of affected tissues to be obtained through array-based methods. This experimental approach has significantly improved our understanding of the molecular changes occurring in ALS, although its limitations in the detection of low-abundance transcripts in tissues with a high level of complexity are becoming increasingly recognized. In this paper, experimental findings based on an expression study in post-mortem spinal cord from sporadic ALS individuals will be discussed in light of recently published data using array analysis in an animal model of the disease. Previous expression data obtained using conventional techniques are also compared. Through the analysis of the information arising from ALS post-mortem and animal model tissues studies, we have identified a pattern of molecular events in which factors implicated in the immune response, cytoprotection and growth-differentiation are differentially regulated in a time-dependent way from early to advanced stages of disease progression.

PACAP maintains cell cycling and inhibits apoptosis in chick neuroblasts

We previously reported that pituitary adenylate cyclase-activating polypeptide (PACAP) increased cAMP in neuroblast-enriched cultures from embryonic day 3.5 chick brain. Also, the neuroblasts expressed the mRNA, peptide, and receptor for PACAP. Here, we investigated downstream effects of increased cAMP by examining PACAP's role in regulating cell numbers during brain development. Using flow cytometry, we quantified proliferating cell nuclear antigen and DNA, and compared apoptotic cells and cells in cell cycle compartments under differing conditions. Untreated cultures showed high proliferative activity with little apoptosis. Addition of exogenous PACAP had no effect on this pattern. However, blocking endogenous PACAP with a receptor antagonist increased cell cycle exit, then increased apoptosis. We conclude that chick neuroblasts require production of PACAP to inhibit apoptosis and maintain full proliferative activity during early brain development.

Relationship between protein phosphatase type-2C activity and induction of apoptosis in cultured neuronal cells

The cellular composition and concentration of fatty acids are crucial for proliferation and survival. We recently showed stimulation of protein phosphatase type-2C (PP2C) by unsaturated fatty acids. Here, we describe that treatment of cultured chick neurons with 100 microM oleic acid for 24h increased the percentage of damaged neurons to 61+/-9% compared with 25+/-4% in controls. Oleic acid-induced cell death showed features of apoptosis such as chromatin condensation, shrinkage of the nucleus, DNA fragmentation and caspase-3 activation. Extensive studies with a variety of fatty acids revealed a striking correlation between activation of PP2C and induction of apoptosis. Lipophilicity, oxidizability, and an acidic group were required for both effects. In addition, activation of PP2C and induction of apoptosis could discriminate between cis- and trans-conformation of the fatty acids. The results are in favor of PP2C playing an important, yet unidentified role in apoptosis.

Release of cytochrome c into the extracellular space contributes to neuronal apoptosis induced by staurosporine

The mitochondrial protein cytochrome c has been identified as one of the key signalling molecules of apoptosis. In the present study, we used primary neuronal cultures to investigate whether cytochrome c was released from the mitochondria into the cytosol and subsequently into the culture medium during staurosporine-induced apoptosis and whether extracellular cytochrome c modulates the degree of damage caused by staurosporine. We found the cytochrome c content in the mitochondria decreased 24 h after and increased in the cytosol 8 h after staurosporine was added to the culture medium. The cytochrome c content of the culture medium increased from 8 h up to 24 h after starting the staurosporine treatment. In parallel with the release of cytochrome c into the culture medium, membrane leakage occurred as determined by the release of LDH. Addition of cytochrome c accelerated, whereas the addition of anti-cytochrome c antibodies reduced staurosporine-induced neuronal death suggesting a pro-apoptotic role of cytochrome c released into the culture medium. Under control conditions, extracellularly added cytochrome c (25 ng/ml), which was in the range of the amount of cytochrome c released from staurosporine-treated neurons into the culture medium, increased the percentage of apoptotic neurons to 30% compared with 18% in vehicle-treated controls. Our results suggest that the release of cytochrome c into the extracellular space contributes to neuronal apoptosis induced by staurosporine.

Ginkgolic acids induce neuronal death and activate protein phosphatase type-2C

The standardized extract from Ginkgo biloba (EGb 761) is used for the treatment of dementia. Because of allergenic and genotoxic effects, ginkgolic acids are restricted in EGb 761 to 5 ppm. The question arises whether ginkgolic acids also have neurotoxic effects. In the present study, ginkgolic acids caused death of cultured chick embryonic neurons in a concentration-dependent manner, in the presence and in the absence of serum. Ginkgolic acids-induced death showed features of apoptosis as we observed chromatin condensation, shrinkage of the nucleus and reduction of the damage by the protein synthesis inhibitor cycloheximide, demonstrating an active type of cell death. However, DNA fragmentation detected by the terminal-transferase-mediated ddUTP-digoxigenin nick-end labeling (TUNEL) assay and caspase-3 activation, which are also considered as hallmarks of apoptosis, were not seen after treatment with 150 microM ginkgolic acids in serum-free medium, a dose which increased the percentage of neurons with chromatin condensation and shrunken nuclei to 88% compared with 25% in serum-deprived, vehicle-treated controls. This suggests that ginkgolic acid-induced death showed signs of apoptosis as well as of necrosis. Ginkgolic acids specifically increased the activity of protein phosphatase type-2C, whereas other protein phosphatases such as protein phosphatases 1A, 2A and 2B, tyrosine phosphatase, and unspecific acid- and alkaline phosphatases were inhibited or remained unchanged, suggesting protein phosphatase 2C to play a role in the neurotoxic effect mediated by ginkgolic acids.