Densitometric quantification of neuronal viability by computerized image analysis

Maintenance of the Neuroprotective Function of the Amino Group Blocked Fluorescence-Agmatine

Agmatine, an endogenous derivative of arginine, has been found to be effective in treating idiopathic pain, convulsion, stress-mediated behavior, and attenuate the withdrawal symptoms of drugs like morphine. In the early stages of ischemic brain injury in animals, exogenous agmatine treatment was found to be neuroprotective. Agmatine is also considered as a putative neurotransmitter and is still an experimental drug. Chemically, agmatine is called agmatine 1-(4-aminobutyl guanidine). Crystallographic study data show that positively-charged guanidine can bind to the protein containing Gly and Asp residues, and the amino group can interact with the complimentary sites of Glu and Ser. In this study, we blocked the amino end of the agmatine by conjugating it with FITC, but the guanidine end was unchanged. We compared the neuroprotective function of the agmatine and agmatine-FITC by treating them in neurons after excitotoxic stimulation. We found that even the amino end blocked neuronal viability in the excitotoxic condition, by NMDA treatment for 1 h, was increased by agmatine-FITC, which was similar to that of agmatine. We also found that the agmatine-FITC treatment reduced the expression of nitric oxide production in NMDA-treated cells. This study suggests that even if the amino end of agmatine is blocked, it can perform its neuroprotective function.

Acetaldehyde-Mediated Neurotoxicity: Relevance to Fetal Alcohol Spectrum Disorders

Ethanol-induced neuro-developmental abnormalities are associated with impaired insulin and IGF signaling, and increased oxidative stress in CNS neurons. We examined the roles of ethanol and its principal toxic metabolite, acetaldehyde, as mediators of impaired insulin/IGF signaling and oxidative injury in immature cerebellar neurons. Cultures were exposed to 3.5 mM acetaldehyde or 50 mM ethanol ± 4-methylpyrazole (4-MP), an inhibitor of ethanol metabolism, and viability, mitochondrial function, oxidative stress, DNA damage, and insulin responsiveness were measured 48 hours later. Acetaldehyde or ethanol increased neuronal death and levels of 8-OHdG and 4-HNE, and reduced mitochondrial function. Ethanol inhibited insulin responsiveness, whereas acetaldehyde did not. 4-MP abated ethanol-induced oxidative stress and mitochondrial dysfunction, but failed to restore insulin responsiveness. Furthermore, alcohol and aldehyde metabolizing enzyme genes were inhibited by prenatal ethanol exposure; this effect was mediated by acetaldehyde and not ethanol + 4MP. These findings suggest that brain insulin resistance in prenatal alcohol exposure is caused by direct effects of ethanol, whereas oxidative stress induced neuronal injury is likely mediated by ethanol and its toxic metabolites. Moreover, the adverse effects of prenatal ethanol exposure on brain development may be exacerbated by down-regulation of genes needed for metabolism and detoxification of alcohol in the brain.

In vivo lamellar keratoplasty using platelet-rich plasma as a bioadhesive

PURPOSE

The use of standard sutures has been replaced by platelet-rich plasma (PRP), a bioadhesive agent, in several surgical procedures. This prompted us to test PRP efficacy in experimental lamellar keratoplasty.

METHODS

After lamellar anterior keratoplasty, PRP with a mean concentration of 807,564 platelets/mm(3) was used to attach the corneal flap to the stromal surface in 12 New Zealand white rabbits. 10-0 nylon sutures were used in one control group of 12 animals and no suture was used in a second control group of six rabbits. Animals were killed at days 2, 7, 30, and 90 for histological and smooth muscle actin (SMA) immunohistochemical analysis.

RESULTS

The PRP group showed a tight corneal graft from the first postoperative hours until they were killed. A transparent cornea was seen at 30 days and remained clear until the end of the protocol. Histological specimens showed no signs of ocular inflammation in any animal within the PRP group. Electron microscopy showed normal morphological features on the flap and stromal bed, and a clear interface zone without cells or debris. The number of stromal myofibroblasts was lower than that seen in the suture group at 3 months postsurgery. The sutured group showed an attached cornea with signs of inflammation around the knots. All flaps without PRP or sutures were completely detached in the immediate postoperative period.

CONCLUSIONS

PRP was useful for attaching the corneal flap and it was well tolerated by the rabbit corneal tissue. Corneal healing was satisfactory. Further studies on PRP adhesiveness in grafts with donor corneas should be performed before considering its use in patients.

Neurotoxic and gliotrophic activity of a synthetic peptide homologous to Gerstmann-Sträussler-Scheinker disease amyloid protein

Amyloid fibrils in Gerstmann-Sträussler-Scheinker (GSS) disease are composed of a fragment of the prion protein (PrP), the N and C termini of which correspond to ragged residues 81-90 and 144-153. A synthetic peptide spanning the sequence 82-146 (PrP 82-146) polymerizes into protease-resistant fibrils with the tinctorial properties of amyloid. We investigated the biological activity of PrP 82-146 and of two nonamyloidogenic variants of PrP 82-146 with scrambled amino acid sequence 106-126 or 127-146. Cortical neurons prepared from rat and mouse embryos were chronically exposed to the PrP 82-146 peptides (10-50 microM). PrP 82-146 and the partially scrambled peptides induced neuronal death with a similar dose-response pattern, indicating that neurotoxicity was independent of amyloid fibril formation. Neurotoxicity was significantly reduced by coadministration of an anti-oligomer antibody, suggesting that PrP 82-146 oligomers are primarily responsible for triggering cell death. Neurons from PrP knock-out (Prnp0/0) mice were significantly less sensitive to PrP 82-146 toxicity than neurons expressing PrP. The gliotrophic effect of PrP 82-146 was determined by [methyl-3H]-thymidine incorporation in cultured astrocytes. Treatment with PrP 82-146 stimulated [methyl-3H]-thymidine uptake 3.5-fold. This activity was significantly less when the 106-126 or 127-146 regions were disrupted, indicating that PrP 82-146 amyloid activates the gliotrophic response. Prnp0/0 astrocytes were insensitive to the proliferative stimulus of PrP 82-146. These results underline the role of cerebral accumulation of abnormally folded PrP fragments and indicate that cellular PrP governs the pathogenic process.

OGT functions as a catalytic chaperone under heat stress response: a unique defense role of OGT in hyperthermia

Protein O-GlcNAcylation is proceeded by O-linked GlcNAc transferase (OGT) in nucleocytoplasm and is involved in many biological processes although its physiological role is not clearly defined. To identify the functional significance of O-GlcNAcylation, we investigated heat stress effects on protein O-GlcNAcylation. Here, we found that protein O-GlcNAcylation was significantly increased in vivo during acute heat stress in mammalian cells and simultaneously, the enhanced protein O-GlcNAcylation was closely associated with cell survival in hyperthermia. Our results demonstrate that hyperthermal cytotoxicity may considerably be facilitated under the condition of insufficient level of protein O-GlcNAcylation inside cells. Furthermore, OGT reaction might be crucial for triggering thermotolerance to recover hyperthermal sensitivity without particular induction of heat shock proteins (hsps). Thus, we propose that OGT can respond rapidly to heat stress through the enhancement of nucleocytoplasmic protein O-GlcNAcylation for a rescue from the early phase of hyperthermal cytotoxicity.

Three-dimensional biocompatible ascorbic acid-containing scaffold for bone tissue engineering

A biodegradable, biocompatible, ascorbic acid-containing three-dimensional polyurethane matrix was developed for bone tissue-engineering scaffolds. This matrix was synthesized with lysine-di-isocyanate (LDI), ascorbic acid (AA), glycerol, and polyethylene glycol (PEG). LDI-glycerol-PEG-AA prepolymer when reacted with water foamed with the liberation of CO(2) to provide a pliable, spongy urethane polymer with pore diameters of 100 to 500 microm. The LDI-glycerol-PEG-AA matrix degraded in aqueous solution and yielded lysine, glycerol, PEG, and ascorbic acid as breakdown products. The degradation products did not significantly affect the solution pH. The LDI-glycerol-PEG-AA matrix can be fabricated into diverse scaffold dimensions and the physicochemical properties of the polymer network supported in vitro cell growth. Green fluorescent protein-transgenic mouse bone marrow cells (GFP-MBMCs) attached to the polymer matrix and remained viable, and the cells became confluent cultures. Furthermore, ascorbic acid released from LDI-glycerol-PEG-AA matrix stimulated cell proliferation, type I collagen, and alkaline phosphatase synthesis in vitro. Cells grown on LDI-glycerol-PEG-AA matrix did not differ phenotypically from cells grown on tissue culture polystyrene plates as assessed by cell growth, expression of mRNA for collagen type I, and transforming growth factor beta(1). These observations suggest that AA-containing polyurethane may be useful in bone tissue-engineering applications.

Dynamic O-GlcNAc modification of nucleocytoplasmic proteins in response to stress. A survival response of mammalian cells

Cellular response to environmental, physiological, or chemical stress is key to survival following injury or disease. Here we describe a unique signaling mechanism by which cells detect and respond to stress in order to survive. A wide variety of stress stimuli rapidly increase nucleocytoplasmic protein modification by O-linked beta-N-acetylglucosamine (O-GlcNAc), an essential post-translational modification of Ser and Thr residues of metazoans. Blocking this post-translational modification, or reducing it, renders cells more sensitive to stress and results in decreased cell survival; and increasing O-GlcNAc levels protects cells. O-GlcNAc regulates both the rates and extent of the stress-induced induction of heat shock proteins, providing a molecular basis for these findings.

P0 and myelin basic protein-like immunoreactivities following ligation of the sciatic nerve in the rat

In this work we analyzed variations in the expression of MBPs and P0 in ligated sciatic nerves of young and adult rats at 3, 7, and 14 days postligation (PL), by immunohistochemistry and SDS-PAGE of isolated myelin. A protein redistribution was seen in the distal stump of ligated nerves with the appearance of immunoreactive clusters. Using the KS400 image analyzer, immunostained area values were obtained from the different nerves dissected. In adult rats, there was an increase of the immunostained area for MBP from 3 to 7 days PL, coincident with a reorganization of the marker in clusters, followed by a marked decrease at 14 days. P0 immunolabeling gave similar results without, however, a decrease of the immunostained area at the longer survival time tested. Young animals showed an acceleration in the process of protein redistribution and digestion within ligated nerves, which followed a similar pattern as that of adult animals. Analysis by electrophoresis showed a marked decrease in P0 and MBP at 7 days PL in young rats and 14 days PL in adult rats. The functional significance of protein clustering within myelin in injured nerves deserves further analysis.

N-methyl-D-aspartate-induced alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA) receptor down-regulation involves interaction of the carboxyl terminus of GluR2/3 with Pick1. Ligand-binding studies using Sindbis vectors carrying AMPA receptor decoys

The dynamics of alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA)-type glutamate receptors, as represented by their exocytosis, endocytosis and cytoskeletal linkage, has often been implicated in N-methyl-d-aspartate (NMDA)-dependent synaptic plasticity. To explore the molecular mechanisms underlying the AMPA receptor dynamics, cultured hippocampal neurons were stimulated with 100 microm NMDA, and the biochemical and pharmacological changes in the ligand binding activity of AMPA receptor complexes and its subunits, GluR1 and GluR2/3, were investigated. The NMDA treatment reduced the total amount of bound [(3)H]AMPA on the surface of the neurons but not in their total membrane fraction. This process was mimicked by a protein kinase C activator, phorbol ester, but blocked by an inhibitor of the same kinase, calphostin C. The NMDA-induced down-regulation of the ligand binding activity was also reflected by the decreased AMPA-triggered channel activity as well as by the cells' reduced immunoreactivity for GluR1. In parallel, the NMDA treatment markedly altered the interaction between the AMPA receptor subunits and their associating molecule(s); the association of PDZ molecules, including Pick1, with GluR2/3 was enhanced in a protein-kinase-C-dependent manner. Viral expression vectors carrying GluR1 and GluR2 C-terminal decoys, both fused to enhanced green fluorescent protein, were transfected into hippocampal neurons to disrupt their interactions. The overexpression of the C-terminal decoy for GluR2 specifically and significantly blocked the NMDA-triggered reduction in [(3)H]AMPA binding, whereas that for GluR1 had no effects. Co-immunoprecipitation using anti-Pick1 antibodies revealed that the overexpressed GluR2 C-terminal decoy indeed prevented Pick1 from interacting with the endogenous GluR2/3. Therefore, these observations suggest that the NMDA-induced down-regulation of the functional AMPA receptors involves the interaction between GluR2/3 subunits and Pick1.

Tetracycline affects abnormal properties of synthetic PrP peptides and PrP(Sc) in vitro

Prion diseases are characterized by the accumulation of altered forms of the prion protein (termed PrP(Sc)) in the brain. Unlike the normal protein, PrP(Sc) isoforms have a high content of beta-sheet secondary structure, are protease-resistant, and form insoluble aggregates and amyloid fibrils. Evidence indicates that they are responsible for neuropathological changes (i.e. nerve cell degeneration and glial cell activation) and transmissibility of the disease process. Here, we show that the antibiotic tetracycline: (i) binds to amyloid fibrils generated by synthetic peptides corresponding to residues 106-126 and 82-146 of human PrP; (ii) hinders assembly of these peptides into amyloid fibrils; (iii) reverts the protease resistance of PrP peptide aggregates and PrP(Sc) extracted from brain tissue of patients with Creutzfeldt-Jakob disease; (iv) prevents neuronal death and astrocyte proliferation induced by PrP peptides in vitro. NMR spectroscopy revealed several through-space interactions between aromatic protons of tetracycline and side-chain protons of Ala(117-119), Val(121-122) and Leu(125) of PrP 106-126. These properties make tetracycline a prototype of compounds with the potential of inactivating the pathogenic forms of PrP.

Influence of mutations associated with familial prion-related encephalopathies on biological activity of prion protein peptides

In transmissible spongiform encephalopathies (TSEs), an altered form of prion protein (PrP), PrPres, aggregates in amyloid fibrils and accumulates in the brain. Several point mutations of the PrP gene have been associated with the TSEs, so, to investigate how the mutations affect the biological activity of PrP, we analyzed the biological effects and chemicophysical characteristics of the peptide homologous to the wild-type and mutated sequence of PrP fragments. The mutation P102L altered the biological activity of PrP 89-106, which became neurotoxic without changing its fibrillogenic capacity. The mutation (D178N) in the PrP 169-185 strongly increased the neurotoxic activity of the native sequence. In this case, there was also a clear alteration of the structural conformation. None of the other mutations considered, including A117V, seemed to influence the biological activities of the respective peptides. These data identify new neurotoxic fragments of PrP in the mutated form and elucidate their genetic influence on the pathogenesis of TSEs.

A betaPP peptide carboxyl-terminal to Abeta is neurotoxic

Extracellular Abeta-amyloid and intraneuronal paired helical filaments (PHFs) composed of tau protein are the neuropathological hallmark of Alzheimer's disease. Abeta is a 39- to 43-residue peptide derived by cleavage of a 695- to 770-amino-acid membrane-associate glycoprotein (termed beta-protein precursor, betaPP). Following the observation that an antiserum to an epitope located between residues 713 and 723 of betaPP770 (ie, the transmembrane region of the betaPP distal to Abeta) labels PHFs and that a synthetic peptide homologous to residues 713 to 730 of betaPP770 (betaPP713-730) is highly fibrillogenic and interacts with tau in vitro, it has been hypothesized that betaPP fragments other than Abeta may feature in the pathogenesis of Alzheimer's disease concurring with neuronal degeneration. To investigate this issue, we have analyzed the effects of the exposure of primary neuronal cultures to the synthetic peptide betaPP713-730. Cultures were prepared from rat hippocampus on embryonic day 17 and incubated with the peptide at 2.5 to 30 micromol/L concentration for 1 to 4 days. Cell viability was compared with that of control cultures exposed to a scrambled sequence of the peptide. A 4-day exposure to 20 micromol/L betaPP713-730 resulted in almost complete neuronal loss, whereas no changes were observed with the scrambled peptide. Degenerating neurons showed DNA fragmentation by agarose gel electrophoresis and apoptotic changes by light and electron microscopy. These findings support the view that betaPP sequences other than Abeta may play a role in nerve cell degeneration in Alzheimer's disease.