Characterization of nucleosome positioning in hepadnaviral covalently closed circular DNA minichromosomes.

Hepadnaviral covalently closed circular DNA (cccDNA) exists as an episomal minichromosome in the nucleus of virus-infected hepatocytes, and serves as the transcriptional template for the synthesis of viral mRNAs. To obtain insight on the structure of hepadnaviral cccDNA minichromosomes, we utilized ducks infected with the duck hepatitis B virus (DHBV) as a model and determined the in vivo nucleosome distribution pattern on viral cccDNA by the micrococcal nuclease (MNase) mapping and genome-wide PCR amplification of isolated mononucleosomal DHBV DNA. Several nucleosome-protected sites in a region of the DHBV genome [nucleotides (nt) 2000 to 2700], known to harbor various cis transcription regulatory elements, were consistently identified in all DHBV-positive liver samples. In addition, we observed other nucleosome protection sites in DHBV minichromosomes that may vary among individual ducks, but the pattern of MNase mapping in those regions is transmittable from the adult ducks to the newly infected ducklings. These results imply that the nucleosomes along viral cccDNA in the minichromosomes are not random but sequence-specifically positioned. Furthermore, we showed in ducklings that a significant portion of cccDNA possesses a few negative superhelical turns, suggesting the presence of intermediates of viral minichromosomes assembled in the liver, where dynamic hepatocyte growth and cccDNA formation occur. This study supplies the initial framework for the understanding of the overall complete structure of hepadnaviral cccDNA minichromosomes.

The effect of an NgR1 antagonist on the neuroprotection of cortical axons after cortical infarction in rats.

We investigated the effect of the soluble Nogo66 receptor (sNgR-Fc) on the protection of cortical axons after cortical infarction in rats. The cortical infarction was induced by photothrombotic cortical injury (PCI) in Sprague-Dawley rats, after which sNgR-Fc was injected into the lateral ventricle. The ipsilesional cortices were harvested for analyses using histochemical and transmission-electron microscope techniques. The involved signaling pathways, which include RhoA, JNK, c-JUN and ATF-2, were detected by Western blot. Serious pathologies were found in the brains of the rats after injury, including edemas in the axoplasms of axons that have no medulla sheath and a thickening or shrinkage in the sheath of the axons that have medulla sheathes. However, these pathologies improved after sNgR-Fc treatment. The levels of GTP-RhoA, p-JNK, p-c-JUN and p-ATF-2 in the PCI group were increased when compared with their levels in the sham-operation group (P < 0.05), and animals receiving the sNgR-Fc treatment showed lower expression levels of these proteins when compared with the sham-operation group (P < 0.05). Our results suggest that sNgR-Fc can alleviate the pathological changes of axons following cortical infarction via decreasing the activation of RhoA/JNK signaling pathways.

Soluble NgR fusion protein modulates the proliferation of neural progenitor cells via the Notch pathway.

NogoA, myelin-associated glycoprotein (MAG) and oligodendrocyte myelin glycoprotein are CNS myelin molecules that bind to the neuronal Nogo-66 receptor (NgR) and inhibit axon growth. The NgR antagonist, soluble NgR1-Fc protein (sNgR-Fc), facilitates axon regeneration by neutralizing the inhibitory effects of myelin proteins in experimental models of CNS injury. Here we aim to investigate the effect of sNgR-Fc on the proliferation of neural progenitor cells (NPCs). The hippocampus cells of embryonic rats were isolated and cultured in vitro. The expression of nestin, ßIII-Tubulin, GFAP and Nogo-A on these cells was observed using immunocytochemistry. In order to investigate the effect on proliferation of NPCs, sNgR-Fc, MAG-Fc chimera and Notch1 blocker were added respectively. The total cell number for the proliferated NPCs was counted. BrdU was applied and the rate of proliferating cells was examined. The level of Notch1 was analyzed using Western blotting. We identified that NogoA is expressed in NPCs. sNgR-Fc significantly enhanced the proliferation of NPCs in vitro as indicated by BrdU labeling and total cell count. This proliferation effect was abolished by the administration of MAG suggesting specificity. In addition, we demonstrate that sNgR-Fc is a potent activator for Notch1 and Notch1 antagonist reversed the effect of sNgR-Fc on NPC proliferation. Our results suggest that sNgR-Fc may modulate Nogo activity to induce NPC proliferation via the Notch pathway.

Blockade of Nogo receptor ligands promotes functional regeneration of sensory axons after dorsal root crush.

A major impediment for regeneration of axons within the CNS is the presence of multiple inhibitory factors associated with myelin. Three of these factors bind to the Nogo receptor, NgR, which is expressed on axons. Administration of exogenous blockers of NgR or NgR ligands promotes the regeneration of descending axonal projections after spinal cord hemisection. A more detailed analysis of CNS regeneration can be made by examining the growth of specific classes of sensory axons into the spinal cord after dorsal root crush injury. In this study, we assessed whether administration of a soluble peptide fragment of the NgR (sNgR) that binds to and blocks all three NgR ligands can promote regeneration after brachial dorsal root crush in adult rats. Intraventricular infusion of sNgR for 1 month results in extensive regrowth of myelinated sensory axons into the white and gray matter of the dorsal spinal cord, but unmyelinated sensory afferents do not regenerate. In concert with the anatomical growth of sensory axons into the cord, there is a gradual restoration of synaptic function in the denervated region, as revealed by extracellular microelectrode recordings from the spinal gray matter in response to stimulation of peripheral nerves. These positive synaptic responses are correlated with substantial improvements in use of the forelimb, as assessed by paw preference, paw withdrawal to tactile stimuli and the ability to grasp. These results suggest that sNgR may be a potential therapy for restoring sensory function after injuries to sensory roots.

Resolution of disulfide heterogeneity in Nogo receptor I fusion proteins by molecular engineering.

NgRI (Nogo-66 receptor) is part of a signalling complex that inhibits axon regeneration in the central nervous system. Truncated soluble versions of NgRI have been used successfully to promote axon regeneration in animal models of spinal-cord injury, raising interest in this protein as a potential therapeutic target. The LRR (leucine-rich repeat) regions in NgRI are flanked by N- and C-terminal disulfide-containing 'cap' domains (LRRNT and LRRCT respectively). In the present work we show that, although functionally active, the NgRI(310)-Fc fusion protein contains mislinked and heterogeneous disulfide patterns in the LRRCT domain, and we report the generation of a series of variant molecules specifically designed to prevent this heterogeneity. Using these variants we explored the effects of modifying the NgRI truncation site or the spacing between the NgRI and Fc domains, or replacing cysteines within the NgRI or IgG hinge regions. One variant, which incorporates replacements of Cys²66 and Cys³°9 with alanine residues, completely eliminated disulfide scrambling while maintaining functional in vitro and in vivo efficacy. This modified NgRI-Fc molecule represents a significantly improved candidate for further pharmaceutical development, and may serve as a useful model for the optimization of other IgG fusion proteins made from LRR proteins.

Synaptic degeneration of retinal ganglion cells in a rat ocular hypertension glaucoma model.

AIMS: Glaucoma is a common neurodegenerative disease that affects retinal ganglion cells (RGCs) and their axons. Little is known of the synaptic degeneration involved in the pathophysiology of glaucoma. Here we used an experimental ocular hypertension model in rats to investigate this issue. METHODS: Elevated intraocular pressure (IOP) was induced by laser coagulation of the episcleral and limbal veins. RGCs were retrogradely labeled with Fluoro-Gold (FG). The c-fos protein was used as a neuronal connectivity marker. Expression of c-fos in the retinas was investigated by immunohistochemistry at 5 days and 2 weeks after the induction of ocular hypertension. Both surviving RGCs as revealed by retrograde FG-labeled and c-fos-labeled RGCs were counted. RESULTS: The c-fos protein was mainly expressed in the nuclei and nucleoli of cells in the ganglion cell layer and inner nuclear layer in the normal retina. We also confirmed that c-fos was also expressed in the nuclei and nucleoli of RGCs retrogradely labeled with FG. There was no significant RGC loss at 5 days but about 13% RGC loss at 2 weeks after the induction of ocular hypertension. The number of RGCs expressing c-fos was significantly lower in the experimental animals at both 5 days and 2 weeks than normal. CONCLUSION: Our study suggests that there is synaptic disconnection for RGCs after ocular hypertension and it may precede the cell death in the early stage. It may provide insight into novel therapeutic strategies to slow the progress of glaucoma.

Subcutaneous Nogo receptor removes brain amyloid-beta and improves spatial memory in Alzheimer's transgenic mice.

The production and aggregation of cerebral amyloid-beta (Abeta) peptide are thought to play a causal role in Alzheimer's disease (AD). Previously, we found that the Nogo-66 receptor (NgR) interacts physically with both Abeta and the amyloid precursor protein (APP). The inverse correlation of Abeta levels with NgR levels within the brain may reflect regulation of Abeta production and/or Abeta clearance. Here, we assess the potential therapeutic benefit of peripheral NgR-mediated Abeta clearance in APPswe/PSEN-1deltaE9 transgenic mice. Through site-directed mutagenesis, we demonstrate that the central 15-28 aa of Abeta associate with specific surface-accessible patches on the leucine-rich repeat concave side of the solenoid structure of NgR. In transgenic mice, subcutaneous NgR(310)ecto-Fc treatment reduces brain Abeta plaque load while increasing the relative levels of serum Abeta. These changes in Abeta are correlated with improved spatial memory in the radial arm water maze. The benefits of peripheral NgR administration are evident when therapy is initiated after disease onset. Thus, the peripheral association of NgR(310)ecto-Fc with central Abeta residues provides an effective therapeutic approach for AD.

Alzheimer precursor protein interaction with the Nogo-66 receptor reduces amyloid-beta plaque deposition.

Pathophysiologic hypotheses for Alzheimer's disease (AD) are centered on the role of the amyloid plaque Abeta peptide and the mechanism of its derivation from the amyloid precursor protein (APP). As part of the disease process, an aberrant axonal sprouting response is known to occur near Abeta deposits. A Nogo to Nogo-66 receptor (NgR) pathway contributes to determining the ability of adult CNS axons to extend after traumatic injuries. Here, we consider the potential role of NgR mechanisms in AD. Both Nogo and NgR are mislocalized in AD brain samples. APP physically associates with the NgR. Overexpression of NgR decreases Abeta production in neuroblastoma culture, and targeted disruption of NgR expression increases transgenic mouse brain Abeta levels, Abeta plaque deposition, and dystrophic neurites. Infusion of a soluble NgR fragment reduces Abeta levels, amyloid plaque deposits, and dystrophic neurites in a mouse transgenic AD model. Changes in NgR level produce parallel changes in secreted APPalpha and Abeta, implicating NgR as a blocker of secretase processing of APP. The NgR provides a novel site for modifying the course of AD and highlights the role of axonal dysfunction in the disease.

Consistent immunohistochemical detection of intracellular beta-amyloid42 in pyramidal neurons of Alzheimer's disease entorhinal cortex.

We compared the effects of three pretreatment immunohistochemical techniques (no pretreatment, pepsin predigestion and heat pretreatment (HEAT)) for detecting intracellular beta-amyloid42 (Abeta42) in pyramidal neurons of formalin-fixed Alzheimer's disease (AD) cortices (n = 25). Although all three protocols immunostained Abeta42 in amyloid plaques using four commercially-obtained Abeta42 specific antibodies, only the HEAT protocol consistently detected prominent intracellular Abeta42 in pyramidal neurons. This suggests that the Abeta42 present in amyloid plaques may be structurally distinct from that located within the neurons perhaps due to differential binding proteins coupling or a consequence of formalin fixation. Detection of an abundant intracellular Abeta42 in neurons may provide alternate explanations for the origin of dense-core amyloid plaques in AD cortices other than the conventional chronic extracellular Abeta42 deposition hypothesis.

Sink hypothesis and therapeutic strategies for attenuating Abeta levels.

Amyloid ß (Aß) plaque, comprised mainly by Aß peptides, is an important pathology of Alzheimer's brains. Major efforts have been devoted to targeting this neurotoxic Aß peptide for discovering disease-modifying treatments for Alzheimer's disease. Inasmuch as Aß is found in both the brain and the periphery, it is hypothesized that there is some form of equilibrium for the Aß in the brain and the periphery such that Aß can be transported across the blood-brain barrier. By modulating the periphery Aß levels, it is predicted that the brain Aß levels will undergo concomitant changes, forming the basis of the "sink hypothesis" for Aß lowering strategies. In this review, the significance and implication of this sink hypothesis as well as how the sink hypothesis may contribute to the recent Aß-based drug discovery in AD are discussed. Ultimately, the validity of the sink hypothesis will be resolved when the appropriate Aß agents are being tested in the clinic.

Soluble Nogo-66 receptor prevents synaptic dysfunction and rescues retinal ganglion cell loss in chronic glaucoma.

PURPOSE: Myelin inhibitory proteins inhibit axon growth and synaptic function by binding to the Nogo-66 receptor (NgR)1 in the central nervous system. Glaucoma is a progressive neuropathy characterized by loss of vision as a result of retinal ganglion cell (RGC) death. Synaptic degeneration is thought to be an early pathology of neurodegeneration in glaucoma and precedes RGC loss. The authors aimed to examine whether the NgR1 antagonist promotes synaptic recovery and RGC survival in glaucoma. METHODS: Experimental ocular hypertension model was induced in adult rats with laser coagulation of the episcleral and limbal veins. NgR1 antagonist, soluble NgR1 (sNgR-Fc) was administrated to examine their effect on synaptic recovery and RGC survival. Expression of c-Fos, a neuronal connectivity marker, in the retinas was investigated using immunohistochemistry. RESULTS: NgR1 was expressed in RGCs and upregulated after intraocular pressure elevation. Treatment with sNgR-Fc significantly reduced RGC loss at 2 and 4 weeks after the induction of ocular hypertension and also promoted RGC survival after optic nerve transection. There was no RGC loss at 5 days but there was significant synaptic degeneration as measured by c-Fos. Administration of sNgR-Fc attenuated synaptic degeneration at 5 days, and at 2 and 4 weeks. CONCLUSIONS: These data suggest that synaptic degeneration may be an initial molecular mechanism for neurodegeneration in glaucoma and appropriate NgR1 antagonism may delay the progression of the disease.

Disulfide structure of the leucine-rich repeat C-terminal cap and C-terminal stalk region of Nogo-66 receptor.

Nogo-66 receptor (NgR1) is a leucine-rich repeat (LRR) protein that forms part of a signaling complex modulating axon regeneration. Previous studies have shown that the entire LRR region of NgR1, including the C-terminal cap of the LRR, LRRCT, is needed for ligand binding, and that the adjacent C-terminal region (CT stalk) of the NgR1 contributes to interaction with its coreceptors. To provide structure-based information for these interactions, we analyzed the disulfide structure of full-length NgR1. Our analysis revealed a novel disulfide structure in the C-terminal region of the NgR1, wherein the two Cys residues, Cys-335 and Cys-336, in the CT stalk are disulfide-linked to Cys-266 and Cys-309 in the LRRCT region: Cys-266 is linked to Cys-335, and Cys-309 to Cys-336. The other two Cys residues, Cys-264 and Cys-287, in the LRRCT region are disulfide-linked to each other. The analysis also showed that Cys-419 and Cys-429, in the CT stalk region, are linked to each other by a disulfide bond. Although published crystal structures of a recombinant fragment of NgR1 had revealed a disulfide linkage between Cys-266 and Cys-309 in the LRRCT region and we verified its presence in the corresponding fragment, this is artificially caused by the truncation of the protein, since this linkage was not detected in intact NgR1 or a slightly larger fragment containing Cys-335 and Cys-336. A structural model of the LRRCT with extended residues 311-344 from the CT stalk region is proposed, and its function in coreceptor binding is discussed.

Differential physiologic responses of alpha7 nicotinic acetylcholine receptors to beta-amyloid1-40 and beta-amyloid1-42.

The beta-amyloid peptides (Abeta), Abeta(1-40) and Abeta(1-42), have been implicated in Alzheimer's disease (AD) pathology. Although Abeta(1-42) is generally considered to be the pathological peptide in AD, both Abeta(1-40) and Abeta(1-42) have been used in a variety of experimental models without discrimination. Here we show that monomeric or oligomeric forms of the two Abeta peptides, when interact with the neuronal cation channel, alpha7 nicotinic acetylcholine receptors (alpha7nAChR), would result in distinct physiologic responses as measured by acetylcholine release and calcium influx experiments. While Abeta(1-42) effectively attenuated these alpha7nAChR-dependent physiology to an extent that was apparently irreversible, Abeta(1-40) showed a lower inhibitory activity that could be restored upon washings with physiologic buffers or treatment with alpha7nAChR antagonists. Our data suggest a clear pharmacological distinction between Abeta(1-40) and Abeta(1-42).

Alpha 7 nicotinic acetylcholine receptors mediate beta-amyloid peptide-induced tau protein phosphorylation.

The Alzheimer's disease pathogenic peptide, beta-amyloid42 (A beta 42), induces tau protein phosphorylation. Because hyperphosphorylated tau is a consistent component of neurofibrillary tangles, a pathological hallmark of Alzheimer's disease, we investigated the signaling molecules involved in A beta 42-induced tau phosphorylation. We show that A beta 42 elicited rapid and reversible tau protein phosphorylation on three proline-directed sites (Ser-202, Thr-181, and Thr-231) in systems enriched in alpha 7 nicotinic acetylcholine receptors (alpha 7nAChR) including serum-deprived human SK-N-MC neuroblastoma cells and hippocampal synaptosomes. Although alpha 7nAChR agonists induced similar phosphorylation, pretreatment with antisense-alpha 7nAChR oligonucleotides (in cells) or alpha 7nAChR antagonists (in cells and synaptosomes) attenuated A beta-induced tau phosphorylation. Western analyses showed that the mitogen-activated kinase cascade proteins, ERKs and c-Jun N-terminal kinase (JNK-1), were concomitantly activated by A beta 42, and their respective kinase inhibitors suppressed A beta-induced tau phosphorylation. More importantly, recombinant-activated ERKs and JNK-1 could differentially phosphorylate tau protein in vitro. Thus, the alpha 7nAChR may mediate A beta-induced tau protein phosphorylation via ERKs and JNK-1.

Synthesis of (-)-5,8-dihydroxy-3R-methyl-2R-(dipropylamino)-1,2,3,4-tetrahydronaphthalene: an inhibitor of beta-amyloid(1-42) aggregation.

A concise synthesis of the beta-amyloid(1-42 )aggregation inhibitor (-)-5,8-dihydroxy-3R-methyl-2R-(dipropylamino)-1,2,3,4-tetrahydronaphthalene [(-)-2] has been developed. The key step is a regio- and diastereoselective hydroboration-amination sequence to convert alkene into amine. Enantiomeric resolution was achieved by recrystallization of amine as the dibenzoyl-D-tartaric acid salt. Hydroquinone is a potent inhibitor of the fibrillar aggregation of beta-amyloid as determined in two different assay systems.

2,3-Diaryl-5-anilino[1,2,4]thiadiazoles as melanocortin MC4 receptor agonists and their effects on feeding behavior in rats.

The melanocortin-4 receptor (MC4) modulates physiological functions such as feeding behavior, nerve regeneration, and drug addiction. Using a high throughput screen based on (125)I-NDP-MSH binding to the human MC4 receptor, we discovered 2,3-diaryl-5-anilino[1,2,4]thiadiazoles 3 as potent and selective MC4 receptor agonists. Through SAR development on the three attached aryl rings, we improved the binding affinity from 174 nM to 4.4 nM IC(50). When delivered intraperitoneally, compounds 3a, 3b, and 3c induced significant inhibition of food intake in a fasting-induced feeding model in rats. When delivered orally, these compounds lost activity, mainly due to rapid metabolism to inactive imidoylthiourea reduction products.

A neutralizing anti-Nogo66 receptor monoclonal antibody reverses inhibition of neurite outgrowth by central nervous system myelin.

The Nogo66 receptor (NgR1) is a neuronal, leucine-rich repeat (LRR) protein that binds three central nervous system (CNS) myelin proteins, Nogo, myelin-associated glycoprotein, and oligodendrocyte myelin glycoprotein, and mediates their inhibitory effects on neurite growth. Although the LRR domains on NgR1 are necessary for binding to the myelin proteins, the exact epitope(s) involved in ligand binding is unclear. Here we report the generation and detailed characterization of an anti-NgR1 monoclonal antibody, 7E11. The 7E11 monoclonal antibody blocks Nogo, myelin-associated glycoprotein, and oligodendrocyte myelin glycoprotein binding to NgR1 with IC50 values of 120, 14, and 4.5 nm, respectively, and effectively promotes neurite outgrowth of P3 rat dorsal root ganglia neurons cultured on a CNS myelin substrate. Further, we have defined the molecular epitope of 7E11 to be DNAQLR located in the third LRR domain of rat NgR1. Our data demonstrate that anti-NgR1 antibodies recognizing this epitope, such as 7E11, can neutralize CNS myelin-dependent inhibition of neurite outgrowth. Thus, specific anti-NgR1 antibodies may represent a useful therapeutic approach for promoting CNS repair after injury.