Age-Dependent Impairment of Mitochondrial Function in Primate Brain

Abstract: It has been hypothesized that some of the functional impairments associated with aging are the result of increasing oxidative damage to mitochondrial DNA that produces defects in oxidative phosphorylation. To test this hypothesis, we examined the enzymes that catalyze oxidative phosphorylation in crude mitochondrial preparations from frontoparietal cortex of 20 rhesus monkeys (5-34 years old). Samples were assayed for complex I, complex II-III, complex IV, complex V, and citrate synthase activities. When enzyme activities were corrected for citrate synthase activities (to account for variable degrees of mitochondrial enrichment), linear regression analysis demonstrated a significant negative correlation of the activities of complex I (p < 0.002) and complex IV (p < 0.03) with age but no significant change in complex II-III or complex V activities. Relative to animals 6.9 ± 0.9 years old (n = 7), the citrate synthase-corrected activity of complex I was reduced by 17% in animals 22.5 ± 0.9 years old (n = 6) (p < 0.05) and by 22% in animals 30.7 ± 0.9 years old (n = 7) (p < 0.01). Similar age-related reductions in the activities of complexes I and IV were obtained when enzyme activities were corrected for complex II-III activity. These findings show an age-associated progressive impairment of mitochondrial complex I and complex IV activities in cerebral cortices of primates.     

Exogenous induction of cerebral beta-amyloidosis in betaAPP-transgenic mice

A key commonality of most age-related neurodegenerative diseases is the accumulation of aggregation-prone proteins in the brain. Except for the prionoses, the initiation and propagation of these proteopathies in vivo remains poorly understood. In a previous study, we found that the deposition of the amyloidogenic peptide Abeta can be induced by injection of dilute extracts of Alzheimeric neocortex into the brains of Tg2576 transgenic mice overexpressing the human beta-amyloid precursor protein. The present study was undertaken to assess the pathology after long-term (12 months) incubation, and to clarify the distinctive anatomical distribution of seeded Abeta-immunoreactivity. All mice were injected at 3 months of age; 5 months later, as expected, Abeta deposits were concentrated mostly in the injected hemisphere. After 12 months, abundant, transgene-derived Abeta deposits were present bilaterally in the forebrain, but plaque load was still clearly greater in the extract-injected hemisphere. There was also evidence of tau hyperphosphorylation in axons of the corpus callosum that had been injured by the injection, most prominently in transgenic mice, but also, to a lesser degree, in non-transgenic mice. Five months following injection of AD-extract, an isolated cluster of Abeta-immunoreactive microglia was sometimes evident in the ipsilateral entorhinal cortex; the strong innervation of the hippocampus by entorhinal cortical neurons suggests the possible spread of seeded pathology from the injection site via neuronal transport mechanisms. Finally, using India Ink to map the local dispersion of injectate, we found that Abeta induction is especially potent in places where the injectate is sequestered. The AD-seeding model can illuminate the emergence and spread of cerebral beta-amyloidosis and tau hyperphosphorylation, and thus could enhance our understanding of AD and its pathogenic commonalties with other cerebral proteopathies.     

Corruption and Spread of Pathogenic Proteins in Neurodegenerative Diseases

With advancing age, the brain becomes increasingly susceptible to neurodegenerative diseases, most of which are characterized by the misfolding and errant aggregation of certain proteins. The induction of aggregation involves a crystallization-like seeding mechanism by which a specific protein is structurally corrupted by its misfolded conformer. The latest research indicates that, once formed, proteopathic seeds can spread from one locale to another via cellular uptake, transport, and release. Impeding this process could represent a unified therapeutic strategy for slowing the progression of a wide range of currently intractable disorders.     

Domain architecture and biochemical characterization of vertebrate Mcm10

Mcm10 plays a key role in initiation and elongation of eukaryotic chromosomal DNA replication. As a first step to better understand the structure and function of vertebrate Mcm10, we have determined the structural architecture of Xenopus laevis Mcm10 (xMcm10) and characterized each domain biochemically. Limited proteolytic digestion of the full-length protein revealed N-terminal-, internal (ID)-, and C-terminal (CTD)-structured domains. Analytical ultracentrifugation revealed that xMcm10 self-associates and that the N-terminal domain forms homodimeric assemblies. DNA binding activity of xMcm10 was mapped to the ID and CTD, each of which binds to single- and double-stranded DNA with low micromolar affinity. The structural integrity of xMcm10-ID and CTD is dependent on the presence of bound zinc, which was experimentally verified by atomic absorption spectroscopy and proteolysis protection assays. The ID and CTD also bind independently to the N-terminal 323 residues of the p180 subunit of DNA polymerase alpha-primase. We propose that the modularity of the protein architecture, with discrete domains for dimerization and for binding to DNA and DNA polymerase alpha-primase, provides an effective means for coordinating the biochemical activities of Mcm10 within the replisome.     

The synthesis and structure–activity relationship of substituted N-phenyl anthranilic acid analogs as amyloid aggregation inhibitors

It is believed that β-amyloid aggregation is an important event in the development of Alzheimer’s disease. In the course of our studies to identify β-amyloid aggregation inhibitors, a series of N-phenyl anthranilic acid analogs were synthesized and studied for β-amyloid inhibition activity. The synthesis, structure–activity relationship, and in vivo activity of these analogs are discussed.     

Heparin activates PKR by inducing dimerization

Protein kinase R (PKR) is an interferon-induced kinase that plays a pivotal role in the innate immunity pathway. PKR is activated to undergo autophosphorylation upon binding to double-stranded RNAs or RNAs that contain duplex regions. Activated PKR phosphorylates the α subunit of eukaryotic initiation factor 2, thereby inhibiting protein synthesis. PKR is also activated by heparin, a highly sulfated glycosaminoglycan. We have used biophysical methods to define the mechanism of PKR activation by heparin. Heparins as short as hexasaccharide bind strongly to PKR and activate autophosphorylation. In contrast to double-stranded RNA, heparin activates PKR by binding to the kinase domain. Analytical ultracentrifugation measurements support a thermodynamic linkage model where heparin binding allosterically enhances PKR dimerization, thereby activating the kinase. These results indicate that PKR can be activated by small molecules and represents a viable target for the development of novel antiviral agents.     

Volatile Compounds of Viola odorata Absolutes: Identification of Odorant Active Markers to Distinguish Plants Originating from France and Egypt

Absolutes isolated from Viola odorata leaves, valuable materials for the flavor and fragrance industry, were studied. Violets are mainly cultivated in France and Egypt and extracted locally. The absolutes of the two origins showed different olfactory profiles both in top and heart notes, as evidenced by sensory analysis. The aims of this study were i) to characterize the volatile compounds, ii) to determine the odorant‐active ones, and iii) to identify some markers of the plant origin. Two complementary analytical methods were used for these purposes, i.e., headspace solid‐phase microextraction (HS‐SPME) using different fiber coatings followed by GC/MS analysis and gas chromatography – olfactometry/mass spectrometry (GC‐O/MS) applied to violet leaf extracts. From a total of 70 identified compounds, 61 have never been reported so far for this species, 17 compounds were characterized by both techniques (with seven among them known from the literature), 23 compounds were solely identified by HS‐SPME GC/MS (among them only two being already mentioned as components of violet absolutes in the literature), and, finally, 30 compounds were only identified by GC‐O/MS. According to the HS‐SPME GC/MS analyses, ethyl hexanoate and (2E,6Z)‐nona‐2,6‐dienol were specific volatile compounds of the sample with French origin, while (E,E)‐hepta‐2,4‐dienal, hexanoic acid, limonene, tridecane, and eugenol were specific of the samples with Egyptian origin. Additional compounds that were not detected by HS‐SPME GC/MS analysis were revealed by GC‐O analyses, some of them being markers of origin. Pent‐1‐en‐3‐ol, 3‐methylbut‐2‐enal, 2‐methoxy‐3‐(1‐methylethyl)pyrazine, 4‐ethylbenzaldehyde, β‐phenethyl formate, and 2‐methoxy‐3‐(2‐methylpropyl)pyrazine revealed to be odorant markers of the French sample, whereas cis‐rose oxide, trans‐rose oxide, and 3,5,5‐trimethylcyclohex‐2‐enone were odorant markers of the Egyptian samples.     

Glycan Specificity of the Vibrio vulnificus Hemolysin Lectin Outlines Evolutionary History of Membrane Targeting by a Toxin Family

Pore-forming toxins (PFTs) are a class of pathogen-secreted molecules that oligomerize to form transmembrane channels in cellular membranes. Determining the mechanism for how PFTs bind membranes is important in understanding their role in disease and for developing possible ways to block their action. Vibrio vulnificus, an aquatic pathogen responsible for severe food poisoning and septicemia in humans, secretes a PFT called V. vulnificus hemolysin (VVH), which contains a single C-terminal targeting domain predicted to resemble a β-trefoil lectin fold. In order to understand the selectivity of the lectin for glycan motifs, we expressed the isolated VVH β-trefoil domain and used glycan-chip screening to identify that VVH displays a preference for terminal galactosyl groups including N-acetyl-d-galactosamine and N-acetyl-d-lactosamine. The X-ray crystal structure of the VVH lectin domain solved to 2.0 Å resolution reveals a heptameric ring arrangement similar to the oligomeric form of the related, but inactive, lectin from Vibrio cholerae cytolysin. Structures bound to glycerol, N-acetyl-d-galactosamine, and N-acetyl-d-lactosamine outline a common and versatile mode of recognition allowing VVH to target a wide variety of cell-surface ligands. Sequence analysis in light of our structural and functional data suggests that VVH may represent an earlier step in the evolution of Vibrio PFTs.     

A distinct subfraction of Aβ is responsible for the high‐affinity Pittsburgh compound B‐binding site in Alzheimer's disease brain

The positron emission tomography (PET) ligand ¹¹C‐labeled Pittsburgh compound B (PIB) is used to image β‐amyloid (Aβ) deposits in the brains of living subjects with the intent of detecting early stages of Alzheimer's disease (AD). However, deposits of human‐sequence Aβ in amyloid precursor protein transgenic mice and non‐human primates bind very little PIB. The high stoichiometry of PIB:Aβ binding in human AD suggests that the PIB‐binding site may represent a particularly pathogenic entity and/or report local pathologic conditions. In this study, ³H‐PIB was employed to track purification of the PIB‐binding site in > 90% yield from frontal cortical tissue of autopsy‐diagnosed AD subjects. The purified PIB‐binding site comprises a distinct, highly insoluble subfraction of the Aβ in AD brain with low buoyant density because of the sodium dodecyl sulfate‐resistant association with a limited subset of brain proteins and lipids with physical properties similar to lipid rafts and to a ganglioside:Aβ complex in AD and Down syndrome brain. Both the protein and lipid components are required for PIB binding. Elucidation of human‐specific biological components and pathways will be important in guiding improvement of the animal models for AD and in identifying new potential therapeutic avenues.

     

Earthworms near leprosy patients' homes are negative for acid-fast bacilli by fite stain,providing no link between leprous armadillos (Dasypus novemcinctus) and human leprosy

Enzootic leprosy has been recognized in armadillos in Louisiana since 1975. Contact with armadillos is being assessed as a risk factor for leprosy in three white women, lifelong residents of separate rural areas in northern Louisiana, which is a region without endemic leprosy. None has had any known exposure to human leprosy. Each was aware of armadillos (Dasypus novemcinctus) near or under her home for decades. In considering Possible environmental sources forMycobacterium leprae, we observed that all three had earthworm growth areas for fishing bait where soil was kept moist near their homes. The worms attracted armadillos. Since armadillos subsist on worms, grubs, and insects and because of the common feature of a worm farm near each home, we reasoned that earthworms might containM. leprae and be part of a cycle involving the armadillo and human beings. Worms from each home worm farm were studied. One site was sampled twice at patient 1's home, five sites were sampled once at patient 2's home, and three sites were sampled once at patient 3's home. A sample consisted of 3–4 worms, which were washed, purged, fixed live in 10% formalin, embedded in paraffin, sectioned, and stained with the Fite stain. Each was sagittally sectioned and examined by three independent observers. No acid-fast bacilli or other acid-fast structures were identified. We conclude that it is unlikely that earthworms are an environmental source or reservoir ofM. leprae.