Modulation of Aβ42 low-n oligomerization using a novel yeast reporter system

Background  

While traditional models of Alzheimer's disease focused on large fibrillar deposits of the Aβ₄₂ amyloid peptide in the brain, recent work suggests that the major pathogenic effects may be attributed to SDS-stable oligomers of Aβ₄₂. These Aβ₄₂ oligomers represent a rational target for therapeutic intervention, yet factors governing their assembly are poorly understood.     

A Cross-Species Analysis Reveals a General Role for Piezo2 in Mechanosensory Specialization of Trigeminal Ganglia from Tactile Specialist Birds

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Effects of 45-Hz magnetic fields on the functional state of the human brain

The influence of sinusoidal 45-Hz magnetic fields on the brain functions of 20 volunteers was investigated in a double-blind study using spectral analysis of EEG and measurements of Omega potentials and reaction time (RT). The field strength was 1,000 A/m (1.26 mT) and the duration of exposure was 1 h. Ten volunteers were exposed to a continuous field and ten received an intermittent exposure (1 s on/1 s off). Each person received one real and one sham exposure. One half of the volunteers got the real exposure first and the sham treatment after at least 24 h. For the rest, the sequence was inverse. The measurements of EEG, omega potentials and RT were performed before and after each exposure. Several statistically significant changes were observed, most of them after intermittent exposure. In the EEG, an increase of alpha (7.6–13.9 Hz) activity and a decrease of delta (1.5–3.9 Hz) activity were observed. β waves (14.2–20 Hz) increased in the frontal derivations as did the total power in occipital derivations. The mean and peak frequencies of EEG increased mainly in the frontal derivations. No direct effects on RT were seen. Learning to perform the RT test (decrease of RT in repeated trials), however, seemed to be affected by the exposure. The persons who received real exposure first learned more slowly than those who got sham exposure first. Further experiments are necessary to confirm the findings and for understanding the mechanisms of the effects. © 1993 Wiley-Liss. Inc.     

Specificity of prion assembly in vivo. [PSI+] and [PIN+] form separate structures in yeast

The yeast prions [PSI+] and [PIN+] are self-propagating amyloid aggregates of the Gln/Asn-rich proteins Sup35p and Rnq1p, respectively. Like the mammalian PrP prion "strains," [PSI+] and [PIN+] exist in different conformations called variants. Here, [PSI+] and [PIN+] variants were used to model in vivo interactions between co-existing heterologous amyloid aggregates. Two levels of structural organization, like those previously described for [PSI+], were demonstrated for [PIN+]. In cells with both [PSI+] and [PIN+] the two prions formed separate structures at both levels. Also, the destabilization of [PSI+] by certain [PIN+] variants was shown not to involve alterations in the [PSI+] prion size. Finally, when two variants of the same prion that have aggregates with distinct biochemical characteristics were combined in a single cell, only one aggregate type was propagated. These studies demonstrate the intracellular organization of yeast prions and provide insight into the principles of in vivo amyloid assembly.     

Biochemical and genetic methods for characterization of [PIN+] prions in yeast

The glutamine- and asparagine-rich Rnq1p protein in Saccharomyces cerevisiae can exist in the cell as a soluble monomer or in one of several aggregated, infectious, prion forms called [PIN(+)]. Interest in [PIN(+)] is heightened by its ability to promote the conversion of other proteins into a prion or an aggregated amyloid state. However, little is known about the function of Rnq1p, which makes it difficult to assay the phenotypes associated with its normal vs. prion forms. In this chapter, we describe methods used to detect [PIN(+)] and distinguish between different variations of the prion. Genetic methods are based on the ability of the [PIN(+)] prion to facilitate the appearance of another yeast prion, [PSI(+)], which has an easily detectable phenotype. Biochemical methods exploit the fact that the [PIN(+)] prion exists in the yeast cytosol in the form of large aggregates, composed of SDS-stable subparticles. Sucrose gradient centrifugation, agarose SDS electrophoresis and GFP fusions are used to distinguish between aggregates and subparticles from different [PIN(+)] variants.     

Expression of an expanded polyglutamine domain in yeast causes death with apoptotic markers

Huntington's disease is caused by specific mutations in huntingtin protein. Expansion of a polyglutamine (polyQ) repeat of huntingtin leads to protein aggregation in neurons followed by cell death with apoptotic markers. The connection between the aggregation and the degeneration of neurons is poorly understood. Here, we show that the physiological consequences of expanded polyQ domain expression in yeast are similar to those in neurons. In particular, expression of expanded polyQ in yeast causes apoptotic changes in mitochondria, caspase activation, nuclear DNA fragmentation and death. Similar to neurons, at the late stages of expression the expanded polyQ accumulates in the nuclei and seems to affect the cell cycle of yeast. Interestingly, nuclear localization of the aggregates is dependent on functional caspase Yca1. We speculate that the aggregates in the nuclei disturb the cell cycle and thus contribute to the development of the cell death process in both systems. Our data show that expression of the polyQ construct in yeast can be used to model patho-physiological effects of polyQ expansion in neurons.     

Effects of curcumin and related compounds on processes involving α-hydroxyethyl radicals

Effects of curcumin and related compounds on product formation in radiolysis of aerated and deaerated ethanol were studied. Ab initio calculations of enthalpy values relating to O-H bond dissociation and H-atom addition to > C = O bonds of the compounds under study have been performed. The obtained data allowed the conclusion that the presence of a 7-carbon chain containing conjugated > C = C < and > C = O bonds in the structures of curcumin and its analogues makes these compounds capable of inhibiting the reactions involving α-hydroxyl-containing carbon-centered radicals. This finding broadens the existing views concerning radical-regulating properties of curcuminoids, and it should be taken into account when practical use of these compounds is envisaged.     

Multiple modalities converge on a common gate to control K2P channel function

Members of the K_2P potassium channel family regulate neuronal excitability and are implicated in pain, anaesthetic responses, thermosensation, neuroprotection, and mood. Unlike other potassium channels, K_2Ps are gated by remarkably diverse stimuli that include chemical, thermal, and mechanical modalities. It has remained unclear whether the various gating inputs act through separate or common channel elements. Here, we show that protons, heat, and pressure affect activity of the prototypical, polymodal K_2P, K_2P2.1 (KCNK2/TREK‐1), at a common molecular gate that comprises elements of the pore‐forming segments and the N‐terminal end of the M4 transmembrane segment. We further demonstrate that the M4 gating element is conserved among K_2Ps and is employed regardless of whether the gating stimuli are inhibitory or activating. Our results define a unique gating mechanism shared by K_2P family members and suggest that their diverse sensory properties are achieved by coupling different molecular sensors to a conserved core gating apparatus.     

Radical-regulating and antiviral properties of ascorbic acid and its derivatives

The ability of ascorbic acid and a number of its derivatives to suppress replication of Herpes simplex virus type I was investigated in human rhabdomyosarcoma cell line. In parallel, interaction of the test compounds with carbon- and oxygen-centered radicals formed on radiolysis of hydroxyl-containing organic compounds was studied using the steady state radiolysis method. It has been shown that 2-O-glycoside of ascorbic acid, displaying marked antiviral properties against Herpes simplex virus type I, is also capable of inhibiting fragmentation and recombination reactions of α-hydroxyl-containing carbon-centered radicals while not affecting processes involving oxygen-centered radicals.