Can Creutzfeldt-Jakob disease unravel the mysteries of Alzheimer?

Recent studies on iatrogenic Creutzfeldt-Jakob disease (CJD) raised concerns that one of the hallmark lesions of Alzheimer disease (AD), amyloid-β (Aβ), may be transmitted from human-to-human. The neuropathology of AD-related lesions is complex. Therefore, many aspects need to be considered in deciding on this issue. Observations of recent studies can be summarized as follows: 1) The frequency of iatrogenic CJD cases with parencyhmal and vascular Aβ deposits is statistically higher than expected; 2) The morphology and distribution of Aβ deposition may show distinct features; 3) The pituitary and the dura mater themselves may serve as potential sources of Aβ seeds; 4) Cadaveric dura mater from 2 examined cases shows Aβ deposition; and 5) There is a lack of evidence that the clinical phenotype of AD appears following the application of cadaveric pituitary hormone or dura mater transplantation. These studies support the notion that neurodegenerative diseases have common features regarding propagation of disease-associated proteins as seeds. However, until further evidence emerges, prions of transmissible spongiform encephalopathies are the only neurodegenerative disease-related proteins proven to propagate clinicopathological phenotypes.     

Modulation of excitatory neurotransmission by neuronal/glial signalling molecules: interplay between purinergic and glutamatergic systems

Glutamate is the main excitatory neurotransmitter of the central nervous system (CNS), released both from neurons and glial cells. Acting via ionotropic (NMDA, AMPA, kainate) and metabotropic glutamate receptors, it is critically involved in essential regulatory functions. Disturbances of glutamatergic neurotransmission can be detected in cognitive and neurodegenerative disorders. This paper summarizes the present knowledge on the modulation of glutamate-mediated responses in the CNS. Emphasis will be put on NMDA receptor channels, which are essential executive and integrative elements of the glutamatergic system. This receptor is crucial for proper functioning of neuronal circuits; its hypofunction or overactivation can result in neuronal disturbances and neurotoxicity. Somewhat surprisingly, NMDA receptors are not widely targeted by pharmacotherapy in clinics; their robust activation or inhibition seems to be desirable only in exceptional cases. However, their fine-tuning might provide a promising manipulation to optimize the activity of the glutamatergic system and to restore proper CNS function. This orchestration utilizes several neuromodulators. Besides the classical ones such as dopamine, novel candidates emerged in the last two decades. The purinergic system is a promising possibility to optimize the activity of the glutamatergic system. It exerts not only direct and indirect influences on NMDA receptors but, by modulating glutamatergic transmission, also plays an important role in glia-neuron communication. These purinergic functions will be illustrated mostly by depicting the modulatory role of the purinergic system on glutamatergic transmission in the prefrontal cortex, a CNS area important for attention, memory and learning.     

Anti-cancer activities of cytokinin ribosides

Phytochemistry Reviews - Cytokinins are plant hormones and play essential roles in regulating plant growth and development. They also have diverse pharmacological effects in animals and humans....     

Membrane fusogenic lysine type lipid assemblies possess enhanced NLRP3 inflammasome activation potency

Lysine (K) type cationic lipid with a propyl spacer and ditetradecyl hydrophobic moieties composing liposomes, K3C14, previously studied for gene delivery, were reported to activate the NLRP3 inflammasomes in human macrophages via the conventional phagolysosomal pathway. In this study, K3C16, a propyl spacer bearing lysine type lipids with dihexadecyl moieties (an extension of two hydrocarbon tail length) were compared with K3C14 as liposomes. Such a small change in tail length did not alter the physical properties such as size distribution, zeta potential and polydispersity index (PDI). The NLRP3 activation potency of K3C16 was shown to be 1.5-fold higher. Yet, the toxicity was minimal, whereas K3C14 has shown to cause significant cell death after 24 h incubation. Even in the presence of endocytosis inhibitors, cytochalasin D or dynasore, K3C16 continued to activate the NLRP3 inflammasomes and to induce IL-1β release. To our surprise, K3C16 liposomes were confirmed to fuse with the plasma membrane of human macrophages and CHO-K1 cells. It is demonstrated that the change in hydrophobic tail length by two hydrocarbons drastically changed a cellular entry route and potency in activating the NLRP3 inflammasomes.     

Myoblast proliferation and syncytial fusion both depend on connexin43 function in transfected skeletal muscle primary cultures

Muscles are formed by fusion of individual postmitotic myoblasts to form multinucleated syncytial myotubes. The process requires a well-coordinated transition from proliferation, through migratory alignment and cycle exit, to breakdown of apposed membranes. Connexin43 protein and cell-cycle inhibitor levels are correlated, and gap junction blockers can delay muscle regeneration, so a coordinating role for gap junctions has been proposed. Here, wild-type and dominant-negative connexin43 variants (wtCx43, dnCx43) were introduced into rat myoblasts in primary culture through pIRES-eGFP constructs that made transfected cells fluoresce. GFP-positive cells and vitally-stained nuclei were counted on successive days to reveal differences in proliferation, and myotubes were counted to reveal differences in fusion. Individual transfected cells were injected with Cascade Blue, which permeates gap junctions, mixed with FITC-dextran, which requires cytoplasmic continuity to enter neighbouring cells. Myoblasts transfected with wtCx43 showed more gap-junctional coupling than GFP-only controls, began fusion sooner as judged by the incidence of cytoplasmic coupling, and formed more myotubes. Myoblasts transfected with dnCx43 remained proliferative for longer than either GFP-only or wtCx43 myoblasts, showed less coupling, and underwent little fusion into myotubes. These results highlight the critical role of gap-junctional coupling in myotube formation.     

Sequestration revisited: integrating traditional electron microscopy, de novo assembly and new results

Electron microscopy analysis of the autophagic sequestration membrane (SM) in various metazoan cell types after different fixation methods shows that: (1) the growing SM cannot derive from preformed rough surfaced endoplasmic reticulum (RER) membranes by transformation; (2) the empty cleft between the two layers of the SM after aldehyde fixation is an artifact of sample preparation; (3) the SM emerges from and grows de novo in cytoplasmic areas where membranous precursors cannot be identified by traditional electron microscopy; (4) the growing SM consists of two tightly packed membrane layers with a sharp bend at the edge; (5) changes in the environment of the growing SM participate in the determination of the size and shape of the autophagosome. We suggest that expansion as well as regression takes place at the edge of the growing SM. Stabilization and irreversibility of formation of the SM is achieved by closure. The immediate source of lipids for the SM must be in the cytoplasmic matrix, supposedly in the form of special phospholipid carrying vesicles that might involve the transmembrane Atg9 protein. To explain the apparent lack of such vesicles by electron microscopy we suggest that they are too small, have a similar density to other frequently occurring structures, or are destroyed during sample preparation.     

Disentangling conformational states of macromolecules in 3D-EM through likelihood optimization

Although three-dimensional electron microscopy (3D-EM) permits structural characterization of macromolecular assemblies in distinct functional states, the inability to classify projections from structurally heterogeneous samples has severely limited its application. We present a maximum likelihood-based classification method that does not depend on prior knowledge about the structural variability, and demonstrate its effectiveness for two macromolecular assemblies with different types of conformational variability: the Escherichia coli ribosome and Simian virus 40 (SV40) large T-antigen.