The toxic behaviour of the two shorter sequences of the native Abeta amyloid peptide required for cytotoxicity i.e., Abeta(31-35) and Abeta(25-35) peptides, was studied. We have shown that Abeta(31-35) peptide induces neurotoxicity in undifferentiated PC 12 cell via an apoptotic cell death pathway, including caspase activation and DNA fragmentation. Abeta(25-35) peptide, like the shorter amyloid peptide has the ability to induce neurotoxicity, as evaluated by the MTS reduction assay and by adherent cell count, but the Abeta(25-35) peptide-induced neurotoxicity is not associated with any biochemical features of apoptosis. The differences observed between the neurotoxic properties of Abeta(31-35) and Abeta(25-35) peptides might result on their different ability to be internalised within the neuronal cells. Furthermore, this study reveals that the redox state of methionine residue, C-terminal in Abeta(31-35) and Abeta(25-35) peptides affect in a different way the toxic behaviour of these two short amyloid fragments. Taken together our results suggest that Abeta(31-35) peptide induces cell death by apoptosis, unlike the Abeta(25-35) peptide and that role played by methionine-35 in Abeta induced neurotoxicity might be related to the Abeta aggregation state.

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Human cervical mucus is a heterogeneous mixture of mucin glycoproteins whose relative concentration changes during the ovulatory phases, thereby producing different mucus aggregation structures that can periodically permit the transit of spermatozoa for fertilization. In preovulatory phase, mucus is arranged in compact fiber-like structures where sperm transit is hindered. Previously, through observations made of fixed and dehydrated samples, a permissive structure in the ovulatory phase was attributed to the larger diameters of pores in the mucus network. Instead, by means of atomic force microscopy, we can show, for the first time, that unfixed ovulatory mucus is composed by floating globules of mucin aggregates. This finding sheds new light on the mechanism that governs spermatozoa transit toward the uterine cavity. In addition, we demonstrate that the switch from globular ovulatory to fibrous preovulatory mucus largely depends on a pH-driven mechanism. Analysis of mucin 5B primary sequence, the main mucin in ovulatory mucus, highlights pH-sensitive domains that are associated to flexible regions prone to drive aggregation. We suggest an involvement of these domains in the fiber-to-globule switch in cervical mucus.

The sequence-dependent curvature is generally recognized as an important and biologically relevant property of DNA because it is involved in the formation and stability of association complexes with proteins. When a DNA tract, intrinsically curved for the periodical recurrence on the same strand of A-tracts phased with the B-DNA periodicity, is deposited on a flat surface, it exposes to that surface either a T-or an A-rich face. The surface of a freshly cleaved mica crystal recognizes those two faces and preferentially interacts with the former one. Statistical analysis of scanning force microscopy (SFM) images provides evidence of this recognition between an inorganic crystal surface and nanoscale structures of double-stranded DNA. This finding could open the way toward the use of the sequence-dependent adhesion to specific crystal faces for nanotechnological purposes.I t is widely accepted that the local, sequence-dependent curvature and dynamics of the double-stranded DNA chain segments play a crucial and active role in DNA packaging, transcription, replication, recombination, and repair processes, and in nucleosome stability and positioning (1). Thus, a quantitative knowledge of the curvature and the flexibility of doublestranded DNA has become important to understand the determinants of DNA-protein recognition. We have recently described how SFM makes it possible to map sequencedependent curvature and flexibility along the DNA chain (2, 3). In these previous investigations, indications of preferential adsorption involving curved DNA tracts on the surface of mica were obtained. To reach definite evidence of such recognition we have investigated a highly curved DNA fragment to amplify this effect.A periodic recurrence of A-tracts phased with the B-DNA periodicity, like tracts of three to six adenine steps centered approximately every 10.5 base pairs, drives extended intrinsic curvatures along a DNA chain (4). These curved DNA tracts give rise to planar or quasi planar superstructures. It is worth noting that, when these short stretches of adenine steps are positioned on the same strand, the adenine bases tend to be preferentially positioned on one side of the curvature plane, while the complementary thymines will be found on the other side. When deposited on a flat surface, these curved DNA tracts will thus interact with that surface, on average, with either an A-or a T-rich face. A tract of DNA with very extensive phasing of repeated A-tracts is readily available in the kinetoplast DNA of the Trypanosomatidae protozoan Crithidia fasciculata. This DNA segment is the most highly curved DNA we know of at present (5). The profiles assumed by these curved DNA molecules on deposition on a flat surface can be observed by scanning force microscopy (SFM). Only if the sequence orientation for each of the imaged molecules could be known would it be possible to determine the face with which the molecules adsorb on the surface (on average) through the study of the average chain-curvature of the molecule ensemble. To remo...

docosahexaenoic acid (dHA) is an omega-3 polyunsaturated fatty acid, derived mainly from fish oil. It is well known that DHA is present in high concentrations in nervous tissue and plays an important role in brain development and neuroprotection. However, the molecular mechanisms underlying its role remain to be fully elucidated. In this study, to enhance our understanding of the pathophysiological role of DHA, we investigated the possible neuroprotective mechanisms of action of dHA against hydrogen peroxide (H 2 O 2 )-induced oxidative damage in a rat pheochromocytoma cell line (PC12). Specifically, we evaluated the viability, oxidation potential, and the expression and production of antioxidant/cytoprotective enzymes, and eventual apoptosis. We found that pre-treatment with DHA (24 h) protected the cells from H 2 O 2 -induced oxidative damage. In particular, pre-treatment with DHA: i) Antagonized the consistent decrease in viability observed following exposure to H 2 O 2 for 24 h; ii) reduced the high levels of intracellular reactive oxygen species (ROS) associated with H 2 O 2 -induced oxidative stress; iii) increased the intracellular levels of enzymatic antioxidants [superoxide dismutase (SOd) and glutathione peroxidase (GSH-Px)] both under basal conditions and following H 2 O 2 exposure; iv) augmented the intracellular levels of reduced glutathione (GSH) and ascorbic acid, while it reduced the malondialdehyde (MdA) levels under conditions of oxidative stress; v) upregulated the expression of nuclear factor (erythroid-derived 2)-like 2 (NFE2L2) and its downstream target protein, heme-oxygenase-1 (HO-1); and vi) induced an anti-apoptotic effect by decreasing Bax and increasing Bcl2 expression. These findings provide evidence suggesting that dHA is able to prevent H 2 O 2 -induced oxidative damage to PC12 cells, which is attributed to its antioxidant and anti-apoptotic effects via the regulation NFE2L2/HO-1 signaling. Therefore, dHA may play protective role in neurodegenerative diseases associated with oxidative stress.