Oxidative and nitrative alpha‐synuclein modifications and proteostatic stress: implications for disease mechanisms and interventions in synucleinopathies

Alpha‐synuclein (ASYN) is a major constituent of the typical protein aggregates observed in several neurodegenerative diseases that are collectively referred to as synucleinopathies. A causal involvement of ASYN in the initiation and progression of neurological diseases is suggested by observations indicating that single‐point (e.g., A30P, A53T) or multiplication mutations of the gene encoding for ASYN cause early onset forms of Parkinson's disease (PD). The relative regional specificity of ASYN pathology is still a riddle that cannot be simply explained by its expression pattern. Also, transgenic over‐expression of ASYN in mice does not recapitulate the typical dopaminergic neuronal death observed in PD. Thus, additional factors must contribute to ASYN‐related toxicity. For instance, synucleinopathies are usually associated with inflammation and elevated levels of oxidative stress in affected brain areas. In turn, these conditions favor oxidative modifications of ASYN. Among these modifications, nitration of tyrosine residues, formation of covalent ASYN dimers, as well as methionine sulfoxidations are prominent examples that are observed in post‐mortem PD brain sections. Oxidative modifications can affect ASYN aggregation, as well as its binding to biological membranes. This would affect neurotransmitter recycling, mitochondrial function and dynamics (fission/fusion), ASYN's degradation within a cell and, possibly, the transfer of modified ASYN to adjacent cells. Here, we propose a model on how covalent modifications of ASYN link energy stress, altered proteostasis, and oxidative stress, three major pathogenic processes involved in PD progression. Moreover, we hypothesize that ASYN may act physiologically as a catalytically regenerated scavenger of oxidants in healthy cells, thus performing an important protective role prior to the onset of disease or during aging.     

Myc Is a Metastasis Gene for Non-Small-Cell Lung Cancer

Background

Metastasis is a process by which cancer cells learn to form satellite tumors in distant organs and represents the principle cause of death of patients with solid tumors. NSCLC is the most lethal human cancer due to its high rate of metastasis.

Methodology/Principal Findings

Lack of a suitable animal model has so far hampered analysis of metastatic progression. We have examined c-MYC for its ability to induce metastasis in a C-RAF-driven mouse model for non-small-cell lung cancer. c-MYC alone induced frank tumor growth only after long latency at which time secondary mutations in K-Ras or LKB1 were detected reminiscent of human NSCLC. Combination with C-RAF led to immediate acceleration of tumor growth, conversion to papillary epithelial cells and angiogenic switch induction. Moreover, addition of c-MYC was sufficient to induce macrometastasis in liver and lymph nodes with short latency associated with lineage switch events. Thus we have generated the first conditional model for metastasis of NSCLC and identified a gene, c-MYC that is able to orchestrate all steps of this process.

Conclusions/Significance

Potential markers for detection of metastasis were identified and validated for diagnosis of human biopsies. These markers may represent targets for future therapeutic intervention as they include genes such as Gata4 that are exclusively expressed during lung development.     

Isolation of a deoxycytidylate methyl transferase capable of protecting DNA uniquely against cleavage by endonuclease R.Aqu I (isoschizomer of Ava I).

A sequence-specific modification methylase (M.AquI) was isolated and purified from Agmenellum quadruplicatum (Synechococcus PCC 7002). This enzyme uniquely methylates the deoxycytidylate residue in the sequence *CYCGRG indicated by the asterisk. It was shown to protect DNA against cleavage by restriction endonucleases AvaI, SmaI and XhoI, which recognize the sequences CYCGRG, CCCGGG, and CTCGAG, respectively.     

Cloning and complete nucleotide sequences of the type II restriction-modification genes of Salmonella infantis.

The complete type II restriction-modification system of Salmonella infantis was cloned in Escherichia coli as an R . Sau3AI fragment of 3,430 base pairs. The clone was shown to express the restriction endonuclease as well as the modification methylase. The nucleotide sequence of the above fragment showed two open reading frames of 461 and 230 codons in tail-to-tail orientation. These were shown to represent the modification methylase M . SinI and the restriction endonuclease R . SinI, respectively. The methylase M . SinI amino acid sequence revealed a considerable similarity to those of other deoxycytidylate methylases. In contrast, endonuclease R . SinI did not exhibit such a similarity to other restriction enzymes.     

Ion Exchange Properties of the Canine Carotid Artery

Properties of the ion exchange mechanisms in the arterial wall were investigated by comparing water and electrolyte contents, and by measuring the steady-state entry of ²²Na, ⁴²K, and ²⁶Cl under similar in vitro conditions. Overnight incubation of freshly dissected slices at 2°C resulted in an accumulation of sodium, chloride, and water and a loss of potassium. Subsequent incubation at 37°C in a physiological solution resulted in a reversal of these processes. Loss of water, sodium, and chloride at 37°C could also take place into a potassium-free solution. Under all conditions studied the quantity of fast exchanging electrolyte (half time less than 3 min) exceeded that contained in the inulin and sucrose spaces. The excess could not be attributed to connective tissue adsorption. A kinetic model was applied to the flux data which incorporated two simultaneous processes: bulk diffusion and a reversible reaction. The assumption that the cell membrane behaved as a discrete barrier for the exchange of all cell electrolyte was relaxed in this approach. A theory based upon the physicochemical properties of proteins, ions, and water in biological systems provided a physical basis for the kinetic model, and for interpreting the ion exchange properties of the vascular wall.     

Kinetics of isobaric counterdiffusion

Isobaric inert gas counterdiffusion has been demonstrated to produce gas lesions in man (Lambertsen and Idicula, 1975) and lethal gas embolism in animals (Lambertsen, Cunnington and Cowley, 1975). Equations have been derived for the stable-state supersaturation pressures developing at interfaces during inert gas counterdiffusion (Graveset al., 1973). The present analysis is a mathematical treatment of the kinetics of the isobaric counterdiffusion of a pair of gases through a membrane consisting of two layers composed of substances with different diffusion coefficients and solubilities for each of the gases involved. The time to reach the stable supersaturation state due to isobaric counterdiffusion, even when circulatory transport and pulmonary washout times are included, is found to be at least an order of magnitude smaller than the time required for visible bubble formation and tissue distortion.     

The Prefrontal Cortex Regulates the Basal Release of Dopamine in the Limbic Striatum: An Effect Mediated by Ventral Tegmental Area

Abstract: The present study examined whether the prefrontal cortex (PFC) exerts a tonic control over the basal release of dopamine in the limbic striatum and whether this control is mediated by glutamatergic afferents to the dopamine cell body or terminal regions. Using intracerebral microdialysis in freely moving rats, it was demonstrated that application of tetrodotoxin in the contralateral PFC significantly decreased the release of dopamine in the medial striatum. Conversely, blockade of the tonic inhibitory GABAergic input in the PFC with bicuculline increased the release of dopamine in the medial striatum. Application of excitatory amino acid receptor antagonists into the striatum, while bicuculline was perfused in the PFC, did not affect the bicuculline-evoked dopamine increase in the striatum. However, infusion of tetrodotoxin or excitatory amino acid receptor antagonists into the ventral tegmental area, a region containing dopamine cell bodies that project to the medial striatum, blocked the stimulation of striatal dopamine release induced by infusion of bicuculline into the PFC. These data demonstrate that the basal output of dopamine terminals in the medial striatum is under a tonic excitatory control of the PFC. Furthermore, this control occurs primarily through glutamatergic projections to the dopamine cell body area rather than the terminal regions.     

Some considerations on a carrier mechanism as a model for ion accumulation

A mechanism is described which accounts for the active transport of Na⁺ ions through a membrane. It is assumed that at one side of the membrane the ion combines with a carrier ion, the resulting carrier compound then diffuses through the membrane and decomposes at the other side of the membrane. The free diffusion of the ions is also taken into account. The time rate of accumulation of the ion in question at the latter side of the membrane is calculated in terms of the concentrations of the ion at both sides of the membrane.