Increase in dNTP pool size during the DNA damage response plays a key role in spontaneous and induced-mutagenesis in Escherichia coli

Exposure of Escherichia coli to UV light increases expression of NrdAB, the major ribonucleotide reductase leading to a moderate increase in dNTP levels. The role of elevated dNTP levels during translesion synthesis (TLS) across specific replication-blocking lesions was investigated. Here we show that although the specialized DNA polymerase PolV is necessary for replication across UV-lesions, such as cyclobutane pyrimidine dimers or pyrimidine(6-4)pyrimidone photoproduct, Pol V per se is not sufficient. Indeed, efficient TLS additionally requires elevated dNTP levels. Similarly, for the bypass of an N-2-acetylaminofluorene-guanine adduct that requires Pol II instead of PolV, efficient TLS is only observed under conditions of high dNTP levels. We suggest that increased dNTP levels transiently modify the activity balance of Pol III (i.e., increasing the polymerase and reducing the proofreading functions). Indeed, we show that the stimulation of TLS by elevated dNTP levels can be mimicked by genetic inactivation of the proofreading function (mutD5 allele). We also show that spontaneous mutagenesis increases proportionally to dNTP pool levels, thus defining a unique spontaneous mutator phenotype. The so-called "dNTP mutator" phenotype does not depend upon any of the specialized DNA polymerases, and is thus likely to reflect an increase in Pol III's own replication errors because of the modified activity balance of Pol III. As up-regulation of the dNTP pool size represents a common physiological response to DNA damage, the present model is likely to represent a general and unique paradigm for TLS pathways in many organisms.     

Protective effect of a novel peptide against methylmercury-induced toxicity in rat primary astrocytes

Methylmercury (MeHg) is an environmental neurotoxicant associated with aberrant central nervous system (CNS) functions. In this study, we examined the protective effect of a novel anti-inflammatory and cytoprotective nonapeptide, termed IIIM1, against MeHg-induced toxicity in cultured rat neonatal primary astrocytes. Astrocytes were pretreated for 66 h with 5 μg/ml IIIM1 (4.95 μM) followed by 6 h exposure to MeHg (5 μM). MeHg significantly increased F(2)-isoprostane generation, a lipid peroxidation biomarker of oxidative injury and this effect was significantly reduced upon pre-treatment with IIIM1. The MeHg-induced increase in levels of prostaglandin E(2) (PGE(2)), biomarkers of inflammatory responses, was also decreased in the peptide-treated cells. Mass spectrometry analysis revealed no chemical or binding interaction between MeHg and IIIM1, indicating that intracellular cytoprotective mechanism of action accounts for the neuroprotection rather than direct intracellular neutralization of the neurotoxicant with the peptide. These findings point to therapeutic potential for IIIM1 in a plethora of conditions associated with reactive oxygen species (ROS) generation. The implication of these findings may prove beneficial in designing new treatment modalities that efficiently suppress neurotoxicity, triggered not only by MeHg, but also by other metals and environmental agents, as well as chronic disease conditions that inherently increase reactive radical production and inflammatory signaling.     

A comparison between different reference genes for expression studies in human hippocampal tissue

The reliability of gene expression studies by mRNA quantification is highly dependent upon several experimental procedures, including the choice of reference genes used for data normalization. In order to contribute to gene expression studies in mesial temporal lobe epilepsy (MTLE) we used microarray data, followed by real time quantitative PCR validation of selected housekeeping genes, to determine the most appropriate reference genes to be used in human hippocampal tissue gene expression studies. Our results unequivocally showed a significant impact of the reference gene chosen for normalization on the overall results of expression studies, clearly demonstrating the importance of adequate validation using stable reference genes. In addition, we found that HPRT, NSE, SDHA and SYP are suitable genes to be used as reference for normalization in expression studies of hippocampal tissue obtained from patients with MTLE.     

Astrocyte-derived GDNF is a potent inhibitor of microglial activation

Neuroinflammation is recognized as a major factor in Parkinson's disease (PD) pathogenesis and increasing evidence propose that microglia is the main source of inflammation contributing to the dopaminergic degeneration observed in PD. Several studies suggest that astrocytes could act as physiological regulators preventing excessive microglia responses. However, little is known regarding how astrocytes modulate microglial activation. In the present study, using Zymosan A-stimulated midbrain microglia cultures, we showed that astrocytes secrete factors capable of modulating microglial activation, namely its phagocytic activity and the production of reactive oxygen species since both parameters were highly diminished in cells incubated with astrocytes conditioned media (ACM). Glial cell line-derived neurotrophic factor (GDNF), cerebral dopamine neurotrophic factor (CDNF) and brain-derived neurotrophic factor (BDNF), known to have a neuroprotective role in the nigrostriatal system, are among the candidates to be astrocyte-secreted molecules involved in the modulation of microglial activation. The effect of ACM on Zymosan A-induced microglial activation was abolished when the GDNF present in the ACM was abrogated using a specific antibody, but not when ACM was neutralized with anti-CDNF, anti-BDNF or with a heat-inactivated GDNF antibody. In addition, media conditioned by astrocytes silenced for GDNF were not able to prevent microglial activation, whereas supplementation of non-conditioned media with GDNF prevented the activation of microglia evoked by Zymosan A. Taken together, these results indicate that astrocyte-derived GDNF plays a major contribution to the control of midbrain microglial activation, suggesting that GDNF can protect from neurodegeneration through the inhibition of neuroinflammation.     

Is magnetic resonance imaging a plausible biomarker for upper motor neuron degeneration in amyotrophic lateral sclerosis/primary lateral sclerosis or merely a useful paraclinical tool to exclude mimic syndromes? A critical review of imaging applicability in clinical routine

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that affects motor neurons in the cerebral cortex, brainstem, and spinal cord, brain regions in which conventional magnetic resonance imaging is often uninformative. Although the mean time from symptom onset to diagnosis is estimated to be about one year, the current criteria only prescribe magnetic resonance imaging to exclude "ALS mimic syndromes". Extensive application of non-conventional magnetic resonance imaging (MRI) to the study of ALS has improved our understanding of the in vivo pathological mechanisms involved in the disease. These modern imaging techniques have recently been added to the list of potential ALS biomarkers to aid in both diagnosis and monitoring of disease progression. This article provides a comprehensive review of the clinical applicability of the neuroimaging progress that has been made over the past two decades towards establishing suitable diagnostic tools for upper motor neuron (UMN) degeneration in ALS.