Activation of Endogenous Antioxidant Defenses in Neuronal Cells Prevents Free Radical-Mediated Damage

Abstract: Dopamine (DA) is oxidized to the neurotoxic prooxidant species H₂O₂, OH^•, and DA quinones. We tested whether dimethyl fumarate (DMF), an electrophile shown to induce a pleiotropic antioxidant response in nonneuronal cells, could reduce the toxicity of DA metabolites in neural cells. Treatment of the N18-RE-105 neuroblastoma-retina hybridoma cell line with 30–150 µ M dopamine led to cell death within 24 h, which increased steeply with dose, decreased with higher plating density, and was blocked by the H₂O₂-metabolizing enzyme catalase. Pretreatment with DMF (30 µ M , 24 h) significantly attenuated DA and H₂O₂ toxicity (40–60%) but not that caused by the calcium ionophore ionomycin. DMF treatment also elevated total intracellular GSH and increased activities of the antioxidant enzymes quinone reductase (QR), glutathione S -transferase (GST), glutathione reductase, and the pentose phosphate enzyme glucose-6-phosphate dehydrogenase. To assess the protective efficacy of QR and GST, a stable cell line was constructed in which these enzymes were overexpressed. Cell death in the overexpressing line was not significantly different from that in a cell line expressing normal QR and GST activities, indicating that these two enzymes alone are insufficient for protection against DA toxicity. Although the relative importance of a single antioxidant enzyme such as QR or GST may be small, antioxidant inducers such as DMF may prove valuable as agents that elicit a broad-spectrum neuroprotective response.     

Effect of Bafilomycin A1 and Nocodazole on Endocytic Transport in HeLa Cells: Implications for Viral Uncoating and Infection

Bafilomycin A1 (baf), a specific inhibitor of vacuolar proton ATPases, is commonly employed to demonstrate the requirement of low endosomal pH for viral uncoating. However, in certain cell types baf also affects the transport of endocytosed material from early to late endocytic compartments. To characterize the endocytic route in HeLa cells that are frequently used to study early events in viral infection, we used ³⁵S-labeled human rhinovirus serotype 2 (HRV2) together with various fluid-phase markers. These virions are taken up via receptor-mediated endocytosis and undergo a conformational change to C-antigenic particles at a pH of <5.6, resulting in release of the genomic RNA and ultimately in infection (E. Prchla, E. Kuechler, D. Blaas, and R. Fuchs, J. Virol. 68:3713–3723, 1994). As revealed by fluorescence microscopy and subcellular fractionation of microsomes by free-flow electrophoresis (FFE), baf arrests the transport of all markers in early endosomes. In contrast, the microtubule-disrupting agent nocodazole was found to inhibit transport by accumulating marker in endosomal carrier vesicles (ECV), a compartment intermediate between early and late endosomes. Accordingly, lysosomal degradation of HRV2 was suppressed, whereas its conformational change and infectivity remained unaffected by this drug. Analysis of the subcellular distribution of HRV2 and fluid-phase markers in the presence of nocodazole by FFE revealed no difference from the control incubation in the absence of nocodazole. ECV and late endosomes thus have identical electrophoretic mobilities, and intraluminal pHs of <5.6 and allow uncoating of HRV2. As bafilomycin not only dissipates the low endosomal pH but also blocks transport from early to late endosomes in HeLa cells, its inhibitory effect on viral infection could in part also be attributed to trapping of virus in early endosomes which might lack components essential for uncoating. Consequently, inhibition of viral uncoating by bafilomycin cannot be taken to indicate a low pH requirement only.     

Broad immunocytochemical localization of the formylpeptide receptor in human organs, tissues, and cells

The formylpeptide receptor (FPR), previously found only on polymorphonuclear leukocytes and monocytes/macrophages, responds to both synthetic N-formyl oligopeptides and those produced by bacteria. The cDNA for human FPR has been cloned and a rabbit polyclonal antiserum directed against a synthetic 11-amino-acid peptide corresponding to the deduced carboxy-terminus has been produced. We have now extensively characterized and used the antibody to detect FPR on normal human tissues and cell types. The receptor antigen is present on some epithelial cells, especially those with a secretory function, and on some endocrine cells, e.g., follicular cells of the thyroid and cortical cells of the adrenal. Liver hepatocytes and Kupffer cells are positive. Smooth muscle and endothelial cells are also generally positive. In the brain and spinal cord, the neurons of the motor, sensory, and cerebellar systems, and those of the parasympathetic and sympathetic systems stain positively. These data suggest that the putative endogenous agonist for FPR or an antigenically similar receptor reacts with cellular targets in the neuromuscular, vascular, endocrine, and immune systems.     

Genotype/phenotype correlation in affected individuals of a family with a deletion of the entire coding sequence of the connexin 32 gene

X-linked Charcot-Marie-Tooth disease (CMTX) is a peripheral nerve disorder that has been linked to mutations in the connexin 32 gene (Cx32). These mutations have been shown to be genetically heterogeneous, though recurrences of specific mutations in apparently unrelated families have been seen. The majority of mutations have been shown to be missense, resulting in non-conservative amino acid changes. A few mutations resulting in a premature termination of protein translation, including both nonsense mutations as well as frameshifting microdeletions, have been documented. We would like to report a deletion mutation that appears to eliminate the entire coding sequence of the Cx32 gene, but which has been shown to segregate with a clinical phenotype not unlike that seen in individuals with a less severe alteration of the Cx32 gene. The causes at a cellular level of the CMTX phenotype are still not fully clear, though there has been speculation that these may involve a dominant negative effect where the mutant connexin 32 suppresses the function of other connexins. Studies of kindreds such as this, where in CMTX-affected males the Cx32 gene product is totally absent, will help us to better understand the molecular mechanisms underlying the clinical phenotype associated with this disorder. Received: 22 December 1997 / Accepted: 8 May 1998     

Demonstration of rhodanese activity in polyacrylamide gels

Rhodanese activity from crude extracts of Thiobacillus sp. strain IV-85 was demonstrated in polyacrylamide gels after incubation in the reaction mixture by staining with dichloroindophenol in the presence of methylphenazonium methosulfate. The sensitivity of the staining system was found to be 8 × 10^-7 moles of sulfite.     

Sequential forms of ATPase activity correlated with changes in cation binding and membrane potential from meiosis to first clevage in R. pipiens

Changes in cortical membrane potential, cation binding, subcellular aggregation, ATPase activity, phosphoprotein phosphatase activity and inorganic phosphate levels have been measured in the R. pipiens egg from meiotic prophase to first cleavage.

1.

1. Between meiotic prophase (oocyte) and metaphase of the second maturation division (ovulated egg), the egg cortex depolarizes and the egg cytoplasm becomes positive relative to the external environment. Fertilization is accompanied by a transient positive hyperpolarization and the potential returns to the level of the ovulated egg by the completion of meiosis (15 to 20 min). The egg cytoplasm remains positive until first cleavage when the cortex slowly repolarizes and the cytoplasm again becomes negative relative to the external medium.