Leber hereditary optic neuropathy--a disease with a known molecular basis but a mysterious mechanism of pathology

Leber hereditary optic neuropathy is a maternally inherited type of blindness caused by degeneration of the optic nerve. It is caused by point mutations in mitochondrial DNA. Like in other mitochondrial diseases, its penetrance and inheritance is complicated by heteroplasmy, tissue distribution, and the bottleneck phenomenon in oocyte maturation. On the cellular level, the mechanism of the disease development is still mysterious. Currently three theories of pathomechanism of LHON are considered: biochemical, ROS (reactive oxygen species) and apoptotic.     

New insights into the possible role of bacteriophages in host defense and disease

BACKGROUND: While the ability of bacteriophages to kill bacteria is well known and has been used in some centers to combat antibiotics - resistant infections, our knowledge about phage interactions with mammalian cells is very limited and phages have been believed to have no intrinsic tropism for those cells. PRESENTATION OF THE HYPOTHESIS: At least some phages (e.g., T4 coliphage) express Lys-Arg-Gly (KGD) sequence which binds beta3 integrins (primarily alphaIIbbeta3). Therefore, phages could bind beta3+ cells (platelets, monocytes, some lymphocytes and some neoplastic cells) and downregulate activities of those cells by inhibiting integrin functions. TESTING THE HYPOTHESIS: Binding of KGD+ phages to beta3 integrin+ cells may be detected using standard techniques involving phage - mediated bacterial lysis and plaque formation. Furthermore, the binding may be visualized by electron microscopy and fluorescence using labelled phages. Binding specificity can be confirmed with the aid of specific blocking peptides and monoclonal antibodies. In vivo effects of phage - cell interactions may be assessed by examining the possible biological effects of beta3 blockade (e.g., anti-metastatic activity). IMPLICATION OF THE HYPOTHESIS: If, indeed, phages can modify functions of beta3+ cells (platelets, monocytes, lymphocytes, cancer cells) they could be important biological response modifiers regulating migration and activities of those cells. Such novel understanding of their role could open novel perspectives in their potential use in treatment of cardiovascular and autoimmune disease, graft rejection and cancer.     

Hypoxia affects root sodium and chloride concentrations and alters water conductance in salt-treated jack pine (<Emphasis Type="Italic">Pinus banksiana</Emphasis>) seedlings

The effects of NaCl were studied in 6-month-old jack pine (Pinus banksiana Lamb.) seedlings growing in solution culture under hypoxic (approximately 2 mg l^у O₂) and well-aerated (approximately 8 mg l^у O₂) conditions. The results showed that hypoxia led to further reduction of stomatal conductance (g_s) in plants treated with 45 mM NaCl. This effect was likely due to a reduction in root hydraulic conductance by both stresses. When applied individually or together, neither 45 mM NaCl nor hypoxia affected cell membrane integrity of needles as measured by tissue electrolyte leakage. Hypoxia did not alter shoot Na⁺ and Cl^m concentrations in NaCl-treated plants. However, root Na⁺ concentrations were lower in NaCl-treated hypoxic plants, suggesting that hypoxia affected the ability of roots to store Na⁺. Hypoxia also induced root electrolyte leakage from NaCl-treated and control plants. The higher root Cl^m concentrations compared with Na⁺ and the positive correlation between root Cl^m concentrations and electrolyte leakage suggest that Cl^m played a major role in salt injury observed in jack pine seedlings. Roots of well-aerated plants treated for 1 week with NaCl contained almost two-fold higher concentration of total non-structural carbohydrates compared with plants from other experimental treatments and these concentrations decreased in subsequent weeks. We suggest that under prolonged hypoxic conditions, roots lose the ability to prevent Cl^m uptake resulting in the increase in root Cl^m concentration, which has damaging effects on root cell membranes.     

Tissue transglutaminase differentially modulates apoptosis in a stimuli-dependent manner

Tissue transglutaminase is a unique member of the transglutaminase family as it not only catalyzes a transamidating reaction, but also binds and hydrolyzes GTP and ATP. Tissue transglutaminase has been reported to be pro-apoptotic, however, conclusive evidence is still lacking. To elucidate the role of tissue transglutaminase in the apoptotic process human neuroblastoma SH-SY5Y cells were stably transfected with vector only (SH/pcDNA), wild-type tissue transglutaminase (SH/tTG) and tissue transglutaminase that has no transamidating activity but retains its other functions (SH/C277S). In these studies three different apoptotic stimuli were used osmotic stress, staurosporine treatment and heat shock to delineate the role of tissue transglutaminase as a transamidating enzyme in the apoptotic process. In SH/tTG cells, osmotic stress and staurosporine treatments resulted in significantly greater caspase-3 activation and apoptotic nuclear changes then in SH/pcDNA or SH/C277S cells. This potentiation of apoptosis in SH/tTG cells was concomitant with a significant increase in the in situ transamidating activity of tissue transglutaminase. However, in the heat shock paradigm, which did not result in any increase in the transamidating activity in SH/tTG cells, there was a significant attenuation of caspase-3 activity, LDH release and apoptotic chromatin condensation in SH/tTG and SH/C277S cells compared with SH/pcDNA cells. These findings indicate for the first time that the effect of tissue transglutaminase on the apoptotic process is highly dependent on the type of the stimuli and how the transamidating activity of the enzyme is affected. Tissue transglutaminase facilitates apoptosis in response to stressors that result in an increase in the transamidating activity of the enzyme. However, when the stressors do not result in an increase in the transamidating activity of tissue transglutaminase, than tissue transglutaminase can ameliorate the apoptotic response through a mechanism that is independent of its transamidating function. Further, neither the phosphatidylinositol-3-kinase pathway nor the extracellular-regulated kinase pathway is downstream of the modulatory effects of wild-type tissue transglutaminase or C277S-tissue transglutaminase in the apoptotic cascade.     

Free radicals-mediated induction of oxidized DNA bases and DNA-protein cross-links by nickel chloride

Using the comet assay, we showed that nickel chloride at 250-1000 microM induced DNA damage in human lymphocytes, measured as the change in comet tail moment, which increased with nickel concentration up to 500 microM and then decreased. Observed increase might follow from the induction of strand breaks or/and alkali-labile sites (ALS) by nickel, whereas decrease from its induction of DNA-DNA and/or DNA-protein cross-links. Proteinase K caused an increase in the tail moment, suggesting that nickel chloride at 1000 microM might cross-link DNA with nuclear proteins. Lymphocytes exposed to NiCl(2) and treated with enzymes recognizing oxidized and alkylated bases: endonuclease III (Endo III), formamidopyrimidine-DNA glycosylase (Fpg) and 3-methyladenine-DNA glycosylase II (AlkA), displayed greater extent of DNA damage than those not treated with these enzymes, indicating the induction of oxidized and alkylated bases by nickel. The incubation of lymphocytes with spin traps, 5,5-dimethyl-pyrroline N-oxide (DMPO) and PBN decreased the extent of DNA damage, which might follow from the production of free radicals by nickel. The pre-treatment with Vitamin C at 10 microM and Vitamin E at 25 microM decreased the tail moment of the cells exposed to NiCl(2) at the concentrations of the metal causing strand breaks or/and ALS. The results obtained suggest that free radicals may be involved in the formation of strand breaks or/and ALS in DNA as well as DNA-protein cross-links induced by NiCl(2). Nickel chloride can also alkylate DNA bases. Our results support thesis on multiple, free radicals-based genotoxicity pathways of nickel.