The effects of several nucleotides on the molecular state and catalytic activity of Thiobacillus novellus cytochrome c oxidase. ATP affects the oxidase uniquely

The catalytic activity and molecular aspects of Thiobacillus novellus cytpchrome c oxidase were affected by ATP. The steady-state kinetics in the oxidation of ferrocytochrome c by the oxidase varied with the presence or absence of ATP; the [S]-v curve of the reaction was sigmoid in the absence of ATP whereas it was a Michaelis-Menten-type hyperbola in the presence of 700 microM ATP. The oxidase was a dimer of the minimal structural subunit consisting of one molecule each of two subunits in the presence of Tween 20 and in the absence of ATP. The dimer dissociated into monomers in the presence of 700 microM ATP. The trough at 452 nm seen in the second derivative absorption spectrum of the CO compound of the oxidase in the absence of ATP, a characteristic of the cytochrome a component of cytochrome aa3, dissappeared in the presence of 700 microM ATP. However, ADP, AMP, GTP, CTP and UTP had little affect on both the [S]-v curve and the molecular mass of the oxidase when used in place of ATP.

Apoptosis of cultured microglia by the deprivation of macrophage colony-stimulating factor

Promotion of microglial proliferation and differentiation by colony-stimulating factors (CSFs) and disappearances of microglia at the late neonatal stage by decreasing of CSFs have been reported. In this study, the effects of the deprivation of macrophage CSF (M-CSF) on enriched microglia in cultures were examined by cytochemical methods including in situ nick-end labeling for DNA fragmentation, and Carrazi's hematoxylin nuclear staining. When M-CSF was deprived from the culture medium: (1) at least 40% of the cells were weakly labeled by nick-end within 3 h and more than 70% of the cells were clearly labeled by 16 h; and (2) nuclear condensation or fragmentation, and formation of apoptotic bodies were observed within 48 h. LeY-positive immunoreactivity, identified as a characteristic of cells undergoing apoptosis, was observed on cells positively labeled by nick-end and condensed nucleus, and ones budding apoptotic bodies. From these results, it is conceivable that microglia undergo apoptosis when M-CSF is deprived from the culture medium and, therefore, require CSFs for their survival. This in vitro phenomenon suggests that one of the mechanisms of microglial disappearance in vivo after synaptogenesis may be due to apoptosis by decreasing level of CSFs.

Expression of type I interleukin-1 receptor mRNA and its regulation in cultured astrocytes

The expression of type I interleukin-1 receptor (IL-1RI) mRNA enriched astrocytes and microglia was investigated by Northern blot analysis. IL-1RI mRNA was expressed in untreated astrocytes, but not in microglia. This expression was markedly suppressed by a treatment with isoproterenol, a beta-adrenoceptor agonist (1 x 10(-8) to 1 x 10(-6) M). This suppression was clearly reversed by propranolol, a beta-adrenoceptor antagonist. Dibutyryl cAMP (dbcAMP) also suppressed the expression of IL-1RI mRNA. The suppression by isoproterenol or dbcAMP was blocked by H8 or H89, inhibitors of cAMP-dependent protein kinase. The present results suggest that IL-1RI mRNA expression in cultured astrocytes may be regulated by intracellular cAMP, elevated upon the activation of beta-adrenoceptors as an example, and cAMP-dependent protein kinase.

Participation of cAMP and cAMP-dependent protein kinase in beta-adrenoceptor-mediated interleukin-1 beta mRNA induction in cultured microglia

We previously reported evidence of beta-adrenoceptor-mediated induction of IL-1 beta mRNA in the rat hypothalamus. The present in vitro studies using northern blot analysis showed that the beta-adrenoceptor agonist isoproterenol (1 x 10(-8) to 1 x 10(-5) M) caused a marked induction of IL-1 beta mRNA in microglia, but not in astrocytes. This induction was remarkably suppressed by pretreatment of cells with the beta-adrenoceptor antagonist propranolol. These phenomena were confirmed by in situ hybridization with digoxigenin-labelled IL-1 beta RNA probe. Furthermore, dibutyryl cyclicAMP (dbcAMP) (5 x 10(-4) and 5 x 10(-5) M) markedly induced IL-1 beta mRNA in microglia. The intracellular level of cAMP in microglia was elevated in a dose-dependent manner when they were treated with isoproterenol, and this elevation was completely blocked by propranolol. The induction of IL-1 beta mRNA by either isoproterenol or dbcAMP was strongly inhibited by a cAMP-dependent protein kinase inhibitor, H8. These results, taken together, suggest that (1) microglia primarily induce IL-1 beta mRNA by stimulation of beta-adrenoceptors, and (2) cAMP and cAMP-dependent protein kinase presumably participate in a signal transduction mechanism involved in the induction of IL-1 beta mRNA via beta-adrenoceptors.

Soluble striatal extracts enhance development of mesencephalic dopaminergic neurons in vitro

Recent studies have suggested that diffusible factors released by neural target tissues enhance survival, growth, and differentiation of neurons within the central, as well as the peripheral, nervous system. In this report, we use catecholamine cytofluorescence to demonstrate that a soluble factor from the striatum produces a 4-fold increase in number of catecholamine cytofluorescent-positive dopaminergic neurons in dissociated mesencephalon cultures prepared from embryonic 14-day-old rats. The same soluble extract enhances the number of neurites per cell and the length of neurites, and also produces a greater than 3.5-fold stimulation of high affinity dopamine uptake into neurons. Such stimulation is significantly reduced following trypsin treatment. The trophic effects on dopaminergic neurons are maximal in extracts of the striatum, but are also found in extracts of the hippocampus-entorhinal cortex-amygdaloid nucleus and the cerebral cortex, although they are less in extracts of the cerebellum, negligible in the olfactory bulb, and absent in the liver. With molecular sieving chromatography, the soluble factors stimulating high affinity dopamine uptake are partially separable from the factors stimulating neuronal high affinity GABA uptake. The approximate molecular weight of the factors influencing dopaminergic neurons is 1500-2200 Da.

Brain peptides and glial growth. I. Glia-promoting factors as regulators of gliogenesis in the developing and injured central nervous system

Glia-promoting factors (GPFs) are peptides of the central nervous system which accelerate the growth of specific glial populations in vitro. Although these factors were first discovered in the goldfish visual system (Giulian, D., Y. Tomozawa, H. Hindman, and R. Allen, 1985, Proc. Natl. Acad. Sci. USA., 83:4287-4290), we now report similar peptides are found in mammalian brain. The cerebral cortex of rat contains oligodendroglia-stimulating peptides, GPF1 (15 kD) and GPF3 (6 kD), as well as astroglia-stimulating peptides, GPF2 (9 kD) and GPF4 (3 kD). The concentrations of specific GPFs increase in brain during periods of gliogenesis. For example, GPF1 and GPF3 are found in postnatal rat brain during a peak of oligondendroglial growth while GPF2 and GPF4 are first detected at a time of astroglial proliferation in the embryo. Stab wound injury to the cerebral cortices of rats stimulates astroglial proliferation and induces marked elevations in levels of GPF2 and GPF4. Our findings suggest that two distinct classes of GPFs, those acting upon oligodendroglia and those acting upon astroglia, help to regulate cell growth in the developing and injured central nervous system.

Peptides from regenerating central nervous system promote specific populations of macroglia

The regenerating central nervous system of goldfish contains peptides referred to as glia-promoting factors (GPFs) that stimulate the proliferation of mammalian macroglia. We find that, in vitro, GPF1 and GPF3 promote the appearance of oligodendroglia and GPF2 and GPF4 stimulate proliferation of astroglia. The activities of GPF1, GPF3, and GPF4 increase during regeneration of the goldfish visual system. These results suggest that brain peptides may play a role in the recovery of the injured central nervous system by regulating the growth and development of specific macroglial populations.

Clonal sublines of rat neurotumor RT4 and cell differentiation. V. Comparison of Na+ influx, Rb+ efflux, and action potential among stem-cell, neuronal, and glial cell types

A multipotential stem-cell-type cell line (RT4-AC) isolated from a rat peripheral neurotumor differentiates in culture into two neuronal-type cells (RT4-B and RT4-E) or into a glial-type cell (RT4-D). The neuronal classification of RT4-B and RT4-E cells is based on their positive response to veratridine in the tetrodotoxin-sensitive Na+-influx and Rb+-efflux assays and on the action potential observed upon hyperpolarized stimulation. In addition, these neuronal cell types do not synthesize two glial proteins, S100 protein (S100P) and glial fibrillary acidic protein (GFAP). The glial classification of RT4-D is based on the syntheses of S100P and GFAP. Additionally, RT4-D does not display veratridine-activated Na+ influx and Rb+ efflux nor action potential. The stem cell type, RT4-AC, expresses both neuronal and glial properties to a lesser degree. In the neuronal-type cell lines of the RT4 family (RT4-B and RT4-E), the large veratridine-activated Na+ influx can further be stimulated by scorpion toxin. The Na+ influx of the stem cell (RT4-AC), however, is only slightly stimulated by veratridine alone, but greatly stimulated by the addition of veratridine and scorpion toxin. These observations suggest that a progressive differentiation of voltage-dependent Na+ channels may have occurred by the cell-type conversion from the stem cell type to the neuronal cell types. The exact nature of the change in Na+ channels is currently not known.

In vitro segregation of different cell lines with neuronal and glial properties from a stem cell line of rat neurotumor RT4

A clonal stem cell line, RT4-AC, of the rat peripheral neurotumor RT4 differentiates in culture into morphologically distinct cell types RT4-B, RT4-D, and RT4-E (cell type conversion). The multipotential stem cell type RT4-AC and cell type RT4-D produce a glial marker, S100 protein, but RT4-B and RT4-E do not. The stem cells also show a small but significant response to veratridine on voltage-dependent Na+ influx. Cell types RT4-B and RT4-E show a clear response of voltage-dependent Na+ influx to veratridine, typical of neuronal cells, whereas cell type RT4-D is completely negative. These results indicate that (i) the stem cell type RT4-AC shows both neuronal and glial properties, (ii) cell types RT4-B and RT4-E have a neuronal property, and (iii) cell type RT4-D has a glial property. Therefore, cell type conversion of stem cell RT4-AC to RT4-B and RT4-E cells seems to result in differentiation towards neuronal cell types, and cell type conversion of RT4-AC to RT4-D results in differentiation towards a glial type in culture.

The influence of pH on the interaction of inhibitors with triosephosphate isomerase and determination of the pKa of the active-site carboxyl group

Ionization effects on the binding of the potential transition state analogues 2-phosphoglycolate and 2-phosphoglycolohydroxamate appear to be attributable to the changing state of ionization of the ligands themselves, therefore it is unnecessary to postulate the additional involvement of an ionizing residue at the active site of triosephosphate isomerase to explain the influence of changing pH on Ki in the neutral range. The binding of the competitive inhibitor inorganic sulfate is insensitive to changing pH in the neutral range. 3-Chloroacetol sulfate, synthesized as an active-site-specific reagent for triosephosphate isomerase, is used to provide an indication of the pKa of the essential carboxyl group of this enzyme. Previously described active-site-specific reagents for the isomerase were phosphate esters, and their changing state of ionization (accompanied by possible changes in their affinity for the active site) may have complicated earlier attempts to determine the pKa of the essential carboxyl group from the pH dependence of the rate of inactivation. Being a strong monoprotic acid, chloroacetol sulfate is better suited to the determination of the pKa of the carboxyl group. Chloroacetol sulfate inactivates triosephosphate isomerase by the selective esterification of the same carboxyl group as that which is esterified by the phosphate esters described earlier. From the pH dependence of the rate of inactivation of yeast triosephosphate isomerase, the apparent pKa of the active-site carboxyl group is estimated as 3.9 +/- 0.1.