Age-related Changes in Bovine α-crystallin and High-molecular-weight Protein

The high-molecular-weight (HMW) protein from the lens is composed mostly of α-crystallin in a highly aggregated state. Bovine HMW protein was carefully separated from α-crystallin by size-exclusion chromatography. α-Crystallin has chaperone-like ability whereby it stabilizes other proteins under conditions of stress (e.g. heat). Comparison of bovine HMW protein and α-crystallin shows that the HMW protein has a markedly reduced chaperone ability compared to α-crystallin. However, in contrast to the results of other workers, we observe no alteration with age in the ability of α-crystallin to act as a chaperone. Using electrospray ionisation mass spectrometry, changes in the phosphorylation of the α-crystallin subunits with age have been quantified. Phosphorylation of α-crystallin occurs early in life but does not alter in proportion after about three years of age. In addition, phosphorylation of the A subunit of α-crystallin has little effect on its chaperone ability. As is found in the artificially prepared HMW complex of α- and γ-crystallin, NMR spectroscopy shows that in the naturally occurring HMW protein, the short C-terminal extension of the α_Bsubunit has lost its flexibility whereas the α_Asubunit extension is still flexible. Post-translational modifications therefore seem to have little effect on the chaperone action of α-crystallin, but alterations in the quaternary structure of α-crystallin via incorporation into the HMW aggregate, lead to major changes in the chaperone ability of the protein. The results are consistent with the notion that one of the contributing factors to cataract formation in the lens is the depletion of α-crystallin with age as it is converted into the HMW protein.     

Alpha-melanocyte-stimulating hormone reduces endotoxin-induced liver inflammation.

Alpha-Melanocyte-stimulating hormone (MSH) is a potent anti-inflammatory agent in many models of inflammation, suggesting that it inhibits a critical step common to different forms of inflammation. We showed previously that alpha-MSH inhibits nitric oxide (NO) production in cultured macro-phages. To determine how alpha-MSH acts in vivo, we induced acute hepatic inflammation by administering endotoxin (LPS) to mice pretreated with Corynebacterium parvum, alpha-MSH prevented liver inflammation even when given 30 min after LPS administration. To determine the mechanisms of action of alpha-MSH, we tested its influence on NO, infiltrating inflammatory cells, cytokines, and chemokines. Alpha-MSH inhibited systemic NO production, hepatic neutrophil infiltration, and increased hepatic mRNA abundance for TNF alpha, and the neutrophil and monocyte chemokines (KC/IL-8 and MCP-1). We conclude that alpha-MSH prevents LPS-induced hepatic inflammation by inhibiting production of chemoattractant chemokines which then modulate infiltration of inflammatory cells. Thus, alpha-MSH has an effect very early in the inflammatory cascade.     

Changes in the Subcellular Distribution of the Rat Uterus Oestrogen Receptor as Induced by Oestradiol,Tamoxifen and ZD 182,780

The aim of this work was to compare the subcellular distribution of the oestrogen receptor from the uteri of rats treated with vehicle alone (control group), oestradiol or one of the antio-estrogenic drugs tamoxifen and ZD 182,780. The nuclear, microsomal and cytosolic oestrogen receptor contents were evaluated by an immunoenzymatic method (“ER-EIA” kit from Abbott Laboratories) and the results in each fraction were expressed as a percentage of the total number of receptors. Parallel studies were performed to assess the uterotrophic effect of these drugs and to assess that they had reached the uterus. In the control group, we found that the oestrogen receptor was distributed mainly between the microsomal (29.1 ± 1.3%) and cytosolic (68.1 ±0.9%) fractions, with only a small amount located in the nucleus (2.8 ± 0.5%). When oestradiol was administered, the oestrogen receptor distribution was: nuclear 11.7 ± 2.0, microsomal 15.5 ± 1.3 and cytosolic 72.8 ± 3.3% and, in the tamoxifen group, the results were: nuclear 18.5 ± 1.5, microsomal 26.0 ± 31 and cytosolic 55.5 ± 3.4%, which shows a relative shift both to the control and the oestradiol-treated groups. In the uteri of rats treated with ZD 182,780 the results were very similar to those obtained in the control group. Our results indicate that the subcellular distribution of the oestrogen receptor varies according to the drug administered and that this receptor may not be located in a single subcellular compartment. Moreover, the nuclear uptake of the ZD 182,780-oestrogen receptor complex seems to be blocked, possibly due to impaired receptor dimerization. In the case of tamoxifen, the intracellular transport of the receptor also seems to be blocked, probably due to the nuclear retention of the receptor, thus suggesting that tamoxifen must impair the oestrogen receptor function on a step subsequent to the receptor dimerization.     

Differential distribution of N-acetylaspartylglutamate and N-acetylaspartate immunoreactivities in rat forebrain

Summary Contradictory immunohistochemical data have been reported on the localization of N-acetylaspartylglutamate in the rat forebrain, using different carbodiimide fixation protocols and antibody purification methods. In one case, N-acetylaspartylglutamate immunoreactivity was observed in apparent interneurons throughout all allocortical and isocortical regions, suggesting possible colocalization with GABA. In another case, strong immunoreactivity was observed in numerous pyramidal cells in neocortex and hippocampus, suggesting colocalization with glutamate or aspartate. Reconciling these disparate findings is crucial to understanding the role of N-acetylaspartylglutamate in nervous system function. Antibodies to N-acetylaspartylglutamate and a structurally related molecule, N-acetylaspartate, were purified in stages, and their cross-reactivities with protein conjugates of N-acetylaspartylglutamate and N-acetylaspartate were monitored at each stage by solidphase immunoassay. Reduction of the cross-reactivity of the anti-N-acetylaspartylglutamate antibodies to N-acetylaspartateprotein conjugates to about 1% eliminated significant staining of most pyramidal neurons in the rat forebrain. Utilizing highly purified antibodies, the distributions of N-acetylaspartylglutamate and N-acetylaspartate were examined in several major telencephalic and diencephalic regions of the rat, and were found to be distinct. N-acetylaspartylglutamate-immunoreactivity was observed in specific neuronal populations, including many groups thought to use GABA as a neurotransmitter. Among these were the globus pallidus, ventral pallidum, entopeducular nucleus, thalamic reticular nucleus, and scattered non-pyramidal neurons in all layers of isocortex and allocortex. N-acetylaspartate-immunoreactivity was more broadly distributed than N-acetylaspartylglutamate-immunoreactivity in the rat forebrain, appearing strongest in many pyramidal neurons. Although N-acetylaspartate-immunoreactivity was found in most neurons, it exhibited a great range of intensities between different neuronal types.     

The effect of oxygen free radicals on calcium current and dihydropyridine binding sites in guinea-pig ventricular myocytes.

1. We used electrophysiological and binding techniques to determine the effects of oxygen free radicals (OFRs) generated by dihydroxyfumaric acid (DHF, 5 mM) on calcium current and dihydropyridine binding sites in guinea-pig isolated ventricular myocytes. 2. Binding of [3H]-PN200-110 to isolated ventricular myocytes revealed one population of binding sites with a KD of 0.11 +/- 0.01 nM and Bmax of 139.1 +/- 6.9 fmol mg-1 protein (n = 24). After 15 min of exposure to DHF, the density, but not the affinity of [3H]-PN200-110 binding sites was significantly (P < 0.01) reduced to 35% of the control value (Bmax = 49.4 +/- 3.7 fmol mg-1 protein, KD = 0.11 +/- 0.01 nM, n = 15). In the presence of superoxide dismutase (SOD) and catalase (CAT) the reduction in [3H]-PN200-110 binding sites was almost completely prevented (Bmax = 120.5 +/- 7.4 in control, n = 4 and 98.8 +/- 7.4 fmol mg-1 protein in DHF plus SOD and CAT, n = 4). KD values were not modified (0.08 +/- 0.01 in control and 0.09 +/- 0.01 nM in DHF plus SOD and CAT). 3. The time-course of the reduction of [3H]-PN200-110 binding sites by OFRs was paralleled by the decrease in L-type calcium current (Ica,L) measured in patch-clamped guinea-pig ventricular myocytes either in the absence or in the presence of EGTA in the patch pipette. In the former conditions OFRs induced the appearance of calcium-dependent alterations, i.e. the transient inward current, within 10 min. After 30 min of incubation with DHF, [3H]-PN200-110 binding sites were reduced to 25% of the control value. 4. In myocytes incubated with the antilipoperoxidant agent, butylated hydroxytoluene (BHT, 50 microM), the decrease in [3H]-PN200-110 binding sites caused by DHF was partially prevented (Bmax values after 30 min exposure to DHF were 55.5 +/- 1.9 and 23.7 +/- 5.9 fmol mg-1 protein in the presence and in the absence of BHT respectively, P < 0.05). BHT did not affect the decrease in [3H]-PN200-110 binding sites during the first 15 min of exposure to DHF, but was able to prevent completely the further decrease occurring during the following 15 min of incubation with OFRs. 5. Our results demonstrate that the OFR-induced decrease in calcium current is associated with a reduction in DHP binding sites. The decrease in calcium current and in calcium channels may be implicated in the mechanical dysfunction associated with oxidative stress.