GSK3beta signalling: casting a wide net in Alzheimer's disease

Glycogen synthase kinase-3beta (GSK3beta) is a kinase that plays a pivotal role in numerous cellular functions from modulation of microtubule dynamics and cell death. It also affects higher functions such as cognition and mood. Deregulation of GSK3beta activity in the adult brain is implicated in several CNS disorders, such as affective disorders, schizophrenia, stroke and neurodegenerative diseases, such as Alzheimer's disease (AD). In AD, GSK3beta has a major role in microtubule stability by its ability to phosphorylate the microtubule associated protein tau. The present review focuses on recent developments in the understanding of GSK3beta with an emphasis on events likely to be critical to the pathophysiology of AD.     

Activation of p38MAPK in Microglia After Ischemia

Abstract: p38^MAPK has been implicated in the regulation of proinflammatory cytokines and apoptosis in vitro. To understand its role in neurodegeneration, we determined the time course and localization of the dually phosphorylated active form of p38^MAPK in hippocampus after global forebrain ischemia. Phosphorylated p38^MAPK and mitogen-activated protein kinase-activated protein 2 activity increased over 4 days after ischemia. Phosphorylated p38^MAPK immunoreactivity was observed in microglia in regions adjacent to, but not in, the dying CA1 neurons. In contrast, neither c-Jun N-terminal kinase 1 nor p42/p44^MAPK activity was altered after ischemia. These results provide the first evidence for localization of activated p38^MAPK in the CNS and support a role for p38^MAPK in the microglial response to stress.     

Regulation of Human Immunodeficiency Virus Replication by 2′,5′-Oligoadenylate-Dependent RNase L

Activation of RNase L by 2′,5′-linked oligoadenylates (2-5A) is one of the antiviral pathways of interferon action. To determine the involvement of the 2-5A system in the control of human immunodeficiency virus type 1 (HIV-1) replication, a segment of the HIV-1 nef gene was replaced with human RNase L cDNA. HIV-1 provirus containing sense orientation RNase L cDNA caused increased expression of RNase L and 500- to 1,000-fold inhibition of virus replication in Jurkat cells for a period of about 2 weeks. Subsequently, a partial deletion of the RNase L cDNA which coincided with increases in virus production occurred. The anti-HIV activity of RNase L correlated with decreases in HIV-1 RNA and with an acceleration in cell death accompanied by DNA fragmentation. Replication of HIV-1 encoding RNase L was also transiently suppressed in peripheral blood lymphocytes (PBL). In contrast, recombinant HIV containing reverse orientation RNase L cDNA caused decreased levels of RNase L, increases in HIV yields, and reductions in the anti-HIV effect of alpha interferon in PBL and in Jurkat cells. To obtain constitutive and continuous expression of RNase L cDNA, Jurkat cells were cotransfected with HIV-1 proviral DNA and with plasmid containing a cytomegalovirus promoter driving expression of RNase L cDNA. The RNase L plasmid suppressed HIV-1 replication by eightfold, while an antisense RNase L construct enhanced virus production by twofold. These findings demonstrate that RNase L can severely impair HIV replication and suggest involvement of the 2-5A system in the anti-HIV effect of alpha interferon.     

Effects of Chronic Nicotine Infusion on Kinetics of High-Affinity Nicotine Binding

Abstract: It is well established that chronic nicotine treatment produces a dose-dependent increase in high-affinity l -[³H]nicotine binding. This increase may be due to chronic desensitization of the receptor. Sophisticated kinetic analyses of high-affinity nicotine binding to rat brain have demonstrated that the association rate is biphasic; the fast phase may represent binding to a high-affinity predesensitized state and the slow phase may represent binding to a lower affinity ground state that then isomerizes to form the high-affinity binding site. This isomerization presumably leads to receptor desensitization. The studies reported here assessed whether binding to mouse brain nicotinic receptors shows these same properties and whether chronic intravenous infusion of nicotine results in changes in these kinetic properties. The results obtained indicate that mouse brain nicotine binding also shows biphasic association kinetics and uniphasic dissociation kinetics, which supports the assertion that the receptor exists in two interconvertible states. However, unlike other results obtained with rat brain, the rate of the slow association process did not change with ligand concentration. Chronic infusion resulted in a dose-dependent increase in l -[³H]-nicotine binding, but the ratio of fast/slow phases of binding was not changed by these treatments. These results suggest that chronic infusion does not alter measurably the kinetics of nicotinic receptor binding when measured in vitro.     

A parental combination analysis for ABO-HP interaction in a Bengali population

Blood samples from 577 couples and their 657 offspring of Bengali caste group derivation were used to study interactions between ABO blood groups and haptoglobin (HP) systems. There was no significant sex difference in HP distribution among the parents. Significantly higher incidences of HP^*1 allele were noted in the offspring of ABO-incompatible parental combinations in comparison with those in the offspring of ABO-compatible parents.     

Proteasome inhibition protects HT22 neuronal cells from oxidative glutamate toxicity

Oxidative stress caused by glutathione depletion after prolonged exposure to extracellular glutamate leads to a form of neuronal cell death that exhibits morphologically mixed features of both apoptosis and necrosis. However, specific downstream executioners involved in this form of cell death have yet to be identified. We report here that glutamate exposure does not activate caspase-3 in the HT22 neuronal cell line. Furthermore, no cytoprotection was achieved with either the pan-caspase inhibitor Z-VAD-fmk or the caspase-3-specific inhibitor DEVD-CHO. In contrast, inhibition of the proteasome by lactacystin protected both HT22 cells and rat primary neuronal cells against cell lysis. In parallel, oxidatively altered and ubiquitinated proteins accumulated in the mitochondrial fraction of cells after proteasome inhibition. These findings suggest that caspases can be decoupled from oxidative stress under some conditions, and implicate the ubiquitin/proteasome pathway in neuronal cell death caused by oxidative glutamate toxicity.     

Retrospective birth dating of cells in humans

The generation of cells in the human body has been difficult to study, and our understanding of cell turnover is limited. Testing of nuclear weapons resulted in a dramatic global increase in the levels of the isotope 14C in the atmosphere, followed by an exponential decrease after 1963. We show that the level of 14C in genomic DNA closely parallels atmospheric levels and can be used to establish the time point when the DNA was synthesized and cells were born. We use this strategy to determine the age of cells in the cortex of the adult human brain and show that whereas nonneuronal cells are exchanged, occipital neurons are as old as the individual, supporting the view that postnatal neurogenesis does not take place in this region. Retrospective birth dating is a generally applicable strategy that can be used to measure cell turnover in man under physiological and pathological conditions.