Ethosuximide Induces Hippocampal Neurogenesis and Reverses Cognitive Deficits in an Amyloid-β Toxin-induced Alzheimer Rat Model via the Phosphatidylinositol 3-Kinase (PI3K)/Akt/Wnt/β-Catenin Pathway

Neurogenesis involves generation of new neurons through finely tuned multistep processes, such as neural stem cell (NSC) proliferation, migration, differentiation, and integration into existing neuronal circuitry in the dentate gyrus of the hippocampus and subventricular zone. Adult hippocampal neurogenesis is involved in cognitive functions and altered in various neurodegenerative disorders, including Alzheimer disease (AD). Ethosuximide (ETH), an anticonvulsant drug is used for the treatment of epileptic seizures. However, the effects of ETH on adult hippocampal neurogenesis and the underlying cellular and molecular mechanism(s) are yet unexplored. Herein, we studied the effects of ETH on rat multipotent NSC proliferation and neuronal differentiation and adult hippocampal neurogenesis in an amyloid β (Aβ) toxin-induced rat model of AD-like phenotypes. ETH potently induced NSC proliferation and neuronal differentiation in the hippocampus-derived NSC in vitro. ETH enhanced NSC proliferation and neuronal differentiation and reduced Aβ toxin-mediated toxicity and neurodegeneration, leading to behavioral recovery in the rat AD model. ETH inhibited Aβ-mediated suppression of neurogenic and Akt/Wnt/β-catenin pathway gene expression in the hippocampus. ETH activated the PI3K·Akt and Wnt·β-catenin transduction pathways that are known to be involved in the regulation of neurogenesis. Inhibition of the PI3K·Akt and Wnt·β-catenin pathways effectively blocked the mitogenic and neurogenic effects of ETH. In silico molecular target prediction docking studies suggest that ETH interacts with Akt, Dkk-1, and GSK-3β. Our findings suggest that ETH stimulates NSC proliferation and differentiation in vitro and adult hippocampal neurogenesis via the PI3K·Akt and Wnt·β-catenin signaling.     

Role of NF-kappaB in the apoptotic-resistant phenotype of keratinocytes

Several studies point to a role for NF-kappaB in modulating epidermal thickness and apoptotic susceptibility of keratinocytes. When phorbol esters such as 12-O-tetradecanoylphorbol-13-acetate (TPA) are topically applied, prominent epidermal thickening occurs, and exposure to interferon (IFN)-gamma promotes increased epidermal thickness producing psoriatic lesions. While keratinocytes derived from psoriatic plaque resist apoptosis, and combination of TPA and IFN-gamma activates NF-kappaB, the molecular mechanism linking NF-kappaB activation and keratinocyte apoptosis resistance was unknown. Therefore, we examined the ability of IFN-gamma plus TPA to influence NF-kappaB activity, gene expression, and response to UV light-induced apoptosis. These responses in normal keratinocytes were compared with immortalized keratinocytes (HaCaT cells). Exposure of normal keratinocytes to IFN-gamma plus TPA produced a synergistic activation of NF-kappaB, compared with when each reagent was used individually. Normal keratinocytes when exposed to IFN-gamma plus TPA acquired a resistance to UV light-induced apoptosis, which was dependent on NF-kappaB because expression of a dominant negative form of IkappaBalpha overcame the resistance. Compared with normal keratinocytes, HaCaT cells have a dysfunctional constitutive NF-kappaB signaling pathway not induced by IFN-gamma and TPA, rendering HaCaT cells highly susceptible to UV-induced apoptosis. Thus, immortalized HaCaT cells have an abnormal constitutive and dysfunctional NF-kappaB signaling system. These results provide evidence that activation and proper regulation of NF-kappaB is essential for acquisition of an apoptotic-resistant phenotype for epidermal-derived keratinocytes.     

IFN-gamma inhibits human airway smooth muscle cell proliferation by modulating the E2F-1/Rb pathway

Elucidating the factors that inhibit the increase in airway smooth muscle (ASM) mass may be of therapeutic benefit in asthma. Here, we investigated whether interferon-gamma (IFN-gamma), a potent inducer of growth arrest in various cell types, regulates mitogen-induced ASM cell proliferation. IFN-gamma (1-100 U/ml) was found to markedly decrease both DNA synthesis and ASM cell number induced by the mitogens epidermal growth factor (EGF) and thrombin. Interestingly, IFN-gamma had no effect on mitogen-induced activation of three major mitogenic signaling pathways, phosphatidylinositol 3-kinase, p70(S6k), or mitogen-activated protein kinases. Mitogen-induced expression of cell cycle regulator cyclin D1 was increased by IFN-gamma, whereas no effect was observed on degradation of p27(Kip1). Expression array analysis of 23 cell cycle-related genes showed that IFN-gamma inhibited EGF-induced increases in E2F-1 expression, whereas induction of c-myc, cyclin D2, Egr-1, and mdm2 were unaffected. Induction of E2F-1 protein and Rb hyperphosphorylation after mitogen stimulation was also suppressed by IFN-gamma. In addition, IFN-gamma decreased activation of cdk2 and expression of cyclin E, upstream signaling molecules responsible for Rb hyperphosphorylation in the late G1 phase. IFN-gamma also increased levels of IFI 16 protein, whose mouse homolog p202 has been associated with growth inhibition. Together, our data indicate that IFN-gamma is an effective inhibitor of ASM cell proliferation by blocking transition from G1-to-S phase by acting at two different levels: modulation of cdk2/cyclin E activation and inhibition of E2F-1 gene expression.     

Mitochondrial swelling impairs the transport of organelles in cerebellar granule neurons

Organelle transport in neuronal processes is central to the organization, developmental fate, and functions of neurons. Organelles must be transported through the slender, highly branched neuronal processes, making the axonal transport vulnerable to any perturbation. However, some intracellular structures like mitochondria are able to considerably modify their volume. We therefore hypothesized that swollen mitochondria could impair the traffic of other organelles in neurite shafts. To test this hypothesis, we have investigated the effects of mitochondrial swellers on the organelle traffic. Our data demonstrate that treatment of neurons with potassium ionophore valinomycin led to the fast time-dependent inhibition of organelle movement in cerebellar granule neurons. Similar inhibition was observed in neurons treated with the inhibitors of the mitochondrial respiratory chain, sodium azide and antimycin, which also induced swelling. No decrease in the motility of organelles was observed in cultures treated with inhibitors of ATP production or transport, oligomycin or bongkrekic acid, suggesting that inhibition of the ATP-generating activity itself without swelling does not affect the motility of organelles. The effect of swellers on the traffic was more important in thin processes, thus indicating the role of steric hindrance of swollen mitochondria. We propose that the size and morphology of the transported cargo is also relevant for seamless axonal transport and speculate that mitochondrial swelling could be one of the reasons for impaired organelle transport in neuronal processes.     

Aim2 deficiency in mice suppresses the expression of the inhibitory Fcgamma receptor (FcgammaRIIB) through the induction of the IFN-inducible p202, a lupus susceptibility protein

Murine Aim2 and Ifi202 genes (encoding for the Aim2 and p202 proteins) are members of the IFN-inducible Ifi200 gene family. The Aim2 deficiency in mice activates IFN signaling and stimulates the expression of the lupus susceptibility gene, the Ifi202, located within the NZB autoimmunity 2 (Nba2) interval. Given that the deficiency in the expression of the Fcgr2b gene (encoding for the inhibitory FcγRIIB receptor) is associated with increased lupus susceptibility in mice, we investigated whether the Aim2 protein could regulate the expression of Fcgr2b gene. In this article, we report that Aim2 deficiency in mice suppresses the expression of the FcγRIIB receptor. Interestingly, the Fcgr2b-deficient cells expressed increased levels of the IFN-β, activated IFN signaling, and expressed reduced levels of the Aim2 protein. Treatment of splenic cells with IFN-α or -γ reduced levels of the FcγRIIB mRNA and protein and also decreased the activity of the FcγRIIB p(-729/+585) Luc reporter. Moreover, levels of the FcγRIIB receptor were significantly higher in the Stat1-deficient splenic cells than in the wild-type cells. Accordingly, increased expression of IFN-β in lupus-prone B6.Nba2-ABC mice, as compared with non-lupus-prone C57BL/6 (B6) or B6.Nba2-C mice, was associated with reduced expression of the FcγRIIB receptor. Notably, overexpression of the p202 protein in cells decreased the expression of the Aim2 gene, activated the IFN response, and suppressed the expression of the Fcgr2b gene. These observations demonstrate that the expression of Aim2 protein is required to maintain the expression of the Fcgr2b gene and also predict epistatic interactions between the Ifi200 genes and the Fcgr2b gene within the Nba2 interval.     

Effect of thyroidectomy on sex & accessory sex organs in a common Indian garden lizard Calotes versicolor (Daud)

In adult male lizards, body weight was unchanged after thyroidectomy. The cell height of the sexual segment of the kidneys was decreased significantly (p .001). Weights of testes, vas deferens, hemipenis, and kidneys of thyroidectomized animals were less than those of controls (p .001). At autopsy of thyroidectomized lizards, the testes and the sexual segment of the kidneys were found to be degenerate and inactive at a time when intact animals were at their peak of development.