Plasmalogens rescue neuronal cell death through an activation of AKT and ERK survival signaling.

Neuronal cells are susceptible to many stresses, which will cause the apoptosis and neurodegenerative diseases. The precise molecular mechanism behind the neuronal protection against these apoptotic stimuli is necessary for drug discovery. In the present study, we have found that plasmalogens (Pls), which are glycerophospholipids containing vinyl ether linkage at sn-1 position, can protect the neuronal cell death upon serum deprivation. Interestingly, caspse-9, but not caspase-8 and caspase-12, was cleaved upon the serum starvation in Neuro-2A cells. Pls treatments effectively reduced the activation of caspase-9. Furthermore, cellular signaling experiments showed that Pls enhanced phosphorylation of the phosphoinositide 3-kinase (PI3K)-dependent serine/threonine-specific protein kinase AKT and extracellular-signal-regulated kinases ERK1/2. PI3K/AKT inhibitor LY294002 and MAPK/ERK kinase (MEK) inhibitor U0126 treatments study clearly indicated that Pls-mediated cell survival was dependent on the activation of these kinases. In addition, Pls also inhibited primary mouse hippocampal neuronal cell death induced by nutrient deprivation, which was associated with the inhibition of caspase-9 and caspase-3 cleavages. It was reported that Pls content decreased in the brain of the Alzheimer's patients, which indicated that the reduction of Pls content could endanger neurons. The present findings, taken together, suggest that Pls have an anti-apoptotic action in the brain. Further studies on precise mechanisms of Pls-mediated protection against cell death may lead us to establish a novel therapeutic approach to cure neurodegenerative disorders.

Role of brain serotonin dysfunction in the pathophysiology of congestive heart failure.

Inherited or non-inherited dilated cardiomyopathy (DCM) patients develop varied disease phenotypes leading to death after developing congestive heart failure (HF) or sudden death with mild or no overt HF symptoms, suggesting that environmental and/or genetic factors may modify the disease phenotype of DCM. In this study, we sought to explore unknown genetic factors affecting the disease phenotype of monogenic inherited human DCM. Knock-in mice bearing a sarcomeric protein mutation that causes DCM were created on different genetic backgrounds; BALB/c and C57Bl/6. DCM mice on the BALB/c background showed cardiac enlargement and systolic dysfunction and developed congestive HF before died. In contrast, DCM mice on the C57Bl/6 background developed no overt HF symptoms and died suddenly, although they showed considerable cardiac enlargement and systolic dysfunction. BALB/c mice have brain serotonin dysfunction due to a single nucleotide polymorphism (SNP) in tryptophan hydroxylase 2 (TPH2). Brain serotonin dysfunction plays a critical role in depression and anxiety and BALB/c mice exhibit depression- and anxiety-related behaviors. Since depression is common and associated with poor prognosis in HF patients, we examined therapeutic effects of anti-depression drug paroxetine and anti-anxiety drug buspirone that could improve the brain serotonin function in mice. Both drugs reduced cardiac enlargement and improved systolic dysfunction and symptoms of severe congestive HF in DCM mice on the BALB/c background. These results strongly suggest that genetic backgrounds involving brain serotonin dysfunction, such as TPH2 gene SNP, may play an important role in the development of congestive HF in DCM.

Cytokine-induced suppression of medial preoptic neurons: mechanisms and neuroimmunomodulatory effects.

We have shown that the medial preoptic area (MPO) in the hypothalamus is a major site where interferon (IFN)-alpha acts to induce suppression of splenic natural killer (NK) cell activity through an activation of sympathetic nervous system (SNS) in rats. Here, we discuss the hypothalamic mechanisms of the cytokine action using in vivo and in vitro preparations in rats. Lesion of the MPO activated the SNS and suppressed splenic NK cell activity in anesthetized rats, suggesting that the MPO had an inhibitory influence on nerve activity. Since both IFN-alpha and interleukin (IL)-1beta are known to suppress MPO neuron activity, it is suggested that the suppression/loss of the MPO caused by cytokine actions/lesions disinhibits the hypothalamic-sympathetic pathway, thereby resulting in an increase in the splenic SNS and reduction of NK activity. To explore the cellular mechanisms of the suppression of MPO neurons, the effects of Prostaglandin E2 (PGE2), one of the major mediators of cytokine action in the brain, on the glutamate-induced membrane currents were examined using the perforated patch-clamp method in mechanically dissociated MPO neurons. Patch-clamp analysis revealed that PGE2 potentiated the Ca2+-dependent K+ current (KCa) stimulated by Ca2+ entry through N-methyl-D-aspartate channels. We suggest that the cytokine-induced decrease in the firing rates of MPO neurons may be a result of an increase in interspike intervals caused by PGE(2)-induced enhancement of KCa in the presence of glutamatergic inputs.

Brain cytokines and the 5-HT system during poly I:C-induced fatigue.

Fatigue is evoked not only by peripheral factors, such as muscle fatigue, but also by the central nervous system (CNS). For example, it is generally known that the feeling of fatigue is greatly influenced by psychological aspects, such as motivation. However, little is known about the central mechanisms of fatigue. The clinical symptoms of chronic fatigue syndrome (CFS) are shown to include disorders in neuroendocrine, autonomic, and immune systems. On the other hand, it has been demonstrated that cytokines produced in the brain play significant roles in neural-immune interactions through their various central actions, including hypothalamo-pituitary and sympathetic activation, as well as immunosuppression. In this article, using the immunologically induced fatigue model, which was achieved by intraperitoneal (i.p.) injection of synthetic double-stranded RNAs, polyriboinosinic: polyribocytidylic acid (poly I:C) in rats, we show an involvement of brain interferon-alpha (IFN-alpha) and serotonin (5-HT) transporter (5-HTT) in the central mechanisms of fatigue. In the poly I:C-induced fatigue rats, expression of IFN-alpha and 5-HTT increased, while extracellular concentration of 5-HT in the medial prefrontal cortex decreased, probably on account of the enhanced expression of 5-HTT. Since the poly I:C-induced reduction of the running wheel activity was attenuated by a 5-HT(1A) receptor agonist, but not by 5-HT(2), 5-HT(3), or dopamine D(3) receptor agonists, it is suggested that the decrease in 5-HT actions on 5-HT(1A) receptors may at least partly contribute to the poly I:C-induced fatigue.

Enhanced expression of brain interferon-alpha and serotonin transporter in immunologically induced fatigue in rats.

Immunologically induced fatigue was induced in rats by intraperitoneal injection of a synthetic double-stranded RNA, polyriboinosinic : polyribocytidylic acid (poly I:C). An injection of poly I:C (3 mg/kg) decreased the daily amounts of spontaneous running wheel activity to approximately 60% of the preinjection level until day 8. Quantitative analysis of mRNA levels demonstrated that interferon-alpha (IFN-alpha) and p38 mitogen-activated protein kinase mRNAs increased in the medial preoptic, paraventricular and ventromedial hypothalamic nuclei and in cortex on both days 1 and 8, while interleukin-1beta and an inhibitor of nuclear factor kappaB (IkappaB)-beta mRNAs increased on day 1, but recovered within a week. Serotonin transporter (5-HTT) mRNA also increased on days 1 and 8 after poly I:C injection in the same brain regions where IFN-alpha mRNA increased. The increased 5-HTT had a functional significance, because in vivo brain microdialysis revealed that an i.p. injection of poly I:C induced a decrease in the extracellular concentration of 5-HT in the prefrontal cortex; the decrease was blocked by local perfusion with a nonselective 5-HT reuptake inhibitor, imipramine. Finally, the poly I:C-induced fatigue was attenuated by a 5-HT1A receptor agonist but not by 5-HT2, 5-HT3 or dopamine D3 agonists. These findings, taken together, suggest that disorders in brain IFN-alpha and 5-HTT expression may be involved in the neuronal mechanisms of the poly I:C-induced fatigue.

Modulation of glutamate-induced outward current by prostaglandin E(2) in rat dissociated preoptic neurons.

The preoptic/anterior hypothalamus (POA) is one of the major brain regions where cytokines and their related mediators (i.e., prostaglandins) exert diverse actions. In the present study, the modulatory effects of prostaglandin E(2) (PGE(2)) on the glutamate-induced membrane currents were examined using perforated-patch clamp method in rat POA neurons that had been mechanically dissociated by vibration without enzyme treatment. Application of glutamate through U-tube induced a slow outward current following fast inward ionotroic current at a holding membrane potential of -30 mV. The slow outward current was also induced by N-methyl-d-aspartate (NMDA), accompanied by an increased membrane conductance, and inhibited by perfusion with Ca(2+)-free solution, tetraethylammonium chloride (TEA), and apamin, suggesting a Ca(2+)-dependent K(+) current (KCa) activated by Ca(2+) entry through NMDA channels. Perfusion with PGE(2) at 0.1-10 microM, a principal mediator of fever and neuroendocrine control at the POA, did not produce apparent current by itself, but selectively potentiated the glutamate- or NMDA-induced KCa without affecting inward currents. The KCa induced by activation of NMDA receptors may serve as a feedback mechanism and the modulatory effects of PGE(2) on the KCa may have an important physiological significance.

Endotoxin inhibitor blocks heat exposure-induced expression of brain cytokine mRNA in aged rats.

To investigate the age-related changes in the expression of interleukin-1beta (IL-1beta) and its related substances in the brain during heat stress, we measured amounts of mRNAs for IL-1beta, cyclooxygenase-2 (COX-2), and an inhibitor of nuclear factor (NF)-kappaB-beta (IkappaB-beta) that is known to reflect an activation of NF-kappaB, in the cortex, cerebellum, and hippocampus using a quantitative real-time capillary PCR method. The basal levels of IL-1beta mRNA in aged rats (108-110 weeks old) was significantly higher than those in young animals (10-11 weeks old) in these brain regions. Heat exposure (33 degrees C) for 1 h enhanced the expression of IL-1beta and COX-2 mRNAs in aged rats but not in young ones. The amount of lipopolysaccharide (LPS) assessed by its bioactivity in the cortex increased by heat exposure only in aged rats. To further examine an involvement of LPS in the increase in mRNAs, an endotoxin inhibitor (EI), a synthetic peptide that detoxifies LPS by binding to the toxic component of LPS, lipid A, was intraperitoneally injected before heat exposure in aged rats. An intraperitoneal injection of EI significantly attenuated the heat exposure-induced increases in mRNAs for IL-1beta, COX-2, IkappaB-beta, and the LPS activity. Administration of EI also debilitated the heat exposure-induced hyperthermia and responses of plasma ACTH and catecholamines. These findings, taken together, suggest that the bacterial translocation is involved in the mechanisms of the responses to heat exposure in aged rats including the increased expression of mRNAs for IL-1beta and its related substances in the brain.