The Journal of biological chemistry
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The restoration of energy balance during ischemia is critical to cellular survival; however, relatively little is known concerning the regulation of neuronal metabolic pathways in response to central nervous system ischemia. AMP-activated protein kinase (AMPK), a master sensor of energy balance in peripheral tissues, is phosphorylated and activated when energy balance is low. We investigated whether AMPK might also modulate neuronal energy homeostasis during ischemia. ⋯ Mice deficient in neuronal nitric-oxide synthase demonstrated a decrease in both stroke damage and AMPK activation compared with wild type, suggesting a possible interaction between NO and AMPK activation in stroke. These data demonstrate a role for AMPK in the response of neurons during metabolic stress and suggest that in ischemia the activation of AMPK is deleterious. The ability to manipulate pharmacologically neuronal energy balance during ischemia represents an innovative approach to neuroprotection.
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We have shown previously that sulforaphane (SFN), a constituent of many edible cruciferous vegetables including broccoli, suppresses growth of prostate cancer cells in culture as well as in vivo by causing apoptosis, but the sequence of events leading to cell death is poorly defined. Using PC-3 and DU145 human prostate cancer cells as a model, we now demonstrate, for the first time, that the initial signal for SFN-induced apoptosis is derived from reactive oxygen species (ROS). Exposure of PC-3 cells to growth-suppressive concentrations of SFN resulted in ROS generation, which was accompanied by disruption of mitochondrial membrane potential, cytosolic release of cytochrome c, and apoptosis. ⋯ In addition, SFN treatment resulted in an increase in the level of Fas, activation of caspase-8, and cleavage of Bid. Furthermore, SV40-immortalized mouse embryonic fibroblasts (MEFs) derived from Bid knock-out mice displayed significant resistance toward SFN-induced apoptosis compared with wild-type MEFs. In conclusion, the results of the present study indicate that SFN-induced apoptosis in prostate cancer cells is initiated by ROS generation and that both intrinsic and extrinsic caspase cascades contribute to the cell death caused by this highly promising cancer chemopreventive agent.
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Peroxisome proliferator-activated receptor gamma co-activator 1alpha (PGC-1alpha) promotes mitochondrial biogenesis and slow fiber formation in skeletal muscle. We hypothesized that activation of the p38 mitogen-activated protein kinase (MAPK) pathway in response to increased muscle activity stimulated Pgc-1alpha gene transcription as part of the mechanisms for skeletal muscle adaptation. Here we report that a single bout of voluntary running induced a transient increase of Pgc-1alpha mRNA expression in mouse plantaris muscle, concurrent with an activation of the p38 MAPK pathway. ⋯ Furthermore, the p38-mediated increase in Pgc-1alpha promoter activity was enhanced by increased expression of the downstream transcription factor ATF2 and completely blocked by ATF2DeltaN, a dominant negative ATF2. Skeletal muscle-specific expression of a constitutively active activator of p38, MKK6E, in transgenic mice resulted in enhanced Pgc-1alpha and cytochrome oxidase IV protein expression in fast-twitch skeletal muscles. These findings suggest that contractile activity-induced activation of the p38 MAPK pathway promotes Pgc-1alpha gene expression and skeletal muscle adaptation.
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Activated protein C (APC) has anti-inflammatory and vascular protective effects independent of anticoagulation. We previously identified the prototypical thrombin receptor, protease-activated receptor-1 (PAR1), as part of a novel APC-endothelial cell protein C receptor (EPCR) signaling pathway in endothelial cells. Experiments in wild-type and PAR1(-/-) mice demonstrated that intravenous injection of APC leads to PAR1-dependent gene induction in the lung. ⋯ Concordant PAR1-dependent effects on protein levels were found. Thus, by signaling through the same receptor PAR1, APC, and thrombin can exert distinct biological effects in perturbed endothelium. These data may explain how APC can be therapeutically protective through the EPCR-PAR1 signaling despite ongoing thrombin generation due to disseminated intravascular coagulopathy.
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Comparative Study
Transient receptor potential vanilloid type 1 activation down-regulates voltage-gated calcium channels through calcium-dependent calcineurin in sensory neurons.
Calcium influx through voltage-activated Ca(2+) channels (VACCs) plays a critical role in neurotransmission. Capsaicin application inhibits VACCs and desensitizes nociceptors. In this study, we determined the signaling mechanisms of the inhibitory effect of capsaicin on VACCs in primary sensory neurons. ⋯ Immunofluorescence labeling revealed that capsaicin induced a rapid internalization of Ca(V)2.2 channels on the membrane. Thus, this study provides novel information that VACCs are tonically modulated by the intracellular Ca(2+) level and endogenous phosphatases in sensory neurons. Stimulation of TRPV1 by capsaicin down-regulates VACCs by dephosphorylation through Ca(2+)-dependent activation of calcineurin.