Spreading depression activates unfolded protein response

Proteostasis During Cerebral Ischemia

Cerebral ischemia is a complex pathology involving a cascade of cellular mechanisms, which deregulate proteostasis and lead to neuronal death. Proteostasis refers to the equilibrium between protein synthesis, folding, transport, and protein degradation. Within the brain proteostasis plays key roles in learning and memory by controlling protein synthesis and degradation. Two important pathways are implicated in the regulation of proteostasis: the unfolded protein response (UPR) and macroautophagy (called hereafter autophagy). Both are necessary for cell survival, however, their over-activation in duration or intensity can lead to cell death. Moreover, UPR and autophagy can activate and potentiate each other to worsen the issue of cerebral ischemia. A better understanding of autophagy and ER stress will allow the development of therapeutic strategies for stroke, both at the acute phase and during recovery. This review summarizes the latest therapeutic advances implicating ER stress or autophagy in cerebral ischemia. We argue that the processes governing proteostasis should be considered together in stroke, rather than focusing either on ER stress or autophagy in isolation.

Cortical spreading depression-induced preconditioning in the brain

Cortical spreading depression is a technique used to depolarize neurons. During focal or global ischemia, cortical spreading depression-induced preconditioning can enhance tolerance of further injury. However, the underlying mechanism for this phenomenon remains relatively unclear. To date, numerous issues exist regarding the experimental model used to precondition the brain with cortical spreading depression, such as the administration route, concentration of potassium chloride, induction time, duration of the protection provided by the treatment, the regional distribution of the protective effect, and the types of neurons responsible for the greater tolerance. In this review, we focus on the mechanisms underlying cortical spreading depression-induced tolerance in the brain, considering excitatory neurotransmission and metabolism, nitric oxide, genomic reprogramming, inflammation, neurotropic factors, and cellular stress response. Specifically, we clarify the procedures and detailed information regarding cortical spreading depression-induced preconditioning and build a foundation for more comprehensive investigations in the field of neural regeneration and clinical application in the future.

Effect of dietary fat to produce non-alcoholic fatty liver in the rat

BACKGROUND AND AIM

Non-alcoholic steatohepatitis (NASH) belongs to a spectrum of non-alcoholic fatty liver disease (NAFLD). Oxidative stress is hypothesized to play an important role in the progression of the disease. We used the Lieber/DeCarli model for NASH to investigate the mechanisms involved in its progression.

METHODS

Male Sprague-Dawley rats were fed standard (35% of energy from fat) or high fat (71% of energy from fat) liquid diets, ad libitum or two-thirds of the amount consumed ad libitum initially for 3 weeks and then extended to 5 weeks.

RESULTS

Steatosis was absent in rats at 3 weeks feeding, but by 5 weeks, the high fat/ad lib group showed microvesicular steatosis and foci of macrovesicular steatosis without inflammation. Serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels were not different. By 5 weeks feeding, hepatic triglycerides were highest in the high fat ad lib group and the ad lib groups were higher compared with their restricted groups. The oxidative stress marker, hydroxyalkenal (HAE) was decreased in the standard ad lib compared with the high fat ad lib group. Liver mRNA of interleukin-6, haem oxygenase-1, and markers of endoplasmic stress: C/EBP homologous protein (CHOP), glucose responsive protein-78 (GRP78) and spliced X-box DNA binding protein (spliced XBP1) were similar in the ad lib groups.

CONCLUSIONS

Extending the feeding period of the high fat/ad lib diet for 5 weeks placed our rats with Type I to II NAFLD compared to the more progressed Type III state previously obtained after 3 weeks feeding. The milder condition obtained raised the prospect of genetic modifiers present in our rats that resist disease progression.

Ischemia-induced neuronal cell death and stress response

Neuronal cell death is a major feature of various diseases, including brain ischemia, neuronal degenerative diseases, and traumatic injury, suggesting the importance of investigating the mechanisms that mediate neuronal cell death. Although the various factors that contribute to brain ischemia have been defined and the mechanism through which each factor causes neuronal cell death has been investigated, definite strategies have not been established. In this brief review, we focus on two important mechanisms that contribute to the pathogenesis of brain ischemia. First, we discuss the glutamate theory, a proposed mechanism for the understanding of ischemia-induced neuronal cell death. Second, an accumulation of recent molecular neurobiology evidence regarding the dysfunction of a cellular organelle, the endoplasmic reticulum (ER), suggests that it plays a major role in the pathogenesis of neuronal cell death. Whereas the former theory reflects the role of neuron-specific factors in the induction of cell death, the stress response of the ER for maintenance of its function is regarded as a defense mechanism. Because hypoxia, another major factor in ischemia, results in further dysfunction of the ER, studies on the malfunction of this cellular organelle may facilitate the development of novel strategies to block ischemia-induced cell death.

Behavioral stress and activated serotonergic neurotransmission induce XBP-1 splicing in the rat brain

The splicing of 26 nucleotides in the coding region of the X-box binding protein-1 (XBP-1) transcript to generate a mature active transcription factor is a part of the unfolded protein response to intracellular endoplasmic reticulum stress. In this study, we demonstrated that XBP-1 splicing is promptly induced in the rat brain including the hippocampus by both inescapable electric foot shock (IS) and pharmacologically manipulated activation of 5-hydroxytryptamine release in a dose-dependent manner. By administering ketanserin, a 5-hydroxytryptamine 2A antagonist, however, we could only partially block the increased splicing by IS and observed that the splicing was not influenced by lithium carbonate pretreatment. Although it is still unclear whether the enhanced unfolded protein response functions neuroprotectively by modulating the rate of general translation and increasing chaperone proteins or whether it eventually induces cellular damage by triggering apoptosis, the present results indicate the possible existence of a new adaptive intracellular signaling pathway in the brain that responds to environmentally challenged behavioral stress loading.

Cyclooxygenase-2 mediates the development of cortical spreading depression-induced tolerance to transient focal cerebral ischemia in rats

We examined the role of cyclooxygenase-2 in the development of ischemic tolerance induced by cortical spreading depression against transient, focal brain ischemia. Cortical spreading depression was continuously induced for 2 h with topical KCl (13+/-1 depolarizations/2 h) in male Wistar rats. At 1, 2, 3, 4, and 5 days following recovery, the middle cerebral artery was transiently occluded for 120 min. Four days later, the animals were killed and infarct volume was determined. Additionally, cyclooxygenase-2 levels in the cerebral cortex and 15 deoxy-Delta(12, 14) PGJ2 levels in cerebrospinal fluid were determined at these times with Western blotting and immunoassay, respectively. Infarct volume was reduced compared with non-cortical spreading depression control animals (274.3+/-15.3 mm3) when cortical spreading depression was performed 3 and 4 days before middle cerebral artery occlusion (163.9+/-14.2 mm3, 154.9+/-14.2 mm3) but not at 1, 2 and 5 days (280.4+/-17.3 mm3, 276.3+/-16.9 mm3 and 268.5+/-17.3 mm3). Cyclooxygenase-2 levels increased most dramatically starting at 2 days, peaked at 3 days, and started to return toward baseline at 4 days after cortical spreading depression. 15 Deoxy-Delta(12, 14) PGJ2 levels increased from 134.7+/-83 pg/ml at baseline to 718+/-98 pg/ml at 3 days. Administration of N-[2-cyclohexyloxy-4-nitrophenyl] methanesulphonamide (10 mg/kg, i.v.), a selective cyclooxygenase-2 inhibitor, at 1 h prior to middle cerebral artery occlusion in cortical spreading depression preconditioned animals did not affect infarct volume (162.6+/-62.1 mm3). However, administration of N-[2-cyclohexyloxy-4-nitrophenyl] methanesulphonamide given three times prior to middle cerebral artery occlusion prevented the reduced infarct volume induced by cortical spreading depression preconditioning (272.9+/-63.2 mm3). Administration of L-nitro-arginine methyl ester (4 mg/kg, i.v.) prior to cortical spreading depression blocked increases in cyclooxygenase-2 normally seen at 3 and 4 days. We conclude that NO-mediated cyclooxygenase-2 upregulation by cortical spreading depression protects the brain against ischemic damage.

Ischemic preconditioning prevents protein aggregation after transient cerebral ischemia

Transient cerebral ischemia leads to protein aggregation mainly in neurons destined to undergo delayed neuronal death after ischemia. This study utilized a rat transient cerebral ischemia model to investigate whether ischemic preconditioning is able to alleviate neuronal protein aggregation, thereby protecting neurons from ischemic neuronal damage. Ischemic preconditioning was introduced by a sublethal 3 min period of ischemia followed by 48 h of recovery. Brains from rats with either ischemic preconditioning or sham-surgery were then subjected to a subsequent 7 min period of ischemia followed by 30 min, 4, 24, 48 and 72 h of reperfusion. Protein aggregation and neuronal death were studied by electron and confocal microscopy, as well as by biochemical analyses. Seven minutes of cerebral ischemia alone induced severe protein aggregation after 4 h of reperfusion mainly in CA1 neurons destined to undergo delayed neuronal death (which took place after 72 h of reperfusion). Ischemic preconditioning reduced significantly protein aggregation and virtually eliminated neuronal death in CA1 neurons. Biochemical analyses revealed that ischemic preconditioning decreased accumulation of ubiquitin-conjugated proteins (ubi-proteins) and reduced free ubiquitin depletion after brain ischemia. Furthermore, ischemic preconditioning also reduced redistribution of heat shock cognate protein 70 and Hdj1 from cytosolic fraction to protein aggregate-containing fraction after brain ischemia. These results suggest that ischemic preconditioning decreases protein aggregation after brain ischemia.