Sonia Carboni

Prion diseases are transmissible neurodegenerative disorders characterized by extensive neuronal apoptosis and accumulation of misfolded prion protein (PrP(SC)). Recent reports indicate that PrP(SC) induces neuronal apoptosis via activation of the endoplasmic reticulum (ER) stress pathway and activation of the ER resident caspase-12. Here, we investigate the relationship between prion replication and induction of ER stress during different stages of the disease in a murine scrapie model. The first alteration observed consists of the upregulation of the ER chaperone of the glucose-regulated protein Grp58, which was detected during the presymptomatic phase and followed closely the formation of PrP(SC). An increase in Grp58 expression correlated with PrP(SC) accumulation at all stages of the disease in different brain areas, suggesting that this chaperone may play an important role in the cellular response to prion infection. Indeed, in vitro studies using N2a neuroblastoma cells demonstrated that inhibition of Grp58 expression with small interfering RNA led to a significant enhancement of PrP(SC) toxicity. Conversely, overexpression of Grp58 protected cells against PrP(SC) toxicity and decreased the rate of caspase-12 activation. Grp58 and PrP were shown to interact by coimmunoprecipitation, observing a higher interaction in cells infected with scrapie prions. Our data indicate that expression of Grp58 is an early cellular response to prion replication, acting as a neuroprotective factor against prion neurotoxicity. Our findings suggest that targeting Grp58 interaction may have applications for developing novel strategies for treatment and early diagnosis of prion diseases.

1 Myocardial ischemia/reperfusion is associated with inflammation, apoptosis and necrosis. During this process, c-jun N-terminal kinase is activated in cardiac myocytes resulting in apoptosis. 2 This study investigates the effects of AS601245, a nonpeptide ATP competitive JNK inhibitor, on infarct size caused by myocardial ischemia/reperfusion in anaesthetized rats. The left descending coronary artery of anaesthetized rats was occluded for 30 min and then reperfused for 3 h. AS601245 was administered 5 min before the end of the ischemia period as an i.v. bolus (1.5, 4.5 or 15 mg kg(-1) i.v.) followed by continuous i.v. infusion (18, 55 and 183 microg kg(-1) min(-1), respectively) during reperfusion. Controls received saline only. 3-Aminobenzamide, a poly(ADP-ribose) polymerase inhibitor, was used as reference compound at 10 mg kg(-1) i.v. bolus plus 0.17 mg kg(-1) min(-1) continuous infusion. 3 AS601245 significantly reduced infarct size at 4.5 mg kg(-1) (-44%; P<0.001) and 15 mg kg(-1) i.v. (-40.3%; P<0.001) similarly to 3-aminobenzamide (-44.2%; P<0.001). This protective effect was obtained without affecting hemodynamics or reducing ST-segment displacement. 4 The beneficial effects on infarct size correlated well with the reduction of c-jun phosphorylation (-85%; P<0.001 versus control) and of TUNEL-positive cells (-82.1%; P<0.001) in post-ischemic cardiomyocytes. No change in the phosphorylation state of p38 MAPK and ERK in post-ischemic heart was observed in the presence of AS601245 in comparison to the vehicle-treated group. 5 These results demonstrate that blocking the JNK pathway may represent a novel therapeutic approach for treating myocardial ischemia/reperfusion-induced cardiomyocyte death.

The role of prefrontal cortical dopamine (DA) in the modulation of working memory functions is well documented, but substantial evidence indicates that the locus ceruleus noradrenergic system also modulates working memory via actions within the prefrontal cortex (PFC). This study shows that PFC noradrenaline (NA) and DA dialysate levels phasically increase when rats perform correctly in a delayed alternation task in a T-maze, a test of spatial working memory. However, NA levels were markedly enhanced in animals trained to alternate compared with rats that acquired the spatial information about the location of food in the maze but were untrained to make a choice to obtain the reward. In contrast, PFC DA elevations occurred independently of whether the animal had acquired the trial-specific information for correct task execution. The contribution of anticipatory responses to catecholamine efflux was also evaluated by exposing rats to an environment signaling the presence of the reward in the successive alternation task. No conditioned NA efflux was observed in either group. In contrast, in both groups, DA efflux increased in the anticipatory phase of the test to the same levels of those reached during the task. These data provide the first direct evidence for a selective activation of PFC NA transmission during a spatial working memory task. We propose that, in the working memory task, DA is primarily associated with reward expectancy, whereas NA is involved in the active maintenance of the information about a goal and the rules to achieve it.

c-Jun N-terminal kinase (JNK), a member of the mitogen-activated protein kinase family, is activated in response to a number of extracellular stimuli, including inflammatory cytokines, UV irradiation and ischaemia. A large body of evidence supports a role for JNK signalling in stress-induced apoptosis. It has been hypothesized that JNK may contribute to the apoptotic response by regulating the intrinsic cell death pathway involving the mitochondria. Here, we examined the role of the JNK signalling pathway in hippocampal CA1 apoptotic neurones following transient ischaemia in gerbils. We showed early activation of death receptor-dependent apoptosis (caspase-8 activation 2 days after ischaemia) and a biphasic activation of caspase-3 and caspase-9 after ischaemia. Activation of the mitochondrial pathway, as measured by cytochrome c release, appeared as a late event (5-7 days after ischaemia). AS601245, a novel JNK inhibitor, antagonized activation of both pathways and significantly protected CA1 neurones from cell death. Our results suggest a key role of JNK in the control of death receptor and mitochondrial-dependent apoptosis after transient ischaemia.