The potential role of rho GTPases in Alzheimer's disease pathogenesis

Alzheimer's disease (AD) is characterized by a wide loss of synapses and dendritic spines. Despite extensive efforts, the molecular mechanisms driving this detrimental alteration have not yet been determined. Among the factors potentially mediating this loss of neuronal connectivity, the contribution of Rho GTPases is of particular interest. This family of proteins is classically considered a key regulator of actin cytoskeleton remodeling and dendritic spine maintenance, but new insights into the complex dynamics of its regulation have recently determined how its signaling cascade is still largely unknown, both in physiological and pathological conditions. Here, we review the growing evidence supporting the potential involvement of Rho GTPases in spine loss, which is a unanimously recognized hallmark of early AD pathogenesis. We also discuss some new insights into Rho GTPase signaling framework that might explain several controversial results that have been published. The study of the connection between AD and Rho GTPases represents a quite unchartered avenue that holds therapeutic potential.

Rho GTPase-dependent plasticity of dendritic spines in the adult brain

Brain activity is associated with structural changes in the neural connections. However, in vivo imaging of the outer cortical layers has shown that dendritic spines, on which most excitatory synapses insist, are predominantly stable in adulthood. Changes in dendritic spines are governed by small GTPases of the Rho family through modulation of the actin cytoskeleton. Yet, while there are abundant data about this functional effect of Rho GTPases in vitro, there is limited evidence that Rho GTPase signaling in the brain is associated with changes in neuronal morphology. In the present work, both chronic in vivo two-photon imaging and Golgi staining reveal that the activation of Rho GTPases in the adult mouse brain is associated with little change of dendritic spines in the apical dendrites of primary visual cortex pyramidal neurons. On the contrary, considerable increase in spine density is observed (i) in the basal dendrites of the same neurons (ii) in both basal and apical dendrites of the hippocampal CA1 pyramidal cells. While confirming that Rho GTPase-dependent increase in spine density can be substantial, the study indicates region and dendrite selectivity with relative stability of superficial cortical circuits.

Finite-time erasing of information stored in fermionic bits

We address the issue of minimizing the heat generated when erasing the information stored in an array of quantum dots in finite time. We identify the fundamental limitations and trade-offs involved in this process and analyze how a feedback operation can help improve it.

Four-jet production at the Large Hadron Collider at next-to-leading order in QCD

We present the cross sections for production of up to four jets at the Large Hadron Collider, at next-to-leading order in the QCD coupling. We use the BLACKHAT library in conjunction with SHERPA and a recently developed algorithm for assembling primitive amplitudes into color-dressed amplitudes. We adopt the cuts used by ATLAS in their study of multijet events in pp collisions at √s=7 TeV. We include estimates of nonperturbative corrections and compare to ATLAS data. We store intermediate results in a framework that allows the inexpensive computation of additional results for different choices of scale or parton distributions.

Long-lasting efficacy of the cognitive enhancer cytotoxic necrotizing factor 1

Rho GTPases are key regulators of the activity-dependent changes of neural circuits. Besides being involved in nervous system development and repair, this neural structural plasticity is believed to constitute the cellular basis of learning and memory. Here we report that concurrent modulation of cerebral Rho GTPases, including Rac, Rho and Cdc42 subfamilies, by Cytotoxic Necrotizing Factor 1 (CNF1, 10 fmol/kg intracerebroventricularly) improves object recognition in both C57BL/6J and CD1 mice. The improvement is long lasting, as it is still observed 90 days post treatment. At this time, the treatment is associated with enhancement of neurotransmission and long-term potentiation. The effects depend on changes in Rho GTPase status, since the recombinant molecule CNF1 C866S, in which the enzymatic activity was abolished through substitution of serine to cysteine at position 866, is ineffective. The study confirms the role of Rho GTPases in learning and suggests that a single administration of CNF1 is effective for a long time after administration. In general, the long-lasting cognition enhancing effect of CNF1 might be beneficial for the treatment of CNS disorders. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

The Rho GTPase activating CNF1 improves associative working memory for object-in-place

Cerebral Rho GTPases are crucially involved in cognitive abilities. This activity is thought to be related to the regulation of actin polymerization and, thereby, of the shape of the dendritic tree. Here we report that Cytotoxic Necrotizing Factor 1 (CNF1, 1fmol/kgicv), a bacterial protein endowed with Rho GTPase activating properties, enhances working memory for object location/discrimination in C57BL/6 mice. CNF1 selectively increased the exploration of a specific familiar object moved to a position that had been previously occupied by another familiar object. Conversely, the treatment left unaffected (i) exploration of a familiar object moved to a location that was previously unoccupied and (ii) exploration of a novel object. The effects were associated with changes in Rho GTPase status, since CNF1 C866S, a recombinant CNF1 in which the enzymatic activity was abolished through substitution of serine to cysteine at position 866, was ineffective in all the experiments. The study suggests that working memory for specific object-location associations critically depends on neural connectivity. It also confirms the therapeutic potential of the manipulation of Rho GTPase signaling in the modulation of memory processes.

[Hemoperitoneum from rupture of liver subcapsular hematoma after laparoscopic cholecystectomy attributed to ketorolac. Report of a case]

Ketorolac is one of the most common nonsteroidal anti-inflammatory drugs used to control postoperative pain. However, peri- and postoperative administration of ketorolac is associated with an increased risk of gastrointestinal bleeding as described in the literature. Notwithstanding this event is not frequent, it can expose the patient to serious complications that should be quickly recognised and effectively treated. We present a report about a female patient with cholelithiasis who underwent a laparoscopic cholecystectomy. After the operation, the patient had a haemorrhage that we attributed to surgery in a first time and then to administration of ketorolac.

Anastomotic leaks after anterior resection for mid and low rectal cancer: survey of the Italian Society of Colorectal Surgery

BACKGROUND

The aim of the survey was to assess the incidence of anastomotic leaks (AL) and to identify risk factors predicting incidence and gravity of AL after low anterior resection (LAR) for rectal cancer performed by colorectal surgeons of the Italian Society of Colorectal Surgery (SICCR).

METHODS

Information about patients with rectal cancers less than 12 cm from the anal verge who underwent LAR during 2005 was collected retrospectively. AL was classified as grade I to IV according to gravity. Fifteen clinical variables were examined by univariate and multivariate analyses. Further analysis was conducted on patients with AL to identify factors correlated with gravity.

RESULTS

There were 520 patients representing 64% of LAR for rectal cancer performed by SICCR members. The overall rate of AL was 15.2%. Mortality was 2.7% including 0.6% from AL. The incidence of AL was correlated with higher age (p<0.05), lower (<20 per year) centre case volume (p<0.05), obesity (p<0.05), malnutrition (p<0.01) and intraoperative contamination (p<0.05), and was lower in patients with a colonic J-pouch reservoir (p<0.05). In the multivariate analysis age, malnutrition and intraoperative contamination were independent predictors. The only predictor of severe (grade III/IV) AL was alcohol/smoking habits (p<0.05) while the absence of a diverting stoma was borderline significant (p<0.07).

CONCLUSION

Our retrospective survey identified several risk factors for AL. This survey was a necessary step to construct prospective interventional studies and to establish benchmark standards for outcome studies.

Enhancement of learning and memory after activation of cerebral Rho GTPases

The mechanism whereby the morphology and connectivity of the dendritic tree is regulated depends on an actin dynamics that, in turn, is controlled by Rho GTPases, a family of small GTP-binding proteins encompassing Rho, Rac, and Cdc42 subfamilies. Cytotoxic necrotizing factor 1 (CNF1), a protein toxin from Escherichia coli, constitutively activates Rho GTPases, thus leading to remodeling of the actin cytoskeleton in intact cells. Here, we show that the modulation of cerebral RhoA and Rac1 activity induced by CNF1 in mice leads to (i) rearrangement of cerebral actin cytoskeleton, (ii) enhanced neurotransmission and synaptic plasticity, and (iii) improved learning and memory in various behavioral tasks. The effects persist for weeks and are not observed in mice treated with a recombinant CNF1, in which the enzymatic activity was abolished by substituting serine to cysteine at position 866. The results suggest that learning ability can be improved through pharmacological manipulation of neural connectivity.

Differential effects of three species ofHypericum in an open field test

The effects of three species of Hypericum (H.) on mice motor activity were compared in an automated open field test. Methanol extracts of H. perforatum L., H. hircinum L. and H. perfoliatum L. were tested at doses ranging from 2.5 to 200 mg i.p. H. hircinum decreased locomotion at most dose levels. Moreover, a dose of 200 mg/kg of all three herbal species sharply decreased motor activity. Ten mg/kg of H. perforatum, a dose that is comparable to that endowed with antidepressant effects in humans, tended to increase exploration and stereotypic activity and to decrease immobility. The study suggests that there are differences in the neuropharmacological actions of the three plant extracts. However, common constituents might explain the reduced motor activity observed at high dose levels.