Simona Nikolova

Stress-inducible phosphoprotein 1 has unique cochaperone activity during development and regulates cellular response to ischemia via the prion protein

Stress‐inducible phosphoprotein 1 (STI1) is part of the chaperone machinery, but it also functions as an extracellular ligand for the prion protein. However, the physiological relevance of these STI1 activities in vivo is unknown. Here, we show that in the absence of embryonic STI1, several Hsp90 client proteins are decreased by 50%, although Hsp90 levels are unaffected. Mutant STI1 mice showed increased caspase‐3 activation and 50% impairment in cellular proliferation. Moreover, placental disruption and lack of cellular viability were linked to embryonic death by E10.5 in STI1‐mutant mice. Rescue of embryonic lethality in these mutants, by transgenic expression of the STI1 gene, supported a unique role for STI1 during embryonic development. The response of STI1 haploinsufficient mice to cellular stress seemed compromised, and mutant mice showed increased vulnerability to ischemic insult. At the cellular level, ischemia increased the secretion of STI1 from wild‐type astrocytes by 3‐fold, whereas STI1 haploinsufficient mice secreted half as much STI1. Interesting, extracellular STI1 prevented ischemia‐mediated neuronal death in a prion protein‐dependent way. Our study reveals essential roles for intracellular and extracellular STI1 in cellular resilience.—Beraldo, F. H., Soares, I. N., Goncalves, D. F., Fan, J., Thomas, A. A., Santos, T. G., Mohammad, A. H., Roffe, M., Calder, M. D., Nikolova, S., Hajj, G. N., Guimaraes, A. N., Massensini, A. R., Welch, I., Betts, D. H., Gros, R., Drangova, M., Watson, A. J., Bartha, R., Prado, V. F., Martins, V. R., and Prado, M. A. M., Stress‐inducible phosphoprotein 1 has unique cochaperone activity during development and regulates cellular response to ischemia via the prion protein. FASEB J. 27, 3594–3607 (2013). www.fasebj.org

Comorbid Aβ toxicity and stroke: hippocampal atrophy, pathology, and cognitive deficit.

Numerous clinical and epidemiological reports indicate that patients with history of vascular illness such as stroke are more likely to develop dementia as the clinical manifestation of Alzheimers disease. However, there are little data regarding the pathologic mechanisms that link vascular risk factors to the factors associated with dementia onset. We provide evidence that suggests intriguing detrimental interactions between stroke and β-amyloid (Aβ) toxicity in the hippocampus. Stroke was induced by unilateral striatal injection of endothelin-1, the potent vasoconstrictor. Aβ toxicity was modeled by bilateral intracerebroventricular injections of the toxic fragment Aβ. Gross morphologic changes in comorbid Aβ and stroke rats were enlargement of the lateral ventricles with concomitant shrinkage of the hippocampus. The hippocampus displayed a series of synergistic biochemical alterations, including microgliosis, deposition of Aβ precursor protein fragments, and cellular degeneration. In addition, there was bilateral induction of connexin43, reduced neuronal survival, and impaired dendritic development of adult-born immature neurons in the dentate gyrus of these rats compared with either rats alone. Behaviorally, there was impairment in the hippocampal-based discriminative fear-conditioning to context task indicating learning and memory deficit. These results suggest an insight into the relationship between hippocampal atrophy, pathology, and functional impairment. Our work not only highlights the exacerbated pathology that emerges when Aβ toxicity and stroke occur comorbidly but also demonstrates that this comorbid rat model exhibits physiopathology that is highly characteristic of the human condition.

Forebrain Deletion of the Vesicular Acetylcholine Transporter Results in Deficits in Executive Function, Metabolic, and RNA Splicing Abnormalities in the Prefrontal Cortex

One of the key brain regions in cognitive processing and executive function is the prefrontal cortex (PFC), which receives cholinergic input from basal forebrain cholinergic neurons. We evaluated the contribution of synaptically released acetylcholine (ACh) to executive function by genetically targeting the vesicular acetylcholine transporter (VAChT) in the mouse forebrain. Executive function was assessed using a pairwise visual discrimination paradigm and the 5-choice serial reaction time task (5-CSRT). In the pairwise test, VAChT-deficient mice were able to learn, but were impaired in reversal learning, suggesting that these mice present cognitive inflexibility. Interestingly, VAChT-targeted mice took longer to reach criteria in the 5-CSRT. Although their performance was indistinguishable from that of control mice during low attentional demand, increased attentional demand revealed striking deficits in VAChT-deleted mice. Galantamine, a cholinesterase inhibitor used in Alzheimers disease, significantly improved the performance of control mice, but not of VAChT-deficient mice on the 5-CSRT. In vivo magnetic resonance spectroscopy showed altered levels of two neurochemical markers of neuronal function, taurine and lactate, suggesting altered PFC metabolism in VAChT-deficient mice. The PFC of these mice displayed a drastic reduction in the splicing factor heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNPA2/B1), whose cholinergic-mediated reduction was previously demonstrated in Alzheimers disease. Consequently, several key hnRNPA2/B1 target transcripts involved in neuronal function present changes in alternative splicing in VAChT-deficient mice, including pyruvate kinase M, a key enzyme involved in lactate metabolism. We propose that VAChT-targeted mice can be used to model and to dissect the neurochemical basis of executive abnormalities.

Endothelin-1 induced MCAO : Dose dependency of cerebral blood flow

The purpose of this study was to characterize the magnitude and duration of cerebral blood flow (CBF) reduction in the somatosensory cortical region in a rat model of middle cerebral artery occlusion (MCAO) induced by endothelin-1 (ET1) microinjection under isoflurane anesthesia. MCAO was induced by microinjection of ET1 proximal to the MCA in 41 isoflurane-anesthetized male Sprague-Dawley rats. Three doses of ET1 were studied, 60 pmol (Group 1), 150 pmol (Group 2), and 300 pmol (Group 3). CBF was monitored for 4h following injection using a laser Doppler probe stereotaxically inserted into the left somatosensory cortical region. Computed tomography perfusion imaging was used to verify the extent and duration of blood flow reduction in a subset of 12 animals. The magnitude and duration of blood flow reduction was variable (60-92% of baseline). The 300 pmol dose provided the greatest sustained decrease in blood flow. Evidence of tissue damage was obtained in cases where CBF decreased to <40% of baseline. At the doses studied, ET1-induced ischemia in the presence of isoflurane anesthesia can be used as a minimally invasive but variable model of MCAO. The model is well suited for acute imaging studies of ischemia.

Registration of in vivo magnetic resonance T1-weighted brain images to triphenyltetrazolium chloride stained sections in small animals

Signal changes observed in high-resolution in vivo magnetic resonance (MR) images acquired during cerebral ischemia in small animal models must be correlated to molecular indicators of tissue damage obtained from digitized histological brain sections. An effective image registration technique that incorporates both a linear and non-linear thin plate spline transform was developed to compensate the distortions that occur in the brain during the extraction, fixation, and staining process. Features in different layers of the brain were utilized in conjunction with a radial guideline-assisted landmark selection method to register tissue layers with few distinguishing characteristics. Quantitative analysis using simulated data demonstrated average registration error of 400 microm (corresponding to approximately 2.5 pixels in the MR images) when > or =50 landmark points are used. Visual agreement was obtained between T(1)-weighted MR images and 2,3,5-triphenyltetrazolium chloride stained histology. These methods will allow accurate registration of in vivo images with histology to correlate in vivo surrogate markers of tissue damage with specific histological indicators of disease.

The endurance lifetime of ice fragments in cometary streams

Abstract The endurance lifetime against sublimation of meter- to decameter-sized ice fragments are calculated for typical cometary orbits. It is found that such bodies can survive for multiple perihelion passages. For fragments traveling along orbits similar to those of typical meteor shower producing comets, the sublimation mass loss rate drives radial variations equivalent to 1–0.5 m per orbit. We review the available data with respect to the possible presence of large objects within the Perseid, Lyrid, Leonid and α-Capricornid streams. Invoking cometary aging and surface fragmentation events as the mechanism for placing large meteoroids within cometary streams, we find no compelling reasons to doubt that large meteoroids are intermittently present in most, if not all cometary-derived meteoroid assemblages.

Functional MRI of neuronal activation in epilepsy patients with malformations of cortical development.

Malformations of cortical development are disturbances in brain formation that arise from abnormalities affecting the processes of cortical development. Surgical treatment of intractable epilepsy in patients with malformations of cortical development requires localization of both epileptogenic and eloquent cortices. Functional magnetic resonance imaging has been shown to detect the reorganization of activation patterns in such patients. The purpose of this study was to determine whether functional reorganization of the primary sensory and motor cortices occurs in patients with epileptogenic malformations of cortical development. Functional MRI data were obtained for 11 patients (four male, seven female) with a mean age of 36 years (range 18-55 years). The mean age at epilepsy onset was 23 years (range 3-55 years). Twelve healthy controls (six male, six female) with mean age of 33 years (range 28-51 years) were also recruited for comparison. High resolution anatomical MRI was used to confirm the presence and the location of the malformation. All imaging experiments were performed using a 3.0T Siemens Tim Trio whole body MRI. Each subject performed four block-paradigm fMRI experiments to study motor and sensory activation for each hand. A total of 132 image sets were collected for each paradigm over 5.5min (2.5s per image). Each paradigm consisted of seven stimulus periods lasting 30s (12 images) and stimulus onset of 30, 90, 150, 210 and 270s. Functional data were obtained from all eligible patients and compared to those of controls. Reorganization and reduction in function in the motor and sensory areas were observed in patients with cortical dysplasia. Patients with polymicrogyria did not present with significant functional reorganization and patients with heterotopias and coexisting polymicrogyria and/or cortical dysplasia had variable patterns of activation. In summary, this study showed evidence of functional reorganization of sensory and motor cortices in patients with cortical dysplasia development. Such information should be carefully considered in surgical planning and treatment.

T2+ measurement during acute cerebral ischemia by carr-purcell MRI at 4T

Metabolic and structural changes occur in brain tissue within minutes of ischemia. The adiabatic multi‐echo (Carr‐Purcell) localization pulse sequence LASER has shown promise in detecting tissue contrast changes within the first hour of ischemia. The purpose of this initial study was to combine the LASER localization sequence with fast 3D echo‐planar imaging (EPI) to quantify the regional apparent transverse relaxation (T2†) in a rabbit model of acute embolic ischemia at 4 Tesla. Carr‐Purcell T2†‐weighted images were acquired at 7 different echo‐times and used to estimate T2† in both cortex and striatum. In ischemic tissue identified by 2,3,5 ‐ triphenyltetrazolium chloride (TTC) staining, the T2† increased by approximately 31% after 1 hour of ischemia and remained elevated until study completion at 4 h of ischemia. Lesion volume, defined as the number of pixels with T2† greater than 90 ms, increased by 40% between 1 and 4 h after induction of ischemia. Carr‐Purcell LASER‐EPI T2†‐weighted images show promise in detecting early tissue changes in focal cerebral ischemia. Magn Reson Med, 2005.

The Severity of Ischemia Varies in Sprague-Dawley Rats from Different Vendors

The purpose of this study was to compare acute cerebral perfusion measured by computed tomography, stroke lesion volume measured by magnetic resonance imaging, and motor function in Sprague-Dawley rats supplied by Charles River (Charles River, Quebec, Canada) and Harlan (Harlan, Michigan, USA). During the acute stages of ischemia (<3 hours), Sprague-Dawley rats supplied by Harlan had a greater reduction in blood flow (67%) than rats supplied by Charles River (37%). MRI at days 1 and 6 after ischemia showed larger lesions in the Charles River animals compared to Harlan animals () at both time points. Lesion volume decreased in both Charles River and Harlan rats at day 6 compared to day 1 () and corresponded to lesion size on histology. The Harlan animals had significant functional deficits () one day after surgery in postural hang reflex, forelimb placement, and tactile fraction first tests, whereas rats supplied by Charles River had no significant functional impairment as a result of surgery. The current study provides evidence that differences in response to ischemia between rats of the same strain supplied by different vendors should be an important consideration when animals are selected for the study of cerebral ischemia.