Development of a Clinical Score to Stratify the Risk for Carbapenem-Resistant Enterobacterales Bacteremia in Patients with Cancer and Hematopoietic Stem Cell Transplantation.

Identifying the risk factors for carbapenem-resistant Enterobacterales (CRE) bacteremia in cancer and hematopoietic stem cell transplantation (HSCT) patients would allow earlier initiation of an appropriate empirical antibiotic treatment. This is a prospective multicenter observational study in patients from 12 centers in Argentina, who presented with cancer or hematopoietic stem-cell transplant and developed Enterobacterales bacteremia. A multiple logistic regression model identified risk factors for CRE bacteremia, and a score was developed according to the regression coefficient. This was validated by the bootstrap resampling technique. Four hundred and forty-three patients with Enterobacterales bacteremia were included: 59 with CRE and 384 with carbapenem-susceptible Enterobacterales (CSE). The risk factors that were identified and the points assigned to each of them were: ≥10 days of hospitalization until bacteremia: OR 4.03, 95% CI 1.88-8.66 (2 points); previous antibiotics > 7 days: OR 4.65, 95% CI 2.29-9.46 (2 points); current colonization with KPC-carbapenemase-producing Enterobacterales: 33.08, 95% CI 11.74-93.25 (5 points). With a cut-off of 7 points, a sensitivity of 35.59%, specificity of 98.43%, PPV of 77.7%, and NPV of 90.9% were obtained. The overall performance of the score was satisfactory (AUROC of 0.85, 95% CI 0.80-0.91). Finally, the post-test probability of CRE occurrence in patients with none of the risk factors was 1.9%, which would virtually rule out the presence of CRE bacteremia.

An update on ophthalmological perspectives in oculodermal melanocytosis (Nevus of Ota).

PURPOSE: To provide a review of the literature on oculodermal melanocytosis (ODM) with a focus on the diagnostic and therapeutic implications of multimodal imaging techniques in the management of ophthalmic complications. METHODS: The authors carried out a literature search on PubMed, Medline, and Scopus of English language articles published on ODM through August 2021. This review presents traditional and novel diagnostic methods in the diagnosis and follow-up of patients with particular emphasis on addressing the role of imaging in the management of the ophthalmic complications of the condition towards improving current practice patterns. RESULTS: ODM is a rare, prevalently unilateral, congenital condition that presents with brown or blue/gray flat asymptomatic lesions of the skin, mucosae, episclera/sclera, and uvea localized within the territory of distribution of the ophthalmic and mandibular branches of the trigeminal nerve. Glaucoma and predisposition to uveal melanoma are the main ophthalmic complications. Diagnosis and management are through comprehensive opthalmological examination and traditional imaging methods such as ultrasonography and fluorescein/indocyanine green angiography as pigmentation of the fundus can conceal subtle retinal and choroidal alterations. Anterior segment optical coherence tomography and ultrasound biomicroscopy are used to evaluate the anterior segment and the ciliary body in the presence of glaucoma or melanoma of the anterior uveal tract. Fundus autofluorescence and retinal pigment epithelium (RPE) alterations are of aid in the differential diagnosis between choroidal nevi and melanoma. Enhanced depth imaging spectral domain optical coherence tomography offers outstanding in vivo evaluation of the dimensions and details of tumors or nevi and surrounding choroidal tissues and small choroidal melanomas may show distortions of the retinal and sub-retinal profile, presence of intra and sub-retinal fluid, abnormalities of the RPE, and compression of the choriocapillaris. CONCLUSIONS: Novel multimodal imaging techniques are significant in the diagnosis and management of the ophthalmic complications of ODM. Fundus autofluorescence and enhanced depth spectral domain optical coherence tomography have adjunctive value in the detection of early-stage melanoma and differential diagnosis between nevi and melanoma. Awareness of current and emerging imaging techniques can propagate improved standardized definition and assessment of the complications of ODM.

Disturbances of brain cholesterol metabolism: A new excitotoxic process associated with status epilepticus.

The understanding of the excitotoxic processes associated with a severe status epilepticus (SE) is of major importance. Changes of brain cholesterol homeostasis is an emerging candidate for excitotoxicity. We conducted an overall analysis of the cholesterol homeostasis both (i) in fluids and tissues from patients with SE: blood (n = 63, n = 87 controls), CSF (n = 32, n = 60 controls), and post-mortem brain tissues (n = 8, n = 8 controls) and (ii) in a mouse model of SE induced by an intrahippocampal injection of kainic acid. 24-hydroxycholesterol levels were decreased in kainic acid mouse hippocampus and in human plasma and post-mortem brain tissues of patients with SE when compared with controls. The decrease of 24-hydroxycholesterol levels was followed by increased cholesterol levels and by an increase of the cholesterol synthesis. Desmosterol levels were higher in human CSF and in mice and human hippocampus after SE. Lanosterol and dihydrolanosterol levels were higher in plasma from SE patients. Our results suggest that a CYP46A1 inhibition could occur after SE and is followed by a brain cholesterol accumulation. The excess of cholesterol is known to be excitotoxic for neuronal cells and may participate to neurological sequelae observed after SE. This study highlights a new pathophysiological pathway involved in SE excitotoxicity.

Association of Clinical, Biological, and Brain Magnetic Resonance Imaging Findings With Electroencephalographic Findings for Patients With COVID-19.

Importance: There is evidence of central nervous system impairments associated with coronavirus disease 2019 (COVID-19) infection, including encephalopathy. Multimodal monitoring of patients with COVID-19 may delineate the specific features of COVID-19-related encephalopathy and guide clinical management. Objectives: To investigate clinical, biological, and brain magnetic resonance imaging (MRI) findings in association with electroencephalographic (EEG) features for patients with COVID-19, and to better refine the features of COVID-19-related encephalopathy. Design, Setting, and Participants: This retrospective cohort study conducted in Pitié-Salpêtrière Hospital, Paris, France, enrolled 78 hospitalized adults who received a diagnosis of severe acute respiratory syndrome coronavirus 2 (SARS-Cov2) and underwent EEG between March 30 and June 11, 2020. Exposures: Detection of SARS-CoV-2 from a nasopharyngeal specimen using a reverse transcription-polymerase chain reaction assay or, in the case of associated pneumonia, on a computed tomography scan of the chest. Main Outcomes and Measures: Data on the clinical and paraclinical features of the 78 patients with COVID-19 were retrieved from electronic patient records. Results: Of 644 patients who were hospitalized for COVID-19, 78 (57 men [73%]; mean [SD] age, 61 [12] years) underwent EEG. The main indications for EEG were delirium, seizure-like events, and delayed awakening in the intensive care unit after stopping treatment with sedatives. Sixty-nine patients showed pathologic EEG findings, including metabolic-toxic encephalopathy features, frontal abnormalities, periodic discharges, and epileptic activities. Of 57 patients who underwent brain MRI, 41 showed abnormalities, including perfusion abnormalities, acute ischemic lesions, multiple microhemorrhages, and white matter-enhancing lesions. Fifty-five patients showed biological abnormalities, including dysnatremia, kidney failure, and liver dysfunction, the same day as the EEG. The results of cerebrospinal fluid analysis were negative for SARS-Cov-2 for all tested patients. Nine patients who had no identifiable cause of brain injury outside COVID-19 were further isolated; their brain injury was defined as COVID-19-related encephalopathy. They represented 1% (9 of 644) of patients with COVID-19 requiring hospitalization. Six of these 9 patients had movement disorders, 7 had frontal syndrome, 4 had brainstem impairment, 4 had periodic EEG discharges, and 3 had MRI white matter-enhancing lesions. Conclusions and Relevance: The results from this cohort of patients hospitalized with COVID-19 suggest there are clinical, EEG, and MRI patterns that could delineate specific COVID-19-related encephalopathy and guide treatment strategy.

Ocular manifestations in phakomatosis pigmentovascularis: Current concepts on pathogenesis, diagnosis, and management.

Phakomatosis pigmentovascularis is a rare congenital multisystemic disease with variable manifestations where a vascular malformation of the skin is associated with a pigmentary nevus. Ocular involvement includes glaucoma, choroidal hemangioma, and pigmentary alterations that predispose to uveal melanoma. Diagnosis is made on clinical grounds, although recent advances in molecular genetics have better clarified the etiopathogenesis of the condition. The advent of improved imaging techniques such as enhanced depth imaging spectral domain optical coherence tomography has provided new insight into the ocular alterations, enabling better follow-up of patients. We review the ophthalmic manifestations of the disease with an update on etiopathogenesis and current management strategies.

TRIM17 and TRIM28 antagonistically regulate the ubiquitination and anti-apoptotic activity of BCL2A1.

BCL2A1 is an anti-apoptotic member of the BCL-2 family that contributes to chemoresistance in a subset of tumors. BCL2A1 has a short half-life due to its constitutive processing by the ubiquitin-proteasome system. This constitutes a major tumor-suppressor mechanism regulating BCL2A1 function. However, the enzymes involved in the regulation of BCL2A1 protein stability are currently unknown. Here, we provide the first insight into the regulation of BCL2A1 ubiquitination. We present evidence that TRIM28 is an E3 ubiquitin-ligase for BCL2A1. Indeed, endogenous TRIM28 and BCL2A1 bind to each other at the mitochondria and TRIM28 knock-down decreases BCL2A1 ubiquitination. We also show that TRIM17 stabilizes BCL2A1 by blocking TRIM28 from binding and ubiquitinating BCL2A1, and that GSK3 is involved in the phosphorylation-mediated inhibition of BCL2A1 degradation. BCL2A1 and its close relative MCL1 are thus regulated by common factors but with opposite outcome. Finally, overexpression of TRIM28 or knock-out of TRIM17 reduced BCLA1 protein levels and restored sensitivity of melanoma cells to BRAF-targeted therapy. Therefore, our data describe a molecular rheostat in which two proteins of the TRIM family antagonistically regulate BCL2A1 stability and modulate cell death.

The Glutaminase-Dependent System Confers Extreme Acid Resistance to New Species and Atypical Strains of Brucella.

Neutralophilic bacteria have developed specific mechanisms to cope with the acid stress encountered in environments such as soil, fermented foods, and host compartments. In Escherichia coli, the glutamate decarboxylase (Gad)-dependent system is extremely efficient: it requires the concerted action of glutamate decarboxylase (GadA/GadB) and of the glutamate (Glu)/γ-aminobutyrate antiporter, GadC. Notably, this system is operative also in new strains/species of Brucella, among which Brucella microti, but not in the "classical" species, with the exception of marine mammals strains. Recently, the glutaminase-dependent system (named AR2_Q), relying on the deamination of glutamine (Gln) into Glu and on GadC activity, was described in E. coli. In Brucella genomes, a putative glutaminase (glsA)-coding gene is located downstream of the gadBC genes. We found that in B. microti these genes are expressed as a polycistronic transcript. Moreover, using a panel of Brucella genus-representative strains, we show that the AR2_Q system protects from extreme acid stress (pH ≤2.5), in the sole presence of Gln, only the Brucella species/strains predicted to have functional glsA and gadC. Indeed, mutagenesis approaches confirmed the involvement of glsA and gadC of B. microti in AR2_Q and that the acid-sensitive phenotype of B. abortus can be ascribed to a Ser248Leu substitution in GlsA, leading to loss of glutaminase activity. Furthermore, we found that the gene BMI_II339, of unknown function and downstream of the gadBC-glsA operon, positively affects Gad- and GlsA-dependent AR. Thus, we identified novel determinants that allow newly discovered and marine mammals Brucella strains to be better adapted to face hostile acidic environments. As for significance, this work may contribute to the understanding of the host preferences of Brucella species and opens the way to alternative diagnostic targets in epidemiological surveillance of brucellosis.

Glutamate decarboxylase-dependent acid resistance in Brucella spp.: distribution and contribution to fitness under extremely acidic conditions.

Brucella is an expanding genus of major zoonotic pathogens, including at least 10 genetically very close species occupying a wide range of niches from soil to wildlife, livestock, and humans. Recently, we have shown that in the new species Brucella microti, the glutamate decarboxylase (Gad)-dependent system (GAD system) contributes to survival at a pH of 2.5 and also to infection in mice by the oral route. In order to study the functionality of the GAD system in the genus Brucella, 47 isolates, representative of all known species and strains of this genus, and 16 strains of the closest neighbor genus, Ochrobactrum, were studied using microbiological, biochemical, and genetic approaches. In agreement with the genome sequences, the GAD system of classical species was not functional, unlike that of most strains of Brucella ceti, Brucella pinnipedialis, and newly described species (B. microti, Brucella inopinata BO1, B. inopinata-like BO2, and Brucella sp. isolated from bullfrogs). In the presence of glutamate, these species were more acid resistant in vitro than classical terrestrial brucellae. Expression in trans of the gad locus from representative Brucella species in the Escherichia coli MG1655 mutant strain lacking the GAD system restored the acid-resistant phenotype. The highly conserved GAD system of the newly described or atypical Brucella species may play an important role in their adaptation to acidic external and host environments. Furthermore, the GAD phenotype was shown to be a useful diagnostic tool to distinguish these latter Brucella strains from Ochrobactrum and from classical terrestrial pathogenic Brucella species, which are GAD negative.

Profiling the physiological and molecular response to sulfonamidic drug in Procambarus clarkii.

Sulfamethoxazole (SMZ) is one of the most widely employed sulfonamides. Because of the widespread use of SMZ, a considerable amount is indeed expected to be introduced into the environment. The cytotoxicity of SMZ relies mainly on arylhydroxylamine metabolites (S-NOH) of SMZ and it is associated with the production of reactive oxygen species (ROS). There is limited information about the toxic potential of SMZ at the cellular and molecular levels, especially in aquatic and/or non-target organisms. In the present study, the red swamp crayfish (Procambarus clarkii), being tolerant to extreme environmental conditions and resistant to disease, was used as a model organism to profile the molecular and physiological response to SMZ. Haemolymphatic-immunological parameters such as glucose serum levels and total haemocyte counts were altered; moreover, a significant increase in Hsp70 plasma levels was detected for the first time. Variations at the transcriptional level of proinflammatory genes (cyclooxygenase-1, COX 1, and cyclooxygenase-2, COX 2), antioxidant enzymes (glutathione-S-transferase, GST and manganese superoxide dismutase MnSOD), stress response and Fenton reaction inhibitor genes (heat-shock protein 70 HSP70, metallothionein, MT and ferritin, FT) were evaluated, and alterations in the canonical gene expression patterns emerged. Considering these results, specific mechanisms involved in maintaining physiological homeostasis and adaptation in response to perturbations are suggested.

Tissue- and cell-specific mitochondrial defect in Parkin-deficient mice.

Loss of Parkin, encoded by PARK2 gene, is a major cause of autosomal recessive Parkinson's disease. In Drosophila and mammalian cell models Parkin has been shown in to play a role in various processes essential to maintenance of mitochondrial quality, including mitochondrial dynamics, biogenesis and degradation. However, the relevance of altered mitochondrial quality control mechanisms to neuronal survival in vivo is still under debate. We addressed this issue in the brain of PARK2-/- mice using an integrated mitochondrial evaluation, including analysis of respiration by polarography or by fluorescence, respiratory complexes activity by spectrophotometric assays, mitochondrial membrane potential by rhodamine 123 fluorescence, mitochondrial DNA content by real time PCR, and oxidative stress by total glutathione measurement, proteasome activity, SOD2 expression and proteins oxidative damage. Respiration rates were lowered in PARK2-/- brain with high resolution but not standard respirometry. This defect was specific to the striatum, where it was prominent in neurons but less severe in astrocytes. It was present in primary embryonic cells and did not worsen in vivo from 9 to 24 months of age. It was not associated with any respiratory complex defect, including complex I. Mitochondrial inner membrane potential in PARK2-/- mice was similar to that of wild-type mice but showed increased sensitivity to uncoupling with ageing in striatum. The presence of oxidative stress was suggested in the striatum by increased mitochondrial glutathione content and oxidative adducts but normal proteasome activity showed efficient compensation. SOD2 expression was increased only in the striatum of PARK2-/- mice at 24 months of age. Altogether our results show a tissue-specific mitochondrial defect, present early in life of PARK2-/- mice, mildly affecting respiration, without prominent impact on mitochondrial membrane potential, whose underlying mechanisms remain to be elucidated, as complex I defect and prominent oxidative damage were ruled out.

Functional interplay between Parkin and Drp1 in mitochondrial fission and clearance.

Autosomal recessive early-onset Parkinson's disease is most often caused by mutations in the genes encoding the cytosolic E3 ubiquitin ligase Parkin and the mitochondrial serine/threonine kinase PINK1. Studies in Drosophila models and mammalian cells have demonstrated that these proteins regulate various aspects of mitochondrial physiology, including organelle transport, dynamics and turnover. How PINK1 and Parkin orchestrate these processes, and whether they always do so within a common pathway remain to be clarified. We have revisited the role of PINK1 and Parkin in mitochondrial dynamics, and explored its relation to the mitochondrial clearance program controlled by these proteins. We show that PINK1 and Parkin promote Drp1-dependent mitochondrial fission by mechanisms that are at least in part independent. Parkin-mediated mitochondrial fragmentation was abolished by treatments interfering with the calcium/calmodulin/calcineurin signaling pathway, suggesting that it requires dephosphorylation of serine 637 of Drp1. Parkinson's disease-causing mutations with differential impact on mitochondrial morphology and organelle degradation demonstrated that the pro-fission effect of Parkin is not required for efficient mitochondrial clearance. In contrast, the use of Förster energy transfer imaging microscopy revealed that Drp1 and Parkin are co-recruited to mitochondria in proximity of PINK1 following mitochondrial depolarization, indicating spatial coordination between these events in mitochondrial degradation. Our results also hint at a major role of the outer mitochondrial adaptor MiD51 in Drp1 recruitment and Parkin-dependent mitophagy. Altogether, our observations provide new insight into the mechanisms underlying the regulation of mitochondrial dynamics by Parkin and its relation to the mitochondrial clearance program mediated by the PINK1/Parkin pathway.

Using informatics-enabled quality improvement techniques to meet health record documentation requirements in radiology reports.

PURPOSE: Medicare requires documented teaching physician involvement (attestation) in trainee-generated radiology reports. Automated attestation statement insertion in reports expedites the process but does not comply with requirements for active attestation. We evaluated an informatics-enabled quality improvement (QI) intervention to improve health record documentation requirements for active attestation. MATERIALS AND METHODS: Institutional review board approval was not needed for this QI project performed in a 776-bed tertiary/quaternary teaching hospital. The intervention consisted of (1) policy requiring staff radiologists to actively attest to trainee-generated reports by personally activating a "macro" in the reporting system and (2) a semiautomated process to detect reports missing attestation; radiologists received daily e-mail reminders until the attestation statement was inserted. A random sample of 600 of 123,561 trainee-generated radiology reports created 17 months after the intervention (May 2011) was manually reviewed to determine attestation policy adherence. The number of attestation statements added in response to reminders throughout the entire study period was also evaluated. Trend analysis of the number of report addenda containing solely the attestation statement (proxy for missing initial attestation) was performed. RESULTS: Of 600 reports, 594 (99%) contained the attestation statement. Monthly attestations in response to email notifications decreased from 585 to 227 by the sixth month, a 2.6-fold reduction (P < .01). No significant trend was observed the following year, indicating a sustained effect. CONCLUSION: Informatics-enabled QI techniques resulted in 99% adherence to our teaching physician attestation policy with sustained results. Similar approaches may help improve adherence to other mandated performance measures in radiology reports.

A role of mitochondrial complex II defects in genetic models of Huntington's disease expressing N-terminal fragments of mutant huntingtin.

Huntington's disease (HD) is a neurodegenerative disorder caused by an abnormal expansion of a CAG repeat encoding a polyglutamine tract in the huntingtin (Htt) protein. The mutation leads to neuronal death through mechanisms which are still unknown. One hypothesis is that mitochondrial defects may play a key role. In support of this, the activity of mitochondrial complex II (C-II) is preferentially reduced in the striatum of HD patients. Here, we studied C-II expression in different genetic models of HD expressing N-terminal fragments of mutant Htt (mHtt). Western blot analysis showed that the expression of the 30 kDa Iron-Sulfur (Ip) subunit of C-II was significantly reduced in the striatum of the R6/1 transgenic mice, while the levels of the FAD containing catalytic 70 kDa subunit (Fp) were not significantly changed. Blue native gel analysis showed that the assembly of C-II in mitochondria was altered early in N171-82Q transgenic mice. Early loco-regional reduction in C-II activity and Ip protein expression was also demonstrated in a rat model of HD using intrastriatal injection of lentiviral vectors encoding mHtt. Infection of the rat striatum with a lentiviral vector coding the C-II Ip or Fp subunits induced a significant overexpression of these proteins that led to significant neuroprotection of striatal neurons against mHtt neurotoxicity. These results obtained in vivo support the hypothesis that structural and functional alterations of C-II induced by mHtt may play a critical role in the degeneration of striatal neurons in HD and that mitochondrial-targeted therapies may be useful in its treatment.

Physiological and agonistic behavioural response of Procambarus clarkii to an acoustic stimulus.

This study examined the effects of an acoustic stimulus on the haemolymph and agonistic behaviour of the red swamp crayfish, Procambarus clarkii. The experiment was conducted in a tank equipped with a video recording system using six groups (three control and three test groups) of five adult crayfish (30 specimens in total). After 1 h of habituation, the behaviour of the crayfish was monitored for 2 h. During the second hour, the animals in the test groups were exposed to a linear sweep (frequency range 0.1-25 kHz; peak amplitude 148 dB(rms) re. 1 µPa at 12 kHz) acoustic stimulus for 30 min. Exposure to the noise produced significant variations in haemato-immunological parameters as well as a reduction in agonistic behaviour.

Neuroprotective effect of Nrf2/ARE activators, CDDO ethylamide and CDDO trifluoroethylamide, in a mouse model of amyotrophic lateral sclerosis.

Oxidative damage, neuroinflammation, and mitochondrial dysfunction contribute to the pathogenesis of amyotrophic lateral sclerosis (ALS), and these pathologic processes are tightly regulated by the Nrf2/ARE (NF-E2-related factor 2/antioxidant response element) signaling program. Therefore, modulation of the Nrf2/ARE pathway is an attractive therapeutic target for neurodegenerative diseases such as ALS. We examined two triterpenoids, CDDO (2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid) ethylamide and CDDO trifluoroethylamide (CDDO-TFEA), that potently activate Nrf2/ARE in a cell culture model of ALS and in the G93A SOD1 mouse model of ALS. Treatment of NSC-34 cells stably expressing mutant G93A SOD1 with CDDO-TFEA upregulated Nrf2 expression and resulted in translocation of Nrf2 into the nucleus. Western blot analysis showed an increase in the expression of Nrf2/ARE-regulated proteins. When treatment started at a "presymptomatic age" of 30days, both of these compounds significantly attenuated weight loss, enhanced motor performance, and extended the survival of G93A SOD1 mice. Treatment started at a "symptomatic age," as assessed by impaired motor performance, was neuroprotective and slowed disease progression. These findings provide further evidence that compounds that activate the Nrf2/ARE signaling pathway may be useful in the treatment of ALS.

Impact of a 4-year quality improvement initiative to improve communication of critical imaging test results.

PURPOSE: To evaluate the impact of a 4-year initiative to develop, implement, monitor, and reinforce a communication of critical test results policy by using continuous-process improvement methods. MATERIALS AND METHODS: This HIPAA-compliant quality-improvement initiative was performed between February 2006 and January 2010. Institutional review board approval was received with waiver of informed consent for medical record reviews. A critical results policy for radiology was developed that was based on recommendations from the Joint Commission, American College of Radiology, and Massachusetts Coalition for the Prevention of Medical Errors. It defined types of findings (critical or discrepant), urgency level (red, orange, or yellow), timelines for notification, acceptable communication and documentation methods, and a communication escalation process. The primary outcome measure, adherence to the communication of critical results policy, was measured by periodic review of radiology reports with feedback of results to staff radiologists. The χ(2) statistic was used to assess for trends. RESULTS: During 21 quality reviews, 16,983 of 1,489,951 (1.14%) total radiology reports were reviewed, 1628 (9.6%) of which were assessed to contain critical results according to policy. Adherence to critical results policy increased from 28.6% (12 of 42) in February 2006 to 90.4% (122 of 135) by the end of the study period (P < .001), with most of the gains occurring in the first 2 years. CONCLUSION: Review and feedback of performance in regard to a policy on communication of critical imaging test results allowed significant improvement and sustained adherence to policy. SUPPLEMENTAL MATERIAL: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11101396/-/DC1.

Mitochondria in Huntington's disease.

Huntington's disease (HD) is an inherited progressive neurodegenerative disorder associated with involuntary abnormal movements (chorea), cognitive deficits and psychiatric disturbances. The disease is caused by an abnormal expansion of a CAG repeat located in exon 1 of the gene encoding the huntingtin protein (Htt) that confers a toxic function to the protein. The most striking neuropathological change in HD is the preferential loss of medium spiny GABAergic neurons in the striatum. The mechanisms underlying striatal vulnerability in HD are unknown, but compelling evidence suggests that mitochondrial defects may play a central role. Here we review recent findings supporting this hypothesis. Studies investigating the toxic effects of mutant Htt in cell culture or animal models reveal mitochondrial changes including reduction of Ca2+ buffering capacity, loss of membrane potential, and decreased expression of oxidative phosphorylation (OXPHOS) enzymes. Striatal neurons may be particularly vulnerable to these defects. One hypothesis is that neurotransmission systems such as dopamine and glutamate exacerbate mitochondrial defects in the striatum. In particular, mitochondrial dysfunction facilitates impaired Ca2+ homeostasis linked to the glutamate receptor-mediated excitotoxicity. Also dopamine receptors modulate mutant Htt toxicity, at least in part through regulation of the expression of mitochondrial complex II. All these observations support the hypothesis that mitochondria, acting as "sensors" of the neurochemical environment, play a central role in striatal degeneration in HD.

Mutant SOD1 in neuronal mitochondria causes toxicity and mitochondrial dynamics abnormalities.

Amyotrophic lateral sclerosis (ALS) is a fatal neurological disorder characterized by motor neuron degeneration. Mutations in Cu,Zn-superoxide dismutase (SOD1) are responsible for 20% of familial ALS cases via a toxic gain of function. In mutant SOD1 transgenic mice, mitochondria of spinal motor neurons develop abnormal morphology, bioenergetic defects and degeneration, which are presumably implicated in disease pathogenesis. SOD1 is mostly a cytosolic protein, but a substantial portion is associated with organelles, including mitochondria, where it localizes predominantly in the intermembrane space (IMS). However, whether mitochondrial mutant SOD1 contributes to disease pathogenesis remains to be elucidated. We have generated NSC34 motor neuronal cell lines expressing wild-type or mutant SOD1 containing a cleavable IMS targeting signal to directly investigate the pathogenic role of mutant SOD1 in mitochondria. We show that mitochondrially-targeted SOD1 localizes to the IMS, where it is enzymatically active. We prove that mutant IMS-targeted SOD1 causes neuronal toxicity under metabolic and oxidative stress conditions. Furthermore, we demonstrate for the first time neurite mitochondrial fragmentation and impaired mitochondrial dynamics in motor neurons expressing IMS mutant SOD1. These defects are associated with impaired maintenance of neuritic processes. Our findings demonstrate that mutant SOD1 localized in the IMS is sufficient to determine mitochondrial abnormalities and neuronal toxicity, and contributes to ALS pathogenesis.

Cell-permeable peptide antioxidants as a novel therapeutic approach in a mouse model of amyotrophic lateral sclerosis.

Reactive oxygen species (ROS) play a major role in the pathogenesis of neurodegenerative diseases. They are important contributors to necrotic and apoptotic cell death. A major proportion of cellular ROS is generated at the inner mitochondrial membrane by the respiratory chain. In the present study, we investigated a novel peptide antioxidant (SS-31) targeted to the inner mitochondrial membrane for its therapeutic effects both in vitro and in vivo in the G93A mouse model of amyotrophic lateral sclerosis (ALS). SS-31 protected against cell death induced by hydrogen peroxide in vitro in neuronal cells stably transfected with either wild-type or mutant Cu/Zn superoxide dismutase (SOD1). Daily intraperitoneal injections of SS-31 (5 mg/kg), starting at 30 days of age, led to a significant improvement in survival and motor performance. In comparison with vehicle-treated G93A mice, SS-31-treated mice showed a decreased cell loss and a decrease in immunostaining for markers of oxidative stress in the lumbar spinal cord. This further enhances the concept that pharmacological modification of oxidative stress is a therapeutic option for the treatment of ALS.

Neural mitochondrial Ca2+ capacity impairment precedes the onset of motor symptoms in G93A Cu/Zn-superoxide dismutase mutant mice.

Mitochondrial respiratory chain dysfunction, impaired intracellular Ca2+ homeostasis and activation of the mitochondrial apoptotic pathway are pathological hallmarks in animal and cellular models of familial amyotrophic lateral sclerosis associated with Cu/Zn-superoxide dismutase mutations. Although intracellular Ca2+ homeostasis is thought to be intimately associated with mitochondrial functions, the temporal and causal correlation between mitochondrial Ca2+ uptake dysfunction and motor neuron death in familial amyotrophic lateral sclerosis remains to be established. We investigated mitochondrial Ca2+ handling in isolated brain, spinal cord and liver of mutant Cu/Zn-superoxide dismutase transgenic mice at different disease stages. In G93A mutant transgenic mice, we found a significant decrease in mitochondrial Ca2+ loading capacity in brain and spinal cord, as compared with age-matched controls, very early on in the course of the disease, long before the onset of motor weakness and massive neuronal death. Ca2+ loading capacity was not significantly changed in liver G93A mitochondria. We also confirmed Ca2+ capacity impairment in spinal cord mitochondria from a different line of mice expressing G85R mutant Cu/Zn-superoxide dismutase. In excitable cells, such as motor neurons, mitochondria play an important role in handling rapid cytosolic Ca2+ transients. Thus, mitochondrial dysfunction and Ca2+-mediated excitotoxicity are likely to be interconnected mechanisms that contribute to neuronal degeneration in familial amyotrophic lateral sclerosis.