Behavioral and quantitative mitochondrial proteome analyses of the effects of simvastatin: implications for models of neural degeneration

Isolated Mitochondrial Preparations and In organello Assays: A Powerful and Relevant Ex vivo Tool for Assessment of Brain (Patho)physiology

Mitochondria regulate multiple aspects of neuronal development, physiology, plasticity, and pathology through their regulatory roles in bioenergetic, calcium, redox, and cell survival/death signalling. While several reviews have addressed these different aspects, a comprehensive discussion focussing on the relevance of isolated brain mitochondria and their utilities in neuroscience research has been lacking. This is relevant because the employment of isolated mitochondria rather than their in situ functional evaluation, offers definitive evidence of organelle-specificity, negating the interference from extra mitochondrial cellular factors/signals. This mini-review was designed primarily to explore the commonly employed in organello analytical assays for the assessment of mitochondrial physiology and its dysfunction, with a particular focus on neuroscience research. The authors briefly discuss the methodologies for biochemical isolation of mitochondria, their quality assessment, and cryopreservation. Further, the review attempts to accumulate the key biochemical protocols for in organello assessment of a multitude of mitochondrial functions critical for neurophysiology, including assays for bioenergetic activity, calcium and redox homeostasis, and mitochondrial protein translation. The purpose of this review is not to examine each and every method or study related to the functional assessment of isolated brain mitochondria, but rather to assemble the commonly used protocols of in organello mitochondrial research in a single publication. The hope is that this review will provide a suitable platform aiding neuroscientists to choose and apply the required protocols and tools to address their particular mechanistic, diagnostic, or therapeutic question dealing within the confines of the research area of mitochondrial patho-physiology in the neuronal perspective.

A Combined N-terminomics and Shotgun Proteomics Approach to Investigate the Responses of Human Cells to Rapamycin and Zinc at the Mitochondrial Level

All but thirteen mammalian mitochondrial proteins are encoded by the nuclear genome, translated in the cytosol and then imported into the mitochondria. For a significant proportion of the mitochondrial proteins, import is coupled with the cleavage of a presequence called the transit peptide, and the formation of a new N-terminus. Determination of the neo N-termini has been investigated by proteomic approaches in several systems, but generally in a static way to compile as many N-termini as possible. In the present study, we have investigated how the mitochondrial proteome and N-terminome react to chemical stimuli that alter mitochondrial metabolism, namely zinc ions and rapamycin. To this end, we have used a strategy that analyzes both internal and N-terminal peptides in a single run, the dN-TOP approach. We used these two very different stressors to sort out what could be a generic response to stress and what is specific to each of these stressors. Rapamycin and zinc induced different changes in the mitochondrial proteome. However, convergent changes to key mitochondrial enzymatic activities such as pyruvate dehydrogenase, succinate dehydrogenase and citrate synthase were observed for both treatments. Other convergent changes were seen in components of the N-terminal processing system and mitochondrial proteases. Investigations into the generation of neo-N-termini in mitochondria showed that the processing system is robust, as indicated by the lack of change in neo N-termini under the conditions tested. Detailed analysis of the data revealed that zinc caused a slight reduction in the efficiency of the N-terminal trimming system and that both treatments increased the degradation of mitochondrial proteins. In conclusion, the use of this combined strategy allowed a detailed analysis of the dynamics of the mitochondrial N-terminome in response to treatments which impact the mitochondria.

Identification of simvastatin-regulated targets associated with JNK activation in DU145 human prostate cancer cell death signaling

The results of this study show that c-Jun N-terminal kinase (JNK) activation was associated with the enhancement of docetaxel-induced cytotoxicity by simvastatin in DU145 human prostate cancer cells. To better understand the basic molecular mechanisms, we investigated simvastatin-regulated targets during simvastatin-induced cell death in DU145 cells using two-dimensional (2D) proteomic analysis. Thus, vimentin, Ras-related protein Rab-1B (RAB1B), cytoplasmic hydroxymethylglutaryl-CoA synthase (cHMGCS), thioredoxin domain-containing protein 5 (TXNDC5), heterogeneous nuclear ribonucleoprotein K (hnRNP K), N-myc downstream-regulated gene 1 (NDRG1), and isopentenyl-diphosphate Delta-isomerase 1 (IDI1) protein spots were identified as simvastatin-regulated targets involved in DU145 cell death signaling pathways. Moreover, the JNK inhibitor SP600125 significantly inhibited the upregulation of NDRG1 and IDI protein levels by combination treatment of docetaxel and simvastatin. These results suggest that NDRG1 and IDI could at least play an important role in DU145 cell death signaling as simvastatin-regulated targets associated with JNK activation.

Brain proteomics identifies potential simvastatin targets in acute phase of stroke in a rat embolic model

Finding an efficient neuroprotectant is of urgent need in the field of stroke research. The goal of this study was to test the effect of acute simvastatin administration after stroke in a rat embolic model and to explore its mechanism of action through brain proteomics. To that end, male Wistar rats were subjected to a Middle Cerebral Arteria Occlusion and simvastatin (20 mg/kg s.c) (n = 11) or vehicle (n = 9) were administered 15 min after. To evaluate the neuroprotective mechanisms of simvastatin, brain homogenates after 48 h were analyzed by two-dimensional fluorescence Difference in Gel Electrophoresis (DIGE) technology. We confirmed that simvastatin reduced the infarct volume and improved neurological impairment at 48 h after the stroke in this model. Considering our proteomics analysis, 66 spots, which revealed significant differences between groups, were analyzed by matrix-assisted laser desorption/ionization-time of flight mass spectrometry allowing the identification of 27 proteins. From these results, we suggest that simvastatin protective effect can be partly explained by the attenuation of the oxidative and stress response at blood-brain barrier level after cerebral ischemia. Interestingly, analyzing one of the proteins (HSP75) in plasma from stroke patients who had received simvastatin during the acute phase, we confirmed the results found in the pre-clinical model. Our aim was to study statins benefits when administered during the acute phase of stroke and to explore its mechanisms of action through brain proteomics assay. Using an embolic model, simvastatin-treated rats showed significant infarct volume reduction and neurological improvement compared to vehicle-treated group. Analyzing their homogenated brains by two-dimensional fluorescence Difference in Gel Electrophoresis (DIGE) technology, we concluded that the protective effect of simvastatin can be attributable to oxidative stress response attenuation and blood-brain barrier protection after cerebral ischemia.

Role of L-thyroxin in counteracting rotenone induced neurotoxicity in rats

A key feature of Parkinson's disease is the dopaminergic neuronal cell loss in the substantia nigra pars compacta. Many triggering pathways have been incriminated in the pathogenesis of this disease including inflammation, oxidative stress, excitotoxicity and apoptosis. Thyroid hormone is an essential agent for the growth and maturation of neurons; moreover, it has variable mechanisms for neuroprotection. So, we tested the efficacy of (L)-thyroxin as a neuroprotectant in rotenone model of Parkinson's disease in rats. Thirty Sprague Dawley rats aged 3 months were divided into 3 equal groups. The first received daily intraperitoneal injections of 0.5% carboxymethyl cellulose (CMC) 3 mL/Kg. The second group received rotenone suspended in 0.5% CMC intraperitoneally at a dose of 3 mg/kg, daily. The third group received the same rotenone regimen subcutaneous l-thyroxine at a dose of 7.5 μg daily. All animals were evaluated regarding locomotor disturbance through blinded investigator who monitored akinesia, catalepsy, tremors and performance in open field test. After 35 days the animals were sacrificed and their brains were immunostained against anti-tyrosine hydroxylase and iba-1. Photomicrographs for coronal sections of the substantia nigra and striatum were taken and analyzed using image J software to evaluate cell count in SNpc and striatal fibers density and number of microglia in the nigrostriatal system. The results were then analyzed statistically. Results showed selective protective effects of thyroxin against rotenone induced neurotoxicity in striatum, however, failed to exert similar protection on SN. Moreover, microglial elevated number in nigrostriatal system that was induced by rotenone injections was diminished selectively in striatum only in the l-thyroxin treated group. One of the possible mechanisms deduced from this work was the selective regulation of microglia in striatal tissues. Thus, this study provides an insight into thyroxin neuroprotection warranting further investigation as therapeutic option for Parkinson's disease patients.

Comparative mitochondrial proteomics: perspective in human diseases

Mitochondria are the most complex and the most important organelles of eukaryotic cells, which are involved in many cellular processes, including energy metabolism, apoptosis, and aging. And mitochondria have been identified as the "hot spot" by researchers for exploring relevant associated dysfunctions in many fields. The emergence of comparative proteomics enables us to have a close look at the mitochondrial proteome in a comprehensive and effective manner under various conditions and cellular circumstances. Two-dimensional electrophoresis combined with mass spectrometry is still the most popular techniques to study comparative mitochondrial proteomics. Furthermore, many new techniques, such as ICAT, MudPIT, and SILAC, equip researchers with more flexibilities inselecting proper methods. This article also reviews the recent development of comparative mitochondrial proteomics on diverse human diseases. And the results of mitochondrial proteomics enhance a better understanding of the pathogenesis associated with mitochondria and provide promising therapeutic targets.

Simvastatin improves morphological and functional recovery of sciatic nerve injury in Wistar rats

AIM

The purpose of this work is to investigate the effects of simvastatin on sciatic nerve regeneration in male Wistar Rats.

MATERIALS AND METHODS

Forty animals were allocated into four groups: (1) control (C); (2) control+simvastatin (CS); (3) lesioned animals+sterile PBS (LC) and (4) lesioned animals+simvastatin (LS). Lesioned animals were submitted to crushing lesion of right sciatic nerve. Simvastatin (20mg/kg/day, i.p.) was administered for five days. Footprints were obtained weekly for evaluation of functional locomotor recovery by means of the Sciatic Function Index (SFI). Blood samples were obtained weekly for quantifying circulating leukocytes. Animals were sacrificed after 21 days for histological analyses of sciatic nerve and spleen.

RESULTS

LS Animals presented increased SFI scores, decreased areas of oedema and mononuclear cell infiltration during Wallerian degeneration and nerve regeneration (7,14 and 21 days; P<0.05). Spleen weight and white pulp areas was increased in LC animals after 21 days. Increased numbers of circulating neutrophils were observed in simvastatin treated animals (CS e LS) at seven, 14 and 21 days, compared to non-treated groups (C and LC).

CONCLUSION

The study suggests that simvastatin accelerates the morphological and functional recovery process of the peripheral nervous system interfering with innate and acquired immunity.

Statins lower calcium-induced oxidative stress in isolated mitochondria

Statins are widely used cholesterol-lowering agents that exert cholesterol-independent effects including antioxidative. The present study delineates the effects of statins, atorvastatin, and simvastatin on oxidative stress and functions of mitochondria that are the primary cellular sources of oxidative stress. In isolated rat liver mitochondria, both the statins prevented calcium-induced cytochrome c release, lipid peroxidation, and opening of the mitochondrial membrane permeability transition (MPT). Both the statins decreased the activity of mitochondrial nitric oxide synthase (mtNOS), lowered the intramitochondrial ionized calcium, and increased the mitochondrial transmembrane potential. Our findings suggest that statins lower intramitochondrial ionized calcium that decreases mtNOS activity, lowers oxidative stress, prevents MPT opening, and prevents the release of cytochrome c from the mitochondria. These results provide a novel framework for understanding the antioxidative properties of statins and their effects on mitochondrial functions.

Comparative neuroprotective profile of statins in quinolinic acid induced neurotoxicity in rats

A possible neuroprotective role has been recently suggested for 3H3MGCoA reductase inhibitors (statins). Here, we sought to determine neuroprotective effect of statins in quinolinic acid induced neurotoxicity in rats. Rats were surgically administered quinolinic acid and treated with Atorvastatin (10, 20 mg/kg), simvastatin (15, 30 mg/kg) and fluvastatin (5, 10 mg/kg) once daily up to 3 weeks. Atorvastatin (10, 20 mg/kg), simvastatin (30 mg/kg) and fluvastatin (10 mg/kg) treatment significantly attenuated the quinolinic acid induced behavioral (locomotor activity, rotarod performance and beam walk test), biochemical (lipid peroxidation, nitrite concentration, SOD and catalase), mitochondrial enzyme complex alterations in rats suggesting their free radical scavenging potential. Additionally, atorvastatin (10, 20 mg/kg), simvastatin (30 mg/kg) and fluvastatin (10 mg/kg) significantly decrease the TNF-α level and striatal lesion volume in quinolinic acid treated animals indicating their anti-inflammatory effects. In comparing the protective effect of different statins, atorvastatin is effective at both the doses while simvastatin and fluvastatins at respective lower doses were not able to produce the protective effect in quinolinic acid treated animals. These modulations can account, at least partly, for the beneficial effect of statins in our rodent model of striatal degeneration. Our findings show that statins could be explored as possible neuroprotective agents for neurodegenerative disorders such as HD.

Striatal neuroprotection with methylene blue

Recent literature indicates that low-dose Methylene Blue (MB), an autoxidizable dye with powerful antioxidant and metabolic enhancing properties, might prevent neurotoxin-induced neural damage and associated functional deficits. This study evaluated whether local MB may counteract the anatomical and functional effects of the intrastriatal infusion of the neurotoxin rotenone (Rot) in the rat. To this end, stereological analyses of striatal lesion volumes were performed and changes in oxidative energy metabolism in the striatum and related motor regions were mapped using cytochrome oxidase histochemistry. The influence of MB on striatal levels of oxidative stress induced by Rot was determined, and behavioral tests were used to investigate the effect of unilateral MB coadministration on motor asymmetry. Rot induced large anatomical lesions resembling "metabolic strokes," whose size was greatly reduced in MB-treated rats. Moreover, MB prevented the decrease in cytochrome oxidase activity and the perilesional increase in oxidative stress associated with Rot infusion in the striatum. MB also prevented the indirect effects of the Rot-induced lesion on cytochrome oxidase activity in related motor regions, such as the striatal regions rostral and caudal to the lesion, the substantia nigra compacta and reticulata, and the pedunculopontine nucleus. At a network level, MB maintained a global strengthening of functional connectivity in basal ganglia-thalamocortical motor circuits, as opposed to the functional decoupling observed in Rot-alone subjects. Finally, MB partially prevented the behavioral sensorimotor asymmetries elicited by Rot. These results are consistent with protective effects of MB against neurotoxic damage in the brain parenchyma. This study provides the first demonstration of the anatomical, metabolic and behavioral neuroprotective effects of MB in the striatum in vivo, and supports the notion that MB could be a valuable intervention against neural damage associated with oxidative stress and energy hypometabolism.