Gene expression profiling of rotenone-mediated cortical neuronal death: Evidence for inhibition of ubiquitin–proteasome system and autophagy-lysosomal pathway, and dysfunction of mitochondrial and calcium signaling

Neuronal degeneration, mitochondrial dysfunction, and disturbance of movements induced by rotenone in the ascidian Styela plicata

Parkinson's disease (PD), a movement disorder caused by dopaminergic degeneration in the midbrain, has been induced in various organisms after injection of different neurotoxins, such as rotenone (ROT), which affect mitochondrial complex I. Due to the conserved characteristics of ascidians, these animals constitute an interesting model for comparative and genetic studies of neurodegenerative diseases. In this study, we investigated the effects of ROT on the ascidian nervous system, evaluating apoptosis, catecholaminergic enzymes, behavioral deficits, and mitochondrial dysfunction. The study revealed morphological disorganization, inducing vacuolation in the ascidian brain. Neuronal death was confirmed by elevated transcriptional levels of caspase-3 and intense caspase-3 staining by immunofluorescence. In addition, there was reduced staining for dopa-decarboxylase (DDC), which is involved in dopamine biosynthesis. Furthermore, the mitochondria exhibited dysfunction in their membrane potential, followed by a decrease in the hydrolytic activity of ATP synthase and high transcriptional levels of ubiquitin. Finally, after administration of the drug l-3,4-dihydroxyphenylalanine (L-DOPA), recovery of motor movements was observed, as revealed by behavioral tests. Overall, the current research provides new data on the effects of rotenone on the ascidian brain, inducing neuronal death, mitochondrial dysfunction, and siphon movement disorders in the ascidian Styela plicata.

Intracerebral Hemorrhage-Induced Brain Injury: the Role of Lysosomal-Associated Transmembrane Protein 5

Intracerebral hemorrhage (ICH) is a lethal stroke with high mortality or disability. However, effective therapy for ICH damage is generally lacking. Previous investigations have suggested that lysosomal protein transmembrane 5 (LAPTM5) is involved in various pathological processes, including autophagy, apoptosis, and inflammation. In this study, we aimed to identify the expression and functions of LAPTM5 in collagenase-induced ICH mouse models and hemoglobin-induced cell models. We found that LAPTM5 was highly expressed in brain tissues around the hematoma, and double immunostaining studies showed that LAPTM5 was co-expressed with microglia cells, neurons, and astrocytes. Following ICH, the mice presented increased brain edema, blood-brain barrier permeability, and neurological deficits, while pathological symptoms were alleviated after the LAPTM5 knockdown. Adeno-associated virus 9-mediated downregulation of LAPTM5 also improves ICH-induced secondary cerebral damage, including neuronal degeneration, the polarization of M1-like microglia, and inflammatory cascades. Furthermore, LAPTM5 promoted activation of the nuclear factor kappa-B (NF-κB) pathway in response to neuroinflammation. Further investigations indicated that brain injury improved by LAPTM5 knockdown was further exacerbated after the overexpression of receptor-interacting protein kinase 1 (RIP1), which is revealed to trigger the NF-κB pathway. In vitro experiments demonstrated that LAPTM5 silencing inhibited hemoglobin-induced cell function and confirmed regulation between RIP1 and LAPTM5. In conclusion, the present study indicates that LAPTM5 may act as a positive regulator in the context of ICH by modulating the RIP1/NF-κB pathway. Thus, it may be a candidate gene for further study of molecular or therapeutic targets.

Neuronal metabotropic glutamate receptor 8 protects against neurodegeneration in CNS inflammation

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system with continuous neuronal loss. Treatment of clinical progression remains challenging due to lack of insights into inflammation-induced neurodegenerative pathways. Here, we show that an imbalance in the neuronal receptor interactome is driving glutamate excitotoxicity in neurons of MS patients and identify the MS risk-associated metabotropic glutamate receptor 8 (GRM8) as a decisive modulator. Mechanistically, GRM8 activation counteracted neuronal cAMP accumulation, thereby directly desensitizing the inositol 1,4,5-trisphosphate receptor (IP3R). This profoundly limited glutamate-induced calcium release from the endoplasmic reticulum and subsequent cell death. Notably, we found Grm8-deficient neurons to be more prone to glutamate excitotoxicity, whereas pharmacological activation of GRM8 augmented neuroprotection in mouse and human neurons as well as in a preclinical mouse model of MS. Thus, we demonstrate that GRM8 conveys neuronal resilience to CNS inflammation and is a promising neuroprotective target with broad therapeutic implications.

Decoding the rosetta stone of mitonuclear communication

Cellular homeostasis in eukaryotic cells requires synchronized coordination of multiple organelles. A key role in this stage is played by mitochondria, which have recently emerged as highly interconnected and multifunctional hubs that process and coordinate diverse cellular functions. Beyond producing ATP, mitochondria generate key metabolites and are central to apoptotic and metabolic signaling pathways. Because most mitochondrial proteins are encoded in the nuclear genome, the biogenesis of new mitochondria and the maintenance of mitochondrial functions and flexibility critically depend upon effective mitonuclear communication. This review addresses the complex network of signaling molecules and pathways allowing mitochondria-nuclear communication and coordinated regulation of their independent but interconnected genomes, and discusses the extent to which dynamic communication between the two organelles has evolved for mutual benefit and for the overall maintenance of cellular and organismal fitness.

Tomatidine protects against ischemic neuronal injury by improving lysosomal function

Cerebral ischemia is a severe neurological disorder with limited therapy. Autophagy refers to the intracellular degradation process via an autophagosome-lysosome pathway. Emerging studies indicated the neuroprotective effects of autophagy against ischemic neuronal injury, suggesting the potential neuroprotection of autophagy-inducing compounds. Tomatidine is a gut microbiota-derived metabolite from unripe tomatoes. Tomatidine activates autophagy either in mammal cells or C elegans. However, potential neuroprotection of tomatidine against ischemic neuronal injury has not been determined. In the present investigation, N₂a cells and primary cultured mice cortical neurons were subjected to oxygen-glucose deprivation followed by reperfusion (OGD/R). Cell injury was determined by MTT and lactate dehydrogenase release. Autophagosomes and autolysosomes were visualized by transfecting mCherry-GFP-tandem fluorescent LC3. The protein levels of LC3, Cathepsin D, Cathepsin B, and transcription factor EB (TFEB) were detected by Western blot. Lysosomes were stained with LysoTracker Red and dequenched-bovine serum albumin (DQ-BSA red). Tomatidine alleviated OGD/R-induced injury in N₂a cells and neurons. Interestingly, tomatidine treatment attenuated, rather than reinforced, the OGD/R-elevated LC3-II, which can be reversed by lysosome inhibitor. These results indicated enhanced lysosomal activity rather than autophagosome generation with tomatidine treatment in our models. Indeed, tomatidine increased the lysosome number, proteolytic activities, as well as the expression of Cathepsin D and Cathepsin B. In addition, tomatidine increased the expression and nucleus translocation of (TFEB). Besides, lysosomal inhibitors chloroquine and bafilomycin, but not wortmannin, abolished the protection of tomatidine. In conclusion, the present study revealed the neuroprotection of tomatidine against ischemic injury by promoting lysosomal activity, possibly with the involvement of TFEB-related mechanisms.

Mitochondrial retrograde signalling in neurological disease

Neuronal mitochondrial dysfunction causes primary mitochondrial diseases and likely contributes to neurodegenerative diseases including Parkinson's and Alzheimer's disease. Mitochondrial dysfunction has also been documented in neurodevelopmental disorders such as tuberous sclerosis complex and autism spectrum disorder. Only symptomatic treatments exist for neurodevelopmental disorders, while neurodegenerative diseases are largely untreatable. Altered mitochondrial function activates mitochondrial retrograde signalling pathways, which enable signalling to the nucleus to reprogramme nuclear gene expression. In this review, we discuss the role of mitochondrial retrograde signalling in neurological diseases. We summarize how mitochondrial dysfunction contributes to neurodegenerative disease and neurodevelopmental disorders. Mitochondrial signalling mechanisms that have relevance to neurological disease are discussed. We then describe studies documenting retrograde signalling pathways in neurons and glia, and in animal models of neuronal mitochondrial dysfunction and neurological disease. Finally, we suggest how specific retrograde signalling pathways can be targeted to develop novel treatments for neurological diseases. This article is part of the theme issue 'Retrograde signalling from endosymbiotic organelles'.

Effect of Curcumin on Protein Damage Induced by Rotenone in Dopaminergic PC12 Cells

Oxidative stress is considered to be a key factor of the pathogenesis of Parkinson's disease, a multifactorial neurodegenerative disorder characterized by reduced dopaminergic neurons in the substantia nigra pars compacta and accumulated protein aggregates. Rotenone is a worldwide-used pesticide that induces the most common features of Parkinson's by direct inhibition of the mitochondrial complex I. Rotenone-induced Parkinson's models, as well as brain tissues from Parkinson's patients, are characterized by the presence of both lipid peroxidation and protein oxidation markers resulting from the increased level of free radical species. Oxidation introduces several modifications in protein structure, including carbonylation and nitrotyrosine formation, which severely compromise cell function. Due to the link existing between oxidative stress and Parkinson's disease, antioxidant molecules could represent possible therapeutic tools for this disease. In this study, we evaluated the effect of curcumin, a natural compound known for its antioxidant properties, in dopaminergic PC12 cells treated with rotenone, a cell model of Parkinsonism. Our results demonstrate that the treatment of PC12 cells with rotenone causes severe protein damage, with formation of both carbonylated and nitrotyrosine-derived proteins, whereas curcumin (10 µM) co-exposure exerts protective effects by reducing the levels of oxidized proteins. Curcumin also promotes proteasome activation, abolishing the inhibitory effect exerted by rotenone on this degradative system.

Cilostazol protects against myocardial ischemia and reperfusion injury by activating transcription factor EB (TFEB)

Although cilostazol was proved to have antitumor biological effects, its function in myocardial ischemia and reperfusion (I/R) injury and the underlying mechanisms were not fully illustrated yet. In this study, a rat model of I/R injury was constructed and quantitative real-time PCR, Western blot, and immunofluorescence (IF) assay were performed. Our results showed that cilostazol increased LC3 II/LC3 I ratio, reduced p62 abundance, and promoted the expressions of LAMP1, LAMP2, cathepsin B, and cathepsin D, indicating that cilostazol could activate autophagy and elevated lysosome activation. Following analysis showed that cilostazol enhanced nuclear protein expression of transcription factor EB (TFEB), an important regulator of autophagy-lysosome pathway. Furthermore, CCI-779, an inhibitor of TFEB, could reverse the effects of cilostazol on autophagic activity and lysosome activation. Importantly, cilostazol suppressed I/R injury-induced apoptosis by decreasing the cleavage of caspase 3 and PARP. Enzyme-linked immunosorbent assay showed that cilostazol reduced the serum levels of CTn1 and CK-MB and decreased infract size caused by I/R injuries. Altogether this study suggested that cilostazol protects against I/R injury by regulating autophagy, lysosome, and apoptosis in a rat model of I/R injury. The protective mechanism of cilostazol was partially through increasing the transcriptional activity of TFEB.

Mitochondrial retrograde signaling in the nervous system

Mitochondria generate the majority of cellular ATP and are essential for neuronal function. Loss of mitochondrial activity leads to primary mitochondrial diseases and may contribute to neurodegenerative diseases such as Alzheimer's and Parkinson's disease. Mitochondria communicate with the cell through mitochondrial retrograde signaling pathways. These signaling pathways are triggered by mitochondrial dysfunction and allow the organelle to control nuclear gene transcription. Neuronal mitochondrial retrograde signaling pathways have been identified in disease model systems and targeted to restore neuronal function and prevent neurodegeneration. In this review, we describe yeast and mammalian cellular models that have paved the way in the investigation of mitochondrial retrograde mechanisms. We then discuss the evidence for retrograde signaling in neurons and our current knowledge of retrograde signaling mechanisms in neuronal model systems. We argue that targeting mitochondrial retrograde pathways has the potential to lead to novel treatments for neurological diseases.

Identification of chemicals that mimic transcriptional changes associated with autism, brain aging and neurodegeneration

Environmental factors, including pesticides, have been linked to autism and neurodegeneration risk using retrospective epidemiological studies. Here we sought to prospectively identify chemicals that share transcriptomic signatures with neurological disorders, by exposing mouse cortical neuron-enriched cultures to hundreds of chemicals commonly found in the environment and on food. We find that rotenone, a pesticide associated with Parkinson's disease risk, and certain fungicides, including pyraclostrobin, trifloxystrobin, famoxadone and fenamidone, produce transcriptional changes in vitro that are similar to those seen in brain samples from humans with autism, advanced age and neurodegeneration (Alzheimer's disease and Huntington's disease). These chemicals stimulate free radical production and disrupt microtubules in neurons, effects that can be reduced by pretreating with a microtubule stabilizer, an antioxidant, or with sulforaphane. Our study provides an approach to prospectively identify environmental chemicals that transcriptionally mimic autism and other brain disorders.

Comparative Microarray Analysis Identifies Commonalities in Neuronal Injury: Evidence for Oxidative Stress, Dysfunction of Calcium Signalling, and Inhibition of Autophagy-Lysosomal Pathway

Mitochondrial dysfunction, ubiquitin-proteasomal system impairment and excitotoxicity occur during the injury and death of neurons in neurodegenerative conditions. The aim of this work was to elucidate the cellular mechanisms that are universally altered by these conditions. Through overlapping expression profiles of rotenone-, lactacystin- and N-methyl-D-aspartate-treated cortical neurons, we have identified three affected biological processes that are commonly affected; oxidative stress, dysfunction of calcium signalling and inhibition of the autophagic-lysosomal pathway. These data provides many opportunities for therapeutic intervention in neurodegenerative conditions, where mitochondrial dysfunction, proteasomal inhibition and excitotoxicity are evident.

Neurotoxin mechanisms and processes relevant to Parkinson's disease: an update

The molecular mechanism responsible for degenerative process in the nigrostriatal dopaminergic system in Parkinson's disease (PD) remains unknown. One major advance in this field has been the discovery of several genes associated to familial PD, including alpha synuclein, parkin, LRRK2, etc., thereby providing important insight toward basic research approaches. There is an consensus in neurodegenerative research that mitochon dria dysfunction, protein degradation dysfunction, aggregation of alpha synuclein to neurotoxic oligomers, oxidative and endoplasmic reticulum stress, and neuroinflammation are involved in degeneration of the neuromelanin-containing dopaminergic neurons that are lost in the disease. An update of the mechanisms relating to neurotoxins that are used to produce preclinical models of Parkinson´s disease is presented. 6-Hydroxydopamine, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and rotenone have been the most wisely used neurotoxins to delve into mechanisms involved in the loss of dopaminergic neurons containing neuromelanin. Neurotoxins generated from dopamine oxidation during neuromelanin formation are likewise reviewed, as this pathway replicates neurotoxin-induced cellular oxidative stress, inactivation of key proteins related to mitochondria and protein degradation dysfunction, and formation of neurotoxic aggregates of alpha synuclein. This survey of neurotoxin modeling-highlighting newer technologies and implicating a variety of processes and pathways related to mechanisms attending PD-is focused on research studies from 2012 to 2014.

Bioenergetic and proteolytic defects in fibroblasts from patients with sporadic Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is a complex disease and the current interest and focus of scientific research is both investigating the variety of causes that underlie PD pathogenesis, and identifying reliable biomarkers to diagnose and monitor the progression of pathology. Investigation on pathogenic mechanisms in peripheral cells, such as fibroblasts derived from patients with sporadic PD and age/gender matched controls, might generate deeper understanding of the deficits affecting dopaminergic neurons and, possibly, new tools applicable to clinical practice.

METHODS

Primary fibroblast cultures were established from skin biopsies. Increased susceptibility to the PD-related toxin rotenone was determined with apoptosis- and necrosis-specific cell death assays. Protein quality control was evaluated assessing the efficiency of the Ubiquitin Proteasome System (UPS) and protein levels of autophagic markers. Changes in cellular bioenergetics were monitored by measuring oxygen consumption and glycolysis-dependent medium acidification. The oxido-reductive status was determined by detecting mitochondrial superoxide production and oxidation levels in proteins and lipids.

RESULTS

PD fibroblasts showed higher vulnerability to necrotic cell death induced by complex I inhibitor rotenone, reduced UPS function and decreased maximal and rotenone-sensitive mitochondrial respiration. No changes in autophagy and redox markers were detected.

CONCLUSIONS

Our study shows that increased susceptibility to rotenone and the presence of proteolytic and bioenergetic deficits that typically sustain the neurodegenerative process of PD can be detected in fibroblasts from idiopathic PD patients. Fibroblasts might therefore represent a powerful and minimally invasive tool to investigate PD pathogenic mechanisms, which might translate into considerable advances in clinical management of the disease.