Uncoupling protein 2 knockout exacerbates depression-like behaviors in mice via enhancing inflammatory response

Emerging role and the signaling pathways of uncoupling protein 2 in kidney diseases

OBJECTIVES

Uncoupling protein 2 (UCP2) was involved in the pathogenesis and development of kidney diseases. Many signaling pathways and factors regulate the expression of UCP2. We aimed to investigate the precise role of UCP2 and its signaling pathways in kidney diseases.

METHODS

We summarized the available evidence to yield a more detailed conclusion of the signal transduction pathways of UCP2 and its role in the development and progression of kidney diseases.

RESULTS

UCP2 could interact with 14.3.3 family proteins, mitochondrial phospholipase iPLA2γ, NMDAR, glucokinase, PPARγ2. There existed a signaling pathway between UCP2 and NMDAR, PPARγ. UCP2 can inhibit the ROS production, inflammatory response, and apoptosis, which may protect against renal injury, particularly AKI. Meanwhile UCP2 can decrease ATP production and inhibit the secretion of insulin, which may alleviate chronic renal damages, such as diabetic nephropathy and kidney fibrosis.

CONCLUSIONS

Homeostasis of UCP2 is helpful for kidney health. UCP2 may play different roles in different kinds of renal injury.

Novel pathogenesis of post-traumatic stress disorder studied in transgenic mice

Posttraumatic stress disorder (PTSD) is very common after exposure to trauma, mental stress or violence. Because objective biological markers for PTSD are lacking, exactly diagnosing PTSD is a challenge for clinical psychologists. In-depth research on the pathogenesis of PTSD is a key for solving this problem. In this work, we used male Thy1-YFP transgenic mice, in which neurons are fluorescently labeled, to research the effects of PTSD on neurons in vivo. We initially discovered that pathological stress associated with PTSD increased the activation of glycogen synthesis kinase-beta (GSK-3β) in neurons and induced the translocation of the transcription factor forkhead box-class O3a (FoxO3a) from the cytoplasm to the nucleus, which decreased the expression of uncoupling protein 2 (UCP2) and increased mitochondrial production of reactive oxygen species (ROS) to trigger neuronal apoptosis in the prefrontal cortex (PFC). Furthermore, the PTSD model mice showed increased freezing and anxiety-like behaviors and more severe decrease of memory and exploratory behavior. Additionally, leptin attenuated neuronal apoptosis by increasing the phosphorylation of signal transducer and activator of transcription 3 (STAT3), which further elevated the expression of UCP2 and inhibited the mitochondrial production of ROS induced by PTSD, thus reducing neuronal apoptosis and ameliorating PTSD-related behaviors. Our study is expected to promote the exploration of PTSD-related pathogenesis in neural cells and the clinical effectiveness of leptin for PTSD.

Ageing related thyroid deficiency increases brain-targeted transport of liver-derived ApoE4-laden exosomes leading to cognitive impairment

Alzheimer’s disease (AD) is the prevalent cause of dementia in the ageing world population. Apolipoprotein E4 (ApoE4) allele is the key genetic risk factor for AD, although the mechanisms linking ApoE4 with neurocognitive impairments and aberrant metabolism remains to be fully characterised. We discovered a significant increase in the ApoE4 content of serum exosomes in old healthy subjects and AD patients carrying ApoE4 allele as compared with healthy adults. Elevated exosomal ApoE4 demonstrated significant inverse correlation with serum level of thyroid hormones and cognitive function. We analysed effects of ApoE4-containing peripheral exosomes on neural cells and neurological outputs in aged or thyroidectomised young mice. Ageing-associated hypothyroidism as well as acute thyroidectomy augmented transport of liver-derived ApoE4 reach exosomes into the brain, where ApoE4 activated nucleotide-binding oligomerisation domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome by increasing cholesterol level in neural cells. This, in turn, affected cognition, locomotion and mood. Our study reveals pathological potential of exosomes-mediated relocation of ApoE4 from the periphery to the brain, this process can represent potential therapeutic target.

The neuroprotective mechanism of lithium after ischaemic stroke

Stroke causes degeneration and death of neurones leading to the loss of motor function and frequent occurrence of cognitive impairment and depression. Lithium (Li⁺), the archetypal mood stabiliser, is neuroprotective in animal models of stroke, albeit underlying mechanisms remain unknown. We discover that Li⁺ inhibits activation of nucleotide-binding oligomerisation domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasomes in the middle cerebral artery occlusion (MCAO) stroke model in mice. This action of Li⁺ is mediated by two signalling pathways of AKT/GSK3β/β-catenin and AKT/FoxO3a/β-catenin which converge in suppressing the production of reactive oxygen species (ROS). Using immunocytochemstry, MRI imaging, and cell sorting with subsequent mRNA and protein quantification, we demonstrate that Li⁺ decreases the infarct volume, improves motor function, and alleviates associated cognitive and depressive impairments. In conclusion, this study reveals molecular mechanisms of Li⁺ neuroprotection during brain ischaemia, thus providing the theoretical background to extend clinical applications of Li⁺ for treatment of ischemic stroke.

Anti-diabetic effects of astaxanthin on an STZ-induced diabetic model in rats

Type 2 diabetes mellitus (T2DM), which is characterized by insulin resistance and relative insulin insufficiency, has become the most common chronic metabolic disease threatening global health. The preferred therapies for T2DM include lifestyle interventions and the use of anti-diabetic drugs. However, considering their adverse reactions, it is important to find a low-toxicity and effective functional food or drug for diabetes prevention and treatment. Astaxanthin is a potent antioxidant carotenoid found in marine organisms has been reported to prevent diet-induced insulin resistance and hepatic steatosis. To investigate the anti-diabetic effects of astaxanthin, male Wistar rats were fed a high-energy diet for 4 weeks, followed by a low dose streptozotocin (STZ) injection to induce the diabetes model, and the rats were then fed an astaxanthin-containing diet for another 3 weeks. Astaxanthin significantly decreased blood glucose and total cholesterol (TC) levels, and increased blood levels of high density lipoprotein cholesterol (HDL-C) in STZ-induced diabetic rats in a dose dependent manner. These results were associated with increased expression of insulin sensitivity related genes (adiponectin, adipoR1, and adipoR2) in vivo, thereby attenuating STZ-induced diabetes. In addition, we also compared the anti-diabetic effects of astaxanthin and monacolin K, which has been reported to downregulate hyperlipidemia and hyperglycemia. The results revealed that astaxanthin and monacolin K showed similar anti-diabetic effects in STZ-induced diabetic rats. Therefore, astaxanthin may be developed as an anti-diabetic agent in the future.

Genetic Liability for Internalizing Versus Externalizing Behavior Manifests in the Developing and Adult Hippocampus: Insight From a Meta-analysis of Transcriptional Profiling Studies in a Selectively Bred Rat Model

BACKGROUND

For more than 16 years, we have selectively bred rats for either high or low levels of exploratory activity within a novel environment. These bred high-responder (bHR) and bred low-responder (bLR) rats model temperamental extremes, exhibiting large differences in internalizing and externalizing behaviors relevant to mood and substance use disorders.

METHODS

We characterized persistent differences in gene expression related to bHR/bLR phenotype across development and adulthood in the hippocampus, a region critical for emotional regulation, by meta-analyzing 8 transcriptional profiling datasets (microarray and RNA sequencing) spanning 43 generations of selective breeding (postnatal day 7: n = 22; postnatal day 14: n = 49; postnatal day 21: n = 21; adult: n = 46; all male). We cross-referenced expression differences with exome sequencing within our colony to pinpoint candidates likely to mediate the effect of selective breeding on behavioral phenotype. The results were compared with hippocampal profiling from other bred rat models.

RESULTS

Genetic and transcriptional profiling results converged to implicate multiple candidate genes, including two previously associated with metabolism and mood: Trhr and Ucp2. Results also highlighted bHR/bLR functional differences in the hippocampus, including a network essential for neurodevelopmental programming, proliferation, and differentiation, centering on Bmp4 and Mki67. Finally, we observed differential expression related to microglial activation, which is important for synaptic pruning, including 2 genes within implicated chromosomal regions: C1qa and Mfge8.

CONCLUSIONS

These candidate genes and functional pathways may direct bHR/bLR rats along divergent developmental trajectories and promote a widely different reactivity to the environment.

Increasing Nrf2 Activity as a Treatment Approach in Neuropsychiatry

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor encoded by NFE2L2. Under oxidative stress, Nrf2 does not undergo its normal cytoplasmic degradation but instead travels to the nucleus, where it binds to a DNA promoter and initiates transcription of anti-oxidative genes. Nrf2 upregulation is associated with increased cellular levels of glutathione disulfide, glutathione peroxidase, glutathione transferases, thioredoxin and thioredoxin reductase. Given its key role in governing the cellular antioxidant response, upregulation of Nrf2 has been suggested as a common therapeutic target in neuropsychiatric illnesses such as major depressive disorder, bipolar disorder and schizophrenia, which are associated with chronic oxidative and nitrosative stress, characterised by elevated levels of reactive oxygen species, nitric oxide and peroxynitrite. These processes lead to extensive lipid peroxidation, protein oxidation and carbonylation, and oxidative damage to nuclear and mitochondrial DNA. Intake of N-acetylcysteine, coenzyme Q₁₀ and melatonin is accompanied by increased Nrf2 activity. N-acetylcysteine intake is associated with improved cerebral mitochondrial function, decreased central oxidative and nitrosative stress, reduced neuroinflammation, alleviation of endoplasmic reticular stress and suppression of the unfolded protein response. Coenzyme Q₁₀, which acts as a superoxide scavenger in neuroglial mitochondria, instigates mitohormesis, ameliorates lipid peroxidation in the inner mitochondrial membrane, activates uncoupling proteins, promotes mitochondrial biogenesis and has positive effects on the plasma membrane redox system. Melatonin, which scavenges mitochondrial free radicals, inhibits mitochondrial nitric oxide synthase, restores mitochondrial calcium homeostasis, deacetylates and activates mitochondrial SIRT3, ameliorates increased permeability of the blood-brain barrier and intestine and counters neuroinflammation and glutamate excitotoxicity.

CYP2D1 Gene Knockout Reduces the Metabolism and Efficacy of Venlafaxine in Rats

Rat CYP2D1 has been considered as an ortholog of human CYP2D6 To assess the role of CYP2D1 in physiologic processes and drug metabolism, a CYP2D1-null rat model was generated with a CRISPR/Cas9 method. Seven base pairs were deleted from exon 4 of CYP2D1 of Sprague-Dawley wild-type (WT) rats. The CYP2D1-null rats were viable and showed no abnormalities in general appearance and behavior. The metabolism of venlafaxine (VLF) was further studied in CYP2D1-null rats. The V _max and intrinsic clearance of the liver microsomes in vitro from CYP2D1-null rats were decreased (by ∼46% and ∼57% in males and ∼47% and ∼58% in females, respectively), while the Michaelis constant was increased (by ∼24% in males and ∼25% in females) compared with WT rats. In the pharmacokinetic studies, compared with WT rats, VLF in CYP2D1-null rats had significantly lower apparent total clearance and apparent volume of distribution (decreased by ∼36% and ∼48% in males and ∼23% and ∼25% in females, respectively), significantly increased area under the curve (AUC) from the time of administration to the last time point, AUC from the start of administration to the theoretical extrapolation, and C _max (increased by ∼64%, ∼59%, and ∼26% in males and ∼43%, ∼35%, and ∼15% in females, respectively). In addition, O-desmethyl venlafaxine formation was reduced as well in CYP2D1-null rats compared with that in WT rats. Rat depression models were developed with CYP2D1-null and WT rats by feeding them separately and exposing them to chronic mild stimulation. VLF showed better efficacy in the WT depression rats compared with that in the CYP2D1-null rats. In conclusion, a CYP2D1-null rat model was successfully generated, and CYP2D1 was found to play a certain role in the metabolism and efficacy of venlafaxine. SIGNIFICANCE STATEMENT: A novel CYP2D1-null rat model was generated using CRISPR/Cas9 technology, and it was found to be a valuable tool in the study of the in vivo function of human CYP2D6. Moreover, our data suggest that the reduced O-desmethyl venlafaxine formation was associated with a lower VLF efficacy in rats.

Green satsuma mandarin orange (Citrus unshiu) extract reduces adiposity and induces uncoupling protein expression in skeletal muscle of obese mice

Increased fat mass, which is induced by the storage of excess nutrients, is considered a causal factor for various metabolic disorders, including insulin resistance, type 2 diabetes, hyperlipidemia, hyperglycemia, hypertension, atherosclerosis, and non-alcoholic fatty liver disease. Therefore, it is necessary to prevent hyperadiposity to sustain a healthy life. Recently, uncoupling proteins (UCPs) were suggested to be molecular targets for curing obesity and its complications. In this study, green satsuma mandarin orange (Citrus unshiu) extract (GME) increased UCP3 expression in cultured myocytes. In a diet-induced obese animal model, administration of GME reduced fat mass and average fat cell size. Similar to in vitro experiments, GME restored expression of UCP3 in skeletal muscle. Moreover, GME also induced UCP2 expression in skeletal muscle. In conclusion, GME is suggested to be a novel functional dietary supplement for adiposity control through induction of UCPs.

Mitochondrial Uncoupling Proteins: Subtle Regulators of Cellular Redox Signaling

SIGNIFICANCE

Mitochondria are the energetic, metabolic, redox, and information signaling centers of the cell. Substrate pressure, mitochondrial network dynamics, and cristae morphology state are integrated by the protonmotive force Δp or its potential component, ΔΨ, which are attenuated by proton backflux into the matrix, termed uncoupling. The mitochondrial uncoupling proteins (UCP1-5) play an eminent role in the regulation of each of the mentioned aspects, being involved in numerous physiological events including redox signaling. Recent Advances: UCP2 structure, including purine nucleotide and fatty acid (FA) binding sites, strongly support the FA cycling mechanism: UCP2 expels FA anions, whereas uncoupling is achieved by the membrane backflux of protonated FA. Nascent FAs, cleaved by phospholipases, are preferential. The resulting Δp dissipation decreases superoxide formation dependent on Δp. UCP-mediated antioxidant protection and its impairment are expected to play a major role in cell physiology and pathology. Moreover, UCP2-mediated aspartate, oxaloacetate, and malate antiport with phosphate is expected to alter metabolism of cancer cells.

CRITICAL ISSUES

A wide range of UCP antioxidant effects and participations in redox signaling have been reported; however, mechanisms of UCP activation are still debated. Switching off/on the UCP2 protonophoretic function might serve as redox signaling either by employing/releasing the extra capacity of cell antioxidant systems or by directly increasing/decreasing mitochondrial superoxide sources. Rapid UCP2 degradation, FA levels, elevation of purine nucleotides, decreased Mg²⁺, or increased pyruvate accumulation may initiate UCP-mediated redox signaling.

FUTURE DIRECTIONS

Issues such as UCP2 participation in glucose sensing, neuronal (synaptic) function, and immune cell activation should be elucidated. Antioxid. Redox Signal. 29, 667-714.

Uncoupling protein 2 modulation of the NLRP3 inflammasome in astrocytes and its implications in depression

Mitochondrial uncoupling protein 2 (UCP2) has been well characterized to control the production of reactive oxygen species (ROS) and astrocytes are the major cells responsible for the ROS production and the inflammatory responses in the brain. However, the function of UCP2 in astrocytes and the contribution of astrocytic UCP2 to depression remain undefined. Herein, we demonstrated that UCP2 knockout (KO) mice displayed aggravated depressive-like behaviors, impaired neurogenesis, and enhanced loss of astrocytes in the chronic mild stress (CMS)-induced anhedonia model of depression. We further found that UCP2 ablation significantly enhanced the activation of the nod-like receptor protein 3 (NLRP3) inflammasome in the hippocampus and in astrocytes. Furthermore, UCP2 deficiency promoted the injury of mitochondria, the generation of ROS and the physical association between thioredoxin-interacting protein (TXNIP) and NLRP3 in astrocytes. Moreover, transiently expressing exogenous UCP2 partially rescued the deleterious effects of UCP2 ablation on the astrocytes. These data indicate that UCP2 negatively regulates the activation of NLRP3 inflammasome and inhibited the ROS-TXNIP-NLRP3 pathway in astrocytes. Collectively, our findings reveal that UCP2 regulates inflammation responses in astrocytes and plays an important role in the pathogenesis of depression and that UCP2 may be a promising therapeutic target for depression.

Metformin Prevents Dopaminergic Neuron Death in MPTP/P-Induced Mouse Model of Parkinson's Disease via Autophagy and Mitochondrial ROS Clearance

BACKGROUND

Our previous study demonstrated that metabolic inflammation exacerbates dopaminergic neuronal degeneration in type 2 diabetes mice. Metformin, a typical oral hypoglycemic agent for diabetes, has been regarded as an activator of AMP-activated protein kinase and a regulator of systemic energy metabolism. Although metformin plays potential protective effects in many disorders, it is unclear whether metformin has a therapeutic role in dopaminergic neuron degeneration in Parkinson's disease.

METHODS

In the present study, a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine plus probenecid-induced mouse model of Parkinson's disease was established to explore the neuroprotective effect of metformin on dopaminergic neurons in substania nigra compacta. We next cultured SH-SY5Y cells to investigate the mechanisms for the neuroprotective effect of metformin.

RESULTS

We showed that treatment with metformin (5mg/mL in drinking water) for 5 weeks significantly ameliorated the degeneration of substania nigra compacta dopaminergic neurons, increased striatal dopaminergic levels, and improved motor impairment induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine plus probenecid. We further found that metformin inhibited microglia overactivation-induced neuroinflammation in substania nigra compacta of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine plus probenecid Parkinson's disease mice, which might contribute to the protective effect of metformin on neurodegeneration. Furthermore, metformin (2mM) activated AMP-activated protein kinase in SH-SY5Y cells, in turn inducing microtubule-associated protein 1 light chain 3-II-mediated autophagy and eliminating mitochondrial reactive oxygen species. Consequently, metformin alleviated MPP⁺-induced cytotoxicity and attenuated neuronal apoptosis.

CONCLUSIONS

Our findings demonstrate that metformin may be a pluripotent and promising drug for dopaminergic neuron degeneration, which will give us insight into the potential of metformin in terms of opening up novel therapeutic avenues for Parkinson's disease.

Linking Mitochondria to Synapses: New Insights for Stress-Related Neuropsychiatric Disorders

The brain evolved cellular mechanisms for adapting synaptic function to energy supply. This is particularly evident when homeostasis is challenged by stress. Signaling loops between the mitochondria and synapses scale neuronal connectivity with bioenergetics capacity. A biphasic “inverted U shape” response to the stress hormone glucocorticoids is demonstrated in mitochondria and at synapses, modulating neural plasticity and physiological responses. Low dose enhances neurotransmission, synaptic growth, mitochondrial functions, learning, and memory whereas chronic, higher doses produce inhibition of these functions. The range of physiological effects by stress and glucocorticoid depends on the dose, duration, and context at exposure. These criteria are met by neuronal activity and the circadian, stress-sensitive and ultradian, stress-insensitive modes of glucocorticoid secretion. A major hallmark of stress-related neuropsychiatric disorders is the disrupted glucocorticoid rhythms and tissue resistance to signaling with the glucocorticoid receptor (GR). GR resistance could result from the loss of context-dependent glucocorticoid signaling mediated by the downregulation of the activity-dependent neurotrophin BDNF. The coincidence of BDNF and GR signaling changes glucocorticoid signaling output with consequences on mitochondrial respiration efficiency, synaptic plasticity, and adaptive trajectories.

The Role of Nitric Oxide in the Antidepressant Actions of 5-Aminoimidazole-4-Carboxamide-1-β-D-Ribofuranoside in Insulin-Resistant Mice

OBJECTIVE

Depression and Type 2 diabetes mellitus are interrelated conditions, but the underlying neurobiology is insufficiently understood. The current study compared the effects of a pharmacological manipulation with 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) that targets neurobiological processes by adenosine 5'-monophosphate-activated protein kinase activation versus exercise on depression-like behavior and nitric oxide (NO)-related measures.

METHODS

A mouse model of a depression-like and insulin-resistant state, induced by the co-treatment of high-fat diet and corticosterone administration, was used to examine the antidepressant action of AICAR and exercise.

RESULTS

Data showed that AICAR was a putative antidepressant in the depression-like and insulin-resistant mice (total ambulatory distance in the open-field test was 5120.69 ± 167.47 cm, mobility duration in the forced swim test was 17.61 ± 1.54 seconds, latency to feed in the novelty suppressed feeding test was 255.67 ± 37.80 seconds; all p values < .05). Furthermore, the antidepressant actions of AICAR required endothelial nitric oxide synthase activity with increased NO production in the prefrontal cortex, whereas corticosterone-induced expression of neuronal nitric oxide synthase and NO production may increase the risk of depression. In contrast to the traditional antidepressants such as ketamine and imipramine, AICAR interfered with the effects of insulin in skeletal muscle in the context of high-fat diet, consistent with the potential antidepressant effects of AICAR. Exercise also resulted in activation of adenosine 5'-monophosphate-activated protein kinase, nitric oxide synthase, and NO production (all p values < .01), which in turn may be implicated in the antidepressant effects of exercise.

CONCLUSIONS

These findings suggest that NO is an essential signal mediating the antidepressant actions of AICAR. Ultimately, the concurrent effects of AICAR on brain insulin action and mitochondrial function suggest a potential of neural insulin resistance, which may contribute to our understanding of the comorbidity of depression and Type 2 diabetes.

Perspectives on mitochondrial uncoupling proteins-mediated neuroprotection

The integrity of mitochondrial function is essential to cell life. It follows that disturbances of mitochondrial function will lead to disruption of cell function, expressed as disease or even death. Considering that neuronal uncoupling proteins (UCPs) decrease reactive oxygen species (ROS) production at the expense of energy production, it is important to understand the underlying mechanisms by which UCPs control the balance between the production of adenosine triphosphate (ATP) and ROS in the context of normal physiological activity and in pathological conditions. Here we review the current understanding of neuronal UCPs-mediated respiratory uncoupling process by performing a survey in their physiology and regulation. The latest findings regarding neuronal UCPs physiological roles and their involvement and interest as potential targets for therapeutic intervention in brain diseases will also be exploited.

After a cold conditioning swim, UCP2-deficient mice are more able to defend against the cold than wild type mice

Uncoupling protein 2 (UCP2) is widely distributed throughout the body including the brain, adipose tissue and skeletal muscles. In contrast to UCP1, UCP2 does not influence resting body temperature and UCP2-deficient (-/-) mice have normal thermoregulatory responses to a single exposure to cold ambient temperatures. Instead, UCP2-deficient mice are more anxious, exhibit anhedonia and have higher circulating corticosterone than wild type mice. To test the possible role of UCP2 in depressive behavior we exposed UCP2-deficient and wild type mice to a cold (26°C) forced swim and simultaneously measured rectal temperatures during and after the swim. The time that UCP2-deficient mice spent immobile did not differ from wild type mice and all mice floated more on day 2. However, UCP2-deficient mice were more able to defend against the decrease in body temperature during a second daily swim at 26°C than wild type mice (area under the curve for wild type mice: 247.0±6.4; for UCP2-deficient mice: 284.4±3.8, P<0.0001, Student's t test). The improved thermoregulation of wild type mice during a second swim at 26°C correlated with their greater immobility whereas defense against the warmth during a swim at 41°C correlated better with greater immobility of UCP2-deficient mice. Together these data indicate that while the lack of UCP2 has no acute effect on body temperature, UCP2 may inhibit rapid improvements in defense against cold, in contrast to UCP1, whose main function is to promote thermogenesis.

Exhaustive training increases uncoupling protein 2 expression and decreases Bcl-2/Bax ratio in rat skeletal muscle

This work investigates the effects of oxidative stress due to exhaustive training on uncoupling protein 2 (UCP2) and Bcl-2/Bax in rat skeletal muscles. A total of 18 Sprague-Dawley female rats were randomly divided into three groups: the control group (CON), the trained control group (TC), and the exhaustive trained group (ET). Malondialdehyde (MDA), superoxide dismutase (SOD), xanthine oxidase (XOD), ATPase, UCP2, and Bcl-2/Bax ratio in red gastrocnemius muscles were measured. Exhaustive training induced ROS increase in red gastrocnemius muscles, which led to a decrease in the cell antiapoptotic ability (Bcl-2/Bax ratio). An increase in UCP2 expression can reduce ROS production and affect mitochondrial energy production. Thus, oxidative stress plays a significant role in overtraining.

Stress, depression and Parkinson's disease

In this review, we focus on the relationship among Parkinson's disease (PD), stress and depression. Parkinson's disease patients have a high risk of developing depression, and it is possible that stress contributes to the development of both pathologies. Stress dysfunction may have a role in the etiology of preclinical non-motor symptoms of PD (such as depression) and, later in the course of the disease, may worsen motor symptoms. However, relatively few studies have examined stress or depression and the injured nigrostriatal system. This review discusses the effects of stress on neurodegeneration and depression, and their association with the symptoms and progression of PD.