Alpha-Synuclein deficiency ameliorates chronic methamphetamine induced neurodegeneration in mice

The Possible Role of Brain-derived Neurotrophic Factor in Epilepsy

Epilepsy is a neurological disease characterized by repeated seizures. Despite of that the brain-derived neurotrophic factor (BDNF) is implicated in the pathogenesis of epileptogenesis and epilepsy, BDNF may have a neuroprotective effect against epilepsy. Thus, the goal of the present review was to highlight the protective and detrimental roles of BDNF in epilepsy. In this review, we also try to find the relation of BDNF with other signaling pathways and cellular processes including autophagy, mTOR pathway, progranulin (PGN), and α-Synuclein (α-Syn) which negatively and positively regulate BDNF/tyrosine kinase receptor B (TrkB) signaling pathway. Therefore, the assessment of BDNF levels in epilepsy should be related to other neuronal signaling pathways and types of epilepsy in both preclinical and clinical studies. In conclusion, there is a strong controversy concerning the potential role of BDNF in epilepsy. Therefore, preclinical, molecular, and clinical studies are warranted in this regard.

α-synuclein-lack expression rescues methamphetamine-induced mossy fiber degeneration in dorsal hippocampal CA3

Methamphetamine (METH) - induced cognitive impairments may be related to synaptic degeneration at mossy fiber terminals, critical for spatial memory formation in hippocampal circuits. We have previously found METH-induced neurodegeneration in the striatum by increasing the α-synuclein (α-SYN) level. However, whether and how the METH-induced mossy fiber degeneration is also blamed for the abnormal accumulation of α-SYN remains to be elucidated. Chronic METH exposure decreased mossy fiber density but upregulatedα-SYN and phosphorylated TAU (TAU-pSer396) in hippocampal CA3, associated with glial cell overactivation, axonal neuropathies, and memory impairment. Notably, the knockout of the α-SYN gene significantly alleviated the METH-induced mossy fiber degeneration and memory impairment. Meanwhile, the TAU-pSer396 accumulation and glial activation were ameliorated by α-SYN knockout. Our findings suggest an essential role of α-SYN in mediating METH-induced mossy fiber degeneration, providing promising therapeutic and prophylactic targets for METH-related neurodegenerative diseases.

Iron chelation prevents nigrostriatal neurodegeneration in a chronic methamphetamine mice model

Methamphetamine (METH) has been established to selectively target and impair dopaminergic neurons through multiple pathways. Ferroptosis is a unique form of non-apoptotic cell death driven by cellular iron accumulation-induced lipid peroxidation. Nonetheless, it remains unclear whether METH can induce ferroptosis. In the present study, we sought to assess alterations in iron levels after chronic METH exposure and reveal the modulatory role of iron on METH-induced pathologies. Importantly, we demonstrated that METH increased iron deposition in the nigrostriatal system, including the substantia nigra (SN) and caudate putamen (CPu). Moreover, decreases in GPx4 levels, increases in lipid peroxidation products, and pathological alterations were observed in the nigrostriatal system as a consequence of chronic METH exposure. The iron chelator deferiprone not only alleviated nigrostriatal iron deposition, dopaminergic cell death, and lipid peroxidation, but alsoattenuated the decreases in GPx4 induced by METH. These findings suggest an alleviation of ferroptosis in dopaminergic neurons. In addition, we found that the ferroptosis inhibitor liproxstatin-1 attenuated METH-induced dopaminergic degeneration in the nigrostriatal system. Our findings corroborated that METH might induce dopaminergic neurodegeneration through iron-dependent ferroptosis. Interestingly, reducing iron levels or inhibiting ferroptosis may alleviate METH-induced dopaminergic neurodegeneration.

Low and high dose methamphetamine differentially regulate synaptic structural plasticity in cortex and hippocampus

Psychostimulants, such as methamphetamine (METH) can induce structural remodeling of synapses by remodeling presynaptic and postsynaptic morphology. Escalating or long-lasting high dose METH accounts for neurodegeneration by targeting multiple neurotransmitters. However, the effects of low dose METH on synaptic structure and the modulation mechanism remain elusive. This study aims to assess the effects of low dose (2 mg/kg) and high dose (10 mg/kg) of METH on synaptic structure alternation in hippocampus and prefrontal cortex (PFC) and to reveal the underlying mechanism involved in the process. Low dose METH promoted spine formation, synaptic number increase, post-synaptic density length elongation, and memory function. High dose of METH induced synaptic degeneration, neuronal number loss and memory impairment. Moreover, high dose, but not low dose, of METH caused gliosis in PFC and hippocampus. Mechanism-wise, low dose METH inactivated ras-related C3 botulinum toxin substrate 1 (Rac1) and activated cell division control protein 42 homolog (Cdc42); whereas high dose METH inactivated Cdc42 and activated Rac1. We provided evidence that low and high doses of METH differentially regulate synaptic plasticity in cortex and hippocampus.

Transfer of neuron-derived α-synuclein to astrocytes induces neuroinflammation and blood-brain barrier damage after methamphetamine exposure: Involving the regulation of nuclear receptor-associated protein 1

The α-synuclein (α-syn) is involved in methamphetamine (METH)-induced neurotoxicity. Neurons can transfer excessive α-syn to neighboring neurons and glial cells. The effects of α-syn aggregation in astrocytes after METH exposure on the blood-brain barrier (BBB) remains unclear. Our previous study demonstrated that nuclear receptor-related protein 1 (Nurr1), a member of the nuclear receptor family widely expressed in the brain, was involved in the process of METH-induced α-syn accumulated in astrocytes to activate neuroinflammation. The role Nurr1 plays in astrocyte-mediated neuroinflammation, which results in BBB injury induced by METH, remains uncertain. This study found that METH up-regulated α-syn expression in neurons extended to astrocytes, thereby eliciting astrocyte activation, increasing and decreasing IL-1β, IL-6, TNF-α, and GDNF levels by down-regulating Nurr1 expression, and ultimately damaging the BBB. Specifically, the permeability of BBB to Evans blue and sodium fluorescein (NaF) increased; IgG deposits in the brain parenchyma increased; the Claudin5, Occludin, and PDGFRβ levels decreased. Several ultrastructural pathological changes occurred in the BBB, such as abnormal cerebral microvascular diameter, astrocyte end-foot swelling, decreased pericyte coverage, and loss of tight junctions. However, knockout or inhibition of α-syn or astrocyte-specific overexpression of Nurr1 partially alleviated these symptoms and BBB injury. Moreover, the in vitro experiments confirmed that METH increased α-syn level in the primary cultured neurons, which could be further transferred to primary cultured astrocytes, resulting in decreased Nurr1 levels. The decreased Nurr1 levels mediated the increase of IL-1β, IL-6, and TNF-α, and the decrease of GDNF, thereby changing the permeability to NaF, transendothelial electrical resistance, and Claudin5 and Occludin levels of primary cultured brain microvascular endothelial cells. Based on our findings, we proposed a new mechanism to elucidate METH-induced BBB injury and presented α-syn and Nurr1 as promising drug intervention targets to reduce BBB injury and resulting neurotoxicity in METH abusers.

Alterations in gut microbiota affect behavioral and inflammatory responses to methamphetamine in mice

RATIONALE AND OBJECTIVES

Methamphetamine (METH) is a highly addictive and widely abused drug that causes severe neuroinflammation in the human brain. The gut microbiota has a tremendous impact on the core symptoms of neuropsychiatric disorders via the microbiota-gut-brain (MGB) axis. However, it is not clear whether alterations in the gut microbiota are involved in METH exposure.

METHODS

We established a mouse model with chronic, escalating doses of METH exposure. Intervene in gut microbiota with antibiotics to observe the changes of locomotor activity caused by METH exposure in mice. qPCR and 16S rRNA gene sequencing were used to analyze the gut microbiota profiles. In addition, we tested the levels of inflammatory factors in the nucleus accumbens (NAc), prefrontal cortex (mPFC), hippocampus (HIp), and spleen. Finally, short-chain fatty acids (SCFAs) were supplemented to determine the interaction between behavior changes and the structure of gut microbiota.

RESULTS

In this research, METH increased the locomotor activity of mice, while antibiotics changed the effect. Antibiotics enhanced the expression of pro-inflammatory cytokines in mPFC, HIp, and spleen of METH-exposed mice. METH altered the gut microbiota of mice after antibiotic treatment, such as Butyricicoccus and Roseburia, which are related to butyrate metabolism. Supplementation with SCFAs changed the behavior of METH-exposed mice and decreased Parabacteroides and increased Lactobacillus in METH-exposed mice gut.

CONCLUSIONS

This research showed that antibiotics affected the behavior of METH-exposed mice and promoted inflammation. Our findings suggest that SCFAs might regulate METH-induced gut microbiota changes and behavior.

Effects of Moderate-Intensity Interval Training on Gene Expression and Antioxidant Status in the Hippocampus of Methamphetamine-Dependent Rats

Methamphetamine (METH) can cause neurotoxicity and increase the risk of neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. This study aimed to investigate the effect of moderate-intensity interval training (MIIT) on gene expression and antioxidant status of the hippocampus of METH-dependent rats. Thirty-two male Wistar rats were randomly divided into four equal groups (n = 8): saline, METH, MIIT, and METH + MIIT. METH was injected intraperitoneally at 5 mg/kg for 21 days. The MIIT(interval running) was performed on the treadmill 5 days a week for 8 weeks. Morris water maze test was performed to measure learning and memory. Then, the hippocampal tissue was extracted to evaluate changes in gene expression and biochemical enzymes. The data were analyzed using one-way and two-way ANOVA methods at p < 0.05. The results showed that METH injection significantly reduced spatial memory and antioxidant enzymes and increased the expression of α-synuclein (α-syn), cyclin-dependent kinase 5 (CDK5), tau, and phosphorylated tau (p-tau) genes compared to the saline group. MIIT significantly increased spatial memory and antioxidant enzymes. However, it reduced α-syn, CDK5, tau, and p-tau expression. Thus, this study depicted that methamphetamine-dependent rats with memory deficits have lower antioxidant enzyme levels and higher expression of α-syn, CDK5, tau, and p-tau genes, and that an 8-week MIIT may have beneficial effects on the memory impairments as well as antioxidant status and gene expression in male rats.

Atypical Parkinsonism: Methamphetamine may play a role

Abusing methamphetamine can be considered as an agent that can cause or affect the course of atypical parkinsonian syndromes (APS), which may raise attention regarding preventing abusing these drugs.

Aerobic Exercise Improves Methamphetamine-Induced Olfactory Dysfunction Through α-Synuclein Intervention in Male Mice

Methamphetamine (Meth) is a predominantly abused neurostimulant, and its abuse is often associated with multiple neurological symptoms. Olfaction, the sense of smell, is a highly neurotransmission-dependent physiological process; however, the effect of Meth on olfactory function and its underlying mechanisms remain largely unknown. This study aimed to explore the impact of Meth abuse on the olfactory system and the potential mechanisms. Chronic Meth abuse was induced by daily administration of Meth in male mice for 4 weeks, and we then systematically examined olfactory performance. Behavioral tests found that Meth-treated animals showed increased olfactory threshold, decreased olfactory sensitivity, reduced olfactory-dependent discrimination, and difficulty in seeking buried food. Notably, the increased deposition of α-synuclein (α-syn) in the olfactory bulb was detected. Adeno-associated virus (AAV)-mediated α-syn intervention therapy in the olfactory bulb significantly alleviated Meth-induced olfactory function impairment, and 8 weeks of aerobic exercise showed similar effects through the same principle of α-syn intervention. Notably, exercise-mediated reduction of α-syn inhibited abnormal firing activity and restored the inhibitory synaptic regulation of mitral cells in the olfactory bulb. These findings suggest the involvement of α-syn in the pathogenic mechanisms of Meth-induced olfactory dysfunction and shed light on the possible therapeutic applications of aerobic exercise in Meth-induced olfactory dysfunction.

Inflammasome Inhibition Prevents Motor Deficit and Cerebellar Degeneration Induced by Chronic Methamphetamine Administration

Methamphetamine (METH), a psychostimulant, has the potential to cause neurodegeneration by targeting the cerebrum and cerebellum. It has been suggested that the NLRP3 inflammasome may be responsible for the neurotoxicity caused by METH. However, the role of NLRP3 in METH-induced cerebellar Purkinje cell (PC) degeneration and the underlying mechanism remain elusive. This study aims to determine the consequences of NLRP3 modulation and the underlying mechanism of chronic METH-induced cerebellar PC degeneration. In METH mice models, increased NLRP3 expression, PC degeneration, myelin sheath destruction, axon degeneration, glial cell activation, and motor coordination impairment were observed. Using the NLRP3 inhibitor MCC950, we found that inhibiting NLRP3 alleviated the above-mentioned motor deficits and cerebellar pathologies. Furthermore, decreased mature IL-1β expression mediated by Caspase 1 in the cerebellum may be associated with the neuroprotective effects of NLRP3 inflammasome inhibition. Collectively, these findings suggest that mature IL-1β secretion mediated by NLRP3-ASC-Caspase 1 may be a critical step in METH-induced cerebellar degeneration and highlight the neuroprotective properties of inflammasome inhibition in cerebellar degeneration.

Luteolin Ameliorates Methamphetamine-Induced Podocyte Pathology by Inhibiting Tau Phosphorylation in Mice

Methamphetamine (METH) can cause kidney dysfunction. Luteolin is a flavonoid compound that can alleviate kidney dysfunction. We aimed to observe the renal-protective effect of luteolin on METH-induced nephropathies and to clarify the potential mechanism of action. The mice were treated with METH (1.0-20.0 mg/kg/d bodyweight) for 14 consecutive days. Morphological studies, renal function, and podocyte specific proteins were analyzed in the chronic METH model in vivo. Cultured podocytes were used to support the protective effects of luteolin on METH-induced podocyte injury. We observed increased levels of p-Tau and p-GSK3β and elevated glomerular pathology, renal dysfunction, renal fibrosis, foot process effacement, macrophage infiltration, and podocyte specific protein loss. Inhibition of GSK3β activation protected METH-induced kidney injury. Furthermore, luteolin could obliterate glomerular pathologies, inhibit podocyte protein loss, and stop p-Tau level increase. Luteolin could also abolish the METH-induced podocyte injury by inactivating GSK3β-p-Tau in cultured podocytes. These results indicate that luteolin might ameliorate methamphetamine-induced podocyte pathology through GSK3β-p-Tau axis.

The Role of Hyperthermia in Methamphetamine-Induced Depression-Like Behaviors: Protective Effects of Coral Calcium Hydride

Methamphetamine (METH) abuse causes irreversible damage to the central nervous system and leads to psychiatric symptoms including depression. Notably, METH-induced hyperthermia is a crucial factor in the development of these symptoms, as it aggravates METH-induced neurotoxicity. However, the role of hyperthermia in METH-induced depression-like behaviors needs to be clarified. In the present study, we treated mice with different doses of METH under normal (NAT) or high ambient temperatures (HAT). We found that HAT promoted hyperthermia after METH treatment and played a key role in METH-induced depression-like behaviors in mice. Intriguingly, chronic METH exposure (10 mg/kg, 7 or 14 days) or administration of an escalating-dose (2 ∼ 15 mg/kg, 3 days) of METH under NAT failed to induce depression-like behaviors. However, HAT aggravated METH-induced damage of hippocampal synaptic plasticity, reaction to oxidative stress, and neuroinflammation. Molecular hydrogen acts as an antioxidant and anti-inflammatory agent and has been shown to have preventive and therapeutic applicability in a wide range of diseases. Coral calcium hydride (CCH) is a newly identified hydrogen-rich powder which produces hydrogen gas gradually when exposed to water. Herein, we found that CCH pretreatment significantly attenuated METH-induced hyperthermia, and administration of CCH after METH exposure also inhibited METH-induced depression-like behaviors and reduced the hippocampal synaptic plasticity damage. Moreover, CCH effectively reduced the activity of lactate dehydrogenase and decreased malondialdehyde, TNF-α and IL-6 generation in hippocampus. These results suggest that CCH is an efficient hydrogen-rich agent, which has a potential therapeutic applicability in the treatment of METH abusers.

Transfer of α-synuclein from neurons to oligodendrocytes triggers myelin sheath destruction in methamphetamine administration mice

Methamphetamine (METH), a widely abused nervous system stimulant, could induce neurotoxicity through α-synuclein (α-syn). Not much is known about the neuronal derived α-syn transmission that underlies oligodendrocyte pathology in METH mice model. In this study, we tested α-syn level, oligodendroglial pathology and autophagy lysosome pathway (ALP) function in corpus callosum in a chronic METH mice model. METH increased α-syn level in neurons and then accumulated in oligodendrocytes. METH increased phosphor-mTOR level, decreased transcription factor EB (TFEB) level and triggered autophagy lysosomal pathway (ALP) impairment, leading to myelin sheath destruction, oligodendroglial proteins loss, mature dendritic spine loss, neuron loss, and astrocyte activation. Deleting endogenous α-syn increased TFEB level, alleviated ALP deficit, and diminished neuropathology induced by METH. TFEB overexpression in oligodendrocytes exerted beneficial effects in METH mice model. These neuroprotective effects were associated with the rescued ALP machinery after oligodendroglial TFEB overexpression. Our study demonstrated, for the first time, that α-syn-TFEB axis might be involve in the METH induced myelin loss, oligodendroglial pathology, and neuropathology. In summary, targeting at the α-syn-TFEB axis might be a promising therapeutic strategy for treating METH induced oligodendroglial pathology, and to a broader view, neurodegenerative diseases.

The Role of α-Synuclein in Methamphetamine-Induced Neurotoxicity

Methamphetamine (METH), a highly addictive psychostimulant, is the second most widely used illicit drug. METH produces damage dopamine neurons and apoptosis via multiple inter-regulating mechanisms, including dopamine overload, hyperthermia, oxidative stress, mitochondria dysfunction, endoplasmic reticulum stress, protein degradation system dysfunction, and neuroinflammation. Increasing evidence suggests that chronic METH abuse is associated with neurodegenerative changes in the human brain and an increased risk of Parkinson's disease (PD). METH use and PD may share some common steps in causing neurotoxicity. Accumulation of α-synuclein, a presynaptic protein, is the pathological hallmark of PD. Intriguingly, α-synuclein upregulation and aggregation are also found in dopaminergic neurons in the substantia nigra in chronic METH users. This suggests α-synuclein may play a role in METH-induced neurotoxicity. The mechanism of α-synuclein cytotoxicity in PD has attracted considerable attention; however, how α-synuclein affects METH-induced neurotoxicity has not been reviewed. In this review, we summarize the relationship between METH use and PD, interdependent mechanisms that are involved in METH-induced neurotoxicity and the significance of α-synuclein upregulation in response to METH use. The identification of α-synuclein overexpression and aggregation as a contributor to METH-induced neurotoxicity may provide a novel therapeutic target for the treatment of the deleterious effect of this drug and drug addiction.

Methamphetamine leads to the alterations of microRNA profiles in the nucleus accumbens of rats

CONTEXT

MicroRNA (miRNA) is an important regulator of gene expression. Methamphetamine (METH) induces a variety of alterations in different systems by affecting gene expression, but the effects of METH on miRNA profiles need to be elucidated.

OBJECTIVES

This study develops a rat model of METH addiction, and analyzes the expression profile alterations of miRNA in nucleus accumbens (NAc) of the METH-addicted rats.

MATERIALS AND METHODS

Sprague-Dawley rats were administered 10 mg/kg METH or vehicle twice a day for 4 weeks. The addictive behaviour of rats was estimated by CPP test. The pathological changes of brain tissues were then observed by HE and Glee silver staining. The miRNA profile analysis of the NAc of the rats was performed using an Illumina HiSeq™ 2500 sequencing system.

RESULTS

CPP test indicated that METH significantly prolonged the residence time of the rats in the drug box (from 307 ± 97 to 592 ± 96 s). The pathological staining showed the distorted axons, and fewer polarized neurons in the METH-treated rats. We further identified 40 differential miRNAs (17 up- and 23 down-regulated) and three novel miRNAs (novel 237, 296 and 501) that responded to METH. The bioinformatic analysis for the potential targets of the differential miRNA suggests that the downstream were concentrated in the Wnt signalling pathway, tuberculosis, toxoplasmosis, spliceosome, lysosome, and axon guidance.

DISCUSSION AND CONCLUSIONS

A number of miRNAs responding to METH were identified in the NAc of rats. These METH-regulated miRNAs provide a new perspective for revealing the molecular mechanisms of METH addiction.

Transfer of pathological α-synuclein from neurons to astrocytes via exosomes causes inflammatory responses after METH exposure

Methamphetamine (METH) is a highly addictive psychostimulant drug whose abuse can cause many health complications. Our previous studies have shown that METH exposure increases α-synuclein (α-syn) expression. Recently, it was shown that α-syn could be transferred from neurons to astrocytes via exosomes. However, the specific role of astrocytes in α-syn pathology involved in METH neurotoxicity remains unclear. The objective of this study was to determine whether exosomes derived from METH-treated neurons contain pathological α-syn and test the hypothesis that exosomes can transfer pathological α-syn from neurons to astrocytes. To this end, using animal and cell line coculture models, we show that exosomes isolated from METH-treated SH-SY5Y cells contained pathological α-syn. Furthermore, the addition of METH exosomes to the medium of primary cultured astrocytes induced α-syn aggregation and inflammatory responses in astrocytes. Then, we evaluated changes in nuclear receptor related 1 protein (Nurr1) expression and the levels of inflammatory cytokines in primary cultured astrocytes exposed to METH or α-syn. We found that METH or α-syn exposure decreased Nurr1 expression and increased proinflammatory cytokine expression in astrocytes. Our results indicate that α-syn can be transferred from neuronal cells to astrocytes through exosomes. When internalized α-syn accumulated in astrocytes, the cells produced inflammatory responses. Nurr1 may play a crucial role in this process and could be a therapeutic target for inflammatory damage caused by METH.