Mitochondrial dysfunction and apoptosis are attenuated through activation of AMPK/GSK-3β/PP2A pathway in Parkinson's disease

AdipoRon improves mitochondrial homeostasis and protects dopaminergic neurons through activation of the AMPK signaling pathway in the 6-OHDA-lesioned rats

The progressive decline of dopaminergic neurons in Parkinson's disease (PD) has been linked to an imbalance in energy and the failure of mitochondrial function. AMP-activated protein kinase (AMPK), the major intracellular energy sensor, regulates energy balance, and damage to nigral dopaminergic neurons induced by 6-hydroxydopamine (6-OHDA) is exacerbated in the absence of AMPK activity. This study aimed to examine the potential therapeutic advantages of AdipoRon, an AMPK activator, on motor function and mitochondrial homeostasis in a 6-OHDA-induced PD model. Male Wistar rats were subjected to unilateral injection of 6-OHDA (10 μg) into the left medial forebrain bundle at two points, and after 7 days, they were treated with intranasal AdipoRon (0.1, 1, and 10 μg) or Levodopa (10 mg/kg, p. o.) for 21 successive days. Following the last treatment day, motor behavior was evaluated through the Murprogo's test, bar test, beam walking test, and apomorphine-induced rotation test. After euthanasia, the left substantia nigra (SN) was separated for evaluation of ATP, mitochondrial membrane potential (MMP), and protein expressions of AMPK, p-AMPK, and mitochondrial dynamics markers (Mfn-2 and Drp-1). Moreover, the number of tyrosine hydroxylase-positive (TH+) cells was quantified in the left substantia nigra. Intranasal AdipoRon effectively reversed muscle rigidity, akinesia, bradykinesia, and rotation caused by 6-OHDA. Moreover, AdipoRon increased the phospho-AMPK/AMPK ratio, mitigated mitochondrial dysfunction, and improved mitochondrial dynamics in the SN. Furthermore, AdipoRon increased the number of TH+ cells in the SN of PD animals. These findings suggest that AdipoRon could protect dopaminergic neurons by activating the AMPK pathway and improving mitochondrial dysfunction.

Impacts of exposure to and subsequent discontinuation of clozapine on tripartite synaptic transmission

BACKGROUND AND PURPOSE

Clozapine is an effective antipsychotic for treatment-resistant schizophrenia, but its discontinuation leads to discontinuation syndrome/catatonia complicated by benzodiazepine-resistance and rhabdomyolysis.

EXPERIMENTAL APPROACH

This study determined time-dependent effects of exposure and subsequent discontinuation of clozapine on expression of connexin43, 5-HT receptors, intracellular L-β-aminoisobutyrate (L-BAIBA) and 2nd-messengers and signalling of AMPK, PP2A and Akt in cultured astrocytes and rat frontal cortex.

KEY RESULTS

Intracellular L-BAIBA levels increased during clozapine exposure but immediately recovered after discontinuation. Both exposure to clozapine and L-BAIBA increased connexin43 and signalling of AMPK/Akt time-dependently, but reduced PP2A signalling, 5-HT receptor expression and IP3 level. These changes recovered within 2 weeks after discontinuation, while 5-HT receptors and IP3 transiently increased during the recovery process. L-BAIBA activated AMPK signalling, leading to attenuated PP2A signalling. Astroglial D-serine release was increased by clozapine exposure but continued to increase within 1 week after discontinuation via activation of IP3 receptor function.

CONCLUSION AND IMPLICATIONS

Clozapine discontinuation restored PP2A signalling due to decreased L-BAIBA, increased 5-HT receptor expression via probably enhanced 5-HT receptor recycling, but increased astroglial D-serine release persisted by transiently activated IP3 receptors via transiently increased IP3 level. Decreased L-BAIBA caused by clozapine discontinuation is, at least partially, involved in the transiently increased 5-HT receptor and astroglial D-serine release.

Dihydromyricetin Improves High Glucose-Induced Dopaminergic Neuronal Damage by Activating AMPK-Autophagy Signaling Pathway

INTRODUCTION

In recent years, a growing number of clinical and biological studies have shown that patients with type 2 diabetes mellitus (T2DM) are at increased risk of developing Parkinson's disease (PD). Prolonged exposure to hyperglycemia results in abnormal glucose metabolism, which in turn causes pathological changes similar to PD, leading to selective loss of dopaminergic neurons in the compact part of the substantia nigra. Dihydromyricetin (DHM) is a naturally occurring flavonoid with various biological activities including antioxidant and hepatoprotective properties. In this study, the effect of DHM on high glucose-induced dopaminergic neuronal damage was investigated.

METHODS

The potential modulatory effects of DHM on high glucose-induced dopaminergic neuronal damage and its mechanism were studied.

RESULTS

DHM ameliorated high glucose-induced dopaminergic neuronal damage and autophagy injury. Inhibition of autophagy by 3-methyladenine abrogated the beneficial effects of DHM on high glucose-induced dopaminergic neuronal damage. In addition, DHM increased levels of p-AMP-activated protein kinase (AMPK) and phosphorylated UNC51-like kinase 1. The AMPK inhibitor compound C eliminated DHM-induced autophagy and subsequently inhibited the ameliorative effects of DHM on high glucose-induced dopaminergic neuronal damage.

DISCUSSION

DHM ameliorates high glucose-induced dopaminergic neuronal damage by activating the AMPK-autophagy pathway.

Therapeutic Potential Effect of Glycogen Synthase Kinase 3 Beta (GSK-3β) Inhibitors in Parkinson Disease: Exploring an Overlooked Avenue

Parkinson's disease (PD) is a progressive neurodegenerative disease of the brain due to degeneration of dopaminergic neurons in the substantia nigra (SN). Glycogen synthase kinase 3 beta (GSK-3β) is implicated in the pathogenesis of PD. Therefore, the purpose of the present review was to revise the mechanistic role of GSK-3β in PD neuropathology, and how GSK-3β inhibitors affect PD neuropathology. GSK-3 is a conserved threonine/serine kinase protein that is intricate in the regulation of cellular anabolic and catabolic pathways by modulating glycogen synthase. Over-expression of GSK-3β is also interconnected with the development of different neurodegenerative diseases. However, the underlying mechanism of GSK-3β in PD neuropathology is not fully clarified. Over-expression of GSK-3β induces the development of PD by triggering mitochondrial dysfunction and oxidative stress in the dopaminergic neurons of the SN. NF-κB and NLRP3 inflammasome are activated in response to dysregulated GSK-3β in PD leading to progressive neuronal injury. Higher expression of GSK-3β in the early stages of PD neuropathology might contribute to the reduction of neuroprotective brain-derived neurotrophic factor (BDNF). Thus, GSK-3β inhibitors may be effective in PD by reducing inflammatory and oxidative stress disorders which are associated with degeneration of dopaminergic in the SN.

Protopanaxadiols Eliminate Behavioral Impairments and Mitochondrial Dysfunction in Parkinson's Disease Mice Model

Currently, there are no effective therapies to cure Parkinson's disease (PD), which is the second most common neurodegenerative disease primarily characterized by motor dysfunction and degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNc). Protopanaxadiols (PPDs), including 20 (R)- protopanaxadiol (R-PPD) and 20 (S)- protopanaxadiol (S-PPD), are main metabolites of ginsenosides. The role of ginsenosides in neurodegenerative diseases has been thoroughly studied, however, it is unknown whether PPDs can attenuate behavioral deficits and dopaminergic neuron injury in PD model mice to date. Here, we administered PPDs to MPTP-induced PD model mice and monitored the effects on behavior and dopaminergic neurons to investigate the effects of R-PPD and S-PPD against PD. Our results showed that R-PPD and S-PPD (at a dose of 20 mg/kg, i.g.) treatment alleviated MPTP (30 mg/kg, i.p.) induced behavioral deficits. Besides, R-PPD and S-PPD protected MPP+-induced neuron injury and mitochondrial dysfunction, and reduced the abnormal expression of Cyt C, Bax, caspase-3 and Bcl-2. These findings demonstrate that R-PPD and S-PPD were potentially useful to ameliorate PD.

Molecular Role of Protein Phosphatases in Alzheimer's and Other Neurodegenerative Diseases

Alzheimer's disease (AD) is distinguished by the gradual loss of cognitive function, which is associated with neuronal loss and death. Accumulating evidence supports that protein phosphatases (PPs; PP1, PP2A, PP2B, PP4, PP5, PP6, and PP7) are directly linked with amyloid beta (Aβ) as well as the formation of the neurofibrillary tangles (NFTs) causing AD. Published data reported lower PP1 and PP2A activity in both gray and white matters in AD brains than in the controls, which clearly shows that dysfunctional phosphatases play a significant role in AD. Moreover, PP2A is also a major causing factor of AD through the deregulation of the tau protein. Here, we review recent advances on the role of protein phosphatases in the pathology of AD and other neurodegenerative diseases. A better understanding of this problem may lead to the development of phosphatase-targeted therapies for neurodegenerative disorders in the near future.

AMPK Signaling Pathway as a Potential Therapeutic Target for Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disease caused by the loss of dopaminergic neurons. Genetic factors, inflammatory responses, oxidative stress, metabolic disorders, cytotoxic factors, and mitochondrial dysfunction are all involved in neuronal death in neurodegenerative diseases. The risk of PD can be higher in aging individuals due to decreased mitochondrial function, energy metabolism, and AMP-activated protein kinase (AMPK) function. The potential of AMPK to regulate neurodegenerative disorders lies in its ability to enhance antioxidant capacity, reduce oxidative stress, improve mitochondrial function, decrease mitophagy and macroautophagy, and inhibit inflammation. In addition, it has been shown that modulating the catalytic activity of AMPK can protect the nervous system. This article reviews the mechanisms by which AMPK activation can modulate PD.

Resveratrol Promotes Autophagy to Improve neuronal Injury in Parkinson's Disease by Regulating SNHG1/miR-128-3p/SNCA Axis

BACKGROUND

Parkinson's disease (PD) is seriously threatening the health and life quality of the elderly, who have a high incidence and high disability rate. Resveratrol (RES) was reported to play a protective role in PD. However, the functions and potential mechanism of RES in PD remain unclear, which need to be further explored.

METHODS

Human neuroblastoma cells (SH-SY5Y and SK-N-SH) were subjected to 1-Methyl-4-phenylpyridium (MPP+) induction to construct a cell model of PD. Cell viability was evaluated using CCK-8. The gene expression was evaluated using qRT-PCR and western blot. Luciferase activity assay and RIP were performed to validate interactions among SNHG1, miR-128-3p and SNCA.

RESULTS

Our results exhibited that RES reduced SNHG1 and SNCA expression but elevated miR-128-3p expression in human neuroblastoma cells upon MPP+ induction. Functionally, RES resulted in the promotion of cell autophagy in MPP+-induced human neuroblastoma cells, while these influences were abolished by SNHG1 overexpression. Mechanistically, SNHG1 could indirectly elevate SNCA expression via sponging miR-128-3p. Moreover, SNCA overexpression reversed SNHG1 silencing-induced cell autophagy in MPP+-induced human neuroblastoma cells upon RES pre-incubation.

CONCLUSIONS

RES prevented MPP+-induced repression of cell autophagy through inhibiting the SNHG1/miR-128-3p/SNCA axis, suggesting that RES might play a preventive effect on PD progression.

Inter and intracellular mitochondrial transfer: Future of mitochondrial transplant therapy in Parkinson's disease

Parkinson's disease (PD) is marked by the gradual degeneration of dopaminergic neurons and the intracellular build-up of Lewy bodies rich in α-synuclein protein. This impairs various aspects of the mitochondria including the generation of ROS, biogenesis, dynamics, mitophagy etc. Mitochondrial dynamics are regulated through the inter and intracellular movement which impairs mitochondrial trafficking within and between cells. This inter and intracellular mitochondrial movement plays a significant role in maintaining neuronal dynamics in terms of energy and growth. Kinesin, dynein, myosin, Mitochondrial rho GTPase (Miro), and TRAK facilitate the retrograde and anterograde movement of mitochondria. Enzymes such as Kinases along with Calcium (Ca²⁺), Adenosine triphosphate (ATP) and the genes PINK1 and Parkin are also involved. Extracellular vesicles, gap junctions, and tunneling nanotubes control intercellular movement. The knowledge and understanding of these proteins, enzymes, molecules, and movements have led to the development of mitochondrial transplant as a therapeutic approach for various disorders involving mitochondrial dysfunction such as stroke, ischemia and PD. A better understanding of these pathways plays a crucial role in establishing extracellular mitochondrial transplant therapy for reverting the pathology of PD. Currently, techniques such as mitochondrial coculture, mitopunch and mitoception are being utilized in the pre-clinical stages and should be further explored for translational value. This review highlights how intercellular and intracellular mitochondrial dynamics are affected during mitochondrial dysfunction in PD. The field of mitochondrial transplant therapy in PD is underlined in particular due to recent developments and the potential that it holds in the near future.

Ginsenoside Rg1 ameliorates chronic intermittent hypoxia-induced vascular endothelial dysfunction by suppressing the formation of mitochondrial reactive oxygen species through the calpain-1 pathway

Background

As the major pathophysiological feature of obstructive sleep apnea (OSA), chronic intermittent hypoxia (CIH) is vital for the occurrence of cardiovascular complications. The activation of calpain-1 mediates the production of endothelial reactive oxygen species (ROS) and impairs nitric oxide (NO) bioavailability, resulting in vascular endothelial dysfunction (VED). Ginsenoside Rg1 is thought to against endothelial cell dysfunction, but the potential mechanism of CIH-induced VED remains unclear.

Methods

C57BL/6 mice and human coronary artery endothelial cells (HCAECs) were exposed to CIH following knockout or overexpression of calpain-1. The effect of ginsenoside Rg1 on VED, oxidative stress, mitochondrial dysfunction, and the expression levels of calpain-1, PP2A and p-eNOS were detected both in vivo and in vitro.

Results

CIH promoted VED, oxidative stress and mitochondrial dysfunction accompanied by enhanced levels of calpain-1 and PP2A and reduced levels of p-eNOS in mice and cellular levels. Ginsenoside Rg1, calpain-1 knockout, OKA, NAC and TEMPOL treatment protected against CIH-induced VED, oxidative stress and mitochondrial dysfunction, which is likely concomitant with the downregulated protein expression of calpain-1 and PP2A and the upregulation of p-eNOS in mice and cellular levels. Calpain-1 overexpression increased the expression of PP2A, reduced the level of p-eNOS, and accelerated the occurrence and development of VED, oxidative stress and mitochondrial dysfunction in HCAECs exposed to CIH. Moreover, scavengers of O₂ ^{• -}, H₂O₂, complex Ⅰ or mitoK_ATP abolished CIH-induced impairment in endothelial-dependent relaxation.

Conclusion

Ginsenoside Rg1 may alleviate CIH-induced vascular endothelial dysfunction by suppressing the formation of mitochondrial reactive oxygen species through the calpain-1 pathway.

Mitochondrial dysfunctions, oxidative stress and neuroinflammation as therapeutic targets for neurodegenerative diseases: An update on current advances and impediments

Neurodegenerative diseases (NDs) such as Alzheimer disease (AD), Parkinson disease (PD), and Huntington disease (HD) represent a major socio-economic challenge in view of their high prevalence yet poor treatment outcomes affecting quality of life. The major challenge in drug development for these NDs is insufficient clarity about the mechanisms involved in pathogenesis and pathophysiology. Mitochondrial dysfunction, oxidative stress and inflammation are common pathways that are linked to neuronal abnormalities and initiation of these diseases. Thus, elucidating the shared initial molecular and cellular mechanisms is crucial for recognizing novel remedial targets, and developing therapeutics to impede or stop disease progression. In this context, use of multifunctional compounds at early stages of disease development unclogs new avenues as it acts on act on multiple targets in comparison to single target concept. In this review, we summarize overview of the major findings and advancements in recent years focusing on shared mechanisms for better understanding might become beneficial in searching more potent pharmacological interventions thereby reducing the onset or severity of various NDs.

Altered Cortical Palmitoylation Induces Widespread Molecular Disturbances in Parkinson's Disease

The relationship between Parkinson's disease (PD), the second-most common neurodegenerative disease after Alzheimer's disease, and palmitoylation, a post-translational lipid modification, is not well understood. In this study, to better understand the role of protein palmitoylation in PD and the pathways altered in this disease, we analyzed the differential palmitoyl proteome (palmitome) in the cerebral cortex of PD patients compared to controls (n = 4 per group). Data-mining of the cortical palmitome from PD patients and controls allowed us to: (i) detect a set of 150 proteins with altered palmitoylation in PD subjects in comparison with controls; (ii) describe the biological pathways and targets predicted to be altered by these palmitoylation changes; and (iii) depict the overlap between the differential palmitome identified in our study with protein interactomes of the PD-linked proteins α-synuclein, LRRK2, DJ-1, PINK1, GBA and UCHL1. In summary, we partially characterized the altered palmitome in the cortex of PD patients, which is predicted to impact cytoskeleton, mitochondrial and fibrinogen functions, as well as cell survival. Our study suggests that protein palmitoylation could have a role in the pathophysiology of PD, and that comprehensive palmitoyl-proteomics offers a powerful approach for elucidating novel cellular pathways modulated in this neurodegenerative disease.

GSK-3β-mediated regulation of Nrf2/HO-1 signaling as a new therapeutic approach in the treatment of movement disorders

Movement disorders are neurological conditions characterized by involuntary motor movements, such as dystonia, ataxia, chorea myoclonus, tremors, Huntington's disease (HD), and Parkinson's disease (PD). It is classified into two categories: hypokinetic and hyperkinetic movements. Globally, movement disorders are a major cause of death. The pathophysiological process is initiated by excessive ROS generation, mitochondrial dysfunction, neuroinflammation, and neurotransmitters imbalance that lead to motor dysfunction in PD and HD patients. Several endogenous targets including Nrf2 maintain oxidative balance in the body. Activation of Nrf2 signaling is regulated by the enzyme glycogen synthase kinase (GSK-3β). In the cytoplasm, inhibition of GSK-3β regulates cellular proliferation, homeostasis, and apoptotic process by stimulating the nuclear factor erythroid 2 (Nrf2) pathway which is involved in the elevation of the cellular antioxidant enzymes which controls the ROS generation. The activation of Nrf2 increases the expression of antioxidant response elements (ARE), such as (Hemeoxygenase-1) HO-1, which decreases excessive cellular stress, mitochondrial dysfunction, apoptosis, and neuronal degeneration, which is the major cause of motor dysfunction. The present review explores the GSK-3β-mediated neuroprotection in various movement disorders through the Nrf2/HO-1 antioxidant pathway. This review provides a link between GSK-3β and the Nrf2/HO-1 signaling pathway in the treatment of PD and HD. In addition to that it highlights various GSK-3β inhibitors and the Nrf2/HO-1 activators, which exert robust neuroprotection against motor disorders. Therefore, the present review will help in the discovery of new therapy for PD and HD patients.

Changes in Tyrosine Hydroxylase Activity and Dopamine Synthesis in the Nigrostriatal System of Mice in an Acute Model of Parkinson's Disease as a Manifestation of Neurodegeneration and Neuroplasticity

The progressive degradation of the nigrostriatal system leads to the development of Parkinson’s disease (PD). The synthesis of dopamine, the neurotransmitter of the nigrostriatal system, depends on the rate-limiting enzyme, tyrosine hydroxylase (TH). In this study, we evaluated the synthesis of dopamine during periods of neurodegradation and neuroplasticity in the nigrostriatal system on a model of the early clinical stage of PD. It was shown that the concentration of dopamine correlated with activity of TH, while TH activity did not depend on total protein content either in the SN or in the striatum. Both during the period of neurodegeneration and neuroplasticity, TH activity in SN was determined by the content of P19-TH, and in the striatum it was determined by P31-TH and P40-TH (to a lesser extent). The data obtained indicate a difference in the regulation of dopamine synthesis between DA-neuron bodies and their axons, which must be considered for the further development of symptomatic pharmacotherapy aimed at increasing TH activity.

AMPK/PPAR-γ/NF-κB axis participates in ROS-mediated apoptosis and autophagy caused by cadmium in pig liver

The experiment was conducted to investigate the effects of Cadmium (Cd) on growth performance, blood biochemical parameters, oxidative stress, hepatocyte apoptosis and autophagy of weaned piglets. A total of 12 healthy weaned piglets were randomly assigned to the control and the Cd group, which were fed with a basal diet and the basal diet supplemented with 15 ± 0.242 mg/kg CdCl₂ for 30 d, respectively. Our results demonstrated that Cd significantly decreased final body weight, average daily feed intake (ADFI), average daily gain (ADG) and increased feed-to-gain (F/G) ratio (P < 0.05). For blood biochemical parameters, Cd treatment significantly decreased the red blood cell (RBC), hemoglobin (HGB), hematocrit (HCT), total protein, albumin, copper content and iron content (P < 0.05). In addition, liver injury was observed in the Cd-exposed group. Our results also demonstrated that Cd exposure contributed to the production of ROS, activated the AMPK/PPAR-γ/NF-κB pathway (increasing the expressions of P-AMPK/AMPK, NF-κB, I-κB-β, COX-2, and iNOS, decreasing the expressions of PPAR-γ and I-κB-α), finally induced autophagy (increasing the expressions of Beclin-1, the ratio of LC3-II/LC3-I and p62), and apoptosis (increasing the expressions of Bax, Bak, Caspase-9, and Caspase-3, decreasing the expression of Bcl-2). Overall, these findings revealed the vital role of AMPK/PPAR-γ/NF-κB pathway in Cd-induced liver apoptosis and autophagy, which provided deeper insights into a better understanding of Cd-induced hepatotoxicity.

Emerging roles of dysregulated adenosine homeostasis in brain disorders with a specific focus on neurodegenerative diseases

In modern societies, with an increase in the older population, age-related neurodegenerative diseases have progressively become greater socioeconomic burdens. To date, despite the tremendous effort devoted to understanding neurodegenerative diseases in recent decades, treatment to delay disease progression is largely ineffective and is in urgent demand. The development of new strategies targeting these pathological features is a timely topic. It is important to note that most degenerative diseases are associated with the accumulation of specific misfolded proteins, which is facilitated by several common features of neurodegenerative diseases (including poor energy homeostasis and mitochondrial dysfunction). Adenosine is a purine nucleoside and neuromodulator in the brain. It is also an essential component of energy production pathways, cellular metabolism, and gene regulation in brain cells. The levels of intracellular and extracellular adenosine are thus tightly controlled by a handful of proteins (including adenosine metabolic enzymes and transporters) to maintain proper adenosine homeostasis. Notably, disruption of adenosine homeostasis in the brain under various pathophysiological conditions has been documented. In the past two decades, adenosine receptors (particularly A₁ and A_2A adenosine receptors) have been actively investigated as important drug targets in major degenerative diseases. Unfortunately, except for an A_2A antagonist (istradefylline) administered as an adjuvant treatment with levodopa for Parkinson's disease, no effective drug based on adenosine receptors has been developed for neurodegenerative diseases. In this review, we summarize the emerging findings on proteins involved in the control of adenosine homeostasis in the brain and discuss the challenges and future prospects for the development of new therapeutic treatments for neurodegenerative diseases and their associated disorders based on the understanding of adenosine homeostasis.

Apoptosis and its therapeutic implications in neurodegenerative diseases

Neurodegenerative disorders are characterized by progressive loss of particular populations of neurons. Apoptosis has been implicated in the pathogenesis of neurodegenerative diseases, including Parkinson disease, Alzheimer disease, Huntington disease, and amyotrophic lateral sclerosis. In this review, we focus on the existing notions relevant to comprehending the apoptotic death process, including the morphological features, mediators and regulators of cellular apoptosis. We also highlight the evidence of neuronal apoptotic death in Parkinson disease, Alzheimer disease, Huntington disease, and amyotrophic lateral sclerosis. Additionally, we present evidence of potential therapeutic agents that could modify the apoptotic pathway in the aforementioned neurodegenerative diseases and delay disease progression. Finally, we review the clinical trials that were conducted to evaluate the use of anti-apoptotic drugs in the treatment of the aforementioned neurodegenerative diseases, in order to highlight the essential need for early detection and intervention of neurodegenerative diseases in humans.