Apelin-36 exerts the cytoprotective effect against MPP+-induced cytotoxicity in SH-SY5Y cells through PI3K/Akt/mTOR autophagy pathway

Hydrogen sulfide improves depression-like behaviors in CUMS-induced mice by regulating autophagy

The pathogenesis of depression is associated with synaptic impairment and dysfunction in autophagy processes. Mendelian randomization (MR) analysis revealed that six GWAS IDs revealed a significant association between Beclin-1 levels and depression risk. Besides, all SNPs had a positive effect on depression risk. Analyzing neurons from depressed individuals using single-cell RNA sequencing (scRNA-seq) uncovered decreased expression of AKT, mTOR, and genes linked to synaptic plasticity. The activation of the PI3K/AKT/mTOR signaling has been demonstrated to control autophagy and have a protective effect on the nervous system. Hydrogen sulfide (H2S) is an endogenous gasotransmitter that can potentially treat various neurological disorders by improving neuronal synaptic plasticity. However, whether H2S regulates autophagy through PI3K/AKT/mTOR signaling, improves neuronal synaptic plasticity damage, and plays an antidepressant role is unclear. Our current research revealed that the reduction in the expression of p-PI3K, p-AKT, and p-mTOR proteins increase in neuronal autophagy activity and decline synaptic plasticity in mice with depression induced by chronic unpredictable mild stress (CUMS). Treatment with the exogenous hydrogen sulfide donor NaHS for one day and continuous treatment for one week improved the depression-like behaviors in the mice. Compared with those after one day of NaHS treatment, the above protein expression levels were restored and maintained, and the antidepressant effect was more significant after one week of continuous treatment with NaHS. Moreover, the PI3K inhibitor LY294002 was used to demonstrate that NaHS suppresses autophagy through activating the PI3K/AKT/mTOR signaling and ameliorates synaptic plasticity impairments. This study provides novel insights into the antidepressant mechanisms of H2S, highlighting its antidepressant therapeutic potential.

Maternal Myo-Inositol Deficiency Involved Autophagy Impairment by PI3K/Akt/mTOR Signaling in Neural Tube Defects During Pregnancy

Previous studies have demonstrated that peri-conceptional inositol supplementation could effectively ameliorate the recurrence of neural tube defects (NTDs); though, the mechanism remains unclear. In the current investigation, we detected the myo-inositol (MI) levels in maternal plasma and embryonic tissues in a Chinese population with high prevalence of NTDs and found maternal MI deficiency increased NTD susceptibility in this area. Pregnant mice were randomly divided into 2 groups. The control group was treated with 0.9% saline, while the experimental group was treated with IMPase inhibitor by intraperitoneal injection on E7.5 to generate the maternal MI-deficient mouse model, followed by comprehensive phenotypic and molecular analysis at E13.5. Corresponding in vitro experiments treated neural stem cells (NSCs) for 16 h with IMPase inhibitor, MI supplementation, or specific PI3K and mTOR inhibitors to systematically investigate the downstream signaling pathways. We observed aberrant activation PI3K/Akt/mTOR signaling and reduced autophagy in a maternal MI deficiency mouse model after ruling out the genetic perturbations. Further in vitro kinase assay showed that MI negatively regulated PI3K activity, in a dose-dependent manner, which possibly due to the hydrogen bond interactions between amino acid residues in the ATP-binding site of PI3K and inositol. MI deficiency NSCs also presented PI3K/AKT/mTOR pathway activation concurrent with reduced autophagy level; MI supplementation or inhibition of the PI3K/Akt/mTOR pathway could rescue MI deficiency-induced autophagy impairment. Finally, we validated decreased autophagy levels as well as hyperactivation of the PI3K/Akt/mTOR pathway by MI deficient human NTD embryonic neural tissues. Our results suggested that maternal MI deficiency might increase susceptibility to NTDs. Low levels of MI might impair autophagy in the developing neural tube involving upregulation of PI3K/Akt/mTOR pathway.

Effects and mechanisms of Apelin in treating central nervous system diseases

Apelin, an endogenous ligand of G protein-coupled receptor APJ, is widely distributed in the central nervous system (CNS). It can be divided into such subtypes as Apelin-13, Apelin-17, and Apelin-36 as they have different amino acid structures. All Apelin is widely studied as an adipokine, showing a significant protective effect through regulating apoptosis, autophagy, oxidative stress, angiogenesis, inflammation, and other pathophysiological processes. As an adipokine, Apelin has been found to play a crucial role in cardiovascular disease development. In this paper, we reviewed the effects and mechanisms of Apelin in treating CNS diseases, such as neurotrauma, stroke, spinal cord injury, primary tumors, neurodegenerative diseases, psychiatric diseases, epilepsy, and pain.

The Aggravating Role of Failing Neuropeptide Networks in the Development of Sporadic Alzheimer's Disease

Alzheimer's disease imposes an increasing burden on aging Western societies. The disorder most frequently appears in its sporadic form, which can be caused by environmental and polygenic factors or monogenic conditions of incomplete penetrance. According to the authors, in the majority of cases, Alzheimer's disease represents an aggravated form of the natural aging of the central nervous system. It can be characterized by the decreased elimination of amyloid β1-42 and the concomitant accumulation of degradation-resistant amyloid plaques. In the present paper, the dysfunction of neuropeptide regulators, which contributes to the pathophysiologic acceleration of senile dementia, is reviewed. However, in the present review, exclusively those neuropeptides or neuropeptide families are scrutinized, and the authors' investigations into their physiologic and pathophysiologic activities have made significant contributions to the literature. Therefore, the pathophysiologic role of orexins, neuromedins, RFamides, corticotrope-releasing hormone family, growth hormone-releasing hormone, gonadotropin-releasing hormone, ghrelin, apelin, and natriuretic peptides are discussed in detail. Finally, the therapeutic potential of neuropeptide antagonists and agonists in the inhibition of disease progression is discussed here.

Exercise, Neuroprotective Exerkines, and Parkinson's Disease: A Narrative Review

Parkinson's disease (PD) is a prevalent neurodegenerative disease in which treatment often includes an exercise regimen. Exercise is neuroprotective in animal models of PD, and, more recently, human clinical studies have verified exercise's disease-modifying effect. Aerobic exercise and resistance training improve many of PD's motor and non-motor symptoms, while neuromotor therapy and stretching/flexibility exercises positively contribute to the quality of life in people with PD. Therefore, understanding the role of exercise in managing this complex disorder is crucial. Exerkines are bioactive substances that are synthesized and released during exercise and have been implicated in several positive health outcomes, including neuroprotection. Exerkines protect neuronal cells in vitro and rodent PD models in vivo. Aerobic exercise and resistance training both increase exerkine levels in the blood, suggesting a role for exerkines in the neuroprotective theory. Many exerkines demonstrate the potential for protecting the brain against pathological missteps caused by PD. Every person (people) with Parkinson's (PwP) needs a comprehensive exercise plan tailored to their unique needs and abilities. Here, we provide an exercise template to help PwP understand the importance of exercise for treating PD, describe barriers confronting many PwP in their attempt to exercise, provide suggestions for overcoming these barriers, and explore the role of exerkines in managing PD. In conclusion, exercise and exerkines together create a powerful neuroprotective system that should contribute to slowing the chronic progression of PD.

The function of previously unappreciated exerkines secreted by muscle in regulation of neurodegenerative diseases

The initiation and progression of neurodegenerative diseases (NDs), distinguished by compromised nervous system integrity, profoundly disrupt the quality of life of patients, concurrently exerting a considerable strain on both the economy and the social healthcare infrastructure. Exercise has demonstrated its potential as both an effective preventive intervention and a rehabilitation approach among the emerging therapeutics targeting NDs. As the largest secretory organ, skeletal muscle possesses the capacity to secrete myokines, and these myokines can partially improve the prognosis of NDs by mediating the muscle-brain axis. Besides the well-studied exerkines, which are secreted by skeletal muscle during exercise that pivotally exert their beneficial function, the physiological function of novel exerkines, e.g., apelin, kynurenic acid (KYNA), and lactate have been underappreciated previously. Herein, this review discusses the roles of these novel exerkines and their mechanisms in regulating the progression and improvement of NDs, especially the significance of their functions in improving NDs' prognoses through exercise. Furthermore, several myokines with potential implications in ameliorating ND progression are proposed as the future direction for investigation. Elucidation of the function of exerkines secreted by skeletal muscle in the regulation of NDs advances the understanding of its pathogenesis and facilitates the development of therapeutics that intervene in these processes to cure NDs.

Active compounds from Calendula officinalis flowers act via PI3K and ERK signaling pathways to offer neuroprotective effects against Parkinson's disease

Calendula officinalis flowers, associated with diverse biological effects, could be utilized as functional food ingredients to play a crucial role in human health. In this study, we examined the anti-PD activity of C. officinalis flower extracts and investigated their bioactive compounds and molecular mechanisms based on LC-MS/MS assay, bioinformatic exploration and in vitro treatment of SH-SY5Y cells. C. officinalis extracts exhibited significant positive effects on the length and fluorescence density of the dopaminergic neuron region in zebrafish larvae. At 10 μg/mL, the extract restored the length to 96.54% and fluorescence density to 87.77% of the control values, which was equivalent to the effect of a positive drug, indicating the extract's powerful potential to alleviate PD symptoms. Five active compounds, including chlorogenic acid, 3,4-dicaffeoylquinic acid (DA), rutin, isorhamnetin 3-O-glucoside (IG) and calenduloside E (CE) were identified in extracts by LC-QTOF-MS/MS. Hsp90α, PI3K and ERK were revealed as core targets of DA, IG and CE in relation to anti-PD activity. The compounds docked deeply within the pocket region of Hsp90α protein, and their binding energies (∆G b) were -6.93 kcal/mol (DA), -6.51 kcal/mol (IG) and -3.03 kcal/mol (CE), respectively. Subsequently, they concurrently activated the PI3K/Akt signaling pathway and inhibited the ERK signaling pathway, thereby preventing neuronal death and alleviating neuronal degeneration. These compounds from C. officinalis could be potent nutraceutical agents with protective properties that may shield dopaminergic neurons against the damage caused by PD. Our findings provide a basis for utilizing the C. officinalis flowers in functional foods.

Autophagy and Biomaterials: A Brief Overview of the Impact of Autophagy in Biomaterial Applications

Macroautophagy (hereafter autophagy), a tightly regulated physiological process that obliterates dysfunctional and damaged organelles and proteins, has a crucial role when biomaterials are applied for various purposes, including diagnosis, treatment, tissue engineering, and targeted drug delivery. The unparalleled physiochemical properties of nanomaterials make them a key component of medical strategies in different areas, such as osteogenesis, angiogenesis, neurodegenerative disease treatment, and cancer therapy. The application of implants and their modulatory effects on autophagy have been known in recent years. However, more studies are necessary to clarify the interactions and all the involved mechanisms. The advantages and disadvantages of nanomaterial-mediated autophagy need serious attention in both the biological and bioengineering fields. In this mini-review, the role of autophagy after biomaterial exploitation and the possible related mechanisms are explored.

Several neuropeptides involved in parkinsonian neuroprotection modulate the firing properties of nigral dopaminergic neurons

Parkinson's disease is characterized by progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta. The surviving nigral dopaminergic neurons display altered spontaneous firing activity in Parkinson's disease. The firing rate of nigral dopaminergic neurons decreases long before complete neuronal death and the appearance of parkinsonian symptoms. A mild stimulation could rescue dopaminergic neurons from death and in turn play neuroprotective effects. Several neuropeptides, including cholecystokinin (CCK), ghrelin, neurotensin, orexin, tachykinins and apelin, within the substantia nigra pars compacta play important roles in the modulation of spontaneous firing activity of dopaminergic neurons and therefore involve motor control and motor disorders. Here, we review neuropeptide-induced modulation of the firing properties of nigral dopaminergic neurons. This review may provide a background to guide further investigations into the involvement of neuropeptides in movement control by modulating firing activity of nigral dopaminergic neurons in Parkinson's disease.

eEF1A2 siRNA Suppresses MPP+-Induced Activation of Akt and mTOR and Potentiates Caspase-3 Activation in a Parkinson’s Disease Model

The tissue-specific protein eEF1A2 has been linked to the development of neurological disorders. The role of eEF1A2 in the pathogenesis of Parkinson’s disease (PD) has yet to be investigated. The aim of this study was to determine the potential neuroprotective effects of eEF1A2 in an MPP+ model of PD. Differentiated SH-SY5Y cells were transfected with eEF1A2 siRNA, followed by MPP+ exposure. The expression of p-Akt1 and p-mTORC1 was determined using Western blotting. The expression of p53, Bax, Bcl-2, and caspase-3 was evaluated using qRT-PCR. Cleaved caspase-3 levels and Annexin V/propidium iodide flow cytometry were used to determine apoptosis. The effects of PI3K inhibition were examined. The results showed that eEF1A2 siRNA significantly reduced the eEF1A2 expression induced by MPP+. MPP+ treatment activated Akt1 and mTORC1; however, eEF1A2 knockdown suppressed this activation. In eEF1A2-knockdown cells, MPP+ treatment increased the expression of p53 and caspase-3 mRNA levels as well as increased apoptotic cell death when compared to MPP+ treatment alone. In cells exposed to MPP+, upstream inhibition of the Akt/mTOR pathway, by either LY294002 or wortmannin, inhibited the phosphorylation of Akt1 and mTORC1. Both PI3K inhibitors increased eEF1A2 expression in cells, whether or not they were also treated with MPP+. In conclusion, eEF1A2 may function as a neuroprotective factor against MPP+, in part by regulating the Akt/mTOR pathway upstream.

Supt16 Haploinsufficiency Impairs PI3K/AKT/mTOR/Autophagy Pathway in Human Pluripotent Stem Cells Derived Neural Stem Cells

The maintenance of neural stem cells (NSCs) plays a critical role in neurodevelopment and has been implicated in neurodevelopmental disorders (NDDs). However, the underlying mechanisms linking defective human neural stem cell self-renewal to NDDs remain undetermined. Our previous study found that Supt16 haploinsufficiency causes cognitive and social behavior deficits by disrupting the stemness maintenance of NSCs in mice. However, its effects and underlying mechanisms have not been elucidated in human neural stem cells (hNSCs). Here, we generated Supt16^+/- induced pluripotent stem cells (iPSCs) and induced them into hNSCs. The results revealed that Supt16 heterozygous hNSCs exhibit impaired proliferation, cell cycle arrest, and increased apoptosis. As the RNA-seq analysis showed, Supt16 haploinsufficiency inhibited the PI3K/AKT/mTOR pathway, leading to rising autophagy, and further resulted in the dysregulated expression of multiple proteins related to cell proliferation and apoptotic process. Furthermore, the suppression of Supt16 heterozygous hNSC self-renewal caused by autophagy activation could be rescued by MHY1485 treatment or reproduced in rapamycin-treated hNSCs. Thus, our results showed that Supt16 was essential for hNSC self-renewal and its haploinsufficiency led to cell cycle arrest, impaired cell proliferation, and increased apoptosis of hNSCs by regulating the PI3K/AKT/mTOR/autophagy pathway. These provided a new insight to understand the causality between the Supt16 heterozygous NSCs and NDDs in humans.

The PI3K-AKT pathway: A plausible therapeutic target in Parkinson's disease

Parkinson's disease is a common progressive and multifactorial neurodegenerative disease, characterized by the loss of midbrain dopaminergic neurons. Numerous pathological processes including, inflammation, oxidative stress, mitochondrial dysfunction, neurotransmitter imbalance, and apoptosis as well as genetic factors may lead to neuronal degeneration. With the emergence of aging population, the health problem and economic burden caused by PD also increase. Phosphatidylinositol 3-kinases-protein kinase B (PI3K-AKT) signaling pathway regulates signal transduction and biological processes such as cell proliferation, apoptosis and metabolism. According to reports, it regulates neurotoxicity and mediates the survival of neurons. Accumulating evidences indicate that some natural products can play a neuroprotective role by activating PI3K-AKT pathway, providing an effective resource for the discovery of potential therapeutic drugs. The current review provides an overview of the PI3K-AKT signaling pathway and review the relationship between this signaling pathway and PD.

Acute Hypoxia Alters Extracellular Vesicle Signatures and the Brain Citrullinome of Naked Mole-Rats (Heterocephalus glaber)

Peptidylarginine deiminases (PADs) and extracellular vesicles (EVs) may be indicative biomarkers of physiological and pathological status and adaptive responses, including to diseases and disorders of the central nervous system (CNS) and related to hypoxia. While these markers have been studied in hypoxia-intolerant mammals, in vivo investigations in hypoxia-tolerant species are lacking. Naked mole-rats (NMR) are among the most hypoxia-tolerant mammals and are thus a good model organism for understanding natural and beneficial adaptations to hypoxia. Thus, we aimed to reveal CNS related roles for PADs in hypoxia tolerance and identify whether circulating EV signatures may reveal a fingerprint for adaptive whole-body hypoxia responses in this species. We found that following in vivo acute hypoxia, NMR: (1) plasma-EVs were remodelled, (2) whole proteome EV cargo contained more protein hits (including citrullinated proteins) and a higher number of associated KEGG pathways relating to the total proteome of plasma-EVs Also, (3) brains had a trend for elevation in PAD1, PAD3 and PAD6 protein expression, while PAD2 and PAD4 were reduced, while (4) the brain citrullinome had a considerable increase in deiminated protein hits with hypoxia (1222 vs. 852 hits in normoxia). Our findings indicate that circulating EV signatures are modified and proteomic content is reduced in hypoxic conditions in naked mole-rats, including the circulating EV citrullinome, while the brain citrullinome is elevated and modulated in response to hypoxia. This was further reflected in elevation of some PADs in the brain tissue following acute hypoxia treatment. These findings indicate a possible selective role for PAD-isozymes in hypoxia response and tolerance.

The involvement of TRPM2 on the MPP+-induced oxidative neurotoxicity and apoptosis in hippocampal neurons from neonatal mice: protective role of resveratrol

Parkinson's disease (PD) is an age-related chronic neurodegenerative disease. Although PD is known to be a result of damage to hippocampal neurons, its molecular mechanism has yet to be completely clarified. The neurodegeneration in hippocampal neurons has been suggested to include excessive production of reactive oxygen species (ROS). Mitochondrial dysfunction and disruption of intracellular Ca²⁺ homeostasis play the most important role in the increase in ROS production for the cells. Remarkably, it is stated in the literature that especially the change of Ca²⁺ homeostasis triggers neuronal degeneration. TRPM2 is a unique calcium-permeable nonselective cation channel, and densest in the numberless neuronal population. The current study aims to elucidate the effect of antioxidant resveratrol (Resv) on TRPM2-mediated oxidative stress (OS) induced by 1-methyl-4-phenylpyridinium (MPP) exposure in the primary mouse hippocampal neurons. The neurons were divided into four groups as Control, Resv , MPP, and MPP+ Resv. In the current results, the activation of TRPM2 was observed in primary hippocampal neurons with MPP incubation. TRPM2 channel expression levels in the MPP group increased in hippocampal neurons after MPP exposure. In addition, intracellular free Ca²⁺ concentration and TRPM2 channel currents were highest in MPP groups, although they were decreased by the Resv treatment. In addition, mitochondrial membrane depolarization, ROS, caspase-3, caspase-9, and apoptosis values induced by MPP decreased with resveratrol treatment. In conclusion, in our study, we observed that the dysregulation of OS-induced TRPM2 channel activation in hippocampal neurons exposed to MPP caused apoptotic cell death in neurons, while the use of resveratrol had a protective effect by reducing OS resources in the environment.

Autophagy and apoptosis cascade: which is more prominent in neuronal death?

Autophagy and apoptosis are two crucial self-destructive processes that maintain cellular homeostasis, which are characterized by their morphology and regulated through signal transduction mechanisms. These pathways determine the fate of cellular organelle and protein involved in human health and disease such as neurodegeneration, cancer, and cardiovascular disease. Cell death pathways share common molecular mechanisms, such as mitochondrial dysfunction, oxidative stress, calcium ion concentration, reactive oxygen species, and endoplasmic reticulum stress. Some key signaling molecules such as p53 and VEGF mediated angiogenic pathway exhibit cellular and molecular responses resulting in the triggering of apoptotic and autophagic pathways. Herein, based on previous studies, we describe the intricate relation between cell death pathways through their common genes and the role of various stress-causing agents. Further, extensive research on autophagy and apoptotic machinery excavates the implementation of selective biomarkers, for instance, mTOR, Bcl-2, BH3 family members, caspases, AMPK, PI3K/Akt/GSK3β, and p38/JNK/MAPK, in the pathogenesis and progression of neurodegenerative diseases. This molecular phenomenon will lead to the discovery of possible therapeutic biomolecules as a pharmacological intervention that are involved in the modulation of apoptosis and autophagy pathways. Moreover, we describe the potential role of micro-RNAs, long non-coding RNAs, and biomolecules as therapeutic agents that regulate cell death machinery to treat neurodegenerative diseases. Mounting evidence demonstrated that under stress conditions, such as calcium efflux, endoplasmic reticulum stress, the ubiquitin-proteasome system, and oxidative stress intermediate molecules, namely p53 and VEGF, activate and cause cell death. Further, activation of p53 and VEGF cause alteration in gene expression and dysregulated signaling pathways through the involvement of signaling molecules, namely mTOR, Bcl-2, BH3, AMPK, MAPK, JNK, and PI3K/Akt, and caspases. Alteration in gene expression and signaling cascades cause neurotoxicity and misfolded protein aggregates, which are characteristics features of neurodegenerative diseases. Excessive neurotoxicity and misfolded protein aggregates lead to neuronal cell death by activating death pathways like autophagy and apoptosis. However, autophagy has a dual role in the apoptosis pathways, i.e., activation and inhibition of the apoptosis signaling. Further, micro-RNAs and LncRNAs act as pharmacological regulators of autophagy and apoptosis cascade, whereas, natural compounds and chemical compounds act as pharmacological inhibitors that rescue neuronal cell death through inhibition of apoptosis and autophagic cell death.

Schwann cells differentiated from skin-derived precursors provide neuroprotection via autophagy inhibition in a cellular model of Parkinson's disease

Autophagy has been shown to play an important role in Parkinson’s disease. We hypothesized that skin-derived precursor cells exhibit neuroprotective effects in Parkinson’s disease through affecting autophagy. In this study, 6-hydroxydopamine-damaged SH-SY5Y cells were pretreated with a culture medium containing skin-derived precursors differentiated into Schwann cells (SKP-SCs). The results showed that the SKP-SC culture medium remarkably enhanced the activity of SH-SY5Y cells damaged by 6-hydroxydopamine, reduced excessive autophagy, increased tyrosine hydroxylase expression, reduced α-synuclein expression, reduced the autophagosome number, and activated the PI3K/AKT/mTOR pathway. Autophagy activator rapamycin inhibited the effects of SKP-SCs, and autophagy inhibitor 3-methyladenine had the opposite effect. These findings confirm that SKP-SCs modulate the PI3K/AKT/mTOR pathway to inhibit autophagy, thereby exhibiting a neuroprotective effect in a cellular model of Parkinson’s disease. This study was approved by the Animal Ethics Committee of Laboratory Animal Center of Nantong University (approval No. S20181009-205) on October 9, 2018.

Protective role of selenium on MPP+ and homocysteine-induced TRPM2 channel activation in SH-SY5Y cells

Homocysteine is an intermediate product of biochemical reactions occurring in living organisms. It is known that drugs that increase dopamine synthesis used in Parkinson's disease (PD) cause an increase in the plasma homocysteine level. As the plasma homocysteine level increases, the amount of intracellular free calcium ion ([Ca²⁺]_i) and oxidative stress increase. As a result, it contributes to the excitotoxic effect by causing neurodegeneration. TRPM2 cation channel is activated by high [Ca²⁺]_i and oxidative stress. The role of TRPM2 in the development of neuronal damage due to the increase in homocysteine in PD has not yet been elucidated. In current study, we aimed to investigate the role of the TRPM2 and selenium (Se) in SH-SY5Y neuronal cells treated with homocysteine (HCT) and MPP . SH-SY5Y cells were divided into four groups: control, MPP, MPP + HCT, and MPP + HCT + Se. The results of plate reader assay, confocal microscope imaging, and western blot analyses indicated upregulation of apoptosis, [Ca²⁺]_i, mitochondrial membrane depolarization, caspase activation, and intracellular ROS values in the cells. The MPP + HCT group had considerably higher values than the other groups. The MPP + HCT + Se group had significantly lower values than all the other groups except the control group. In addition, incubation of MPP + HCT and MPP + HCT + Se groups with TRPM2 antagonist 2-APB increased cell viability and reduced intracellular calcium influx and apoptosis levels. It is concluded that the activation of TRPM2 was propagated in HCT and MPP-induced SH-SY5Y cells by the increase of oxidative stress. The antioxidant property of Se regulated the TRPM2 channel activation and neurodegeneration by providing intracellular oxidant/antioxidant balance.

Platelet-derived growth factor (PDGF)-BB protects dopaminergic neurons via activation of Akt/ERK/CREB pathways to upregulate tyrosine hydroxylase

Aims

The neurotropic growth factor PDGF‐BB was shown to have vital neurorestorative functions in various animal models of Parkinson's disease (PD). Previous studies indicated that the regenerative property of PDGF‐BB contributes to the increased intensity of tyrosine hydroxylase (TH) fibers in vivo. However, whether PDGF‐BB directly modulates the expression of TH, and the underlying mechanism is still unknown. We will carefully examine this in our current study.

Method

MPTP‐lesion mice received PDGF‐BB treatment via intracerebroventricular (i.c.v) administration, and the expression of TH in different brain regions was assessed by RT‐PCR, Western blot, and immunohistochemistry staining. The molecular mechanisms of PDGF‐BB‐mediated TH upregulation were examined by RT‐PCR, Western blot, ChIP assay, luciferase reporter assay, and immunocytochemistry.

Results

We validated a reversal expression of TH in MPTP‐lesion mice upon i.c.v administration of PDGF‐BB for seven days. Similar effects of PDGF‐BB‐mediated TH upregulation were also observed in MPP⁺‐treated primary neuronal culture and dopaminergic neuronal cell line SH‐SY5Y cells. We next demonstrated that PDGF‐BB rapidly activated the pro‐survival PI3K/Akt and MAPK/ERK signaling pathways, as well as the downstream CREB in SH‐SY5Y cells. We further confirmed the significant induction of p‐CREB in PDGF‐BB‐treated animals in vivo. Using a genetic approach, we demonstrated that the transcription factor CREB is critical for PDGF‐BB‐mediated TH expression. The activation and nucleus translocation of CREB were promoted in PDGF‐BB‐treated SH‐SY5Y cells, and the enrichment of CREB on the promoter region of TH gene was also increased upon PDGF‐BB treatment.

Conclusion

Our data demonstrated that PDGF‐BB directly regulated the expression of TH via activating the downstream Akt/ERK/CREB signaling pathways. Our finding will further support the therapeutic potential of PDGF‐BB in PD, and provide the possibility that targeting PDGF signaling can be harnessed as an adjunctive therapy in PD in the future.

Impact of the apelin/APJ axis in the pathogenesis of Parkinson's disease with therapeutic potential

The pathogenesis of Parkinson's disease (PD) remains elusive. There is still no available disease-modifying strategy against PD, whose management is mainly symptomatic. A growing amount of preclinical evidence shows that a complex interplay between autophagy dysregulation, mitochondrial impairment, endoplasmic reticulum stress, oxidative stress, and excessive neuroinflammation underlies PD pathogenesis. Identifying key molecules linking these pathological cellular processes may substantially aid in our deeper understanding of PD pathophysiology and the development of novel effective therapeutic approaches. Emerging preclinical evidence indicates that apelin, an endogenous neuropeptide acting as a ligand of the orphan G protein-coupled receptor APJ, may play a key neuroprotective role in PD pathogenesis, via inhibition of apoptosis and dopaminergic neuronal loss, autophagy enhancement, antioxidant effects, endoplasmic reticulum stress suppression, as well as prevention of synaptic dysregulation in the striatum, excessive neuroinflammation, and glutamate-induced excitotoxicity. Underlying signaling pathways involve phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin, extracellular signal-regulated kinase 1/2, and inositol requiring kinase 1α/XBP1/C/EBP homologous protein. Herein, we discuss the role of apelin/APJ axis and associated molecular mechanisms on the pathogenesis of PD in vitro and in vivo and provide evidence for its challenging therapeutic potential.

Neuroprotective gain of Apelin/APJ system

Apelin is an endogenous ligand of G protein-coupled receptor APJ. In recent years, many studies have shown that the apelin/APJ system has neuroprotective properties, such as anti-inflammatory, anti-oxidative stress, anti-apoptosis, and regulating autophagy, blocking excitatory toxicity. Apelin/APJ system has been proven to play a role in various neurological diseases and may be a promising therapeutic target for nervous system diseases. In this paper, the neuroprotective properties of the apelin/APJ system and its role in neurologic disorders are reviewed. Further understanding of the pathophysiological effect and mechanism of the apelin/APJ system in the nervous system will help develop new therapeutic interventions for various neurological diseases.

Physical Exercise-Induced Myokines in Neurodegenerative Diseases

Neurodegenerative diseases (NDs), such as Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD), and amyotrophic lateral sclerosis (ALS), are disorders characterized by progressive degeneration of the nervous system. Currently, there is no disease-modifying treatments for most NDs. Meanwhile, numerous studies conducted on human and animal models over the past decades have showed that exercises had beneficial effects on NDs. Inter-tissue communication by myokine, a peptide produced and secreted by skeletal muscles during exercise, is thought to be an important underlying mechanism for the advantages. Here, we reviewed studies about the effects of myokines regulated by exercise on NDs and their mechanisms. Myokines could exert beneficial effects on NDs through a variety of regulatory mechanisms, including cell survival, neurogenesis, neuroinflammation, proteostasis, oxidative stress, and protein modification. Studies on exercise-induced myokines are expected to provide a novel strategy for treating NDs, for which there are no adequate treatments nowadays. To date, only a few myokines have been investigated for their effects on NDs and studies on mechanisms involved in them are in their infancy. Therefore, future studies are needed to discover more myokines and test their effects on NDs.

Apelin Rejuvenates Aged Human Mesenchymal Stem Cells by Regulating Autophagy and Improves Cardiac Protection After Infarction

The protective effects of mesenchymal stem cell (MSC)-based therapy for myocardial infarction (MI) are largely hampered as they age. Apelin is an endogenous ligand of its receptor APJ and plays an essential role in regulating multiple biological activities including MSC proliferation and survival. In this study, we investigated whether Apelin regulates MSC senescence and whether its overexpression could rejuvenate aged MSCs (AMSCs) to improve cardiac protection following infarction in mice. MSC senescence was evaluated by senescence-associated β-galactosidase assays. Apelin level was examined by western blotting. Autophagy was determined by transmission electron microscopy. The cardioprotective effect of AMSCs with Apelin overexpression (Apelin-AMSCs) was assessed in a mouse MI model. Apelin expression was dramatically reduced in AMSCs. Interestingly, knockdown of Apelin induced young MSCs (YMSC) senescence, whereas overexpression rescued AMSC senescence. Apelin overexpression also increased AMSC angiogenic capacity. Mechanistically, Apelin overexpression upregulated the autophagy level of AMSCs by activating AMP-activated protein kinase (AMPK) signaling, thereby rejuvenating AMSCs. Compared with AMSCs, transplantation of Apelin-AMSCs achieved better therapeutic efficacy for MI by enhancing cell survival and angiogenesis. In conclusion, our results reveal that Apelin activates AMPK to rejuvenate AMSCs by increasing autophagy and promotes cardioprotection following infarction in mice. This study identified a novel target to rejuvenate AMSCs and enhance their therapeutic efficacy.

Apelin-36 Protects HT22 Cells Against Oxygen-Glucose Deprivation/Reperfusion-Induced Oxidative Stress and Mitochondrial Dysfunction by Promoting SIRT1-Mediated PINK1/Parkin-Dependent Mitophagy

Oxidative stress and mitochondrial dysfunction are involved in cerebral ischemia/reperfusion injury-induced neuronal apoptosis. Mitophagy is the main method to eliminate dysfunctional mitochondria. Apelin-36, a type of neuropeptide, has been reported to exert protective effects in cerebral I/R (I/R) injury, but its precise mechanisms remain to be elucidated. To study the effects of Apelin-36 on oxidative stress and mitochondrial dysfunction in cerebral I/R injury, the oxygen-glucose deprivation/reperfusion (OGD/R) model with 6 h of ischemia and 6 h of reperfusion was established in HT22 cells. Results demonstrated that Apelin-36 protected against OGD/R injury by improving cell viability, decreasing the apoptotic cells ratio and increasing the ratio of Bcl-2/Bax. In addition, Apelin-36 treatment inhibited oxidative stress by downregulating the level of reactive oxygen species (ROS) and malondialdehyde (MDA) as well as the expression of inducible nitric oxide synthase (iNOS). And Apelin-36 also activated the level of superoxide dismutase (SOD) and glutathione (GSH). Mitochondrial apoptosis was also alleviated with Apelin-36 treatment detected by the mitochondrial membrane potential (MMP) and the expression of Cytochrome c (Cyt c), Cleaved caspase-9, and Cleaved caspase-3. Furthermore, the SIRT1-mediated PINK1/Parkin-dependent mitophagy was activated by Apelin-36 treatment with the downregulation of p62 and upregulation of LC3B-II and Beclin1. Both EX527 and Cyclosporine A (CsA), which are inhibitors of SIRT1 and mitophagy, markedly alleviated the inhibition of oxidative stress and mitochondrial dysfunction caused by Apelin-36. These findings suggest that SIRT1-mediated PINK1/Parkin-dependent mitophagy is involved in the neuroprotective effects of Apelin-36 on OGD/R-induced oxidative stress and mitochondrial dysfunction.

Apelin‑36 protects against lipopolysaccharide‑induced acute lung injury by inhibiting the ASK1/MAPK signaling pathway

Apelin-36 is able to mediate a range of effects on various diseases, and is upregulated in lipopolysaccharide (LPS)-induced acute lung injury (ALI). However, to the best of our knowledge, whether apelin-36 is able to regulate LPS-induced ALI has yet to be investigated. The present study aimed to investigate the role of apelin-36 in LPS-induced ALI, and the putative underlying mechanisms. Rats were assigned to one of four treatment groups: The Control group, apelin-36 group, LPS group and LPS + apelin-36 group. At 4 h after intratracheal instillation of LPS (5 mg/kg), rats were intraperitoneally treated with 10 nmol/kg apelin-36. Subsequently, pathological manifestations and the extent of inflammation and apoptosis of the lung tissues were assessed. Untransfected and apoptosis signal-regulating kinase 1 (ASK1)-overexpressing Beas-2B cells were treated with LPS in the absence or presence of apelin-36, and subsequently the levels of inflammation and apoptosis were assessed. The results obtained showed that the level of apelin-36 was increased in the bronchoalveolar lavage fluid (BALF) of LPS-treated rats. Co-treatment with apelin-36 alleviated LPS-induced lung injury and pulmonary edema, reduced the levels of pro-inflammatory cytokines, including interleukin-6, monocyte chemoattractant protein-1 and tumor necrosis factor-α, in BALF, and inhibited apoptosis in the lung tissues. The presence of apelin-36 also blocked the activation of LPS-induced ASK1, p38, c-Jun N-terminal kinase and extracellular signal-regulated kinase in lung tissues. In vitro studies performed with Beas-2B cells showed that the addition of apelin-36 led to an increase in the cell viability of LPS-induced Beas-2B cells in a concentration-dependent manner. Additionally, co-treatment with 1 µM apelin-36 prevented LPS-induced inflammation and apoptosis. However, overexpression of ASK1 significantly reversed the inhibitory effects of apelin-36 on LPS-induced inflammation and apoptosis. Taken together, the results of the present study demonstrated that apelin-36 was able to protect against LPS-induced lung injury both in vivo and in vitro, and these actions may be dependent on inhibition of the ASK1/mitogen-activated protein kinase signaling pathway.

Inhibition of the antioxidant enzyme PRDX1 activity promotes MPP+-induced death in differentiated SH-SY5Y cells and may impair its colocalization with eEF1A2

AIM

eEF1A2 is highly expressed in postmitotic cells and has been reported to interact with the antioxidant enzyme peroxiredoxin 1 (PRDX1). PRDX1 is involved in motor neuron differentiation. Here, we studied the relationship between eEF1A2 and PRDX1 during dopaminergic neuron differentiation, and examined their possible association in an oxidative stress model of Parkinson's disease (PD).

MAIN METHODS

Expression of eEF1A2 and PRDX1 in SH-SY5Y cells at various durations of retinoic acid (RA) induction was detected using qRT-PCR, Western blotting and immunofluorescence. Neurons of 10-day differentiation were treated with the PRDX1 inhibitor H7, MPP⁺ and H7 plus MPP⁺. The cell viability, the amounts of apoptotic nuclei, DHE signals, and the expression of p53, p-Akt and p-mTOR were determined. The colocalization of eEF1A2 and PRDX1 was visualized using confocal microscopy.

KEY FINDINGS

eEF1A2 gradually increased after RA-induced differentiation of SH-SY5Y cells, while PRDX1 protein gradually decreased. MPP⁺ treatment increased eEF1A2 in both undifferentiated and differentiated neurons; however, PRDX1 appeared to elevate only in mature neurons. The inhibition of the PRDX1 activity with H7 promoted MPP⁺-induced cell death, as evidenced by decreased cell viability, increased apoptotic nuclei, increased the DHE signal, and increased p53. However, H7 induced the activation of the prosurvival Akt and mTOR in MPP⁺-treated cells. Besides, a colocalization of eEF1A2 and PRDX1 was evidenced in MPP⁺-treated neurons. This colocalization was possibly prevented by inhibiting the PRDX1 activity, resulting in aggravated neuronal death.

SIGNIFICANCE

Our results suggest that the possible association between eEF1A2 and PRDX1 may be a promising target for modifying neuronal death in PD.

Ghrelin protects dopaminergic neurons against MPTP neurotoxicity through promoting autophagy and inhibiting endoplasmic reticulum mediated apoptosis

Parkinson's disease (PD) is the second most common progressive neurodegenerative disorder, the important pathology of PD due to the prominent loss of the dopaminergic neurodegeneration in the substantia nigra pars compacta (SNpc) and striatum (STR). Although the etiology of PD is not fully understood, aggregation of α-synuclein, impaired autophagy, and endoplasmic reticulum stress (ERS) are involved in the pathogenesis of PD. Previously it has been demonstrated that Ghrelin is a kind of peptide protected dopaminergic neurons against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyran (MPTP)-induced neurotoxicity, but the detailed mechanism remains to be elucidated. In the present work, we investigated the effects of Ghrelin on autophagy and ERS-mediated apoptosis in the MPTP-lesioned PD mice model. We found that Ghrelin was neuroprotective against MPTP-induced dopaminergic neurodegeneration. Subsequently, we investigated Ghrelin inhibited the accumulation and phosphorylation of α-synuclein induced by MPTP. Moreover, Ghrelin promoted autophagy indicated by the up-regulation of microtubule-associated protein 1 Light Chain 3B-II/I (LC3B-II/I) and Beclin1, as well as decreasing the level of p62 in the SNpc and STR. Besides, the activation of the ERS-related apoptosis signaling pathway including IRE1α and Caspase-12 signaling pathway induced by MPTP was suppressed by Ghrelin treatment. Furthermore, Ghrelin also decreased Caspase-3 expression. Taken together, our results indicated that Ghrelin may exert neuroprotective effects via regulating α-synuclein activities, enhancing autophagy, and ameliorating ERS-mediated apoptosis in MPTP-lesioned mice, which provides a new target for potential pharmacologic interventions of PD treatment in the future.

The protective effect of decoction of Rehmanniae via PI3K/Akt/mTOR pathway in MPP+-induced Parkinson's disease model cells

This research aims to explore the function of DOR in 1-methyl-4-phenylpyridinium (MPP⁺)-induced Parkinson's disease model cell SH-SY5Y. SH-SY5Y cells were exposed with various doses of MPP + or DOR. Cell counting Kit-8 (CCK-8) assay and flow cytometry (FCM) were used to detect the cell viability, apoptosis and reactive oxygen species (ROS) levels in MPP⁺ Parkinson's disease model cells SH-SY5Y. The oxidative stress markers were measured by Enzyme-linked immunosorbent assay (ELISA), Western blot and quantitative real-time reverse transcription PCR (qRT-PCR) assays. To further determine the protective effect of DOR on acute injury via PI3K/Akt/mTOR pathway, cells were treated with LY294002 (LY), a PI3K/Akt/mTOR pathway inhibitor, with MMP + or DOR or not. MPP⁺ at various doses caused cell injury with decrease of viability, increase of apoptosis and ROS level, while DOR partly prevented the cell against injury induced by MPP⁺. Bax, Cyt-c and cleaved-Caspase-12, 9 and 3 were increased, and meanwhile Bcl-2 was decreased in MPP⁺ stimulated cells, while those changes could be partly inhibited by DOR incubation. Furthermore, the phosphorylation level of PI3K, AKT and mTOR was suppressed by MPP⁺, while DOR treatment could enhanced the level of phosphorylated-PI3K (p-PI3K), AKT (P-AKT) and mTOR. LY aggravated the injury of SH-SY5Y cells treated with MPP⁺, and DOR could partly alleviate those effects. DOR had a protective effect against MPP⁺ induced injury of Parkinson's disease model cell through activating the PI3K/Akt/mTOR pathway. It suggests that DOR should be further explored in Parkinson's disease.

Apelin enhances IL-1β expression in human synovial fibroblasts by inhibiting miR-144-3p through the PI3K and ERK pathways

Much data suggests intersecting activities between the adipokine apelin (APLN) and the pathologic processes of obesity and osteoarthritis (OA), with APLN modulating cartilage, synovium, bone, and various immune cell activities. The synovium plays an important role in the pathogenesis of OA. We investigated the crosstalk between APLN, a major OA-related adipokine, and interleukin 1 beta (IL-1β), a major proinflammatory cytokine, in human OA synovial fibroblasts (OASFs). We showed that APLN stimulated the synthesis of IL-1β in a concentration- and time-dependent manner, which was mitigated by blockade of the PI3K and ERK pathway. We also showed that APLN inhibited the expression of miRNA-144-3p, which blocks IL-1β transcription; this suppression activity was reversed via blockade of the PI3K and ERK pathway. Moreover, pathologic changes in OA cartilage were rescued when APLN was silenced by shAPLN transfection both in vitro and in vivo. Our evidence is the first to show that APLN stimulates the expression of IL-1β by activating the PI3K and ERK pathway and suppressing downstream expression of miRNA-144-3p in OASFs. We also demonstrate that knockdown of APLN expression by shAPLN transfection ameliorated changes in OA cartilage severity. These results shed light on OA pathogenesis and suggest a novel treatment pathway.

Protein Deimination Signatures in Plasma and Plasma-EVs and Protein Deimination in the Brain Vasculature in a Rat Model of Pre-Motor Parkinson's Disease

The identification of biomarkers for early diagnosis of Parkinson’s disease (PD) is of pivotal importance for improving approaches for clinical intervention. The use of translatable animal models of pre-motor PD therefore offers optimal opportunities for novel biomarker discovery in vivo. Peptidylarginine deiminases (PADs) are a family of calcium-activated enzymes that contribute to protein misfolding through post-translational deimination of arginine to citrulline. Furthermore, PADs are an active regulator of extracellular vesicle (EV) release. Both protein deimination and extracellular vesicles (EVs) are gaining increased attention in relation to neurodegenerative diseases, including in PD, while roles in pre-motor PD have yet to be investigated. The current study aimed at identifying protein candidates of deimination in plasma and plasma-EVs in a rat model of pre-motor PD, to assess putative contributions of such post-translational changes in the early stages of disease. EV-cargo was further assessed for deiminated proteins as well as three key micro-RNAs known to contribute to inflammation and hypoxia (miR21, miR155, and miR210) and also associated with PD. Overall, there was a significant increase in circulating plasma EVs in the PD model compared with sham animals and inflammatory and hypoxia related microRNAs were significantly increased in plasma-EVs of the pre-motor PD model. A significantly higher number of protein candidates were deiminated in the pre-motor PD model plasma and plasma-EVs, compared with those in the sham animals. KEGG (Kyoto encyclopedia of genes and genomes) pathways identified for deiminated proteins in the pre-motor PD model were linked to “Alzheimer’s disease”, “PD”, “Huntington’s disease”, “prion diseases”, as well as for “oxidative phosphorylation”, “thermogenesis”, “metabolic pathways”, “Staphylococcus aureus infection”, gap junction, “platelet activation”, “apelin signalling”, “retrograde endocannabinoid signalling”, “systemic lupus erythematosus”, and “non-alcoholic fatty liver disease”. Furthermore, PD brains showed significantly increased staining for total deiminated proteins in the brain vasculature in cortex and hippocampus, as well as increased immunodetection of deiminated histone H3 in dentate gyrus and cortex. Our findings identify EVs and post-translational protein deimination as novel biomarkers in early pre-motor stages of PD.

Targeting α-synuclein for PD Therapeutics: A Pursuit on All Fronts

Parkinson's Disease (PD) is characterized both by the loss of dopaminergic neurons in the substantia nigra and the presence of cytoplasmic inclusions called Lewy Bodies. These Lewy Bodies contain the aggregated α-synuclein (α-syn) protein, which has been shown to be able to propagate from cell to cell and throughout different regions in the brain. Due to its central role in the pathology and the lack of a curative treatment for PD, an increasing number of studies have aimed at targeting this protein for therapeutics. Here, we reviewed and discussed the many different approaches that have been studied to inhibit α-syn accumulation via direct and indirect targeting. These analyses have led to the generation of multiple clinical trials that are either completed or currently active. These clinical trials and the current preclinical studies must still face obstacles ahead, but give hope of finding a therapy for PD with time.

Apelin-36 mediates neuroprotective effects by regulating oxidative stress, autophagy and apoptosis in MPTP-induced Parkinson's disease model mice

Parkinson's disease (PD), a common human neurodegenerative disorder, is characterized by the presence of intraneuronal Lewy bodies composed principally of abnormal aggregated and post-translationally modified α-synuclein. In our previous research, we have demonstrated the neuroprotective effect of Apelin-36, a neuroendocrine peptide in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridin (MPTP)-lesioned PD model mice. Therefore, this study was designed to evaluate the neuroprotective mechanism of Apelin-36 against MPTP-induced neurotoxicity in mice. The results showed that MPTP-induced the depletion of dopamine in the striatum (STR) was partially reversed by Apelin-36. Apelin-36 also improved the activity of antioxidant system including superoxide dismutase (SOD) and glutathione (GSH), and decreased the overproduction of malondialdehyde (MDA) in the substantia nigra pars compacta (SNpc) and STR of MPTP-treated mice. Moreover, Apelin-36 downregulated inducible nitric oxide synthase (iNOS) and nitrated α-synuclein expression. Furthermore, Apelin-36 significantly promoted autophagy indicated by the up-regulation of LC3-II and Beclin1 and inhibition of p62 expression in the SNpc and STR of MPTP-treated mice. The protective effect of Apelin-36 was also associated with the inhibition of the apoptosis signal-regulating kinase 1 (ASK1)/c-Jun N-terminal kinase (JNK) signaling pathway and inactivation of caspase-3. Taken together, our findings demonstrated that the neuroprotective mechanism of Apelin-36 against MPTP-induced neurotoxicity in mice might be related to decreasing the aggregation of nitrated α-synuclein and alleviating oxidative stress as well as promoting autophagy and inhibiting ASK1/JNK/caspase-3 apoptotic pathway, which provides a novel strategy for PD treatment.