Calpain-regulated p35/cdk5 plays a central role in dopaminergic neuron death through modulation of the transcription factor myocyte enhancer factor 2

High-fat diet exacerbates 1-Bromopropane-induced loss of dopaminergic neurons in the substantia nigra of mice through mitochondrial damage associated necroptotic pathway

In recent years, accumulating evidence supports that occupational exposure to solvents is associated with an increased incidence of Parkinson's disease (PD) among workers. The neurotoxic effects of 1-bromopropane (1-BP), a widely used new-type solvent, are well-established, yet data on its relationship with the etiology of PD remain limited. Simultaneously, high-fat consumption in modern society is recognized as a significant risk factor for PD. However, whether there is a synergistic effect between a high-fat diet and 1-BP exposure remains unclear. In this study, adult C57BL/6 mice were fed either a chow or a high-fat diet for 18 weeks prior to 12-week 1-BP treatment. Subsequent neurobehavioral and neuropathological examinations were conducted to assess the effects of 1-BP exposure on parkinsonian pathology. The results demonstrated that 1-BP exposure produced obvious neurobehavioral abnormalities and dopaminergic degeneration in the nigral region of mice. Importantly, a high-fat diet further exacerbated the impact of 1-BP on motor and cognitive abnormalities in mice. Mechanistic investigation revealed that mitochondrial damage and mtDNA release induced by 1-BP and high-fat diet activate NLRP3 and cGAS-STING pathway- mediated neuroinflammatory response, and ultimately lead to necroptosis of dopaminergic neurons. In summary, our study unveils a potential link between chronic 1-BP exposure and PD-like pathology with motor and no-motor defects in experimental animals, and long-term high-fat diet can further promote 1-BP neurotoxicity, which underscores the pivotal role of environmental factors in the etiology of PD.

Mitigating aberrant Cdk5 activation alleviates mitochondrial defects and motor neuron disease symptoms in spinal muscular atrophy

Spinal muscular atrophy (SMA), the top genetic cause of infant mortality, is characterized by motor neuron degeneration. Mechanisms underlying SMA pathogenesis remain largely unknown. Here, we report that the activity of cyclin-dependent kinase 5 (Cdk5) and the conversion of its activating subunit p35 to the more potent activator p25 are significantly up-regulated in mouse models and human induced pluripotent stem cell (iPSC) models of SMA. The increase of Cdk5 activity occurs before the onset of SMA phenotypes, suggesting that it may be an initiator of the disease. Importantly, aberrant Cdk5 activation causes mitochondrial defects and motor neuron degeneration, as the genetic knockout of p35 in an SMA mouse model rescues mitochondrial transport and fragmentation defects, and alleviates SMA phenotypes including motor neuron hyperexcitability, loss of excitatory synapses, neuromuscular junction denervation, and motor neuron degeneration. Inhibition of the Cdk5 signaling pathway reduces the degeneration of motor neurons derived from SMA mice and human SMA iPSCs. Altogether, our studies reveal a critical role for the aberrant activation of Cdk5 in SMA pathogenesis and suggest a potential target for therapeutic intervention.

Disturb mitochondrial associated proteostasis: Neurodegeneration and imperfect ageing

The disturbance in mitochondrial functions and homeostasis are the major features of neuron degenerative conditions, like Parkinson’s disease, Amyotrophic Lateral Sclerosis, and Alzheimer’s disease, along with protein misfolding. The aberrantly folded proteins are known to link with impaired mitochondrial pathways, further contributing to disease pathogenesis. Despite their central significance, the implications of mitochondrial homeostasis disruption on other organelles and cellular processes remain insufficiently explored. Here, we have reviewed the dysfunction in mitochondrial physiology, under neuron degenerating conditions. The disease misfolded proteins impact quality control mechanisms of mitochondria, such as fission, fusion, mitophagy, and proteasomal clearance, to the detriment of neuron. The adversely affected mitochondrial functional roles, like oxidative phosphorylation, calcium homeostasis, and biomolecule synthesis as well as its axes and contacts with endoplasmic reticulum and lysosomes are also discussed. Mitochondria sense and respond to multiple cytotoxic stress to make cell adapt and survive, though chronic dysfunction leads to cell death. Mitochondria and their proteins can be candidates for biomarkers and therapeutic targets. Investigation of internetworking between mitochondria and neurodegeneration proteins can enhance our holistic understanding of such conditions and help in designing more targeted therapies.

The Role of MEF2 Transcription Factor Family in Neuronal Survival and Degeneration

The family of myocyte enhancer factor 2 (MEF2) transcription factors comprises four highly conserved members that play an important role in the nervous system. They appear in precisely defined time frames in the developing brain to turn on and turn off genes affecting growth, pruning and survival of neurons. MEF2s are known to dictate neuronal development, synaptic plasticity and restrict the number of synapses in the hippocampus, thus affecting learning and memory formation. In primary neurons, negative regulation of MEF2 activity by external stimuli or stress conditions is known to induce apoptosis, albeit the pro or antiapoptotic action of MEF2 depends on the neuronal maturation stage. By contrast, enhancement of MEF2 transcriptional activity protects neurons from apoptotic death both in vitro and in preclinical models of neurodegenerative diseases. A growing body of evidence places this transcription factor in the center of many neuropathologies associated with age-dependent neuronal dysfunctions or gradual but irreversible neuron loss. In this work, we discuss how the altered function of MEF2s during development and in adulthood affecting neuronal survival may be linked to neuropsychiatric disorders.

A focus on natural products for preventing and cure of mitochondrial dysfunction in Parkinson's disease

Mitochondria are considered the only source of energy production within cells. This organelle is vital for neural function and survival by producing energy (adenosine triphosphate (ATP)) and regulating intracellular calcium. Mitochondrial dysfunction, which significantly contributes to both idiopathic and familial types of Parkinson's disease (PD), depletes cellular energy, disrupts homeostasis, and induces oxidative stress, leading to cell death. In recent years several natural products have been discovered to be protective against mitochondrial dysfunction. This review discusses the role of mitochondria in the progression of PD to define the path for using natural products to prevent and/or cure PD.

Molecular Mechanisms and Therapeutic Potential of α- and β-Asarone in the Treatment of Neurological Disorders

Neurological disorders are important causes of morbidity and mortality around the world. The increasing prevalence of neurological disorders, associated with an aging population, has intensified the societal burden associated with these diseases, for which no effective treatment strategies currently exist. Therefore, the identification and development of novel therapeutic approaches, able to halt or reverse neuronal loss by targeting the underlying causal factors that lead to neurodegeneration and neuronal cell death, are urgently necessary. Plants and other natural products have been explored as sources of safe, naturally occurring secondary metabolites with potential neuroprotective properties. The secondary metabolites α- and β-asarone can be found in high levels in the rhizomes of the medicinal plant Acorus calamus (L.). α- and β-asarone exhibit multiple pharmacological properties including antioxidant, anti-inflammatory, antiapoptotic, anticancer, and neuroprotective effects. This paper aims to provide an overview of the current research on the therapeutic potential of α- and β-asarone in the treatment of neurological disorders, particularly neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), as well as cerebral ischemic disease, and epilepsy. Current research indicates that α- and β-asarone exert neuroprotective effects by mitigating oxidative stress, abnormal protein accumulation, neuroinflammation, neurotrophic factor deficit, and promoting neuronal cell survival, as well as activating various neuroprotective signalling pathways. Although the beneficial effects exerted by α- and β-asarone have been demonstrated through in vitro and in vivo animal studies, additional research is required to translate laboratory results into safe and effective therapies for patients with AD, PD, and other neurological and neurodegenerative diseases.

Neuroprotection against 1-Methyl-4-phenylpyridinium-induced cytotoxicity by naturally occurring polydatin through activation of transcription factor MEF2D

Polydatin is the major active ingredient of Polygonum cuspidatum Sieb. Et Zucc. A recent study indicated that polydatin could protect against substantia nigra dopaminergic degeneration in rodent models associated with Parkinson's disease. However, mechanisms that underlie the neuroprotection of polydatin have not been fully elucidated. In the current study, the neuroprotective effects and detailed mechanisms of action of polydatin were investigated in Parkinson's disease-related cellular models. Polydatin dose- and time-dependently prevented neurotoxicity caused by 1-methyl-4-phenylpyridinium ion (MPP+) in primary cerebellar granule neurons. Moreover, we found that polydatin enhanced the activity of the transcription factor myocyte enhancer factor 2D (MEF2D) at both basal and pathological conditions using luciferase reporter gene assay. Additionally, western blot analysis revealed that polydatin could downregulate glycogen synthase kinase 3β (GSK3β), which is a negative regulator of MEF2D. Molecular docking simulations finally suggested an interaction between polydatin and a hydrophobic pocket within GSK3β. All these results suggest that polydatin prevents MPP+-induced neurotoxicity via enhancing MEF2D through the inhibition of GSK3β and that treatment with polydatin is worthy of further anti-Parkinson's disease study in future.

MiR-421 Aggravates Neurotoxicity and Promotes Cell Death in Parkinson's Disease Models by Directly Targeting MEF2D

Parkinson's disease (PD) is a severe neurodegenerative disease characterized by selective loss of dopaminergic neurons, which reduces quality of life of patients and poses a heavy burden to the society. The pathological mechanism of PD remains unclear, and increasing efforts are aimed to solve this problem. MiRNAs are a kind of small noncoding RNA regulating target gene expression. Previous studies have shown that dysregulation of miRNAs is involved in the development of PD. In the present study, we determined that miR-421 and MEF2D are increased and decreased, respectively, in a cellular model of PD. The data on the mechanism of action indicate that miR-421 directly binds to MEF2D mRNA and negatively regulates MEF2D expression. An increase in miR-421 disrupted the Bcl2/Bax system. Functional assays indicated that enhanced miR-421 promotes cell death by negative modulation of MEF2D expression. Inhibition of miR-421 or restoration of MEF2D protected neurons from neurotoxicity in cellular and animal models of PD. Our study is the first to demonstrate that miR-421 is decreased in PD models and to determine a novel putative mechanism of PD pathogenesis.

MEF2 transcription factors differentially contribute to retinal ganglion cell loss after optic nerve injury

Loss of retinal ganglion cells (RGCs) in optic neuropathies results in permanent partial or complete blindness. Myocyte enhancer factor 2 (MEF2) transcription factors have been shown to play a pivotal role in neuronal systems, and in particular MEF2A knockout was shown to enhance RGC survival after optic nerve crush injury. Here we expanded these prior data to study bi-allelic, tri-allelic and heterozygous allele deletion. We observed that deletion of all MEF2A, MEF2C, and MEF2D alleles had no effect on RGC survival during development. Our extended experiments suggest that the majority of the neuroprotective effect was conferred by complete deletion of MEF2A but that MEF2D knockout, although not sufficient to increase RGC survival on its own, increased the positive effect of MEF2A knockout. Conversely, MEF2A over-expression in wildtype mice worsened RGC survival after optic nerve crush. Interestingly, MEF2 transcription factors are regulated by post-translational modification, including by calcineurin-catalyzed dephosphorylation of MEF2A Ser-408 known to increase MEF2A-dependent transactivation in neurons. However, neither phospho-mimetic nor phospho-ablative mutation of MEF2A Ser-408 affected the ability of MEF2A to promote RGC death in vivo after optic nerve injury. Together these findings demonstrate that MEF2 gene expression opposes RGC survival following axon injury in a complex hierarchy, and further support the hypothesis that loss of or interference with MEF2A expression might be beneficial for RGC neuroprotection in diseases such as glaucoma and other optic neuropathies.

Core cell cycle machinery is crucially involved in both life and death of post-mitotic neurons

A persistent dogma in neuroscience supported the idea that terminally differentiated neurons permanently withdraw from the cell cycle. However, since the late 1990s, several studies have shown that cell cycle proteins are expressed in post-mitotic neurons under physiological conditions, indicating that the cell cycle machinery is not restricted to proliferating cells. Moreover, many studies have highlighted a clear link between cell cycle-related proteins and neurological disorders, particularly relating to apoptosis-induced neuronal death. Indeed, cell cycle-related proteins can be upregulated or overactivated in post-mitotic neurons in case of acute or degenerative central nervous system disease. Given the considerable lack of effective treatments for age-related neurological disorders, new therapeutic approaches targeting the cell cycle machinery might thus be considered. This review aims at summarizing current knowledge about the role of the cell cycle machinery in post-mitotic neurons in healthy and pathological conditions.

Cell-Permeable Calpain Inhibitor SJA6017 Provides Functional Protection to Spinal Motoneurons Exposed to MPP. Neurotox Res 2020;38:640-649. [PMID: 32761446 DOI: 10.1007/s12640-020-00264-3]

Extra-nigral central nervous system sites have been found to be affected in Parkinson's disease (PD). In addition to substantia nigra, degeneration of spinal cord motor neurons may play a role in the motor symptoms of PD. To this end, hybrid rodent VSC 4.1 cells differentiated into motoneurons were used as a cell culture model following exposure to Parkinsonian neurotoxicant MPP⁺. SJA6017, a cell-permeable calpain inhibitor, was tested for its neuroprotective efficacy against the neurotoxicant. SJA6017 attenuated MPP⁺-induced rise in intracellular free Ca²⁺ and concomitant increases in the active form of calpain. It also significantly prevented increased levels of proteases and their activities, as shown by reduced levels of 145 kDa calpain-specific and 120 kDa caspase-3-specific spectrin breakdown products. Exposure to MPP⁺ elevated the levels of reactive oxygen species in VSC 4.1 motoneurons; this was significantly diminished with SJA6017. The motor proteins in spinal motoneurons, i.e., dynein and kinesin, were also impaired following exposure to MPP⁺ through calpain-mediated mechanisms; this process was partially ameliorated by SJA6017 pretreatment. Cytoprotection provided by SJA6017 against MPP⁺-induced damage to VSC 4.1 motoneurons was confirmed by restoration of membrane potential via whole-cell patch-clamp assay. This study demonstrates that calpain inhibition is a prospective route for neuroprotection in experimental PD; moreover, calpain inhibitor SJA6017 appears to be an effective neuroprotective agent against MPP⁺-induced damage in spinal motoneurons.

Physiological and Pathological Roles of Cdk5: Potential Directions for Therapeutic Targeting in Neurodegenerative Disease

Cyclin-dependent kinase 5 (Cdk5) is a proline-directed serine (ser)/threonine (Thr) kinase that has been demonstrated to be one of the most functionally diverse kinases within neurons. Cdk5 is regulated via binding with its neuron-specific regulatory subunits, p35 or p39. Cdk5-p35 activity is critical for a variety of developmental and cellular processes in the brain, including neuron migration, memory formation, microtubule regulation, and cell cycle suppression. Aberrant activation of Cdk5 via the truncated p35 byproduct, p25, is implicated in the pathogenesis of several neurodegenerative diseases. The present review highlights the importance of Cdk5 activity and function in the brain and demonstrates how deregulation of Cdk5 can contribute to the development of neurodegenerative conditions such as Alzheimer's and Parkinson's disease. Additionally, we cover past drug discovery attempts at inhibiting Cdk5-p25 activity and discuss which types of targeting strategies may prove to be the most successful moving forward.

Lanthionine ketimine ester improves outcome in an MPTP-induced mouse model of Parkinson's disease via suppressions of CRMP2 phosphorylation and microglial activation

Parkinson's disease (PD) is characterized by progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNc). Levodopa (L-Dopa), the current main treatment for PD, reduces PD symptoms by partially replacing dopamine, but it does not slow neurodegeneration. Recent studies have evidenced that neuroinflammatory processes contribute to the degeneration of dopaminergic neurons in the SNc under cytopathic conditions, while other lines of inquiry have implicated phosphorylation of collapsin response mediator protein 2 (CRMP2) as a causal factor in axonal retraction after neural injury. We recently reported on the therapeutic effect of lanthionine ketimine ester (LKE) which associates with CRMP2 following axonal injury in the spinal cord. In the present study, we report that LKE protects SNc dopaminergic neurons after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) challenge, a common model for PD, and reduces the number of activated microglia proximal to the damaged SNc. The results also show that MPTP-induced motor impairment was suppressed in LKE treatment. Furthermore, the results show that LKE inhibits the elevation of CRMP2 phosphorylation in dopaminergic neurons in the SNc after MPTP injection. These data suggest that modification of CRMP2 phosphorylation and suppression of microglial activation with LKE administration may represent a novel strategy for slowing progress of pathological processes in PD.

Update on the association between alpha-synuclein and tau with mitochondrial dysfunction: Implications for Parkinson's disease

The critical role of mitochondrial dysfunction in the pathological mechanisms of neurodegenerative disorders, particularly Parkinson's disease (PD), is well established. Compelling evidence indicates that Parkinson's proteins (e.g., α-synuclein, Parkin, PINK1, DJ-1, and LRRK2) are associated with mitochondrial dysfunction and oxidative stress in PD. Significantly, there is a possible central role of alpha-synuclein (α-Syn) in the occurrence of mitochondrial dysfunction and oxidative stress by the mediation of different signaling pathways. Also, tau, traditionally considered as the main component of neurofibrillary tangles, aggregates and amplifies the neurotoxic effects on mitochondria by interacting with α-Syn. Moreover, oxidative stress caused by mitochondrial dysfunction favors assembly of both α-Syn and tau and also plays a key role in the formation of protein aggregates. In this review, we provide an overview of the relationship between these two pathological proteins and mitochondrial dysfunction in PD, and also summarize the underlying mechanisms in the interplay of α-Syn aggregation and phosphorylated tau targeting the mitochondria, to find new strategies to prevent PD processing.

Autophagic and endo-lysosomal dysfunction in neurodegenerative disease

Due to their post-mitotic state, metabolic demands and often large polarised morphology, the function and survival of neurons is dependent on an efficient cellular waste clearance system both for generation of materials for metabolic processes and removal of toxic components. It is not surprising therefore that deficits in protein clearance can tip the balance between neuronal health and death. Here we discuss how autophagy and lysosome-mediated degradation pathways are disrupted in several neurological disorders. Both genetic and cell biological evidence show the diversity and complexity of vesicular clearance dysregulation in cells, and together may ultimately suggest a unified mechanism for neuronal demise in degenerative conditions. Causative and risk-associated mutations in Alzheimer's disease, Frontotemporal Dementia, Amyotrophic Lateral Sclerosis, Parkinson's disease, Huntington's disease and others have given the field a unique mechanistic insight into protein clearance processes in neurons. Through their broad implication in neurodegenerative diseases, molecules involved in these genetic pathways, in particular those involved in autophagy, are emerging as appealing therapeutic targets for intervention in neurodegeneration.

miR-124 and Parkinson's disease: A biomarker with therapeutic potential

Parkinson's disease (PD) is a multifactorial disorder, attributed to a complex interplay between genetic and epigenetic factors. Although the exact etiology of the disease remains elusive, dysregulation of signaling pathways implicated in cell survival, apoptosis, protein aggregation, mitochondrial dysfunction, autophagy, oxidative damage and neuroinflammation, contributes to its pathogenesis. MicroRNAs (miRs) are endogenous short non-coding RNA molecules that negatively regulate gene expression at a post-transcriptional level. MiR-124 is one of the most abundantly expressed miRs in the brain that participates in neurogenesis, synapse morphology, neurotransmission, inflammation, autophagy and mitochondrial function. Accumulating pre-clinical evidence shows that miR-124 may act through calpain 1/p25/cyclin-dependent kinases 5 (CDK5), nuclear factor-kappa B (NF-κB), signal transducer and activator of transcription 3 (STAT3), Bcl-2-interacting mediator of cell death (Bim), 5' adenosine monophosphate-activated protein kinase (AMPK) and extracellular signal-regulated kinase (ERK)-mediated pathways to regulate cell survival, apoptosis, autophagy, mitochondrial dysfunction, oxidative damage and neuroinflammation in PD. Moreover, clinical evidence indicates that reduced plasma miR-124 levels may serve as a potential diagnostic biomarker in PD. This review provides an update of the pathogenic implication of miR-124 activity in PD and discusses its targeting potential for the development of future therapeutic strategies.

Down-regulation of cyclin-dependent kinase 5 attenuates p53-dependent apoptosis of hippocampal CA1 pyramidal neurons following transient cerebral ischemia

Abnormal activation of cyclin-dependent kinase 5 (Cdk5) is associated with pathophysiological conditions. Ischemic preconditioning (IPC) can provide neuroprotective effects against subsequent lethal ischemic insult. The objective of this study was to determine how Cdk5 and related molecules could affect neuroprotection in the hippocampus of gerbils after with IPC [a 2-min transient cerebral ischemia (TCI)] followed by 5-min subsequent TCI. Hippocampal CA1 pyramidal neurons were dead at 5 days post-TCI. However, treatment with roscovitine (a potent inhibitor of Cdk5) and IPC protected CA1 pyramidal neurons from TCI. Expression levels of Cdk5, p25, phospho (p)-Rb and p-p53 were increased in nuclei of CA1 pyramidal neurons at 1 and 2 days after TCI. However, these expressions were attenuated by roscovitine treatment and IPC. In particular, Cdk5, p-Rb and p-p53 immunoreactivities in their nuclei were decreased. Furthermore, TUNEL-positive CA1 pyramidal neurons were found at 5 days after TCI with increased expression levels of Bax, PUMA, and activated caspase-3. These TUNEL-positive cells and increased molecules were decreased by roscovitine treatment and IPC. Thus, roscovitine treatment and IPC could protect CA1 pyramidal neurons from TCI through down-regulating Cdk5, p25, and p-p53 in their nuclei. These findings indicate that down-regulating Cdk5 might be a key strategy to attenuate p53-dependent apoptosis of CA1 pyramidal neurons following TCI.

Neuronal Myocyte-Specific Enhancer Factor 2D (MEF2D) Is Required for Normal Circadian and Sleep Behavior in Mice

The transcription factor, myocyte enhancer factor-2 (MEF2), is required for normal circadian behavior in Drosophila; however, its role in the mammalian circadian system has not been established. Of the four mammalian Mef2 genes, Mef2d is highly expressed in the suprachiasmatic nucleus (SCN) of the hypothalamus, a region critical for coordinating peripheral circadian clocks. Using both conventional and brain-specific Mef2d KO (Mef2d ^-/-) mouse lines, we demonstrate that MEF2D is essential for maintaining the length of the circadian free-running period of locomotor activity and normal sleep patterns in male mice. Crossing Mef2d ^-/- with Per2::luc reporter mice, we show that these behavioral changes are achieved without altering the endogenous period of the master circadian oscillator in the SCN. Together, our data suggest that alterations in behavior in Mef2d ^-/- mice may be the result of an effect on SCN output, rather than an effect on timekeeping within the SCN itself. These findings add to the growing body of evidence that MEF2 proteins play important roles in the brain.SIGNIFICANCE STATEMENT These studies are the first to show a role for MEF2 proteins in the brain outside of the hippocampus, and our findings suggest that these proteins may play diverse roles in the CNS. It is important to continue to build on our understanding of the roles of proteins acting in the SCN because SCN dysfunction underlies jet lag in humans and influences the response to shift work schedules, which are now known as risk factors for the development of cancer. Our work on MEF2D could be the basis for opening new lines of research in the development and regulation of circadian rhythms.

Morphine reverses the effects of 1-methyl-4-phenylpyridinium in PC12 cells through activating PI3K/Akt

AIM OF THE STUDY

Parkinson's disease (PD) is a neurodegenerative disorder. It is caused by the degeneration of dopaminergic neurons and the dopamine (DA) deletion in the substantia nigra pars compacta (SNpc). Morphine elevates the level of dopamine in the mesolimbic dopamine system and plays a role in alleviating PD symptoms. However, the molecular mechanism is still unclear. The aim of the study is to investigate the mechanism on morphine alleviating PD symptoms.

MATERIALS AND METHODS

The viability of PC12 cells was measured by using MTT assay. The expressions of tyrosine hydroxylase (TH), thioredoxin-1 (Trx-1), CyclinD1 and Cyclin-dependent kinase5 (Cdk5) were detected by Western Blot.

RESULTS

In present study, we found that morphine increased the cell viability in PC12 cells. 1-methyl-4-phenylpyridi-nium (MPP+) reduced the cell viability and TH expression, which were reversed by morphine. MPP+ decreased the expressions of Trx-1, CyclinD1, Cdk5, which were restored by morphine. Moreover, the role of morphine in restoring the expressions of Trx-1, CyclinD1 and Cdk5 decreased by MPP+ was abolished by LY294002, phosphatidylinositol-3-kinase (PI3K)/Akt inhibitor.

CONCLUSIONS

These results suggest that morphine reverses effects induced by MPP þ through activating PI3K/Akt pathway.

Melatonin and pancreatic cancer: Current knowledge and future perspectives

Pancreatic cancer has a high mortality rate due to the absence of early symptoms and subsequent late diagnosis; additionally, pancreatic cancer has a high resistance to radio- and chemotherapy. Multiple inflammatory pathways are involved in the pathophysiology of pancreatic cancer. Melatonin an indoleamine produced in the pineal gland mediated and receptor-independent action is the pancreas and other where has both receptors. Melatonin is a potent antioxidant and tissue protector against inflammation and oxidative stress. In vivo and in vitro studies have shown that melatonin supplementation is an appropriate therapeutic approach for pancreatic cancer. Melatonin may be an effective apoptosis inducer in cancer cells through regulation of a large number of molecular pathways including oxidative stress, heat shock proteins, and vascular endothelial growth factor. Limited clinical studies, however, have evaluated the role of melatonin in pancreatic cancer. This review summarizes what is known regarding the effects of melatonin on pancreatic cancer and the mechanisms involved.

Neuroprotection Against MPP+-Induced Cytotoxicity Through the Activation of PI3-K/Akt/GSK3β/MEF2D Signaling Pathway by Rhynchophylline, the Major Tetracyclic Oxindole Alkaloid Isolated From Uncaria rhynchophylla

Rhynchophylline is a major tetracyclic oxindole alkaloid in Uncaria rhynchophylla, which has been extensively used as traditional herb medicine for the prevention of convulsions and hypertension. However, there is still little evidence about the neuroprotective effects of rhynchophylline for Parkinson’s disease (PD), a neurodegenerative condition currently without any effective cure. In this present study, the neuroprotective molecular mechanisms of rhynchophylline were investigated in a cellular model associated with PD. It is shown that rhynchophylline (10–50 μM) greatly prevented neurotoxicity caused by 1-methyl-4-phenylpyridinium ion (MPP⁺) in primary cerebellar granule neurons, as evidenced by the promotion of cell viability as well as the reversal of dysregulated protein expression of Bax/Bcl-2 ratio. Very encouragingly, we found that rhynchophylline markedly enhanced the activity of the transcription factor myocyte enhancer factor 2D (MEF2D) at both basal and pathological conditions using luciferase reporter gene assay, and reversed the inhibition of MEF2D caused by MPP⁺. Additionally, pharmacological inhibition of PI3-Kinase or short hairpin RNA-mediated gene down-regulation of MEF2D abrogated the protection provided by rhynchophylline. Furthermore, Western blot analysis revealed that rhynchophylline could potentiate PI3-K/Akt to attenuate GSK3β (the MEF2D inhibitor) in response to MPP⁺ insult. In conclusion, rhynchophylline inhibits MPP⁺-triggered neurotoxicity by stimulating MEF2D via activating PI3-K/Akt/GSK3β cascade. Rhynchophylline is served as a novel MEF2D enhancer and might be a potential candidate for further preclinical study in the prevention of PD.

Cdk5 Inhibitory Peptide Prevents Loss of Dopaminergic Neurons and Alleviates Behavioral Changes in an MPTP Induced Parkinson's Disease Mouse Model

Parkinson’s disease (PD) is one of the most affected neurodegenerative diseases in the world. Deregulation of cyclin-dependent kinase 5 (Cdk5) is believed to play an important role in neurodegenerative diseases including PD. p25 is a cleavage peptide of p35, a physiologic activator of Cdk5. p25 combines to Cdk5 and leads to the hyperactivity of Cdk5, which in turn hyperphosphorylates downstream substrates and leads to neuroinflammation and apoptosis of neurons. Previously, we have demonstrated that adeno-associated virus serotype-9 (AAV9) mediated Cdk5 inhibitory peptide (CIP) inhibits the activity of Cdk5/p25 complex and alleviates pathologic and behavioral changes in Alzheimer’s disease mouse model. In this study, we evaluated whether AAV9-CIP protected dopaminergic (DA) neurons in 1-methyl-4-phe-nyl-1,2,3,6-tetrahydropyridine-probenecid (MPTP/p) induced PD mouse model. The data showed that administration of AAV9-CIP by intracerebroventricular injection 1 week before MPTP/p exposure protected loss of DA neurons in substantia nigra compact of the model mice. Importantly, AAV9-CIP also alleviated the motor and anxiety-like symptoms of the disease animals. In summary, AAV9 mediated CIP might be a potential intervention for PD.

Chaperone-mediated autophagy: Advances from bench to bedside

Protein homeostasis or proteostasis is critical for proper cellular function and survival. It relies on the balance between protein synthesis and degradation. Lysosomes play an important role in degrading and recycling intracellular components via autophagy. Among the three types of lysosome-based autophagy pathways, chaperone-mediated autophagy (CMA) selectively degrades cellular proteins with KFERQ-like motif by unique machinery. During the past several years, significant advances have been made in our understanding of how CMA itself is modulated and what physiological and pathological processes it may be involved in. One particularly exciting discovery is how other cellular stress organelles such as ER signal to CMA. As more proteins are identified as CMA substrates, CMA function has been associated with an increasing number of important cellular processes, organelles, and diseases, including neurodegenerative diseases. Here we will summarize the recent advances in CMA biology, highlight ER stress-induced CMA, and discuss the role of CMA in diseases.

Cdk5 suppression blocks SIRT1 degradation via the ubiquitin-proteasome pathway in Parkinson's disease models

The NAD⁺-dependent protein deacetylase sirtuin 1 (SIRT1), a member of the sirtuin family, may have a neuroprotective effect in multiple neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD) and Amyotrophic lateral sclerosis (ALS). Many studies have suggested that overexpression-induced or resveratrol-treated activation of SIRT1 could significantly ameliorate several neurodegenerative diseases in mouse models. However, the type of SIRT1, protein expression levels and underlying mechanisms remain unclear, especially in PD. In this study, the results demonstrated that SIRT1 knockout markedly worsened the movement function in MPTP-lesioned animal model of PD. SIRT1 expression was found to be markedly decreased not only in environmental factor PD models, neurotoxin MPP⁺-treated primary culture neurons and MPTP-induced mice but also in genetic factor PD models, overexpressed α-synuclein-A30PA53T SH-SY5Y stable cell line and hm²α-SYN-39 transgenic mouse strain. Importantly, the degradation of SIRT1 during MPP⁺ treatment was mediated by the ubiquitin-proteasome pathway. Furthermore, the results indicated that cyclin-dependent kinase 5 (Cdk5) was also involved in the decrease of SIRT1 expression, which could be efficiently blocked by the inhibition of Cdk5. In conclusion, our findings revealed that the Cdk5-dependent ubiquitin-proteasome pathway mediated degradation of SIRT1 plays a vital role in the progression of PD.

Synaptic roles of cyclin-dependent kinase 5 & its implications in epilepsy

There is an urgent need to understand the molecular mechanisms underlying epilepsy to find novel prognostic/diagnostic biomarkers to prevent epilepsy patients at risk. Cyclin-dependent kinase 5 (CDK5) is involved in multiple neuronal functions and plays a crucial role in maintaining homeostatic synaptic plasticity by regulating intracellular signalling cascades at synapses. CDK5 deregulation is shown to be associated with various neurodegenerative diseases such as Alzheimer's disease. The association between chronic loss of CDK5 and seizures has been reported in animal models of epilepsy. Genetic expression of CDK5 at transcriptome level has been shown to be abnormal in intractable epilepsy. In this review various possible mechanisms by which deregulated CDK5 may alter synaptic transmission and possibly lead to epileptogenesis have been discussed. Further, CDK5 has been proposed as a potential biomarker as well as a pharmacological target for developing treatments for epilepsy.

Interaction of Cdk5 and cAMP/PKA Signaling in the Mediation of Neuropsychiatric and Neurodegenerative Diseases

Both cyclin-dependent kinase 5 (Cdk5) and cyclic AMP (cAMP)/protein kinase A (PKA) regulate fundamental central nervous system (CNS) functions including neuronal survival, neurite and axonal outgrowth, neuron development and cognition. Cdk5, a serine/threonine kinase, is activated by p35 or p39 and phosphorylates multiple signaling components of various pathways, including cAMP/PKA signaling. Here, we review the recent literature on the interaction between Cdk5 and cAMP/PKA signaling and their role in the mediation of CNS functions and neuropsychiatric and neurodegenerative diseases.

Stress-induced Cdk5 activity enhances cytoprotective basal autophagy in Drosophila melanogaster by phosphorylating acinus at serine437

Cdk5 is a post-mitotic kinase with complex roles in maintaining neuronal health. The various mechanisms by which Cdk5 inhibits and promotes neurodegeneration are still poorly understood. Here, we show that in Drosophila melanogaster Cdk5 regulates basal autophagy, a key mechanism suppressing neurodegeneration. In a targeted screen, Cdk5 genetically interacted with Acinus (Acn), a primarily nuclear protein, which promotes starvation-independent, basal autophagy. Loss of Cdk5, or its required cofactor p35, reduces S437-Acn phosphorylation, whereas Cdk5 gain-of-function increases pS437-Acn levels. The phospho-mimetic S437D mutation stabilizes Acn and promotes basal autophagy. In p35 mutants, basal autophagy and lifespan are reduced, but restored to near wild-type levels in the presence of stabilized AcnS437D. Expression of aggregation-prone polyQ-containing proteins or the Amyloid-β42 peptide, but not alpha-Synuclein, enhances Cdk5-dependent phosphorylation of S437-Acn. Our data indicate that Cdk5 is required to maintain the protective role of basal autophagy in the initial responses to a subset of neurodegenerative challenges.

Leucine-rich repeat kinase 2 exacerbates neuronal cytotoxicity through phosphorylation of histone deacetylase 3 and histone deacetylation

Parkinson's disease (PD) is characterized by slow, progressive degeneration of dopaminergic neurons in the substantia nigra. The cause of neuronal death in PD is largely unknown, but several genetic loci, including leucine-rich repeat kinase 2 (LRRK2), have been identified. LRRK2 has guanosine triphosphatase (GTPase) and kinase activities, and mutations in LRRK2 are the major cause of autosomal-dominant familial PD. Histone deacetylases (HDACs) remove acetyl groups from lysine residues on histone tails, promoting transcriptional repression via condensation of chromatin. Here, we demonstrate that LRRK2 binds to and directly phosphorylates HDAC3 at Ser-424, thereby stimulating HDAC activity. Specifically, LRRK2 promoted the deacetylation of Lys-5 and Lys-12 on histone H4, causing repression of gene transcription. Moreover, LRRK2 stimulated nuclear translocation of HDAC3 via the phoshorylation of karyopherin subunit α2 and α6. HDAC3 phosphorylation and its nuclear translocation were increased in response to 6-hydroxydopamine (6-OHDA) treatment. LRRK2 also inhibited myocyte-specific enhancer factor 2D activity, which is required for neuronal survival. LRRK2 ultimately promoted 6-OHDA-induced cell death via positive modulation of HDAC3. These findings suggest that LRRK2 affects epigenetic histone modification and neuronal survival by facilitating HDAC3 activity and regulating its localization.

The potential role of neuroinflammation and transcription factors in Parkinson disease

Parkinson disease (PD) is a neurodegenerative disorder characterized by dopaminergic neurons affected by inflammatory processes. Post-mortem analyses of brain and cerebrospinal fluid from PD patients show the accumulation of proinflammatory cytokines, confirming an ongoing neuroinflammation in the affected brain regions. These inflammatory mediators may activate transcription factors—notably nuclear factor κB, Ying-Yang 1 (YY1), fibroblast growth factor 20 (FGF20), and mammalian target of rapamycin (mTOR)—which then regulate downstream signaling pathways that in turn promote death of dopaminergic neurons through death domain-containing receptors. Dopaminergic neurons are vulnerable to oxidative stress and inflammatory attack. An increased level of inducible nitric oxide synthase observed in the substantia nigra and striatum of PD patients suggests that both cytokine—and chemokine-induced toxicity and inflammation lead to oxidative stress that contributes to degeneration of dopaminergic neurons and to disease progression. Lipopolysaccharide activation of microglia in the proximity of dopaminergic neurons in the substantia nigra causes their degeneration, and this appears to be a selective vulnerability of dopaminergic neurons to inflammation. In this review, we will look at the role of various transcription factors and signaling pathways in the development of PD.

Substantial protection against MPTP-associated Parkinson's neurotoxicity in vitro and in vivo by anti-cancer agent SU4312 via activation of MEF2D and inhibition of MAO-B

We have previously demonstrated the unexpected neuroprotection of the anti-cancer agent SU4312 in cellular models associated with Parkinson's disease (PD). However, the precise mechanisms underlying its neuroprotection are still unknown, and the effects of SU4312 on rodent models of PD have not been characterized. In the current study, we found that the protection of SU4312 against 1-methyl-4-phenylpyridinium ion (MPP⁺)-induced neurotoxicity in PC12 cells was achieved through the activation of transcription factor myocyte enhancer factor 2D (MEF2D), as evidenced by the fact that SU4312 stimulated myocyte enhancer factor 2 (MEF2) transcriptional activity and prevented the inhibition of MEF2D protein expression caused by MPP⁺, and that short hairpin RNA (ShRNA)-mediated knockdown of MEF2D significantly abolished the neuroprotection of SU4312. Additionally, Western blotting analysis revealed that SU4312 potentiated pro-survival PI3-K/Akt pathway to down-regulate MEF2D inhibitor glycogen synthase kinase-3beta (GSK3β). Furthermore, using the in vivo PD model of C57BL/6 mice insulted with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), we found that intragastrical administration of SU4312 (0.2 and 1 mg/kg) greatly ameliorated Parkinsonian motor defects, and restored protein levels of MEF2D, phosphorylated-Ser473-Akt and phosphorylated-Ser9-GSK3β. Meanwhile, SU4312 effectively reversed the decrease in protein expression of tyrosine hydroxylase in substantia nigra pars compacta dopaminergic neurons, inhibited oxidative stress, maintained mitochondrial biogenesis and partially prevented the depletion of dopamine and its metabolites. Very encouragingly, SU4312 was able to selectively inhibit monoamine oxidase-B (MAO-B) activity both in vitro and in vivo, with an IC₅₀ value of 0.2 μM. These findings suggest that SU4312 provides therapeutic benefits in cellular and animal models of PD, possibly through multiple mechanisms including enhancement of MEF2D through the activation of PI3-K/Akt pathway, maintenance of mitochondrial biogenesis and inhibition of MAO-B activity. SU4312 thus may be an effective drug candidate for the prevention or even modification of the pathological processes of PD.

Mechanisms and Consequences of Dopamine Depletion-Induced Attenuation of the Spinophilin/Neurofilament Medium Interaction

Signaling changes that occur in the striatum following the loss of dopamine neurons in the Parkinson disease (PD) are poorly understood. While increases in the activity of kinases and decreases in the activity of phosphatases have been observed, the specific consequences of these changes are less well understood. Phosphatases, such as protein phosphatase 1 (PP1), are highly promiscuous and obtain substrate selectivity via targeting proteins. Spinophilin is the major PP1-targeting protein enriched in the postsynaptic density of striatal dendritic spines. Spinophilin association with PP1 is increased concurrent with decreases in PP1 activity in an animal model of PD. Using proteomic-based approaches, we observed dopamine depletion-induced decreases in spinophilin binding to multiple protein classes in the striatum. Specifically, there was a decrease in the association of spinophilin with neurofilament medium (NF-M) in dopamine-depleted striatum. Using a heterologous cell line, we determined that spinophilin binding to NF-M required overexpression of the catalytic subunit of protein kinase A and was decreased by cyclin-dependent protein kinase 5. Functionally, we demonstrate that spinophilin can decrease NF-M phosphorylation. Our data determine mechanisms that regulate, and putative consequences of, pathological changes in the association of spinophilin with NF-M that are observed in animal models of PD.

Calpain-2/p35-p25/Cdk5 pathway is involved in the neuronal apoptosis induced by polybrominated diphenyl ether-153

Polybrominated diphenyl ethers (PBDEs) have been demonstrated to induce neurotoxicity in experimental rats and mice, with neuronal apoptosis as one of the major mechanisms, however, the mechanisms underlying PBDEs-induced neuronal apoptosis remain unclear. In this study, we aimed to investigate the role of calpain/p35-p25/Cdk5 pathway in BDE-153-induced neuronal apoptosis in the hippocampus and primary neurons in rats. Results showed that compared to the controls, neuronal apoptosis was significantly increased in vivo and ex vivo, as manifested by the increased hippocampus TUNEL-positive cell rates, apoptotic neurons in Hoechst and AO/EB staining, and the increased LDH activity and percentage of Annexin V-positive cells in rat hippocampus and primary neurons. Calpain activity was significantly increased in all the BDE-153-treated groups in vivo and ex vivo when compared to non-treatment controls. In addition, we showed that calpain-2 accounted for the calpain activation instead of calpain-1, as demonstrated by the up-regulated mRNA and protein expressions in calpain-2 but not calpain-1. Activated calpain truncated p35 into p25, which resulted in the p25/Cdk5 formation and activation. Calpain inhibitor PD150606 or p25/Cdk5 inhibitor Roscovitine relieved neuronal apoptosis mainly via inhibiting the p25/Cdk5 activation. Overall, the findings suggested that calpain-2/p35-p25/Cdk5 pathway was involved in BDE-153-induced neuronal apoptosis, which provides novel insight into the mechanisms of PBDE neurotoxicity.

The role of Ca2+ signaling in Parkinson's disease

Across all kingdoms in the tree of life, calcium (Ca2+) is an essential element used by cells to respond and adapt to constantly changing environments. In multicellular organisms, it plays fundamental roles during fertilization, development and adulthood. The inability of cells to regulate Ca2+ can lead to pathological conditions that ultimately culminate in cell death. One such pathological condition is manifested in Parkinson's disease, the second most common neurological disorder in humans, which is characterized by the aggregation of the protein, α-synuclein. This Review discusses current evidence that implicates Ca2+ in the pathogenesis of Parkinson's disease. Understanding the mechanisms by which Ca2+ signaling contributes to the progression of this disease will be crucial for the development of effective therapies to combat this devastating neurological condition.

Neuroprotective Mechanisms Mediated by CDK5 Inhibition

Cyclin-dependent kinase 5 (CDK5) is a proline-directed serine/threonine kinase belonging to the family of cyclin-dependent kinases. In addition to maintaining the neuronal architecture, CDK5 plays an important role in the regulation of synaptic plasticity, neurotransmitter release, neuron migration and neurite outgrowth. Although various reports have shown links between neurodegeneration and deregulation of cyclin-dependent kinases, the specific role of CDK5 inhibition in causing neuroprotection in cases of neuronal insult or in neurodegenerative diseases is not wellunderstood. This article discusses current evidence for the involvement of CDK5 deregulation in neurodegenerative disorders and neurodegeneration associated with stroke through various mechanisms. These include upregulation of cyclin D1 and overactivation of CDK5 mediated neuronal cell death pathways, aberrant hyperphosphorylation of human tau proteins and/or neurofilament proteins, formation of neurofibrillary lesions, excitotoxicity, cytoskeletal disruption, motor neuron death (due to abnormally high levels of CDK5/p25) and colchicine- induced apoptosis in cerebellar granule neurons. A better understanding of the role of CDK5 inhibition in neuroprotective mechanisms will help scientists and researchers to develop selective, safe and efficacious pharmacological inhibitors of CDK5 for therapeutic use against human neurodegenerative disorders, such as Alzheimer's disease, amyotrophic lateral sclerosis and neuronal loss associated with stroke.

No synergism between bis(propyl)-cognitin and rasagiline on protecting dopaminergic neurons in Parkinson's disease mice

Rasagiline, a monoamine oxidase-B inhibitor, and bis(propyl)-cognitin (B3C), a novel dimer are reported to be neuroprotective. Herein, the synergistical neuroprotection produced by rasagiline and B3C was investigated in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mice of Parkinsonism. By using neurobehavioural tests, high-performance liquid chromatography and western blot assay, we showed that B3C at 0.3 mg/kg, rasagiline at 0.02 mg/kg, as well as co-treatment with B3C and rasagiline prevented MPTP-induced behavioural abnormities, increased the concentrations of dopamine and its metabolites in the striatum, and up-regulated the expression of tyrosine hydroxylase in the substantia nigra. However, the neuroprotective effects of co-treatment were not significantly improved when compared with those of B3C or rasagiline alone. Collectively, we have demonstrated that B3C at 0.3 mg/kg and rasagline at 0.02 mg/kg could not produce synergistic neuroprotective effects.

Melatonin attenuates MPTP-induced neurotoxicity via preventing CDK5-mediated autophagy and SNCA/α-synuclein aggregation

Autophagy is involved in the pathogenesis of neurodegenerative diseases including Parkinson disease (PD). However, little is known about the regulation of autophagy in neurodegenerative process. In this study, we characterized aberrant activation of autophagy induced by neurotoxin 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) and demonstrated that melatonin has a protective effect on neurotoxicity. We found an excessive activation of autophagy in monkey brain tissues and C6 cells, induced by MPTP, which is mediated by CDK5 (cyclin-dependent kinase 5). MPTP treatment significantly reduced total dendritic length and dendritic complexity of cultured primary cortical neurons and melatonin could reverse this effect. Decreased TH (tyrosine hydroxylase)-positive cells and dendrites of dopaminergic neurons in the substantia nigra pars compacta (SNc) were observed in MPTP-treated monkeys and mice. Along with decreased TH protein level, we observed an upregulation of CDK5 and enhanced autophagic activity in the striatum of mice with MPTP injection. These changes could be salvaged by melatonin treatment or knockdown of CDK5. Importantly, melatonin or knockdown of CDK5 reduced MPTP-induced SNCA/α-synuclein aggregation in mice, which is widely thought to trigger the pathogenesis of PD. Finally, melatonin or knockdown of CDK5 counteracted the PD phenotype in mice induced by MPTP. Our findings uncover a potent role of CDK5-mediated autophagy in the pathogenesis of PD, and suggest that control of autophagic pathways may provide an important clue for exploring potential target for novel therapeutics of PD.

TFP5 prevents 1-methyl-4-phenyl pyridine ion-induced neurotoxicity in mouse cortical neurons

The present study aimed to investigate the protective effect of a modified p5 peptide, TFP5, on 1-methyl-4-phenyl pyridine ion (MPP⁺)-induced neurotoxicity in cortical neurons and explore the therapeutic effect of TFP5 on Parkinson's disease (PD). MPP⁺ was applied to a primary culture of mouse cortical neurons to establish the cell model of PD. Neurons were divided into four groups: Control, model (MPP⁺), scrambled peptide (Scb) (Scb + MPP⁺) and TFP5 (TFP5 + MPP⁺) groups. Pretreatment with Scb or TFP5 was applied to the latter two groups, respectively, for 3 h, while phosphate-buffered saline was applied to the control and model groups. MPP⁺ was then applied to all groups, with the exception of the control group, and neurons were cultured for an additional 24 h. Neuron viability was evaluated using a Cell Counting kit-8 (CCK8) assay. To explore the mechanism underlying the protective effects of TFP5, the expression levels of p35, p25 and phosphorylated myocyte enhancer factor 2 (p-MEF2D) were determined by western blotting. Fluorescence microscopy showed that TFP5 was able to pass through cell membranes and distribute around the nucleus. CCK8 assay showed that neuronal apoptosis was dependent on MPP⁺ concentration and exposure time. Cell viability decreased significantly in the model group compared with the control group (55±7 vs. 100±0%; P<0.01), and increased significantly in the TFP5 group compared with the model group (98±2 vs. 55±5%; P<0.01) and Scb group (98±2 vs. 54±4%; P<0.01). Scb exhibited no protective effect. Western blotting results showed that MPP⁺ induced p25 and p-MEF2D expression, TFP5 and Scb did not affect MPP⁺-induced p25 expression, but TFP5 reduced MPP⁺-induced p-MEF2D expression. In summary, TFP5 protects against MPP⁺-induced neurotoxicity in mouse cortical neurons, possibly through inhibiting the MPP⁺-induced formation and elevated kinase activity of a cyclin-dependent kinase 5/p25 complex.

Cdk5/p25 specific inhibitory peptide TFP5 rescues the loss of dopaminergic neurons in a sub-acute MPTP induced PD mouse model

Parkinson's disease (PD) is pathologically characterized by progressively loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc) and the formation of Lewy bodies. In 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) induced PD mice models, the calpain- cyclin-dependent kinase 5 (Cdk5)-myocyte enhancer factor 2 (MEF2) signaling has been proven in governing dopaminergic neuronal death. Under MPTP insult, p35 is cleaved by calpain into p25, which binds to Cdk5 and exhibits hyperactivity of Cdk5/p25. Cdk5/p25 inactivates MEF2, a survivor factor, which is critical for DA neuronal death. In this study, neuroprotective effect of the Cdk5/p25 specific peptide, TFP5, was evaluated in sub-acute MPTP induced PD mouse model by intraperitoneal (i.p.) injection of MPTP for five consecutive days. The results indicated that the levels of p35 and p25, and p25/p35 ratio increased in the sub-acute MPTP mice. TFP5 broadly reached cortex neuron, hippocampus and SNpc areas after i.p. injections. Pretreatment with 45mg/kg/day TFP5, as well as 10mgkg/day Cdk5 inhibitor roscovitine, for three days significantly rescued DA neuronal loss up to 9.8% or 9.7% respectively compared to the saline treated group. Treatment of TFP5 and roscovitine reduced the levels of inactive form of MEF2 and cleaved caspase 3, thus protected apoptosis of DA neurons against MPTP insult. Our results propose that TFP5 might be a potential therapeutic candidate for PD.

Indirubin-3-Oxime Prevents H2O2-Induced Neuronal Apoptosis via Concurrently Inhibiting GSK3β and the ERK Pathway

Oxidative stress-induced neuronal apoptosis plays an important role in many neurodegenerative disorders. In this study, we have shown that indirubin-3-oxime, a derivative of indirubin originally designed for leukemia therapy, could prevent hydrogen peroxide (H₂O₂)-induced apoptosis in both SH-SY5Y cells and primary cerebellar granule neurons. H₂O₂ exposure led to the increased activities of glycogen synthase kinase 3β (GSK3β) and extracellular signal-regulated kinase (ERK) in SH-SY5Y cells. Indirubin-3-oxime treatment significantly reversed the altered activity of both the PI3-K/Akt/GSK3β cascade and the ERK pathway induced by H₂O₂. In addition, both GSK3β and mitogen-activated protein kinase inhibitors significantly prevented H₂O₂-induced neuronal apoptosis. Moreover, specific inhibitors of the phosphoinositide 3-kinase (PI3-K) abolished the neuroprotective effects of indirubin-3-oxime against H₂O₂-induced neuronal apoptosis. These results strongly suggest that indirubin-3-oxime prevents H₂O₂-induced apoptosis via concurrent inhibiting GSK3β and the ERK pathway in SH-SY5Y cells, providing support for the use of indirubin-3-oxime to treat neurodegenerative disorders caused or exacerbated by oxidative stress.

Multifunction of Chrysin in Parkinson's Model: Anti-Neuronal Apoptosis, Neuroprotection via Activation of MEF2D, and Inhibition of Monoamine Oxidase-B

Chrysin, a flavonoid compound existing in several plants, is applied as a dietary supplement because of its beneficial effects on general human health and alleviation of neurological disorders. However, mechanisms underlying neuroprotection of chrysin has not been fully elucidated, and the effects of chrysin on the Parkinson's disease (PD) model in vivo have not been investigated. It is here shown that chrysin protects primary granular neurons against 1-methyl-4-phenylpyridinium ion insult via antiapoptosis by reversing the dysregulated expression of Bcl-2, Bax, and caspase 3. The mechanisms also involved activating transcriptional factor myocyte enhancer factor 2D (MEF2D) via regulation of AKT-GSK3β signaling. In this in vivo model of PD, chrysin rescued the dopaminergic neurons loss and alleviated the decrease in dopamine level induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in mice. Moreover, chrysin markedly inhibited monoamine oxidase-B activity in vitro and in vivo. In conclusion, chrysin exerts beneficial effects to PD, possibly through multitarget mechanisms including antineuronal apoptosis, activation of the AKT-GSK3β/MEF2D pathway, and inhibition of the MAO-B activity.

TFP5/TP5 peptide provides neuroprotection in the MPTP model of Parkinson's disease

Cyclin-dependent kinase 5 (Cdk5) is a member of the serine-threonine kinase family of cyclin-dependent kinases. Cdk5 is critical to normal mammalian nervous system development and plays important regulatory roles in multiple cellular functions. Recent evidence indicates that Cdk5 is inappropriately activated in several neurodegenerative conditions, including Parkinson's disease (PD). PD is a chronic neurodegenerative disorder characterized by the loss of dopamine neurons in the substantia nigra, decreased striatal dopamine levels, and consequent extrapyramidal motor dysfunction. During neurotoxicity, p35 is cleaved to form p25. Binding of p25 with Cdk5 leads deregulation of Cdk5 resulting in number of neurodegenerative pathologies. To date, strategies to specifically inhibit Cdk5 hyperactivity have not been successful without affecting normal Cdk5 activity. Here we show that inhibition of p25/Cdk5 hyperactivation through TFP5/TP5, truncated 24-aa peptide derived from the Cdk5 activator p35 rescues nigrostriatal dopaminergic neurodegeneration induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP/MPP⁺) in a mouse model of PD. TP5 peptide treatment also blocked dopamine depletion in the striatum and improved gait dysfunction after MPTP administration. The neuroprotective effect of TFP5/TP5 peptide is also associated with marked reduction in neuroinflammation and apoptosis. Here we show inhibition of Cdk5/p25-hyperactivation by TFP5/TP5 peptide, which identifies Cdk5/p25 as a potential therapeutic target to reduce neurodegeneration in PD.

Chaperone-Mediated Autophagy and Mitochondrial Homeostasis in Parkinson's Disease

Parkinson's disease (PD), a complex neurodegenerative disorder, is pathologically characterized by the formation of Lewy bodies and loss of dopaminergic neurons in the substantia nigra pars compacta (SNc). Mitochondrial dysfunction is considered to be one of the most important causative mechanisms. In addition, dysfunction of chaperone-mediated autophagy (CMA), one of the lysosomal proteolytic pathways, has been shown to play an important role in the pathogenesis of PD. An exciting and important development is recent finding that CMA and mitochondrial quality control may be linked. This review summarizes the studies revealing the link between autophagy and mitochondrial function. Discussions are focused on the connections between CMA and mitochondrial failure and on the role of MEF2D, a neuronal survival factor, in mediating the regulation of mitochondria in the context of CMA. These new findings highlight the need to further explore the possibility of targeting the MEF2D-mitochondria-CMA network in both understanding the PD pathogenesis and developing novel therapeutic strategies.

Proteolytic degradation and potential role of onconeural protein cdr2 in neurodegeneration

Cerebellar degeneration-related protein 2 (cdr2) is expressed in the central nervous system, and its ectopic expression in tumor cells of patients with gynecological malignancies elicits immune responses by cdr2-specific autoantibodies and T lymphocytes, leading to neurological symptoms. However, little is known about the regulation and function of cdr2 in neurodegenerative diseases. Because we found that cdr2 is highly expressed in the midbrain, we investigated the role of cdr2 in experimental models of Parkinson's disease (PD). We found that cdr2 levels were significantly reduced after stereotaxic injection of 1-methyl-4-phenylpyridinium (MPP(+)) into the striatum. cdr2 levels were also decreased in the brains of post-mortem PD patients. Using primary cultures of mesencephalic neurons and MN9D cells, we confirmed that MPP(+) reduces cdr2 in tyrosine hydroxylase-positive dopaminergic neuronal cells. The MPP(+)-induced decrease of cdr2 was primarily caused by calpain- and ubiquitin proteasome system-mediated degradation, and cotreatment with pharmacological inhibitors of these enzymes or overexpression of calcium-binding protein rendered cells less vulnerable to MPP(+)-mediated cytotoxicity. Consequently, overexpression of cdr2 rescued cells from MPP(+)-induced cytotoxicity, whereas knockdown of cdr2 accelerated toxicity. Collectively, our findings provide insights into the novel regulatory mechanism and potentially protective role of onconeural protein during dopaminergic neurodegeneration.

Cdk5-Dependent Activation of Neuronal Inflammasomes in Parkinson's Disease

BACKGROUND

Inflammasomes, which mediate the activation of caspase-1 and maturation of IL-1β and IL-18, have been unambiguously verified to participate in many diseases, such as lung diseases, infectious diseases and Alzheimer's disease, but the relation between Parkinson's disease and inflammasomes is poorly understood.

METHODS

The expression, maturation, and secretion of inflammasomes in neurons were measured. The activation of inflammasomes in the substantia nigra of the brain was tested in acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and an α-synuclein transgenic mouse model. The levels of IL-1β and IL-18 in cerebrospinal fluid and serum samples of Parkinson's disease (PD) patients and control subjects were measured. The role of cyclin-dependent kinase 5 (Cdk5) in neuronal inflammasome activation was evaluated using the pharmacological Cdk5 inhibitor roscovitine or Cdk5-targeted deletion.

RESULTS

Here, we observed the expression of core molecules of inflammasomes, including NALP3, ASC, caspase-1, and IL-1β, in neuronal cells. The PD inducer rotenone could activate neuronal inflammasomes and promote the maturation and secretion of the cleaved IL-1β and IL-18 in a dose- and time-dependent manner. We also detected the activation of inflammasomes in the substantia nigra of a PD mouse model and in cerebrospinal fluid of PD patients. Furthermore, Cdk5 is required for the activation of inflammasomes, and both inhibition and deletion of Cdk5 could efficiently block inflammasome activation in PD models.

CONCLUSIONS

Together, our results indicated that Cdk5-dependent activation of neuronal inflammasomes was involved in the progression of PD.

Potential application of lithium in Parkinson's and other neurodegenerative diseases

Lithium, the long-standing hallmark treatment for bipolar disorder, has recently been identified as a potential neuroprotective agent in neurodegeneration. Here we focus on introducing numerous in vitro and in vivo studies that have shown lithium treatment to be efficacious in reducing oxidative stress and inflammation, increasing autophagy, inhibiting apoptosis, and decreasing the accumulation of α-synulcein, with an emphasis on Parkinson's disease. A number of biological pathways have been shown to be involved in causing these neuroprotective effects. The inhibition of GSK-3β has been the mechanism most studied; however, other modes of action include the regulation of apoptotic proteins and glutamate excitotoxicity as well as down-regulation of calpain. This review provides a framework of the neuroprotective effects of lithium in neurodegenerative diseases and the putative mechanisms by which lithium provides the protection. Lithium-only treatment may not be a suitable therapeutic option for neurodegenerative diseases due to inconsistent efficacy and potential side-effects, however, the use of low dose lithium in combination with other potential or existing therapeutic compounds may be a promising approach to reduce symptoms and disease progression in neurodegenerative diseases.

Cdk5 at crossroads of protein oligomerization in neurodegenerative diseases: facts and hypotheses

Cyclin-dependent kinase 5 (Cdk5) is involved in proper neurodevelopment and brain function and serves as a switch between neuronal survival and death. Overactivation of Cdk5 is associated with many neurodegenerative disorders such as Alzheimer's or Parkinson's diseases. It is believed that in those diseases Cdk5 may be an important link between disease-initiating factors and cell death effectors. A common hallmark of neurodegenerative disorders is incorrect folding of specific proteins, thus leading to their intra- and extracellular accumulation in the nervous system. Abnormal Cdk5 signaling contributes to dysfunction of individual proteins and has a substantial role in either direct or indirect interactions of proteins common to, and critical in, different neurodegenerative diseases. While the roles of Cdk5 in α-synuclein (ASN) - tau or β-amyloid peptide (Aβ) - tau interactions are well documented, its contribution to many other pertinent interactions, such as that of ASN with Aβ, or interactions of the Aβ - ASN - tau triad with prion proteins, did not get beyond plausible hypotheses and remains to be proven. Understanding of the exact position of Cdk5 in the deleterious feed-forward loop critical for development and progression of neurodegenerative diseases may help designing successful therapeutic strategies of several fatal neurodegenerative diseases. Cyclin-dependent kinase 5 (Cdk5) is associated with many neurodegenerative disorders such as Alzheimer's or Parkinson's diseases. It is believed that in those diseases Cdk5 may be an important factor involved in protein misfolding, toxicity and interaction. We suggest that Cdk5 may contribute to the vicious circle of neurotoxic events involved in the pathogenesis of different neurodegenerative diseases.

Peptide TFP5/TP5 derived from Cdk5 activator P35 provides neuroprotection in the MPTP model of Parkinson's disease

TFP5/TP5 rescues dopaminergic neurodegeneration induced by MPTP in a mouse model of Parkinson’s disease (PD). The neuroprotective effect of TFP5/TP5 peptide is also associated with marked reduction in neuroinflammation and apoptosis. Selective inhibition of Cdk5/p25 by TFP5/TP5 peptide identifies the kinase as a potential target to reduce neurodegeneration in PD.

Parkinson’s disease (PD) is a chronic neurodegenerative disorder characterized by the loss of dopamine neurons in the substantia nigra, decreased striatal dopamine levels, and consequent extrapyramidal motor dysfunction. Recent evidence indicates that cyclin-dependent kinase 5 (Cdk5) is inappropriately activated in several neurodegenerative conditions, including PD. To date, strategies to specifically inhibit Cdk5 hyperactivity have not been successful without affecting normal Cdk5 activity. Previously we reported that TFP5 peptide has neuroprotective effects in animal models of Alzheimer’s disease. Here we show that TFP5/TP5 selective inhibition of Cdk5/p25 hyperactivation in vivo and in vitro rescues nigrostriatal dopaminergic neurodegeneration induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP/MPP+) in a mouse model of PD. TP5 peptide treatment also blocked dopamine depletion in the striatum and improved gait dysfunction after MPTP administration. The neuroprotective effect of TFP5/TP5 peptide is also associated with marked reduction in neuroinflammation and apoptosis. Here we show selective inhibition of Cdk5/p25 ­hyperactivation by TFP5/TP5 peptide, which identifies the kinase as a potential therapeutic target to reduce neurodegeneration in Parkinson’s disease.