Death-Associated Protein Kinase 1 Phosphorylation in Neuronal Cell Death and Neurodegenerative Disease

Discovery and optimization of isoliquiritigenin as a death-associated protein kinase 1 inhibitor

Death-associated protein kinase 1 (DAPK1) is a phosphotransferase in the serine/threonine kinase family. Inhibiting DAPK1 is expected to be beneficial in treating Alzheimer's disease and protecting neuronal cells during cerebral ischemia. In this study, we demonstrated that the natural chalcone isoliquiritigenin inhibits DAPK1 in an ATP-competitive manner, and we synthesized halogen derivatives to amplify the inhibitory effect. Among the compounds tested, the chlorine, bromine, and iodine derivatives exhibited high DAPK1 inhibitory activity and binding affinity. Crystal structure analysis revealed that this improvement is attributable to the halogen atoms fitting well into the hydrophobic pocket formed by I77, L93, and I160. In particular, the chlorine derivative showed a significant enthalpic contribution to the interaction with DAPK1, suggesting its potential as a primary compound for new DAPK1 inhibitors.

Macrophage membrane‒biomimetic nanoparticles target inflammatory microenvironment for epilepsy treatment

Rationale: The clinical treatment of epilepsy is faced with challenges. On the one hand, the effectiveness of existing antiepileptic drugs (AEDs) is limited by the blood‒brain barrier (BBB); on the other hand, changes in the inflammatory microenvironment during epileptogenesis are often neglected. Methods: The death-associated protein kinase 1 inhibitor TC-DAPK6 and the fluorescent probe rhodamine B were encapsulated in hollow mesoporous silica nanocarriers (HMSNs), which were then coated with a macrophage membrane to prepare macrophage membrane-biomimetic nanoparticles, namely, MA@RT-HMSNs. In vitro biotoxicity, cellular uptake, BBB permeability and inflammatory targeting ability were evaluated in cells. The effects of MA@RT-HMSN treatment were explored by immunohistochemistry, TUNEL assay, Western blot analysis, quantitative real-time polymerase chain reaction, electroencephalogram recording and behavioural tests in kainic acid-induced acute and chronic epilepsy model mice. Results: MA@RT-HMSNs showed excellent biocompatibility both in vitro and in vivo. MA@RT-HMSNs successfully crossed the BBB and exhibited increased efficacy in targeted delivery of TC-DAPK6 to inflammatory lesions in epileptic foci. Macrophage membrane coating conferred MA@RT-HMSNs with higher stability, greater cellular uptake, and enhanced TC-DAPK6 bioavailability. Furthermore, MA@RT-HMSNs exerted beneficial therapeutic effects on acute and chronic epilepsy models by alleviating microenvironment inflammation, preventing neuronal death, and inhibiting neuronal excitability and gliosis. Conclusions: MA@RT-HMSNs target inflammatory foci to inhibit death-related protein kinase 1 and exert antiepileptic effects. This study provides a promising biomimetic nanodelivery system for targeted epilepsy therapy.

Targeting cis-p-tau and neuro-related gene expression in traumatic brain injury: therapeutic insights from TC-DAPK6 treatment in mice

BACKGROUND

Traumatic brain injury (TBI) is a significant global health concern and is characterized by brain dysfunction resulting from external physical forces, leading to brain pathology and neuropsychiatric disorders such as anxiety. This study investigates the effects of TC-DAPK6 on tau hyper-phosphorylation, gene expression, anxiety, and behavior impairment in the TBI mice model.

METHODS AND RESULTS

A weight drop model induced the TBI and the anxiety levels were evaluated using an elevated plus maze (EPM) test. TC-DAPK6 was intraperitoneally administered one-month post-TBI and continued for two months. The total cis-p-tau ratio in the brain was assessed using western blot and immunofluorescence staining. Molecular analysis was conducted on Aff2, Zkscan16, Kcna1, Pcdhac2, and Pcdhga8 to investigate the function and pathogenic role of TC-DAPK6 in neurological diseases in the cerebral cortex tissues of TBI-model mice, and the results were compared with TC-DAPK6 TBI-treatment group. The anxiety level and phosphorylation of tau protein in the TBI group were significantly increased compared to the sham groups and decreased substantially in the TBI-treatment group after TC-DAPK6 administration; the TBI group mostly spent their time with open arms. TC-DAPK6 decreased the expression level of genes as much as the sham group. Meanwhile, KCNA1 showed the highest fold of changes in the TBI and TBI-treatment groups.

CONCLUSIONS

The study demonstrates a clear association between cis-p-tau and neuro-related gene expression levels in TBI-induced mice. Targeting these pathways with DAPK1 inhibitors, shows promise for therapeutic interventions in TBI and related neurodegenerative disorders.

Is autism a PIN1 deficiency syndrome? A proposed etiological role for glyphosate

Autism is a neurodevelopmental disorder, the prevalence of which has increased dramatically in the United States over the past two decades. It is characterized by stereotyped behaviors and impairments in social interaction and communication. In this paper, we present evidence that autism can be viewed as a PIN1 deficiency syndrome. Peptidyl-prolyl cis/trans isomerase, NIMA-Interacting 1 (PIN1) is a peptidyl-prolyl cis/trans isomerase, and it has widespread influences in biological organisms. Broadly speaking, PIN1 deficiency is linked to many neurodegenerative diseases, whereas PIN1 over-expression is linked to cancer. Death-associated protein kinase 1 (DAPK1) strongly inhibits PIN1, and the hormone melatonin inhibits DAPK1. Melatonin deficiency is strongly linked to autism. It has recently been shown that glyphosate exposure to rats inhibits melatonin synthesis as a result of increased glutamate release from glial cells and increased expression of metabotropic glutamate receptors. Glyphosate's inhibition of melatonin leads to a reduction in PIN1 availability in neurons. In this paper, we show that PIN1 deficiency can explain many of the unique morphological features of autism, including increased dendritic spine density, missing or thin corpus callosum, and reduced bone density. We show how PIN1 deficiency disrupts the functioning of powerful high-level signaling molecules, such as nuclear factor erythroid 2-related factor 2 (NRF2) and p53. Dysregulation of both of these proteins has been linked to autism. Severe depletion of glutathione in the brain resulting from chronic exposure to oxidative stressors and extracellular glutamate leads to oxidation of the cysteine residue in PIN1, inactivating the protein and further contributing to PIN1 deficiency. Impaired autophagy leads to increased sensitivity of neurons to ferroptosis. It is imperative that further research be conducted to experimentally validate whether the mechanisms described here take place in response to chronic glyphosate exposure and whether this ultimately leads to autism.

DAPK1 mediates cognitive dysfunction and neuronal apoptosis in PSD rats through the ERK/CREB/BDNF signaling pathway

Post-stroke depression (PSD) is one of the most common mental sequelae after a stroke and can damage the brain. Although PSD has garnered increasing attention in recent years, the precise mechanism remains unclear. Studies have indicated that the expression of DAPK1 is elevated in various neurodegenerative conditions, including depression, ischemic stroke, and Alzheimer's disease. However, the specific molecular mechanism of DAPK1-mediated cognitive dysfunction and neuronal apoptosis in PSD rats is unclear. In this study, we established a rat model of PSD, and then assessed depression-like behaviors and cognitive dysfunction in rats using behavioral tests. In addition, we detected neuronal apoptosis and analyzed the expression of DAPK1 protein and proteins related to the ERK/CREB/BDNF signaling pathway. The findings revealed that MCAO combined with CUMS can induce more severe depression-like behaviors and cognitive dysfunction in rats, while overexpression of DAPK1 may hinder the downstream ERK/CREB/BDNF signaling pathways, resulting in neuronal loss and exacerbation of brain tissue damage. In this study, we will focus on DAPK1 and explore its role in PSD.

Mechanism of DAPK1 for Regulating Cancer Stem Cells in Thyroid Cancer

Death-associated protein kinase 1 (DAPK1) is a calcium/calmodulin (Ca2+/CaM)-dependent serine/threonine (Ser/Thr) protein kinase and is characteristically downregulated in metastatic cancer. Several studies showed that DAPK1 is involved in both the early and late stages of cancer. DAPK1 downregulation is elaborately controlled by epigenetic, transcriptional, posttranscriptional, and posttranslational processes. DAPK1 is known to regulate not only cancer cells but also stromal cells. Recent studies showed that DAPK1 was involved not only in tumor suppression but also in epithelial-mesenchymal transition (EMT) and cancer stem cell (CSC) formation in colon and thyroid cancers. CSCs are major factors in determining cancer aggressiveness in cancer metastasis and treatment prognosis by influencing EMT. However, the molecular mechanism involved in the regulation of cancer cells by DAPK1 remains unclear. In particular, little is known about the existence of CSCs and how they are regulated in papillary thyroid carcinoma (PTC) among thyroid cancers. In this review, we describe the molecular mechanism of CSC regulation by DAPK1 in PTC progression.

The role of serum/glucocorticoid-regulated kinase 1 in brain function following cerebral ischemia

Cardiopulmonary arrest (CA) is a major cause of death/disability in the U.S. with poor prognosis and survival rates. Current therapeutic challenges are physiologically complex because they involve hypoperfusion (decreased cerebral blood flow), neuroinflammation, and mitochondrial dysfunction. We previously discovered novel serum/glucocorticoid-regulated kinase 1 (SGK1) is highly expressed in brain of neurons that are susceptible to ischemia (hippocampus and cortex). We inhibited SGK1 and utilized pharmacological (specific inhibitor, GSK650394) and neuron-specific genetic approaches (shRNA) in rodent models of CA to determine if SGK1 is responsible for hypoperfusion, neuroinflammation, mitochondrial dysfunctional, and neurological deficits after CA. Inhibition of SGK1 alleviated cortical hypoperfusion and neuroinflammation (via Iba1, GFAP, and cytokine array). Treatment with GSK650394 enhanced mitochondrial function (via Seahorse respirometry) in the hippocampus 3 and 7 days after CA. Neuronal injury (via MAP2, dMBP, and Golgi staining) in the hippocampus and cortex was observed 7 days after CA but ameliorated with SGK1-shRNA. Moreover, SGK1 mediated neuronal injury by regulating the Ndrg1-SOX10 axis. Finally, animals subjected to CA exhibited learning/memory, motor, and anxiety deficits after CA, whereas SGK1 inhibition via SGK1-shRNA improved neurocognitive function. The present study suggests the fundamental roles of SGK1 in brain circulation and neuronal survival/death in cerebral ischemia-related diseases.

The underlying mechanism of calcium toxicity-induced autophagic cell death and lysosomal degradation in early stage of cerebral ischemia

Cerebral ischemia is the important cause of worldwide disability and mortality, that is one of the obstruction of blood vessels supplying to the brain. In early stage, glutamate excitotoxicity and high level of intracellular calcium (Ca2+) are the major processes which can promote many downstream signaling involving in neuronal death and brain tissue damaging. Moreover, autophagy, the reusing of damaged cell organelles, is affected in early ischemia. Under ischemic conditions, autophagy plays an important role to maintain energy of the brain and its function. In the other hand, over intracellular Ca2+ accumulation triggers excessive autophagic process and lysosomal degradation leading to autophagic process impairment which finally induce neuronal death. This article reviews the association between intracellular Ca2+ and autophagic process in acute stage of ischemic stroke.

Quantitative Proteomic and Phosphoproteomic Analyses Reveal a Role of Death-Associated Protein Kinase 1 in Regulating Hippocampal Synapse

Death-associated protein kinase 1 (DAPK1) is a stress-responsive calcium/calmodulin (CaM)-regulated serine/threonine protein kinase that is actively involved in stress-induced cell death. The dysregulation of DAPK1 has been established in various neurological disorders such as epilepsy, Alzheimer's disease (AD), and Parkinson's disease (PD). Recent research indicates a synaptic localization of DAPK1 in neurons, suggesting a potential role of DAPK1 in modulating synaptic structure and function. However, the key molecules and pathways underlying the influence of DAPK1 on synapses remain elusive. We utilized quantitative proteomic and phosphoproteomic analyses to compare the differences in protein expression and phosphorylation in hippocampal tissues of wild-type (WT) and DAPK1-knockout (KO) mice. Bioinformatic analysis of differentially expressed proteins and phosphoproteins revealed a preferential enrichment of proteins involved in regulating synaptic function, cytoskeletal structure, and neurotransmission. Gene set enrichment analysis (GESA) highlighted altered presynaptic functions including synaptic vesicle priming and glutamate secretion in KO mice. Besides, we observed that proteins with potential phosphorylation motifs of ERK and DAPK1 were overrepresented among the differential phosphoproteins and were highly enriched in neuronal function-related pathways. Furthermore, Western blot analysis validated differences in the expression of several proteins closely associated with presynaptic organization, dendrites and calcium transmembrane transport between KO and WT mice, further corroborating the potential involvement of DAPK1 in the regulation of synaptic functions. Overall, our data provide molecular evidence to elucidate the physiological links between DAPK1 and neuronal functions and help clarify the role of DAPK1 in the pathogenesis of neurodevelopmental and neurodegenerative diseases.

Caspase-dependent apoptosis in Riboflavin Transporter Deficiency iPSCs and derived motor neurons

Riboflavin Transporter Deficiency (RTD) is a rare genetic, childhood-onset disease. This pathology has a relevant neurological involvement, being characterized by motor symptoms, ponto-bulbar paralysis and sensorineural deafness. Such clinical presentation is associated with muscle weakness and motor neuron (MN) degeneration, so that RTD is considered part of the MN disease spectrum. Based on previous findings demonstrating energy dysmetabolism and mitochondrial impairment in RTD induced Pluripotent Stem cells (iPSCs) and iPSC-derived MNs, here we address the involvement of intrinsic apoptotic pathways in disease pathogenesis using these patient-specific in vitro models by combined ultrastructural and confocal analyses. We show impaired neuronal survival of RTD iPSCs and MNs. Focused Ion Beam/Scanning Electron Microscopy (FIB/SEM) documents severe alterations in patients' cells, including deranged mitochondrial ultrastructure, and altered plasma membrane and nuclear organization. Occurrence of aberrantly activated apoptosis is confirmed by immunofluorescence and TUNEL assays. Overall, our work provides evidence of a role played by mitochondrial dysfunction in RTD, and identifies neuronal apoptosis as a contributing event in disease pathogenesis, indicating intrinsic apoptosis pathways as possible relevant targets for more effective therapeutical approaches.

Death-associated protein kinase 1 as a therapeutic target for Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent form of dementia in the elderly and represents a major clinical challenge in the ageing society. Neuropathological hallmarks of AD include neurofibrillary tangles composed of hyperphosphorylated tau, senile plaques derived from the deposition of amyloid-β (Aβ) peptides, brain atrophy induced by neuronal loss, and synaptic dysfunctions. Death-associated protein kinase 1 (DAPK1) is ubiquitously expressed in the central nervous system. Dysregulation of DAPK1 has been shown to contribute to various neurological diseases including AD, ischemic stroke and Parkinson's disease (PD). We have established an upstream effect of DAPK1 on Aβ and tau pathologies and neuronal apoptosis through kinase-mediated protein phosphorylation, supporting a causal role of DAPK1 in the pathophysiology of AD. In this review, we summarize current knowledge about how DAPK1 is involved in various AD pathological changes including tau hyperphosphorylation, Aβ deposition, neuronal cell death and synaptic degeneration. The underlying molecular mechanisms of DAPK1 dysregulation in AD are discussed. We also review the recent progress regarding the development of novel DAPK1 modulators and their potential applications in AD intervention. These findings substantiate DAPK1 as a novel therapeutic target for the development of multifunctional disease-modifying treatments for AD and other neurological disorders.

Alzheimer's Disease and Cancer: Common Targets

There is growing epidemiologic evidence of an inverse association between cancer and AD. In addition, both cell survival and death are regulated by the same signaling pathways, and their abnormal regulation may be implicated in the occurrence and development of cancer and AD. Research shows that there may be a common molecular mechanism between cancer and AD. This review will discuss the role of GSK3, DAPK1, PP2A, P53 and CB2R in the pathogenesis of cancer and AD and describe the current research status of drug development based on these targets.

Unraveling the role of miRNAs in the diagnosis, progression, and therapeutic intervention of Parkinson's disease

Parkinson's disease (PD) is a debilitating neurological disorder characterized by the impairment of the motor system, resulting in symptoms such as resting tremor, cogwheel rigidity, bradykinesia, difficulty with gait, and postural instability. The occurrence of striatal dopamine insufficiency can be attributed to a notable decline in dopaminergic neurons inside the substantia nigra pars compacta. Additionally, the development of Lewy bodies serves as a pathological hallmark of PD. While current therapy approaches for PD aim to preserve dopaminergic neurons or replenish dopamine levels in the brain, it is important to acknowledge that achieving complete remission of the condition remains elusive. MicroRNAs (miRNAs, miR) are a class of small, non-coding ribonucleic acids involved in regulating gene expression at the post-transcriptional level. The miRNAs play a crucial part in the underlying pathogenic mechanisms of several neurodegenerative illnesses, including PD. The aim of this review is to explore the role of miRNAs in regulating genes associated with the onset and progression of PD, investigate the potential of miRNAs as a diagnostic tool, assess the effectiveness of targeting specific miRNAs as an alternative therapeutic strategy to impede disease advancement, and discuss the utilization of newly developed nanoparticles for delivering miRNAs as neurodegenerative therapies.

In Silico Prediction of Quercetin Analogs for Targeting Death-Associated Protein Kinase 1 (DAPK1) Against Alzheimer's Disease

Alzheimer's Disease (AD) is a progressive neurodegenerative disorder that greatly affects the health and life quality of the elderly population. Existing drugs mainly alleviate symptoms but fail to halt disease progression, underscoring the urgent need for the development of novel drugs. Based on the neuroprotective effects of flavonoid quercetin in AD, this study was designed to identify potential AD-related targets for quercetin and perform in silico prediction of promising analogs for the treatment of AD. Database mining suggested death-associated protein kinase 1 (DAPK1) as the most promising AD-related target for quercetin among seven protein candidates. To achieve better biological effects for the treatment of AD, we devised a series of quercetin analogs as ligands for DAPK1, and molecular docking analyses, absorption, distribution, metabolism, and excretion (ADME) predictions, as well as molecular dynamics (MD) simulations, were performed. The energy for drug-protein interaction was predicted and ranked. As a result, quercetin-A1a and quercetin-A1a1 out of 19 quercetin analogs exhibited the lowest interaction energy for binding to DAPK1 than quercetin, and they had similar dynamics performance with quercetin. In addition, quercetin-A1a and quercetin-A1a1 were predicted to have better water solubility. Thus, quercetin-A1a and quercetin-A1a1 could be promising agents for the treatment of AD. Our findings paved the way for further experimental studies and the development of novel drugs.

Tu-Xian Decoction ameliorates diabetic cognitive impairment by inhibiting DAPK-1

Tu-Xian decoction (TXD), a traditional Chinese medicine (TCM) formula, has been frequently administered to manage diabetic cognitive impairment (DCI). Despite its widespread use, the mechanisms underlying TXD's protective effects on DCI have yet to be fully elucidated. As a significant regulator in neurodegenerative conditions, death-associated protein kinase-1 (DAPK-1) serves as a focus for understanding the action of TXD. This study was designed to whether TXD mediates its beneficial outcomes by inhibiting DAPK-1. To this end, a diabetic model was established using Sprague-Dawley (SD) rats through a high-fat, high-sugar (HFHS) diet regimen, followed by streptozotocin (STZ) injection. The experimental cohort was stratified into six groups: Control, Diabetic, TC-DAPK6, high-dose TXD, medium-dose TXD, and low-dose TXD groups. Following a 12-week treatment period, various assessments-including blood glucose levels, body weight measurements, Morris water maze (MWM) testing for cognitive function, brain magnetic resonance imaging (MRI), and histological analyses using hematoxylin-eosin (H&E), and Nissl staining-were conducted. Protein expression in the hippocampus was quantified through Western blotting analysis. The results revealed that TXD significantly improved spatial learning and memory abilities, and preserved hippocampal structure in diabetic rats. Importantly, TXD administration led to a down-regulation of proteins indicative of neurological damage and suppressed DAPK-1 activity within the hippocampal region. These results underscore TXD's potential in mitigating DCIvia DAPK-1 inhibition, positioning it as a viable therapeutic candidate for addressing this condition. Further investigation into TXD's molecular mechanisms may elucidate new pathways for the treatment of DCI.

Suppression of DAPK1 reduces ischemic brain injury through inhibiting cell death signaling and promoting neural remodeling

The role of death-associated protein kinase1 (DAPK1) in post-stroke functional recovery is controversial, as is its mechanism of action and any neural remodeling effect after ischemia. To assess the debatable role of DAPK1, we established the middle cerebral artery occlusion (MCAo) model in DAPK1 knockout mice and Sprague-Dawley (SD) rats. We identified that the genetic deletion of the DAPK1 as well as pharmacological inhibition of DAPK1 showed reduced brain infarct volume and neurological deficit. We report that DAPK1 inhibition (DI) reduces post-stroke neuronal death by inhibiting BAX/BCL2 and LC3/Beclin1 mediated apoptosis and autophagy, respectively. Histological analysis displayed a reduction in nuclear condensation, neuronal dissociation, and degraded cytoplasm in the DI group. The DI treatment showed enhanced dendrite spine density and neurite outgrowth, upregulated neural proliferation marker proteins like brain-derived neurotrophic factor, and reduced structural abnormalities of the cortical pyramidal neurons. This research shows that DAPK1 drives cell death, its activation exacerbates functional recovery after cerebral ischemia and shows that oxazolone-based DI could be an excellent candidate for stroke and ischemic injury intervention.

Identification of potential death-associated protein kinase-1 (DAPK1) inhibitors by an integrated ligand-based and structure-based computational drug design approach

Death-associated protein kinase 1 (DAPK1) is a calcium/calmodulin (Ca2+/CaM)-dependent serine/threonine kinase that is abundantly expressed in the memory- and cognition-related brain areas. DAPK1 is associated with several pathological hallmarks of Alzheimer's disease (AD); it is an attractive target for designing a novel DAPK1 inhibitor as an effective therapeutic treatment for AD. In the present study, we have used an integrated ligand-based and structure-based drug design method to identify DAPK1 inhibitors. The pharmacophoric features of compound 38 G (PDB ID 4TXC) were mapped, and the models were evaluated using enrichment factor (EF) and goodness of hit (GH) score. The selected models were used to screen Zinc 15 compounds library. The identified hits were passed through drug-likeliness and PAINS filtering. The docking study was performed in three steps to yield molecules with good binding energy and ligand-target interactions. Finally, three hits were obtained, that is, ZINC000020648330, ZINC000006755051 and ZINC000020650468, which were subjected to rigorous molecular dynamics simulation. All three hits exhibited optimal stability under simulated conditions and low predicted toxicity.Communicated by Ramaswamy H. Sarma.

Death-associated protein kinase 1 phosphorylates MDM2 and inhibits its protein stability and function

Breast cancer is one of the major malignancies in women, and most related deaths are due to recurrence, drug resistance, and metastasis. The expression of the mouse double minute 2 (MDM2) oncogene is upregulated in breast cancer; however, its regulatory mechanism has yet to be fully elucidated. Herein, we identified the tumor suppressor death-associated protein kinase 1 (DAPK1) as a novel MDM2 regulator by unbiased peptide library screening. DAPK1 is directly bound to MDM2 and phosphorylates it at Thr419. DAPK1-mediated MDM2 phosphorylation promoted its protein degradation via the ubiquitin-proteasome pathway, resulting in upregulated p53 expression. DAPK1 overexpression, but not its kinase activity-deficient form, decreased colony formation and increased doxorubicin-induced cell death; however, DAPK1 knockdown produced the opposite effects in human breast cancer cells. In a xenograft tumorigenesis assay, DAPK1 overexpression significantly reduced tumor formation, whereas inhibition of DAPK1 kinase activity reduced its antitumorigenic effect. Finally, DAPK1 expression was negatively correlated with MDM2 levels in human breast cancer tissues. Thus, these results suggest that DAPK1-mediated MDM2 phosphorylation and its protein degradation may contribute to its antitumorigenic function in breast cancer.

Potential Implications of miRNAs in the Pathogenesis, Diagnosis, and Therapeutics of Alzheimer's Disease

Alzheimer's disease (AD) is a complex multifactorial disorder that poses a substantial burden on patients, caregivers, and society. Considering the increased aging population and life expectancy, the incidence of AD will continue to rise in the following decades. However, the molecular pathogenesis of AD remains controversial, superior blood-based biomarker candidates for early diagnosis are still lacking, and effective therapeutics to halt or slow disease progression are urgently needed. As powerful genetic regulators, microRNAs (miRNAs) are receiving increasing attention due to their implications in the initiation, development, and theranostics of various diseases, including AD. In this review, we summarize miRNAs that directly target microtubule-associated protein tau (MAPT), amyloid precursor protein (APP), and β-site APP-cleaving enzyme 1 (BACE1) transcripts and regulate the alternative splicing of tau and APP. We also discuss related kinases, such as glycogen synthase kinase (GSK)-3β, cyclin-dependent kinase 5 (CDK5), and death-associated protein kinase 1 (DAPK1), as well as apolipoprotein E, that are directly targeted by miRNAs to control tau phosphorylation and amyloidogenic APP processing leading to Aβ pathologies. Moreover, there is evidence of miRNA-mediated modulation of inflammation. Furthermore, circulating miRNAs in the serum or plasma of AD patients as noninvasive biomarkers with diagnostic potential are reviewed. In addition, miRNA-based therapeutics optimized with nanocarriers or exosomes as potential options for AD treatment are discussed.

Molecular Study of the Protective Effect of a Low-Carbohydrate, High-Fat Diet against Brain Insulin Resistance in an Animal Model of Metabolic Syndrome

Brain insulin resistance is linked to metabolic syndrome (MetS). A low-carbohydrate, high-fat (LCHF) diet has been proposed to have a protective effect. Therefore, this study aimed to investigate the brain insulin resistance markers in a rat animal model of MetS and the protective effects of the LCHF diet. Four groups of male rats (10/group) were created. Group I (Control) was fed a regular diet. Groups II-IV were injected with dexamethasone (DEX) to induce MetS. Group II received DEX with a regular diet. Group III (DEX + LCHF) rates were fed a low-carbohydrate, high-fat diet, while Group IV (DEX + HCLF) rats were fed a high-carbohydrate, low-fat (HCLF) diet. At the end of the four-week experiment, HOMA-IR was calculated. Moreover, cerebral gene expression analysis of S-100B, BDNF, TNF-α, IGF-1, IGF-1 R, IGFBP-2, IGFBP-5, Bax, Bcl-2, and caspase-3 was carried out. In the DEX group, rats showed a significant increase in the HOMA-IR and a decrease in the gene expression of IGF-1, IGF-1 R, IGFBP-2, IGFBP-5, BDNF, and Bcl2, with a concomitant rise in S100B, TNF-α, Bax, and caspase-3. The LCHF diet group showed a significantly opposite effect on all parameters. In conclusion, MetS is associated with dysregulated cerebral gene expression of BDNF, S100B, and TNF-α and disturbed IGF-1 signaling, with increased apoptosis and neuroinflammation. Moreover, the LCHF diet showed a protective effect, as evidenced by preservation of the investigated biochemical and molecular parameters.

Autophagy and mitophagy-related extracellular mitochondrial dysfunction of cerebrospinal fluid cells in patients with hemorrhagic moyamoya disease

We aimed to investigate whether mitochondrial dysfunction in extracellular cerebrospinal fluid (CSF), which is associated with autophagy and mitophagy, might be involved in neurological outcomes in adult patients with hemorrhagic moyamoya disease (MMD) whose pathogenesis related to poor outcomes is not well-known. CSF samples were collected from 43 adult MMD patients and analyzed according to outcomes at 3 months. Fluorescence-activated cell sorter analysis (FACS) and the JC-1 red/green ratio were used to assess mitochondrial cells and intact mitochondrial membrane potential (MMP). We performed quantitative real-time polymerase chain reaction and Western blotting analyses of autophagy and mitophagy-related markers, including HIF1α, ATG5, pBECN1, BECN1, BAX, BNIP3L, DAPK1, and PINK1. Finally, FACS analysis with specific fluorescence-conjugated antibodies was performed to evaluate the potential cellular origin of CSF mitochondrial cells. Twenty-seven females (62.8%) with a mean age of 47.4 ± 9.7 years were included in the study. Among 43 patients with hemorrhagic MMD, 23 (53.5%) had poor outcomes. The difference in MMP was evident between the two groups (2.4 ± 0.2 in patients with poor outcome vs. 3.5 ± 0.4 in patients with good outcome; p = 0.02). A significantly higher expression (2-ΔCt) of HIF1α, ATG5, DAPK1 followed by BAX and BNIP3L mRNA and protein was also observed in poor-outcome patients compared to those with good outcomes. Higher percentage of vWF-positive mitochondria, suggesting endothelial cell origins, was observed in patients with good outcome compared with those with poor outcome (25.0 ± 1.4% in patients with good outcome vs. 17.5 ± 1.5% in those with poor outcome; p < 0.01). We observed the association between increased mitochondrial dysfunction concomitant with autophagy and mitophagy in CSF cells and neurological outcomes in adult patients with hemorrhagic MMD. Further prospective multicenter studies are needed to determine whether it has a diagnostic value for risk prediction.

Mechanism of cAMP Response Element-binding Protein 1/Death-associated Protein Kinase 1 Axis-mediated Hippocampal Neuron Apoptosis in Rat Brain Injury After Cardiopulmonary Resuscitation

Brain injury represents a leading cause of deaths following cardiac arrest (CA) and cardiopulmonary resuscitation (CPR). This study explores the role of CREB1 (cAMP responsive element binding protein 1)/DAPK1 (death associated protein kinase 1) axis in brain injury after CPR. CA was induced by asphyxia in rats, followed by CPR. After CREB1 over-expression, the survival rate and neurological function score of rats were measured. Nissl and TUNEL staining evaluated the pathological condition of hippocampus and apoptosis of hippocampal neurons respectively. H19-7 cells were subjected to OGD/R and infected with oe-CREB1. CCK-8 assay and flow cytometry measured the cell viability and apoptosis. CREB1, DAPK1, and cleaved Caspase-3 expressions were examined using Western blot. The binding between CREB1 and DAPK1 was determined using ChIP and dual-luciferase reporter assays. CREB1 was poorly expressed while DAPK1 was highly expressed in rat hippocampus after CPR. CREB1 overexpression improved rat neurological function, repressed neuron apoptosis, and reduced cleaved Caspase-3 expression. CREB1 was enriched on the DAPK1 promoter and suppressed DAPK1 expression. DAPK1 overexpression reversed the inhibition of OGD/R-insulted apoptosis by CREB1 overexpression. To conclude, CREB1 suppresses hippocampal neuron apoptosis and mitigates brain injury after CPR by inhibiting DAPK1 expression.

Ablation of Death-Associated Protein Kinase 1 Changes the Transcriptomic Profile and Alters Neural-Related Pathways in the Brain

Death-associated protein kinase 1 (DAPK1), a Ca2+/calmodulin-dependent serine/threonine kinase, mediates various neuronal functions, including cell death. Abnormal upregulation of DAPK1 is observed in human patients with neurological diseases, such as Alzheimer’s disease (AD) and epilepsy. Ablation of DAPK1 expression and suppression of DAPK1 activity attenuates neuropathology and behavior impairments. However, whether DAPK1 regulates gene expression in the brain, and whether its gene profile is implicated in neuronal disorders, remains elusive. To reveal the function and pathogenic role of DAPK1 in neurological diseases in the brain, differential transcriptional profiling was performed in the brains of DAPK1 knockout (DAPK1-KO) mice compared with those of wild-type (WT) mice by RNA sequencing. We showed significantly altered genes in the cerebral cortex, hippocampus, brain stem, and cerebellum of both male and female DAPK1-KO mice compared to those in WT mice, respectively. The genes are implicated in multiple neural-related pathways, including: AD, Parkinson’s disease (PD), Huntington’s disease (HD), neurodegeneration, glutamatergic synapse, and GABAergic synapse pathways. Moreover, our findings imply that the potassium voltage-gated channel subfamily A member 1 (Kcna1) may be involved in the modulation of DAPK1 in epilepsy. Our study provides insight into the pathological role of DAPK1 in the regulatory networks in the brain and new therapeutic strategies for the treatment of neurological diseases.

Kinases control of regulated cell death revealing druggable targets for Parkinson's disease

Parkinson's disease (PD) is the second most prevalent neurodegenerative disorder in the world. Motor impairment seen in PD is associated with dopaminergic neurotoxicity in the striatum, and dopaminergic neuronal death in the substantia nigra pars compacta. Cell death has a significant effect on the development and progression of PD. Extensive research over the last few decades has unveiled new regulated cell death (RCD) mechanisms that are not dependent on apoptosis such as necroptosis, ferroptosis, and others. In this review, we will overview the mechanistic pathways of different types of RCD. Unlike accidental cell death, RCD subroutines can be regulated and the RCD-associated kinases are potential druggable targets. Hence, we will address an overview and analysis of different kinases regulating apoptosis such as receptor-interacting protein kinase 1 (RIPK-1), RIPK3, mixed lineage kinase (MLK), Ataxia telangiectasia muted (ATM), cyclin-dependent kinase (CDK), death-associated protein kinase 1 (DAPK1), Apoptosis-signaling kinase-1 (ASK-1), and Leucine-rich repeat kinase-2 (LRRK2). In addition to the role of RIPK1, RIPK3, and Mixed Lineage Kinase Domain like Pseudokinase (MLKL) in necroptosis. We also overview functions of AMP-kinase (AMPK), protein kinase C (PKC), RIPK3, and ATM in ferroptosis. We will recap the anti-apoptotic, anti-necroptotic, and anti-ferroptotic effects of different kinase inhibitors in different models of PD. Finally, we will discuss future challenges in the repositioning of kinase inhibitors in PD. In conclusion, this review kicks-start targeting RCD from a kinases perspective, opening novel therapeutic disease-modifying therapeutic avenues for PD.

Targeting Death-Associated Protein Kinases for Treatment of Human Diseases: Recent Advances and Future Directions

The death-associated protein kinase (DAPK) family is a member of the calcium/calmodulin-regulated serine/threonine protein kinase family, and studies have shown that its role, as its name suggests, is mainly to regulate cell death. The DAPK family comprises five members, including DAPK1, DAPK2, DAPK3, DRAK1 and DRAK2, which show high homology in the common N-terminal kinase domain but differ in the extra-catalytic domain. Notably, previous research has suggested that the DAPK family plays an essential role in both the development and regulation of human diseases. However, only a few small-molecule inhibitors have been reported. In this Perspective, we mainly discuss the structure, biological function, and role of DAPKs in diseases and the currently discovered small-molecule inhibitors, providing valuable information for the development of the DAPK field.

NMDA Receptor GluN2B Subunit Is Involved in Excitotoxicity Mediated by Death-Associated Protein Kinase 1 in Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is the most common form of neurodegenerative dementia among the elderly. Excitotoxicity has been implicated as playing a dominant role in AD, especially related to the hyperactivation of excitatory neurons. Death-associated protein kinase 1 (DAPK1) is a calcium/calmodulin-dependent kinase and involved in the pathogenesis of AD, but the roles and mechanisms of DAPK1 in excitotoxicity in AD are still uncertain.

OBJECTIVE

We mainly explored the underlying mechanisms of DAPK1 involved in the excitotoxicity of AD and its clinical relevance.

METHODS

Differentiated SH-SY5Y human neuroblastoma cells, PS1 V97 L transgenic mice, and human plasma samples were used. Protein expression was assayed by immunoblotting, and intracellular calcium and neuronal damage were analyzed by flow cytometry. Plasma DAPK1 was measured by ELISA.

RESULTS

We found that DAPK1 was activated after amyloid-β oligomers (AβOs) exposure in differentiated SH-SY5Y cells. Besides, we found the phosphorylation of GluN2B subunit at Ser1303 was increased, which contributing to excitotoxicity and Ca2+ overload in SH-SY5Y cells. Inhibiting DAPK1 activity, knockdown of DAPK1 expression, and antagonizing GluN2B subunits could effectively prevent AβOs-induced activation of GluN2B subunit, Ca2+ overload, and neuronal apoptosis. Additionally, we found that DAPK1 was elevated in the brain of AD transgenic mouse and in the plasma of AD patients.

CONCLUSION

Our finding will help to understand the mechanism of DAPK1 in the excitotoxicity in AD and provide a reference for the diagnosis and therapy of AD.

DYRK1A Inhibitors and Perspectives for the Treatment of Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is a chronic neurodegenerative disease and the most common form of dementia, especially in the elderly. Due to the increase in life expectancy, in recent years, there has been an excessive growth in the number of people affected by this disease, causing serious problems for health systems. In recent years, research has been intensified to find new therapeutic approaches that prevent the progression of the disease. In this sense, recent studies indicate that the dual-specificity tyrosine phosphorylation regulated kinase 1A (DYRK1A) gene, which is located on chromosome 21q22.2 and overexpressed in Down syndrome (DS), may play a significant role in developmental brain disorders and early onset neurodegeneration, neuronal loss and dementia in DS and AD. Inhibiting DYRK1A may serve to stop the phenotypic effects of its overexpression and, therefore, is a potential treatment strategy for the prevention of ageassociated neurodegeneration, including Alzheimer-type pathology.

OBJECTIVE

In this review, we investigate the contribution of DYRK1A inhibitors as potential anti-AD agents.

METHODS

A search in the literature to compile an in vitro dataset including IC50 values involving DYRK1A was performed from 2014 to the present day. In addition, we carried out structure-activity relationship studies based on in vitro and in silico data.

RESULTS

molecular modeling and enzyme kinetics studies indicate that DYRK1A may contribute to AD pathology through its proteolytic process, reducing its kinase specificity.

CONCLUSION

further evaluation of DYRK1A inhibitors may contribute to new therapeutic approaches for AD.

MiR-191-5p Attenuates Tau Phosphorylation, Aβ Generation, and Neuronal Cell Death by Regulating Death-Associated Protein Kinase 1

Dysregulation of microRNAs has been implicated in diverse diseases, including Alzheimer's disease (AD). MiR-191-5p in plasma/serum has been identified as a novel and promising noninvasive diagnostic biomarker for AD. However, whether miR-191-5p is involved in AD pathogenesis is largely unknown, and its levels in human AD brains are undetermined. Herein, we demonstrated that miR-191-5p downregulated tau phosphorylation at multiple AD-related sites and promoted neurite outgrowth using immunoblotting, immunofluorescence, and neurite outgrowth assays. Moreover, immunoblotting and enzyme-linked immunosorbent assays indicated that miR-191-5p decreased amyloid precursor protein phosphorylation levels and beta-amyloid (Aβ) generation. Furthermore, miR-191-5p reduced ceramide-induced neuronal cell death analyzed by trypan blue staining, the in situ cell death detection kit, and Annexin V-FITC/PI flow cytometry. Next, we verified that death-associated protein kinase 1 (DAPK1) was a direct target of miR-191-5p through the dual luciferase reporter assay and confirmed that the effects of miR-191-5p were antagonized by restoration of DAPK1 expression. Finally, the hippocampal miR-191-5p level was found to be decreased in humans with AD compared with controls and was inversely correlated with the DAPK1 expression level. Collectively, these findings suggest that miR-191-5p might exert inhibitory effects on tau phosphorylation, Aβ secretion, and neuronal cell death by directly targeting DAPK1, providing an attractive therapeutic option for AD.

Inhibition of Synaptic Glutamate Exocytosis and Prevention of Glutamate Neurotoxicity by Eupatilin from Artemisia argyi in the Rat Cortex

The inhibition of synaptic glutamate release to maintain glutamate homeostasis contributes to the alleviation of neuronal cell injury, and accumulating evidence suggests that natural products can repress glutamate levels and associated excitotoxicity. In this study, we investigated whether eupatilin, a constituent of Artemisia argyi, affected glutamate release in rat cortical nerve terminals (synaptosomes). Additionally, we evaluated the effect of eupatilin in an animal model of kainic acid (KA) excitotoxicity, particularly on the levels of glutamate and N-methyl-D-aspartate (NMDA) receptor subunits (GluN2A and GluN2B). We found that eupatilin decreased depolarization-evoked glutamate release from rat cortical synaptosomes and that this effect was accompanied by a reduction in cytosolic Ca2+ elevation, inhibition of P/Q-type Ca2+ channels, decreased synapsin I Ca2+-dependent phosphorylation and no detectable effect on the membrane potential. In a KA-induced glutamate excitotoxicity rat model, the administration of eupatilin before KA administration prevented neuronal cell degeneration, glutamate elevation, glutamate-generating enzyme glutaminase increase, excitatory amino acid transporter (EAAT) decrease, GluN2A protein decrease and GluN2B protein increase in the rat cortex. Taken together, the results suggest that eupatilin depresses glutamate exocytosis from cerebrocortical synaptosomes by decreasing P/Q-type Ca2+ channels and synapsin I phosphorylation and alleviates glutamate excitotoxicity caused by KA by preventing glutamatergic alterations in the rat cortex. Thus, this study suggests that eupatilin can be considered a potential therapeutic agent in the treatment of brain impairment associated with glutamate excitotoxicity.

miR-143-3p Inhibits Aberrant Tau Phosphorylation and Amyloidogenic Processing of APP by Directly Targeting DAPK1 in Alzheimer’s Disease

The neuropathology of Alzheimer’s disease (AD) is characterized by intracellular aggregation of hyperphosphorylated tau and extracellular accumulation of beta-amyloid (Aβ). Death-associated protein kinase 1 (DAPK1), as a novel therapeutic target, shows promise for the treatment of human AD, but the regulatory mechanisms of DAPK1 expression in AD remain unclear. In this study, we identified miR-143-3p as a promising candidate for targeting DAPK1. miR-143-3p directly bound to the 3′ untranslated region of human DAPK1 mRNA and inhibited its translation. miR-143-3p decreased tau phosphorylation and promoted neurite outgrowth and microtubule assembly. Moreover, miR-143-3p attenuated amyloid precursor protein (APP) phosphorylation and reduced the generation of Aβ40 and Aβ42. Furthermore, restoring DAPK1 expression with miR-143-3p antagonized the effects of miR-143-3p in attenuating tau hyperphosphorylation and Aβ production. In addition, the miR-143-3p levels were downregulated and correlated inversely with the expression of DAPK1 in the hippocampus of AD patients. Our results suggest that miR-143-3p might play critical roles in regulating both aberrant tau phosphorylation and amyloidogenic processing of APP by targeting DAPK1 and thus offer a potential novel therapeutic strategy for AD.

MicroRNA-124/Death-Associated Protein Kinase 1 Signaling Regulates Neuronal Apoptosis in Traumatic Brain Injury via Phosphorylating NR2B

Death-associated protein kinase 1 (DAPK1), a Ca²⁺/calmodulin-dependent serine/threonine-protein kinase, promotes neurons apoptosis in ischemic stroke and Alzheimer’s disease (AD). We hypothesized that knockdown DAPK1 may play a protective role in traumatic brain injury (TBI) and explore underlying molecular mechanisms. ELISA, Western blotting, immunofluorescence, dual-luciferase assay, and Reverse Transcription and quantitative Polymerase Chain Reaction (RT-qPCR) were used to determine the mechanism for the role of DAPK1 in TBI. Open field and novel objective recognition tests examined motor and memory functions. The morphology and number of synapses were observed by transmission electron microscopy and Golgi staining. DAPK1 was mainly found in neurons and significantly increased in TBI patients and TBI mice. The dual-luciferase assay showed that DAPK1 was upregulated by miR-124 loss. The number of TUNEL⁺ cells, expression levels of cleaved caspase3 and p-NR2B/NR2B were significantly reduced after knocking-down DAPK1 or overexpressing miR-124 in TBI mice; and motor and memory dysfunction was recovered. After Tat-NR2B were injected in TBI mice, pathological and behavioral changes were mitigated while the morphology while the number of synapses were not affected. Overall, DAPK1 is a downstream target gene of miR-124 that regulates neuronal apoptosis in TBI mice via NR2B. What’s more, DAPK1 restores motor and memory dysfunctions without affecting the number and morphology of synapses.

Regulation of DAPK1 by Natural Products: An Important Target in Treatment of Stroke

Stroke is a sudden neurological disorder that occurs due to impaired blood flow to an area of the brain. Stroke can be caused by the blockage or rupture of a blood vessel in the brain, called ischemic stroke and hemorrhagic stroke, respectively. Stroke is more common in men than women. Atrial fibrillation, hypertension, kidney disease, high cholesterol and lipids, genetic predisposition, inactivity, poor nutrition, diabetes mellitus, family history and smoking are factors that increase the risk of stroke. Restoring blood flow by repositioning blocked arteries using thrombolytic agents or endovascular therapy are the most effective treatments for stroke. However, restoring circulation after thrombolysis can cause fatal edema or intracranial hemorrhage, and worsen brain damage in a process known as ischemia-reperfusion injury. Therefore, there is a pressing need to find and develop more effective treatments for stroke. In the past, the first choice of treatment was based on natural compounds. Natural compounds are able to reduce the symptoms and reduce various diseases including stroke that attract the attention of the pharmaceutical industry. Nowadays, as a result of the numerous studies carried out in the field of herbal medicine, many useful and valuable effects of plants have been identified. The death-associated protein kinase (DAPK) family is one of the vital families of serine/threonine kinases involved in the regulation of some biological functions in human cells. DAPK1 is the most studied kinase within the DAPKs family as it is involved in neuronal and recovery processes. Dysregulation of DAPK1 in the brain is involved in the developing neurological diseases such as stroke. Natural products can function in a variety of ways, including reducing cerebral edema, reducing brain endothelial cell death, and inhibiting TNFα and interleukin-1β (IL-1β) through regulating the DAPK1 signal against stroke. Due to the role of DAPK1 in neurological disorders, the aim of this article was to investigate the role of DAPK1 in stroke and its modulation by natural compounds.

Blocking ERK-DAPK1 Axis Attenuates Glutamate Excitotoxicity in Epilepsy

Glutamate excitotoxicity induces neuronal cell death during epileptic seizures. Death-associated protein kinase 1 (DAPK1) expression is highly increased in the brains of epilepsy patients; however, the underlying mechanisms by which DAPK1 influences neuronal injury and its therapeutic effect on glutamate excitotoxicity have not been determined. We assessed multiple electroencephalograms and seizure grades and performed biochemical and cell death analyses with cellular and animal models. We applied small molecules and peptides and knocked out and mutated genes to evaluate the therapeutic efficacy of kainic acid (KA), an analog of glutamate-induced neuronal damage. KA administration increased DAPK1 activity by promoting its phosphorylation by activated extracellular signal-regulated kinase (ERK). DAPK1 activation increased seizure severity and neuronal cell death in mice. Selective ERK antagonist treatment, DAPK1 gene ablation, and uncoupling of DAPK1 and ERK peptides led to potent anti-seizure and anti-apoptotic effects in vitro and in vivo. Moreover, a DAPK1 phosphorylation-deficient mutant alleviated glutamate-induced neuronal apoptosis. These results provide novel insight into the pathogenesis of epilepsy and indicate that targeting DAPK1 may be a potential therapeutic strategy for treating epilepsy.

Circular RNA circTLK1 regulates dopaminergic neuron injury during Parkinson's disease by targeting miR-26a-5p／DAPK1

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative disorder that is featured by the elevated loss of substantia nigra pars compacta dopaminergic neurons and the disruption of motor functions. Aberrant expression of circular RNAs (circRNAs) is correlated with neurodegenerative diseases. This study aimed to explore the role of circTLK1 in PD pathology.

METHODS

MPTP-stimulated in vivo PD mouse model and MPP+ and rotenone-induced in vitro PD model were established to investigate the function of circTLK1/miR-26a-5p/DAPK1 axis during dopaminergic neuron injury. The motor function of mice was evaluated by using the Rotarod test. Brain tissue damage was checked by hematoxylin and eosin, TdT-mediated dUTP-biotin nick end labeling. Cell viability, apoptosis, and cytotoxicity were evaluated by cell counting kit 8 (CCK-8), flow cytometry, and LDH activity. The interaction between circTLK1 and miR-26a-5p as well as miR-26a-5p and DAPK1 was detected by luciferase reporter assay.

RESULTS

The expression of circTLK1 was notably elevated in in vitro and in vivo PD models. Knockdown of circTLK1 significantly improved cell viability, suppressed apoptosis and cytotoxicity, whereas inhibition of miR-16a-5p and overexpression of DAPK1 abolished these effects. MiR-26a-5p acts as a sponge of DAPK1 to mediate circTLK1 functions. Luciferase reporter gene assay confirmed the interaction between circTLK1 and miR-26a-5p as well as miR-26a-5p and DAPK1.

CONCLUSION

Depletion of circTLK1 mitigates dopaminergic neuron injury in vitro and in vivo, via releasing miR-26a-5p to target DAPK1 expression. Targeting circTLK1 may contribute to improving PD therapy.

Activation of TGR5 Ameliorates Streptozotocin-Induced Cognitive Impairment by Modulating Apoptosis, Neurogenesis, and Neuronal Firing

Takeda G protein-coupled receptor 5 (TGR5) is the first known G protein-coupled receptor specific for bile acids and is recognized as a new and critical target for type 2 diabetes and metabolic syndrome. It is expressed in many brain regions associated with memory such as the hippocampus and frontal cortex. Here, we hypothesize that activation of TGR5 may ameliorate streptozotocin- (STZ-) induced cognitive impairment. The mouse model of cognitive impairment was established by a single intracerebroventricular (ICV) injection of STZ (3.0 mg/kg), and we found that TGR5 activation by its agonist INT-777 (1.5 or 3.0 μg/mouse, ICV injection) ameliorated spatial memory impairment in the Morris water maze and Y-maze tests. Importantly, INT-777 reversed STZ-induced downregulation of TGR5 and glucose usage deficits. Our results further showed that INT-777 suppressed neuronal apoptosis and improved neurogenesis which were involved in tau phosphorylation and CREB-BDNF signaling. Moreover, INT-777 increased action potential firing of excitatory pyramidal neurons in the hippocampal CA3 and medial prefrontal cortex of ICV-STZ groups. Taken together, these findings reveal that activation of TGR5 has a neuroprotective effect against STZ-induced cognitive impairment by modulating apoptosis, neurogenesis, and neuronal firing in the brain and TGR5 might be a novel and potential target for Alzheimer's disease.

Unraveling the Roles of Protein Kinases in Autophagy: An Update on Small-Molecule Compounds for Targeted Therapy

Protein kinases, which catalyze the phosphorylation of proteins, are involved in several important cellular processes, such as autophagy. Of note, autophagy, originally described as a mechanism for intracellular waste disposal and recovery, has been becoming a crucial biological process closely related to many types of human diseases. More recently, the roles of protein kinases in autophagy have been gradually elucidated, and the design of small-molecule compounds to modulate targets to positively or negatively interfere with the cytoprotective autophagy or autophagy-associated cell death may provide a new clue on the current targeted therapy. Thus, in this Perspective, we focus on summarizing the different roles of protein kinases, including positive, negative, and bidirectional regulations of autophagy. Moreover, we discuss several small-molecule compounds targeting these protein kinases in human diseases, highlighting their pivotal roles in autophagy for targeted therapeutic purposes.

Neurodegenerative effect of DAPK1 after cerebral hypoxia-ischemia is associated with its post-transcriptional and signal transduction regulations: A systematic review and meta-analysis

Cerebral hypoxia-ischemia (CHI) causes brain aging, neurological disorders, cognitive decline, motor function impairment, and mortality. Inhibiting death-associated protein kinase 1 (DAPK1) has shown therapeutic potential against CHI, but several reports contradict its protective function, mechanism of activation, and signal transduction. Here, we systematically reviewed the role and the activation mechanism of DAPK1, and quantitatively assess the efficacy of DAPK1 inhibition (DI) methods in neuroprotection, following a CHI in animal models. Embase and PubMed were searched for relevant studies. Overall, 13 studies met the inclusion criteria, and the SYRCLE Risk of bias tool (RoB) tool was used to assess RoB. StataSE 16 was used for meta-analysis and network meta-analysis (NMA). Standardized mean differences (SMD) with 95% confidence intervals (CI) were calculated to estimate the effect size. DI was associated with the reduction of brain infarct volume (BIV) [SMD = -1.70, 95% CI (-2.10, -1.30); p = 0.00], neurological score (N.S.), neuronal degeneration, with no change in the level of in cell death [SMD = -0.83, 95% CI (-2.00, 0.35); p = 0.17], indicating the protective role of DI against CHI. No differences were found in DAPK1 mRNA and protein levels [SMD = 0.50, 95% CI (-0.05, 1.04); p = 0.07] {single-study driven; upregulated after exclusion (p = 0.01, I² = 36.43)}, whereas phospho-DAPK1 [SMD = -2.22, 95% CI (-3.69, -0.75); p = 0.00] was downregulated and phosphorylated myosin light chain [SMD = 3.37, 95% CI (2.51, 4.96); p = 0.00] was upregulated between CHI and sham groups. Furthermore, we performed NMA to understand the molecular level at which DI offers maximum protection against BIV. Post-transcriptional inhibition (PTI; SUCRA, 82.6%) and gene knockout showed best (KO; SUCRA, 81.3%), signal transduction inhibition (STI; SUCRA, 49.5%) offered 3^rd best, while catalytic activity inhibition (CAI; SUCRA, 0.3%) exhibited the lowest reduction in BIV against CHI. The results demonstrate that DI has a neuroprotective effect against CHI and DAPK1 might be regulated at the post-transcriptional and post-translational levels after CHI. Inhibiting DAPK1 at the post-transcriptional level and blocking multiple signal transduction pathways of DAPK1 could lead to better functional recovery against CHI. AVAILABILITY OF DATA AND MATERIALS: The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Chemotherapy Resistance: Role of Mitochondrial and Autophagic Components

Simple Summary

Chemotherapy resistance is a common occurrence during cancer treatment that cancer researchers are attempting to understand and overcome. Mitochondria are a crucial intracellular signaling core that are becoming important determinants of numerous aspects of cancer genesis and progression, such as metabolic reprogramming, metastatic capability, and chemotherapeutic resistance. Mitophagy, or selective autophagy of mitochondria, can influence both the efficacy of tumor chemotherapy and the degree of drug resistance. Regardless of the fact that mitochondria are well-known for coordinating ATP synthesis from cellular respiration in cellular bioenergetics, little is known its mitophagy regulation in chemoresistance. Recent advancements in mitochondrial research, mitophagy regulatory mechanisms, and their implications for our understanding of chemotherapy resistance are discussed in this review.

Abstract

Cancer chemotherapy resistance is one of the most critical obstacles in cancer therapy. One of the well-known mechanisms of chemotherapy resistance is the change in the mitochondrial death pathways which occur when cells are under stressful situations, such as chemotherapy. Mitophagy, or mitochondrial selective autophagy, is critical for cell quality control because it can efficiently break down, remove, and recycle defective or damaged mitochondria. As cancer cells use mitophagy to rapidly sweep away damaged mitochondria in order to mediate their own drug resistance, it influences the efficacy of tumor chemotherapy as well as the degree of drug resistance. Yet despite the importance of mitochondria and mitophagy in chemotherapy resistance, little is known about the precise mechanisms involved. As a consequence, identifying potential therapeutic targets by analyzing the signal pathways that govern mitophagy has become a vital research goal. In this paper, we review recent advances in mitochondrial research, mitophagy control mechanisms, and their implications for our understanding of chemotherapy resistance.

Combination of Stem Cells with Chinese Herbs for Secondary Depression in Neurodegenerative Diseases Based on Traditional Chinese Medicine Theories

Depression is a common secondary symptom in neurodegenerative diseases (NDs) caused by the loss of neurons and glial cells. Recent research focuses on stem cell therapy to replace dead nerve cells, but the low efficiency of stem cell differentiation and short survival time are obstacles limiting the therapy's effectiveness. Clinically, patients with different diseases cannot obtain the same effect by using the same cell therapy. However, traditional Chinese medicine (TCM) often uses syndrome differentiation to determine the treatment plan for NDs. Based on TCM syndrome differentiation and treatment, this article summarizes the advantages of Chinese herbal medicine combined with stem cell therapy, mainly for the effects of various herbs on diseases and stem cells, including prolonging the survival time of stem cells, resisting inflammation, and antidepressant-like effects. In particular, it analyzes the unique pathways of the influence of drugs and acupuncture on different therapies, seeking to clarify the scientific TCM system. This review mainly elaborates on the treatment of secondary depression in TCM and the advantages of a herbal combined stem cell therapy in various methods. We believe it can provide a new clinical concept for secondary depression to obtain good clinical effects and reduce the risks borne by patients.

Death-associated protein kinase 1 mediates Aβ42 aggregation-induced neuronal apoptosis and tau dysregulation in Alzheimer's disease

The aggregation of amyloid-β (Aβ) peptides into oligomers and fibrils is a key pathological feature of Alzheimer's disease (AD). An increasing amount of evidence suggests that oligomeric Aβ might be the major culprit responsible for various neuropathological changes in AD. Death-associated protein kinase 1 (DAPK1) is abnormally elevated in brains of AD patients and plays an important role in modulating tau homeostasis by regulating prolyl isomerase Pin1 phosphorylation. However, it remains elusive whether and how Aβ species influence the function of DAPK1, and whether this may further affect the function and phosphorylation of tau in neurons. Herein, we demonstrated that Aβ aggregates (both oligomers and fibrils) prepared from synthetic Aβ42 peptides were able to upregulate DAPK1 protein levels and thereby its function through heat shock protein 90 (HSP90)-mediated protein stabilization. DAPK1 activation not only caused neuronal apoptosis, but also phosphorylated Pin1 at the Ser71 residue, leading to tau accumulation and phosphorylation at multiple AD-related sites in primary neurons. Both DAPK1 knockout (KO) and the application of a specific DAPK1 inhibitor could effectively protect primary neurons against Aβ aggregate-induced cell death and tau dysregulation, corroborating the critical role of DAPK1 in mediating Aβ aggregation-induced neuronal damage. Our study suggests a mechanistic link between Aβ oligomerization and tau hyperphosphorylation mediated by DAPK1, and supports the role of DAPK1 as a promising target for early intervention in AD.

A brain proteomic signature of incipient Alzheimer's disease in young APOE ε4 carriers identifies novel drug targets

Aptamer-based proteomics revealed differentially abundant proteins in Alzheimer’s disease (AD) brains in the Baltimore Longitudinal Study of Aging and Religious Orders Study (mean age, 89 ± 9 years). A subset of these proteins was also differentially abundant in the brains of young APOE ε4 carriers relative to noncarriers (mean age, 39 ± 6 years). Several of these proteins represent targets of approved and experimental drugs for other indications and were validated using orthogonal methods in independent human brain tissue samples as well as in transgenic AD models. Using cell culture–based phenotypic assays, we showed that drugs targeting the cytokine transducer STAT3 and the Src family tyrosine kinases, YES1 and FYN, rescued molecular phenotypes relevant to AD pathogenesis. Our findings may accelerate the development of effective interventions targeting the earliest molecular triggers of AD.

Inhibition of Death-associated Protein Kinase 1 protects against Epileptic Seizures in mice

Epilepsy is a chronic encephalopathy and one of the most common neurological disorders. Death-associated protein kinase 1 (DAPK1) expression has been shown to be upregulated in the brains of human epilepsy patients compared with those of normal subjects. However, little is known about the impact of DAPK1 on epileptic seizure conditions. In this study, we aim to clarify whether and how DAPK1 is regulated in epilepsy and whether targeting DAPK1 expression or activity has a protective effect against epilepsy using seizure animal models. Here, we found that cortical and hippocampal DAPK1 activity but not DAPK1 expression was increased immediately after convulsive pentylenetetrazol (PTZ) exposure in mice. However, DAPK1 overexpression was found after chronic low-dose PTZ insults during the kindling paradigm. The suppression of DAPK1 expression by genetic knockout significantly reduced PTZ-induced seizure phenotypes and the development of kindled seizures. Moreover, pharmacological inhibition of DAPK1 activity exerted rapid antiepileptic effects in both acute and chronic epilepsy mouse models. Mechanistically, PTZ stimulated the phosphorylation of NR2B through DAPK1 activation. Combined together, these results suggest that DAPK1 regulation is a novel mechanism for the control of both acute and chronic epilepsy and provide new therapeutic strategies for the treatment of human epilepsy.

Inhibition of death-associated protein kinase 1 attenuates cis P-tau and neurodegeneration in traumatic brain injury

Traumatic brain injury (TBI) is the leading cause of mortality and disability in young people and may lead to the development of progressive neurodegeneration, such as that observed in chronic traumatic encephalopathy. We have recently found that the conformation-specific cis phosphorylated form of tau (cis P-tau) is a major early driver of neurodegeneration after TBI. However, not much is known about how cis P-tau is regulated in TBI. In this study, we demonstrated a novel critical role of death-associated protein kinase 1 (DAPK1) in regulating cis P-tau induction after TBI. We found that DAPK1 is significantly upregulated in mouse brains after TBI and subsequently promotes cis P-tau induction. Genetic deletion of DAPK1 in mice not only significantly decreases cis P-tau expression, but also effectively attenuates neuropathology development and rescues behavioral impairments after TBI. Mechanistically, DAPK1-mediated cis P-tau induction is regulated by the phosphorylation of Pin1 at Ser71, a unique prolyl isomerase known to control the conformational status of P-tau. Furthermore, pharmacological suppression of DAPK1 kinase activity dramatically decreases the levels of Pin1 phosphorylated at Ser71 as well as cis P-tau after neuronal stress. Thus, DAPK1 is a novel regulator of TBI that, in combination with its downstream targets, has a major impact on the development and/or outcome of TBI, and targeting DAPK1 might offer a potential therapeutic impact on TBI-related neurodegenerative diseases.

miR-214 Alleviates Ischemic Stroke-Induced Neuronal Death by Targeting DAPK1 in Mice

BACKGROUND

Ischemic stroke induces neuronal cell death and causes brain dysfunction. Preventing neuronal cell death after stroke is key to protecting the brain from stroke damage. Nevertheless, preventative measures and treatment strategies for stroke damage are scarce. Emerging evidence suggests that microRNAs (miRNAs) play critical roles in the pathogenesis of central nervous system (CNS) disorders and may serve as potential therapeutic targets.

METHODS

A photochemically induced thrombosis (PIT) mouse model was used as an ischemic stroke model. qRT-PCR was employed to assess changes in miRNAs in ischemic lesions of PIT-stroke mice and primary cultured neurons subjected to oxygen-glucose deprivation (OGD). 2,3,5-triphenyltetrazolium chloride (TTC) staining was performed to evaluate brain infarction tissues in vivo. TUNEL staining was employed to assess neuronal death in vitro. Neurological scores and motor coordination were investigated to evaluate stroke damage, including neurological deficits and motor function.

RESULTS

In vivo and in vitro results demonstrated that levels of miR-124 were significantly decreased following stroke, whereas changes in death-associated protein kinase 1 (DAPK1) levels exhibited the converse pattern. DAPK1 was identified as a direct target of miR-124. N-methyl-D-aspartate (NMDA) and OGD-induced neuronal death was rescued by miR-124 overexpression. Upregulation of miR-124 levels significantly improved PIT-stroke damage, including the overall neurological function in mice.

CONCLUSION

We demonstrate the involvement of the miR-124/DAPK1 pathway in ischemic neuronal death. Our results highlight the therapeutic potential of targeting this pathway for ischemic stroke.

DAPK1 Promotes Extrasynaptic GluN2B Phosphorylation and Striatal Spine Instability in the YAC128 Mouse Model of Huntington Disease

Huntington disease (HD) is a devastating neurodegenerative disorder caused by a CAG repeat expansion in the huntingtin gene. Disrupted cortico-striatal transmission is an early event that contributes to neuronal spine and synapse dysfunction primarily in striatal medium spiny neurons, the most vulnerable cell type in the disease, but also in neurons of other brain regions including the cortex. Although striatal and cortical neurons eventually degenerate, these synaptic and circuit changes may underlie some of the earliest motor, cognitive, and psychiatric symptoms. Moreover, synaptic dysfunction and spine loss are hypothesized to be therapeutically reversible before neuronal death occurs, and restoration of normal synaptic function may delay neurodegeneration. One of the earliest synaptic alterations to occur in HD mouse models is enhanced striatal extrasynaptic NMDA receptor expression and activity. This activity is mediated primarily through GluN2B subunit-containing receptors and is associated with increased activation of cell death pathways, inhibition of survival signaling, and greater susceptibility to excitotoxicity. Death-associated protein kinase 1 (DAPK1) is a pro-apoptotic kinase highly expressed in neurons during development. In the adult brain, DAPK1 becomes re-activated and recruited to extrasynaptic NMDAR complexes during neuronal death, where it phosphorylates GluN2B at S1303, amplifying toxic receptor function. Approaches to reduce DAPK1 activity have demonstrated benefit in animal models of stroke, Alzheimer's disease, Parkinson's disease, and chronic stress, indicating that DAPK1 may be a novel target for neuroprotection. Here, we demonstrate that dysregulation of DAPK1 occurs early in the YAC128 HD mouse model, and contributes to elevated extrasynaptic GluN2B S1303 phosphorylation. Inhibition of DAPK1 normalizes extrasynaptic GluN2B phosphorylation and surface expression, and completely prevents YAC128 striatal spine loss in cortico-striatal co-culture, thus validating DAPK1 as a potential target for synaptic protection in HD and warranting further development of DAPK1-targeted therapies for neurodegeneration.

Melatonin directly binds and inhibits death-associated protein kinase 1 function in Alzheimer's disease

Death-associated protein kinase 1 (DAPK1) is upregulated in the brains of human Alzheimer's disease (AD) patients compared with normal subjects, and aberrant DAPK1 regulation is implicated in the development of AD. However, little is known about whether and how DAPK1 function is regulated in AD. Here, we identified melatonin as a critical regulator of DAPK1 levels and function. Melatonin significantly decreases DAPK1 expression in a post-transcriptional manner in neuronal cell lines and mouse primary cortical neurons. Moreover, melatonin directly binds to DAPK1 and promotes its ubiquitination, resulting in increased DAPK1 protein degradation through a proteasome-dependent pathway. Furthermore, in tau-overexpressing mouse brain slices, melatonin treatment and the inhibition of DAPK1 kinase activity synergistically decrease tau phosphorylation at multiple sites related to AD. In addition, melatonin and DAPK1 inhibitor dramatically accelerate neurite outgrowth and increase the assembly of microtubules. Mechanistically, melatonin-mediated DAPK1 degradation increases the activity of Pin1, a prolyl isomerase known to play a protective role against tau hyperphosphorylation and tau-related pathologies. Finally, elevated DAPK1 expression shows a strong correlation with the decrease in melatonin levels in human AD brains. Combined, these results suggest that DAPK1 regulation by melatonin is a novel mechanism that controls tau phosphorylation and function and offers new therapeutic options for treating human AD.

Cellular Mechanisms of Melatonin: Insight from Neurodegenerative Diseases

Neurodegenerative diseases are the second most common cause of death and characterized by progressive impairments in movement or mental functioning in the central or peripheral nervous system. The prevention of neurodegenerative disorders has become an emerging public health challenge for our society. Melatonin, a pineal hormone, has various physiological functions in the brain, including regulating circadian rhythms, clearing free radicals, inhibiting biomolecular oxidation, and suppressing neuroinflammation. Cumulative evidence indicates that melatonin has a wide range of neuroprotective roles by regulating pathophysiological mechanisms and signaling pathways. Moreover, melatonin levels are decreased in patients with neurodegenerative diseases. In this review, we summarize current knowledge on the regulation, molecular mechanisms and biological functions of melatonin in neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis, vascular dementia and multiple sclerosis. We also discuss the clinical application of melatonin in neurodegenerative disorders. This information will lead to a better understanding of the regulation of melatonin in the brain and provide therapeutic options for the treatment of various neurodegenerative diseases.

Peptidyl-Prolyl Cis/Trans Isomerase Pin1 and Alzheimer's Disease

Alzheimer’s disease (AD) is the most common cause of dementia with cognitive decline. The neuropathology of AD is characterized by intracellular aggregation of neurofibrillary tangles consisting of hyperphosphorylated tau and extracellular deposition of senile plaques composed of beta-amyloid peptides derived from amyloid precursor protein (APP). The peptidyl-prolyl cis/trans isomerase Pin1 binds to phosphorylated serine or threonine residues preceding proline and regulates the biological functions of its substrates. Although Pin1 is tightly regulated under physiological conditions, Pin1 deregulation in the brain contributes to the development of neurodegenerative diseases, including AD. In this review, we discuss the expression and regulatory mechanisms of Pin1 in AD. We also focus on the molecular mechanisms by which Pin1 controls two major proteins, tau and APP, after phosphorylation and their signaling cascades. Moreover, the major impact of Pin1 deregulation on the progression of AD in animal models is discussed. This information will lead to a better understanding of Pin1 signaling pathways in the brain and may provide therapeutic options for the treatment of AD.

Protopanaxadiol ginsenoside Rd protects against NMDA receptor-mediated excitotoxicity by attenuating calcineurin-regulated DAPK1 activity

Neuroprotective strategies in the treatment of stroke have been attracting a great deal of attentions. Our previous clinical and basic studies have demonstrated that protopanaxadiol ginsenoside-Rd (Rd), a monomer compound extracted from Panax ginseng or Panax notoginseng, has neuroprotective effects against ischemic stroke, probably due to its ability to block Ca²⁺ overload, an usual consequence of the overactivation of NMDA receptor (NMDAR). As an extending study, we explored here whether Rd exerted its neuroprotection as a novel NMDAR blocker. Our whole-cell patch-clamp results showed that Rd reduced NMDAR currents of cultured rat cortical neurons (EC50 = 7.7 μM) dose-dependently by acting on extrasynaptic NMDAR NR2b subunit. However, unexpectedly, cell transfection and radioligand binding assays revealed that Rd did not bind to the NMDAR channel directly. Alternatively, it inhibited the phosphorylation of NR2b at Ser-1303, a target of death associated protein kinase 1 (DAPK1). Moreover, cell-based and cell-free enzymatic assays showed that Rd did not inhibit the activity of DAPK1 directly, but blocked the activity of calcineurin, a key phosphatase for activating DAPK1. Importantly, other protopanaxadiol ginsenosides were also found to have potential inhibitory effects on calcineurin activity. Furthermore, as expected, calcineurin inhibition by cyclosporin A could mimic Rd's effects and protect against NMDA-, oxygen glucose deprivation- or transient ischemic stroke-induced neuronal injury. Therefore, our present study provided the first evidence that Rd could exert an inhibitive effect on NMDAR-triggered currents and sequential excitotoxicity through mitigation of DAPK1-mediated NR2b phosphorylation by attenuating calcineurin activity.