p38 kinase is activated in the Alzheimer's disease brain

Tailoring MAPK Pathways: New Therapeutic Avenues for Treating Alzheimer's Disease

Alzheimer's disease (AD) is irreversible, progressive, and refractory in nature and is managed very poorly clinically due to very limited treatment outcomes. Unfortunately, most of the multiple clinical trials involving AD patients were unsuccessful in improving the disease prognosis. At the cellular level, many signaling pathways have been proposed to be involved in the sterile/refractory behavior of degenerating neurons in AD. Due to the involvement of p38MAPK in the pathogenesis of Alzheimer's disease, numerous investigations have attempted to determine the beneficial effects of MAPK targeting on memory, inflammatory programming of the brain, and synaptic plasticity. In view of this, various clinical trials involving several MAPK inhibitors (with good safety profiles and few side effects) have yielded positive results in AD patients, suggesting that MAPK targeting may be effective for reducing the pathogenesis of AD, but due to selectivity, dosing, and patient stratification, this aspect still needs further development. In view of their selectivity and off-target effects, only a few MAPK inhibitors have been employed in clinical trials against AD, indicating the scope of their development in this area. Therefore, this study focused on MAPK-based interventions as an upcoming and innovative approach for alleviating AD, with a special emphasis on clinical studies.

Going beyond ATP binding site as a novel inhibitor design strategy for tau protein kinases in the treatment of Alzheimer's disease: A review

Alzheimer's disease (AD) is among the top mortality causing diseases worldwide. The presence of extracellular β-amyloidosis, as well as intraneuronal neurofibrillary aggregates of the abnormally hyperphosphorylated tau protein are two major characteristics of AD. Targeting protein kinases that are involved in the disease pathways has been a common approach in the fight against AD. Unfortunately, most kinase inhibitors currently available target the adenosine triphosphate (ATP)- binding site, which has proven unsuccessful due to issues with selectivity and resistance. As a result, a pressing need to find other alternative sites beyond the ATP- binding site has profoundly evolved. In this review, we will showcase some case studies of inhibitors of tau protein kinases acting beyond ATP binding site which have shown promising results in alleviating AD.

Human Stress Response Specificity through Bioresonance Selectivity

In all eukaryotes, the mitogen activated protein kinase (MAPK) cascade, a multilayered interconnected network of enzymes, connects external stimuli to gene regulation, dictating cellular fate. However, mechanisms for encoding information in this complex, fluctuating network to activate specific responses remain elusive. Here, we demonstrate that the central human stress regulator protein p38 MAPK encodes information regarding experienced stresses as different frequency oscillations of its activation state. These oscillations are used to drive specific responses through frequency-dependent resonance of oscillating biochemical phosphorylation reactions between p38 and downstream targets. These interactions closely mirror those of electronic alternating current (AC) circuits and their components, providing a unique framework through which to understand signal transduction in the MAPK cascade. Finally, we demonstrate how this understanding of bioresonance allows us to induce specific genetic responses simply by exposing cells to sugar to force activation state oscillations of p38 at predetermined frequencies.

Therapeutic agents for Alzheimer's disease: a critical appraisal

Alzheimer's disease (AD) is the most common form of dementia. Mutations in genes and precursors of β amyloid (Aβ) are found in the familial form of the disease. This led to the evaluation of seven monoclonal antibodies against Aβ in subjects with AD, two of which were approved for use by the FDA. They caused only a small improvement in cognitive function, probably because they were given to those with much more prevalent sporadic forms of dementia. They also have potentially serious adverse effects. Oxidative stress and elevated pro-inflammatory cytokines are present in all subjects with AD and are well correlated with the degree of memory impairment. Drugs that affect these processes include TNFα blocking antibodies and MAPK p38 inhibitors that reduce cognitive impairment when given for other inflammatory conditions. However, their adverse effects and inability to penetrate the brain preclude their use for dementia. Rosiglitazone is used to treat diabetes, a risk factor for AD, but failed in a clinical trial because it was given to subjects that already had dementia. Ladostigil reduces oxidative stress and suppresses the release of pro-inflammatory cytokines from activated microglia without blocking their effects. Chronic oral administration to aging rats prevented the decline in memory and suppressed overexpression of genes adversely affecting synaptic function in relevant brain regions. In a phase 2 trial, ladostigil reduced the decline in short-term memory and in whole brain and hippocampal volumes in human subjects with mild cognitive impairment and had no more adverse effects than placebo.

Inhibition of the P38 MAPK/NLRP3 pathway mitigates cognitive dysfunction and mood alterations in aged mice after abdominal surgery plus sevoflurane

BACKGROUND

Cognitive dysfunction, encompassing perioperative psychological distress and cognitive impairment, is a prevalent postoperative complication within the elderly population, and in severe cases, it may lead to dementia. Building upon our prior research that unveiled a connection between postoperative mood fluctuations and cognitive dysfunction with the phosphorylation of P38, this present investigation aims to delve deeper into the involvement of the P38 MAPK/NLRP3 pathway in perioperative neurocognitive disorders (PND) in an abdominal exploratory laparotomy (AEL) aged mice model.

METHODS

C57BL/6 mice (male, 18-month-old) underwent AEL with 3 % anesthesia. Then, inhibitors targeting P38 MAPK (SB202190, 1 mg/kg) and GSK3β (TWS119, 10 mg/kg) were administered multiple times daily for 7 days post-surgery. The NLRP3-cKO AEL and WT AEL groups only underwent the AEL procedure. Behavioral assessments, including the open field test (OFT), novel object recognition (NOR), force swimming test (FST), and fear conditioning (FC), were initiated on postoperative day 14. Additionally, mice designated for neuroelectrophysiological monitoring had electrodes implanted on day 14 before surgery and underwent novel object recognition while their local field potential (LFP) was concurrently recorded on postoperative day 14. Lastly, after they were euthanasized, pathological analysis and western blot were performed.

RESULTS

SB202190, TWS119, and astrocyte-conditional knockout NLRP3 all ameliorated the cognitive impairment behaviors induced by AEL in mice and increased mean theta power during novel location exploration. However, it is worth noting that SB202190 may exacerbate postoperative depressive and anxiety-like behaviors in mice, while TWS119 may induce impulsive behaviors.

CONCLUSIONS

Our study suggests that anesthesia and surgical procedures induce alterations in mood and cognition, which may be intricately linked to the P38 MAPK/NLRP3 pathway.

Evolving significance of kinase inhibitors in the management of Alzheimer's disease

Alzheimer's disease is a neurodegenerative problem with progressive loss of memory and other cognitive function disorders resulting in the imbalance of neurotransmitter activity and signaling progression, which poses the need of the potential therapeutic target to improve the intracellular signaling cascade brought by kinases. Protein kinase plays a significant and multifaceted role in the treatment of Alzheimer's disease, by targeting pathological mechanisms like tau hyperphosphorylation, neuroinflammation, amyloid-beta production and synaptic dysfunction. In this review, we thoroughly explore the essential protein kinases involved in Alzheimer's disease, detailing their physiological roles, regulatory impacts, and the newest inhibitors and compounds that are progressing into clinical trials. All the findings of studies exhibited the promising role of kinase inhibitors in the management of Alzheimer's disease. However, it still poses the need of addressing current challenges and opportunities involved with this disorder for the future perspective of kinase inhibitors in the management of Alzheimer's disease. Further study includes the development of biomarkers, combination therapy, and next-generation kinase inhibitors with increased potency and selectivity for its future prospects.

p38α Mitogen-Activated Protein Kinase-An Emerging Drug Target for the Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder, characterized by the formation of amyloid β and tau protein aggregates in the brain, neuroinflammation, impaired cholinergic neurotransmission, and oxidative stress, resulting in the gradual loss of neurons and neuronal function, which leads to cognitive and memory deficits in AD patients. Chronic neuroinflammation plays a particularly important role in the progression of AD since the excessive release of proinflammatory cytokines from glial cells (microglia and astrocytes) induces neuronal damage, which subsequently causes microglial activation, thus facilitating further neurodegenerative changes. Mitogen-activated protein kinase (MAPK) p38α is one of the key enzymes involved in the control of innate immune response. The increased activation of the p38α MAPK pathway, observed in AD, has been for a long time associated not only with the maintenance of excessive inflammatory process but is also linked with pathophysiological hallmarks of this disease, and therefore is currently considered an attractive drug target for novel AD therapeutics. This review aims to summarize the current state of knowledge about the involvement of p38α MAPK in different aspects of AD pathophysiology and also provides insight into the possible therapeutic effects of novel p38α MAPK inhibitors, which are currently studied as potential drug candidates for AD treatment.

Naringenin ameliorates amyloid-β pathology and neuroinflammation in Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia characterized by amyloid-β (Aβ) deposition, tau hyperphosphorylation, and neuroinflammation. Naringenin (NRG), a natural flavonoid widely present in citrus fruits, has been reported can penetrate the blood-brain barrier and exert anti-inflammatory effects in the central nervous system. Here, we investigate the protective effects of long-term NRG treatment on AD. The novel object recognition test and Morris water maze test reveal that NRG treatment can improve the learning and memory ability of APP/PS1 mice. Besides, we find that NRG can significantly reduce Aβ deposition, microglial and astrocytic activation, and pro-inflammatory cytokine levels in APP/PS1 mice. Results further show that NRG effectively decreases pro-inflammatory cytokines in LPS/Aβ-stimulated BV2 cells. Lastly, the molecular mechanistic study reveals that NRG attenuates neuroinflammatory responses via inhibition of the MAPK signaling pathway in vivo and in vitro. Overall, NRG may emerge as a promising compound for the prevention and treatment of AD.

Apoptosis signal-regulating kinase 1 promotes inflammation in senescence and aging

Cellular senescence is a stress-induced, permanent cell cycle arrest involved in tumor suppression and aging. Senescent cells secrete bioactive molecules such as pro-inflammatory cytokines and chemokines. This senescence-associated secretory phenotype (SASP) has been implicated in immune-mediated elimination of senescent cells and age-associated chronic inflammation. However, the mechanisms regulating the SASP are incompletely understood. Here, we show that the stress-responsive kinase apoptosis signal-regulating kinase 1 (ASK1) promotes inflammation in senescence and aging. ASK1 is activated during senescence and increases the expression of pro-inflammatory cytokines and chemokines by activating p38, a kinase critical for the SASP. ASK1-deficient mice show impaired elimination of oncogene-induced senescent cells and an increased rate of tumorigenesis. Furthermore, ASK1 deficiency prevents age-associated p38 activation and inflammation and attenuates glomerulosclerosis. Our results suggest that ASK1 is a driver of the SASP and age-associated chronic inflammation and represents a potential therapeutic target for age-related diseases.

Somatostatin and the pathophysiology of Alzheimer's disease

Among the central features of Alzheimer's disease (AD) progression are altered levels of the neuropeptide somatostatin (SST), and the colocalisation of SST-positive interneurons (SST-INs) with amyloid-β plaques, leading to cell death. In this theoretical review, I propose a molecular model for the pathogenesis of AD based on SST-IN hypofunction and hyperactivity. Namely, hypofunctional and hyperactive SST-INs struggle to control hyperactivity in medial regions in early stages, leading to axonal Aβ production through excessive presynaptic GABAB inhibition, GABAB1a/APP complex downregulation and internalisation. Concomitantly, excessive SST-14 release accumulates near SST-INs in the form of amyloids, which bind to Aβ to form toxic mixed oligomers. This leads to differential SST-IN death through excitotoxicity, further disinhibition, SST deficits, and increased Aβ release, fibrillation and plaque formation. Aβ plaques, hyperactive networks and SST-IN distributions thereby tightly overlap in the brain. Conversely, chronic stimulation of postsynaptic SST2/4 on gulutamatergic neurons by hyperactive SST-INs promotes intense Mitogen-Activated Protein Kinase (MAPK) p38 activity, leading to somatodendritic p-tau staining and apoptosis/neurodegeneration - in agreement with a near complete overlap between p38 and neurofibrillary tangles. This model is suitable to explain some of the principal risk factors and markers of AD progression, including mitochondrial dysfunction, APOE4 genotype, sex-dependent vulnerability, overactive glial cells, dystrophic neurites, synaptic/spine losses, inter alia. Finally, the model can also shed light on qualitative aspects of AD neuropsychology, especially within the domains of spatial and declarative (episodic, semantic) memory, under an overlying pattern of contextual indiscrimination, ensemble instability, interference and generalisation.

Role of Metalloproteinases in Diabetes-associated Mild Cognitive Impairment

Diabetes has been linked to an increased risk of mild cognitive impairment (MCI), a condition characterized by a subtle cognitive decline that may precede the development of dementia. The underlying mechanisms connecting diabetes and MCI involve complex interactions between metabolic dysregulation, inflammation, and neurodegeneration. A critical mechanism implicated in diabetes and MCI is the activation of inflammatory pathways. Chronic low-grade inflammation, as observed in diabetes, can lead to the production of pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), interleukin-1 beta (IL-1β), and interferon-gamma (IFNγ), each of which can exacerbate neuroinflammation and contribute to cognitive decline. A crucial enzyme involved in regulating inflammation is ADAM17, a disintegrin, and metalloproteinase, which can cleave and release TNF-α from its membrane-bound precursor and cause it to become activated. These processes, in turn, activate additional inflammation-related pathways, such as AKT, NF-κB, NLP3, MAPK, and JAK-STAT pathways. Recent research has provided novel insights into the role of ADAM17 in diabetes and neurodegenerative diseases. ADAM17 is upregulated in both diabetes and Alzheimer's disease, suggesting a shared mechanism and implicating inflammation as a possible contributor to much broader forms of pathology and pointing to a possible link between inflammation and the emergence of MCI. This review provides an overview of the different roles of ADAM17 in diabetes-associated mild cognitive impairment diseases. It identifies mechanistic connections through which ADAM17 and associated pathways may influence the emergence of mild cognitive impairment.

Inflammatory signaling pathways in the treatment of Alzheimer's disease with inhibitors, natural products and metabolites (Review)

The intricate nature of Alzheimer's disease (AD) pathogenesis poses a persistent obstacle to drug development. In recent times, neuroinflammation has emerged as a crucial pathogenic mechanism of AD, and the targeting of inflammation has become a viable approach for the prevention and management of AD. The present study conducted a comprehensive review of the literature between October 2012 and October 2022, identifying a total of 96 references, encompassing 91 distinct pharmaceuticals that have been investigated for their potential impact on AD by inhibiting neuroinflammation. Research has shown that pharmaceuticals have the potential to ameliorate AD by reducing neuroinflammation mainly through regulating inflammatory signaling pathways such as NF‑κB, MAPK, NLRP3, PPARs, STAT3, CREB, PI3K/Akt, Nrf2 and their respective signaling pathways. Among them, tanshinone IIA has been extensively studied for its anti‑inflammatory effects, which have shown significant pharmacological properties and can be applied clinically. Thus, it may hold promise as an effective drug for the treatment of AD. The present review elucidated the inflammatory signaling pathways of pharmaceuticals that have been investigated for their therapeutic efficacy in AD and elucidates their underlying mechanisms. This underscores the auspicious potential of pharmaceuticals in ameliorating AD by impeding neuroinflammation.

Research on the Chemical Constituents against Alzheimer's Disease of the Fruits of Physalis alkekengi L. var. franchetii (Mast.) Makino

Physalis alkekengi L. var. franchetii (Mast.) Makino (PA) is a natural plant which is utilised as a traditional herbal medicine. It has properties that make it effective against inflammation and free radical damage. In the present study, the major constituents of four extraction parts of the fruits of PA (PAF) were investigated by combining ultra-performance liquid chromatography with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS). The mice model of Alzheimer's disease (AD) induced by aluminum chloride (AlCl3 ) combined with D-galactose (D-gal) was established to comprehend the mechanism behind PAF's anti-AD activity from both behavioural and pathological perspectives. The results showed that four extraction parts of PAF (PAFE) had favorable anti-AD effects and the ethyl acetate (EA) group showed the best activity. UPLC-Q-TOF-MS analysis identified Physalin B, Nobiletin and Caffeic acid as the main anti-AD active constituents in EA extract. This study reveals that PAF can reduce neuroinflammatory damage by inhibiting p38 mitogen-activated protein kinase (p38 MAPK) signaling pathway, which is the theoretical basis for clinical development and utilization of PAF in AD therapy.

The S1P receptor 1 antagonist Ponesimod reduces TLR4-induced neuroinflammation and increases Aβ clearance in 5XFAD mice

BACKGROUND

Previously, we showed that the sphingosine-1-phosphate (S1P) transporter spinster 2 (Spns2) mediates activation of microglia in response to amyloid β peptide (Aβ). Here, we investigated if Ponesimod, a functional S1P receptor 1 (S1PR1) antagonist, prevents Aβ-induced activation of glial cells and Alzheimer's disease (AD) pathology.

METHODS

We used primary cultures of glial cells and the 5XFAD mouse model to determine the effect of Aβ and Ponesimod on glial activation, Aβ phagocytosis, cytokine levels and pro-inflammatory signaling pathways, AD pathology, and cognitive performance.

FINDINGS

Aβ42 increased the levels of TLR4 and S1PR1, leading to their complex formation. Ponesimod prevented the increase in TLR4 and S1PR1 levels, as well as the formation of their complex. It also reduced the activation of the pro-inflammatory Stat1 and p38 MAPK signaling pathways, while activating the anti-inflammatory Stat6 pathway. This was consistent with increased phagocytosis of Aβ42 in primary cultured microglia. In 5XFAD mice, Ponesimod decreased the levels of TNF-α and CXCL10, which activate TLR4 and Stat1. It also increased the level of IL-33, an anti-inflammatory cytokine that promotes Aβ42 phagocytosis by microglia. As a result of these changes, Ponesimod decreased the number of Iba-1+ microglia and GFAP+ astrocytes, and the size and number of amyloid plaques, while improving spatial memory as measured in a Y-maze test.

INTERPRETATION

Ponesimod targeting S1PR1 is a promising therapeutic approach to reprogram microglia, reduce neuroinflammation, and increase Aβ clearance in AD.

FUNDING

NIHR01AG064234, RF1AG078338, R21AG078601, VAI01BX003643.

Rapid degeneration of iPSC-derived motor neurons lacking Gdap1 engages a mitochondrial-sustained innate immune response

Charcot-Marie-Tooth disease is a chronic hereditary motor and sensory polyneuropathy targeting Schwann cells and/or motor neurons. Its multifactorial and polygenic origin portrays a complex clinical phenotype of the disease with a wide range of genetic inheritance patterns. The disease-associated gene GDAP1 encodes for a mitochondrial outer membrane protein. Mouse and insect models with mutations in Gdap1 have reproduced several traits of the human disease. However, the precise function in the cell types affected by the disease remains unknown. Here, we use induced-pluripotent stem cells derived from a Gdap1 knockout mouse model to better understand the molecular and cellular phenotypes of the disease caused by the loss-of-function of this gene. Gdap1-null motor neurons display a fragile cell phenotype prone to early degeneration showing (1) altered mitochondrial morphology, with an increase in the fragmentation of these organelles, (2) activation of autophagy and mitophagy, (3) abnormal metabolism, characterized by a downregulation of Hexokinase 2 and ATP5b proteins, (4) increased reactive oxygen species and elevated mitochondrial membrane potential, and (5) increased innate immune response and p38 MAP kinase activation. Our data reveals the existence of an underlying Redox-inflammatory axis fueled by altered mitochondrial metabolism in the absence of Gdap1. As this biochemical axis encompasses a wide variety of druggable targets, our results may have implications for developing therapies using combinatorial pharmacological approaches and improving therefore human welfare. A Redox-immune axis underlying motor neuron degeneration caused by the absence of Gdap1. Our results show that Gdap1^-/- motor neurons have a fragile cellular phenotype that is prone to degeneration. Gdap1^-/- iPSCs differentiated into motor neurons showed an altered metabolic state: decreased glycolysis and increased OXPHOS. These alterations may lead to hyperpolarization of mitochondria and increased ROS levels. Excessive amounts of ROS might be the cause of increased mitophagy, p38 activation and inflammation as a cellular response to oxidative stress. The p38 MAPK pathway and the immune response may, in turn, have feedback mechanisms, leading to the induction of apoptosis and senescence, respectively. CAC, citric acid cycle; ETC, electronic transport chain; Glc, glucose; Lac, lactate; Pyr, pyruvate.

Transcriptomic Profiling Reveals Discrete Poststroke Dementia Neuronal and Gliovascular Signatures

Poststroke dementia (PSD) is associated with pathology in frontal brain regions, in particular dorsolateral prefrontal cortex (DLPFC) neurons and white matter, remote from the infarct. We hypothesised that PSD results from progressive DLPFC neuronal damage, associated with frontal white matter gliovascular unit (GVU) alterations. We investigated the transcriptomic profile of the neurons and white matter GVU cells previously implicated in pathology. Laser-capture microdissected neurons, astrocytes and endothelial cells were obtained from the Cognitive Function After Stroke cohort of control, PSD and poststroke non-dementia (PSND) human subjects. Gene expression was assessed using microarrays and pathway analysis to compare changes in PSD with controls and PSND. Neuronal findings were validated using NanoString technology and compared with those in the bilateral common carotid artery stenosis (BCAS) mouse model. Comparing changes in PSD compared to controls with changes in PSND compared to controls identified transcriptomic changes associated specifically with dementia. DLPFC neurons showed defects in energy production (tricarboxylic acid (TCA) cycle, adenosine triphosphate (ATP) binding and mitochondria), signalling and communication (MAPK signalling, Toll-like receptor signalling, endocytosis). Similar changes were identified in neurons isolated from BCAS mice. Neuronal findings accompanied by altered astrocyte communication and endothelium immune changes in the frontal white matter, suggesting GVU dysfunction. We propose a pathogenic model in PSD whereby neuronal changes are associated with frontal white matter GVU dysfunction leading to astrocyte failure in supporting neuronal circuits resulting in delayed cognitive decline associated with PSD. Therefore, targeting these processes could potentially ameliorate the dementia seen in PSD.

Probenecid, an Old Drug with Potential New Uses for Central Nervous System Disorders and Neuroinflammation

Probenecid is an old uricosuric agent used in clinics to treat gout and reduce the renal excretion of antibiotics. In recent years, probenecid has gained attention due to its ability to interact with membrane proteins such as TRPV2 channels, organic anion transporters, and pannexin 1 hemichannels, which suggests new potential therapeutic utilities in medicine. Some current functions of probenecid include their use as an adjuvant to increase the bioavailability of several drugs in the Central Nervous System (CNS). Numerous studies also suggest that this drug has important neuroprotective, antiepileptic, and anti-inflammatory properties, as evidenced by their effect against neurological and neurodegenerative diseases. In these studies, the use of probenecid as a Panx1 hemichannel blocker to reduce neuroinflammation is highlighted since neuroinflammation is a major trigger for diverse CNS alterations. Although the clinical use of probenecid has declined over the years, advances in its use in preclinical research indicate that it may be useful to improve conventional therapies in the psychiatric field where the drugs used have a low bioavailability, either because of a deficient passage through the blood-brain barrier or a high efflux from the CNS or also a high urinary clearance. This review summarizes the history, pharmacological properties, and recent research uses of probenecid and discusses its future projections as a potential pharmacological strategy to intervene in neurodegeneration as an outcome of neuroinflammation.

Synthesis and Preclinical Positron Emission Tomography Imaging of the p38 MAPK Inhibitor [11C]Talmapimod: Effects of Drug Efflux and Sex Differences

Stress-activated kinases are targets of interest in neurodegenerative disease due to their involvement in inflammatory signaling and synaptic dysfunction. The p38α kinase has shown clinical and preclinical promise as a druggable target in several neurodegenerative conditions. We report the radiosynthesis and evaluation of the first positron emission tomography (PET) radiotracer for imaging MAPK p38α/β through radiolabeling of the inhibitor talmapimod (SCIO-469) with carbon-11. [¹¹C]Talmapimod was reliably synthesized by carbon-11 methylation with non-decay corrected radiochemical yields of 3.1 ± 0.7%, molar activities of 38.9 ± 13 GBq/μmol, and >95% radiochemical purity (n = 20). Preclinical PET imaging in rodents revealed a low baseline brain uptake and retention with standardized uptake values (SUV) of ∼0.2 over 90 min; however, pretreatment with the P-glycoprotein (P-gp) drug efflux transporter inhibitor elacridar enabled [¹¹C]talmapimod to pass the blood-brain barrier (>1.0 SUV) with distinct sex differences in washout kinetics. Blocking studies with a structurally dissimilar p38α/β inhibitor, neflamapimod (VX-745), and displacement imaging studies with talmapimod were attempted in elacridar-pretreated rodents, but neither compound displaced radiotracer uptake in the brain of either sex. Ex vivo radiometabolite analysis revealed substantial differences in the composition of radioactive species present in blood plasma but not in brain homogenates at 40 min post radiotracer injection. Digital autoradiography in fresh-frozen rodent brain tissue confirmed that the radiotracer signal was largely non-displaceable in vitro, where self-blocking and blocking with neflamapimod marginally decreased the total signal by 12.9 ± 8.8% and 2.66 ± 2.1% in C57bl/6 healthy controls and 29.3 ± 2.7% and 26.7 ± 12% in Tg2576 rodent brains, respectively. An MDCK-MDR1 assay suggests that talmapimod is likely to suffer from drug efflux in humans as well as rodents. Future efforts should focus on radiolabeling p38 inhibitors from other structural classes to avoid P-gp efflux and non-displaceable binding.

Chemical Knockdown of Phosphorylated p38 Mitogen-Activated Protein Kinase (MAPK) as a Novel Approach for the Treatment of Alzheimer's Disease

Targeted protein degradation (TPD) provides unique advantages over gene knockdown in that it can induce selective degradation of disease-associated proteins attributed to pathological mutations or aberrant post-translational modifications (PTMs). Herein, we report a protein degrader, PRZ-18002, that selectively binds to an active form of p38 MAPK. PRZ-18002 induces degradation of phosphorylated p38 MAPK (p-p38) and a phosphomimetic mutant of p38 MAPK in a proteasome-dependent manner. Given that the activation of p38 MAPK plays pivotal roles in the pathophysiology of Alzheimer's disease (AD), selective degradation of p-p38 may provide an attractive therapeutic option for the treatment of AD. In the 5xFAD transgenic mice model of AD, intranasal treatment of PRZ-18002 reduces p-p38 levels and alleviates microglia activation and amyloid beta (Aβ) deposition, leading to subsequent improvement of spatial learning and memory. Collectively, our findings suggest that PRZ-18002 ameliorates AD pathophysiology via selective degradation of p-p38, highlighting a novel therapeutic TPD modality that targets a specific PTM to induce selective degradation of neurodegenerative disease-associated protein.

Thymol improves autism-like behaviour in VPA-induced ASD rats through the Pin1/p38 MAPK pathway

Inflammation plays an essential role in the pathogenesis of autism spectrum disorder (ASD). Thymol is a bioactive monoterpene isolated from Thymus vulgaris that has anti-inflammatory properties and is helpful in neurodevelopmental disorders. The purpose of this study was to investigate the effects of thymol on autism-like behaviours in rats with VPA-induced ASD and to assess the related molecular mechanisms. In the prefrontal cortex (PFC) of the valproic acid (VPA)-exposed rat model, the levels of Pin1, phosphorylated p38 MAPK, interleukin-1β (IL-1β) and tumour necrosis factor (TNF)-α, were increased, and the levels of PSD95 and synaptophysin (SYP) decreased. After thymol treatment (30 mg/kg), the VPA-induced autism-like behaviours were alleviated. Moreover, thymol also rescued the dysregulated levels of Pin1, phosphorylated p38 MAPK, IL-1β, TNF-α, PSD95, and SYP. In addition, immunofluorescence experiments showed that thymol treatment decreased the correlation between Pin1 and phosphorylated p38 MAPK. Mechanistically, Pin1 knockdown by RNA interference confirmed that Pin1 promotes inflammation via phosphorylation of p38 MAPK in the VPA exposure rat model. In conclusion, thymol improved autism-like behaviours in VPA-induced ASD rats by reducing inflammation and improving neurodevelopment. This effect was mediated by the Pin1/p38 MAPK pathway. These results experimentally provide the potential for thymol in new therapeutic avenues for autism.

Molecular Mechanisms Underlying Neuroinflammation Elicited by Occupational Injuries and Toxicants

Occupational injuries and toxicant exposures lead to the development of neuroinflammation by activating distinct mechanistic signaling cascades that ultimately culminate in the disruption of neuronal function leading to neurological and neurodegenerative disorders. The entry of toxicants into the brain causes the subsequent activation of glial cells, a response known as 'reactive gliosis'. Reactive glial cells secrete a wide variety of signaling molecules in response to neuronal perturbations and thus play a crucial role in the progression and regulation of central nervous system (CNS) injury. In parallel, the roles of protein phosphorylation and cell signaling in eliciting neuroinflammation are evolving. However, there is limited understanding of the molecular underpinnings associated with toxicant- or occupational injury-mediated neuroinflammation, gliosis, and neurological outcomes. The activation of signaling molecules has biological significance, including the promotion or inhibition of disease mechanisms. Nevertheless, the regulatory mechanisms of synergism or antagonism among intracellular signaling pathways remain elusive. This review highlights the research focusing on the direct interaction between the immune system and the toxicant- or occupational injury-induced gliosis. Specifically, the role of occupational injuries, e.g., trips, slips, and falls resulting in traumatic brain injury, and occupational toxicants, e.g., volatile organic compounds, metals, and nanoparticles/nanomaterials in the development of neuroinflammation and neurological or neurodegenerative diseases are highlighted. Further, this review recapitulates the recent advancement related to the characterization of the molecular mechanisms comprising protein phosphorylation and cell signaling, culminating in neuroinflammation.

Tau Loss of Function, by Deletion or Aggregation, Contributes to Peripheral Insulin Resistance

BACKGROUND

Several epidemiological data revealed an association between Alzheimer's disease (AD) and type 2 diabetes. Researchers concentrated on brain insulin resistance with little emphasis on the link between systemic insulin resistance and AD, despite the fact that the incidence of type 2 diabetes is higher in AD patients and that impairment in insulin signaling is a risk factor for AD.

OBJECTIVE

The goal of this study is to determine the role of systemic insulin resistance in the pathogenesis of Alzheimer's disease by evaluating the consequences of tau loss-of-function on peripheral insulin sensitivity.

METHODS

Primary hepatocytes isolated from transgenic mouse models (Tau KO, P301 L) and wild type mice (C57BL/6) were evaluated for their insulin sensitivity using glucose uptake assays as well as biochemical analysis of insulin signaling markers.

RESULTS

Our data show that tau deletion or loss of function promotes peripheral insulin resistance as seen in primary hepatocytes isolated from Tau KO and P301 L mice, respectively. Furthermore, exposure of wild-type primary hepatocytes to sub-toxic concentrations of tau oligomers results in a dose-dependent inhibition of glucose uptake, associated with downregulation of insulin signaling. Tau oligomers-induced inactivation of insulin signaling proteins was rescued by inhibition of p38 MAPK, suggesting the involvement of p38 MAPK.

CONCLUSIONS

This is the first study testing tau role in peripheral insulin resistance at the cellular level using multiple transgenic mouse models. Moreover, this study suggests that tau should be functional for insulin sensitivity, therefore, any loss of function by deletion or aggregation would result in insulin resistance.

Computational screening for new neuroprotective ingredients against Alzheimer's disease from bilberry by cheminformatics approaches

Bioactive ingredients from natural products have always been an important resource for the discovery of drugs for Alzheimer's disease (AD). Senile plaques, which are formed with amyloid-beta (Aβ) peptides and excess metal ions, are found in AD brains and have been suggested to play an important role in AD pathogenesis. Here, we attempted to design an effective and smart screening method based on cheminformatics approaches to find new ingredients against AD from Vaccinium myrtillus (bilberry) and verified the bioactivity of expected ingredients through experiments. This method integrated advanced artificial intelligence models and target prediction methods to realize the stepwise analysis and filtering of all ingredients. Finally, we obtained the expected new compound malvidin-3-O-galactoside (Ma-3-gal-Cl). The in vitro experiments showed that Ma-3-gal-Cl could reduce the OH· generation and intracellular ROS from the Aβ/Cu²⁺/AA mixture and maintain the mitochondrial membrane potential of SH-SY5Y cells. Molecular docking and Western blot results indicated that Ma-3-gal-Cl could reduce the amount of activated caspase-3 via binding with unactivated caspase-3 and reduce the expression of phosphorylated p38 via binding with mitogen-activated protein kinase kinases-6 (MKK6). Moreover, Ma-3-gal-Cl could inhibit the Aβ aggregation via binding with Aβ monomer and fibers. Thus, Ma-3-gal-Cl showed significant effects on protecting SH-SY5Y cells from Aβ/Cu²⁺/AA induced damage via antioxidation effect and inhibition effect to the Aβ aggregation.

Toxicities of amyloid-beta and tau protein are reciprocally enhanced in the Drosophila model

Extracellular aggregation of amyloid-beta (Aβ) and intracellular tau tangles are two major pathogenic hallmarks and critical factors of Alzheimer’s disease. A linear interaction between Aβ and tau protein has been characterized in several models. Aβ induces tau hyperphosphorylation through a complex mechanism; however, the master regulators involved in this linear process are still unclear. In our study with Drosophila melanogaster, we found that Aβ regulated tau hyperphosphorylation and toxicity by activating c-Jun N-terminal kinase. Importantly, Aβ toxicity was dependent on tau hyperphosphorylation, and flies with hypophosphorylated tau were insulated against Aβ-induced toxicity. Strikingly, tau accumulation reciprocally interfered with Aβ degradation and correlated with the reduction in mRNA expression of genes encoding Aβ-degrading enzymes, including dNep1, dNep3, dMmp2, dNep4, and dIDE. Our results indicate that Aβ and tau protein work synergistically to further accelerate Alzheimer’s disease progression and may be considered as a combined target for future development of Alzheimer’s disease therapeutics.

A Pathophysiological Intersection of Diabetes and Alzheimer's Disease

Diabetes is among the most prevalent diseases of the modern world and is strongly linked to an increased risk of numerous neurodegenerative disorders, although the exact pathophysiological mechanisms are not clear yet. Insulin resistance is a serious pathological condition, connecting type 2 diabetes, metabolic syndrome, and obesity. Recently, insulin resistance has been proven to be connected also to cognitive decline and dementias, including the most prevalent form, Alzheimer's disease. The relationship between diabetes and Alzheimer's disease regarding pathophysiology is so significant that it has been proposed that some presentations of the condition could be termed type 3 diabetes.

DHPA Protects SH-SY5Y Cells from Oxidative Stress-Induced Apoptosis via Mitochondria Apoptosis and the Keap1/Nrf2/HO-1 Signaling Pathway

Oxidative stress in the brain is highly related to the pathogenesis of Alzheimer’s disease (AD). It could be induced by the overproduction of reactive oxygen species (ROS), produced by the amyloid beta (Aβ) peptide and excess copper (Cu) in senile plaques and cellular species, such as ascorbic acid (AA) and O₂. In this study, the protective effect of 5-hydroxy-7-(4′-hydroxy-3′-methoxyphenyl)-1-phenyl-3-heptanone (DHPA) on Aβ_(1–42)/Cu²⁺/AA mixture-treated SH-SY5Y cells was investigated via in vitro and in silico studies. The results showed that DHPA could inhibit Aβ/Cu²⁺/AA-induced SH-SY5Y apoptosis, OH· production, intracellular ROS accumulation, and malondialdehyde (MDA) production. Further research demonstrated that DHPA could decrease the ratio of Bax/Bcl-2 and repress the increase of mitochondrial membrane potential (MMP) of SH-SY5Y cells, to further suppress the activation of caspase-3, and inhibit cell apoptosis. Meanwhile, DHPA could inhibit the Aβ/Cu²⁺/AA-induced phosphorylation of Erk1/2 and P38 in SH-SY5Y cells, and increase the expression of P-AKT. Furthermore, DHPA could bind to Keap1 to promote the separation of Nrf2 to Keap1 and activate the Keap1/Nrf2/HO-1 signaling pathway to increase the expression of heme oxygenase-1 (HO-1), quinone oxidoreductase-1 (NQO1), glutathione (GSH), and superoxide dismutase (SOD). Thus, our results demonstrated that DHPA could inhibit Aβ/Cu²⁺/AA-induced SH-SY5Y apoptosis via scavenging OH·, inhibit mitochondria apoptosis, and activate the Keap1/Nrf2/HO-1 signaling pathway.

The Chemerin/CMKLR1 Axis Is Involved in the Recruitment of Microglia to Aβ Deposition through p38 MAPK Pathway

The accumulation of microglia around senile plaques is one of the pathological features of Alzheimer's disease (AD). Chemerin is an adipokine with immune-modulating properties. Our previous study showed that chemokine-like receptor 1 (CMKLR1), the receptor for chemerin, is also a functional receptor of Aβ. However, it remains unclear whether and how the chemerin/CMKLR1 axis affects the migration of microglia. The impact of CMKLR1 on microglial activation and recruitment toward Aβ deposits was examined in APP/PS1 mice mated with CMKLR1 knockout (CMKLR1^-/-) mice. CMKLR1 deficiency reduced the number of microglia around Aβ deposits in aged APP/PS1-CMKLR1^-/- mice compared with APP/PS1 mice. Chemerin expression was significantly decreased in the hippocampus and cortex of aged APP/PS1 mice compared with WT mice. In vitro assays demonstrated that activation of the chemerin/CMKLR1 axis promoted the migration of primary cultures of microglia and murine microglial N9 cells. Mechanistic studies found that chemerin/CMKLR1 induced polarization and protrusion formation of microglia by promoting the remodeling of actin filaments and microtubules, and Golgi apparatus reorientation. The inhibition of p38 MAPK attenuated the promotion of the chemerin/CMKLR1 axis on microglial migration and polarization. In addition, chemerin inhibited Aβ-induced microglial clustering. The inhibition of p38 MAPK alleviated the suppressive effect of chemerin on Aβ-induced microglial aggregation. Our data indicate that the chemerin/CMKLR1 axis is involved in the migration and recruitment of microglia to senile plaques via the p38 MAPK pathway. Modulation of the chemerin/CMKLR1 axis is a potential new strategy for AD therapy.

p38α‐MAPK‐deficient myeloid cells ameliorate symptoms and pathology of APP ‐transgenic Alzheimer's disease mice

Alzheimer's disease (AD), the most common cause of dementia in the elderly, is pathologically characterized by extracellular deposition of amyloid‐β peptides (Aβ) and microglia‐dominated inflammatory activation in the brain. p38α‐MAPK is activated in both neurons and microglia. How p38α‐MAPK in microglia contributes to AD pathogenesis remains unclear. In this study, we conditionally knocked out p38α‐MAPK in all myeloid cells or specifically in microglia of APP‐transgenic mice, and examined animals for AD‐associated pathologies (i.e., cognitive deficits, Aβ pathology, and neuroinflammation) and individual microglia for their inflammatory activation and Aβ internalization at different disease stages (e.g., at 4 and 9 months of age). Our experiments showed that p38α‐MAPK‐deficient myeloid cells were more effective than p38α‐MAPK‐deficient microglia in reducing cerebral Aβ and neuronal impairment in APP‐transgenic mice. Deficiency of p38α‐MAPK in myeloid cells inhibited inflammatory activation of individual microglia at 4 months but enhanced it at 9 months. Inflammatory activation promoted microglial internalization of Aβ. Interestingly, p38α‐MAPK‐deficient myeloid cells reduced IL‐17a‐expressing CD4‐positive lymphocytes in 9 but not 4‐month‐old APP‐transgenic mice. By cross‐breeding APP‐transgenic mice with Il‐17a‐knockout mice, we observed that IL‐17a deficiency potentially activated microglia and reduced Aβ deposition in the brain as shown in 9‐month‐old myeloid p38α‐MAPK‐deficient AD mice. Thus, p38α‐MAPK deficiency in all myeloid cells, but not only in microglia, prevents AD progression. IL‐17a‐expressing lymphocytes may partially mediate the pathogenic role of p38α‐MAPK in peripheral myeloid cells. Our study supports p38α‐MAPK as a therapeutic target for AD patients.

Adenosine receptor signalling in Alzheimer’s disease

Alzheimer’s disease (AD) is the most common dementia in the elderly and its increasing prevalence presents treatment challenges. Despite a better understanding of the disease, the current mainstay of treatment cannot modify pathogenesis or effectively address the associated cognitive and memory deficits. Emerging evidence suggests adenosine G protein-coupled receptors (GPCRs) are promising therapeutic targets for Alzheimer’s disease. The adenosine A₁ and A_2A receptors are expressed in the human brain and have a proposed involvement in the pathogenesis of dementia. Targeting these receptors preclinically can mitigate pathogenic β-amyloid and tau neurotoxicity whilst improving cognition and memory. In this review, we provide an accessible summary of the literature on Alzheimer’s disease and the therapeutic potential of A₁ and A_2A receptors. Although there are no available medicines targeting these receptors approved for treating dementia, we provide insights into some novel strategies, including allosterism and the targeting of oligomers, which may increase drug discovery success and enhance the therapeutic response.

Oncogenic Pathways in Neurodegenerative Diseases

Cancer and neurodegenerative diseases are two of the leading causes of premature death in modern societies. Their incidence continues to increase, and in the near future, it is believed that cancer will kill more than 20 million people per year, and neurodegenerative diseases, due to the aging of the world population, will double their prevalence. The onset and the progression of both diseases are defined by dysregulation of the same molecular signaling pathways. However, whereas in cancer, these alterations lead to cell survival and proliferation, neurodegenerative diseases trigger cell death and apoptosis. The study of the mechanisms underlying these opposite final responses to the same molecular trigger is key to providing a better understanding of the diseases and finding more accurate treatments. Here, we review the ten most common signaling pathways altered in cancer and analyze them in the context of different neurodegenerative diseases such as Alzheimer's (AD), Parkinson's (PD), and Huntington's (HD) diseases.

Glycogen Synthase Kinase 3β Involvement in Neuroinflammation and Neurodegenerative Diseases

BACKGROUND

GSK-3β activity has been strictly related to neuroinflammation and neurodegeneration. Alzheimer's disease is the most studied neurodegenerative disease, but GSK-3β seems to be involved in almost all neurodegenerative diseases including Parkinson's disease, amyotrophic lateral sclerosis, frontotemporal dementia, Huntington's disease and the autoimmune disease multiple sclerosis.

OBJECTIVE

The aim of this review is to help researchers both working on this research topic or not to have a comprehensive overview on GSK-3β in the context of neuroinflammation and neurodegeneration.

METHOD

Literature has been searched using PubMed and SciFinder databases by inserting specific keywords. A total of more than 500 articles have been discussed.

RESULTS

First of all, the structure and regulation of the kinase were briefly discussed and then, specific GSK-3β implications in neuroinflammation and neurodegenerative diseases were illustrated also with the help of figures, to conclude with a comprehensive overview on the most important GSK-3β and multitarget inhibitors. For all discussed compounds, the structure and IC50 values at the target kinase have been reported.

CONCLUSION

GSK-3β is involved in several signaling pathways both in neurons as well as in glial cells and immune cells. The fine regulation and interconnection of all these pathways are at the base of the rationale use of GSK-3β inhibitors in neuroinflammation and neurodegeneration. In fact, some compounds are now under clinical trials. Despite this, pharmacodynamic and ADME/Tox profiles of the compounds were often not fully characterized and this is deleterious in such a complex system.

p38 activation occurs mainly in microglia in the P301S Tauopathy mouse model

Tauopathies are a group of neurodegenerative diseases characterized by the accumulation of hyperphosphorylated tau protein in the brain. Many of these pathologies also present an inflammatory component determined by the activation of microglia, the resident immune cells of the brain. p38 MAPK is one of the molecular pathways involved in neuroinflammation. Although this kinase is expressed mainly in glia, its activation in certain neurodegenerative diseases such as Alzheimer's Disease has been associated with its ability to phosphorylate tau in neurons. Using the P301S Tauopathy mouse model, here we show that p38 activation increases during aging and that this occurs mainly in microglia of the hippocampus rather than in neurons. Furthermore, we have observed that these mice present an activated microglial variant called rod microglia. Interestingly, p38 activation in this subpopulation of microglia is decreased. On the basis of our findings, we propose that rod microglia might have a neuroprotective phenotype in the context of tau pathology.

p38 Inhibition Decreases Tau Toxicity in Microglia and Improves Their Phagocytic Function

Alzheimer’s disease (AD) and other tauopathies are histopathologically characterized by tau aggregation, along with a chronic inflammatory response driven by microglia. Over the past few years, the role of microglia in AD has been studied mainly in relation to amyloid-β (Aβ) pathology. Consequently, there is a substantial knowledge gap concerning the molecular mechanisms involved in tau-mediated toxicity and neuroinflammation, thus hindering the development of therapeutic strategies. We previously demonstrated that extracellular soluble tau triggers p38 MAPK activation in microglia. Given the activation of this signaling pathway in AD and its involvement in neuroinflammation processes, here we evaluated the effect of p38 inhibition on primary microglia cultures subjected to tau treatment. Our data showed that the toxic effect driven by tau in microglia was diminished through p38 inhibition. Furthermore, p38 blockade enhanced microglia-mediated tau phagocytosis, as reflected by an increase in the number of lysosomes. In conclusion, these results contribute to our understanding of the functions of p38 in the central nervous system (CNS) beyond tau phosphorylation in neurons and provide further insights into the potential of p38 inhibition as a therapeutic strategy to halt neuroinflammation in tauopathies.

At the intersection of sulfur redox chemistry, cellular signal transduction and proteostasis: A useful perspective from which to understand and treat neurodegeneration

Although we can thoroughly describe individual neurodegenerative diseases from the molecular level through cell biology to histology and clinical presentation, our understanding of them and hence treatment gains have been depressingly limited, partly due to difficulty conceptualizing different diseases as variations within the same overarching pathological rubric. This review endeavors to create such rubric by knitting together the seemingly disparate phenomena of oxidative stress, dysregulated proteostasis, and neuroinflammation into a cohesive triad that highlights mechanistic connectivities. We begin by considering that brain metabolic demands necessitate careful control of oxidative homeostasis, largely through sulfur redox chemistry and glutathione (GSH). GSH is essential for brain antioxidant defense, but also for redox signaling and thus neuroinflammation. Delicate regulation of neuroinflammatory pathways (NFκB, MAPK-p38, and NLRP3 particularly) occurs through S-glutathionylation of protein phosphatases but also through redox-sensing elements like ASK1; the 26S proteasome and cysteine deubiquitinases (DUBs). The relationship amongst triad elements is underscored by our discovery that LanCL1 (lanthionine synthetase-like protein-1) protects against oxidant toxicity; mediates GSH-dependent reactivation of oxidized DUBs; and antagonizes the pro-inflammatory cytokine, tumor necrosis factor-α (TNFα). We highlight currently promising pharmacological efforts to modulate key triad elements and suggest nexus points that might be exploited to further clinical advantage.

Dysregulated Protein Phosphorylation as Main Contributor of Granulovacuolar Degeneration at the First Stages of Neurofibrillary Tangles Pathology

The hippocampus of cases with neurofibrillary tangles (NFT) pathology classified as stages I-II, III-IV, and V-VI without comorbidities, and middle-aged (MA) individuals with no NFT pathology, were examined to learn about the composition of granulovacuolar degeneration (GVD). Our results confirm the presence of CK1-δ, p38-P Thr180/Tyr182, SAPK/JNK-P Thr183/Thr185, GSK-3α/β-P Tyr279/Tyr216, and GSK-3β Ser9 in the cytoplasmic granules in a subset of neurons of the CA1 and CA2 subfields of the hippocampus. Also, we identify the presence of PKA α/β-P Thr197, SRC-P Tyr416, PAK1-P Ser199/Ser204, CAMK2A-P Tyr197, and PKCG-P Thr655 in cytoplasmic granules in cases with NFT pathology, but not in MA cases. Our results also confirm the presence of β-catenin-P Ser45/Thr41, IREα-P Ser274, eIF2α-P Ser51, TDP-43-P Ser403-404 (but absent TDP-43), and ubiquitin in cytoplasmic granules. Other components of the cytoplasmic granules are MAP2-P Thr1620/1623, MAP1B-P Thr1265, ADD1-P Ser726, and ADD1/ADD1-P Ser726/Ser713, in addition to several tau species including 3Rtau, 4Rtau, and tau-P Ser262. The analysis of GVD at progressive stages of NFT pathology reveals the early appearance of phosphorylated kinases and proteins in cytoplasmic granules at stages I-II, before the appearance of pre-tangles and NFTs. Most of these granules are not surrounded by LAMP1-positive membranes. Markers of impaired ubiquitin-protesome system, abnormal reticulum stress response, and altered endocytic and autophagic pathways occur in a subpopulation of neurons containing cytoplasmic granules, and they appear later. These observations suggest early phosphorylation of kinases leading to their activation, and resulting in the abnormal phosphorylation of various substrates, including tau, as a main alteration at the first stages of GVD.

Amyloid peptide exerts a rapid induction of Dicer1 protein in neuron via reducing phosphorylation

A growing number of evidence suggests that altered microRNA network in the brain contributes to the risk of Alzheimer's disease(AD). Dicer1 is a type III riboendonuclease which cleaves pre-microRNA into functional microRNA. Reduction of Dicer1 or Dicer1 mutation has been involved in cancer, aging or age-related macular degeneration. Recently, we found a possible link between Dicer1 and AD. In particular, Dicer1 protein and Dicer1 mRNA is reduced in the hippocampus and the cortex of an animal model of AD and exposure to Aβ42 oligomer(AβO) longer than 6 h reduces the transcription of Dicer1 gene in neuron, via depletion of NF-E2-related factor-2. In this study, exposure to AβO at shorter time increased Dicer1 protein in neuron in a dose-dependent mode; but the mRNA level remained unaltered. Under this treatment regime,AβO reduced phosphorylation level of Dicer1 and of its binding partner, transactivation response element RNA-binding protein(TRBP). Addition of a JNK inhibitor,SP600125, or an ERK inhibitor,U0126, further increased Dicer1 protein compared to Aβo treatment alone, with simultaneaous reduction of phospho-Dicer1, but with different effects on phospho-TRBP. Finally, an inhibitor of calcineurin,FK506, further increased Dicer1 protein compared to Aβo treatment alone. Thus, phosphorylation of Dicer1 and TRBP was determined by mitogen activated protein kinases JNK,ERK, and protein phosphatase 2B(calcineurin) which together determined Dicer1 stability. In summary, reduced phosphorylation of Dicer1 accounted for the rapid induction of Dicer1 by AβO. This study highlights a novel way by which AβO regulates Dicer1.

Roles and Interaction of the MAPK Signaling Cascade in Aβ25-35-Induced Neurotoxicity Using an Isolated Primary Hippocampal Cell Culture System

Alzheimer's disease (AD) is characterized with increased formation of amyloid-β (Aβ) in the brain. Aβ peptide toxicity is associated with disturbances of several intracellular signaling pathways such as mitogen activated protein kinases (MAPKs). The aim of this study was to investigate the role of MAPKs and their interactions in Aβ-induced neurotoxicity using isolated hippocampal neurons from the rat. Primary hippocampal cells were cultured in neurobasal medium for 4 days. Cells were treated with Aβ25-35 and/or MAPKs inhibitors for 24 h. Cell viability was determined by an MTT assay and phosphorylated levels of P38, JNK, and ERK were measured by Western blots. Aβ treatment (10-40 µM) significantly decreased hippocampal cell viability in a dose-dependent manner. Inhibition of P38 and ERK did not restore cell viability, while JNK inhibition potentiated the Aβ-induced neurotoxicity. Compared to the controls, Aβ treatment increased levels of phosphorylated JNK, ERK, and c-Jun, while it had no effect on levels of phosphorylated P38. In addition, P38 inhibition led to decreased expression levels of phosphorylated ERK; inhibition of JNK resulted in decreased expression of c-Jun; and inhibition of ERK, decreased phosphorylated levels of JNK. These results strongly suggest that P38, ERK, and JNK are not independently involved in Aβ-induced toxicity in the hippocampal cells. In AD, which is a multifactorial disease, inhibiting a single member of the MAPK signaling pathway, does not seem to be sufficient to mitigate Aβ-induced toxicity and thus their interactions with each other or potentially with different signaling pathways should be taken into account.

P38α-MAPK phosphorylates Snapin and reduces Snapin-mediated BACE1 transportation in APP-transgenic mice

Amyloid β peptide (Aβ) is the major pathogenic molecule in Alzheimer's disease (AD). BACE1 enzyme is essential for the generation of Aβ. Deficiency of p38α-MAPK in neurons increases lysosomal degradation of BACE1 and decreases Aβ deposition in the brain of APP-transgenic mice. However, the mechanisms mediating effects of p38α-MAPK are largely unknown. In this study, we used APP-transgenic mice and cultured neurons and observed that deletion of p38α-MAPK specifically in neurons decreased phosphorylation of Snapin at serine, increased retrograde transportation of BACE1 in axons and reduced BACE1 at synaptic terminals, which suggests that p38α-MAPK deficiency promotes axonal transportation of BACE1 from its predominant locations, axonal terminals, to lysosomes in the cell body. In vitro kinase assay revealed that p38α-MAPK directly phosphorylates Snapin. By further performing mass spectrometry analysis and site-directed mutagenic experiments in SH-SY5Y cell lines, we identified serine residue 112 as a p38α-MAPK-phosphorylating site on Snapin. Replacement of serine 112 with alanine did abolish p38α-MAPK knockdown-induced reduction of BACE1 activity and protein level, and transportation to lysosomes in SH-SY5Y cells. Taken together, our study suggests that activation of p38α-MAPK phosphorylates Snapin and inhibits the retrograde transportation of BACE1 in axons, which might exaggerate amyloid pathology in AD brain.

Quantitative phosphoproteomics uncovers dysregulated kinase networks in Alzheimer’s disease

Alzheimer's disease (AD) is a form of dementia characterized by amyloid-β plaques and tau neurofibrillary tangles that progressively disrupt neural circuits in the brain. The signaling networks underlying AD pathological changes are poorly characterized at the phosphoproteome level. Using mass spectrometry, we analyzed the proteome and tyrosine, serine and threonine phosphoproteomes of temporal cortex tissue from patients with AD and aged-matched controls. We identified cocorrelated peptide clusters that were linked to varying levels of phospho-tau, oligodendrocyte, astrocyte, microglia and neuron pathologies. We found that neuronal synaptic protein abundances were strongly anti-correlated with markers of microglial reactivity. We also observed that phosphorylation sites on kinases targeting tau and other new signaling factors were correlated with these peptide modules. Finally, we used data-driven statistical modeling to identify individual peptides and peptide clusters that were predictive of AD histopathologies. Together, these results build a map of pathology-associated phosphorylation signaling events occurring in AD.

When Good Kinases Go Rogue: GSK3, p38 MAPK and CDKs as Therapeutic Targets for Alzheimer's and Huntington's Disease

Alzheimer's disease (AD) is a mostly sporadic brain disorder characterized by cognitive decline resulting from selective neurodegeneration in the hippocampus and cerebral cortex whereas Huntington's disease (HD) is a monogenic inherited disorder characterized by motor abnormalities and psychiatric disturbances resulting from selective neurodegeneration in the striatum. Although there have been numerous clinical trials for these diseases, they have been unsuccessful. Research conducted over the past three decades by a large number of laboratories has demonstrated that abnormal actions of common kinases play a key role in the pathogenesis of both AD and HD as well as several other neurodegenerative diseases. Prominent among these kinases are glycogen synthase kinase (GSK3), p38 mitogen-activated protein kinase (MAPK) and some of the cyclin-dependent kinases (CDKs). After a brief summary of the molecular and cell biology of AD and HD this review covers what is known about the role of these three groups of kinases in the brain and in the pathogenesis of the two neurodegenerative disorders. The potential of targeting GSK3, p38 MAPK and CDKS as effective therapeutics is also discussed as is a brief discussion on the utilization of recently developed drugs that simultaneously target two or all three of these groups of kinases. Multi-kinase inhibitors either by themselves or in combination with strategies currently being used such as immunotherapy or secretase inhibitors for AD and knockdown for HD could represent a more effective therapeutic approach for these fatal neurodegenerative diseases.

Design and Synthesis of Highly Selective Brain Penetrant p38α Mitogen-Activated Protein Kinase Inhibitors

Stress-induced p38α mitogen-activated protein (MAP) kinase activation modulates cytokine overproduction and is associated with neuroinflammation and neurodegeneration. As a potential therapeutic approach, novel Skepinone-based p38α MAP kinase inhibitors were optimized to cross the blood-brain barrier via either amino acid transporters or hydrophobic diffusion. To enhance absorption from the oral route, we used methyl ester prodrugs of the active carboxy analogs. Of these, 3-(8-((2,4-difluorophenyl)amino)-5-oxo-10,11-dihydro-5H-dibenzo[a,d][7]annulene-3-carboxamido)propanoic acid (43; p38α, IC₅₀ = 5.5 nM) and 4-(8-((2,4-difluorophenyl)amino)-5-oxo-10,11-dihydro-5H-dibenzo[a,d][7]annulene-3-carboxamido)butanoic acid (44; p38α, IC₅₀ = 12 nM) had brain-to-plasma ratios of 1.4 and 4.4, respectively. Compound 70, 3-(8-((2-aminophenyl)amino)-5-oxo-10,11-dihydro-5H-dibenzo[a,d][7]annulene-3-carboxamido)propanoic acid (p38α, IC₅₀ = 1.0 nM), the Skepinone-N counterpart of 43, was most present in the mouse brain (brain-to-plasma ratio of 4.7; 0.4 mg/kg p.o., 2 h, 580 nmol/kg). Compounds 43, 44, and 70 were p38α-MAP-kinase-selective, metabolically stable, hERG nonbinding, and able to modulate IL-6 and TNF-α production in cell-based assays.

The PKR/P38/RIPK1 Signaling Pathway as a Therapeutic Target in Alzheimer's Disease

Neuropathological lesions in Alzheimer’s disease (AD) include amyloid plaques formed by the accumulation of amyloid peptides, neurofibrillary tangles made of hyperphosphorylated tau protein, synaptic and neuronal degenerations, and neuroinflammation. The cause of AD is unknown, but according to the amyloid hypothesis, amyloid oligomers could lead to the activation of kinases such as eukaryotic translation initiation factor 2-alpha kinase 2 (PKR), p38, and receptor-interacting serine/threonine-protein kinase 1 (RIPK1), which all belong to the same stress-activated pathway. Many toxic kinase activations have been described in AD patients and in experimental models. A p38 mitogen-activated protein kinase inhibitor was recently tested in clinical trials but with unsuccessful results. The complex PKR/P38/RIPK1 (PKR/dual specificity mitogen-activated protein kinase kinase 6 (MKK6)/P38/MAP kinase-activated protein kinase 2 (MK2)/RIPK1) is highly activated in AD brains and in the brains of AD transgenic animals. To delineate the implication of this pathway in AD, we carried out a search on PubMed including PKR/MKK6/p38/MK2/RIPK1, Alzheimer, and therapeutics. The involvement of this signaling pathway in the genesis of AD lesions, including Aβ accumulations and tau phosphorylation as well as cognitive decline, is demonstrated by the reports described in this review. A future combination strategy with kinase inhibitors should be envisaged to modulate the consequences for neurons and other brain cells linked to the abnormal activation of this pathway.

Design, crystal structure determination, molecular dynamic simulation and MMGBSA calculations of novel p38-alpha MAPK inhibitors for combating Alzheimer's disease

The hallmark of the Alzheimer's disease (AD) is the accumulation of aggregated, misfolded proteins. The cause for this accumulation is increased production of misfolded proteins and impaired clearance of them. Amyloid aggregation and tau hyperphosphorylation are the two proteinopathies which accomplish deprivation of cell and tissue hemostasis during neuropathological process of the AD, as a result of which progressive neuronal degeneration and the loss of cognitive functions. p38 mitogen-activated protein kinase (p38 MAPK) has been implicated in both the events associated with AD: tau protein phosphorylation and inflammation. p38α MAPK pathway is activated by a dual phosphorylation at Thr180 and Tyr182 residues. Clinical and preclinical evidence implicates the stress related kinase p38α MAPK as a potential neurotherapeutic target. Drug design of p38α MAPK inhibitors is mainly focused on small molecules that compete for Adenosine triphosphate in the catalytic site. Here we have carried out the synthesis of phenyl sulfonamide derivatives Sulfo (I) and Sulfo (II). Crystal structures of Sulfo (I) and Sulfo (II) were solved by direct methods using SHELXS-97. Sulfo (I) and Sulfo (II) have R_int values of 0.0283 and 0.0660, respectively, indicating good quality of crystals and investigated their ability against p38α MAPK. Docking studies revealed that the Sulfo (I) had better binding affinity (-62.24 kcal/mol) as compared to Sulfo (II) and cocrystal having binding affinity of -54.61 kcal/mol and -59.84 kcal/mol, respectively. Molecular dynamics simulation studies of Sulfo (I) and cocrystal of p38α MAPK suggest that during the course of 30 ns simulation run, compound Sulfo (I) attained stability, substantiating the consistency of its binding to p38α MAPK compared to cocrystal. Binding free energy analysis suggests that the compound Sulfo (I) is better than the cocrystal. Thus, this study corroborates the therapeutic potential of synthesized Sulfo (I) in combatting AD.Communicated by Ramaswamy H. Sarma.

Diversity and versatility of p38 kinase signalling in health and disease

The ability of cells to deal with different types of stressful situations in a precise and coordinated manner is key for survival and involves various signalling networks. Over the past 25 years, p38 kinases — in particular, p38α — have been implicated in the cellular response to stress at many levels. These span from environmental and intracellular stresses, such as hyperosmolarity, oxidative stress or DNA damage, to physiological situations that involve important cellular changes such as differentiation. Given that p38α controls a plethora of functions, dysregulation of this pathway has been linked to diseases such as inflammation, immune disorders or cancer, suggesting the possibility that targeting p38α could be of therapeutic interest. In this Review, we discuss the organization of this signalling pathway focusing on the diversity of p38α substrates, their mechanisms and their links to particular cellular functions. We then address how the different cellular responses can be generated depending on the signal received and the cell type, and highlight the roles of this kinase in human physiology and in pathological contexts.

p38α — the best-characterized member of the p38 kinase family — is a key mediator of cellular stress responses. p38α is activated by a plethora of signals and functions through a multitude of substrates to regulate different cellular behaviours. Understanding context-dependent p38α signalling provides important insights into p38α roles in physiology and pathology.

Astrocytes: a double-edged sword in neurodegenerative diseases

Astrocytes play multifaceted and vital roles in maintaining neurophysiological function of the central nervous system by regulating homeostasis, increasing synaptic plasticity, and sustaining neuroprotective effects. Astrocytes become activated as a result of inflammatory responses during the progression of pathological changes associated with neurodegenerative disorders. Reactive astrocytes (neurotoxic A1 and neuroprotective A2) are triggered during disease progression and pathogenesis due to neuroinflammation and ischemia. However, only a limited body of literature describes morphological and functional changes of astrocytes during the progression of neurodegenerative diseases. The present review investigated the detrimental and beneficial roles of astrocytes in neurodegenerative diseases reported in recent studies, as these cells have promising therapeutic potential and offer new approaches for treatment of neurodegenerative diseases.

c-Jun N-Terminal Kinase Inhibitors as Potential Leads for New Therapeutics for Alzheimer's Diseases

Alzheimer's Disease (AD) is becoming more prevalent as the population lives longer. For individuals over 60 years of age, the prevalence of AD is estimated at 40.19% across the world. Regarding the cognitive decline caused by the disease, mitogen-activated protein kinases (MAPK) pathways such as the c-Jun N-terminal kinase (JNK) pathway are involved in the progressive loss of neurons and synapses, brain atrophy, and augmentation of the brain ventricles, being activated by synaptic dysfunction, oxidative stress, and excitotoxicity. Nowadays, AD symptoms are manageable, but the disease itself remains incurable, thus the inhibition of JNK3 has been explored as a possible therapeutic target, considering that JNK is best known for its involvement in propagating pro-apoptotic signals. This review aims to present biological aspects of JNK, focusing on JNK3 and how it relates to AD. It was also explored the recent development of inhibitors that could be used in AD treatment since several drugs/compounds in phase III clinical trials failed. General aspects of the MAPK family, therapeutic targets, and experimental treatment in models are described and discussed throughout this review.

Wip1 phosphatase deficiency impairs spatial learning and memory

Spatial learning and memory are typically assessed to evaluate hippocampus-dependent cognitive and memory functions in vivo. Protein phosphorylation and dephosphorylation by kinases and phosphatases play critical roles in spatial learning and memory. Here we report that the Wip1 phosphatase is essential for spatial learning, with knockout mice lacking Wip1 phosphatase exhibiting dysfunctional spatial cognition. Aberrant phosphorylation of the Wip1 substrates p38, ATM, and p53 were observed in the hippocampi of Wip1^-/- mice, but only p38 inhibition reversed impairments in long-term potentiation in Wip1-knockout mice. p38 inhibition consistently ameliorated the spatial learning dysfunction caused by Wip1 deficiency. Our results demonstrate that deletion of Wip1 phosphatase impairs hippocampus-dependent spatial learning and memory, with aberrant downstream p38 phosphorylation involved in this process and providing a potential therapeutic target.

Development and Application of a Chemical Probe Based on a Neuroprotective Flavonoid Hybrid for Target Identification Using Activity-Based Protein Profiling

Alzheimer's disease (AD) is the most common form of dementia, and up to now, there are no disease-modifying drugs available. Natural product hybrids based on the flavonoid taxifolin and phenolic acids have shown a promising pleiotropic neuroprotective profile in cell culture assays and even disease-modifying effects in vivo. However, the detailed mechanisms of action remain unclear. To elucidate the distinct intracellular targets of 7-O-esters of taxifolin, we present in this work the development and application of a chemical probe, 7-O-cinnamoyltaxifolin-alkyne, for target identification using activity-based protein profiling. 7-O-Cinnamoyltaxifolin-alkyne remained neuroprotective in all cell culture assays. Western blot analysis showed a comparable influence on the same intracellular pathways as that of the lead compound 7-O-cinnamoyltaxifolin, thereby confirming its suitability as a probe for target identification experiments. Affinity pulldown and MS analysis revealed adenine nucleotide translocase 1 (ANT-1) and sarco/endoplasmic reticulum Ca²⁺ ATPase (SERCA) as intracellular interaction partners of 7-O-cinnamoyltaxifolin-alkyne and thus of 7-O-esters of taxifolin.

Dual functional liposomes carrying antioxidants against tau hyperphosphorylation and apoptosis of neurons

Quercetin (QU) and rosmarinic acid (RA) were loaded in phosphatidic acid-liposomes (QU/RA-PA-liposomes) with surface apolipoprotein E (ApoE) using a process of thin-film hydration, followed by covalent crosslinking to activate biological pathways for penetrating the blood-brain barrier (BBB) and redeeming the neuronal apoptosis from attack of β-amyloid 1-42 (Aβ1-42) and neurofibrillary tangles. The conjugation of liposomes with PA improved the activity of QU and RA against neurotoxicity of Aβ1-42. The fluorescent images of brain capillaries revealed that surface modification with ApoE improved the permeation ability of QU/RA-PA-ApoE-liposomes across the BBB. In addition, the highest therapeutic efficacy was obtained in the case of QU/RA-PA-ApoE-liposomes, compared to other QU/RA formulations studied using in vivo Aβ1-42-insulted rats mimicking Alzheimer's disease (AD). The cellular and molecular evidence from AD rats included the decrease in Aβ1-42 plaque formation and interleukin-6 secretion, increase in the neuronal count in Nissl staining, and reduction in the expression of phosphorylated extracellular signal-regulated kinase 1/2, c-Jun N-terminal kinase, p38 kinase and tau protein at serine 202 as well as caspase-3. The use of PA-ApoE-liposomes as a dual targeting formulation enhances the QU and RA ability to infiltrate the BBB, docks Aβ1-42 plaques and can be a potent approach to rescue degenerated neurons from AD.

Clinically Precedented Protein Kinases: Rationale for Their Use in Neurodegenerative Disease

Kinases are an intensively studied drug target class in current pharmacological research as evidenced by the large number of kinase inhibitors being assessed in clinical trials. Kinase-targeted therapies have potential for treatment of a broad array of indications including central nervous system (CNS) disorders. In addition to the many variables which contribute to identification of a successful therapeutic molecule, drug discovery for CNS-related disorders also requires significant consideration of access to the target organ and specifically crossing the blood-brain barrier (BBB). To date, only a small number of kinase inhibitors have been reported that are specifically designed to be BBB permeable, which nonetheless demonstrates the potential for success. This review considers the potential for kinase inhibitors in the context of unmet medical need for neurodegenerative disease. A subset of kinases that have been the focus of clinical investigations over a 10-year period have been identified and discussed individually. For each kinase target, the data underpinning the validity of each in the context of neurodegenerative disease is critically evaluated. Selected molecules for each kinase are identified with information on modality, binding site and CNS penetrance, if known. Current clinical development in neurodegenerative disease are summarized. Collectively, the review indicates that kinase targets with sufficient rationale warrant careful design approaches with an emphasis on improving brain penetrance and selectivity.