Common mechanisms of Alzheimer's disease and ischemic stroke: the role of protein kinase C in the progression of age-related neurodegeneration

Protein Kinase C (PKC) in Neurological Health: Implications for Alzheimer's Disease and Chronic Alcohol Consumption

Protein kinase C (PKC) is a diverse enzyme family crucial for cell signalling in various organs. Its dysregulation is linked to numerous diseases, including cancer, cardiovascular disorders, and neurological problems. In the brain, PKC plays pivotal roles in synaptic plasticity, learning, memory, and neuronal survival. Specifically, PKC's involvement in Alzheimer's Disease (AD) pathogenesis is of significant interest. The dysregulation of PKC signalling has been linked to neurological disorders, including AD. This review elucidates PKC's pivotal role in neurological health, particularly its implications in AD pathogenesis and chronic alcohol addiction. AD, characterised by neurodegeneration, implicates PKC dysregulation in synaptic dysfunction and cognitive decline. Conversely, chronic alcohol consumption elicits neural adaptations intertwined with PKC signalling, exacerbating addictive behaviours. By unravelling PKC's involvement in these afflictions, potential therapeutic avenues emerge, offering promise for ameliorating their debilitating effects. This review navigates the complex interplay between PKC, AD pathology, and alcohol addiction, illuminating pathways for future neurotherapeutic interventions.

Early ultrasonic vocalization deficits and related thyroarytenoid muscle pathology in the transgenic TgF344-AD rat model of Alzheimer's disease

Background

Alzheimer's disease (AD) is a progressive neurologic disease and the most common cause of dementia. Classic pathology in AD is characterized by inflammation, abnormal presence of tau protein, and aggregation of β-amyloid that disrupt normal neuronal function and lead to cell death. Deficits in communication also occur during disease progression and significantly reduce health, well-being, and quality of life. Because clinical diagnosis occurs in the mid-stage of the disease, characterizing the prodrome and early stages in humans is currently challenging. To overcome these challenges, we use the validated TgF344-AD (F344-Tg(Prp-APP, Prp-PS1)19/Rrrc) transgenic rat model that manifests cognitive, behavioral, and neuropathological dysfunction akin to AD in humans.

Objectives

The overarching goal of our work is to test the central hypothesis that pathology and related behavioral deficits such as communication dysfunction in part manifest in the peripheral nervous system and corresponding target tissues already in the early stages. The primary aims of this study are to test the hypotheses that: (1) changes in ultrasonic vocalizations (USV) occur in the prodromal stage at 6 months of age and worsen at 9 months of age, (2) inflammation as well as AD-related pathology can be found in the thyroarytenoid muscle (TA) at 12 months of age (experimental endpoint tissue harvest), and to (3) demonstrate that the TgF344-AD rat model is an appropriate model for preclinical investigations of early AD-related vocal deficits.

Methods

USVs were collected from male TgF344-AD (N = 19) and wildtype (WT) Fischer-344 rats (N = 19) at 6 months (N = 38; WT: n = 19; TgF344-AD: n = 19) and 9 months of age (N = 18; WT: n = 10; TgF344-AD: n = 8) and acoustically analyzed for duration, mean power, principal frequency, low frequency, high frequency, peak frequency, and call type. RT-qPCR was used to assay peripheral inflammation and AD-related pathology via gene expressions in the TA muscle of male TgF344-AD rats (n = 6) and WT rats (n = 6) at 12 months of age.

Results

This study revealed a significant reduction in mean power of ultrasonic calls from 6 to 9 months of age and increased peak frequency levels over time in TgF344-AD rats compared to WT controls. Additionally, significant downregulation of AD-related genes Uqcrc2, Bace2, Serpina3n, and Igf2, as well as downregulation of pro-inflammatory gene Myd88 was found in the TA muscle of TgF344-AD rats at 12 months of age.

Discussion

Our findings demonstrate early and progressive vocal deficits in the TgF344-AD rat model. We further provide evidence of dysregulation of AD-pathology-related genes as well as inflammatory genes in the TA muscles of TgF344-AD rats in the early stage of the disease, confirming this rat model for early-stage investigations of voice deficits and related pathology.

Association of the Triglyceride-Glucose Index With Risk of Alzheimer's Disease: A Prospective Cohort Study

INTRODUCTION

Triglyceride-glucose index (TyG) is a reliable surrogate marker of insulin resistance, and insulin resistance has been implicated in Alzheimer's disease pathophysiology. However, the relationship between the TyG index and Alzheimer's disease remains unclear. This study aimed to evaluate the association of the TyG index with the risk of Alzheimer's disease.

METHODS

This prospective study included 2,170 participants free of Alzheimer's disease from the Framingham Heart Study Offspring Cohort Exam 7 (1998-2001), whose follow-up data were collected until 2018. The TyG index was calculated as Ln(fasting triglyceride [mg/dL] × fasting glucose [mg/dL]/2). The association of the TyG index with Alzheimer's disease was evaluated by competing risk regression model. Statistical analyses were performed in 2023.

RESULTS

During a median follow-up of 13.8 years, 163 (7.5%) participants developed Alzheimer's disease. When compared with the reference (TyG index ≤8.28), a significantly elevated risk of Alzheimer's disease was seen in the group with a triglyceride-glucose index of 8.68-9.09 (adjusted hazard ratio=1.69, 95% CI=1.02, 2.81). When the TyG index was considered as a continuous variable, each unit increment in the TyG index was not significantly associated with the risk of Alzheimer's disease (adjusted hazard ratio=1.32, 95% CI=0.98, 1.77).

CONCLUSIONS

This study showed that moderately elevated TyG index was independently associated with a higher incidence of Alzheimer's disease. TheTyG index might be used to define a high-risk population of Alzheimer's disease.

Development of Kinase-Centric Drugs: A Computational Perspective

Kinases are prominent drug targets in the pharmaceutical and research community due to their involvement in signal transduction, physiological responses, and upon dysregulation, in diseases such as cancer, neurological and autoimmune disorders. Several FDA-approved small-molecule drugs have been developed to combat human diseases since Gleevec was approved for the treatment of chronic myelogenous leukemia. Kinases were considered "undruggable" in the beginning. Several FDA-approved small-molecule drugs have become available in recent years. Most of these drugs target ATP-binding sites, but a few target allosteric sites. Among kinases that belong to the same family, the catalytic domain shows high structural and sequence conservation. Inhibitors of ATP-binding sites can cause off-target binding. Because members of the same family have similar sequences and structural patterns, often complex relationships between kinases and inhibitors are observed. To design and develop drugs with desired selectivity, it is essential to understand the target selectivity for kinase inhibitors. To create new inhibitors with the desired selectivity, several experimental methods have been designed to profile the kinase selectivity of small molecules. Experimental approaches are often expensive, laborious, time-consuming, and limited by the available kinases. Researchers have used computational methodologies to address these limitations in the design and development of effective therapeutics. Many computational methods have been developed over the last few decades, either to complement experimental findings or to forecast kinase inhibitor activity and selectivity. The purpose of this review is to provide insight into recent advances in theoretical/computational approaches for the design of new kinase inhibitors with the desired selectivity and optimization of existing inhibitors.

Proteomic changes of the bilateral M1 and spinal cord in hemiplegic cerebral palsy mouse: Effects of constraint-induced movement therapy

Hemiplegic cerebral palsy (HCP) is a non-progressive movement and posture disorder that affects one side of the body. Constraint-induced movement therapy (CIMT) can improve the hand function of children with HCP. We used label-free proteomic quantification technology to evaluate proteomic changes in the bilateral M1 and spinal cord in HCP mouse induced by hypoxia/ischemia and CIMT. Nissl staining showed reduced neuron density in the HCP mice's lesioned and contralesional M1. The rotarod test and grip strength test showed motor dysfunction in mice with HCP and improved motor ability after CIMT. A total of 5147 proteins were identified. Fifty-one, five, and sixty common differentially expressed proteins (DEPs), which were co-regulated by HCP and CIMT, were found in the lesioned M1, the contralesional M1 and the spinal cord respectively. The significant proteins included alpha-centractin, metaxin complex, PKC, septin 11, choline transporter-like proteins, protein 4.1, teneurin-4, and so on, which mainly related to synapse stability, neuronal development and maintenance, axon development, and myelin formation. The KEGG pathways of HCP-induced DEPs mainly related to lipid metabolism, synaptic remodeling, SNARE interactions in vesicular transport and axon formation. The CIMT-induced DEPs were mainly related to synaptic remodeling and axon formation in the lesioned M1 and spinal cord. This study investigated the proteomic changes of the bilateral M1 and spinal cord as well as the CIMT-induced proteomic changes in HCP mice, which might provide new insights into the therapy of HCP.

Challenges in the pharmacological treatment of patients under suspicion of chronic traumatic encephalopathy: A review

Chronic traumatic encephalopathy (CTE) is caused by progressive neurodegeneration associated with repetitive head impacts. This disease is more common in professionals who practice contact sports, resulting in a concussion and subconcussive trauma. CTE is characterized by the accumulation of hyperphosphorylated tau protein in neurons, astrocytes, and frontotemporal lobe degeneration. Symptoms are usually nonspecific and overlap with other neurodegenerative diseases, such as Alzheimer's disease and frontotemporal dementia, making it difficult to provide drug treatment for patients with this comorbidity. Therefore, the objective of this article is to present an updated review of the pharmacological treatment of chronic traumatic encephalopathy and its challenges.

Transcriptomic analysis identifies shared biological foundations between ischemic stroke and Alzheimer's disease

AIM

Alzheimer's disease (AD) and ischemic stroke (IS), two major neurological diseases, are suggested to be associated in clinical and pathophysiological levels. Previous studies have provided some insights into the possible genetic mechanisms behind the correlation between AD and IS, but this issue is still not clear. We implemented transcriptomic analysis to detect common hub genes and pathways to help promote the understanding of this issue.

MATERIALS AND METHODS

Four gene expression profiling datasets (GSE16561, GSE58294, GSE63060, and GSE63061) of peripheral whole blood, which contain 108 IS samples, 284 AD samples, and 285 matched controls, were employed to detect differentially expressed genes (DEGs) for AD and IS, which were further analyzed for shared biological pathways, candidate drugs, and transcription factors. Protein-protein interaction (PPI) network and drug-target interaction analysis were applied to identify hub genes and drug targets, respectively. Result verification was done with other independent datasets (GSE37587, GSE46480, and GSE140829). The difference in proportions of various immune cells in the peripheral blood of AD and IS patients were evaluated using CIBERSORT.

RESULTS

We identified 74 DEGs and 18 biological processes with statistical significance shared by AD and IS, 9 of which were immune-related pathways. Five hub genes scored high in the topological analysis of the PPI network, and we also found eight drug target genes and candidate drugs which were associated with AD and IS. As for immunological changes, an increase in the proportion of M0 macrophages was found in the peripheral circulation of both AD and IS patients, and SOD1 expression was significantly correlated with this change.

CONCLUSION

Collectively, the common DEGs and shared pathways found in this study suggest a potential shared etiology between AD and IS, behind which immune system, particularly the M0 macrophage elevation, might have important roles. While, the shared hub genes, potential therapeutic gene targets and drugs reported in this study provide promising treatment strategies for AD and IS.

Role of Biliverdin Reductase A in the Regulation of Insulin Signaling in Metabolic and Neurodegenerative Diseases: An Update

Insulin signaling is a conserved pathway that orchestrates glucose and lipid metabolism, energy balance, and inflammation, and its dysregulation compromises the homeostasis of multiple systems. Insulin resistance is a shared hallmark of several metabolic diseases, including obesity, metabolic syndrome, and type 2 diabetes, and has been associated with cognitive decline during aging and dementia. Numerous mechanisms promoting the development of peripheral and central insulin resistance have been described, although most of them were not completely clarified. In the last decades, several studies have highlighted that biliverdin reductase-A (BVR-A), over its canonical role in the degradation of heme, acts as a regulator of insulin signaling. Evidence from human and animal studies show that BVR-A alterations are associated with the aberrant activation of insulin signaling, metabolic syndrome, liver steatosis, and visceral adipose tissue inflammation in obese and diabetic individuals. In addition, recent findings demonstrated that reduced BVR-A levels or impaired BVR-A activation contribute to the development of brain insulin resistance and metabolic alterations in Alzheimer’s disease. In this narrative review, we will provide an overview on the literature by focusing on the role of BVR-A in the regulation of insulin signaling and how BVR-A alterations impact on cell dysfunctions in both metabolic and neurodegenerative disorders.

Protein Kinase C Involvement in Neuroprotective Effects of Thymol and Carvacrol Against Toxicity Induced by Amyloid-β in Rat Hippocampal Neurons

INTRODUCTION

We have reported that thymol and carvacrol can improve cognitive abilities in Alzheimer Disease (AD) rat models. However, the mechanism of their action is not yet fully understood. Recently, our in vitro results suggested that PC12 cell death induced by Aβ25-35 can be protected by thymol and carvacrol via Protein Kinase C (PKC) and Reactive Oxygen Species (ROS) pathways. So, we hypothesize that the mechanisms of thymol and carvacrol in improving the learning impairment in the AD rat model may be related to their effects on PKC. So, the activity of PKC and protein expression levels of PKCα were examined in the hippocampal cells of the AD rat model.

METHODS

To examine the thymol and carvacrol effects, we performed a behavioral test in AD rat models induced by Aβ_25-35 neurotoxicity. To access the underlying mechanism of the protective effects, western blotting was performed with antibodies against PKCα. We also measured the PKC activity assay by Elisa. Histopathological studies were carried out in the hippocampus with Hematoxylin and Eosin (H&E) staining.

RESULTS

The escape latency increased in Aβ-received rats compared to the control group, and thymol and carvacrol reversed this deficit. Furthermore, these compounds could enhance the PKC activity and increase the PKCα expression ratio. Moreover, H&E staining showed that Aβ caused shrinkage of the CA1 pyramidal neurons. However, thymol and carvacrol treatments could prevent this effect of Aβ peptides.

CONCLUSION

This study suggests that Amyloid-Beta (Aβ) results in memory decline and histochemical disturbances in the hippocampus. Moreover, these results revealed that thymol and carvacrol could have protective effects on cognition in AD-like models via PKC activation.

HIGHLIGHTS

Rat's ability to find the invisible platform in the Morris Water Maze (MWM) was impaired by Amyloid-Beta (Aβ) infusion in the hippocampus, while this effect was reversed by thymol or carvacrol administration.Aβ significantly downregulated the Protein Kinase C (PKC) activity in rats' hippocampus.Western blot analysis demonstrated that Aβ significantly reduced PKCα protein expression in AD rat model hippocampal cells.The expression ratio of PKCα was upregulated following the injection of thymol and carvacrol in rats.Injection of Aβ in the hippocampus resulted in histochemical disturbances in CA1 pyramidal neurons.Carvacrol and thymol can prevent several histological changes induced by Aβ.

PLAIN LANGUAGE SUMMARY

Alzheimer's disease is one of the most important brain diseases in which the learning and memory are impaired. One of the main causes of Alzheimer's disease is the presence of amyloid beta plaques in the neurons. Protein kinase C enzyme reduces amyloid production and accumulation in the brain. In the present study, we tested the possible effects of carvacrol and thymol in a rat model of Alzheimer's disease. Memory impairment was induced in adult rats by intra-cerebral infusion of amyloid β. One week later, the memory-impaired animals were treated with carvacrol and thymol. Finally, we tested their memory in a Morris water maze apparatus. Furthermore, their hippocampus was dissected and PKC activity and the neuronal injury was evaluated. Our findings exhibited that thymol and carvacrol improved rats' memory performance. In addition, thymol and carvacrol significantly increased PKC activity and prevented neuronal cell loss in the rat hippocampus. This study shows that thymol and carvacrol have beneficial effects on memory and cognitive function via PKC activation.

Memory related molecular signatures: The pivots for memory consolidation and Alzheimer's related memory decline

Age-related cognitive decline is the major cause of concern due to its 70% more incidence than dementia cases worldwide. Moreover, aging is also the major risk factor of Alzheimer's disease (AD), associated with progressive memory loss. Approx. 13 million people will have Alzheimer-related memory decline by 2050. Learning and memory is the fundamental process of brain functions. However, the mechanism for the same is still under investigation. Thus, it is critical to understand the process of memory consolidation in the brain and extrapolate its understanding to the memory decline mechanism. Research on learning and memory has identified several molecular signatures such as Protein kinase M zeta (PKMζ), Calcium/calmodulin-dependent protein kinase II (CaMKII), Brain-derived neurotrophic factor (BDNF), cAMP-response element binding protein (CREB) and Activity-regulated cytoskeleton-associated protein (Arc) crucial for the maintenance and stabilization of long-term memory in the brain. Interestingly, memory decline in AD has also been linked to the abnormality in expressing these memory-related molecular signatures. Hence, in the present consolidated review, we explored the role of these memory-related molecular signatures in long-term memory consolidation. Additionally, the effect of amyloid-beta toxicity on these molecular signatures is discussed in detail.

Arsenic alters nitric oxide signaling similar to autism spectrum disorder and Alzheimer's disease-associated mutations

Epidemiological studies have proven that exposure to Arsenic (AS) leads to the development of many neurological disorders. However, few studies have investigated its molecular mechanisms in the brain. Our previous work has revealed nitric oxide (NO)-mediated apoptosis and SNO reprogramming in the cortex following arsenic treatment, yet the role of NO and S-nitrosylation (SNO) in AS-mediated neurotoxicity has not been investigated. Therefore, we have conducted a multidisciplinary in-vivo study in mice with two different doses of Sodium Arsenite (SA) (0.1 ppm and 1 ppm) in drinking water. We used the novel SNOTRAP-based mass spectrometry method followed by the bioinformatics analysis, Western blot validation, and five different behavioral tests. Bioinformatics analysis of SA-treated mice showed significant SNO-enrichment of processes involved in mitochondrial respiratory function, endogenous antioxidant systems, transcriptional regulation, cytoskeleton maintenance, and regulation of apoptosis. Western blotting showed increased levels of cleaved PARP-1 and cleaved caspase-3 in SA-treated mice consistent with SA-induced apoptosis. Behavioral studies showed significant cognitive dysfunctions similar to those of Autism spectrum disorder (ASD) and Alzheimer's disease (AD). A comparative analysis of the SNO-proteome of SA-treated mice with two transgenic mouse strains, models of ASD and AD, showed molecular convergence of SA environmental neurotoxicity and the genetic mutations causing ASD and AD. This is the first study to show the effects of AS on SNO-signaling in the striatum and hippocampus and its effects on behavioral characteristics. Finally, further investigation of the NO-dependent mechanisms of AS-mediated neurotoxicity may reveal new drug targets for its prevention.

Post-Translational Modification of Cav1.2 and its Role in Neurodegenerative Diseases

Cav1.2 plays an essential role in learning and memory, drug addiction, and neuronal development. Intracellular calcium homeostasis is disrupted in neurodegenerative diseases because of abnormal Cav1.2 channel activity and modification of downstream Ca²⁺ signaling pathways. Multiple post-translational modifications of Cav1.2 have been observed and seem to be closely related to the pathogenesis of neurodegenerative diseases. The specific molecular mechanisms by which Cav1.2 channel activity is regulated remain incompletely understood. Dihydropyridines (DHPs), which are commonly used for hypertension and myocardial ischemia, have been repurposed to treat PD and AD and show protective effects. However, further studies are needed to improve delivery strategies and drug selectivity. Better knowledge of channel modulation and more specific methods for altering Cav1.2 channel function may lead to better therapeutic strategies for neurodegenerative diseases.

Chiral 2-phenyl-3-hydroxypropyl esters as PKC-alpha modulators: HPLC enantioseparation, NMR absolute configuration assignment, and molecular docking studies

Protein kinase C (PKC) isoforms play a pivotal role in the regulation of numerous cellular functions, making them extensively studied and highly attractive drug targets. In our previous work, we identified in racemate 1-2, based on the 2-benzyl-3-hydroxypropyl ester scaffold, two new potent and promising PKCα and PKCδ ligands, targeting the C1 domain of these two kinases. Herein, we report the resolution of the racemates by enantioselective semi-preparative HPLC. The attribution of the absolute configuration (AC) of homochirals 1 was performed by NMR, via methoxy-α-trifluoromethyl-α-phenylacetic acid derivatization (MTPA or Mosher's acid). Moreover, the match between the experimental and predicted electronic circular dichroism (ECD) spectra confirmed the assigned AC. These results proved that Mosher's esters can be properly exploited for the determination of the AC also for chiral primary alcohols. Lastly, homochiral 1 and 2 were assessed for binding affinity and functional activity against PKCα. No significative differences in the K_i of the enantiopure compounds was observed, thus suggesting that chirality does not seem to play a significant role in targeting PKC C1 domain. These results are in accordance with the molecular docking studies performed using a new homology model for the human PKCαC1B domain.

Role of neurotoxicants in the pathogenesis of Alzheimer's disease: a mechanistic insight

Alzheimer's disease (AD) is the most conspicuous chronic neurodegenerative syndrome, which has become a significant challenge for the global healthcare system. Multiple studies have corroborated a clear association of neurotoxicants with AD pathogenicity, such as Amyloid beta (Aβ) proteins and neurofibrillary tangles (NFTs), signalling pathway modifications, cellular stress, cognitive dysfunctions, neuronal apoptosis, neuroinflammation, epigenetic modification, and so on. This review, therefore, aimed to address several essential mechanisms and signalling cascades, including Wnt (wingless and int.) signalling pathway, autophagy, mammalian target of rapamycin (mTOR), protein kinase C (PKC) signalling cascades, cellular redox status, energy metabolism, glutamatergic neurotransmissions, immune cell stimulations (e.g. microglia, astrocytes) as well as an amyloid precursor protein (APP), presenilin-1 (PSEN1), presenilin-2 (PSEN2) and other AD-related gene expressions that have been pretentious and modulated by the various neurotoxicants. This review concluded that neurotoxicants play a momentous role in developing AD through modulating various signalling cascades. Nevertheless, comprehension of this risk agent-induced neurotoxicity is far too little. More in-depth epidemiological and systematic investigations are needed to understand the potential mechanisms better to address these neurotoxicants and improve approaches to their risk exposure that aid in AD pathogenesis.Key messagesInevitable cascade mechanisms of how Alzheimer's Disease-related (AD-related) gene expressions are modulated by neurotoxicants have been discussed.Involvement of the neurotoxicants-induced pathways caused an extended risk of AD is explicited.Integration of cell culture, animals and population-based analysis on the clinical severity of AD is addressed.

Further insights for the role of Morin in mRTBI: Implication of non-canonical Wnt/PKC-α and JAK-2/STAT-3 signaling pathways

The slightly available data about the pathogenesis process of mild repetitive traumatic brain injury (mRTBI) indicates to the necessity of further exploration of mRTBI consequences. Several cellular changes are believed to contribute to the cognitive disabilities, and neurodegenerative changes observed later in persons subjected to mRTBI. We investigated glial fibrillary acidic protein (GFAP), the important severity related biomarker, where it showed further increase after multiple trauma compared to single one. To authenticate our aim, Morin (10 mg/kg loading dose, then twice daily 5 mg/kg for 7 days), MK-801 (1 mg/kg; i.p) and their combination were used. The results obtained has shown that all the chosen regimens opposed the upregulated dementia markers (Aβ1-40,p(Thr231)Tau) and inflammatory protein contents/expression of p(Ser53s6)NF-κBp65, TNF-α, IL-6,and IL-1β and the elevated GFAP in immune stained cortex sections. Additionally, they exerted anti-apoptotic activity by decreasing caspase-3 activity and increasing Bcl-2 contents. Saving brain tissues was evident after these therapeutic agents via upregulating the non-canonical Wnt-1/PKC-α cue and IL-10/p(Tyr(1007/1008))JAK-2/p(Tyr705)STAT-3 signaling pathway to confirm enhancement of survival pathways on the molecular level. Such results were imitated by correcting the injury dependent deviated behavior, where Morin alone or in combination enhanced behavior outcome. On one side, our study refers to the implication of two survival signaling pathways; viz.,the non-canonical Wnt-1/PKC-α and p(Tyr(1007/1008))JAK-2/p(Tyr705)STAT-3 in single and repetitive mRTBI along with distorted dementia markers, inflammation and apoptotic process that finally disrupted behavior. On the other side, intervention through affecting all these targets by Morin alone or with MK-801 affords a promising neuroprotective effect.

Deregulated Protein Kinases: Friend and Foe in Ischemic Stroke

Ischemic stroke is the third leading cause of mortality worldwide, but its medical management is still limited to the use of thrombolytics as a lifesaving option. Multiple molecular deregulations of the protein kinase family occur during the period of ischemia/reperfusion. However, experimental studies have shown that alterations in the expression of essential protein kinases and their pharmacological modulation can modify the neuropathological milieu and hasten neurophysiological recovery. This review highlights the role of key protein kinase members and their implications in the evolution of stroke pathophysiology. Activation of ROCK-, MAPK-, and GSK-3β-mediated pathways following neuronal ischemia/reperfusion injury in experimental conditions aggravate the neuropathology and delays recovery. Targeting ROCK, MAPK, and GSK-3β will potentially enhance myelin regeneration, improve blood-brain barrier (BBB) function, and suppress inflammation, which ameliorates neuronal survival. Conversely, protein kinases such as PKA, Akt, PKCα, PKCε, Trk, and PERK salvage neurons post-ischemia by mechanisms including enhanced toxin metabolism, restoring BBB integrity, neurotrophic effects, and apoptosis suppression. Certain protein kinases such as ERK1/2, JNK, and AMPK have favourable and unfavourable effects in salvaging ischemia-injured neurons. Targeting multiple protein kinase-mediated pathways simultaneously may improve neuronal recovery post-ischemia.

Neuroprotective Effects of Curcumin in Cerebral Ischemia: Cellular and Molecular Mechanisms

Despite being a major global health concern, cerebral ischemia/stroke has limited therapeutic options. Tissue plasminogen activator (tPA) is the only available medication to manage acute ischemic stroke, but this medication is associated with adverse effects and has a narrow therapeutic time window. Curcumin, a polyphenol that is abundantly present in the rhizome of the turmeric plant (Curcuma longa), has shown promising neuroprotective effects in animal models of neurodegenerative diseases, including cerebral ischemia. In the central nervous system (CNS), neuroprotective effects of curcumin have been experimentally validated in Alzheimer's disease, Parkinson's disease, multiple sclerosis, and cerebral ischemia. Curcumin can exert pleiotropic effects in the postischemic brain including antioxidant, anti-inflammatory, antiapoptotic, vasculoprotective, and direct neuroprotective efficacies. Importantly, neuroprotective effects of curcumin has been reported in both ischemic and hemorrhagic stroke models. A broad-spectrum neuroprotective efficacy of curcumin suggested that curcumin can be an appealing therapeutic strategy to treat cerebral ischemia. In this review, we aimed to address the pharmacotherapeutic potential of curcumin in cerebral ischemia including its cellular and molecular mechanisms of neuroprotection revealing curcumin as an appealing therapeutic candidate for cerebral ischemia.

Vascular Risk Factors and Alzheimer's Disease: Blood-Brain Barrier Disruption, Metabolic Syndromes, and Molecular Links

Alzheimer's disease (AD) is a neurodegenerative disorder, marked by cortical and hippocampal deposition of amyloid-β (Aβ) plaques and neurofibrillary tangles and cognitive impairment. Studies indicate a prominent link between cerebrovascular abnormalities and the onset and progression of AD, where blood-brain barrier (BBB) dysfunction and metabolic disorders play key risk factors. Pericyte degeneration, endothelial cell damage, astrocyte depolarization, diminished tight junction integrity, and basement membrane disarray trigger BBB damage. Subsequently, the altered expression of low-density lipoprotein receptor-related protein 1 and receptor for advanced glycation end products at the microvascular endothelial cells dysregulate Aβ transport across the BBB. White matter lesions and microhemorrhages, dyslipidemia, altered brain insulin signaling, and insulin resistance contribute to tau and Aβ pathogenesis, and oxidative stress, mitochondrial damage, inflammation, and hypoperfusion serve as mechanistic links between pathophysiological features of AD and ischemia. Deregulated calcium homeostasis, voltage gated calcium channel functioning, and protein kinase C signaling are also common mechanisms for both AD pathogenesis and cerebrovascular abnormalities. Additionally, APOE polymorphic alleles that characterize impaired cerebrovascular integrity function as primary genetic determinants of AD. Overall, the current review enlightens key vascular risk factors for AD and underscores pathophysiologic relationship between AD and vascular dysfunction.

Sequestration of the PKC ortholog Pck2 in stress granules as a feedback mechanism of MAPK signaling in fission yeast

Protein kinase C (PKC) signaling is a highly conserved signaling module that plays a central role in a myriad of physiological processes, ranging from cell proliferation to cell death, via various signaling pathways, including MAPK signaling. Stress granules (SGs) are non-membranous cytoplasmic foci that aggregate in cells exposed to environmental stresses. Here, we explored the role of SGs in PKC/MAPK signaling activation in fission yeast. High-heat stress (HHS) induced Pmk1 MAPK activation and Pck2 translocation from the cell tips into poly(A)-binding protein (Pabp)-positive SGs. Pck2 dispersal from the cell tips required Pck2 kinase activity, and constitutively active Pck2 exhibited increased translocation to SGs. Importantly, Pmk1 deletion impaired Pck2 recruitment to SGs, indicating that MAPK activation stimulates Pck2 SG translocation. Consistently, HHS-induced SGs delayed Pck2 relocalization at the cell tips, thereby blocking subsequent Pmk1 reactivation after recovery from HHS. HHS partitioned Pck2 into the Pabp-positive SG-containing fraction, which resulted in reduced Pck2 abundance and kinase activity in the soluble fraction. Taken together, these results indicate that MAPK-dependent Pck2 SG recruitment serves as a feedback mechanism to intercept PKC/MAPK activation induced by HHS, which might underlie PKC-related diseases.

Toxicity of Amyloid-β Peptides Varies Depending on Differentiation Route of SH-SY5Y Cells

Alzheimer's disease (AD) is a currently incurable neurodegenerative disorder being the major form of dementia worldwide. AD pathology is initiated by cerebral aggregation of amyloid-β (Aβ) peptides in the form of amyloid plaques; however, the mechanism how Aβ peptide aggregates participate in the disease progression and neurodegeneration is still under debate. Human neuroblastoma cell line SH-SY5Y is a convenient cellular model, which is widely used in biochemical and toxicological studies of neurodegenerative diseases. This model can be further improved by differentiation of the cells toward more neuron-like culture using different protocols. In the current study, dbcAMP, retinoic acid with TPA, or BDNF were used for differentiation of SH-SY5Y cells, and the resulting cultures were tested for the toxicity toward the Aβ42 peptide. The toxicity of Aβ42 peptide depended on the type of differentiated cells: RA and TPA- differentiated cells were most resistant, whereas dbcAMP and RA/BDNF- differentiated cells were more sensitive to Aβ toxicity as compared with non-differentiated cells. The differentiated cultures provide more appropriate cellular models of human origin that can be used for studies of the mechanism of Aβ pathogenesis and for a screening of compounds antagonistic to the toxicity of Aβ peptides.

Protein kinase C eta is activated in reactive astrocytes of an Alzheimer's disease mouse model: Evidence for its immunoregulatory function in primary astrocytes

Alzheimer's disease (AD) is the primary cause of age-related dementia. Pathologically, AD is characterized by synaptic loss, the accumulation of β-amyloid peptides and neurofibrillary tangles, glial activation, and neuroinflammation. Whereas extensive studies focused on neurons and activation of microglia in AD, the role of astrocytes has not been well-characterized. Protein kinase C (PKC) was also implicated in AD; however, its role in astrocyte activation was not elucidated. Using the 5XFAD mouse model of AD, we show that PKC-eta (PKCη), an astrocyte-specific stress-activated and anti-apoptotic kinase, plays a role in reactive astrocytes. We demonstrate that PKCη staining is highly enriched in cortical astrocytes in a disease-dependent manner and in the vicinity of amyloid-β peptides plaques. Moreover, activation of PKCη, as indicated by its increased phosphorylation levels, is exhibited mainly in cortical astrocytes derived from adult 5XFAD mice. PKCη activation was associated with elevated levels of reactive astrocytic markers and upregulation of the pro-inflammatory cytokine interleukin 6 (IL-6) compared to littermate controls. Notably, inhibiting the kinase activity of PKCη in 5XFAD astrocyte cultures markedly increased the levels of secreted IL-6-a phenomenon that was also observed in wild-type astrocytes stimulated by inflammatory cytokines (e.g., TNFα, IL-1). Similar increase in the release of IL-6 was also observed upon inhibition of either the mammalian target of rapamycin (mTOR) or the protein phosphatase 2A (PP2A). Our findings suggest that the mTOR-PKCη-PP2A signaling cascade functions as a negative feedback loop of NF-κB-induced IL-6 release in astrocytes. Thus, we identify PKCη as a regulator of neuroinflammation in AD.

The PERK-Dependent Molecular Mechanisms as a Novel Therapeutic Target for Neurodegenerative Diseases

Higher prevalence of neurodegenerative diseases is strictly connected with progressive aging of the world population. Interestingly, a broad range of age-related, neurodegenerative diseases is characterized by a common pathological mechanism-accumulation of misfolded and unfolded proteins within the cells. Under certain circumstances, such protein aggregates may evoke endoplasmic reticulum (ER) stress conditions and subsequent activation of the unfolded protein response (UPR) signaling pathways via the protein kinase RNA-like endoplasmic reticulum kinase (PERK)-dependent manner. Under mild to moderate ER stress, UPR has a pro-adaptive role. However, severe or long-termed ER stress conditions directly evoke shift of the UPR toward its pro-apoptotic branch, which is considered to be a possible cause of neurodegeneration. To this day, there is no effective cure for Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), or prion disease. Currently available treatment approaches for these diseases are only symptomatic and cannot affect the disease progression. Treatment strategies, currently under detailed research, include inhibition of the PERK-dependent UPR signaling branches. The newest data have reported that the use of small-molecule inhibitors of the PERK-mediated signaling branches may contribute to the development of a novel, ground-breaking therapeutic approach for neurodegeneration. In this review, we critically describe all the aspects associated with such targeted therapy against neurodegenerative proteopathies.

The potential of drug repurposing combined with reperfusion therapy in cerebral ischemic stroke: A supplementary strategy to endovascular thrombectomy

Stroke is the major cause of adult disability and the second or third leading cause of death in developed countries. The treatment options for stroke (thrombolysis or thrombectomy) are restricted to a small subset of patients with acute ischemic stroke because of the limited time for an efficacious response and the strict criteria applied to minimize the risk of cerebral hemorrhage. Attempts to develop new treatments, such as neuroprotectants, for acute ischemic stroke have been costly and time-consuming and to date have yielded disappointing results. The repurposing approved drugs known to be relatively safe, such as statins and minocycline, may provide a less costly and more rapid alternative to new drug discovery in this clinical condition. Because adequate perfusion is thought to be vital for a neuroprotectant to be effective, endovascular thrombectomy (EVT) with advanced imaging modalities offers the possibility of documenting reperfusion in occluded large cerebral vessels. An examination of established medications that possess neuroprotective characters using in a large-vessel occlusive disorder with EVT may speed the identification of new and more broadly efficacious medications for the treatment of ischemic stroke. These approaches are highlighted in this review along with a critical assessment of drug repurposing combined with reperfusion therapy as a supplementary means for halting or mitigating stroke-induced brain damage.

Gender- and region-specific changes in estrogen signaling in aging rat brain mitochondria

Recently epidemiological studies suggest females lose neuroprotection from neurodegenerative diseases as they go through menopause. It has been hypothesized that this neuroprotection is hormone-dependent. The current study characterized cell signaling molecules downstream of estrogen receptor beta that are known to play a role in memory, PKC, ERK, and connexin-43, in regions of the brain associated with memory decline in an attempt to elucidate significant changes that occur post-estrus. Total whole cell lysates were compared to isolated mitochondrial protein because mitochondrial function is known to be altered during aging. As hypothesized, protein concentrations differed depending on age, gender, and brain region. Additionally, many of these changes occurred within mitochondria but not within whole cell lysates indicating that these are epigenetic alterations. These findings accentuate the complexity of aging and provide insight into the gender-specific cellular processes that occur throughout this process.

Age-Dependent Levels of Protein Kinase Cs in Brain: Reduction of Endogenous Mechanisms of Neuroprotection

Neurodegenerative diseases are among the leading causes of mortality and disability worldwide. However, current therapeutic approaches have failed to reach significant results in their prevention and cure. Protein Kinase Cs (PKCs) are kinases involved in the pathophysiology of neurodegenerative diseases, such as Alzheimer's Disease (AD) and cerebral ischemia. Specifically ε, δ, and γPKC are associated with the endogenous mechanism of protection referred to as ischemic preconditioning (IPC). Existing modulators of PKCs, in particular of εPKC, such as ψεReceptor for Activated C-Kinase (ψεRACK) and Resveratrol, have been proposed as a potential therapeutic strategy for cerebrovascular and cognitive diseases. PKCs change in expression during aging, which likely suggests their association with IPC-induced reduction against ischemia and increase of neuronal loss occurring in senescent brain. This review describes the link between PKCs and cerebrovascular and cognitive disorders, and proposes PKCs modulators as innovative candidates for their treatment. We report original data showing εPKC reduction in levels and activity in the hippocampus of old compared to young rats and a reduction in the levels of δPKC and γPKC in old hippocampus, without a change in their activity. These data, integrated with other findings discussed in this review, demonstrate that PKCs modulators may have potential to restore age-related reduction of endogenous mechanisms of protection against neurodegeneration.

Identification of key genes and upstream regulators in ischemic stroke

INTRODUCTION

Ischemic stroke (IS) causes severe neurological impairments and physical disabilities and has a high economic burden. Our study aims to identify the key genes and upstream regulators in IS by integrated microarray analysis.

METHODS

An integrated analysis of microarray studies of IS was performed to identify the differentially expressed genes (DEGs) in IS compared to normal control. Based on these DEGs, we performed the functional annotation and transcriptional regulatory network constructions. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to verify the expression of DEGs.

RESULTS

From two Gene Expression Omnibus datasets obtained, we obtained 1526 DEGs (534 up-regulated and 992 down-regulated genes) between IS and normal control. The results of functional annotation showed that Oxidative phosphorylation and Alzheimer's disease were significantly enriched pathways in IS. Top four transcription factors (TFs) with the most downstream genes including PAX4, POU2F1, ELK1, and NKX2-5. The expression of six genes (ID3, ICAM2, DCTPP1, ANTXR2, DUSP1, and RGS2) was detected by qRT-PCR. Except for DUSP1 and RGS2, the other four genes in qRT-PCR played the same pattern with that in our integrated analysis.

CONCLUSIONS

The dysregulation of these six genes may involve with the process of ischemic stroke (IS). Four TFs (PAX4, POU2F1, ELK1 and NKX2-5) were concluded to play a role in IS. Our finding provided clues for exploring mechanism and developing novel diagnostic and therapeutic strategies for IS.

Phosphoregulation on mitochondria: Integration of cell and organelle responses

Mitochondria are highly integrated organelles that are crucial to cell adaptation and mitigating adverse physiology. Recent studies demonstrate that fundamental signal transduction pathways incorporate mitochondrial substrates into their biological programs. Reversible phosphorylation is emerging as a useful mechanism to modulate mitochondrial function in accordance with cellular changes. Critical serine/threonine protein kinases, such as the c-Jun N-terminal kinase (JNK), protein kinase A (PKA), PTEN-induced kinase-1 (PINK1), and AMP-dependent protein kinase (AMPK), readily translocate to the outer mitochondrial membrane (OMM), the interface of mitochondria-cell communication. OMM protein kinases phosphorylate diverse mitochondrial substrates that have discrete effects on organelle dynamics, protein import, respiratory complex activity, antioxidant capacity, and apoptosis. OMM phosphorylation events can be tempered through the actions of local protein phosphatases, such as mitogen-activated protein kinase phosphatase-1 (MKP-1) and protein phosphatase 2A (PP2A), to regulate the extent and duration of signaling. The central mediators of OMM signal transduction are the scaffold proteins because the relative abundance of these accessory proteins determines the magnitude and duration of a signaling event on the mitochondrial surface, which dictates the biological outcome of a local signal transduction pathway. The concentrations of scaffold proteins, such as A-kinase anchoring proteins (AKAPs) and Sab (or SH3 binding protein 5-SH3BP5), have been shown to influence neuronal survival and vulnerability, respectively, in models of Parkinson's disease (PD), highlighting the importance of OMM signaling to health and disease. Despite recent progress, much remains to be discovered concerning the mechanisms of OMM signaling. Nonetheless, enhancing beneficial OMM signaling events and inhibiting detrimental protein-protein interactions on the mitochondrial surface may represent highly selective approaches to restore mitochondrial health and homeostasis and mitigate organelle dysfunction in conditions such as PD.

Protein Kinase C: Targets to Regenerate Brain Injuries?

Acute or chronic injury to the central nervous system (CNS), causes neuronal death and irreversible cognitive deficits or sensory-motor alteration. Despite the capacity of the adult CNS to generate new neurons from neural stem cells (NSC), neuronal replacement following an injury is a restricted process, which does not naturally result in functional regeneration. Therefore, potentiating endogenous neurogenesis is one of the strategies that are currently being under study to regenerate damaged brain tissue. The insignificant neurogenesis that occurs in CNS injuries is a consequence of the gliogenic/non-neurogenic environment that inflammatory signaling molecules create within the injured area. The modification of the extracellular signals to generate a neurogenic environment would facilitate neuronal replacement. However, in order to generate this environment, it is necessary to unearth which molecules promote or impair neurogenesis to introduce the first and/or eliminate the latter. Specific isozymes of the protein kinase C (PKC) family differentially contribute to generate a gliogenic or neurogenic environment in injuries by regulating the ADAM17 mediated release of growth factor receptor ligands. Recent reports describe several non-tumorigenic diterpenes isolated from plants of the Euphorbia genus, which specifically modulate the activity of PKC isozymes promoting neurogenesis. Diterpenes with 12-deoxyphorbol or lathyrane skeleton, increase NPC proliferation in neurogenic niches in the adult mouse brain in a PKCβ dependent manner exerting their effects on transit amplifying cells, whereas PKC inhibition in injuries promotes neurogenesis. Thus, compounds that balance PKC activity in injuries might be of use in the development of new drugs and therapeutic strategies to regenerate brain injuries.

Targeting MAPK phosphorylation of Connexin43 provides neuroprotection in stroke

This study demonstrates that astrocytic connexin43 gap junction hemichannels are largely controlled by four C-terminal tail–located serine residues and provides mechanistic insight on how phosphorylation of these residues affects recovery from stroke.

Connexin43 (Cx43) function is influenced by kinases that phosphorylate specific serine sites located near its C-terminus. Stroke is a powerful inducer of kinase activity, but its effect on Cx43 is unknown. We investigated the impact of wild-type (WT) and knock-in Cx43 with serine to alanine mutations at the protein kinase C (PKC) site Cx43^S368A, the casein kinase 1 (CK1) sites Cx43^{S325A/328Y/330A}, and the mitogen-activated protein kinase (MAPK) sites Cx43^{S255/262/279/282A} (MK4) on a permanent middle cerebral artery occlusion (pMCAO) stroke model. We demonstrate that MK4 transgenic animals exhibit a significant decrease in infarct volume that was associated with improvement in behavioral performance. An increase in astrocyte reactivity with a concomitant decrease in microglial reactivity was observed in MK4 mice. In contrast to WT, MK4 astrocytes displayed reduced Cx43 hemichannel activity. Pharmacological blockade of Cx43 hemichannels with TAT-Gap19 also significantly decreased infarct volume in WT animals. This study provides novel molecular insights and charts new avenues for therapeutic intervention associated with Cx43 function.

Developmental Axon Degeneration Requires TRPV1-Dependent Ca2+ Influx

Development of the nervous system relies on a balance between axon and dendrite growth and subsequent pruning and degeneration. The developmental degeneration of dorsal root ganglion (DRG) sensory axons has been well studied in part because it can be readily modeled by removing the trophic support by nerve growth factor (NGF) in vitro. We have recently reported that axonal fragmentation induced by NGF withdrawal is dependent on Ca²⁺, and here, we address the mechanism of Ca²⁺ entry required for developmental axon degeneration of mouse embryonic DRG neurons. Our results show that the transient receptor potential vanilloid family member 1 (TRPV1) cation channel plays a critical role mediating Ca²⁺ influx in DRG axons withdrawn from NGF. We further demonstrate that TRPV1 activation is dependent on reactive oxygen species (ROS) generation that is driven through protein kinase C (PKC) and NADPH oxidase (NOX)-dependent pathways that become active upon NGF withdrawal. These findings demonstrate novel mechanistic links between NGF deprivation, PKC activation, ROS generation, and TRPV1-dependent Ca²⁺ influx in sensory axon degeneration.

Protein kinase C -activating isophthalate derivatives mitigate Alzheimer's disease-related cellular alterations

Abnormal protein kinase C (PKC) function contributes to many pathophysiological processes relevant for Alzheimer's disease (AD), such as amyloid precursor protein (APP) processing. Phorbol esters and other PKC activators have been demonstrated to enhance the secretion of soluble APPα (sAPPα), reduce the levels of β-amyloid (Aβ), induce synaptogenesis, and promote neuroprotection. We have previously described isophthalate derivatives as a structurally simple family of PKC activators. Here, we characterised the effects of isophthalate derivatives HMI-1a3 and HMI-1b11 on neuronal viability, neuroinflammatory response, processing of APP and dendritic spine density and morphology in in vitro. HMI-1a3 increased the viability of embryonic primary cortical neurons and decreased the production of the pro-inflammatory mediator TNFα, but not that of nitric oxide, in mouse neuron-BV2 microglia co-cultures upon LPS- and IFN-γ-induced neuroinflammation. Furthermore, both HMI-1a3 and HMI-1b11 increased the levels of sAPPα relative to total sAPP and the ratio of Aβ42/Aβ40 in human SH-SY5Y neuroblastoma cells. Finally, bryostatin-1, but not HMI-1a3, increased the number of mushroom spines in proportion to total spine density in mature mouse hippocampal neuron cultures. These results suggest that the PKC activator HMI-1a3 exerts neuroprotective functions in the in vitro models relevant for AD by reducing the production of TNFα and increasing the secretion of neuroprotective sAPPα.

Cerebral Hypoperfusion and Other Shared Brain Pathologies in Ischemic Stroke and Alzheimer's Disease

Newly emerged evidence reveals that ischemic stroke and Alzheimer's disease (AD) share pathophysiological changes in brain tissue including hypoperfusion, oxidative stress, immune exhaustion, and inflammation. A mechanistic link between hypoperfusion and amyloid β accumulation can lead to cell damage as well as to motor and cognitive deficits. This review will discuss decreased cerebral perfusion and other related pathophysiological changes common to both ischemic stroke and AD, such as vascular damages, cerebral blood flow alteration, abnormal expression of amyloid β and tau proteins, as well as behavioral and cognitive deficits. Furthermore, this review highlights current treatment options and potential therapeutic targets that warrant further investigation.

Inhibition of PKCδ reduces amyloid-β levels and reverses Alzheimer disease phenotypes

β-amyloid protein (Aβ) plays a central role in the pathogenesis of Alzheimer disease (AD). Aβ is generated from sequential cleavage of amyloid precursor protein (APP) by β-site APP-cleaving enzyme 1 (BACE1) and the γ-secretase complex. Although activation of some protein kinase C (PKC) isoforms such as PKCα and ε has been shown to regulate nonamyloidogenic pathways and Aβ degradation, it is unclear whether other PKC isoforms are involved in APP processing/AD pathogenesis. In this study, we report that increased PKCδ levels correlate with BACE1 expression in the AD brain. PKCδ knockdown reduces BACE1 expression, BACE1-mediated APP processing, and Aβ production. Conversely, overexpression of PKCδ increases BACE1 expression and Aβ generation. Importantly, inhibition of PKCδ by rottlerin markedly reduces BACE1 expression, Aβ levels, and neuritic plaque formation and rescues cognitive deficits in an APP Swedish mutations K594N/M595L/presenilin-1 with an exon 9 deletion-transgenic AD mouse model. Our study indicates that PKCδ plays an important role in aggravating AD pathogenesis, and PKCδ may be a potential target in AD therapeutics.

Advances in Drug Discovery and Development in Geriatric Psychiatry

PURPOSE OF REVIEW

This article reviews recent advances in drug discovery and development for geriatric psychiatry. Drug discovery for disorders of the central nervous system is a long and challenging process, with a high attrition rate from the preclinical stages through to marketing a compound. Developing drugs for geriatric neuropsychiatric conditions presents additional challenges, due to the complexity of the symptoms, comorbid diagnoses, and the variability of the population. Despite there being limited success over the past two decades, a number of new approaches have identified potential targets for preclinical development and ultimately clinical testing.

RECENT FINDINGS

Recent approaches have tried to address specific mechanisms that relate to the disease progression. These approaches include combining a number of ligands into to multi-target compounds, or targeting specific types of cells such as protein kinases or myeloid cells. In addition, the increased use of induced pluripotent stem cell cultures has enabled new compounds to be tested on disease-specific tissues, increasing the success rate of the lead compounds going through the preclinical stages. New pharmacological agents designed with advanced screening techniques and the shift towards systems pharmacology is changing the landscape of drug discovery in geriatric psychiatry. There is potential for these new agents to produce targeted effects in the framework of disorders that have long been untreatable.

Identification of Protein Kinase C Isoforms Involved in Type 1 Diabetic Encephalopathy in Mice

Diabetic encephalopathy is a complication of diabetes mellitus characterized by impaired cognitive functions. Protein kinase C (PKC) isoforms are rarely reported on diabetic encephalopathy, although they have been believed to play crucial roles in other diabetic complications. In this study, streptozotocin- (STZ-) induced diabetic mice were found to exhibit learning and memory deficits in the Morris water maze test. Meanwhile, the expression of cPKCβII, nPKCε, and cPKCγ did not change in the hippocampus, cortex, and striatum at 2 and 8 weeks after STZ injection. The nPKCε translocation to the membrane, where it is activated, was not altered in the above brain regions at 2 and 8 weeks after STZ injection. Nevertheless, cPKCβII translocation to the membrane was significantly decreased in the cortex and hippocampus at 8 weeks after STZ injection. The translocation of cPKCγ from the cytosol to the membrane was remarkably decreased in the hippocampus at 2 and 8 weeks and in the cortex and striatum at 8 weeks after STZ injection. In addition, deletion of cPKCγ aggravated the impairment of spatial learning and memory. In conclusion, our results suggest that the decrease in the activity of cPKCβII and cPKCγ, especially cPKCγ, may play key roles in the pathogenesis of diabetic encephalopathy.

Role of Tau Acetylation in Alzheimer's Disease and Chronic Traumatic Encephalopathy: The Way Forward for Successful Treatment

Progressive neurodegenerative diseases plague millions of individuals both in the United States and across the world. The current pathology of progressive neurodegenerative tauopathies, such as Alzheimer's disease (AD), Pick's disease, frontotemporal dementia (FTD), and progressive supranuclear palsy, primarily revolves around phosphorylation and hyperphosphorylation of the tau protein. However, more recent evidence suggests acetylation of tau protein at lysine 280 may be a critical step in molecular pathology of these neurodegenerative diseases prior to the tau hyperphosphorylation. Secondary injury cascades such as oxidative stress, endoplasmic reticulum stress, and neuroinflammation contribute to lasting damage within the brain and can be induced by a number of different risk factors. These injury cascades funnel into a common pathway of early tau acetylation, which may serve as the catalyst for progressive degeneration. The post translational modification of tau can result in production of toxic oligomers, contributing to reduced solubility as well as aggregation and formation of neurofibrillary tangles, the hallmark of AD pathology. Chronic Traumatic Encephalopathy (CTE), caused by repetitive brain trauma is also associated with a hyperphosphorylation of tau. We postulated acetylation of tau at lysine 280 in CTE disease could be present prior to the hyperphosphorylation and tested this hypothesis in CTE pathologic specimens. We also tested for ac-tau 280 in early stage Alzheimer's disease (Braak stage 1). Histopathological examination using the ac tau 280 antibody was performed in three Alzheimer's cases and three CTE patients. Presence of ac-tau 280 was confirmed in all cases at early sites of disease manifestation. These findings suggest that tau acetylation may precede tau phosphorylation and could be the first "triggering" event leading to neuronal loss. To the best of our knowledge, this is the first study to identify acetylation of the tau protein in CTE. Prevention of tau acetylation could possibly serve as a novel target for stopping neurodegeneration before it fully begins. In this study, we highlight what is known about tau acetylation and neurodegeneration.

The C1 domain of Vav3, a novel potential therapeutic target

Vav1/2/3 comprise a protein family with guanyl nucleotide exchange activity for Rho and Rac as well as with motifs conferring adapter activity. Biologically, Vav1 plays a critical role in hematologic cell signaling, whereas Vav2/3 have a wider tissue distribution, but all 3 Vav proteins are implicated in cancer development. A structural feature of Vav1/2/3 is the presence of an atypical C1 domain, which possesses close structural homology to the typical C1 domains of protein kinase C but which fails to bind the second messenger diacylglycerol or the potent analogs, the phorbol esters. Previously, we have shown that five residues in the Vav1 C1 domain are responsible for its lack of phorbol ester binding. Here, we show that the lack of phorbol ester binding of Vav3 has a similar basis. We then explore the consequences of phorbol ester binding to a modified Vav3 in which the C1 domain has been altered to allow phorbol ester binding. We find both disruption of the guanyl nucleotide exchange activity of the modified Vav 3 as well as a shift in localization to the membrane upon phorbol ester treatment. This change in localization is associated with altered interactions with other signaling proteins. The studies provide a first step in assessing the potential for the design of custom C1 domain targeted molecules selective for the atypical C1 domains of Vav family proteins.

Computer-Aided Drug Design Applied to Marine Drug Discovery: Meridianins as Alzheimer's Disease Therapeutic Agents

Computer-aided drug discovery/design (CADD) techniques allow the identification of natural products that are capable of modulating protein functions in pathogenesis-related pathways, constituting one of the most promising lines followed in drug discovery. In this paper, we computationally evaluated and reported the inhibitory activity found in meridianins A-G, a group of marine indole alkaloids isolated from the marine tunicate Aplidium, against various protein kinases involved in Alzheimer's disease (AD), a neurodegenerative pathology characterized by the presence of neurofibrillary tangles (NFT). Balance splitting between tau kinase and phosphate activities caused tau hyperphosphorylation and, thereby, its aggregation and NTF formation. Inhibition of specific kinases involved in its phosphorylation pathway could be one of the key strategies to reverse tau hyperphosphorylation and would represent an approach to develop drugs to palliate AD symptoms. Meridianins bind to the adenosine triphosphate (ATP) binding site of certain protein kinases, acting as ATP competitive inhibitors. These compounds show very promising scaffolds to design new drugs against AD, which could act over tau protein kinases Glycogen synthetase kinase-3 Beta (GSK3β) and Casein kinase 1 delta (CK1δ, CK1D or KC1D), and dual specificity kinases as dual specificity tyrosine phosphorylation regulated kinase 1 (DYRK1A) and cdc2-like kinases (CLK1). This work is aimed to highlight the role of CADD techniques in marine drug discovery and to provide precise information regarding the binding mode and strength of meridianins against several protein kinases that could help in the future development of anti-AD drugs.

Insulin signaling: An opportunistic target to minify the risk of Alzheimer's disease

Alzheimer's disease (AD) is progressive neurodegenerative disorder characterized by accumulation of senile plaques, neurofibrillary tangles (NFT) and neurodegeneration. The diabetes mellitus (DM) is one of the risk factors for AD pathogenesis by impairment in insulin signaling and glucose metabolism in central as well as peripheral system. Insulin resistance, impaired glucose and lipid metabolism are leading to the Aβ (Aβ) aggregation, Tau phosphorylation, mitochondrial dysfunction, oxidative stress, protein misfolding, memory impairment and also mark over Aβ transport through central to peripheral and vice versa. Several pathways, like enzymatic degradation of Aβ, forkhead box protein O1 (FOXO) signaling, insulin signaling shared common pathological mechanism for both AD and DM. Recent evidence showed that hyperinsulinemia and hyperglycemia affect the onset and progression of AD differently. Some researchers have suggested that hyperglycemia influences vascular tone, while hyperinsulinemia may underlie mitochondrial deficit. The objective of this review is to determine whether existing evidence supports the concept that impairment in insulin signaling and glucose metabolism play an important role in pathogenesis of AD. In the first part of this review, we tried to explain the interconnecting link between AD and DM, whereas the second part includes more information on insulin resistance and its involvement in AD pathogenesis. In the final part of this review, we have focused more toward the AD treatment by targeting insulin signaling like anti-diabetic, antioxidant, nutraceuticals and dietary supplements. To date, more researches should be done in this field in order to explore the pathways in insulin signaling, which might ameliorate the treatment options and reduce the risk of AD due to DM.

Metabolic Syndrome as a Risk Factor for Alzheimer's Disease: Is Aβ a Crucial Factor in Both Pathologies?

SIGNIFICANCE

Recently, chronic degenerative diseases have become one of the main health problems worldwide. That is the case of Alzheimer's disease (AD) and metabolic syndrome (MetS), whose expression can be influenced by different risk factors. Recent Advances: In recent decades, it has been widely described that MetS increases the risk of cognitive impairment and dementia. MetS pathogenesis involves several vascular risk factors such as diabetes, dyslipidemia, hypertension, and insulin resistance (I/R).

CRITICAL ISSUES

Reported evidence shows that vascular risk factors are associated with AD, particularly in the development of protein aggregation, inflammation, oxidative stress, neuronal dysfunction, and disturbances in signaling pathways, with insulin receptor signaling being a common alteration between MetS and AD.

FUTURE DIRECTIONS

Insulin signaling has been involved in tau phosphorylation and amyloid β (Aβ) metabolism. However, it has also been demonstrated that Aβ oligomers can bind to insulin receptors, triggering their internalization, decreasing neuron responsiveness to insulin, and promoting insulin I/R. Thus, it could be argued that Aβ could be a convergent factor in the development of both pathologies. Antioxid. Redox Signal. 26, 542-560.

Urine Formaldehyde Predicts Cognitive Impairment in Post-Stroke Dementia and Alzheimer's Disease

Although Alzheimer's disease (AD) was first described over 100 years ago, there is still no suitable biomarker for diagnosing AD in easily collectable samples (e.g., blood plasma, saliva, and urine). Here, we investigated the relationship between morning urine formaldehyde concentration and cognitive impairment in patients with post-stroke dementia (PSD) or AD in this cross-sectional survey for 7 years. Cognitive abilities of the study participants (n = 577, four groups: 231 controls, 61 stroke, 65 PSD, and 220 AD) were assessed by Mini-Mental State Examination (MMSE). Morning urine formaldehyde concentrations were measured by high performance liquid chromatography (HPLC). Gender- and age-matched participants were selected from the four groups (n = 42 in each group). Both semicarbazide-sensitive amine oxidase (SSAO, a formaldehyde-generating enzyme) and formaldehyde levels in the blood and urine were analyzed by using an enzyme-linked immunosorbent assay (ELISA) and HPLC, respectively. We found that morning urine formaldehyde levels were inversely correlated with MMSE scores. The threshold value (the best Cut-Off value) of formaldehyde concentration for predicting cognitive impairment was 0.0418 mM in patients with PSD (Sensitivity: 92.3%; Specificity: 77.1%), and 0.0449 mM in patients with AD (Sensitivity: 94.1%; Specificity: 81.8%), respectively. The results of biochemical analysis revealed that the observed increase in urine formaldehyde resulted from an overexpression of SSAO in the blood. The findings suggest that measuring the concentration of formaldehyde in overnight fasting urine could be used as a potentially noninvasive method for evaluating the likelihood of ensuing cognitive impairment or dementia.

Implication of protein kinase C of the left intermediate medial mesopallium in memory impairments induced by early prenatal morphine exposure in one-day old chicks

Previously we reported that prenatal morphine exposure during embryonic days 5-8 can cause cognitive deficits of one-trial passive avoidance learning (PAL) in one-day old chicks. Because protein kinase C (PKC) has been associated with memory capacity, we investigated the effects of prenatal morphine exposure on PKC isoforms expression in the left intermediate medial mesopallium (IMM) of chick brain at a time when memory tests were performed at 30, 120 and 360min respectively following training in PAL paradigm. We found that the level of PKCα in the membrane fractions in left IMM was decreased but that in the cytosol fractions showed a increased trend in prenatally morphine-exposed chicks with impaired long-term memory (120 and 360min). Moreover, the translocation of PKC δ from cytosol to membrane in left IMM was shown in prenatal morphine group which had significantly impaired long-term memory at 360min after training. Furthermore, there were no statistical differences between the two groups regarding the expressions of PKCα and PKC δ in the membrane fraction, although their levels in the cytosol fraction of prenatal morphine group which showed impaired intermediate-term memory at 30min after training, were quite different from that of prenatal saline group. Taken together, these results indicate that PKCα and PKC δ in the left IMM are differentially involved in the impairments of long-term memory induced by prenatal morphine exposure. Neither PKCα nor PKC δ in left IMM may be associated with the disruption of intermediate-term memory of chicks prenatally exposed to morphine.

Protein Kinase Activity Decreases with Higher Braak Stages of Alzheimer's Disease Pathology

Alzheimer’s disease (AD) is characterized by a long pre-clinical phase (20–30 years), during which significant brain pathology manifests itself. Disease mechanisms associated with pathological hallmarks remain elusive. Most processes associated with AD pathogenesis, such as inflammation, synaptic dysfunction, and hyper-phosphorylation of tau are dependent on protein kinase activity. The objective of this study was to determine the involvement of protein kinases in AD pathogenesis. Protein kinase activity was determined in postmortem hippocampal brain tissue of 60 patients at various stages of AD and 40 non-demented controls (Braak stages 0-VI) using a peptide-based microarray platform. We observed an overall decrease of protein kinase activity that correlated with disease progression. The phosphorylation of 96.7% of the serine/threonine peptides and 37.5% of the tyrosine peptides on the microarray decreased significantly with increased Braak stage (p-value <0.01). Decreased activity was evident at pre-clinical stages of AD pathology (Braak I-II). Increased phosphorylation was not observed for any peptide. STRING analysis in combination with pathway analysis and identification of kinases responsible for peptide phosphorylation showed the interactions between well-known proteins in AD pathology, including the Ephrin-receptor A1 (EphA1), a risk gene for AD, and sarcoma tyrosine kinase (Src), which is involved in memory formation. Additionally, kinases that have not previously been associated with AD were identified, e.g., protein tyrosine kinase 6 (PTK6/BRK), feline sarcoma oncogene kinase (FES), and fyn-associated tyrosine kinase (FRK). The identified protein kinases are new biomarkers and potential drug targets for early (pre-clinical) intervention.