PP2A blockade inhibits autophagy and causes intraneuronal accumulation of ubiquitinated proteins

ZLDI-8 facilitates pexophagy by ROS-mediated activation of TFEB and ATM in HeLa cells

Autophagy-mediated organelle quality control is vital for cellular homeostasis. However, the mechanisms underlying selective autophagy of peroxisomes, known as pexophagy, are less well understood than those of other organelles, such as mitochondria. In this study, we screened a phosphatase inhibitor library using a cell-based system and identified several potent pexophagy inducers, including ZLDI-8, a known inhibitor of lymphoid-specific tyrosine phosphatase. Notably, treatment with ZLDI-8 selectively induces the loss of peroxisomes without affecting other organelles, such as mitochondria, the endoplasmic reticulum, or the Golgi apparatus. The peroxisome loss induced by ZLDI-8 was significantly blocked in ATG5-knockout HeLa cells, confirming its dependence on autophagy. We further found that ZLDI-8 treatment increases both cellular and peroxisomal reactive oxygen species (ROS), which were effectively scavenged by N-acetylcysteine (NAC). The increase in peroxisomal ROS leads to the activation of ATM kinase and the dephosphorylation of TFEB. Moreover, ROS scavenging prevents all of these processes. Taken together, these findings demonstrate that ZLDI-8 induces pexophagy through a mechanism involving peroxisomal ROS-mediated activation of TFEB and ATM. This study provides valuable insights into the molecular mechanisms regulating selective peroxisome degradation and potential therapeutic strategies for targeting pexophagy.

Targeting of PP2 A/GSK3β/PTEN Axis in Alzheimer Disease: The Mooting Evidence, Divine, and Devil

Alzheimer disease (AD) is a progressive neurodegenerative disease of the brain due to extracellular accumulation of Aβ. In addition, intracellular accumulation of hyperphosphorlyated tau protein which form neurofibrillary tangle (NFT) is associated with progressive neuronal injury and the development of AD. Aβ and NFTs interact together to induce inflammation and oxidative stress which further induce neurodegeneration in AD. The exact relationship between Aβ and tau, the two proteins that accumulate within these lesions, has proven elusive. A growing body of work supports the notion that Aβ may directly or indirectly interact with tau to accelerate NFTs formation. Aβ can adversely affect distinct molecular and cellular pathways, thereby facilitating tau phosphorylation, aggregation, mislocalization, and accumulation. Aβ may drive tau pathology by activating specific kinases, providing a straightforward mechanism by which Aβ may enhance tau hyperphosphorylation and NFT formation. Many cellular signaling pathways such as protein phosphatase 2A (PP2A), glycogen synthase kinase 3β (GSK3β), and phosphatase and tensin homologue (PTEN) are intricate in AD neuropathology. PP2A which involved in the dephosphorylation of tau protein is deregulated in AD, and correlated with cognitive impairment. PTEN is a critical regulator of neuronal growth, survival, and development, improving synaptic plasticity and axonal regeneration. Nevertheless, mutated PTEN is associated with the development of cognitive impairment by inhibiting the expression and the activity of PP2A. Furthermore, dysregulation of GSK3β affects Aβ, tau protein phosphorylation, synaptic plasticity and other signaling pathways involved in the pathogenesis of AD. Therefore, there is a close interaction among GSK3β, PTEN, and PP2A. GSK3β exaggerates AD neuropathology by inhibiting PP2A and activates the expression of PTEN. These findings specified a related interaction among GSK3β, PTEN, and PP2A, and modulation of the single component of this axis may not produce an effective effect against AD neuropathology. Modulation of this axis by metformin and statins can reduce AD neuropathology. Therefore, this review aims to discuss the role of GSK3β/PTEN/PP2A axis in AD neuropathology and how targeting of this axis by metformin and statins can produce effective therapeutic strategy in the management of AD. In conclusion, inhibition of GSK3β and PTEN and activation of PP2A may be more suitable than modulation of single signaling pathway. Metformin and statins by activating PP2A and inhibiting of GSK3β and PTEN attenuate the development and progression of AD.

Hyperphosphorylated tau targeting human serum albumin Fusion protein as therapeutics for Alzheimer's diseases

Introduction

Neurofibrillary tangles (NFTs) are composed of hyperphosphorylated forms of microtubule-associated protein tau (Tau), which is responsible for neurodegeneration in Alzheimer's disease (AD). The hippocampal region has been a major focus of AD research because the deposits of phosphorylated tau protein in these regions are correlated with early memory deficits. Despite extensive studies, therapeutic strategies to reduce tau hyperphosphorylation and NFTs deposition remain unclear. AL04, a recently developed recombinant fusion protein comprising Cystatin C, human serum albumin, and a novel blood brain barrier (BBB) penetrating peptide, is currently under investigation. Previous studies have demonstrated its effectiveness in reducing amyloid beta plaques in AD mouse model.

Methods

In this study, we investigated the effects of AL04 on lowering hyperphosphorylated tau and NFTs in JNPL3 mouse model harboring human tau-P301L mutation. 3-month-old female mice intraperitoneally received AL04 (5 mg/kg) or PBS treatment every other week for 24 weeks. We used confocal microscopy and western blot to visualize and analyze changes in hyperphosphorylated tau Ser202/Thr205 labeled with AT8 antibody in the brain.

Results

We found that the AL04 treatment decreases hyperphosphorylated tau at PP2A-sensitive epitope Ser202/Thr205 in the hippocampus of the brain. In the brain lysates of AL04 treated mice, we observed the reduction of I2PP2A, inhibitor of PP2A, and the induction of autophagy receptor proteins such as SQSTM-1/p62 and OPTN.

Conclusion

Our data suggests that AL04 can be used as an AD prophylactic/therapeutic agent as it lowers the hyperphosphorylated tau by downregulating I2PP2A. We also propose that AL04 can induce the degradation of hyperphosphorylated tau aggregates through the upregulation of the autophagy pathway.

Epigenetic and post-translational modifications in autophagy: biological functions and therapeutic targets

Autophagy is a conserved lysosomal degradation pathway where cellular components are dynamically degraded and re-processed to maintain physical homeostasis. However, the physiological effect of autophagy appears to be multifaced. On the one hand, autophagy functions as a cytoprotective mechanism, protecting against multiple diseases, especially tumor, cardiovascular disorders, and neurodegenerative and infectious disease. Conversely, autophagy may also play a detrimental role via pro-survival effects on cancer cells or cell-killing effects on normal body cells. During disorder onset and progression, the expression levels of autophagy-related regulators and proteins encoded by autophagy-related genes (ATGs) are abnormally regulated, giving rise to imbalanced autophagy flux. However, the detailed mechanisms and molecular events of this process are quite complex. Epigenetic, including DNA methylation, histone modifications and miRNAs, and post-translational modifications, including ubiquitination, phosphorylation and acetylation, precisely manipulate gene expression and protein function, and are strongly correlated with the occurrence and development of multiple diseases. There is substantial evidence that autophagy-relevant regulators and machineries are subjected to epigenetic and post-translational modulation, resulting in alterations in autophagy levels, which subsequently induces disease or affects the therapeutic effectiveness to agents. In this review, we focus on the regulatory mechanisms mediated by epigenetic and post-translational modifications in disease-related autophagy to unveil potential therapeutic targets. In addition, the effect of autophagy on the therapeutic effectiveness of epigenetic drugs or drugs targeting post-translational modification have also been discussed, providing insights into the combination with autophagy activators or inhibitors in the treatment of clinical diseases.

Targeting T-type channels in cancer: What is on and what is off?

Over the past 20 years, various studies have demonstrated a pivotal role of T-type calcium channels (TTCCs) in tumor progression. Cytotoxic effects of TTCC pharmacological blockers have been reported in vitro and in preclinical models. However, their roles in cancer physiology are only beginning to be understood. In this review, we discuss evidence for the signaling pathways and cellular processes stemming from TTCC activity, mainly inferred by inverse reasoning from pharmacological blocks and, only in a few studies, by gene silencing or channel activation. A thorough analysis indicates that drug-induced cytotoxicity is partially an off-target effect. Dissection of on/off-target activity is paramount to elucidate the physiological roles of TTCCs, and to deliver efficacious therapies suited to different cancer types and stages.

Regulation PP2Ac methylation ameliorating autophagy dysfunction caused by Mn is associated with mTORC1/ULK1 pathway

Manganese (Mn) exposure leads to autophagy dysfunction and causes neurodegenerative diseases such as Parkinson's syndrome and Alzheimer's disease. However, the mechanism of neurotoxicity of Mn has been less clear. The methylation of the protein phosphatase 2A catalytic subunit determines the dephosphorylation activity of protein phosphatase and plays an important role in autophagy regulation. In this investigation, we established a model of Mn (0-2000 μmol/L) exposure to N2a cells for 12 h, used the PPME-1 inhibitor ABL-127, and constructed an LCMT1-overexpressing N2a cell line. We also regulated the PP2Ac methylation level and explored the effect of PP2Ac methylation on Mn-induced (0-1000 μmol/L) N2a cellular autophagy. Our results showed that Mn > 500 μmol/L induced N2a cell damage and increased oxidative stress. Moreover, Mn modulated autophagy in N2a cells by downregulating PP2Ac methylation, which regulated mTORC1 signaling pathway activation. Both ABL-127 and LCMT1 overexpression can upregulate PP2Ac methylation in parallel with ameliorating N2a cell abnormal autophagy induced by Mn, Briefly, the upregulation of PP2Ac methylation can ameliorate the autophagy disorder of N2a by Mn and effectively alleviate Mn-induced cytotoxicity and oxidative stress, indicating that regulation of autophagy is a protective strategy against Mn-induced neurotoxicity.

Autophagy-targeted therapy to modulate age-related diseases: Success, pitfalls, and new directions

Autophagy is a critical metabolic process that supports homeostasis at a basal level and is dynamically regulated in response to various physiological and pathological processes. Autophagy has some etiologic implications that support certain pathological processes due to alterations in the lysosomal-degradative pathway. Some of the conditions related to autophagy play key roles in highly relevant human diseases, e.g., cardiovascular diseases (15.5%), malignant and other neoplasms (9.4%), and neurodegenerative conditions (3.7%). Despite advances in the discovery of new strategies to treat these age-related diseases, autophagy has emerged as a therapeutic option after preclinical and clinical studies. Here, we discuss the pitfalls and success in regulating autophagy initiation and its lysosome-dependent pathway to restore its homeostatic role and mediate therapeutic effects for cancer, neurodegenerative, and cardiac diseases. The main challenge for the development of autophagy regulators for clinical application is the lack of specificity of the repurposed drugs, due to the low pharmacological uniqueness of their target, including those that target the PI3K/AKT/mTOR and AMPK pathway. Then, future efforts must be conducted to deal with this scenery, including the disclosure of key components in the autophagy machinery that may intervene in its therapeutic regulation. Among all efforts, those focusing on the development of novel allosteric inhibitors against autophagy inducers, as well as those targeting autolysosomal function, and their integration into therapeutic regimens should remain a priority for the field.

CIP2A silencing alleviates doxorubicin resistance in MCF7/ADR cells through activating PP2A and autophagy

Background

Cancerous inhibitor of protein phosphatase 2A (CIP2A) plays a critical role in the pathogenesis of various types of cancer. Here, we investigated whether manipulating CIP2A abundance could enhance the treatment effects of doxorubicin in MCF-7/ADR cells.

Methods

CIP2A silencing was achieved by specific siRNAs. Proliferation of breast cancer cell line MCF-7/ADR under effective doxorubicin concentrations after CIP2A silencing was examined by MTT assay. Wound healing assay was performed to quantify cell migration and caspase-3/-7 activities were measured for assessing the extent of apoptosis.

Results

First, our data confirmed that MCF-7/ADR cell proliferation was suppressed by doxorubicin in a dose-dependent manner. Additionally, knocking down of CIP2A could further decrease MCF-7 cell proliferation and migration, even in the presence of doxorubicin. Mechanistically, we have found that CIP2A silencing promoted cell apoptosis relative to doxorubicin alone or vehicle control groups. Lastly, phosphatase2A (PP2A) activity was potentiated and the autophagy markers, LC3B and Beclin1, were upregulated after knocking down CIP2A.

Conclusion

Our findings support the potential benefits of using CIP2A inhibitor as a therapeutic agent to treat doxorubicin-resistant breast cancer.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12094-021-02616-7.

Taurine Antagonizes Macrophages M1 Polarization by Mitophagy-Glycolysis Switch Blockage via Dragging SAM-PP2Ac Transmethylation

The excessive M1 polarization of macrophages drives the occurrence and development of inflammatory diseases. The reprogramming of macrophages from M1 to M2 can be achieved by targeting metabolic events. Taurine promotes for the balance of energy metabolism and the repair of inflammatory injury, preventing chronic diseases and complications. However, little is known about the mechanisms underlying the action of taurine modulating the macrophage polarization phenotype. In this study, we constructed a low-dose LPS/IFN-γ-induced M1 polarization model to simulate a low-grade pro-inflammatory process. Our results indicate that the taurine transporter TauT/SlC6A6 is upregulated at the transcriptional level during M1 macrophage polarization. The nutrient uptake signal on the membrane supports the high abundance of taurine in macrophages after taurine supplementation, which weakens the status of methionine metabolism, resulting in insufficient S-adenosylmethionine (SAM). The low availability of SAM is directly sensed by LCMT-1 and PME-1, hindering PP2Ac methylation. PP2Ac methylation was found to be necessary for M1 polarization, including the positive regulation of VDAC1 and PINK1. Furthermore, its activation was found to promote the elimination of mitochondria by macrophages via the mitophagy pathway for metabolic adaptation. Mechanistically, taurine inhibits SAM-dependent PP2Ac methylation to block PINK1-mediated mitophagy flux, thereby maintaining a high mitochondrial density, which ultimately hinders the conversion of energy metabolism to glycolysis required for M1. Our findings reveal a novel mechanism of taurine-coupled M1 macrophage energy metabolism, providing novel insights into the occurrence and prevention of low-grade inflammation, and propose that the sensing of taurine and SAM availability may allow communication to inflammatory response in macrophages.

Role of mitochondrial dysfunction, oxidative stress and autophagy in progression of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia. The pathological hallmarks of AD are amyloid plaques [aggregates of amyloid beta (A)] and neurofibrillary tangles (aggregates of tau protein). Growing evidence suggests that tau accumulation is pathologically more relevant to the development of neurodegeneration and cognitive decline in AD patients than A plaques. Mitochondrial damage plays an important role in AD. Mitochondrial damage has been related to amyloid-beta or tau pathology or to the presence of specific presenilin-1 mutations. Elevate reactive oxygen species/reactive nitrogen species production and defective mitochondrial dynamic balance has been suggested to be the reason as well as the consequence of AD related pathology. Oxidative stress is a prominent early event in the pathogenesis of AD and is therefore believed to contribute to tau hyperphosphorylation. Several studies have shown that the autophagy pathway in neurons is important under physiological and pathological conditions. Therefore, this pathway plays a crucial role for the degradation of endogenous soluble tau. However, the relationship between mitochondrial dysfunctioning, oxidative stress, autophagy dysregulation, and neuronal cell death in AD remains unclear. Here, we review the latest progress in AD, with a special emphasis on mitochondrial dysfunctioning, oxidative stress, and autophagy. We also discuss the interlink mechanism of these three factors in AD.

P2X7 Receptor is Involved in Mitochondrial Dysfunction Induced by Extracellular Alpha Synuclein in Neuroblastoma SH-SY5Y Cells

The purinergic P2X7 receptor (P2X7R) belongs to a family of trimeric ion channels that are gated by extracellular adenosine 5′-triphosphate (ATP). Several studies have pointed to a role of P2X7R-dependent signalling in Parkinson's disease (PD)-related neurodegeneration. The pathology of (PD) is characterized by the formation of insoluble alpha-synuclein (α-Syn) aggregates—Lewy bodies, but the mechanisms underlying α-Syn-induced dopaminergic cell death are still partially unclear. Our previous studies indicate that extracellular α-Syn directly interact with neuronal P2X7R and induces intracellular free calcium mobilization in neuronal cells. The main objective of this study was to examine the involvement of P2X7R receptor in α-Syn-induced mitochondrial dysfunction and cell death. We found that P2X7R stimulation is responsible for α-Syn-induced oxidative stress and activation of the molecular pathways of programmed cell death. Exogenous α-Syn treatment led to P2X7R-dependent decrease in mitochondrial membrane potential as well as elevation of mitochondrial ROS production resulting in breakdown of cellular energy production. Moreover, P2X7R-dependent deregulation of AMP-activated protein kinase as well as decrease in parkin protein level could be responsible for α-Syn-induced mitophagy impairment and accumulation of dysfunctional mitochondria. P2X7R might be putative pharmacological targets in molecular mechanism of extracellular α-Syn toxicity.

Nebivolol Improves Obesity-Induced Vascular Remodeling by Suppressing NLRP3 Activation

Nebivolol is a novel β-adrenergic receptor (β-AR) blocker with anti-inflammatory and antioxidant properties. The NLRP3 inflammasome plays a pivotal role in the pathogenesis of obesity-induced vascular dysfunction. Our study aimed to explore the effect of nebivolol on the NLRP3 inflammasome and vascular remodeling in diet-induced obese rats. Eight-week-old Sprague-Dawley male rats were fed with either a standard chow diet or a high-fat diet (HFD) for 8 weeks. Next, the obese rats were subdivided into 3 groups as follows: (1) HFD control group, (2) HFD with low doses of nebivolol (5 mg/kg·d), and (3) HFD with high doses of nebivolol (10 mg/kg·d). A 4-week treatment with nebivolol improved acetylcholine-induced vascular relaxation in accordance with an increased aortic endothelial nitric oxide synthase. Nebivolol attenuated NLRP3 inflammasome activation and suppressed autophagy. In parallel, nebivolol enhanced the levels of phase-II detoxifying enzymes, including superoxide dismutase and catalase. These effects were associated with an increased β3-AR level. Moreover, nebivolol treatment significantly increased Adenosine 5'-monophosphate (AMP)-activated protein kinase activity and decreased phosphorylation of the mammalian target of rapamycin. These results demonstrated that nebivolol improves obesity-induced vascular remodeling by attenuating NLRP3 inflammasome activation and restoring the antioxidant defense.

Pharmacological doses of melatonin impede cognitive decline in tau-related Alzheimer models, once tauopathy is initiated, by restoring the autophagic flux

Alterations in autophagy are increasingly being recognized in the pathogenesis of proteinopathies like Alzheimer's disease (AD). This study was conducted to evaluate whether melatonin treatment could provide beneficial effects in an Alzheimer model related to tauopathy by improving the autophagic flux and, thereby, prevent cognitive decline. The injection of AAV-hTau^P301L viral vectors and treatment/injection with okadaic acid were used to achieve mouse and human ex vivo, and in vivo tau-related models. Melatonin (10 μmol/L) impeded oxidative stress, tau hyperphosphorylation, and cell death by restoring autophagy flux in the ex vivo models. In the in vivo studies, intracerebroventricular injection of AAV-hTau^P301L increased oxidative stress, neuroinflammation, and tau hyperphosphorylation in the hippocampus 7 days after the injection, without inducing cognitive impairment; however, when animals were maintained for 28 days, cognitive decline was apparent. Interestingly, late melatonin treatment (10 mg/kg), starting once the alterations mentioned above were established (from day 7 to day 28), reduced oxidative stress, neuroinflammation, tau hyperphosphorylation, and caspase-3 activation; these observations correlated with restoration of the autophagy flux and memory improvement. This study highlights the importance of autophagic dysregulation in tauopathy and how administration of pharmacological doses of melatonin, once tauopathy is initiated, can restore the autophagy flux, reduce proteinopathy, and prevent cognitive decline. We therefore propose exogenous melatonin supplementation or the development of melatonin derivatives to improve autophagy flux for the treatment of proteinopathies like AD.

Expression of WIPI2B counteracts age-related decline in autophagosome biogenesis in neurons

Autophagy defects are implicated in multiple late-onset neurodegenerative diseases including Amyotrophic Lateral Sclerosis (ALS) and Alzheimer's, Huntington's, and Parkinson's diseases. Since aging is the most common shared risk factor in neurodegeneration, we assessed rates of autophagy in mammalian neurons during aging. We identified a significant decrease in the rate of constitutive autophagosome biogenesis during aging and observed pronounced morphological defects in autophagosomes in neurons from aged mice. While early stages of autophagosome formation were unaffected, we detected the frequent production of stalled LC3B-negative isolation membranes in neurons from aged mice. These stalled structures recruited the majority of the autophagy machinery, but failed to develop into LC3B-positive autophagosomes. Importantly, ectopically expressing WIPI2B effectively restored autophagosome biogenesis in aged neurons. This rescue is dependent on the phosphorylation state of WIPI2B at the isolation membrane, suggesting a novel therapeutic target in age-associated neurodegeneration.

Ouabain activates transcription factor EB and exerts neuroprotection in models of Alzheimer's disease

The number of neurofibrillary tangles containing abnormal hyperphosphorylated tau protein correlates with the degree of dementia in Alzheimer's disease (AD). In addition, autophagosome accumulation and disturbance of autophagy, the process by which toxic aggregate proteins are degraded in the cytosol, are also found in AD models. These indicate that regulation of the autophagy-lysosome system may be a potential therapeutic target for AD. Activation of transcription factor EB (TFEB), a master regulator of autophagy-lysosome system gene transcription, reduces the amount of tau in APP mice. Here, to identify potential therapeutic compounds for AD, we performed two types of screening to determine pharmacologically active compounds that increase 1) neuronal viability in okadaic acid-induced tau hyperphosphorylation-related neurodegeneration models and 2) nuclear localization of TFEB in high-contents screening. Ouabain, a cardiac glycoside, was discovered as a common hit compound in both screenings. It also exhibited a significant protective effect in tau transgenic fly and mouse models in vivo. This work demonstrates that ouabain enhances activation of TFEB through inhibition of the mTOR pathway and induces downstream autophagy-lysosomal gene expression and cellular restorative properties. Therefore, therapeutic approaches using ouabain reduce the accumulation of abnormal toxic tau in vitro and in vivo.

Metabolic Regulation of Methionine Restriction in Diabetes

Although the effects of dietary methionine restriction have been investigated in the physiology of aging and diseases related to oxidative stress, the relationship between methionine restriction (MR) and the development of metabolic disorders has not been explored extensively. This review summarizes studies of the possible involvement of dietary methionine restriction in improving insulin resistance, glucose homeostasis, oxidative stress, lipid metabolism, the pentose phosphate pathway (PPP), and inflammation, with an emphasis on the fibroblast growth factor 21 and protein phosphatase 2A signals and autophagy in diabetes. Diets deficient in methionine may be a useful nutritional strategy in patients with diabetes.

Modulating Protein Phosphatase 2A Rescues Disease Phenotype in Neurodegenerative Tauopathies

Alzheimer's disease (AD) is the leading cause of dementia worldwide accounting for around 70% of all cases. There is currently no treatment for AD beyond symptom management and attempts at developing disease-modifying therapies have yielded very little. These strategies have traditionally targeted the peptide Aβ, which is thought to drive pathology. However, the lack of clinical translation of these Aβ-centric strategies underscores the need for diverse treatment strategies targeting other aspects of the disease. Metal dyshomeostasis is a common feature of several neurodegenerative diseases such as AD, Parkinson's disease, and frontotemporal dementia, and manipulation of metal homeostasis has been explored as a potential therapeutic avenue for these diseases. The copper ionophore glyoxalbis-[N4-methylthiosemicarbazonato]Cu(II) (Cu^II(gtsm)) has previously been shown to improve the cognitive deficits seen in an AD animal model; however, the molecular mechanism remained unclear. Here we report that the treatment of two animal tauopathy models (APP/PS1 and rTg4510) with Cu^II(gtsm) recovers the cognitive deficits seen in both neurodegenerative models. In both models, markers of tau pathology were significantly reduced with Cu^II(gtsm) treatment, and in the APP/PS1 model, the levels of Aβ remained unchanged. Analysis of tau kinases (GSK3β and CDK5) revealed no drug induced changes; however, both models exhibited a significant increase in the levels of the structural subunit of the tau phosphatase, PP2A. These findings suggest that targeting the tau phosphatase PP2A has therapeutic potential for preventing memory impairments and reducing the tau pathology seen in AD and other tauopathies.

Clearance of Amyloid Beta and Tau in Alzheimer's Disease: from Mechanisms to Therapy

Alzheimer's disease (AD) is the most common neurodegenerative disease. Pathological proteins of AD mainly contain amyloid-beta (Aβ) and tau. Their deposition will lead to neuron damage by a series of pathways, and then induce memory and cognitive impairment. Thus, it is pivotal to understand the clearance pathways of Aβ and tau in order to delay or even halt AD. Aβ clearance mechanisms include ubiquitin-proteasome system, autophagy-lysosome, proteases, microglial phagocytosis, and transport from the brain to the blood via the blood-brain barrier (BBB), arachnoid villi and blood-CSF barrier, which can be named blood circulatory clearance. Recently, lymphatic clearance has been demonstrated to play a key role in transport of Aβ into cervical lymph nodes. The discovery of meningeal lymphatic vessels is another direct evidence for lymphatic clearance in the brain. Furthermore, periphery clearance also contributes to Aβ clearance. Tau clearance is almost the same as Aβ clearance. In this review, we will mainly introduce the clearance mechanisms of Aβ and tau proteins, and summarize corresponding targeted drug therapies for AD.

Longitudinal evaluation of ventricular volume changes associated with mild traumatic brain injury in military service members

PRIMARY OBJECTIVE

To investigate differences in longitudinal trajectories of ventricle-brain ratio (VBR), a general measure of brain atrophy, between Veterans with and without history of mild traumatic brain injury (mTBI).

RESEARCH DESIGN

Structural magnetic resonance imaging (MRI) was used to calculate VBR in 70 Veterans with a history of mTBI and 34 Veterans without such history at two time points approximately 3 and 8 years after a combat deployment.

MAIN OUTCOMES AND RESULTS

Both groups demonstrated a quadratic relationship between VBR and age that is consistent with normal developmental trajectories. Veterans with history of mTBI had larger total brain volume, but no interaction between mTBI and age was observed for brain volume, ventricular volume, or VBR.

CONCLUSIONS

In our longitudinal sample of deployed Veterans, mTBI was not associated with gross brain atrophy as reflected by abnormally high VBR or abnormal increases in VBR over time.

PP2A as the Main Node of Therapeutic Strategies and Resistance Reversal in Triple-Negative Breast Cancer

Triple negative breast cancer (TNBC), is defined as a type of tumor lacking the expression of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2). The ER, PR and HER2 are usually the molecular therapeutic targets for breast cancers, but they are ineffective for TNBC because of their negative expressions, so chemotherapy is currently the main treatment strategy in TNBC. However, drug resistance remains a major impediment to TNBC chemotherapeutic treatment. Recently, the protein phosphatase 2A (PP2A) has been found to regulate the phosphorylation of some substrates involved in the relevant target of TNBC, such as cell cycle control, DNA damage responses, epidermal growth factor receptor, immune modulation and cell death resistance, which may be the effective therapeutic strategies or influence drug sensitivity to TNBCs. Furthermore, PP2A has also been found that could induce ER re-expression in ER-negative breast cancer cells, and which suggests PP2A could promote the sensitivity of tamoxifen to TNBCs as a resistance reversal agent. In this review, we will summarize the potential therapeutic value of PP2A as the main node in developing targeting agents, disrupting resistance or restoring drug sensitivity in TNBC.

Ceramide inhibits PKCθ by regulating its phosphorylation and translocation to lipid rafts in Jurkat cells

Protein kinase C theta (PKCθ) is a novel, calcium-independent member of the PKC family of kinases that was identified as a central player in T cell signaling and proliferation. Upon T cell activation by antigen-presenting cells, PKCθ gets phosphorylated and activated prior to its translocation to the immunological synapse where it couples with downstream effectors. PKCθ may be regulated by ceramide, a crucial sphingolipid that is known to promote differentiation, growth arrest, and apoptosis. To further investigate the mechanism, we stimulated human Jurkat T cells with either PMA or anti-CD3/anti-CD28 antibodies following induction of ceramide accumulation by adding exogenous ceramide, bacterial sphingomyelinase, or Fas ligation. Our results suggest that ceramide regulates the PKCθ pathway through preventing its critical threonine 538 (Thr538) phosphorylation and subsequent activation, thereby inhibiting the kinase's translocation to lipid rafts. Moreover, this inhibition is not likely to be a generic effect of ceramide on membrane reorganization. Other lipids, namely dihydroceramide, palmitate, and sphingosine, did not produce similar effects on PKCθ. Addition of the phosphatase inhibitors okadaic acid and calyculin A reversed the inhibition exerted by ceramide, and this suggests involvement of a ceramide-activated protein phosphatase. Such previously undescribed mechanism of regulation of PKCθ raises the possibility that ceramide, or one of its derivatives, and may prove valuable in novel therapeutic approaches for disorders involving autoimmunity or excessive inflammation-where PKCθ plays a critical role.

Sortilin limits EGFR signaling by promoting its internalization in lung cancer

Tyrosine kinase receptors such as the epidermal growth factor receptor (EGFR) transduce information from the microenvironment into the cell and activate homeostatic signaling pathways. Internalization and degradation of EGFR after ligand binding limits the intensity of proliferative signaling, thereby helping to maintain cell integrity. In cancer cells, deregulation of EGFR trafficking has a variety of effects on tumor progression. Here we report that sortilin is a key regulator of EGFR internalization. Loss of sortilin in tumor cells promoted cell proliferation by sustaining EGFR signaling at the cell surface, ultimately accelerating tumor growth. In lung cancer patients, sortilin expression decreased with increased pathologic grade, and expression of sortilin was strongly correlated with survival, especially in patients with high EGFR expression. Sortilin is therefore a regulator of EGFR intracellular trafficking that promotes receptor internalization and limits signaling, which in turn impacts tumor growth.

Autophagy impairment by caspase-1-dependent inflammation mediates memory loss in response to β-Amyloid peptide accumulation

β-Amyloid peptide accumulation in the cortex and in the hippocampus results in neurodegeneration and memory loss. Recently, it became evident that the inflammatory response triggered by β-Amyloid peptides promotes neuronal cell death and degeneration. In addition to inflammation, β-Amyloid peptides also induce alterations in neuronal autophagy, eventually leading to neuronal cell death. Thus, here we evaluated whether the inflammatory response induced by the β-Amyloid peptides impairs memory via disrupting the autophagic flux. We show that male mice overexpressing β-Amyloid peptides (5XFAD) but lacking caspase-1, presented reduced β-Amyloid plaques in the cortex and in the hippocampus; restored brain autophagic flux and improved learning and memory capacity. At the molecular level, inhibition of the inflammatory response in the 5XFAD mice restored LC3-II levels and prevented the accumulation of oligomeric p62 and ubiquitylated proteins. Furthermore, caspase-1 deficiency reinstates activation of the AMPK/Raptor pathway while down-regulating AKT/mTOR pathway. Consistent with this, we found an inverse correlation between the increase of autophagolysosomes in the cortex of 5XFAD mice lacking caspase-1 and the presence of mitochondria with altered morphology. Together our results indicate that β-Amyloid peptide-induced caspase-1 activation, disrupts autophagy in the cortex and in the hippocampus resulting in neurodegeneration and memory loss.

Orchestrated Action of PP2A Antagonizes Atg13 Phosphorylation and Promotes Autophagy after the Inactivation of TORC1

Target of rapamycin complex 1 (TORC1) phosphorylates autophagy-related Atg13 and represses autophagy under nutrient-rich conditions. However, when TORC1 becomes inactive upon nutrient depletion or treatment with the TORC1 inhibitor rapamycin, Atg13 dephosphorylation occurs rapidly, and autophagy is induced. At present, the phosphatases involved in Atg13 dephosphorylation remain unknown. Here, we show that two protein phosphatase 2A (PP2A) phosphatases, PP2A-Cdc55 and PP2A-Rts1, which are activated by inactivation of TORC1, are required for sufficient Atg13 dephosphorylation and autophagy induction after TORC1 inactivation in budding yeast. After rapamycin treatment, dephosphorylation of Atg13, activation of Atg1 kinase, pre-autophagosomal structure (PAS) formation and autophagy induction are all impaired in PP2A-deleted cells. Conversely, overexpression of non-phosphorylatable Atg13 suppressed defects in autophagy in PP2A mutant. This study revealed that the orchestrated action of PP2A antagonizes Atg13 phosphorylation and promotes autophagy after the inactivation of TORC1.

Knockdown of GSK3β increases basal autophagy and AMPK signalling in nutrient-laden human aortic endothelial cells

Suppression of the enzyme glycogen synthase kinase 3β (GSK3β) increases both the turnover of damaged cellular material and the activity of the enzyme AMP-activated protein kinase (AMPK) to potentially attenuate the damage inflicted by excess sugar and fat on blood vessels.

High concentrations of glucose and palmitate increase endothelial cell inflammation and apoptosis, events that often precede atherogenesis. They may do so by decreasing basal autophagy and AMP-activated protein kinase (AMPK) activity, although the mechanisms by which this occurs are not clear. Decreased function of the lysosome, an organelle required for autophagy and AMPK, have been associated with hyperactivity of glycogen synthase kinase 3β (GSK3β). To determine whether GSK3β affects nutrient-induced changes in autophagy and AMPK activity, we used a primary human aortic endothelial cell (HAEC) model of type 2 diabetes that we had previously characterized with impaired AMPK activity and autophagy [Weikel et al. (2015) Am. J. Phys. Cell Physiol. 308, C249–C263]. Presently, we found that incubation of HAECs with excess nutrients (25 mM glucose and 0.4 mM palmitate) increased GSK3β activity and impaired lysosome acidification. Suppression of GSK3β in these cells by treatment with a chemical inhibitor or overexpression of kinase-dead GSK3β attenuated these lysosomal changes. Under control and excess nutrient conditions, knockdown of GSK3β increased autophagosome formation, forkhead box protein O1 (FOXO1) activity and AMPK signalling and decreased Akt signalling. Similar changes in autophagy, AMPK and Akt signalling were observed in aortas from mice treated with the GSK3β inhibitor CHIR 99021. Thus, increasing basal autophagy and AMPK activity by inhibiting GSK3β may be an effective strategy in the setting of hyperglycaemia and dyslipidaemia for restoring endothelial cell health and reducing atherogenesis.

GBA deficiency promotes SNCA/α-synuclein accumulation through autophagic inhibition by inactivated PPP2A

Loss-of-function mutations in the gene encoding GBA (glucocerebrosidase, β, acid), the enzyme deficient in the lysosomal storage disorder Gaucher disease, elevate the risk of Parkinson disease (PD), which is characterized by the misprocessing of SNCA/α-synuclein. However, the mechanistic link between GBA deficiency and SNCA accumulation remains poorly understood. In this study, we found that loss of GBA function resulted in increased levels of SNCA via inhibition of the autophagic pathway in SK-N-SH neuroblastoma cells, primary rat cortical neurons, or the rat striatum. Furthermore, expression of the autophagy pathway component BECN1 was downregulated as a result of the GBA knockdown-induced decrease in glucocerebrosidase activity. Most importantly, inhibition of autophagy by loss of GBA function was associated with PPP2A (protein phosphatase 2A) inactivation via Tyr307 phosphorylation. C2-ceramide (C2), a PPP2A agonist, activated autophagy in GBA-silenced cells, while GBA knockdown-induced SNCA accumulation was reversed by C2 or rapamycin (an autophagy inducer), suggesting that PPP2A plays an important role in the GBA knockdown-mediated inhibition of autophagy. These findings demonstrate that loss of GBA function may contribute to SNCA accumulation through inhibition of autophagy via PPP2A inactivation, thereby providing a mechanistic basis for the increased PD risk associated with GBA deficiency.

Defective autophagy is a key feature of cerebral cavernous malformations

Cerebral cavernous malformation (CCM) is a major cerebrovascular disease affecting approximately 0.3-0.5% of the population and is characterized by enlarged and leaky capillaries that predispose to seizures, focal neurological deficits, and fatal intracerebral hemorrhages. Cerebral cavernous malformation is a genetic disease that may arise sporadically or be inherited as an autosomal dominant condition with incomplete penetrance and variable expressivity. Causative loss-of-function mutations have been identified in three genes, KRIT1 (CCM1), CCM2 (MGC4607), and PDCD10 (CCM3), which occur in both sporadic and familial forms. Autophagy is a bulk degradation process that maintains intracellular homeostasis and that plays essential quality control functions within the cell. Indeed, several studies have identified the association between dysregulated autophagy and different human diseases. Here, we show that the ablation of the KRIT1 gene strongly suppresses autophagy, leading to the aberrant accumulation of the autophagy adaptor p62/SQSTM1, defective quality control systems, and increased intracellular stress. KRIT1 loss-of-function activates the mTOR-ULK1 pathway, which is a master regulator of autophagy, and treatment with mTOR inhibitors rescues some of the mole-cular and cellular phenotypes associated with CCM. Insufficient autophagy is also evident in CCM2-silenced human endothelial cells and in both cells and tissues from an endothelial-specific CCM3-knockout mouse model, as well as in human CCM lesions. Furthermore, defective autophagy is highly correlated to endothelial-to-mesenchymal transition, a crucial event that contributes to CCM progression. Taken together, our data point to a key role for defective autophagy in CCM disease pathogenesis, thus providing a novel framework for the development of new pharmacological strategies to prevent or reverse adverse clinical outcomes of CCM lesions.

Advances in Autophagy Regulatory Mechanisms

Autophagy plays a critical role in cell metabolism by degrading and recycling internal components when challenged with limited nutrients. This fundamental and conserved mechanism is based on a membrane trafficking pathway in which nascent autophagosomes engulf cytoplasmic cargo to form vesicles that transport their content to the lysosome for degradation. Based on this simple scheme, autophagy modulates cellular metabolism and cytoplasmic quality control to influence an unexpectedly wide range of normal mammalian physiology and pathophysiology. In this review, we summarise recent advancements in three broad areas of autophagy regulation. We discuss current models on how autophagosomes are initiated from endogenous membranes. We detail how the uncoordinated 51-like kinase (ULK) complex becomes activated downstream of mechanistic target of rapamycin complex 1 (MTORC1). Finally, we summarise the upstream signalling mechanisms that can sense amino acid availability leading to activation of MTORC1.

New Potential Pharmacological Functions of Chinese Herbal Medicines via Regulation of Autophagy

Autophagy is a universal catabolic cellular process for quality control of cytoplasm and maintenance of cellular homeostasis upon nutrient deprivation and environmental stimulus. It involves the lysosomal degradation of cellular components such as misfolded proteins or damaged organelles. Defects in autophagy are implicated in the pathogenesis of diseases including cancers, myopathy, neurodegenerations, infections and cardiovascular diseases. In the recent decade, traditional drugs with new clinical applications are not only commonly found in Western medicines, but also highlighted in Chinese herbal medicines (CHM). For instance, pharmacological studies have revealed that active components or fractions from Chaihu (Radix bupleuri), Hu Zhang (Rhizoma polygoni cuspidati), Donglingcao (Rabdosia rubesens), Hou po (Cortex magnoliae officinalis) and Chuan xiong (Rhizoma chuanxiong) modulate cancers, neurodegeneration and cardiovascular disease via autophagy. These findings shed light on the potential new applications and formulation of CHM decoctions via regulation of autophagy. This article reviews the roles of autophagy in the pharmacological actions of CHM and discusses their new potential clinical applications in various human diseases.

Autophagy signal transduction by ATG proteins: from hierarchies to networks

Autophagy represents an intracellular degradation process which is involved in both cellular homeostasis and disease settings. In the last two decades, the molecular machinery governing this process has been characterized in detail. To date, several key factors regulating this intracellular degradation process have been identified. The so-called autophagy-related (ATG) genes and proteins are central to this process. However, several additional molecules contribute to the outcome of an autophagic response. Several review articles describing the molecular process of autophagy have been published in the recent past. In this review article we would like to add the most recent findings to this knowledge, and to give an overview of the network character of the autophagy signaling machinery.

Mitochondria-Associated Endoplasmic Reticulum Membranes Microenvironment: Targeting Autophagic and Apoptotic Pathways in Cancer Therapy

Autophagy is a tightly regulated catabolic pathway that terminates in the lysosomal compartment after the formation of a cytoplasmic vacuole that engulfs macromolecules and organelles. Notably, autophagy is associated with several human pathophysiological conditions, playing either a cytoprotective or cytopathic role. Many studies have investigated the role of autophagy in cancer. However, whether autophagy suppresses tumorigenesis or provides cancer cells with a rescue mechanism under unfavorable conditions remains unclear. Mitochondria-associated membranes (MAMs) are juxtaposed between the endoplasmic reticulum and mitochondria and have been identified as critical hubs in the regulation of apoptosis and tumor growth. One key function of MAMs is to provide asylum to a number of proteins with tumor suppressor and oncogenic properties. Accordingly, mechanistic studies during tumor progression suggest a strong involvement of these proteins at various steps of the autophagic process. This paper discusses the present state of our knowledge about the intimate molecular networks between MAMs and autophagy in cancer cells and addresses how these networks might be manipulated to improve anticancer therapeutics.

The Ambiguous Relationship of Oxidative Stress, Tau Hyperphosphorylation, and Autophagy Dysfunction in Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia. The pathological hallmarks of AD are amyloid plaques [aggregates of amyloid-beta (Aβ)] and neurofibrillary tangles (aggregates of tau). Growing evidence suggests that tau accumulation is pathologically more relevant to the development of neurodegeneration and cognitive decline in AD patients than Aβ plaques. Oxidative stress is a prominent early event in the pathogenesis of AD and is therefore believed to contribute to tau hyperphosphorylation. Several studies have shown that the autophagic pathway in neurons is important under physiological and pathological conditions. Therefore, this pathway plays a crucial role for the degradation of endogenous soluble tau. However, the relationship between oxidative stress, tau protein hyperphosphorylation, autophagy dysregulation, and neuronal cell death in AD remains unclear. Here, we review the latest progress in AD, with a special emphasis on oxidative stress, tau hyperphosphorylation, and autophagy. We also discuss the relationship of these three factors in AD.

Ischaemia-induced autophagy leads to degradation of gap junction protein connexin43 in cardiomyocytes

GJIC (gap junction intercellular communication) between cardiomyocytes is essential for synchronous heart contraction and relies on Cx (connexin)-containing channels. Increased breakdown of Cx43 has been often associated with various cardiac diseases. However, the mechanisms whereby Cx43 is degraded in ischaemic heart remain unknown. The results obtained in the present study, using both HL-1 cells and organotypic heart cultures, show that simulated ischaemia induces degradation of Cx43 that can be prevented by chemical or genetic inhibitors of autophagy. Additionally, ischaemia-induced degradation of Cx43 results in GJIC impairment in HL-1 cells, which can be restored by autophagy inhibition. In cardiomyocytes, ubiquitin signals Cx43 for autophagic degradation, through the recruitment of the ubiquitin-binding proteins Eps15 (epidermal growth factor receptor substrate 15) and p62, that assist in Cx43 internalization and targeting to autophagic vesicles, via LC3 (light chain 3). Moreover, we establish that degradation of Cx43 in ischaemia or I/R (ischaemia/reperfusion) relies upon different molecular players. Indeed, degradation of Cx43 during early periods of ischaemia depends on AMPK (AMP-activated protein kinase), whereas in late periods of ischaemia and I/R Beclin 1 is required. In the Langendorff-perfused heart, Cx43 is dephosphorylated in ischaemia and degraded during I/R, where Cx43 degradation correlates with autophagy activation. In summary, the results of the present study provide new evidence regarding the molecular mechanisms whereby Cx43 is degraded in ischaemia, which may contribute to the development of new strategies that aim to preserve GJIC and cardiac function in ischaemic heart.

Autophagy in neurodegenerative diseases: From pathogenic dysfunction to therapeutic modulation

Neuronal homeostasis depends on the proper functioning of quality control systems like autophagy. This mechanism is responsible of the clearance of misfolded proteins, aggregates and the turnover of organelles within the neuron. Autophagic dysfunction has been described in many neurodegenerative diseases. It can occur at several steps of the autophagic machinery and can contribute to the formation of intracellular aggregates and ultimately to neuronal death. Accordingly restoring autophagy activity in affected neurons can be an attractive therapeutic approach to fight neurodegeneration. In this review we summarize the present encouraging strategies that have been achieved with pharmacological and genetic treatments aimed to induce neuronal autophagy in experimental models of neurodegenerative diseases.

Degradation of misfolded proteins in neurodegenerative diseases: therapeutic targets and strategies

Mammalian cells remove misfolded proteins using various proteolytic systems, including the ubiquitin (Ub)-proteasome system (UPS), chaperone mediated autophagy (CMA) and macroautophagy. The majority of misfolded proteins are degraded by the UPS, in which Ub-conjugated substrates are deubiquitinated, unfolded and cleaved into small peptides when passing through the narrow chamber of the proteasome. The substrates that expose a specific degradation signal, the KFERQ sequence motif, can be delivered to and degraded in lysosomes via the CMA. Aggregation-prone substrates resistant to both the UPS and the CMA can be degraded by macroautophagy, in which cargoes are segregated into autophagosomes before degradation by lysosomal hydrolases. Although most misfolded and aggregated proteins in the human proteome can be degraded by cellular protein quality control, some native and mutant proteins prone to aggregation into β-sheet-enriched oligomers are resistant to all known proteolytic pathways and can thus grow into inclusion bodies or extracellular plaques. The accumulation of protease-resistant misfolded and aggregated proteins is a common mechanism underlying protein misfolding disorders, including neurodegenerative diseases such as Huntington's disease (HD), Alzheimer's disease (AD), Parkinson's disease (PD), prion diseases and Amyotrophic Lateral Sclerosis (ALS). In this review, we provide an overview of the proteolytic pathways in neurons, with an emphasis on the UPS, CMA and macroautophagy, and discuss the role of protein quality control in the degradation of pathogenic proteins in neurodegenerative diseases. Additionally, we examine existing putative therapeutic strategies to efficiently remove cytotoxic proteins from degenerating neurons.

Sortilin mediates the release and transfer of exosomes in concert with two tyrosine kinase receptors

The transfer of exosomes containing both genetic and protein materials is necessary for the control of the cancer cell microenvironment to promote tumor angiogenesis. The nature and function of proteins found in the exosomal cargo, and the mechanism of their action in membrane transport and related signaling events are not clearly understood. In this study, we demonstrate, in human lung cancer A549 cells, that the exosome release mechanism is closely linked to the multifaceted receptor sortilin (also called neurotensin receptor 3). Sortilin is already known to be important for cancer cell function. Here, we report for the first time its role in the assembly of a tyrosine kinase complex and subsequent exosome release. This new complex (termed the TES complex) is found in exosomes and results in the linkage of the two tyrosine kinase receptors TrkB (also known as NTRK2) and EGFR with sortilin. Using in vitro models, we demonstrate that this sortilin-containing complex exhibits a control on endothelial cells and angiogenesis activation through exosome transfer.

A systems biology investigation of neurodegenerative dementia reveals a pivotal role of autophagy

Background

Neurodegenerative dementia comprises chronic and progressive illnesses with major clinical features represented by progressive and permanent loss of cognitive and mental performance, including impairment of memory and brain functions. Many different forms of neurodegenerative dementia exist, but they are all characterized by death of specific subpopulation of neurons and accumulation of proteins in the brain. We incorporated data from OMIM and primary molecular targets of drugs in the different phases of the drug discovery process to try to reveal possible hidden mechanism in neurodegenerative dementia. In the present study, a systems biology approach was used to investigate the molecular connections among seemingly distinct complex diseases with the shared clinical symptoms of dementia that could suggest related disease mechanisms.

Results

Network analysis was applied to characterize an interaction network of disease proteins and drug targets, revealing a major role of metabolism and, predominantly, of autophagy process in dementia and, particularly, in tauopathies. Different phases of the autophagy molecular pathway appear to be implicated in the individual disease pathophysiology and specific drug targets associated to autophagy modulation could be considered for pharmacological intervention. In particular, in view of their centrality and of the direct association to autophagy proteins in the network, PP2A subunits could be suggested as a suitable molecular target for the development of novel drugs.

Conclusion

The present systems biology investigation identifies the autophagy pathway as a central dis-regulated process in neurodegenerative dementia with a prevalent involvement in diseases characterized by tau inclusion and indicates the disease-specific molecules in the pathway that could be considered for therapy.

Combining affinity proteomics and network context to identify new phosphatase substrates and adapters in growth pathways

Protein phosphorylation homoeostasis is tightly controlled and pathological conditions are caused by subtle alterations of the cell phosphorylation profile. Altered levels of kinase activities have already been associated to specific diseases. Less is known about the impact of phosphatases, the enzymes that down-regulate phosphorylation by removing the phosphate groups. This is partly due to our poor understanding of the phosphatase-substrate network. Much of phosphatase substrate specificity is not based on intrinsic enzyme specificity with the catalytic pocket recognizing the sequence/structure context of the phosphorylated residue. In addition many phosphatase catalytic subunits do not form a stable complex with their substrates. This makes the inference and validation of phosphatase substrates a non-trivial task. Here, we present a novel approach that builds on the observation that much of phosphatase substrate selection is based on the network of physical interactions linking the phosphatase to the substrate. We first used affinity proteomics coupled to quantitative mass spectrometry to saturate the interactome of eight phosphatases whose down regulations was shown to affect the activation of the RAS-PI3K pathway. By integrating information from functional siRNA with protein interaction information, we develop a strategy that aims at inferring phosphatase physiological substrates. Graph analysis is used to identify protein scaffolds that may link the catalytic subunits to their substrates. By this approach we rediscover several previously described phosphatase substrate interactions and characterize two new protein scaffolds that promote the dephosphorylation of PTPN11 and ERK by DUSP18 and DUSP26, respectively.

The protective role of AMP-activated protein kinase in alpha-synuclein neurotoxicity in vitro

In the present study, we investigated the role of the main intracellular energy sensor, AMP-activated protein kinase (AMPK), in the in vitro neurotoxicity of α-synuclein (ASYN), one of the key culprits in the pathogenesis of Parkinson's disease. The loss of viability in retinoic acid-differentiated SH-SY5Y human neuroblastoma cells inducibly overexpressing wild-type ASYN was associated with the reduced activation of AMPK and its activator LKB1, as well as AMPK target Raptor. ASYN-overexpressing rat primary neurons also displayed lower activity of LKB1/AMPK/Raptor pathway. Restoration of AMPK activity by metformin or AICAR reduced the in vitro neurotoxicity of ASYN overexpression, acting independently of the prosurvival kinase Akt or the induction of autophagic response. The conditioned medium from ASYN-overexpressing cells, containing secreted ASYN, as well as dopamine-modified or nitrated recombinant ASYN oligomers, all inhibited AMPK activation in differentiated SH-SY5Y cells and reduced their viability, but not in the presence of metformin or AICAR. The RNA interference-mediated knockdown of AMPK increased the sensitivity of SH-SY5Y cells to the harmful effects of secreted ASYN. AMPK-dependent protection from extracellular ASYN was also observed in rat neuron-like pheochromocytoma cell line PC12. These data demonstrate the protective role of AMPK against the toxicity of both intracellular and extracellular ASYN, suggesting that modulation of AMPK activity may be a promising therapeutic strategy in Parkinson's disease.

The role of autophagy in neurodegenerative disease

Autophagy is a lysosomal degradative process used to recycle obsolete cellular constituents and eliminate damaged organelles and protein aggregates. These substrates reach lysosomes by several distinct mechanisms, including delivery within endosomes as well as autophagosomes. Completion of digestion involves dynamic interactions among compartments of the autophagic and endocytic pathways. Neurons are particularly vulnerable to disruptions of these interactions, especially as the brain ages. Not surprisingly, mutations of genes regulating autophagy cause neurodegenerative diseases across the age spectrum with exceptional frequency. In late-onset disorders such as Alzheimer's disease, amyotrophic lateral sclerosis and familial Parkinson's disease, defects arise at different stages of the autophagy pathway and have different implications for pathogenesis and therapy. This Review provides an overview of the role of autophagy in neurodegenerative disease, focusing particularly on less frequently considered lysosomal clearance mechanisms and their considerable impact on disease. Various therapeutic strategies for modulating specific stages of autophagy and the current state of drug development for this purpose are also evaluated.

Nilotinib induces autophagy in hepatocellular carcinoma through AMPK activation

Hepatocellular carcinoma (HCC) is the most common liver cancer and the third-leading cause of cancer death worldwide. Nilotinib is an orally available receptor tyrosine kinase inhibitor approved for chronic myelogenous leukemia. This study investigated the effect of nilotinib on HCC. Nilotinib did not induce cellular apoptosis. Instead, staining with acridine orange and microtubule-associated protein 1 light chain 3 revealed that nilotinib induced autophagy in a dose- and time-dependent manner in HCC cell lines, including PLC5, Huh-7, and Hep3B. Moreover, nilotinib up-regulated the phosphryaltion of AMP-activated kinase (AMPK) and protein phosphatase PP2A inactivation were detected after nilotinib treatment. Up-regulating PP2A activity suppressed nilotinib-induced AMPK phosphorylation and autophagy, suggesting that PP2A mediates the effect of nilotinib on AMPK phosphorylation and autophagy. Our data indicate that nilotinib-induced AMPK activation is mediated by PP2A, and AMPK activation and subsequent autophagy might be a major mechanism of action of nilotinib. Growth of PLC5 tumor xenografts in BALB/c nude mice was inhibited by daily oral treatment with nilotinib. Western blot analysis showed both increased phospho-AMPK expression and decreased PP2A activity in vivo. Together, our results reveal that nilotinib induces autophagy, but not apoptosis in HCC, and that the autophagy-inducing activity is associated with PP2A-regulated AMPK phosphorylation.