Dysfunctionally phosphorylated type 1 insulin receptor substrate in neural-derived blood exosomes of preclinical Alzheimer's disease

A review on protein markers of exosome from different bio-resources and the antibodies used for characterization

Exosomes are small membrane vesicles (ranging from 30 nm to 150 nm), secreted by different cell types upon fusion of multivesicular bodies (MVB) to the cell plasma membrane under a variety of normal and pathological conditions. Through transferring their cargos such as proteins, lipids and nucleic acids from donor cells to recipient cells, exosomes play a crucial role in cell-to-cell communication. Due to their presence in most body fluids (such as blood, breast milk, saliva, urine, bile, pancreatic juice, cerebrospinal and peritoneal fluids), and their role in carrying bioactive molecules from the cells of origin, exosomes have attracted great interest in their diagnostic and prognostic value for various diseases and therapeutic approaches. Although a large body of literature has documented the importance of exosomes over the past decade, there is no article systematically summarizing protein markers of exosome from different resources and the antibodies that are suited to characterize exosomes. In this review, we briefly summarize the exosome marker proteins, exosomal biomarkers for different diseases, and the antibodies suitable for different bio-resources exosomes characterization.

(-)-Phenserine and Inhibiting Pre-Programmed Cell Death: In Pursuit of a Novel Intervention for Alzheimer's Disease

BACKGROUND

Concussion (mild) and other moderate traumatic brain injury (TBI) and Alzheimer's disease (AD) share overlapping neuropathologies, including neuronal pre-programmed cell death (PPCD), and clinical impairments and disabilities. Multiple clinical trials targeting mechanisms based on the Amyloid Hypothesis of AD have so far failed, indicating that it is prudent for new drug developments to also pursue mechanisms independent of the Amyloid Hypothesis. To address these issues, we have proposed the use of an animal model of concussion/TBI as a supplement to AD transgenic mice to provide an indication of an AD drug candidate's potential for preventing PPCD and resulting progression towards dementia in AD.

METHODS

We searched PubMed/Medline and the references of identified articles for background on the neuropathological progression of AD and its implications for drug target identification, for AD clinical trial criteria used to assess disease modification outcomes, for plasma biomarkers associated with AD and concussion/TBI, neuropathologies and especially PPCD, and for methodological critiques of AD and other neuropsychiatric clinical trial methods.

RESULTS

We identified and address seven issues and highlight the Thal-Sano AD 'Time to Onset of Impairment' Design for possible applications in our clinical trials. Diverse and significant pathological cascades and indications of self-induced neuronal PPCD were found in concussion/TBI, anoxia, and AD animal models. To address the dearth of peripheral markers of AD and concussion/TBI brain pathologies and PPCD we evaluated Extracellular Vesicles (EVs) enriched for neuronal origin, including exosomes. In our concussion/TBI, anoxia and AD animal models we found evidence consistent with the presence of time-dependent PPCD and (-)-phenserine suppression of neuronal self-induced PPCD. We hence developed an extended controlled release formulation of (-)-phenserine to provide individualized dosing and stable therapeutic brain concentrations, to pharmacologically interrogate PPCD as a drug development target. To address the identified problems potentially putting any clinical trial at risk of failure, we developed exploratory AD and concussion/TBI clinical trial designs.

CONCLUSIONS

Our findings inform the biomarker indication of progression of pathological targets in neurodegenerations and propose a novel approach to these conditions through neuronal protection against self-induced PPCD.

Exosome release and cargo in Down syndrome

Down syndrome (DS) is a multisystem disorder affecting 1 in 800 births worldwide. Advancing technology, medical treatment, and social intervention have dramatically increased life expectancy, yet there are many etiologies of this disorder that are in need of further research. The advent of the ability to capture extracellular vesicles (EVs) in blood from specific cell types allows for the investigation of novel intracellular processes. Exosomes are one type of EVs that have demonstrated great potential in uncovering new biomarkers of neurodegeneration and disease, and also that appear to be intricately involved in the transsynaptic spread of pathogenic factors underlying Alzheimer's disease and other neurological diseases. Exosomes are nanosized vesicles, generated in endosomal multivesicular bodies (MVBs) and secreted by most cells in the body. Since exosomes are important mediators of intercellular communication and genetic exchange, they have emerged as a major research focus and have revealed novel biological sequelae involved in conditions afflicting the DS population. This review summarizes current knowledge on exosome biology in individuals with DS, both early in life and in aging individuals. Collectively these studies have demonstrated that complex multicellular processes underlying DS etiologies may include abnormal formation and secretion of extracellular vesicles such as exosomes.

Brain Insulin Resistance and Hippocampal Plasticity: Mechanisms and Biomarkers of Cognitive Decline

In the last decade, much attention has been devoted to the effects of nutrient-related signals on brain development and cognitive functions. A turning point was the discovery that brain areas other than the hypothalamus expressed receptors for hormones related to metabolism. In particular, insulin signaling has been demonstrated to impact on molecular cascades underlying hippocampal plasticity, learning and memory. Here, we summarize the molecular evidence linking alteration of hippocampal insulin sensitivity with changes of both adult neurogenesis and synaptic plasticity. We also review the epidemiological studies and experimental models emphasizing the critical role of brain insulin resistance at the crossroad between metabolic and neurodegenerative disease. Finally, we brief novel findings suggesting how biomarkers of brain insulin resistance, involving the study of brain-derived extracellular vesicles and brain glucose metabolism, may predict the onset and/or the progression of cognitive decline.

Emerging roles of extracellular vesicles in neurodegenerative disorders

Extracellular vesicles (EVs) are heterogeneous cell-derived membranous vesicles which carry a large diversity of molecules such as proteins and RNA species. They are now considered to be a general mode of intercellular communication by direct transfer of biomolecules. Emerging evidence demonstrates that EVs are involved in multiple pathological processes of brain diseases including neurodegenerative disorders. In this review, we investigate the current knowledge about EV biology. We also provide an overview of the roles of EVs in related brain diseases, particularly in neurodegenerative disorders. Finally, we discuss their potential applications as novel biomarkers as well as the developments of EV-based therapies.

Noninvasive assessment of fetal central nervous system insult: Potential application to prenatal diagnosis

OBJECTIVE

We have developed novel methods for isolating fetal central nervous system (CNS)-derived extracellular vesicles (FCEs) from maternal plasma as a non-invasive platform for testing aspects of fetal neurodevelopment in early pregnancy. We investigate the hypothesis that levels of defined sets of functional proteins in FCEs can be used to detect abnormalities in fetal neuronal and glial proliferation, differentiation, and survival.

METHOD

Maternal plasma was obtained between 10 and 19 weeks from women with current heavy EtOH exposure and matched controls. FCE levels of synaptophysin, synaptotagmin, synaptopodin, and neurogranin were quantified normalized to the exosome marker CD81. Quantitative RT-PCR was performed with specific primers for miR-9.

RESULTS

FCE cargo protein levels of synaptophysin, synaptotagmin, synaptopodin, and neurogranin were all significantly reduced in pregnancies exposed to current heavy EtOH use (P < .001 for all). Both synaptophysin and neurogranin appeared to be particularly discriminatory with no overlap between exposed and control subjects. Up to tenfold inhibition (90%) in MicroRNA-9 was observed in FCEs from EtOH exposed fetuses compared with controls.

CONCLUSION

Our results suggest that FCEs purified from maternal plasma may be a powerful tool to assess abnormal proliferation and differentiation of CNS stem cells as early as the late first trimester. What's already known about this topic? Exosomes/extracellular vesicles (ECVs) are emerging as exciting novel biomarkers in neurologic disease (Alzheimers) What does this study add? Evidence that Fetal CNS ECVs can be isolated from maternal blood The origin of the ECVs appears to be the fetal brain and not the placenta Findings with ECVs correlates with fetal exposure to alcohol. Potential for first trimester prenatal diagnosis of fetal neurologic disease.

Neuronally derived extracellular vesicles: an emerging tool for understanding Alzheimer's disease

In order for Alzheimer’s disease (AD) to manifest, cells must communicate “pathogenic material” such as proteins, signaling molecules, or genetic material to ensue disease propagation. Small extracellular vesicles are produced via the endocytic pathways and released by nearly all cell types, including neurons. Due to their intrinsic interrelationship with endocytic processes and autophagy, there has been increased interest in studying the role of these neuronally-derived extracellular vesicles (NDEVs) in the propagation of AD. Pathologic cargo associated with AD have been found in a number of studies, and NDEVs have been shown to induce pathogenesis in vivo and in vitro. Exogenous NDEVs are also shown to reduce plaque burden in AD models. Thus, the NDEV has the potential to become a useful biomarker, a pathologic potentiator, and a therapeutic opportunity. While the field of NDEV research in AD is still in its infancy, we review the current literature supporting these three claims.

Brain insulin resistance and altered brain glucose are related to memory impairments in schizophrenia

Memory is robustly impaired in schizophrenia (SZ) and related to functional outcome. Memory dysfunction has been shown to be related to altered brain glucose metabolism and brain insulin resistance in animal models and human studies of Alzheimer's disease. In this study, differences in brain glucose using magnetic resonance spectroscopy (MRS) and blood Extracellular Vesicle (EV) biomarkers of neuronal insulin resistance (i.e. Akt and signaling effectors) between SZ and controls were investigated, as well as whether these measures were related to memory impairments. Neuronal insulin resistance biomarkers showed a trend for being lower in SZ compared to controls, and memory measures were lower in SZ compared to controls. Occipital cortex glucose was higher in SZ compared to controls indicating lower brain glucose utilization. Linear regression analyses revealed significant relationships between neuronal insulin resistance biomarkers, memory measures, and brain glucose. More specifically, p70S6K, an insulin signaling effector, was related to verbal learning and brain MRS glucose in the SZ group. For the first time, we show that memory impairments in SZ may be related to brain glucose and brain insulin resistance. These data suggest that brain insulin resistance may play a role in the pathophysiology of learning and memory dysfunction in SZ.

MicroRNAs in Post-traumatic Stress Disorder

Post-traumatic stress disorder (PTSD) is a psychiatric disorder that can develop following exposure to or witnessing of a (potentially) threatening event. A critical issue is to pinpoint the (neuro)biological mechanisms underlying the susceptibility to stress-related disorder such as PTSD, which develops in the minority of ~15% of individuals exposed to trauma. Over the last few years, a first wave of epigenetic studies has been performed in an attempt to identify the molecular underpinnings of the long-lasting behavioral and mental effects of trauma exposure. The potential roles of non-coding RNAs (ncRNAs) such as microRNAs (miRNAs) in moderating or mediating the impact of severe stress and trauma are increasingly gaining attention. To date, most studies focusing on the roles of miRNAs in PTSD have, however, been completed in animals, using cross-sectional study designs and focusing almost exclusively on subjects with susceptible phenotypes. Therefore, there is a strong need for new research comprising translational and cross-species approaches that use longitudinal designs for studying trajectories of change contrasting susceptible and resilient subjects. The present review offers a comprehensive overview of available studies of miRNAs in PTSD and discusses the current challenges, pitfalls, and future perspectives of this field.

Extracellular Vesicle as a Source of Alzheimer's Biomarkers: Opportunities and Challenges

Alzheimer’s disease (AD) is a chronic progressive neurodegenerative disease characterized by memory decline and cognitive dysfunction. Although the primary causes of AD are not clear, it is widely accepted that the accumulation of amyloid beta (Aβ) and consecutive hyper-phosphorylation of tau, synaptic loss, oxidative stress and neuronal death might play a vital role in AD pathogenesis. Recently, it has been widely suggested that extracellular vesicles (EVs), which are released from virtually all cell types, are a mediator in regulating AD pathogenesis. Clinical evidence for the diagnostic performance of EV-associated biomarkers, particularly exosome biomarkers in the blood, is also emerging. In this review, we briefly introduce the biological function of EVs in the central nervous system and discuss the roles of EVs in AD pathogenesis. In particular, the roles of EVs associated with autophagy and lysosomal degradation systems in AD proteinopathy and in disease propagation are discussed. Next, we summarize candidates for biochemical AD biomarkers in EVs, including proteins and miRNAs. The accumulating data brings hope that the application of EVs will be helpful for early diagnostics and the identification of new therapeutic targets for AD. However, at the same time, there are several challenges in developing valid EV biomarkers. We highlight considerations for the development of AD biomarkers from circulating EVs, which includes the standardization of pre-analytical sources of variability, yield and purity of isolated EVs and quantification of EV biomarkers. The development of valid EV AD biomarkers may be facilitated by collaboration between investigators and the industry.

Understanding the link between insulin resistance and Alzheimer's disease: Insights from animal models

Alzheimer's disease (AD) is a devastating neurodegenerative disease affecting millions of people worldwide. AD is characterized by a profound impairment of higher cognitive functions and still lacks any effective disease-modifying treatment. Defective insulin signaling has been implicated in AD pathophysiology, but the mechanisms underlying this process are not fully understood. Here, we review the molecular mechanisms underlying defective brain insulin signaling in rodent models of AD, and in a non-human primate (NHP) model of the disease that recapitulates features observed in AD brains. We further highlight similarities between the NHP and human brains and discuss why NHP models of AD are important to understand disease mechanisms and to improve the translation of effective therapies to humans. We discuss how studies using different animal models have contributed to elucidate the link between insulin resistance and AD.

Exosomes from MiR-21-5p-Increased Neurons Play a Role in Neuroprotection by Suppressing Rab11a-Mediated Neuronal Autophagy In Vitro After Traumatic Brain Injury

Background

Traumatic brain injury (TBI) produces a series of pathological processes. Recent studies have indicated that autophagy pathway is persistently activated after TBI, which may lead to deterioration of nerve injury. Our preliminary work found miR-21-5p was upregulated in both in vivo and in vitro TBI models. MicroRNAs (miRNAs) could be loaded into exosomes to perform cell-to-cell interactions. This research aimed to evaluate the therapeutic effect of neuron-derived exosomes enriched with miR-21-5p on the TBI in vitro and to further explore the possible mechanisms.

Material/Methods

Brain extracts harvested from an rTBI mouse model were added to cultured HT-22 neurons to imitate the microenvironment of injured brain on in vitro cultured cells. Ultracentrifugation was performed to isolate exosomes. Transmission electron microscopy and Nano sight technology were used to examine exosomes. An in vitro model of TBI was established to study the effect of exosomal miR-21-5p on nerve injury and on neuronal autophagy regulation.

Results

The expression of miR-21-5p was increased in exosomes derived from HT-22 neurons after treatment with rTBI mouse brain extracts. Autophagy was activated in HT-22 neurons after scratch injury. Exosomal miR-21-5p produced a protective effect by suppressing autophagy in a TBI model in vitro. MiR-21-5p could directly target the Rab11a 3′UTR region to reduce its translation and further suppressed Rab11a-mediated neuronal autophagy.

Conclusions

The levels of miR-21-5p in neuronal exosomes increased from the acute to the chronic phase of TBI. Neuronal exosomes enriched with miR-21-5p can inhibit the activity of neuronal autophagy by targeting Rab11a, thus attenuating trauma-induced, autophagy-mediated nerve injury in vitro.

The Link Between Tau and Insulin Signaling: Implications for Alzheimer's Disease and Other Tauopathies

The microtubule-associated protein tau (MAPT) is mainly identified as a tubulin binding protein essential for microtubule dynamics and assembly and for neurite outgrowth. However, several other possible functions for Tau remains to be investigated. Insulin signaling is important for synaptic plasticity and memory formation and therefore is essential for proper brain function. Tau has recently been characterized as an important regulator of insulin signaling, with evidence linking Tau to brain and peripheral insulin resistance and beta cell dysfunction. In line with this notion, the hypothesis of Tau pathology as a key trigger of impaired insulin sensitivity and secretion has emerged. Conversely, insulin resistance can also favor Tau dysfunction, resulting in a vicious cycle of these events. In this review article, we discuss recent evidence linking Tau pathology, insulin resistance and insulin deficiency. We further highlight the deleterious consequences of Tau pathology-induced insulin resistance to the brain and/or peripheral tissues, suggesting that these are key events mediating cognitive decline in Alzheimer’s disease (AD) and other tauopathies.

New windows into the brain: Central nervous system-derived extracellular vesicles in blood

Extracellular vesicles (EVs), including exosomes and (shedding) microvesicles, are released by nearly all cell types and carry a cargo of proteins and nucleic acids that varies by the cell of origin. They are thought to play critical roles in normal central nervous system (CNS) function and neurological disorders. A recently revealed key characteristic of EVs is that they may travel between the CNS and peripheral circulation. This property has led to intense interest in how EVs might serve as a vehicle for toxic protein clearance and as a readily accessible source of biomarkers for CNS disorders. Furthermore, by bypassing the blood-brain barrier, modified EVs could serve as a unique drug delivery system that targets specific neuronal populations. Further work is necessary to develop and optimize techniques that enable high-yield capture of relevant EV populations, analyze individual EVs and their cargos, and validate preliminary results of EV-derived biomarkers in independent cohorts.

Brain insulin response and peripheral metabolic changes in a Tau transgenic mouse model

Accumulation of hyper-phosphorylated and aggregated Tau proteins is a neuropathological hallmark of Alzheimer's Disease (AD) and Tauopathies. AD patient brains also exhibit insulin resistance. Whereas, under normal physiological conditions insulin signaling in the brain mediates plasticity and memory formation, it can also regulate peripheral energy homeostasis. Thus, in AD, brain insulin resistance affects both cognitive and metabolic changes described in these patients. While a role of Aβ oligomers and APOE4 towards the development of brain insulin resistance emerged, contribution of Tau pathology has been largely overlooked. Our recent data demonstrated that one of the physiological function of Tau is to sustain brain insulin signaling. We postulated that under pathological conditions, hyper-phosphorylated/aggregated Tau is likely to lose this function and to favor the development of brain insulin resistance. This hypothesis was substantiated by observations from patient brains with pure Tauopathies. To address the potential link between Tau pathology and brain insulin resistance, we have evaluated the brain response to insulin in a transgenic mouse model of AD-like Tau pathology (THY-Tau22). Using electrophysiological and biochemical evaluations, we surprisingly observed that, at a time when Tau pathology and cognitive deficits are overt and obvious, the hippocampus of THY-Tau22 mice exhibits enhanced response to insulin. In addition, we demonstrated that the ability of i.c.v. insulin to promote body weight loss is enhanced in THY-Tau22 mice. In line with this, THY-Tau22 mice exhibited a lower body weight gain, hypoleptinemia and hypoinsulinemia and finally a metabolic resistance to high-fat diet. The present data highlight that the brain of transgenic Tau mice exhibit enhanced brain response to insulin. Whether these observations are ascribed to the development of Tau pathology, and therefore relevant to human Tauopathies, or unexpectedly results from the Tau transgene overexpression is debatable and discussed.

Complement protein levels in plasma astrocyte-derived exosomes are abnormal in conversion from mild cognitive impairment to Alzheimer's disease dementia

Introduction

Levels of complement proteins (CPs) in plasma astrocyte-derived exosomes (ADEs) that are abnormal in Alzheimer's disease (AD) have not been assessed in mild cognitive impairment (MCI).

Methods

Participants (n = 20 per group) had either MCI converting to dementia within 3 years (MCIC), MCI remaining stable over 3 years (MCIS), Alzheimer's disease, or were controls. CPs of ADEs isolated from plasmas by anti-human glutamine aspartate transporter antibody absorption were quantified by ELISAs.

Results

ADE levels of C1q and C4b of the classical pathway, factor D and fragment Bb of the alternative pathway, and C5b, C3b, and C5b-C9 of both pathways were significantly higher in patients with MCIC than those with MCIS. ADE levels of inhibitory CPs decay-accelerating factor, CD46, CD59, and type 1 complement receptor were significantly lower in patients with MCIC than those with MCIS.

Discussion

ADE CPs are components of neurotoxic neuroinflammation that may be predictive biomarkers of MCI conversion to Alzheimer's disease.

Plasma neuronal exosomes serve as biomarkers of cognitive impairment in HIV infection and Alzheimer's disease

Fluid biomarkers for cognitive impairment have the advantage of being relatively noninvasive and capable of monitoring neuronal and other brain cell health in real time. Biomarkers can predict the onset of dementing illness, but also correlate with cognition in a dynamic way allowing us to follow treatment responses and determine brain recovery. Chronic HIV infection causes cognitive impairment in a subset of individuals suggesting "premature aging." Exosomes are small extracellular vesicles that are shed from all cells. They are important in normal cell-to-cell communication as they contain cellular proteins, mRNA transcripts, and miRNAs. Exosome cargo varies depending on the health of the cell and pathological state; specific proteins/mRNAs and/or miRNAs are present and may serve as biomarkers. Exosomes of variable cellular origin can be isolated from peripheral blood by various methods. Neuron-derived exosomes (NDEs) can be isolated using a precipitation/immunoaffinity approach using antibodies against neuronal cell adhesion molecule L1CAM and the contents queried for central nervous system (CNS) disorders including HIV-associated neurological disorders (HAND) and Alzheimer's disease (AD). As these studies are recent, numerous questions arise including which neuronal proteins are in NDEs and whether their contents differ in different CNS pathologies or with age. In addition, can the NDE cargo predict as well as diagnose cognitive impairment and could exosomal contents be used as therapeutic biomarkers, or theramarkers, of neuronal recovery from effective treatment? This mini-review will show some new data and review recent studies on NDE from individuals with HIV infection and AD. HIV-associated neurocognitive disorders (HAND) are pathologies seen in a subset of individuals with chronic HIV infection. They belong to the spectrum of neurodegenerative diseases that result in death or dysfunction of neurons with similarities to Alzheimer disease (AD) but also distinctive differences (reviewed (Canet et al., Front Cell Neurosci 12: 307, 2018)). Both disorders are difficult to diagnose without neuropsychological testing and both need new biomarkers to judge progression as well as recovery with treatment. Both disorders involve neuroinflammation and several common targets. AD is associated with aging and HIV is thought to initiate premature aging. In HIV infection, amyloid beta (Aβ), which is deposited in "plaques" in AD, is soluble and its relevance to HIV-associated cognitive impairment is controversial (Achim et al., J Neuroimmune Pharmacol 4: 190-199, 2009; Rempel and Pulliam, AIDS 19: 127-135, 2005). Aβ deposition is required for AD pathological diagnosis, but is not necessarily causative (Barage and Sonawane, Neuropeptides 52: 1-18, 2015; Hardy and Selkoe, Science 297: 353-356, 2002; Morris et al., Acta Neuropathol Commun 2: 135, 2014). Neurofilament light (NF-L) is a surrogate marker in plasma and cerebrospinal fluid (CSF) for neurodegeneration (Abu-Rumeileh et al., Alzheimers Res Ther 10: 3, 2018; Mattsson et al., JAMA Neurol 74: 557-566, 2017) but continues to be a controversial biomarker for both HAND and AD (Gisslen et al., EBioMedicine 3: 135-140, 2016; Kovacs et al., Eur J Neurol 24:1326-e77, 2017; Norgren et al., Brain Res 987: 25-31, 2003; Rolstad et al., J Alzheimers Dis 45: 873-881, 2015; Yilmaz et al., Expert Rev Mol Diagn 17: 761-770, 2017). Blood biomarkers are needed to advance both HAND and AD fields, as blood draws are less costly than neuroimaging and are minimally invasive compared to lumbar punctures required for CSF acquisition. Extracellular vesicles (EVs) are nanoscale membranous vesicles shed from all cells including those of the central nervous system (CNS) and found in all biofluids; they are divided into exosomes (30-150 nm) originating from late endosomes/multivesicular bodies and microvesicles (150-1000 nm) produced through budding of the plasma membrane. Both types of vesicles are implicated in the pathogenesis of neurodegenerative diseases and may provide biomarkers (Bellingham et al., Front Physiol 3: 124, 2012). In this report, we call the vesicles exosomes, since they are the predominant vesicles in our preparations. They are involved in cell-to-cell communication in normal homeostasis and can be carriers of toxic proteins (Aβ, tau) (Sardar Sinha et al., Acta Neuropathol 136: 41-56, 2018) shed by cells as waste or actively secreted in a degenerative process (review Gupta and Pulliam, J Neuroinflammation 11: 68, 2014). The idea that exosomes originating from a specific cell can be recovered in the plasma using cellular surface markers of interest is intriguing. Neuron derived exosomes (NDEs) were first described in 2015 and isolated using antibodies against neural cell adhesion molecules NCAM or L1CAM, after total plasma exosome isolation (Fiandaca et al., Alzheimers Dement 11: 600-607 e1, 2015). Characterization of NDEs follows guidelines endorsed by the International Society for Extracellular Vesicles and includes Nanoparticle Tracking Analysis (NTA) to determine EV concentration and average diameter; Western Blots for EV markers; ELISAs for neuronal proteins and transmission EM for visualization (Sun et al., AIDS 31: F9-F17, 2017; Tang et al., FASEB J 30: 3097-106, 2016). This innovative isolation of an exosome sub-population has generated interest in using NDE as biomarkers for neurodegenerative diseases like AD, HAND, traumatic brain injury, posttraumatic stress disorder and more (reviews Agoston et al., Brain Inj 31: 1195-1203, 2017; Gupta and Pulliam, J Neuroinflammation 11: 68, 2014; Hu et al., Cell Death Dis 7: e2481, 2016; Karnati et al., J Neurotrauma, 2018; Osier et al., Mol Neurobiol, 2018). Several biomarkers from plasma NDEs were recently reported by the Pulliam lab to be elevated in general cognitive impairment (Sun et al., AIDS 31: F9-F17, 2017). We review our collective data here on HAND and AD and add to the characterization of plasma NDEs as exciting biomarkers of neurodegeneration.

Altered levels of plasma neuron-derived exosomes and their cargo proteins characterize acute and chronic mild traumatic brain injury

Neuron-derived exosomes (NDEs) were enriched by anti-L1CAM antibody immunoabsorption from plasmas of subjects ages 18-26 yr within 1 wk after a sports-related mild traumatic brain injury (acute mTBI) ( n = 18), 3 mo or longer after the last of 2-4 mTBIs (chronic mTBI) ( n = 14) and with no recent history of TBI (controls) ( n = 21). Plasma concentrations of NDEs, assessed by counts and levels of extracted exosome marker CD81, were significantly depressed by a mean of 45% in acute mTBI ( P < 0.0001), but not chronic mTBI, compared with controls. Mean CD81-normalized NDE levels of a range of functional brain proteins were significantly abnormal relative to those of controls in acute but not chronic mTBI, including ras-related small GTPase 10, 73% decrease; annexin VII, 8.8-fold increase; ubiquitin C-terminal hydrolase L1, 2.5-fold increase; AII spectrin fragments, 1.9-fold increase; claudin-5, 2.7-fold increase; sodium-potassium-chloride cotransporter-1, 2.8-fold increase; aquaporin 4, 8.9-fold increase (3.6-fold increase in chronic mTBI); and synaptogyrin-3, 3.1-fold increase (1.3-fold increase in chronic mTBI) (all acute mTBI proteins P < 0.0001). In chronic mTBI, there were elevated CD81-normalized NDE levels of usually pathologic β-amyloid peptide 1-42 (1.6-fold, P < 0.0001), P-T181-tau (2.2-fold, P < 0.0001), P-S396-tau (1.6-fold, P < 0.01), IL-6 (16-fold, P < 0.0001), and prion cellular protein (PRPc) (5.1-fold, P < 0.0001) with lesser or greater (IL-6, PRPc) increases in acute mTBI. Increases in NDE levels of most neurofunctional proteins in acute, but not chronic, mTBI, and elevations of most NDE neuropathological proteins in chronic and acute mTBI delineated phase-specificity. Longitudinal studies of more mTBI subjects may identify biomarkers predictive of and etiologically involved in mTBI-induced neurodegeneration.-Goetzl, E. J., Elahi, F. M., Mustapic, M., Kapogiannis, D., Pryhoda, M., Gilmore, A., Gorgens, K. A., Davidson, B., Granholm, A.-C., Ledreux, A. Altered levels of plasma neuron-derived exosomes and their cargo proteins characterize acute and chronic mild traumatic brain injury.

Tortuous Paths of Insulin Signaling and Mitochondria in Alzheimer's Disease

Due to the exponential growth of aging population worldwide, neurodegenerative diseases became a major public health concern. Among them, Alzheimer's disease (AD) prevails as the most common in the elderly, rendering it a research priority. After several decades considering the brain as an insulin-insensitive organ, recent advances proved a central role for this hormone in learning and memory processes and showed that AD shares a high number of features with systemic conditions characterized by insulin resistance. Mitochondrial dysfunction has also been widely demonstrated to play a major role in AD development supporting the idea that this neurodegenerative disease is characterized by a pronounced metabolic dysregulation. This chapter is intended to discuss evidence demonstrating the key role of insulin signaling and mitochondrial anomalies in AD.

Shotgun Proteomic Profiling of Bloodborne Nanoscale Extracellular Vesicles

Analyses of bloodborne nanoscale extracellular vesicles (nsEVs) have shown tremendous promise in enabling the development of noninvasive blood-based clinical diagnostic tests, predicting and monitoring the efficacy of treatment programs, and identifying new drug targets in the context of health conditions such as cancer and Alzheimer's disease. In this chapter we present a protocol for generating global nsEV proteomic profiles that can further the utility of nsEV analysis for the above biomedical applications by enlightening us of differences in protein abundance across normal and disease state nsEVs. This protocol features the use of magnetic particle-based immunoprecipitation to enrich highly purified populations of nsEVs directly from plasma or serum samples. The constituent proteins of these vesicles are subsequently characterized using a comparative shotgun proteomics approach that entails bottom-up, tandem mass spectrometric analysis of peptides generated by proteolytic digestion of nsEV-derived proteins. The methods described here are compatible with parallel processing of dozens of plasma or serum samples and can be valuable tools in enabling nsEV biomarker discoveries that have high translational relevance in the development of both novel therapeutics and blood sample diagnostic assays.

Association of Transfusion With Risks of Dementia or Alzheimer's Disease: A Population-Based Cohort Study

Purpose: The association between neurodegenerative diseases and transfusion remains to be investigated. Methods: The study population comprised 63,813 patients who underwent a blood transfusion and 63,813 propensity score-matched controls between 2000 and 2010. Data were obtained from the Taiwan National Health Insurance Research Database, which is maintained by the National Health Research Institutes. A Cox regression analysis was conducted to elucidate the relationship between blood transfusions and the risk of dementia. Results: A multivariate Cox regression analysis of factors, such as age, sex, cardiovascular ischemia disease, and depression, revealed that patients who underwent a blood transfusion showed a 1.73-fold higher risk of dementia [95% confidence interval (CI) = 1.62-1.84] and a 1.37-fold higher risk of Alzheimer's disease (AD) [95% CI = 1.13-1.66] than those who did not. Patients who received a transfusion of washed red blood cells showed a 2.37-fold higher risk of dementia (95% CI = 1.63-3.44) than those who did not. Conclusion: Blood transfusion, especially transfusion of any type of red blood cells is associated with an increased risk of dementia.

Insulin Resistance in Alzheimer's Disease

The epidemiological connection between diabetes, obesity, and dementia represents an important public health challenge but also an opportunity to further understand these conditions. The key intersection among the three diseases is insulin resistance, which has been classically described to occur in peripheral tissues in diabetes and obesity and has recently been shown to develop in Alzheimer's disease (AD) brains. Here we review encouraging preclinical and clinical data indicating the potential of targeting impaired insulin signaling with antidiabetic drugs to treat dementia. We further discuss biological mechanisms through which peripheral metabolic dysregulation may lead to brain malfunction, providing possible explanations for the connection between diabetes, obesity, and AD. Finally, we briefly discuss how lifelong allostatic load may interact with aging to increase the risk of dementia in late life.

AXL phosphorylates and up-regulates TNS2 and its implications in IRS-1-associated metabolism in cancer cells

Background

TNS2 is a focal adhesions protein and a binding partner for many proteins, including the receptor tyrosine kinase Axl. Although TNS2 can bind with Axl, the details of their interactions have not been elucidated. TNS2 is involved in IRS-1 signaling pathway. In this study, we confirmed the relationship between TNS2 expression and the expression of Axl, IRS-1, PDK1 and Glut4 in pancreatic cancer patients.

Methods

The expression levels of TNS2, Axl, IRS-1, PDK1 and Glut4 in human cancer cells were measured by Western blot and/or IP-Western blot assays. Paired samples of pancreatic cancer and non-cancer tissues were obtained from 33 patients and were used to construct tissue microarrays. The expression levels of these markers in the tissue microarrays were measured by enzyme-linked Immunohistochemistry assay, and the relationships were analyzed by Pearson’s chi-square test and two-tailed t-test analysis.

Results

We demonstrated for the first time that TNS2 is a phosphorylation substrate of Axl. Moreover, we found a positive relationship between TNS2 expression and the expression of Axl, IRS-1, PDK1 and Glut4 in pancreatic cancer patients. Based on these results, we suggest that Axl modulates glucose metabolism potentially through TNS2 and IRS-1. We hypothesize that there exists a novel mechanism whereby Axl binds to and phosphorylates TNS2, releasing TNS2 from interaction with IRS-1 and resulting in increased stability of IRS-1. The two key enzymes of aerobic glycolysis (Glut4 and PDK1) were found to be up-regulated by Axl/TNS2/IRS-1 cross-talk and may play a critical role in glucose metabolism of cancer cells.

Conclusions

Our results revealed for the first time that Axl binds to and phosphorylates TNS2 and that Axl/TNS2/IRS-1 cross-talk may potentially play a critical role in glucose metabolism of cancer cells.

Electronic supplementary material

The online version of this article (10.1186/s12929-018-0465-x) contains supplementary material, which is available to authorized users.

Neuronal Enriched Extracellular Vesicle Proteins as Biomarkers for Traumatic Brain Injury

Traumatic brain injury (TBI) is a major cause of injury-related death throughout the world and lacks effective treatment. Surviving TBI patients often develop neuropsychiatric symptoms, and the molecular mechanisms underlying the neuronal damage and recovery following TBI are not well understood. Extracellular vesicles (EVs) are membranous nanoparticles that are divided into exosomes (originating in the endosomal/multi-vesicular body [MVB] system) and microvesicles (larger EVs produced through budding of the plasma membrane). Both types of EVs are generated by all cells and are secreted into the extracellular environment, and participate in cell-to-cell communication and protein and RNA delivery. EVs enriched for neuronal origin can be harvested from peripheral blood samples and their contents quantitatively examined as a window to follow potential changes occurring in brain. Recent studies suggest that the levels of exosomal proteins and microRNAs (miRNAs) may represent novel biomarkers to support the clinical diagnosis and potential response to treatment for neurological disorders. In this review, we focus on the biogenesis of EVs, their molecular composition, and recent advances in research of their contents as potential diagnostic tools for TBI.

Therapeutic implications of how TNF links apolipoprotein E, phosphorylated tau, α-synuclein, amyloid-β and insulin resistance in neurodegenerative diseases

While cytokines such as TNF have long been recognized as essential to normal cerebral physiology, the implications of their chronic excessive production within the brain are now also increasingly appreciated. Syndromes as diverse as malaria and lead poisoning, as well as non‐infectious neurodegenerative diseases, illustrate this. These cytokines also orchestrate changes in tau, α‐synuclein, amyloid‐β levels and degree of insulin resistance in most neurodegenerative states. New data on the effects of salbutamol, an indirect anti‐TNF agent, on α‐synuclein and Parkinson's disease, APOE4 and tau add considerably to the rationale of the anti‐TNF approach to understanding, and treating, these diseases. Therapeutic advances being tested, and arguably useful for a number of the neurodegenerative diseases, include a reduction of excess cerebral TNF, whether directly, with a specific anti‐TNF biological agent such as etanercept via Batson's plexus, or indirectly via surgically implanting stem cells. Inhaled salbutamol also warrants investigating further across the neurodegenerative disease spectrum. It is now timely to integrate this range of new information across the neurodegenerative disease spectrum, rather than keep seeing it through the lens of individual disease states.

Extracellular Vesicle Biology in Alzheimer's Disease and Related Tauopathy

Extracellular vesicles (EVs) are physiological vesicles secreted from most eukaryotes and contain cargos of their cell of origin. EVs, and particularly a subset of EV known as exosomes, are emerging as key mediators of cell to cell communication and waste management for cells both during normal organismal function and in disease. In this review, we investigate the rapidly growing field of exosome biology, their biogenesis, cargo loading, and uptake by other cells. We particularly consider the role of exosomes in Alzheimer's disease, both as a pathogenic agent and as a disease biomarker. We also explore the emerging role of exosomes in chronic traumatic encephalopathy. Finally, we highlight open questions in these fields and the possible use of exosomes as therapeutic targets and agents.

Insulin resistance is associated with smaller brain volumes in a preliminary study of depressed and obese children

OBJECTIVE

During childhood, the brain can consume up to 65% of total calories, and a steady supply of the brain's main fuel glucose needs to be maintained. Although the brain itself is not dependent on insulin for the uptake of glucose, insulin plays an important role in energy homeostasis. Thus, the risk for insulin resistance during brain development may negatively impact the whole brain volume.

METHODS

We investigated the link between the insulin resistance and the whole brain volume as measured by structural Magnetic resonance imaging (MRI) in 46 unmedicated depressed and overweight youths between the ages of 9 and 17 years.

RESULTS

Smaller whole brain volumes were associated with insulin resistance independent of age, sex, depression severity, body mass index, socioeconomic status, Tanner Stage, and Intelligence quotient (IQ) (r = 0.395, P = .014)

CONCLUSIONS

There may be a significant cost for developing insulin resistance on the developing brain. Disentangling the precise relationship between the insulin resistance and the developing brain is critical.

Higher exosomal tau, amyloid-beta 42 and IL-10 are associated with mild TBIs and chronic symptoms in military personnel

OBJECTIVE

Identify biomarkers in peripheral blood that relate to chronic post-concussive and behavioural symptoms following traumatic brain injuries (TBIs) to ultimately improve clinical management.

RESEARCH DESIGN

We compared military personnel with mild TBIs (mTBIs) (n = 42) to those without TBIs (n = 22) in concentrations of tau, amyloid-beta (Aβ42) and cytokines (tumour necrosis factor alpha (TNFα, interleukin (IL)-6 and -10) in neuronal-derived exosomes from the peripheral blood. We utilized nanosight technology coupled with ultra-sensitivity immunoassay methods. We also examined the impact of post-concussive and behavioural symptoms including depression and post-traumatic stress disorder (PTSD) on these neuronal-derived markers.

RESULTS

We report that concentrations of exosomal tau (F_1, 62 = 10.50), Aβ42 (F_1, 61 = 5.32) and IL-10 (F_1, 59 = 4.32) were elevated in the mTBI group compared to the controls. Within the mTBI group, regression models show that post-concussive symptoms were most related to exosomal tau elevations, whereas exosomal IL-10 levels were related to PTSD symptoms.

CONCLUSIONS

These findings suggest that chronic post-concussive symptoms following an mTBI relate to altered exosomal activity, and that greater tau pathology may underlie chronic post-concussive symptoms that develop following mTBIs. It also suggests that central inflammatory activity contributes to PTSD symptoms following an mTBI, providing necessary insights into the role of inflammation in chronic PTSD symptoms.

Hallmarks of Brain Aging: Adaptive and Pathological Modification by Metabolic States

During aging, the cellular milieu of the brain exhibits tell-tale signs of compromised bioenergetics, impaired adaptive neuroplasticity and resilience, aberrant neuronal network activity, dysregulation of neuronal Ca2+ homeostasis, the accrual of oxidatively modified molecules and organelles, and inflammation. These alterations render the aging brain vulnerable to Alzheimer's and Parkinson's diseases and stroke. Emerging findings are revealing mechanisms by which sedentary overindulgent lifestyles accelerate brain aging, whereas lifestyles that include intermittent bioenergetic challenges (exercise, fasting, and intellectual challenges) foster healthy brain aging. Here we provide an overview of the cellular and molecular biology of brain aging, how those processes interface with disease-specific neurodegenerative pathways, and how metabolic states influence brain health.

Cerebrospinal fluid and blood biomarkers for neurodegenerative dementias: An update of the Consensus of the Task Force on Biological Markers in Psychiatry of the World Federation of Societies of Biological Psychiatry

In the 12 years since the publication of the first Consensus Paper of the WFSBP on biomarkers of neurodegenerative dementias, enormous advancement has taken place in the field, and the Task Force takes now the opportunity to extend and update the original paper. New concepts of Alzheimer's disease (AD) and the conceptual interactions between AD and dementia due to AD were developed, resulting in two sets for diagnostic/research criteria. Procedures for pre-analytical sample handling, biobanking, analyses and post-analytical interpretation of the results were intensively studied and optimised. A global quality control project was introduced to evaluate and monitor the inter-centre variability in measurements with the goal of harmonisation of results. Contexts of use and how to approach candidate biomarkers in biological specimens other than cerebrospinal fluid (CSF), e.g. blood, were precisely defined. Important development was achieved in neuroimaging techniques, including studies comparing amyloid-β positron emission tomography results to fluid-based modalities. Similarly, development in research laboratory technologies, such as ultra-sensitive methods, raises our hopes to further improve analytical and diagnostic accuracy of classic and novel candidate biomarkers. Synergistically, advancement in clinical trials of anti-dementia therapies energises and motivates the efforts to find and optimise the most reliable early diagnostic modalities. Finally, the first studies were published addressing the potential of cost-effectiveness of the biomarkers-based diagnosis of neurodegenerative disorders.

Plasma α-synuclein and cognitive impairment in the Parkinson's Associated Risk Syndrome: A pilot study

Plasma total and nervous system derived exosomal (NDE) α-synuclein have been determined as potential biomarkers of Parkinson's disease (PD). To explore the utility of plasma α-synuclein in the prodromal phase of PD, plasma total and NDE α-synuclein were evaluated in baseline and 2-year follow-up samples from 256 individuals recruited as part of the Parkinson's Associated Risk Syndrome (PARS) study. The results demonstrated that baseline and longitudinal increases in total α-synuclein predicted progression of cognitive decline in hyposmic individuals with dopamine transporter (DAT) binding reduction. On the other hand, a longitudinal decrease in NDE α-synuclein predicted worsening cognitive scores in hyposmic individuals with DAT binding reduction. Finally, in individuals with faster DAT progression, decreasing NDE/total α-synuclein ratio was associated with a larger reduction in DAT from baseline to follow-up. These results suggest that, though underlying mechanisms remain to be defined, alterations in plasma total and NDE α-synuclein concentrations are likely associated with PD progression, especially in the aspect of cognitive impairment, at early stages of the disease.

Exosomes in Acquired Neurological Disorders: New Insights into Pathophysiology and Treatment

Exosomes are endogenous nanovesicles that play critical roles in intercellular signaling by conveying functional genetic information and proteins between cells. Exosomes readily cross the blood-brain barrier and have promise as therapeutic delivery vehicles that have the potential to specifically deliver molecules to the central nervous system (CNS). This unique feature also makes exosomes attractive as biomarkers in diagnostics, prognostics, and therapeutics in the context of multiple significant public health conditions, including acquired neurological disorders. The purpose of this review is to summarize the state of the science surrounding the relevance of extracellular vesicles (EVs), particularly exosomes, to acquire neurological disorders, specifically traumatic brain injury (TBI), spinal cord injury (SCI), and ischemic stroke. In total, ten research articles were identified that examined exosomes in the context of TBI, SCI, or stroke; these manuscripts were reviewed and synthesized to further understand the current role of exosomes in the context of acquired neurological disorders. Of the ten published studies, four focused exclusively on TBI, one on both TBI and SCI, and five on ischemic stroke; notably, eight of the ten studies were limited to pre-clinical samples. The present review is the first to discuss the current body of knowledge surrounding the role of exosomes in the pathophysiology, diagnosis, and prognosis, as well as promising therapeutic strategies in TBI, SCI, and stroke research.

Lipidomic Profiles in Diabetes and Dementia

Lipids are a diverse class of hydrophobic and amphiphilic molecules which make up the bulk of most biological systems and are essential for human life. The role of lipids in health and disease has been recognized for many decades, as evidenced by the early identification of cholesterol as an important risk factor of heart disease and the development and introduction of statins as a one of the most successful therapeutic interventions to date. While several studies have demonstrated an increased risk of dementia, including Alzheimer's disease (AD), in those with diabetes mellitus, the nature of this risk is not well understood. Recent developments in the field of lipidomics, driven primarily by technological advances in high pressure liquid chromatography and particularly mass spectrometry, have enabled the detailed characterization of the many hundreds of individual lipid species in mammalian systems and their association with disease states. Diabetes mellitus and AD have received particular attention due to their prominence in Western societies as a result of the ongoing obesity epidemic and the aging populations. In this review, we examine how these lipidomic studies are informing on the relationship between lipid metabolism with diabetes and AD and how this may inform on the common pathological pathways that link diabetes risk with dementia.

Does traumatic brain injury hold the key to the Alzheimer's disease puzzle?

INTRODUCTION

Neurodegenerative disorders have been a graveyard for hundreds of well-intentioned efforts at drug discovery and development. Concussion and other traumatic brain injuries (TBIs) and Alzheimer's disease (AD) share many overlapping pathologies and possible clinical links.

METHODS

We searched the literature since 1995 using MEDLINE and Google Scholar for the terms concussion, AD, and shared neuropathologies. We also studied a TBI animal model as a supplement to transgenic (Tg) mouse AD models for evaluating AD drug efficacy by preventing neuronal losses. To evaluate TBI/AD pathologies and neuronal self-induced cell death (apoptosis), we are studying brain extracellular vesicles in plasma and (-)-phenserine pharmacology to probe, in animal models of AD and humans, apoptosis and pathways common to concussion and AD.

RESULTS

Neuronal cell death and a diverse and significant pathological cascade follow TBIs. Many of the developing pathologies are present in early AD. The use of an animal model of concussion as a supplement to Tg mice provides an indication of an AD drug candidate's potential for preventing apoptosis and resulting progression toward dementia in AD. This weight drop supplementation to Tg mouse models, the experimental drug (-)-phenserine, and plasma-derived extracellular vesicles enriched for neuronal origin to follow biomarkers of neurodegenerative processes, each and in combination, show promise as tools useful for probing the progression of disease in AD, TBI/AD pathologies, apoptosis, and drug effects on rates of apoptosis both preclinically and in humans. (-)-Phenserine both countered many subacute post-TBI pathologies that could initiate clinical AD and, in the concussion and other animal models, showed evidence consistent with direct inhibition of neuronal preprogrammed cell death in the presence of TBI/AD pathologies.

DISCUSSION

These findings may provide support for expanding preclinical Tg mouse studies in AD with a TBI weight drop model, insights into the progression of pathological targets, their relations to apoptosis, and timing of interventions against these targets and apoptosis. Such studies may demonstrate the potential for drugs to effectively and safely inhibit preprogrammed cell death as a new drug development strategy for use in the fight to defeat AD.

Detection of Aggregation-Competent Tau in Neuron-Derived Extracellular Vesicles

Progressive cerebral accumulation of tau aggregates is a defining feature of Alzheimer's disease (AD). A popular theory that seeks to explain the apparent spread of neurofibrillary tangle pathology proposes that aggregated tau is passed from neuron to neuron. Such a templated seeding process requires that the transferred tau contains the microtubule binding repeat domains that are necessary for aggregation. While it is not clear how a protein such as tau can move from cell to cell, previous reports have suggested that this may involve extracellular vesicles (EVs). Thus, measurement of tau in EVs may both provide insights on the molecular pathology of AD and facilitate biomarker development. Here, we report the use of sensitive immunoassays specific for full-length (FL) tau and mid-region tau, which we applied to analyze EVs from human induced pluripotent stem cell (iPSC)-derived neuron (iN) conditioned media, cerebrospinal fluid (CSF), and plasma. In each case, most tau was free-floating with a small component inside EVs. The majority of free-floating tau detected by the mid-region assay was not detected by our FL assays, indicating that most free-floating tau is truncated. Inside EVs, the mid-region assay also detected more tau than the FL assay, but the ratio of FL-positive to mid-region-positive tau was higher inside exosomes than in free solution. These studies demonstrate the presence of minute amounts of free-floating and exosome-contained FL tau in human biofluids. Given the potential for FL tau to aggregate, we conclude that further investigation of these pools of extracellular tau and how they change during disease is merited.

Acidity and Acid-Sensing Ion Channels in the Normal and Alzheimer's Disease Brain

Alzheimer's disease prevalence has reached epidemic proportion with very few treatment options, which are associated with a multitude of side effects. A potential avenue of research for new therapies are protons, and their associated receptor: acid-sensing ion channels (ASIC). Protons are often overlooked neurotransmitters, and proton-gated currents have been identified in the brain. Furthermore, ASICs have been determined to be crucial for proper brain function. While there is more work to be done, this review is intended to highlight protons as neurotransmitters and their role along with the role of ASICs within physiological functioning of the brain. We will also cover the pathophysiological associations between ASICs and modulators of ASICs. Finally, this review will sum up how the studies of protons, ASICs and their modulators may generate new therapeutic molecules for Alzheimer's disease and other neurodegenerative diseases.

mTORC2 (Rictor) in Alzheimer's Disease and Reversal of Amyloid-β Expression-Induced Insulin Resistance and Toxicity in Rat Primary Cortical Neurons

Mammalian target of rapamycin complex 1 (mTORC1), a nutrient sensor and central controller of cell growth and proliferation, is altered in various models of Alzheimer's disease (AD). Even less studied or understood in AD is mammalian target of rapamycin complex 2 (mTORC2) that influences cellular metabolism, in part through the regulations of Akt/PKB and SGK. Dysregulation of insulin/PI3K/Akt signaling is another important feature of AD pathogenesis. We found that both total mTORC1 and C2 protein levels and individual C1 and C2 enzymatic activities were decreased in human AD brain samples. In two rodent AD models, mTORC1 and C2 activities were also decreased. In a neuronal culture model of AD characterized by accumulation of cellular amyloid-β (Aβ)42, mTORC1 activity was reduced. Autophagic vesicles and markers were correspondingly increased and new protein synthesis was inhibited, consistent with mTORC1 hypofunction. Interestingly, mTORC2 activity in neural culture seemed resistant to the effects of intracellular amyloid. In various cell lines, Aβ expression provoked insulin resistance, characterized by inhibition of stimulated Akt phosphorylation, and an increase in negative mTORC1 regular, p-AMPK, itself a nutrient sensor. Rapamycin decreased phospho-mTOR and to lesser degree p-Rictor. This further suppression of mTORC1 activity protected cells from Aβ-induced toxicity and insulin resistance. More striking, Rictor over-expression fully reversed the Aβ-effects on primary neuronal cultures. Finally, using in vitro assay, Rictor protein addition completely overcame oligomeric Aβ-induced inhibition of the PDK-Akt activation step. We conclude that striking a new balance by restoring mTORC2 abundance and/or inhibition of mTORC1 has therapeutic potential in AD.

New Technologies for Analysis of Extracellular Vesicles

Extracellular vesicles (EVs) are diverse, nanoscale membrane vesicles actively released by cells. Similar-sized vesicles can be further classified (e.g., exosomes, microvesicles) based on their biogenesis, size, and biophysical properties. Although initially thought to be cellular debris, and thus under-appreciated, EVs are now increasingly recognized as important vehicles of intercellular communication and circulating biomarkers for disease diagnoses and prognosis. Despite their clinical potential, the lack of sensitive preparatory and analytical technologies for EVs poses a barrier to clinical translation. New analytical platforms including molecular ones are thus actively being developed to address these challenges. Recent advances in the field are expected to have far-reaching impact in both basic and translational studies. This article aims to present a comprehensive and critical overview of emerging analytical technologies for EV detection and their clinical applications.

Shared pathological pathways of Alzheimer's disease with specific comorbidities: current perspectives and interventions

Alzheimer's disease (AD) belongs to one of the most multifactorial, complex and heterogeneous morbidity-leading disorders. Despite the extensive research in the field, AD pathogenesis is still at some extend obscure. Mechanisms linking AD with certain comorbidities, namely diabetes mellitus, obesity and dyslipidemia, are increasingly gaining importance, mainly because of their potential role in promoting AD development and exacerbation. Their exact cognitive impairment trajectories, however, remain to be fully elucidated. The current review aims to offer a clear and comprehensive description of the state-of-the-art approaches focused on generating in-depth knowledge regarding the overlapping pathology of AD and its concomitant ailments. Thorough understanding of associated alterations on a number of molecular, metabolic and hormonal pathways, will contribute to the further development of novel and integrated theranostics, as well as targeted interventions that may be beneficial for individuals with age-related cognitive decline.

Perspectives in Lipocalin-2: Emerging Biomarker for Medical Diagnosis and Prognosis for Alzheimer's Disease

Lipocalin-2 (LCN2), a secreted glycoprotein belonging to the lipocalin superfamily was reported to participate in various biological processes including cell migration, cell survival, inflammatory responses, and insulin sensitivity. LCN2 is expressed in the multiple tissues such as kidney, liver, uterus, and bone marrow. The receptors for LCN2 were additionally found in microglia, astrocytes, epithelial cells, and neurons, but the role of LCN2 in the central nervous system (CNS) has not been fully understood yet. Recently, in vitro, in vivo, and clinical studies reported the association between LCN2 and the risk of Alzheimer's disease (AD). Here, we reviewed the significant evidences showing that LCN2 contributes to the onset and progression of AD. It may suggest that the manipulation of LCN2 in the CNS would be a crucial target for regulation of the pathogenesis and risk of AD.

Declining levels of functionally specialized synaptic proteins in plasma neuronal exosomes with progression of Alzheimer's disease

Interactions of the presynaptic proteins, neuronal pentraxin 2 (NPTX2) and neurexin 2α (NRXN2α), with their respective postsynaptic functional partners, GluA4-containing glutamate (AMPA4) receptor and neuroligin 1 (NLGN1), enhance excitatory synaptic activity in some areas of the hippocampus and cerebral cortex. As early damage of such excitatory circuits in the brain tissues of participants with Alzheimer's disease (AD) correlates with cognitive losses, plasma neuron-derived exosome (NDE) levels of these 2 pairs of specialized synaptic proteins were quantified to assess their biomarker characteristics. The NDE contents of all 4 proteins were decreased significantly in AD dementia ( n = 46), and diminished levels of AMPA4 and NLGN1 correlated with the extent of cognitive loss. In a preclinical period, 6-11 yr before the onset of dementia, the NDE levels of all but NPTX2 were significantly lower than those of matched controls, and levels of all proteins declined significantly with the development of dementia. Reductions in NDE levels of these specialized excitatory synaptic proteins may therefore be indicative of the extent of cognitive loss and may reflect progression of the severity of AD.-Goetzl, E. J., Abner, E. L., Jicha, G. A., Kapogiannis, D., Schwartz, J. B. Declining levels of functionally specialized synaptic proteins in plasma neuronal exosomes with progression of Alzheimer's disease.

Exosomal biomarkers in Down syndrome and Alzheimer's disease

Every person with Down syndrome (DS) has the characteristic features of Alzheimer's disease (AD) neuropathology in their brain by the age of forty, and most go on to develop AD dementia. Since people with DS show highly variable levels of baseline function, it is often difficult to identify early signs of dementia in this population. The discovery of blood biomarkers predictive of dementia onset and/or progression in DS is critical for developing effective clinical diagnostics. Our recent studies show that neuron-derived exosomes, which are small extracellular vesicles secreted by most cells in the body, contain elevated levels of amyloid-beta peptides and phosphorylated-Tau that could indicate a preclinical AD phase in people with DS starting in childhood. We also found that the relative levels of these biomarkers were altered following dementia onset. Exosome release and signaling are dependent on cellular redox homeostasis as well as on inflammatory processes, and exosomes may be involved in the immune response, suggesting a dual role as both triggers of inflammation in the brain and propagators of inflammatory signals between brain regions. Based on recently reported connections between inflammatory processes and exosome release, the elevated neuroinflammatory state observed in people with DS may affect exosomal AD biomarkers. Herein, we discuss findings from studies of people with DS, people with DS and AD (DS-AD), and mouse models of DS showing new connections between neuroinflammatory pathways, oxidative stress, exosomes, and exosome-mediated signaling, which may inform future AD diagnostics, preventions, and treatments in the DS population as well as in the general population.

Post-translational add-ons mark the path in exosomal protein sorting

Extracellular vesicles (EVs) are released by cells to the extracellular environment to mediate inter-cellular communication. Proteins, lipids, nucleic acids and metabolites shuttled in these vesicles modulate specific functions in recipient cells. The enrichment of selected sets of proteins in EVs compared with global cellular levels suggests the existence of specific sorting mechanisms to specify EV loading. Diverse post-translational modifications (PTMs) of proteins participate in the loading of specific elements into EVs. In this review, we offer a perspective on PTMs found in EVs and discuss the specific role of some PTMs, specifically Ubiquitin and Ubiquitin-like modifiers, in exosomal sorting of protein components. The understanding of these mechanisms will provide new strategies for biomedical applications. Examples include the presence of defined PTM marks on EVs as novel biomarkers for the diagnosis and prognosis of certain diseases, or the specific import of immunogenic components into EVs for vaccine generation.

Diagnostic Potential of Neural Exosome Cargo as Biomarkers for Acute Brain Injury

Objective

Neuronal exosomes purified from peripheral blood samples have been proposed as diagnostic tool in the setting of acute brain injury but never tested clinically. We hypothesized that exosome protein biomarkers would change over time following acute hypoxic brain injury and would predict response to therapy.

Methods

Synaptopodin (SYNPO), an actin-associated protein present in postsynaptic spines, was evaluated as a potential biomarker as well as: synaptophysin, neuron-specific enolase, and mitochondrial cytochrome c oxidase. A secondary analysis was performed on neonatal samples collected at 8, 10, and 14 h after the initiation of therapeutic-controlled hypothermia for acute hypoxic-ischemic encephalopathy (n = 14). Neuronal exosomes were purified from serum and protein levels were quantified using standard ELISA methods. The primary study outcomes were length of stay (LOS), discharge on seizure medication (DCMED), and composite neuroimaging score (NIS).

Results

The slope of change in neuronal exosome SYNPO between 8 and 14 h appeared to be the most promising biomarker for all three clinical study outcomes. SYNPO was highly correlated with LOS (-0.91, P < 0.001). SYNPO increased in 6/8 without DCMED and was worse or neutral in 5/5 with DCMED (P = 0.02). All four neonates with an abnormal NIS had neutral or decreasing SYNPO (P = 0.055). Other candidate biomarkers were not associated with outcomes.

Interpretation

This report provides the first clinical evidence that neural exosomes turn over rapidly enough in the peripheral circulation to be used as a "troponin-like" test following acute brain injury. Optimal sampling and biomarkers likely vary with type of brain injury.