In recent years, we have accomplished a deeper understanding about the pathophysiology of major depressive disorder (MDD). Nevertheless, this improved comprehension has not translated to improved ...treatment outcome, as identification of specific biologic markers of disease may still be crucial to facilitate a more rapid, successful treatment. Ongoing research explores the importance of screening biomarkers using neuroimaging, neurophysiology, genomics, proteomics, and metabolomics measures.
In the present review, we highlight the biomarkers that are differentially expressed in MDD and treatment response and place a particular emphasis on the most recent progress in advancing technology which will continue the search for blood-based biomarkers.
Due to space constraints, we are unable to detail all biomarker platforms, such as neurophysiological and neuroimaging markers, although their contributions are certainly applicable to a biomarker review and valuable to the field.
Although the search for reliable biomarkers of depression and/or treatment outcome is ongoing, the rapidly-expanding field of research along with promising new technologies may provide the foundation for identifying key factors which will ultimately help direct patients toward a quicker and more effective treatment for MDD.
•We summarize current therapeutic interventions for depression and discuss the need for biomarker identification.•We discuss the utility of “omics” screening tools and their applicability to discovering biomarkers.•We review studies using blood based “omics” analyses with MDD and treatment response.
Growth differentiation factor 15 (GDF15), a distant member of the transforming growth factor (TGF)-β family, is a secreted protein that circulates as a 25-kDa dimer. In humans, elevated GDF15 ...correlates with weight loss, and the administration of GDF15 to mice with obesity reduces body weight, at least in part, by decreasing food intake. The mechanisms through which GDF15 reduces body weight remain poorly understood, because the cognate receptor for GDF15 is unknown. Here we show that recombinant GDF15 induces weight loss in mice fed a high-fat diet and in nonhuman primates with spontaneous obesity. Furthermore, we find that GDF15 binds with high affinity to GDNF family receptor α-like (GFRAL), a distant relative of receptors for a distinct class of the TGF-β superfamily ligands. Gfral is expressed in neurons of the area postrema and nucleus of the solitary tract in mice and humans, and genetic deletion of the receptor abrogates the ability of GDF15 to decrease food intake and body weight in mice. In addition, diet-induced obesity and insulin resistance are exacerbated in GFRAL-deficient mice, suggesting a homeostatic role for this receptor in metabolism. Finally, we demonstrate that GDF15-induced cell signaling requires the interaction of GFRAL with the coreceptor RET. Our data identify GFRAL as a new regulator of body weight and as the bona fide receptor mediating the metabolic effects of GDF15, enabling a more comprehensive assessment of GDF15 as a potential pharmacotherapy for the treatment of obesity.
Proteopathic tau seeding predicts tauopathy in vivo Holmes, Brandon B; Furman, Jennifer L; Mahan, Thomas E ...
Proceedings of the National Academy of Sciences,
10/2014, Letnik:
111, Številka:
41
Journal Article
Recenzirano
Odprti dostop
Transcellular propagation of protein aggregates, or proteopathic seeds, may drive the progression of neurodegenerative diseases in a prion-like manner. In tauopathies such as Alzheimer’s disease, ...this model predicts that tau seeds propagate pathology through the brain via cell–cell transfer in neural networks. The critical role of tau seeding activity is untested, however. It is unknown whether seeding anticipates and correlates with subsequent development of pathology as predicted for a causal agent. One major limitation has been the lack of a robust assay to measure proteopathic seeding activity in biological specimens. We engineered an ultrasensitive, specific, and facile FRET-based flow cytometry biosensor assay based on expression of tau or synuclein fusions to CFP and YFP, and confirmed its sensitivity and specificity to tau (∼300 fM) and synuclein (∼300 pM) fibrils. This assay readily discriminates Alzheimer’s disease vs. Huntington's disease and aged control brains. We then carried out a detailed time-course study in P301S tauopathy mice, comparing seeding activity versus histological markers of tau pathology, including MC1, AT8, PG5, and Thioflavin S. We detected robust seeding activity at 1.5 mo, >1 mo before the earliest histopathological stain. Proteopathic tau seeding is thus an early and robust marker of tauopathy, suggesting a proximal role for tau seeds in neurodegeneration.
Significance Prion-like propagation of proteopathic seeds may underlie the progression of neurodegenerative diseases, including the tauopathies and synucleinopathies. We aimed to construct a versatile and simple cell assay to sensitively and specifically detect proteopathic seeding activity. Using a combination of FRET flow cytometry and a tau monoclonal FRET biosensor cell line, we report seed detection in the femtomolar range. This assay is easily applied to human brain homogenates and selectively responds to Alzheimer's disease but not Huntington's disease brains. By comparing seeding activity in a mouse model of human tauopathy, we demonstrate detection of proteopathic seeding far in advance of standard histopathological markers. Proteopathic seeding is thus an early marker of tauopathy, consistent with a causal role for tau seeds in neurodegeneration.
Astrocytes are the most abundant cell type in the brain and play a critical role in maintaining healthy nervous tissue. In Alzheimer's disease (AD) and most other neurodegenerative disorders, many ...astrocytes convert to a chronically "activated" phenotype characterized by morphologic and biochemical changes that appear to compromise protective properties and/or promote harmful neuroinflammatory processes. Activated astrocytes emerge early in the course of AD and become increasingly prominent as clinical and pathological symptoms progress, but few studies have tested the potential of astrocyte-targeted therapeutics in an intact animal model of AD. Here, we used adeno-associated virus (AAV) vectors containing the astrocyte-specific Gfa2 promoter to target hippocampal astrocytes in APP/PS1 mice. AAV-Gfa2 vectors drove the expression of VIVIT, a peptide that interferes with the immune/inflammatory calcineurin/NFAT (nuclear factor of activated T-cells) signaling pathway, shown by our laboratory and others to orchestrate biochemical cascades leading to astrocyte activation. After several months of treatment with Gfa2-VIVIT, APP/PS1 mice exhibited improved cognitive and synaptic function, reduced glial activation, and lower amyloid levels. The results confirm a deleterious role for activated astrocytes in AD and lay the groundwork for exploration of other novel astrocyte-based therapies.
The diagnosis and treatment of diseases involving tau-based pathology such as Alzheimer disease and certain frontotemporal dementias is hampered by the inability to detect pathological forms of tau ...with sufficient sensitivity, specificity and practicality. In these neurodegenerative diseases, tau accumulates in self-seeding filaments. For example, Pick disease (PiD) is associated with frontotemporal degeneration and accumulation of 3-repeat (3R) tau isoforms in filaments constituting Pick bodies. Exploiting the self-seeding activity of tau deposits, and using a 3R tau fragment as a substrate, we have developed an assay (tau RT-QuIC) that can detect tau seeds in 2 µl aliquots of PiD brain dilutions down to 10
−7
–10
−9
. PiD seeding activities were 100-fold higher in frontal and temporal lobes compared to cerebellar cortex. Strikingly, this test was 10
3
- to 10
5
-fold less responsive when seeded with brain containing predominant 4-repeat (4R) tau aggregates from cases of corticobasal degeneration, argyrophilic grain disease, and progressive supranuclear palsy. Alzheimer disease brain, with 3R + 4R tau deposits, also gave much weaker responses than PiD brain. When applied to cerebrospinal fluid samples (5 µl), tau RT-QuIC analyses discriminated PiD from non-PiD cases. These findings demonstrate that abnormal tau aggregates can be detected with high sensitivity and disease-specificity in crude tissue and fluid samples. Accordingly, this tau RT-QuIC assay exemplifies a new approach to diagnosing tauopathies and monitoring therapeutic trials using aggregated tau itself as a biomarker.
To site-specifically incorporate an unnatural amino acid (UAA) into target proteins in Escherichia coli, we use a suppressor plasmid that provides an engineered suppressor tRNA and an aminoacyl-tRNA ...synthetase (aaRS) specific for the UAA of interest. The continuous drive to further improve UAA incorporation efficiency in E. coli has resulted in several generations of suppressor plasmids. Here we describe a new, highly efficient suppressor plasmid, pUltra, harboring a single copy each of the tRNA and aaRS expression cassettes that exhibits higher suppression activity than its predecessors. This system is able to efficiently incorporate up to three UAAs within the same protein at levels up to 30% of the level of wild-type protein expression. Its unique origin of replication (CloDF13) and antibiotic resistance marker (spectinomycin) allow pUltra to be used in conjunction with the previously reported pEVOL suppressor plasmid, each encoding a distinct tRNA/aaRS pair, to simultaneously insert two different UAAs into the same protein. We demonstrate the utility of this system by efficiently incorporating two bio-orthogonal UAAs containing keto and azido side chains into ketosteroid isomerase and subsequently derivatizing these amino acid residues with two distinct fluorophores, capable of Förster resonance energy transfer interaction. Finally, because of its minimal composition, two different tRNA/aaRS pairs were encoded in pUltra, allowing the generation of a single plasmid capable of dual suppression. The high suppression efficiency and the ability to harbor multiple tRNA/aaRS pairs make pUltra a useful system for conducting single- and multiple-UAA mutagenesis in E. coli.
•Interleukin 4 (IL-4) levels are lower in adolescents and young adults with depression and suicidality.•Other inflammation-related markers didn’t differ in those with recent suicidality vs. healthy ...controls and those at-risk.•IL-4 levels were negatively correlated with self-reported depression severity.•Lower IL-4 levels were associated with higher autoantibody levels in an unrelated sample of depressed outpatients.
Immune system dysfunction has been implicated in the pathophysiology of suicide behavior. Here, we conducted an exploratory analysis of immune profile differences of three groups of adolescents and young adults (ages 10–25 years): healthy controls (n = 39), at risk of major depressive disorder (MDD; at-risk, n = 33), and MDD with recent suicide behavior/ ideation (suicide behavior, n = 37).
Plasma samples were assayed for chemokines and cytokines using Bio-Plex Pro Human Chemokine 40-plex assay. Log-transformed cytokine and chemokine levels were compared after controlling for age, gender, body mass index, race, ethnicity, and C-reactive protein (CRP) levels. In post-hoc analyses to understand the effect of dysregulated immune markers identified in this exploratory analysis, their association with autoantibodies was tested in an unrelated sample (n = 166).
Only levels of interleukin 4 (IL-4) differed significantly among the three groups false discovery rate (FDR) adjusted p = 0.0007. Participants with suicide behavior had lower IL-4 median = 16.8 pg/ml, interquartile range (IQR) = 7.9 levels than healthy controls (median = 29.1 pg/ml, IQR = 16.1, effect size ES = 1.30) and those at-risk (median = 24.4 pg/ml, IQR = 16.3, ES = 1.03). IL-4 levels were negatively correlated with depression severity (r= −0.38, p = 0.024). In an unrelated sample of outpatients with MDD, levels of IL-4 were negatively correlated (all FDR p < 0.05) with several autoantibodies 54/117 in total and 12/18 against innate immune markers.
Adolescent and young adult patients with recent suicide behavior exhibit lower IL-4 levels. One biological consequence of reduced IL-4 levels may be increased risk of autoimmunity.
Parkinson’s disease (PD) and multiple system atrophy (MSA) are distinct clinical syndromes characterized by the pathological accumulation of α-synuclein (α-syn) protein fibrils in neurons and glial ...cells. These disorders and other neurodegenerative diseases may progress via prion-like mechanisms. The prion model of propagation predicts the existence of “strains” that link pathological aggregate structure and neuropathology. Prion strains are aggregated conformers that stably propagate in vivo and cause disease with defined incubation times and patterns of neuropathology. Indeed, tau prions have been well defined, and research suggests that both α-syn and β-amyloid may also form strains. However, there is a lack of studies characterizing PD- versus MSA-derived α-syn strains or demonstrating stable propagation of these unique conformers between cells or animals. To fill this gap, we used an assay based on FRET that exploits a HEK293T “biosensor” cell line stably expressing α-syn (A53T)-CFP/YFP fusion proteins to detect α-syn seeds in brain extracts from PD and MSA patients. Both soluble and insoluble fractions of MSA extracts had robust seeding activity, whereas only the insoluble fractions of PD extracts displayed seeding activity. The morphology of MSA-seeded inclusions differed from PD-seeded inclusions. These differences persisted upon propagation of aggregation to second-generation biosensor cells. We conclude that PD and MSA feature α-syn conformers with very distinct biochemical properties that can be transmitted to α-syn monomers in a cell system. These findings are consistent with the idea that distinct α-syn strains underlie PD and MSA and offer possible directions for synucleinopathy diagnosis.
Transcellular propagation of tau aggregates may underlie the progression of pathology in Alzheimer’s disease (AD) and other tauopathies. Braak staging (B1, B2, B3) is based on phospho-tau ...accumulation within connected brain regions: entorhinal cortex (B1); hippocampus/limbic system (B2); and frontal and parietal lobes (B3). We previously developed a specific and sensitive assay that uses flow cytometry to quantify tissue seeding activity based on fluorescence resonance energy transfer (FRET) in cells that stably express tau reporter proteins. In a tauopathy mouse model, we have detected seeding activity far in advance of histopathological changes. It remains unknown whether individuals with AD also develop seeding activity prior to accumulation of phospho-tau. We measured tau seeding activity across four brain regions (hippocampus, frontal lobe, parietal lobe, and cerebellum) in 104 fresh-frozen human AD brain samples from all Braak stages. We observed widespread seeding activity, notably in regions predicted to be free of phospho-tau deposition, and in detergent-insoluble fractions that lacked tau detectable by ELISA. Seeding activity correlated positively with Braak stage and negatively with MMSE. Our results are consistent with early transcellular propagation of tau seeds that triggers subsequent development of neuropathology. The FRET-based seeding assay may also complement standard neuropathological classification of tauopathies.
Similar to peripheral immune/inflammatory cells, neuroglial cells appear to rely on calcineurin (CN) signaling pathways to regulate cytokine production and cellular activation. Several studies ...suggest that harmful immune/inflammatory responses may be the most impactful consequence of aberrant CN activity in glial cells. However, newly identified roles for CN in glutamate uptake, gap junction regulation, Ca2+ dyshomeostasis, and amyloid production suggest that CN's influence in glia may extend well beyond neuroinflammation. The following review will discuss the various actions of CN in glial cells, with particular emphasis on astrocytes, and consider the implications for neurologic dysfunction arising with aging, injury, and/or neurodegenerative disease.
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