Showing papers on "Proteotoxicity published in 2016"

Failure of RQC machinery causes protein aggregation and proteotoxic stress

Abstract: Translation of messenger RNAs lacking a stop codon results in the addition of a carboxy-terminal poly-lysine tract to the nascent polypeptide, causing ribosome stalling. Non-stop proteins and other stalled nascent chains are recognized by the ribosome quality control (RQC) machinery and targeted for proteasomal degradation. Failure of this process leads to neurodegeneration by unknown mechanisms. Here we show that deletion of the E3 ubiquitin ligase Ltn1p in yeast, a key RQC component, causes stalled proteins to form detergent-resistant aggregates and inclusions. Aggregation is dependent on a C-terminal alanine/threonine tail that is added to stalled polypeptides by the RQC component, Rqc2p. Formation of inclusions additionally requires the poly-lysine tract present in non-stop proteins. The aggregates sequester multiple cytosolic chaperones and thereby interfere with general protein quality control pathways. These findings can explain the proteotoxicity of ribosome-stalled polypeptides and demonstrate the essential role of the RQC in maintaining proteostasis.

Roles for ROS and hydrogen sulfide in the longevity response to germline loss in Caenorhabditis elegans

Abstract: In Caenorhabditis elegans, removing germ cells slows aging and extends life. Here we show that transcription factors that extend life and confer protection to age-related protein-aggregation toxicity are activated early in adulthood in response to a burst of reactive oxygen species (ROS) and a shift in sulfur metabolism. Germline loss triggers H2S production, mitochondrial biogenesis, and a dynamic pattern of ROS in specific somatic tissues. A cytoskeletal protein, KRI-1, plays a key role in the generation of H2S and ROS. These kri-1-dependent redox species, in turn, promote life extension by activating SKN-1/Nrf2 and the mitochondrial unfolded-protein response, respectively. Both H2S and, remarkably, kri-1-dependent ROS are required for the life extension produced by low levels of the superoxide-generator paraquat and by a mutation that inhibits respiration. Together our findings link reproductive signaling to mitochondria and define an inducible, kri-1-dependent redox-signaling module that can be invoked in different contexts to extend life and counteract proteotoxicity.

Control of the structural landscape and neuronal proteotoxicity of mutant Huntingtin by domains flanking the polyQ tract

Abstract: Many neurodegenerative diseases are linked to amyloid aggregation. In Huntington's disease (HD), neurotoxicity correlates with an increased aggregation propensity of a polyglutamine (polyQ) expansion in exon 1 of mutant huntingtin protein (mHtt). Here we establish how the domains flanking the polyQ tract shape the mHtt conformational landscape in vitro and in neurons. In vitro, the flanking domains have opposing effects on the conformation and stabilities of oligomers and amyloid fibrils. The N-terminal N17 promotes amyloid fibril formation, while the C-terminal Proline Rich Domain destabilizes fibrils and enhances oligomer formation. However, in neurons both domains act synergistically to engage protective chaperone and degradation pathways promoting mHtt proteostasis. Surprisingly, when proteotoxicity was assessed in rat corticostriatal brain slices, either flanking region alone sufficed to generate a neurotoxic conformation, while the polyQ tract alone exhibited minimal toxicity. Linking mHtt structural properties to its neuronal proteostasis should inform new strategies for neuroprotection in polyQ-expansion diseases.

Amyloid proteotoxicity initiates an inflammatory response blocked by cannabinoids.

Abstract: The beta amyloid (Aβ) and other aggregating proteins in the brain increase with age and are frequently found within neurons. The mechanistic relationship between intracellular amyloid, aging and neurodegeneration is not, however, well understood. We use a proteotoxicity model based upon the inducible expression of Aβ in a human central nervous system nerve cell line to characterize a distinct form of nerve cell death caused by intracellular Aβ. It is shown that intracellular Aβ initiates a toxic inflammatory response leading to the cell's demise. Aβ induces the expression of multiple proinflammatory genes and an increase in both arachidonic acid and eicosanoids, including prostaglandins that are neuroprotective and leukotrienes that potentiate death. Cannabinoids such as tetrahydrocannabinol stimulate the removal of intraneuronal Aβ, block the inflammatory response, and are protective. Altogether these data show that there is a complex and likely autocatalytic inflammatory response within nerve cells caused by the accumulation of intracellular Aβ, and that this early form of proteotoxicity can be blocked by the activation of cannabinoid receptors.

Commentary: XBP-1 Is a Cell-Nonautonomous Regulator of Stress Resistance and Longevity.

Abstract: The life expectancy in the world's population is increasing, highlighting the need of better understanding of the cellular and molecular pathways that drive the aging process. Because aging is the major risk factor to develop neurodegenerative conditions such as Alzheimer's and Parkinson's disease, the number of patients affected is constantly increasing, representing a major social and economic problem. Importantly, abnormal protein aggregation is a transversal pathological event of most aging-related brain diseases, suggesting that the ability of neurons to handle alterations in the proteome is specifically altered (Kaushik and Cuervo, 2015). Several hallmarks of aging have been identified at the cellular and molecular level (Lopez-Otin et al., 2013; Kennedy et al., 2014), highlighting alterations in protein homeostasis or proteostasis. In fact, studies in simple model organisms indicate that the buffering capacity of the proteostasis network (PN) is reduced during aging (Douglas and Dillin, 2010; Mardones et al., 2015). The PN can be decomposed in different interrelated sub-networks including mechanisms responsible for protein synthesis, translation, folding, trafficking, quality control, secretion, and degradation (Balch et al., 2008). Sustained dysfunction of one or more components of the PN may translate into cell dysfunction and even proteotoxicity (Figure ​(Figure11). Figure 1 Global proteostasis network impairment during aging. Aging is the main risk factor to develop most neurodegenerative conditions and new evidence has pointed out to a progressive decline in the buffering capacity of the proteostasis network (PN) to handle ... Around 30% of the total proteome is synthetized at the endoplasmic reticulum (ER), an essential compartment involved in calcium handling, lipid synthesis among other functions. Different physiological and pathological stimuli can alter the function of this organelle, resulting in the accumulation of misfolded proteins. Importantly ER stress has been proposed as a central driver of several neurodegenerative conditions (Hetz and Mollereau, 2014). ER stress triggers the activation of the unfolded protein response (UPR), a central homeostatic pathway that orchestrates cells adaptation (Hetz et al., 2015). Studies in Caenorhabditis elegans and rats indicate that the activity of the UPR is drastically ablated during aging (Paz Gavilan et al., 2006; Naidoo et al., 2008; Ben-Zvi et al., 2009; Gavilan et al., 2009; Taylor and Dillin, 2013). The UPR is mediated by three main stress sensors located at the ER membrane including ATF6, PERK, and IRE1 (Ron and Walter, 2007). In brief, activation of IRE1 controls to the expression of the transcription factor XBP1s, leading to the upregulation of genes related with protein quality control, folding, ERAD, among other targets (Hetz et al., 2015). PERK phosphorylates eIF2α; inhibiting the translation of proteins into the ER, in addition to induce the expression of the transcription factor ATF4 regulating genes involved in the antioxidant response, amino acid metabolism and folding. Under irreversible ER stress ATF4 is essential to trigger apoptosis. ATF6 encodes a transcription factor in its cytosolic domain that upon processing is realized to control gene expression. Altogether, the activation of the UPR enforces adaptive mechanisms to sustain proteostasis or trigger cell demise when protein misfolding cannot be mitigated determining cell fate. Several studies in model organisms have uncovered the significance of UPR signaling to the aging process. IRE1 is the only ER stress sensor expressed in yeast and contributes to lifespan extension (Labunskyy et al., 2014), consistent with the fact that UPR activation in this organism is a relevant feature involved in the health span control triggered by caloric restriction (Choi et al., 2013). Similarly, genetic modifications that enhance the activity of the UPR improve replicative lifespan in Saccharomyces cerevisiae (Cui et al., 2015). Studies in C. elegans demonstrated that ablating the expression of XBP1 reduces life expectancy, associated with altered FOXO and insulin/IGF-1 signaling, a canonical aging pathway (Henis-Korenblit et al., 2010). Importantly, another report indicated that the ectopic expression of XBP1s in neurons has a significant effect in increasing lifespan in C. elegans (around 30%), representing one of the strongest aging modulator described so far in this specie (Taylor and Dillin, 2013). In D. melanogaster, the occurrence of ER stress and chronic inflammation alters the stem cell pool in the gut, affecting intestinal homeostasis during aging (Wang et al., 2014). Unexpectedly, a recent study indicated that chronic PERK signaling limits lifespan by controlling intestinal homeostasis, having important consequences to organismal health (Wang et al., 2015). In mammals, it was reported that the capacity to response to ER stress and activate IRE1 is attenuated in macrophages during aging, increasing the susceptibility to apoptosis (Song et al., 2013). Accordantly, aged rats present more pro-apoptotic UPR components as opposed to adaptive mediators such as BIP, calnexin, and PDI after ER stress induction (Paz Gavilan et al., 2006; Naidoo et al., 2008). In contrast, during the aging process B cells, osteoclasts, adipocyte tissue, the retina, and muscle experience elevated levels of ER stress and UPR activation (Chalil et al., 2015; Ghosh et al., 2015; Lenox et al., 2015; Baehr et al., 2016; Kannan et al., 2016). These observations suggest that aging maybe associated with accumulative damage to the ER rather than an attenuation of UPR responses. However, the role of ER proteostasis impartment in mammalian aging needs to be functionally defined. The UPR is emerging as a key player in the integration of systemic responses to handle proteostasis alterations at the whole organism, governed by the central nervous system (Sun et al., 2012; Taylor and Dillin, 2013). In addition to regulate the intrinsic capacity of the cell to respond to ER stress, activation of IRE1 in neurons engages an organismal reaction to promote stress resistance and longevity on a cell-nonautonomous manner (Taylor and Dillin, 2013). Interestingly, the activation of XBP1s in neurons per se was irrelevant to sustain organismal homeostasis, suggesting that the nervous system operates as a global adjustor of proteostasis, where the effectors in terms of enforcing aging resistance operate in the periphery, highlighting the intestine. Importantly, other studies have shown a similar mode of control for the heat shock response and the innate immunity in C. elegans (reviewed in Mardones et al., 2015). Similarly, in flies activation of PERK engages cell-nonautonomous responses in the gut during aging (Wang et al., 2015). The concept cell-nonautonomous UPR was recently validated in mammals, where the expression of XBP1s in the hypothalamus propagates signals to the periphery (i.e., the liver) to adjust energy metabolism (Williams et al., 2014). However, the specific mechanism of proteostasis control in mammals and the neuronal circuits mediating the propagation of UPR signals between cells remain to be determined. Importantly, in C. elegans the propagation of ER stress signals to the periphery depends on neurotransmitters, suggesting that signaling mechanisms may mediate the activation of UPR-like responses in the targeted tissue probably on a stress-independent manner (Taylor and Dillin, 2013). In this line, we recently reported that XBP1s has a novel function in controlling synaptic plasticity and behavior in mammals, where growth factors like BDNF can engage the pathway (Martinez et al., 2016). Although several studies are placing the ER PN as a relevant adjustor of organismal aging in several species, its actual impact to human aging remains to be established. Many important questions need to be solved in this emerging field: Why is the UPR buffering capacity attenuated during aging? How does the nervous system control organismal proteostasis? Is there a connection between ER stress and aging in protein misfolding disorders affecting the nervous system? Can we exploit the control of cell-nonautonomous UPR as a therapeutic strategy to delay aging? Importantly, recent studies suggest that oxidative damage could directly modify UPR stress sensors, ablating adaptive responses (Nakato et al., 2015). In addition, the redox status of the ER is altered during aging in C. elegans, suggesting that intrinsic physiological alterations to this subcellular compartment may underlay the reduced capacity of the pathway to handle proteostasis alterations when cells get old (Kirstein et al., 2015). Several novel drugs are available to fine-tune the UPR and reduce ER stress levels (Hetz et al., 2013), which promises new avenues to intervene brain aging which may reduce the risk to develop neurodegenerative diseases, improving health span.

Model systems of protein-misfolding diseases reveal chaperone modifiers of proteotoxicity

Abstract: Chaperones and co-chaperones enable protein folding and degradation, safeguarding the proteome against proteotoxic stress. Chaperones display dynamic responses to exogenous and endogenous stressors and thus constitute a key component of the proteostasis network (PN), an intricately regulated network of quality control and repair pathways that cooperate to maintain cellular proteostasis. It has been hypothesized that aging leads to chronic stress on the proteome and that this could underlie many age-associated diseases such as neurodegeneration. Understanding the dynamics of chaperone function during aging and disease-related proteotoxic stress could reveal specific chaperone systems that fail to respond to protein misfolding. Through the use of suppressor and enhancer screens, key chaperones crucial for proteostasis maintenance have been identified in model organisms that express misfolded disease-related proteins. This review provides a literature-based analysis of these genetic studies and highlights prominent chaperone modifiers of proteotoxicity, which include the HSP70-HSP40 machine and small HSPs. Taken together, these studies in model systems can inform strategies for therapeutic regulation of chaperone functionality, to manage aging-related proteotoxic stress and to delay the onset of neurodegenerative diseases.

Aging and Neurodegeneration: A Tangle of Models and Mechanisms.

Abstract: The research on aging and age-related diseases, especially the neurodegenerative diseases, is on the fast track. However, the results have so far not been translated to actual benefit for the patients in terms of treatment or diagnosis of age-related degenerative diseases including those of the CNS. As far as the prevention of the cognitive decline during non-pathological aging is concerned, there is nothing much to offer other than calorie restriction and physical exercise. Needless to say, the benefits are not up to our expectations. However, over the years at the experimental level it has been possible to identify several cellular and molecular mechanisms that are intricately associated with aging in general and neurodegenerative diseases in particular. These include oxidative stress and altered redox-signaling, mitochondrial dysfunction, inflammation, proteotoxicity and altered gene expressions. These inter-dependent pathways mediate cellular senescence and often culminate in programmed cell death like apoptosis and autophagy, and in the context of brain these changes are manifested clinically as cognitive decline and pathologically as neurodegeneration. This special issue provides the readers with glimpses of this complex scenario from different angles primarily in the context of brain and also attempts to identify the potential drug targets against neurodegenerative diseases.

The Role of the Protein Quality Control System in SBMA

Abstract: Spinal and bulbar muscular atrophy (SBMA) or Kennedy's disease is an X-linked disease associated with the expansion of the CAG triplet repeat present in exon 1 of the androgen receptor (AR) gene. This results in the production of a mutant AR containing an elongated polyglutamine tract (polyQ) in its N-terminus. Interestingly, the ARpolyQ becomes toxic only after its activation by the natural androgenic ligands, possibly because of aberrant androgen-induced conformational changes of the ARpolyQ, which generate misfolded species. These misfolded ARpolyQ species must be cleared from motoneurons and muscle cells, and this process is mediated by the protein quality control (PQC) system. Experimental evidence suggested that failure of the PQC pathways occurs in disease, leading to ARpolyQ accumulation and toxicity in the target cells. In this review, we summarized the overall impact of mutant and misfolded ARpolyQ on the PQC system and described how molecular chaperones and the degradative pathways (ubiquitin-proteasome system (UPS), the autophagy-lysosome pathway (ALP), and the unfolded protein response (UPR), which activates the endoplasmic reticulum-associated degradation (ERAD)) are differentially affected in SBMA. We also extensively and critically reviewed several molecular and pharmacological approaches proposed to restore a global intracellular activity of the PQC system. Collectively, these data suggest that the fine and delicate equilibrium existing among the different players of the PQC system could be restored in a therapeutic perspective by the synergic/additive activities of compounds designed to tackle sequential or alternative steps of the intracellular defense mechanisms triggered against proteotoxic misfolded species.

Linking F-box protein 7 and parkin to neuronal degeneration in Parkinson’s disease (PD)

Abstract: Mutations of F-box protein 7 (FBXO7) and Parkin, two proteins in ubiquitin-proteasome system (UPS), are both implicated in pathogenesis of dopamine (DA) neuron degeneration in Parkinson’s disease (PD). Parkin is a HECT/RING hybrid ligase that physically receives ubiquitin on its catalytic centre and passes ubiquitin onto its substrates, whereas FBXO7 is an adaptor protein in Skp-Cullin-F-box (SCF) SCFFBXO7 ubiquitin E3 ligase complex to recognize substrates and mediate substrates ubiquitination by SCFFBXO7 E3 ligase. Here, we discuss the overlapping pathophysiologic mechanisms and clinical features linking Parkin and FBXO7 with autosomal recessive PD. Both proteins play an important role in neuroprotective mitophagy to clear away impaired mitochondria. Parkin can be recruited to impaired mitochondria whereas cellular stress can promote FBXO7 mitochondrial translocation. PD-linked FBXO7 can recruit Parkin into damaged mitochondria and facilitate its aggregation. WT FBXO7, but not PD-linked FBXO7 mutants can rescue DA neuron degeneration in Parkin null Drosophila. A better understanding of the common pathophysiologic mechanisms of these two proteins could unravel specific pathways for targeted therapy in PD.

Crosstalk between cellular compartments protects against proteotoxicity and extends lifespan

Abstract: In cells living under optimal conditions, protein folding defects are usually prevented by the action of chaperones. Here, we investigate the cell-wide consequences of loss of chaperone function in cytosol, mitochondria or the endoplasmic reticulum (ER) in budding yeast. We find that the decline in chaperone activity in each compartment results in loss of respiration, demonstrating the dependence of mitochondrial activity on cell-wide proteostasis. Furthermore, each chaperone deficiency triggers a response, presumably via the communication among the folding environments of distinct cellular compartments, termed here the cross-organelle stress response (CORE). The proposed CORE pathway encompasses activation of protein conformational maintenance machineries, antioxidant enzymes, and metabolic changes simultaneously in the cytosol, mitochondria, and the ER. CORE induction extends replicative and chronological lifespan in budding yeast, highlighting its protective role against moderate proteotoxicity and its consequences such as the decline in respiration. Our findings accentuate that organelles do not function in isolation, but are integrated in a functional crosstalk, while also highlighting the importance of organelle communication in aging and age-related diseases.

Formaldehyde Is a Potent Proteotoxic Stressor Causing Rapid Heat Shock Transcription Factor 1 Activation and Lys48-Linked Polyubiquitination of Proteins.

Abstract: Endogenous and exogenous formaldehyde (FA) has been linked to cancer, neurotoxicity, and other pathophysiologic effects. Molecular and cellular mechanisms that underlie FA-induced damage are poorly understood. In this study, we investigated whether proteotoxicity is an important, unrecognized factor in cell injury caused by FA. We found that irrespective of their cell cycle phases, all FA-treated human cells rapidly accumulated large amounts of proteins with proteasome-targeting K48-linked polyubiquitin, which was comparable with levels of polyubiquitination in proteasome-inhibited MG132 controls. Both nuclear and cytoplasmic proteins were damaged and underwent K48-polyubiquitination. There were no significant changes in the nonproteolytic K63-polyubiquitination of soluble and insoluble cellular proteins. FA also rapidly induced nuclear accumulation and Ser326 phosphorylation of the main heat shock-responsive transcription factor HSF1, which was not a result of protein polyubiquitination. Consistent with the activation of the functional heat shock response, FA strongly elevated the expression of HSP70 genes. In contrast to the responsiveness of the cytoplasmic protein damage sensor HSF1, FA did not activate the unfolded protein response in either the endoplasmic reticulum or mitochondria. Inhibition of HSP90 chaperone activity increased the levels of K48-polyubiquitinated proteins and diminished cell viability after FA treatment. Overall, our results indicate that FA is a strong proteotoxic agent, which helps explain its diverse pathologic effects, including injury in nonproliferative tissues.

The pleiotropic deubiquitinase Ubp3 confers aneuploidy tolerance

Abstract: Aneuploidy-or an unbalanced karyotype in which whole chromosomes are gained or lost-causes reduced fitness at both the cellular and organismal levels but is also a hallmark of human cancers. Aneuploidy causes a variety of cellular stresses, including genomic instability, proteotoxic and oxidative stresses, and impaired protein trafficking. The deubiquitinase Ubp3, which was identified by a genome-wide screen for gene deletions that impair the fitness of aneuploid yeast, is a key regulator of aneuploid cell homeostasis. We show that deletion of UBP3 exacerbates both karyotype-specific phenotypes and global stresses of aneuploid cells, including oxidative and proteotoxic stress. Indeed, Ubp3 is essential for proper proteasome function in euploid cells, and deletion of this deubiquitinase leads to further proteasome-mediated proteotoxicity in aneuploid yeast. Notably, the importance of UBP3 in aneuploid cells is conserved. Depletion of the human homolog of UBP3, USP10, is detrimental to the fitness of human cells upon chromosome missegregation, and this fitness defect is accompanied by autophagy inhibition. We thus used a genome-wide screen in yeast to identify a guardian of aneuploid cell fitness conserved across species. We propose that interfering with Ubp3/USP10 function could be a productive avenue in the development of novel cancer therapeutics.

Adapt, Recycle, and Move on: Proteostasis and Trafficking Mechanisms in Melanoma.

Abstract: Melanoma has emerged as a paradigm of a highly aggressive and plastic cancer, capable to co-opt the tumor stroma in order to adapt to the hostile microenvironment, suppress immunosurveillance mechanisms, and disseminate. In particular, oncogene- and aneuploidy-driven dysregulations of proteostasis in melanoma cells impose a rewiring of central proteostatic processes, such as the heat shock and unfolded protein responses, autophagy, and the endo-lysosomal system, to avoid proteotoxicity. Research over the past decade has indicated that alterations in key nodes of these proteostasis pathways act in conjunction with crucial oncogenic drivers to increase intrinsic adaptations of melanoma cells against proteotoxic stress, modulate the high metabolic demand of these cancer cells and the interface with other stromal cells, through the heightened release of soluble factors or exosomes. Here, we overview and discuss how key proteostasis pathways and vesicular trafficking mechanisms are turned into vital conduits of melanoma progression, by supporting cancer cell's adaptation to the microenvironment, limiting or modulating the ability to respond to therapy and fueling melanoma dissemination.

Mahogunin Ring Finger-1 (MGRN1), a Multifaceted Ubiquitin Ligase: Recent Unraveling of Neurobiological Mechanisms

Abstract: In healthy cell, inappropriate accumulation of poor or damaged proteins is prevented by cellular quality control system. Autophagy and ubiquitin proteasome system (UPS) provides regular cytoprotection against proteotoxicity induced by abnormal or disruptive proteins. E3 ubiquitin ligases are crucial components in this defense mechanism. Mahogunin Ring Finger-1 (MGRN1), an E3 ubiquitin ligase of the Really Interesting New Gene (RING) finger family, plays a pivotal role in many biological and cellular mechanisms. Previous findings indicate that lack of functions of MGRN1 can cause spongiform neurodegeneration, congenital heart defects, abnormal left-right patterning, and mitochondrial dysfunctions in mice brains. However, the detailed molecular pathomechanism of MGRN1 in cellular functions and diseases is not well known. This article comprehensively represents the molecular nature, characterization, and functions of MGRN1; we also summarize possible beneficiary aspects of this novel E3 ubiquitin ligase. Here, we review recent literature on the role of MGRN1 in the neuro-pathobiological mechanisms, with precise focus on the processes of neurodegeneration, and thereby propose new lines of potential targets for therapeutic intervention.

Autophagy: a decisive process for stemness

Abstract: Mature skeletal muscle is a stable tissue imposing low homeostatic demand on its stem cells, which remain in a quiescent state in their niche over time. We have shown that these long-lived resting stem cells attenuate proteotoxicity and avoid senescence through basal autophagy. This protective "clean-up" system is lost during aging, resulting in stem cell regenerative decline. Thus, autophagy is required for muscle stem cell homeostasis maintenance.

The inhibition of IGF-1 signaling promotes proteostasis by enhancing protein aggregation and deposition

Abstract: The discovery that the alteration of aging by reducing the activity of the insulin/IGF-1 signaling (IIS) cascade protects nematodes and mice from neurodegeneration-linked, toxic protein aggregation (proteotoxicity) raises the prospect that IIS inhibitors bear therapeutic potential to counter neurodegenerative diseases. Recently, we reported that NT219, a highly efficient IGF-1 signaling inhibitor, protects model worms from the aggregation of amyloid β peptide and polyglutamine peptides that are linked to the manifestation of Alzheimer's and Huntington's diseases, respectively. Here, we employed cultured cell systems to investigate whether NT219 promotes protein homeostasis (proteostasis) in mammalian cells and to explore its underlying mechanisms. We found that NT219 enhances the aggregation of misfolded prion protein and promotes its deposition in quality control compartments known as "aggresomes." NT219 also elevates the levels of certain molecular chaperones but, surprisingly, reduces proteasome activity and impairs autophagy. Our findings show that IGF-1 signaling inhibitors in general and NT219 in particular can promote proteostasis in mammalian cells by hyperaggregating hazardous proteins, thereby bearing the potential to postpone the onset and slow the progression of neurodegenerative illnesses in the elderly.-Moll, L., Ben-Gedalya, T., Reuveni, H., Cohen, E. The inhibition of IGF-1 signaling promotes proteostasis by enhancing protein aggregation and deposition.

Maple Syrup Decreases TDP-43 Proteotoxicity in a Caenorhabditis elegans Model of Amyotrophic Lateral Sclerosis (ALS).

Abstract: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease causing death of the motor neurons. Proteotoxicity caused by TDP-43 protein is an important aspect of ALS pathogenesis, with TDP-43 being the main constituent of the aggregates found in patients. We have previously tested the effect of different sugars on the proteotoxicity caused by the expression of mutant TDP-43 in Caenorhabditis elegans. Here we tested maple syrup, a natural compound containing many active molecules including sugars and phenols, for neuroprotective activity. Maple syrup decreased several age-dependent phenotypes caused by the expression of TDP-43A315T in C. elegans motor neurons and requires the FOXO transcription factor DAF-16 to be effective.

Small heat shock proteins mediate cell-autonomous and -nonautonomous protection in a Drosophila model for environmental-stress-induced degeneration.

Abstract: Cell and tissue degeneration, and the development of degenerative diseases, are influenced by genetic and environmental factors that affect protein misfolding and proteotoxicity. To better understand the role of the environment in degeneration, we developed a genetic model for heat shock (HS)-stress-induced degeneration in Drosophila This model exhibits a unique combination of features that enhance genetic analysis of degeneration and protection mechanisms involving environmental stress. These include cell-type-specific failure of proteostasis and degeneration in response to global stress, cell-nonautonomous interactions within a simple and accessible network of susceptible cell types, and precise temporal control over the induction of degeneration. In wild-type flies, HS stress causes selective loss of the flight ability and degeneration of three susceptible cell types comprising the flight motor: muscle, motor neurons and associated glia. Other motor behaviors persist and, accordingly, the corresponding cell types controlling leg motor function are resistant to degeneration. Flight motor degeneration was preceded by a failure of muscle proteostasis characterized by diffuse ubiquitinated protein aggregates. Moreover, muscle-specific overexpression of a small heat shock protein (HSP), HSP23, promoted proteostasis and protected muscle from HS stress. Notably, neurons and glia were protected as well, indicating that a small HSP can mediate cell-nonautonomous protection. Cell-autonomous protection of muscle was characterized by a distinct distribution of ubiquitinated proteins, including perinuclear localization and clearance of protein aggregates associated with the perinuclear microtubule network. This network was severely disrupted in wild-type preparations prior to degeneration, suggesting that it serves an important role in muscle proteostasis and protection. Finally, studies of resistant leg muscles revealed that they sustain proteostasis and the microtubule cytoskeleton after HS stress. These findings establish a model for genetic analysis of degeneration and protection mechanisms involving contributions of environmental factors, and advance our understanding of the protective functions and therapeutic potential of small HSPs.

Phycocyanin moderates aging and proteotoxicity in Caenorhabditis elegans

Abstract: Phycocyanin (PC, isolated from Leptolyngbya sp. N62DM) was tested for its anti-aging and proteostasis-suppressive potential by using the Caenorhabditis elegans model. PC (100 μg mL−1) treatment to wild-type (N2) C. elegans extended the mean life span from 14.8 ± 0.5 to 19.1 ± 0.7 days. PC-treated aged worms showed better pharyngeal pumping and locomotion rate compared to similar age untreated animals. PC treatment also enhanced tolerance under thermo- and oxidative-stress in N2 C. elegans. Insulin/IGF-1 signalling (IIS) pathway has been reported as the major regulator of life span in C. elegans. We checked the involvement of insulin/IGF-1 signalling (IIS) pathway in PC-mediated life span extension. PC treatment prolonged the life span in mutants of both upstream (daf-2 and age-1) and downstream (daf-16) regulators of IIS pathway. Results thus indicated that PC-mediated life span expansion is independent from DAF-2–AGE-1–DAF-16 signalling pathway. Furthermore, PC curtailed the polyQ aggregation mediated proteotoxicity in C. elegans AM141 Huntington disease model under stressed (paraquat stress) as well as normal conditions. In conclusion, this report recognizes the in vivo antioxidant activity of PC in C. elegans and illustrates its potential to be used as a tonic against aging and age associated detrimental changes.

Human amylin proteotoxicity impairs protein biosynthesis, and alters major cellular signaling pathways in the heart, brain and liver of humanized diabetic rat model in vivo

Abstract: Chronic hypersecretion of the 37 amino acid amylin is common in type 2 diabetics (T2D). Recent studies implicate human amylin aggregates cause proteotoxicity (cell death induced by misfolded proteins) in both the brain and the heart. Identify systemic mechanisms/markers by which human amylin associated with cardiac and brain defects might be identified. We investigated the metabolic consequences of amyloidogenic and cytotoxic amylin oligomers in heart, brain, liver, and plasma using non-targeted metabolomics analysis in a rat model expressing pancreatic human amylin (HIP model). Four metabolites were significantly different in three or more of the four compartments (heart, brain, liver, and plasma) in HIP rats. When compared to a T2D rat model, HIP hearts uniquely had significant DECREASES in five amino acids (lysine, alanine, tyrosine, phenylalanine, serine), with phenylalanine decreased across all four tissues investigated, including plasma. In contrast, significantly INCREASED circulating phenylalanine is reported in diabetics in multiple recent studies. DECREASED phenylalanine may serve as a unique marker of cardiac and brain dysfunction due to hyperamylinemia that can be differentiated from alterations in T2D in the plasma. While the deficiency in phenylalanine was seen across tissues including plasma and could be monitored, reduced tyrosine was seen only in the brain. The 50 % reduction in phenylalanine and tyrosine in HIP brains is significant given their role in supporting brain chemistry as a precursor for catecholamines (dopamine, norepinephrine, epinephrine), which may contribute to the increased morbidity and mortality in diabetics at a multi-system level beyond the effects on glucose metabolism.

Viewing Extrinsic Proteotoxic Stress Through the Lens of Amyloid Cardiomyopathy.

Abstract: Proteotoxicity refers to toxic stress caused by misfolded proteins of extrinsic or intrinsic origin and plays an integral role in the pathogenesis of cardiovascular diseases. Herein, we provide an overview of the current understanding of mechanisms underlying proteotoxicity and its contribution in the pathogenesis of amyloid cardiomyopathy.

Shape matters: the complex relationship between aggregation and toxicity in protein-misfolding diseases

Abstract: A particular subgroup of protein-misfolding diseases, comprising Alzheimer9s and Parkinson9s disease, involves amyloidogenic proteins that can form alternative pathogenic conformations with a high tendency to self-assemble into oligomeric and fibrillar species. Although misfolded proteins have been clearly linked to disease, the exact nature of the toxic species remains highly controversial. Increasing evidence suggests that there is little correlation between the occurrence of macroscopic protein deposits and toxic phenotypes in affected cells and tissues. In this article, we recap amyloid aggregation pathways, describe prion-like propagation, elaborate on detrimental interactions of protein aggregates with the cellular protein quality control system and discuss why some aggregates are toxic, whereas others seem to be beneficial. On the basis of recent studies on prion strains, we reason that the specific aggregate conformation and the resulting individual interaction with the cellular environment might be the major determinant of toxicity.

Pre-amyloid oligomers budding: A metastatic mechanism of proteotoxicity

Abstract: The pathological hallmark of misfolded protein diseases and aging is the accumulation of proteotoxic aggregates. However, the mechanisms of proteotoxicity and the dynamic changes in fiber formation and dissemination remain unclear, preventing a cure. Here we adopted a reductionist approach and used atomic force microscopy to define the temporal and spatial changes of amyloid aggregates, their modes of dissemination and the biochemical changes that may influence their growth. We show that pre-amyloid oligomers (PAO) mature to form linear and circular protofibrils, and amyloid fibers, and those can break reforming PAO that can migrate invading neighbor structures. Simulating the effect of immunotherapy modifies the dynamics of PAO formation. Anti-fibers as well as anti-PAO antibodies fragment the amyloid fibers, however the fragmentation using anti-fibers antibodies favored the migration of PAO. In conclusion, we provide evidence for the mechanisms of misfolded protein maturation and propagation and the effects of interventions on the resolution and dissemination of amyloid pathology.

Mechanisms of aging: neuronal orchestration of stress resistance and protein homeostasis in the nematode Caenorhabditis elegans

Abstract: 5 CHAPTER 1: RELATED LITERATURE 7 1.1. Aging 9 1.1.1. Aging as a regulated process 9 1.1.1.1. In search for a valuable approach to study stress resistance, proteostasis, and aging: Caenorhabditis elegans as a resourceful model 10 1.1.1.2. The insulin/IGF-1 signaling (IIS) pathway 12 1.1.1.3. Does the regulation of aging oppose cumulative damages? 15 1.2. The proteome and its challenges 15 1.2.1. Facing the inevitable or how to maintain a pristine proteome 15 1.2.1.1. The proteostasis network: the chaperone, proteasomal, and autophagic systems 16 1.2.1.2. Cellular stress responses: heat shock response (HSR) and unfolded protein response (UPR) 18 1.3. When the system starts failing: aging, loss of proteostasis, and consequences 20 1.3.1. Aging-dependent decline in the system’s homeostasis: what are the evidences? Can aging be manipulated to prevent this decline? 21 1.3.2. Manipulating aging: what can we expect at the proteostasis level? 22 1.3.3. The alteration of aging is associated with elevated stress resistance 25 1.4. The old paradigm changes: regulation of aging at the organismal level 26 1.4.1. Neuronal regulation of aging 26 1.4.2. Neuron-independent regulation of aging 29 1.5. The scope of this work 32

Human amylin proteotoxicity impairs protein biosynthesis, and alters major cellular signaling pathways in the heart, brain and liver of humanized diabetic rat model in vivo

Abstract: IntroductionChronic hypersecretion of the 37 amino acid amylin is common in type 2 diabetics (T2D). Recent studies implicate human amylin aggregates cause proteotoxicity (cell death induced by misfolded proteins) in both the brain and the heart.ObjectivesIdentify systemic mechanisms/markers by which human amylin associated with cardiac and brain defects might be identified.MethodsWe investigated the metabolic consequences of amyloidogenic and cytotoxic amylin oligomers in heart, brain, liver, and plasma using non-targeted metabolomics analysis in a rat model expressing pancreatic human amylin (HIP model).ResultsFour metabolites were significantly different in three or more of the four compartments (heart, brain, liver, and plasma) in HIP rats. When compared to a T2D rat model, HIP hearts uniquely had significant DECREASES in five amino acids (lysine, alanine, tyrosine, phenylalanine, serine), with phenylalanine decreased across all four tissues investigated, including plasma. In contrast, significantly INCREASED circulating phenylalanine is reported in diabetics in multiple recent studies.ConclusionDECREASED phenylalanine may serve as a unique marker of cardiac and brain dysfunction due to hyperamylinemia that can be differentiated from alterations in T2D in the plasma. While the deficiency in phenylalanine was seen across tissues including plasma and could be monitored, reduced tyrosine was seen only in the brain. The 50 % reduction in phenylalanine and tyrosine in HIP brains is significant given their role in supporting brain chemistry as a precursor for catecholamines (dopamine, norepinephrine, epinephrine), which may contribute to the increased morbidity and mortality in diabetics at a multi-system level beyond the effects on glucose metabolism.