Surface enhanced fluorescence effect improves the in vivo detection of amyloid aggregates.

The ß-amyloid (Aß) peptide is one of the key etiological agents in Alzheimer's disease (AD). The in vivo detection of Aß species is challenging in all stages of the illness. Currently, the development of fluorescent probes allows the detection of Aß in animal models in the near-infrared region (NIR). However, considering future applications in biomedicine, it is relevant to develop strategies to improve detection of amyloid aggregates using NIR probes. An innovative approach to increase the fluorescence signal of these fluorophores is the use of plasmonic gold nanoparticles (surface-enhanced fluorescence effect). In this work, we improved the detection of Aß aggregates in C. elegans and mouse models of AD by co-administering functionalized gold nanorods (GNRs-PEG-D1) with the fluorescent probes CRANAD-2 or CRANAD-58, which bind selectively to different amyloid species (soluble and insoluble). This work shows that GNRs improve the detection of Aß using NIR probes in vivo.

Temporal pattern of neuronal insulin release during Caenorhabditis elegans aging: Role of redox homeostasis.

The insulin-IGF-1/DAF-2 pathway has a central role in the determination of aging and longevity in Caenorhabditis elegans and other organisms. In this paper, we measured neuronal insulin secretion (using INS-22::Venus) during C. elegans lifespan and monitored how this secretion is modified by redox homeostasis. We showed that INS-22::Venus secretion fluctuates during the organism lifetime reaching maximum levels in the active reproductive stage. We also demonstrate that long-lived daf-2 insulin receptor mutants show remarkable low levels of INS-22::Venus secretion. In contrast, we found that short-lived mutant worms that lack the oxidation repair enzyme MSRA-1 show increased levels of INS-22::Venus secretion, specifically during the reproductive stage. MSRA-1 is a target of the insulin-IGF-1/DAF-2 pathway, and the expression of this antioxidant enzyme exclusively in the nervous system rescues the mutant insulin release phenotype and longevity. The msra-1 mutant phenotype can also be reverted by antioxidant treatment during the active reproductive stage. We showed for the first time that there is a pattern of neuronal insulin release with a noticeable increment during the peak of reproduction. Our results suggest that redox homeostasis can modulate longevity through the regulation of insulin secretion, and that the insulin-IGF-1/DAF-2 pathway could be regulated, at least in part, by a feedback loop. These findings highlight the importance of timing for therapeutic interventions aimed at improving health span.

Age-related NMDA signaling alterations in SOD2 deficient mice.

Oxidative stress affects the survival and function of neurons. Hence, they have a complex and highly regulated machinery to handle oxidative changes. The dysregulation of this antioxidant machinery is associated with a wide range of neurodegenerative conditions. Therefore, we evaluated signaling alterations, synaptic properties and behavioral performance in 2 and 6-month-old heterozygous manganese superoxide dismutase knockout mice (SOD2+/- mice). We found that their low antioxidant capacity generated direct oxidative damage in proteins, lipids, and DNA. However, only 6-month-old heterozygous knockout mice presented behavioral impairments. On the other hand, synaptic plasticity, synaptic strength and NMDA receptor (NMDAR) dependent postsynaptic potentials were decreased in an age-dependent manner. We also analyzed the phosphorylation state of the NMDAR subunit GluN2B. We found that while the levels of GluN2B phosphorylated on tyrosine 1472 (synaptic form) remain unchanged, we detected increased levels of GluN2B phosphorylated on tyrosine 1336 (extrasynaptic form), establishing alterations in the synaptic/extrasynaptic ratio of GluN2B. Additionally, we found increased levels of two phosphatases associated with dephosphorylation of p-1472: striatal-enriched protein tyrosine phosphatase (STEP) and phosphatase and tensin homolog deleted on chromosome Ten (PTEN). Moreover, we found decreased levels of p-CREB, a master transcription factor activated by synaptic stimulation. In summary, we describe mechanisms by which glutamatergic synapses are altered under oxidative stress conditions. Our results uncovered new putative therapeutic targets for conditions where NMDAR downstream signaling is altered. This work also contributes to our understanding of processes such as synapse formation, learning, and memory in neuropathological conditions.

Peptide multifunctionalized gold nanorods decrease toxicity of ß-amyloid peptide in a Caenorhabditis elegans model of Alzheimer's disease.

The properties of nanometric materials make nanotechnology a promising platform for tackling problems of contemporary medicine. In this work, gold nanorods were synthetized and stabilized with polyethylene glycols and modified with two kinds of peptides. The D1 peptide that recognizes toxic aggregates of Aß, a peptide involved in Alzheimer's disease (AD); and the Angiopep 2 that can be used to deliver nanorods to the mammalian central nervous system. The nanoconjugates were characterized using absorption spectrophotometry, dynamic light scattering, and transmission electron microscopy, among other techniques. We determined that the nanoconjugate does not affect neuronal viability; it penetrates the cells, and decreases aggregation of Aß peptide in vitro. We also showed that when we apply our nanosystem to a Caenorhabditis elegans AD model, the toxicity of aggregated Aß peptide is decreased. This work may contribute to the development of therapies for AD based on metallic nanoparticles.

The protein oxidation repair enzyme methionine sulfoxide reductase a modulates Aß aggregation and toxicity in vivo.

AIMS: To examine the role of the enzyme methionine sulfoxide reductase A-1 (MSRA-1) in amyloid-ß peptide (Aß)-peptide aggregation and toxicity in vivo, using a Caenorhabditis elegans model of the human amyloidogenic disease inclusion body myositis. RESULTS: MSRA-1 specifically reduces oxidized methionines in proteins. Therefore, a deletion of the msra-1 gene was introduced into transgenic C. elegans worms that express the Aß-peptide in muscle cells to prevent the reduction of oxidized methionines in proteins. In a constitutive transgenic Aß strain that lacks MSRA-1, the number of amyloid aggregates decreases while the number of oligomeric Aß species increases. These results correlate with enhanced synaptic dysfunction and mislocalization of the nicotinic acetylcholine receptor ACR-16 at the neuromuscular junction (NMJ). INNOVATION: This approach aims at modulating the oxidation of Aß in vivo indirectly by dismantling the methionine sulfoxide repair system. The evidence presented here shows that the absence of MSRA-1 influences Aß aggregation and aggravates locomotor behavior and NMJ dysfunction. The results suggest that therapies which boost the activity of the Msr system could have a beneficial effect in managing amyloidogenic pathologies. CONCLUSION: The absence of MSRA-1 modulates Aß-peptide aggregation and increments its deleterious effects in vivo.

Copper reduces Aß oligomeric species and ameliorates neuromuscular synaptic defects in a C. elegans model of inclusion body myositis.

Alzheimer's disease and inclusion body myositis (IBM) are disorders frequently found in the elderly and characterized by the presence of amyloid-ß peptide (Aß) aggregates. We used Caenorhabditis elegans that express Aß in muscle cells as a model of IBM, with the aim of analyzing Aß-induced muscle pathology and evaluating the consequences of modulating Aß aggregation. First, we tested whether the altered motility we observed in the Aß transgenic strain could be the result of a compromised neuromuscular synapse. Our pharmacological analyses show that synaptic transmission is defective in our model and suggest a specific defect on nicotine-sensitive acetylcholine receptors (AChRs). Through GFP-coupled protein visualization, we found that synaptic dysfunction correlates with mislocalization of ACR-16, the AChR subunit essential for nicotine-triggered currents. Histological and biochemical analysis allowed us to determine that copper treatment increases the amyloid deposits and decreases Aß oligomers in this model. Furthermore, copper treatment improves motility, ACR-16 localization, and synaptic function and delays Aß-induced paralysis. Our results indicate that copper modulates Aß-induced pathology and suggest that Aß oligomers are triggering neuromuscular dysfunction. Our findings emphasize the importance of neuromuscular synaptic dysfunction and the relevance of modulating the amyloidogenic component as an alternative therapeutic approach for this debilitating disease.

Methionine sulfoxide reductase A expression is regulated by the DAF-16/FOXO pathway in Caenorhabditis elegans.

The methionine sulfoxide reductase system has been implicated in aging and protection against oxidative stress. This conserved system reverses the oxidation of methionine residues within proteins. We analyzed one of the components of this system, the methionine sulfoxide reductase A gene, in Caenorhabditis elegans. We found that the msra-1 gene is expressed in most tissues, particularly in the intestine and the nervous system. Worms carrying a deletion of the msra-1 gene are more sensitive to oxidative stress, show chemotaxis and locomotory defects, and a 30% decrease in median survival. We established that msra-1 expression decreases during aging and is regulated by the DAF-16/FOXO3a transcription factor. The absence of this enzyme decreases median survival and affects oxidative stress resistance of long lived daf-2 worms. A similar effect of MSRA-1 absence in wild-type and daf-2 (where most antioxidant enzymes are activated) backgrounds, suggests that the lack of this member of the methionine repair system cannot be compensated by the general antioxidant response. Moreover, FOXO3a directly activates the human MsrA promoter in a cell culture system, implying that this could be a conserved mechanism of MsrA regulation. Our results suggest that repair of oxidative damage in proteins influences the rate at which tissues age. This repair mechanism, rather than the general decreased of radical oxygen species levels, could be one of the main determinants of organisms' lifespan.

Intracellular amyloid formation in muscle cells of Abeta-transgenic Caenorhabditis elegans: determinants and physiological role in copper detoxification.

BACKGROUND: The amyloid beta-peptide is a ubiquitous peptide, which is prone to aggregate forming soluble toxic oligomers and insoluble less-toxic aggregates. The intrinsic and external/environmental factors that determine Abeta aggregation in vivo are poorly understood, as well as the cellular meaning of this process itself. Genetic data as well as cell biological and biochemical evidence strongly support the hypothesis that Abeta is a major player in the onset and development of Alzheimer's disease. In addition, it is also known that Abeta is involved in Inclusion Body Myositis, a common myopathy of the elderly in which the peptide accumulates intracellularly. RESULTS: In the present work, we found that intracellular Abeta aggregation in muscle cells of Caenorhabditis elegans overexpressing Abeta peptide is affected by two single amino acid substitutions, E22G (Arctic) and V18A (NIC). Both variations show decrease intracellular amyloidogenesis compared to wild type Abeta. We show that intracellular amyloid aggregation of wild type Abeta is accelerated by Cu2+ and diminished by copper chelators. Moreover, we demonstrate through toxicity and behavioral assays that Abeta-transgenic worms display a higher tolerance to Cu2+ toxic effects and that this resistance may be linked to the formation of amyloid aggregates. CONCLUSION: Our data show that intracellular Abeta amyloid aggregates may trap excess of free Cu2+ buffering its cytotoxic effects and that accelerated intracellular Abeta aggregation may be part of a cell protective mechanism.

Inclusion body myositis: a view from the Caenorhabditis elegans muscle.

Inclusion body myositis (IBM) is the most common myopathy in people over 50 years of age. It involves an inflammatory process that, paradoxically, does not respond to anti-inflammatory drugs. A key feature of IBM is the presence of amyloid-beta-peptide aggregates called amyloid deposits, which are also characteristic of Alzheimer's disease. The use of animals that mimic at least some characteristics of a disease has become very important in the quest to elucidate the molecular mechanisms underlying this and other pathogeneses. Although there are some transgenic mouse strains that recreate some aspects of IBM, in this review, we hypothesize that the great degree of similarity between nematode and human genes known to be involved in IBM as well as the considerable conservation of biological mechanisms across species is an important feature that must be taken into consideration when deciding on the use of this nematode as a model. Straightforward laboratory techniques (culture, transformation, gene knockdown, genetic screenings, etc.) as well as anatomical, physiological, and behavioral characteristics add to the value of this model. In the present work, we review evidence that supports the use of Caenorhabditis elegans as a biological model for IBM.

Circadian stress tolerance in adult Caenorhabditis elegans.

Circadian rhythms control several behaviors through neural networks, hormones and gene expression. One of these outputs in invertebrates, vertebrates and plants is the stress resistance behavior. In this work, we studied the circadian variation in abiotic stress resistance of adult C. elegans as well as the genetic mechanisms that underlie such behavior. Measuring the stress resistance by tap response behavior we found a rhythm in response to osmotic (NaCl LC50 = 340 mM) and oxidative (H2O2 LC50 = 50 mM) shocks, with a minimum at ZT0 (i.e., lights off) and ZT12 (lights on), respectively. In addition, the expression of glutathione peroxidase (C11E4.1) and glycerol-3-phosphate dehydrogenase (gpdh-1) (genes related to the control of stress responses) also showed a circadian fluctuation in basal levels with a peak at night. Moreover, in the mutant osr-1 (AM1 strain), a negative regulator of the gpdh-1 pathway, the osmotic resistance rhythms were masked at 350 mM but reappeared when the strain was treated with a higher NaCl concentration. This work demonstrates for the first time that in the adult nematode, C. elegans stress responses vary daily, and provides evidence of an underlying rhythmic gene expression that governs these behaviors.

Is there a role for copper in neurodegenerative diseases?

Copper is an essential metal in living organisms; thus, the maintenance of adequate copper levels is of vital importance and is highly regulated. Dysfunction of copper metabolism leading to its excess or deficiency results in severe ailments. Two examples of illnesses related to alterations in copper metabolism are Menkes and Wilson diseases. Several proteins are involved in the maintenance of copper homeostasis, including copper transporters and metal chaperones. In the last several years, the beta-amyloid-precursor protein (beta-APP) and the prion protein (PrP(C)), which are related to the neurodegenerative disorders Alzheimer and prion diseases respectively, have been associated with copper metabolism. Both proteins bind copper through copper-binding domains that also have been shown to reduce copper in vitro. Moreover, this ability to reduce copper is associated with a neuroprotective effect exerted by the copper-binding domain of both proteins against copper in vivo. In addition to a functional link between copper and beta-APP or PrP(C), evidence suggests that copper has a role in Alzheimer and prion diseases. Here, we review the evidence that supports both, the role of beta-APP and PrP(C), in copper metabolism and the putative role of copper in neurodegenerative diseases.

Caenorhabditis elegans syndecan (SDN-1) is required for normal egg laying and associates with the nervous system and the vulva.

In Caenorhabditis elegans, the identification of many enzymes involved in the synthesis and modification of glycosaminoglycans (GAGs), essential components of proteoglycans, has attained special attention in recent years. Mutations in all the genes that encode for GAG biosynthetic enzymes show defects in the development of the vulva, specifically in the invagination of the vulval epithelium. Mutants for certain heparan sulfate modifying enzymes present axonal and cellular guidance defects in specific neuronal classes. Although most of the enzymes involved in the biosynthesis and modification of heparan sulfate have been characterized in C. elegans, little is known regarding the core proteins to which these GAGs covalently bind in proteoglycans. A single syndecan homologue (sdn-1) has been identified in the C. elegans genome through sequence analysis. In the present study, we show that C. elegans synthesizes sulfated proteoglycans, seen as three distinct species in western blot analysis. In the sdn-1 (ok449) deletion mutant allele we observed the lack of one species, which corresponds to a 50 kDa product after heparitinase treatment. The expression of sdn-1 mRNA and sequencing revealed that sdn-1 (ok449) deletion mutants lack two glycosylation sites. Hence, the missing protein in the western blot analysis probably corresponds to SDN-1. In addition, we show that SDN-1 localizes to the C. elegans nerve ring, nerve cords and to the vulva. SDN-1 is found specifically phosphorylated in nerve ring neurons and in the vulva, in both wild-type worms and sdn-1 (ok449) deletion mutants. These mutants show a defective egg-laying phenotype. Our results show for the first time, the identification, localization and some functional aspects of syndecan in the nematode C. elegans.