While it is generally recognized that misfolding of specific proteins can cause late-onset disease, the contribution of protein aggregation to the normal aging process is less well understood. To address this issue, a mass spectrometry-based proteomic analysis was performed to identify proteins that adopt sodium dodecyl sulfate (SDS)-insoluble conformations during aging in Caenorhabditis elegans. SDS-insoluble proteins extracted from young and aged C. elegans were chemically labeled by isobaric tagging for relative and absolute quantification (iTRAQ) and identified by liquid chromatography and mass spectrometry. Two hundred and three proteins were identified as being significantly enriched in an SDS-insoluble fraction in aged nematodes and were largely absent from a similar protein fraction in young nematodes. The SDS-insoluble fraction in aged animals contains a diverse range of proteins including a large number of ribosomal proteins. Gene ontology analysis revealed highly significant enrichments for energy production and translation functions. Expression of genes encoding insoluble proteins observed in aged nematodes was knocked down using RNAi, and effects on lifespan were measured. 41% of genes tested were shown to extend lifespan after RNAi treatment, compared with 18% in a control group of genes. These data indicate that genes encoding proteins that become insoluble with age are enriched for modifiers of lifespan. This demonstrates that proteomic approaches can be used to identify genes that modify lifespan. Finally, these observations indicate that the accumulation of insoluble proteins with diverse functions may be a general feature of aging.

SummaryA strategy used by extracellular pathogens to evade phagocytosis is the utilization of exotoxins that kill host phagocytes. We have recently shown that one major pathogenicity strategy of Photobacterium damselae subsp. piscicida ( Phdp ), the agent of the widespread fish pasteurellosis, is the induction of extensive apoptosis of sea bass macrophages and neutrophils that results in lysis of these phagocytes by post-apoptotic secondary necrosis. Here we show that this unique process is mediated by a novel plasmid-encoded apoptosis inducing protein of 56 kDa (AIP56), an exotoxin abundantly secreted by all virulent, but not avirulent, Phdp strains tested. AIP56 is related to an unknown protein of the enterohemorrhagic Escherichia coli O157:H7 and NleC, a Citrobacter rodentium type III secreted effector of unknown function. Passive immunization of sea bass with a rabbit anti-AIP56 serum conferred protection against Phdp challenge, indicating that AIP56 represents a key virulence factor of that pathogen and is a candidate for the design of an anti-pasteurellosis vaccine.

Microglial activation and subsequent release of toxic pro-inflammatory factors are believed to play an important role in neuronal cell death associated with Parkinson’s disease (PD). Compounds that inhibit microglia activation and suppress pro-inflammatory factor release have been reported to have neuroprotective effects in animal models of PD. In this study, we tested whether diadzein, a natural isoflavone found in soybean, attenuated lipopolysaccharide (LPS)-induced release of inflammatory mediators in BV-2, a murine microglial cell line. Diadzein pretreatment was found to significantly suppress the production of the pro-inflammatory factors nitric oxide and IL-6 as well as their mRNA expression in conjunction with reductions in ROS production, p38 MAPK phosphorylation, and NF-κB activation. Furthermore, transfer of conditioned media (CM) from BV-2 cells pretreated with diadzein resulted in a significantly reduction in dopaminergic neurotoxicity compared with CM from microglia stimulated with LPS alone. Together, our results suggest that diadzein’s neuroprotective properties may be due to its ability to dampen induction of microglial activation and the subsequent release of soluble pro-inflammatory factors. This appears to be via inhibition of oxidative induction of the p38 MAP kinase-NFκB pathway, resulting in reduced expression of pro-inflammatory genes and release of their corresponding gene products.

The transition of proteins targeted for autophagic degradation from the soluble to the insoluble phase is regulated in an ATG1-independent mechanism by TORC1. This process is likely a critical mechanism for maintaining protein homeostasis when challenged with proteomic stress.

The dauer larva is an alternate developmental stage in C. elegans which allows the animal to survive adverse environmental conditions for extended periods of time. Upon exposure to a more favourable environment, the worm can exit this diapause stage and develop into a reproductive adult, with minimal effects on subsequent survival. Genetic analysis of dauer formation has identifi ed genes and pathways that are involved in dauer entry, maintenance and recovery from the dauer stage. Many of the genes that infl uence dauer development also infl uence adult lifespan and thus the dauer larva has been an invaluable tool with which to decipher the components of novel signalling pathways that have the potential to infl uence ageing in humans. Indeed, orthologs of genes involved in dauer formation have also been shown to infl uence ageing in mammals. This chapter will review the links between dauer formation and post-reproductive ageing.