The nematode Caenorhabditis elegans: a versatile model for the study of proteotoxicity and aging.

Toxicity arising from protein misfolding and aggregation (proteotoxicity) is tightly mechanistically linked to the emergence of late-onset neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. Why these maladies manifest in late stages of life and what mechanisms protect the young organism from disease are key enigmas. The nematode Caenorhabditis elegans offers key advantages that enable systematic exploration of many cell biological and functional aspects of neurodegeneration-linked proteotoxicity. Here we review the abundantly used nematode-based proteotoxicity models and delineate common techniques for the measurement of protein aggregation and rate of proteotoxicity. We also discuss the advantages offered by the worm for genetic screening, drug development and for the exploration of the links between proteotoxicity and the aging process.

A neuronal GPCR is critical for the induction of the heat shock response in the nematode C. elegans.

In the nematode Caenorhabditis elegans, the heat shock response (HSR) is regulated at the organismal level by a network of thermosensory neurons that senses elevated temperatures and activates the HSR in remote tissues. Which neuronal receptors are required for this signaling mechanism and in which neurons they function are largely unanswered questions. Here we used worms that were engineered to exhibit RNA interference hypersensitivity in neurons to screen for neuronal receptors that are required for the activation of the HSR and identified a putative G-protein coupled receptor (GPCR) as a novel key component of this mechanism. This gene, which we termed GPCR thermal receptor 1 (gtr-1), is expressed in chemosensory neurons and has no role in heat sensing but is critically required for the induction of genes that encode heat shock proteins in non-neural tissues upon exposure to heat. Surprisingly, the knock-down of gtr-1 by RNA interference protected worms expressing the Alzheimer's-disease-linked aggregative peptide Aß3-42 from proteotoxicity but had no effect on lifespan. This study provides several novel insights: (1) it shows that chemosensory neurons play important roles in the nematode's HSR-regulating mechanism, (2) it shows that lifespan and heat stress resistance are separable, and (3) it strengthens the emerging notion that the ability to respond to heat comes at the expense of protein homeostasis (proteostasis).

The insulin/IGF signaling cascade modulates SUMOylation to regulate aging and proteostasis in Caenorhabditis elegans.

Although aging-regulating pathways were discovered a few decades ago, it is not entirely clear how their activities are orchestrated, to govern lifespan and proteostasis at the organismal level. Here, we utilized the nematode Caenorhabditis elegans to examine whether the alteration of aging, by reducing the activity of the Insulin/IGF signaling (IIS) cascade, affects protein SUMOylation. We found that IIS activity promotes the SUMOylation of the germline protein, CAR-1, thereby shortening lifespan and impairing proteostasis. In contrast, the expression of mutated CAR-1, that cannot be SUMOylated at residue 185, extends lifespan and enhances proteostasis. A mechanistic analysis indicated that CAR-1 mediates its aging-altering functions, at least partially, through the notch-like receptor glp-1. Our findings unveil a novel regulatory axis in which SUMOylation is utilized to integrate the aging-controlling functions of the IIS and of the germline and provide new insights into the roles of SUMOylation in the regulation of organismal aging.

The roles of cellular and organismal aging in the development of late-onset maladies.

Numerous disorders, including neurodegenerative diseases and certain types of cancer, manifest late in life. This common feature raises the prospect that an aging-associated decline in the activity of cellular and organismal maintenance mechanisms enables the emergence of these maladies in late life stages. Accordingly, the alteration of aging bears the promise of harnessing the mechanisms that protect the young organism to prevent illness in the elderly. The identification of aging-regulatory pathways has enabled scrutiny of this hypothesis and revealed that the alteration of aging protects invertebrates and mammals from toxic protein aggregation linked to neurodegeneration and from cancer. Here we review the current knowledge on the regulation of aging at the cellular and organismal levels, delineate the mechanistic links between aging and late-onset disorders, describe efforts to develop compounds that protect from these maladies by selectively manipulating aging, and discuss future research directions and possible therapeutic implications of this approach.

A novel inhibitor of the insulin/IGF signaling pathway protects from age-onset, neurodegeneration-linked proteotoxicity.

Aging manipulation is an emerging strategy aimed to postpone the manifestation of late-onset neurodegenerative disorders such as Alzheimer's (AD) and Huntington's diseases (HD) and to slow their progression once emerged. Reducing the activity of the insulin/IGF signaling cascade (IIS), a prominent aging-regulating pathway, protects worms from proteotoxicity of various aggregative proteins, including the AD-associated peptide, Aß- and the HD-linked peptide, polyQ40. Similarly, IGF1 signaling reduction protects mice from AD-like disease. These discoveries suggest that IIS inhibitors can serve as new drugs for the treatment of neurodegenerative maladies including AD and HD. Here, we report that NT219, a novel IIS inhibitor, mediates a long-lasting, highly efficient inhibition of this signaling cascade by a dual mechanism; it reduces the autophosphorylation of the IGF1 receptor and directs the insulin receptor substrates 1 and 2 (IRS 1/2) for degradation. NT219 treatment promotes stress resistance and protects nematodes from AD- and HD-associated proteotoxicity without affecting lifespan. Our discoveries strengthen the theme that IIS inhibition has a therapeutic potential as a cure for neurodegenerative maladies and point at NT219 as a promising compound for the treatment of these disorders through a selective manipulation of aging.

Differential regulation of the heat shock factor 1 and DAF-16 by neuronal nhl-1 in the nematode C. elegans.

In the nematode Caenorhabditis elegans, insulin/insulin-like growth factor 1 (IGF-1) signaling (IIS) reduction hyperactivates the transcription factors DAF-16 and heat shock factor 1 (HSF-1), creating long-lived, stress-resistant worms that are protected from proteotoxicity. How DAF-16 executes its distinct functions in response to IIS reduction is largely obscure. Here, we report that NHL-1, a member of the TRIM-NHL protein family, acts in chemosensory neurons to promote stress resistance in distal tissues by DAF-16 activation but is dispensable for the activation of HSF-1. The expression of nhl-1 is regulated by the IIS, defining a neuronal regulatory circuit that controls the organismal stress response. The knockdown of nhl-1 protects nematodes that express the Alzheimer-disease-associated Aß peptide from proteotoxicity but has no effect on lifespan. Our findings indicate that DAF-16- and HSF-1-regulated heat-responsive mechanisms are differentially controlled by neurons and show that one neuronal protein can be involved in the activation of different stress responses in remote tissues.

Temporal requirements of heat shock factor-1 for longevity assurance.

Reducing the activity of the insulin/IGF-1 signaling pathway (IIS) modifies development, elevates stress resistance, protects from toxic protein aggregation (proteotoxicity), and extends lifespan (LS) of worms, flies, and mice. In the nematode Caenorhabditis elegans, LS extension by IIS reduction is entirely dependent upon the activity of the transcription factors DAF-16 and the heat shock factor-1 (HSF-1). While DAF-16 determines LS exclusively during early adulthood, it is required for proteotoxicity protection also during late adulthood. In contrast, HSF-1 protects from proteotoxicity during larval development. Despite the critical requirement for HSF-1 for LS extension, the temporal requirements for this transcription factor as a LS determinant are unknown. To establish the temporal requirements of HSF-1 for longevity assurance, we conditionally knocked down hsf-1 during larval development and adulthood of C. elegans and found that unlike daf-16, hsf-1 is foremost required for LS determination during early larval development, required for a lesser extent during early adulthood and has small effect on longevity also during late adulthood. Our findings indicate that early developmental events affect LS and suggest that HSF-1 sets during development of the conditions that enable DAF-16 to promote longevity during reproductive adulthood. This study proposes a novel link between HSF-1 and the longevity functions of the IIS.

Temporal requirements of insulin/IGF-1 signaling for proteotoxicity protection.

Toxic protein aggregation (proteotoxicity) is a unifying feature in the development of late-onset human neurodegenerative disorders. Reduction of insulin/IGF-1 signaling (IIS), a prominent lifespan, developmental and reproductive regulatory pathway, protects worms from proteotoxicity associated with the aggregation of the Alzheimer's disease-linked Abeta peptide. We utilized transgenic nematodes that express human Abeta and found that late life IIS reduction efficiently protects from Abeta toxicity without affecting development, reproduction or lifespan. To alleviate proteotoxic stress in the animal, the IIS requires heat shock factor (HSF)-1 to modulate a protein disaggregase, while DAF-16 regulates a presumptive active aggregase, raising the question of how these opposing activities could be co-regulated. One possibility is that HSF-1 and DAF-16 have distinct temporal requirements for protection from proteotoxicity. Using a conditional RNAi approach, we found an early requirement for HSF-1 that is distinct from the adult functions of DAF-16 for protection from proteotoxicity. Our data also indicate that late life IIS reduction can protect from proteotoxicity when it can no longer promote longevity, strengthening the prospect that IIS reduction might be a promising strategy for the treatment of neurodegenerative disorders caused by proteotoxicity.