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Aging, Metabolism, Stress, Pathogenesis, and Small RNAs, Madison, WI,
2010]
The stability of the proteome is an essential aspect of cellular health during development, aging, and exposure to environmental and physiological stress. This is achieved by the Proteostasis Network (PN) and the cytoprotective Heat Shock Response (HSR) and Unfolded Protein Response (UPR) that function in concert to suppress the accumulation of misfolded and damaged proteins and direct the expression of a highly functional proteome. We have observed that aging in C. elegans is associated with a sharp decline in the function and folding of metastable proteins during early adulthood. This is associated with a decline in the HSR and UPR, during the peak of fecundity. Activation of Hsf1 (or DAF-16) in early development restores youthful proteostasis revealing the potential to re-adapt, if not restore a protective state. These studies provide a basis to understand the role of Hsf1 and other stress sensors that function at a cellular and molecular level. At the organismal level, however, the HSR is regulated by the AFD thermosensory neurons that transmit the stress signal via specific neurohormones and neuropeptides to somatic tissues to regulate HS gene expression in a cell non-autonomous manner. Unexpectedly, in the presence of functional thermosensory neurons, muscle and intestinal cells accumulate toxic misfolded proteins, which is insufficient to activate the HSR. However, when the activity of thermosensory neurons is altered, the cellular response to misfolded proteins is restored and protein aggregation and toxicity is suppressed. Neuronal control of proteostasis is also regulated at yet another level by cholinergic signaling at the neuromuscular junction. Overexcitation results in enhanced misfolding in post-synaptic muscle cells, whereas increased levels of the cholinergic receptor results in the activation of the HSR, elevated levels of chaperones, and suppression of proteostatic imbalance. These results, reveal that the HSR is organized at the systems level of the organism to sense the stress signal through active neuronal activity, and together with the metabolic state, sets the proteostasis network to ensure stability of the proteome and the health of the organism.
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C.elegans Aging, Stress, Pathogenesis, and Heterochrony Meeting,
2008]
The long-term health of the cell is inextricably linked to proteostasis, a complex network of molecular interactions that maintains the health of proteins. An imbalance in proteostasis, whether caused by environmental or physiological stress, ageing, or the chronic expression of disease-associated proteins (mutant SOD1, huntingtin, polyQ, or Abeta) can be restored by genes that control lifespan (Daf-16) and the heat shock response (Hsf-1). How such folding networks and stress responses are integrated at the molecular and cellular level to the organism has not been examined. The response of C. elegans to heat shock requires the AFD thermosensory neurons and animals harboring mutations in AFD function are defective for induction of the heat shock response in other somatic cells. This AFD requirement is highly selective for activation of heat shock genes by cadmium is unaffected in mutant animals. This reveals that transmission of the heat shock signal is cell non-autonomous and requires active neuronal signaling which serves to integrate temperature-dependent behavioral, metabolic, and stress-specific responses. We draw similar conclusions from a forward genetic screen for enhancers of protein misfolding in body wall muscle cells that identified a mutation in
unc-30 that regulates GABAergic signaling. Whether caused by mutations in the GABAergic or cholinergic pathways or by small molecule agonists and antagonists, an imbalance in cholinergic signaling enhances misfolding of polyQ and other metastable proteins in post-synaptic body wall muscle cells.
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International Worm Meeting,
2013]
The mechanisms that allow for stable physiology, despite the temperature sensitivity of metabolic reactions, are poorly understood. Many organisms, like C. elegans possess neurosensory circuits dedicated to seeking out optimal temperatures. In addition cells within the animal possess conserved mechanisms such as the heat shock response (HSR) mediated by the transcription factor HSF-1, to maintain protein homeostasis despite temperature fluctuations. We discovered that in C. elegans, circuits formed by thermosensory AFD neurons that control behavioral responses to temperature change also control the activation of HSF-1 within all cells throughout the organism, linking sensation of temperature fluctuations to the regulation of metabolic homeostasis. Here we present evidence that the thermosensory control of HSF-1 may occur through the modulation of serotonin signaling by the AFD neurons. Specifically, we show that acute heat shock results in a change in serotonin localization, consistent with its release from the NSM neurons, within minutes after temperature increase. This is concomitant with activation of HSF-1 visualized by changes in its nuclear localization. Serotonergic signaling is necessary for HSF-1 activation and the subsequent induction of the protective heat shock proteins (HSPs): loss of tryptophan hydroxylase or the serotonergic receptors (
ser-1/ser-4) prevents HSP induction upon heat shock. In animals harboring loss-of-function mutations in the guanylyl cyclase
gcy-8/23 genes required for AFD neuronal response to temperature, serotonin is not released from NSM neurons and HSF1 is not activated after heat shock. HSF-1 activation can be rescued in these thermosensory mutants by the delivery of exogenous serotonin. We are currently investigating how the AFD neurons affect serotonin release by the NSM neurons, and how serotonin influences HSF-1 activity. Serotonergic signaling regulates core body temperature and energy metabolism in mammals. We propose that neuronal control of HSF-1 through serotonin signaling is a conserved mechanism that allows multicellular organisms to adapt to their environment by linking their sensory response to temperature fluctuations with their metabolic state.
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International Worm Meeting,
2021]
Stress and aging can compromise cellular proteostasis and lead to the loss of proteome integrity, a hallmark of many degenerative diseases. Efforts to maintain the functional capacity of the proteostasis network hold promise for prolonging organismal health and reducing the burden of disease, however, the underlying basis for the decline are at present unknown. This is in part due to a lack of available methods for observing the consequence of stressful stimuli on proteome integrity in real time. Here we report a new genetically-encoded biosensor that allows quantitative assessment of proteostasis network capacity in living Caenorhabditis elegans. It is based on a metastable version of dihydrofolate reductase and a conditional proteasome-targeting signal, thereby linking conformational state to protein levels, and fused to a fluorescent protein tag for visualization inside cells. The sensor reveals systemic remodeling of the proteostasis network and identifies distinct cellular states in stress, early aging, and C. elegans models of human disease. Our results indicate that this multi-modal biosensor is a convenient tool for in vivo investigations into proteostasis network regulation in health and disease states.
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International Worm Meeting,
2021]
The proteostasis network (PN) comprises the cellular machineries that regulate protein synthesis, folding, and degradation, to promote proteome integrity. Reduced functionality of the PN during aging results in the accumulation of misfolded and aggregated species that are detrimental for cellular health, and is a hallmark of many age-associated diseases. In multicellular organisms, the PN is regulated by transcellular communication to coordinate proteostasis across tissues and organs in response to physiological and environmental stimuli. The reproductive system in particular is a critical tissue for proteostasis regulation, and signals from the germline initiate the decline of somatic proteostasis and cellular stress responses at reproductive maturity in C. elegans. Here we show that stress resilience and proteostasis are also regulated by embryo-to-mother communication in reproductive adults. To identify genes that act directly in the reproductive system to influence somatic proteostasis, we performed a tissue-targeted RNAi screen for germline modifiers of muscle polyglutamine aggregation. We found that inhibiting the formation of the extracellular vitelline layer of the fertilized embryo inside the uterus suppresses aggregation in multiple somatic tissues and improves maternal stress resilience in an HSF-1-dependent manner. Damage to the vitelline layer of the embryo also prevents the collapse of the heat shock response that normally occurs in early adulthood. This embryo-to-mother pathway relies on DAF-16/FOXO activation in vulva tissues to maintain organismal stress resilience, suggesting that the vulva senses the integrity of the fertilized embryo to detect damage and initiate the organismal response. Gene expression analysis of vitelline layer defective animals using RNA sequencing also revealed that genes involved in lipid metabolism are activated, which is accompanied by elevated fat stores, suggesting a link between fat metabolism and proteostasis in these animals. Our findings reveal a previously undescribed transcellular pathway that links the integrity of the developing progeny to somatic proteostasis regulation and lipid metabolism in the parent. This pathway may serve to reassess commitment to reproduction and promote somatic endurance when progeny production is compromised.
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International C. elegans Meeting,
1995]
We hope to provide a demonstration of the current state of the ACeDB worm database on Unix workstations, and if possible Apple Macintosh, throughout the poster sessions. This will be based on the new version 4 release of the acedb software (Jean Thierry-Mieg, Richard Durbin and numerous others), which contains many new features for greater efficiency, more flexible printing, and display of new features.
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International Worm Meeting,
2009]
The cellular ability to restore protein folding during proteotoxic stress requires activation of the heat shock response (HSR), which involves the activation of heat shock factor-1 (HSF-1). HSF-1 is a transcription factor that is repressed in the absence of stress by the Hsp70 and Hsp90 molecular chaperones. Although the HSR is well-understood on the cellular level, little is known about its regulation in the context of an intact, multicellular organism. Therefore, we performed a genome-wide RNAi screen for negative regulators of the HSR using a stress-inducible reporter,
hsp70p::GFP. We identified 40 genes that repress
hsp70p::GFP expression in an HSF-1-dependent manner. Knock-down of these genes also induces another HSF-1-dependent reporter,
hsp-16.2p::GFP. Most of the identified genes fall into functional classes involved in protein synthesis, folding, transport, and degradation. Whether these genes directly or indirectly regulate HSF-1, they are influencing proteostasis, or protein homeostasis. HSF-1 is ubiquitous and most of the identified genes are broadly expressed; however, we found that the reporters are induced in a tissue-specific manner. Hence, we named the identified genes Tissue-Specific Proteostasis Regulators (TSPRs). We show that TSPRs are enriched in self-interactions and cluster into distinct networks that correlate with their tissue-specific reporter induction. We used these networks to successfully predict additional TSPRs. Together, these results suggest that specific networks regulate proteostasis in distinct tissues by repressing HSF-1 activity in the absence of stress.
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International Worm Meeting,
2013]
A major challenge for metazoans is to ensure that different tissues each expressing distinctive proteomes are, nevertheless, well protected at an organismal level from proteotoxic stress. We have examined this and show that expression of endogenous metastable protein sensors in muscle cells induces a systemic stress response throughout multiple tissues of C. elegans. Suppression of misfolding in muscle cells can be achieved not only by enhanced expression of HSP90 (DAF-21) in muscle cells, but as effective by elevated expression of HSP90 in intestine or neuronal cells. This cell-non-autonomous control of HSP90 expression relies upon transcriptional feedback between somatic tissues that is regulated by the FoxA transcription factor PHA-4. This trans-cellular chaperone signaling response maintains organismal proteostasis when challenged by a local tissue imbalance in folding and provides the basis for a novel form of organismal stress sensing surveillance.
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International Worm Meeting,
2011]
The regulation of the Heat Shock Response (HSR) in eukaryotes, mediated by the HSF1 transcription factor, has been primarily studied in unicellular organisms or cultured cells as a transient stress response. However, in metazoans, HSF1 is known to be essential from the start of development through the end of aging. Therefore, a genetic and systems-level approach including genome-wide RNAi screens was taken to identify and analyze regulators of the HSR in C. elegans. We identified seven enhancers of the HSR, including HSF1, that when knocked-down prevent full HSR activation, but do not affect the unfolded protein response (a stress response distinct from the HSR). The enhancers cannot act through a hormesis-type (stress preconditioning) mechanism because they do not enhance thermotolerance. Rather, these enhancers likely act at or downstream of chaperone-mediated HSF1 repression since they are epistatic to chaperone depletion. Further, these regulators are functionally conserved through humans as all seven enhance the HSR in HeLa cells. Five of the seven enhancers are splicing factors or associated with splicing. Although splicing has not previously been implicated in regulation of the HSR, it is well-established that heat shock leads to an inhibition of splicing. Systems-level analysis revealed these regulatory circuits form a network motif that functions to maintain a transient, self-limiting response to stress. The final HSR enhancer is a subunit of the NuRD complex. Although not been previously implicated in HSR regulation, NuRD has been shown to bind HSF1 suggesting that this regulation is direct. A second genome-wide screen identified fifty-two suppressors of the HSR, including the HSP70 and HSP90 chaperones, established as HSR regulators in other model systems. HSR suppressors include known regulators of protein synthesis and gene expression, folding, trafficking, and clearance. Our data show that HSR suppressors form interaction networks, function in an HSF1-dependent manner, and confer differential tissue selective patterns of HSR induction. Taken together, the combined genetic and systems level approaches have led to unique insights into HSR regulation. The genetic approaches led to the identification of novel regulators of the HSR. In addition, we have shown that suppressors, but not enhancers of the HSR, create differential, tissue-selective HSR regulation. Finally, systems-level network analysis of our data has revealed new features of the response, such as motifs that contribute to the transient dynamics of HSR induction.
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International Worm Meeting,
2005]
As exposures to the space environment become longer, information regarding the effects on biological aging will become important. We have not yet fully clarified aging processes in space environments. The aging process and lifespan are affected by various kinds of environmental factors including oxygen concentration (1), temperature and radiation. The aging phenomena that we usually see occur under certain conditions on the ground. Space environments differ from ground environments especially with regard to the radiation spectrum and gravity. We participated in the International C. elegans Experiment(ICE)First that examined the effects of a 10-day space flight on the nematode C. elegans. C. elegans has frequently been used for study of aging because of its short lifespan. Recently, Morley et al. reported that Huntington's-like polyglutamine (polyQ)-repeat proteins expressed in the muscle of C. elegans form aggregates as the animals age, and that this aggregation is delayed in long-lived mutants(2). We measured the polyQ aggregates in these nematodes after space flight as an aging marker. Herndon et al. showed that the sarcomere orientation in the body-wall muscle becomes disorderly as the animals age(3). We also observed the sarcomere orientation in the body-wall muscle of these nematodes after space flight as another aging marker. Acknowledgement: We thank Dr. R. L. Morimoto (Northwestern University) for providing us polyQ-YFP C. elegans strains. We also thank CGC for other strains. ICE-First was mainly conducted by the French Space Agency (CNES), with support of the European Space Agency and the Space Research Organization of the Netherlands. We are grateful to Dr. Michel Viso (CNES), Dr. K. Kuriyama (JAXA) and Dr. A. Higashitani (Tohoku University) for their support and suggestion for our experiment. References: 1) Honda S., Ishii N, Suzuki K, Matsuo M. J Gerontol. 48:B57-61. 1993 2) James F. Morley, Heather R. Brignull, Jill J. Weyers, and Richard I. Morimoto. Proc. Natl. Acad. Sci. USA, 99: 10417-10422. 2002 3) Herndon LA, Schmeissner PJ, Dudaronek JM, Brown PA, Listner KM, Sakano Y, Paupard MC, Hall DH, Driscoll M. Nature. 419:808-814. 2002