Heat-shock factor (HSF) is the master transcriptional regulator of the heat-shock response (HSR) and is essential for stress resilience. HSF is also required for metazoan development; however, its function and regulation in this process are poorly understood. Here, we characterize the genomic distribution and transcriptional activity of Caenorhabditis elegans HSF-1 during larval development and show that the developmental HSF-1 transcriptional program is distinct from the HSR. HSF-1 developmental activation requires binding of E2F/DP to a GC-rich motif that facilitates HSF-1 binding to a heat-shock element (HSE) that is degenerate from the consensus HSE sequence and adjacent to the E2F-binding site at promoters. In contrast, induction of the HSR is independent of these promoter elements or E2F/DP and instead requires a distinct set of tandem canonical HSEs. Together, E2F and HSF-1 directly regulate a gene network, including a specific subset of chaperones, to promote protein biogenesis and anabolic metabolism, which are essential in development.

Polyglutamine diseases are a class of dominantly inherited neurodegenerative disorders for which there is no effective treatment. Here we provide evidence that activation of serotonergic signalling is beneficial in animal models of Machado-Joseph disease. We identified citalopram, a selective serotonin reuptake inhibitor, in a small molecule screen of FDA-approved drugs that rescued neuronal dysfunction and reduced aggregation using a Caenorhabditis elegans model of mutant ataxin 3-induced neurotoxicity. MOD-5, the C. elegans orthologue of the serotonin transporter and cellular target of citalopram, and the serotonin receptors SER-1 and SER-4 were strong genetic modifiers of ataxin 3 neurotoxicity and necessary for therapeutic efficacy. Moreover, chronic treatment of CMVMJD135 mice with citalopram significantly reduced ataxin 3 neuronal inclusions and astrogliosis, rescued diminished body weight and strikingly ameliorated motor symptoms. These results suggest that small molecule modulation of serotonergic signalling represents a promising therapeutic target for Machado-Joseph disease.

Prions are unconventional self-propagating proteinaceous particles, devoid of any coding nucleic acid. These proteinaceous seeds serve as templates for the conversion and replication of their benign cellular isoform. Accumulating evidence suggests that many protein aggregates can act as self-propagating templates and corrupt the folding of cognate proteins. Although aggregates can be functional under certain circumstances, this process often leads to the disruption of the cellular protein homeostasis (proteostasis), eventually leading to devastating diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), Amyotrophic lateral sclerosis (ALS), or transmissible spongiform encephalopathies (TSEs). The exact mechanisms of prion propagation and cell-to-cell spreading of protein aggregates are still subjects of intense investigation. To further this knowledge, recently a new metazoan model in Caenorhabditis elegans, for expression of the prion domain of the cytosolic yeast prion protein Sup35 has been established. This prion model offers several advantages, as it allows direct monitoring of the fluorescently tagged prion domain in living animals and ease of genetic approaches. Described here are methods to study prion-like behavior of protein aggregates and to identify modifiers of prion-induced toxicity using C. elegans.

Summary In Caenorhabditis elegans, the programmed repression of the heat shock response (HSR) accompanies the transition to reproductive maturity, leaving cells vulnerable to environmental stress and protein aggregation with age. To identify the factors driving this event, we performed an unbiased genetic screen for suppressors of stress resistance, and identified the mitochondrial electron transport chain (ETC) as a central regulator of the age-related decline of the HSR and cytosolic proteostasis. Mild down-regulation of ETC activity, either by genetic modulation or exposure to mitochondria targeted xenobiotics, maintained the HSR in adulthood by increasing HSF-1 binding and RNA polymerase II recruitment at HSF-1 target genes. This resulted in a robust restoration of cytoplasmic proteostasis and increased vitality later in life, without detrimental effects on fecundity. We propose that low levels of mitochondrial stress regulate cytoplasmic proteostasis and healthspan during aging by coordinating the long-term activity of HSF-1 with conditions preclusive to optimal fitness.

The proteostasis network is regulated by transcellular communication to promote health and fitness in metazoans. In Caenorhabditis elegans, signals from the germline initiate the decline of proteostasis and repression of cell stress responses at reproductive maturity, indicating that commitment to reproduction is detrimental to somatic health. Here we show that proteostasis and stress resilience are also regulated by embryo-to-mother communication in reproductive adults. To identify genes that act directly in the reproductive system to regulate somatic proteostasis, we performed a tissue targeted genetic screen for germline modifiers of polyglutamine aggregation in muscle cells. We found that inhibiting the formation of the extracellular vitelline layer of the fertilized embryo inside the uterus suppresses aggregation, improves stress resilience in an HSF-1-dependent manner, and restores the heat-shock response in the somatic tissues of the parent. This pathway relies on DAF-16/FOXO activation in vulval tissues to maintain stress resilience in the mother, suggesting that the integrity of the embryo is monitored by the vulva to detect damage and initiate an organismal protective response. Our findings reveal a previously undescribed transcellular pathway that links the integrity of the developing progeny to proteostasis regulation in the parent.

Reduced motor control is one of the most frequent features associated with aging and disease. Nonlinear and fractal analyses have proved to be useful in investigating human physiological alterations with age and disease. Similar findings have not been established for any of the model organisms typically studied by biologists, though. If the physiology of a simpler model organism displays the same characteristics, this fact would open a new research window on the control mechanisms that organisms use to regulate physiological processes during aging and stress. Here, we use a recently introduced animal-tracking technology to simultaneously follow tens of Caenorhabdits elegans for several hours and use tools from fractal physiology to quantitatively evaluate the effects of aging and temperature stress on nematode motility. Similar to human physiological signals, scaling analysis reveals long-range correlations in numerous motility variables, fractal properties in behavioral shifts, and fluctuation dynamics over a wide range of timescales. These properties change as a result of a superposition of age and stress-related adaptive mechanisms that regulate motility.

Carboxy terminal fragments (CTFs) of TDP-43 contain an intrinsically disordered region (IDR) and form cytoplasmic condensates containing amyloid fibrils. Such condensates are toxic and associated with pathogenicity in several neurodegenerative disorders, including amyotrophic lateral sclerosis and frontotemporal lobar degeneration. However, the molecular details of how the domain of TDP-43 CTFs leads to condensation and cytotoxicity remain elusive. Here, we show that truncated RNA/DNA-recognition motif (RRM) at the N-terminus of TDP-43 CTFs is assembled and leads to the structural transition of the IDR, whereas the IDR itself of TDP-43 CTFs is difficult to assemble even if they are proximate intermolecularly. Hetero-oligomers of TDP-43 CTFs that have recruited other proteins that are essential for proteostasis into low mobile condensates are more toxic than homo-oligomers inside highly mobile condensates, implicating loss-of-function of the endogenous proteins by such oligomers, not necessarily the condensates, is associated with cytotoxicity. Furthermore, such toxicity of TDP-43 CTFs was cell-nonautonomously affected in the nematodes. We speculate that the misfolding and oligomeric characteristics of the truncated RRM at the N-terminus of TDP-43 CTFs define their condensation properties and toxicity by implanting and transmitting structures with toxic properties of the truncated RRM into the IDR.

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