[
Nature,
1999]
Caenorhabditis elegans senses environmental signals through ciliated sensory neurons located primarily in sensory organs in the head and tail. Cilia function as sensory receptors, and mutants with defective sensory cilia have impaired sensory perception. Cilia are membrane-bound microtubule-based structures and in C. elegans are only found at the dendritic endings of sensory neurons. Here we show that mutations that cause defects in sensory cilia or their support cells, or in sensory signal transduction, extend lifespan. Our findings imply that sensory perception regulates the lifespan of this animal, and suggest that in nature, its lifespan may be regulated by environmental cues.AD - Department of Biochemistry and Biophysics, University of California at San Francisco, 94143-0448, USA.FAU - Apfeld, JAU - Apfeld JFAU - Kenyon, CAU - Kenyon CLA - engPT - Journal ArticleCY - ENGLANDTA - NatureJID - 0410462RN - 0 (DAF-16 transcription factor)RN - 0 (DAF-2 protein)RN - 0 (Helminth Proteins)RN - 0 (Transcription Factors)RN - EC 2.7.11.- (Receptor, Insulin)SB - IM
[
MicroPubl Biol,
2021]
From the beginning of Caenorhabditis elegans inception as a genetic model organism by Sydney Brenner (Brenner 1974), the ability to measure and quantify behavior in these nematodes led to numerous and powerful insights (Apfeld et al. 2018). The experimental amenability of worms makes them not just superb research subjects but also useful pedagogical tools. While excellent classroom additions to illustrate many biological processes, the educational potential of worms has lagged due to the expensive equipment required for their study. In most educational settings, lack of equipment discourages individual exploration and falls short of the promise owed to young and driven students. One of the places where this is felt strongly is in the automated quantification of animal behavior. Many systems have been developed over the years (and are currently used across the world) for the rapid and unbiased quantification of behavioral phenotypes. For example, we used tracking systems to compare the ability of mutant C. elegans strains to transition between gaits (Vidal-Gadea et al., 2011), and Deng and colleagues used them to study the role of inhibitory GABAergic motorneurons during rapid locomotion (Deng et al., 2020, see Husson et al. 2012 for a review of the use of tracking systems in C. elegans). Until recently, the automated quantification of C. elegans behavior was only feasible in specialized labs. Recent advances have begun to reduce the expense and complexity of automatically quantifying animal behavior. For example, the Haspel lab at NJIT made use of the recently developed Tierpsy behavioral software (Avelino et al. 2018) to build numerous animal tracking systems that are user friendly, and able to achieve levels of kinematic analysis that previously required considerably more expensive setups (Deng et al. 2020).
Sedore, Christine A., Johnson, Erik, Banse, Stephen A., Lithgow, Gordon J., Driscoll, Monica, Coleman-Hulbert, Anna L., Guo, Max, Phillips, Patrick C.
[
microPublication Biology,
2020]
The Caenorhabditis Intervention Testing Program (CITP) is a multi-institutional, National Institutes of Aging (NIA)-funded consortium charged with identifying chemical compounds that robustly extend lifespan in a genetically diverse panel of Caenorhabditis strains. Compounds are prioritized for screening if they are highly ranked via computational prediction for lifespan or healthspan effects (Coleman-Hulbert et al. 2019), if they are predicted to engage known lifespan regulating pathways, or if they have previously been reported as extending lifespan or healthspan in model systems (Lucanic et al. 2017). -guanidinopropionic acid (-GPA) is a creatine analog (Shields and Whitehair 1973), commonly used as a dietary supplement, and has been shown to extend lifespan in Drosophila under stress via 5′ AMP-activated protein kinase (AMPK) activity (Yang et al. 2015). The AMPK pathway is conserved in nematodes and humans (Apfeld et al. 2004) and is involved in multiple pathways affecting stress response and metabolism (Wang et al. 2012).
We assayed lifespan in response to -GPA exposure in three Caenorhabditis species using our previously published workflow (Lucanic et al. 2017). In brief, worms were age-synchronized by timed egg-lays on standard 60 mm diameter Nematode Growth Media (NGM) plates and transferred at a density of 50 individuals per 35 mm treated plate in triplicate when they reached adulthood (for control plates, there were six replicates of 50 animals each). -GPA (Sigma-Aldrich) was dissolved in water and diluted appropriately such that addition of 125 l of solution to 35 mm diameter plates containing NGM with lawns of E. coli OP50-1 and 51 m FUdR would generate the following final -GPA concentrations: 0.1 M, 1 M, 10 M, 50 M, 100 M, 500 M, 1 mM, 10 mM and 300 mM. Worms were maintained at 20 C and moved to fresh plates on the first, second, and fourth (C. tropicalis) or fifth (C. elegans and C. briggsae) day of adulthood, then once weekly afterward. Due to our previous experience with compound interventions that potentially alter bacterial viability through transient pH changes upon plate treatment (Banse et al. 2019), we investigated the effects of -GPA on our assay plates. At the above listed concentrations, -GPA-treated plates had a pH of 6.5 and the bacterial lawns survived treatment when tested by replica plating. Thrice weekly, we observed animals for spontaneous movement or movement after gentle perturbation with a 0.2 mm diameter platinum wire. Death was scored as a lack of movement.
Our results indicate that -GPA does not extend lifespan in the three nematode species at the concentrations tested here; in fact, in only one instance was an effect detected and, in that case, the compound reduced lifespan (Fig. 1). This conclusion is based on one biological replicate per concentration and, as such, could be considered preliminary. While interventions may be ineffective due to a range of causes, including permeability barriers, compound stability in vivo, and metabolism by the bacterial food source, we believe that the lack of response in this study was due to a lack of physiological relevance in C. elegans. In Drosophila and mammalian models, -GPA reduces the level of intracellular phosphocreatine that can be used by creatine kinases to regenerate ATP (Oudman et al. 2013; Yang et al. 2015) resulting in a decreased cellular ATP/AMP ratio, which activates AMPK and ultimately increases lifespan and stress-resistance. Our a priori expectation for lifespan extension in C. elegans was built on the observations that: (1) creatine is reported as detectible in C. elegans (Atherton et al. 2008; Jones et al. 2012; Wan et al. 2017); (2) C. elegans has a creatine-like kinase, ARGK-1, whose activity modulates AMPK signaling (McQuary et al. 2016); (3) modulation of AMPK (Apfeld et al. 2004; Greer et al. 2007) and ARGK-1 (McQuary et al. 2016) in C. elegans can affect lifespan and stress resistance; and (4) regulation of lifespan by insulin signaling is partially dependent on AMPK signaling in C. elegans (Tullet et al. 2014). As such, we were surprised to find no changes in lifespan upon treatment with a creatine analog. One possible explanation is that, despite the similarity between ARGK-1 and mammalian creatine kinase, the enzymes substrates differ. Biochemical analysis suggests that ARGK-1 uses arginine instead of creatine as a substrate to recharge ADP (Fraga et al. 2015). Additionally, it has been postulated that the biochemical characterization of C. elegans metabolites may have misidentified creatine, and that creatine is not relevant to C. elegans physiology (Witting et al. 2018). Given these caveats, it may not be surprising that -GPA does not alter Caenorhabditis lifespan.