Metabolic shift from glycogen to trehalose promotes lifespan and healthspan in Caenorhabditis elegans.

As Western diets continue to include an ever-increasing amount of sugar, there has been a rise in obesity and type 2 diabetes. To avoid metabolic diseases, the body must maintain proper metabolism, even on a high-sugar diet. In both humans and Caenorhabditis elegans, excess sugar (glucose) is stored as glycogen. Here, we find that animals increased stored glycogen as they aged, whereas even young adult animals had increased stored glycogen on a high-sugar diet. Decreasing the amount of glycogen storage by modulating the C. elegans glycogen synthase, gsy-1, a key enzyme in glycogen synthesis, can extend lifespan, prolong healthspan, and limit the detrimental effects of a high-sugar diet. Importantly, limiting glycogen storage leads to a metabolic shift whereby glucose is now stored as trehalose. Two additional means to increase trehalose show similar longevity extension. Increased trehalose is entirely dependent on a functional FOXO transcription factor DAF-16 and autophagy to promote lifespan and healthspan extension. Our results reveal that when glucose is stored as glycogen, it is detrimental, whereas, when stored as trehalose, animals live a longer, healthier life if DAF-16 is functional. Taken together, these results demonstrate that trehalose modulation may be an avenue for combatting high-sugar-diet pathology.

An Integrative Approach to STEM Concepts in an Introductory Neuroscience Course: Gains in Interdisciplinary Awareness.

Neuroscience is an integrative discipline for which students must achieve broad-based proficiency in many of the sciences. We are motivated by the premise that student pursuit of proficiency in science, technology, engineering, and mathematics (STEM) can be supported by awareness of the application of knowledge and tools from the various disciplines for solving complex problems. We refer to this awareness as "interdisciplinary awareness." Faculty from biology, chemistry, mathematics/computer science, physics, and psychology departments contributed to a novel integrative introductory neuroscience course with no pre-requisites. STEM concepts were taught in "flipped" class modules throughout the semester: Students viewed brief videos and completed accompanying homework assignments independently. In subsequent class meetings, students applied the STEM concepts to understand nervous system structure and function through engaged learning activities. The integrative introduction to neuroscience course was compared to two other courses to test the hypothesis that it would lead to greater gains in interdisciplinary awareness than courses that overlap in content but were not designed for this specific goal. Data on interdisciplinary awareness were collected using previously published tools at the beginning and end of each course, enabling within-subject analyses. Students in the integrative course significantly increased their identification of scientific terms as relevant to neuroscience in a term-discipline relevance survey and increased their use of terms related to levels of analysis (e.g., molecular, cellular, systems) in response to an open-ended prompt. These gains were seen over time within the integrative introduction to neuroscience course as well as relative to the other two courses.

Dynamic O-GlcNAc cycling at promoters of Caenorhabditis elegans genes regulating longevity, stress, and immunity.

Nutrient-driven O-GlcNAcylation of key components of the transcription machinery may epigenetically modulate gene expression in metazoans. The global effects of GlcNAcylation on transcription can be addressed directly in C. elegans because knockouts of the O-GlcNAc cycling enzymes are viable and fertile. Using anti-O-GlcNAc ChIP-on-chip whole-genome tiling arrays on wild-type and mutant strains, we detected over 800 promoters where O-GlcNAc cycling occurs, including microRNA loci and multigene operons. Intriguingly, O-GlcNAc-marked promoters are biased toward genes associated with PIP3 signaling, hexosamine biosynthesis, and lipid/carbohydrate metabolism. These marked genes are linked to insulin-like signaling, metabolism, aging, stress, and pathogen-response pathways in C. elegans. Whole-genome transcriptional profiling of the O-GlcNAc cycling mutants confirmed dramatic deregulation of genes in these key pathways. As predicted, the O-GlcNAc cycling mutants show altered lifespan and UV stress susceptibility phenotypes. We propose that O-GlcNAc cycling at promoters participates in a molecular program impacting nutrient-responsive pathways in C. elegans, including stress, pathogen response, and adult lifespan. The observed impact of O-GlcNAc cycling on both signaling and transcription in C. elegans has important implications for human diseases of aging, including diabetes and neurodegeneration.

Timing of High-glucose Diet in the C. elegans Lifecycle Impacts Fertility Phenotypes.

Human metabolic diseases and high-sugar diets have been associated with infertility. Previous studies show that high-glucose diet also affects fertility in C. elegans, leading to decreased offspring production and delayed reproductive timing. We tested whether the timing of glucose exposure affects these fertility defects or the embryo to larval transition. We found that decreased offspring production was strictly a response to high-glucose exposure in adulthood, whereas the delayed reproductive profile was influenced by both developmental and adult diets. We found no effect of high-glucose diet on the number of embryos that develop to the first larval stage. Together, these results suggest that the decreased offspring production and delayed reproductive profile may be separable phenotypes, and that a high-glucose diet reduces the number of offspring by interfering with processes regulated during adulthood.

Integrative STEM education for undergraduate neuroscience: Design and implementation.

As an integrative discipline, neuroscience can serve as a vehicle for the development of integrative thinking skills and broad-based scientific proficiency in undergraduate students. Undergraduate neuroscience curricula incorporate fundamental concepts from multiple disciplines. Deepening the explicit exploration of these connections in a neuroscience core curriculum has the potential to support more meaningful and successful undergraduate STEM learning for neuroscience students. Curriculum and faculty development activities related to an integrative core curriculum can provide opportunities for faculty across disciplines and departments to advance common goals of inclusive excellence in STEM. These efforts facilitate analysis of the institutional STEM curriculum from the student perspective, and assist in creating an internal locus of accountability for diversity, equity, and inclusion within the institution. Faculty at the College of the Holy Cross have undertaken the collaborative design and implementation of an integrative core curriculum for neuroscience that embraces principles of inclusive pedagogy, emphasizes the connections between neuroscience and other disciplines, and guides students to develop broad proficiency in fundamental STEM concepts and skills.

Subtelomeric elements influence but do not determine silencing levels at Saccharomyces cerevisiae telomeres.

In Saccharomyces cerevisiae, genes placed near telomeres are transcriptionally repressed (telomere position effect, TPE). Although telomeric DNA sequence is the same at all chromosome ends, the subtelomeric elements (STEs) and level of TPE vary from telomere to telomere. We tested whether STEs determine TPE levels. STEs contributed to TPE, as deleting the X element from the VI-R telomere modestly decreased silencing at this telomere. However, STEs were not the major determinant of TPE levels, as inserting the VI-R X element at the truncated VII-L telomere did not increase TPE. These data suggest that the TPE levels of individual telomeres are dependent on some aspect of chromosome context.

Differential nuclear localization does not determine the silencing status of Saccharomyces cerevisiae telomeres.

In Saccharomyces cerevisiae, genes near telomeres are transcriptionally repressed, a phenomenon termed telomere position effect (TPE). Yeast telomeres cluster near the nuclear periphery, as do foci of proteins essential for TPE: Rap1p, Sir2-4p, and yKu70p/yKu80p. However, it is not clear if localization of telomeres to the periphery actually contributes to TPE. We examined the localization patterns of two telomeres with different levels of TPE: truncated VII-L and native VI-R. For both telomeres, localization to the nuclear periphery or to the silencing foci was neither necessary nor sufficient for TPE. Moreover, there was no correlation between TPE levels and the extent of localization. Tethering the truncated VII-L telomere to the nuclear periphery resulted in a modest increase in TPE. However, tethering did not bypass the roles of yKu70p, Sir4p, or Esc1p in TPE. Using mutations in RIF genes that bypass the role of Ku in TPE, a correlation between the level of silencing and the number of Rap1p foci present in the nucleus was observed, suggesting that Sir protein levels at telomeres determine both the level of TPE and the number of foci.

Integrating cell and molecular biology concepts: Comparing learning gains and self-efficacy in corresponding live and virtual undergraduate laboratory experiences.

Multiple pedagogical approaches, such as experimental experiences or computer-based activities, have been shown to increase student learning and engagement. We have developed a laboratory module that includes both a traditional "live" experimental component and a student-designed "virtual" computer simulation component. This laboratory employs the mating pathway of Saccharomyces cerevisiae (yeast) to demonstrate four fundamental cell and molecular biology concepts: cell signaling, cytoskeleton, cell cycle, and cell cycle checkpoints. In the live laboratory, students add mating pheromone to cultures, then measure changes in cell division and morphology characteristics of the S. cerevisiae mating response. We also developed a "virtual" complement to this laboratory. Using the principles of Design Thinking and Agile methodology, we collaborated with an undergraduate Computer Science course to generate two computer simulations which can support the live laboratory or provide a virtual laboratory experience. We assessed how both the live and virtual laboratories contributed to learning gains in analytical skills and course content. Students who performed the simulation alone or the simulation plus live lab demonstrated learning gains, with greater gains for the live lab, but students who performed neither lab did not. Attitudinal assessment demonstrated increased student engagement and self-efficacy after performing the live and virtual labs. © 2018 by The International Union of Biochemistry and Molecular Biology, 46:361-372, 2018.

High-glucose diets have sex-specific effects on aging in C. elegans: toxic to hermaphrodites but beneficial to males.

Diet and sex are important determinants of lifespan. In humans, high sugar diets, obesity, and type 2 diabetes correlate with decreased lifespan, and females generally live longer than males. The nematode Caenorhabditis elegans is a classical model for aging studies, and has also proven useful for characterizing the response to high-glucose diets. However, studies on male animals are lacking. We found a surprising dichotomy: glucose regulates lifespan and aging in a sex-specific manner, with beneficial effects on males compared to toxic effects on hermaphrodites. High-glucose diet resulted in greater mobility with age for males, along with a modest increase in median lifespan. In contrast, high-glucose diets decrease both lifespan and mobility for hermaphrodites. Understanding sex-specific responses to high-glucose diets will be important for determining which evolutionarily conserved glucose-responsive pathways that regulate aging are "universal" and which are likely to be cell-type or sex-specific.

O-linked-N-acetylglucosamine cycling and insulin signaling are required for the glucose stress response in Caenorhabditis elegans.

In a variety of organisms, including worms, flies, and mammals, glucose homeostasis is maintained by insulin-like signaling in a robust network of opposing and complementary signaling pathways. The hexosamine signaling pathway, terminating in O-linked-N-acetylglucosamine (O-GlcNAc) cycling, is a key sensor of nutrient status and has been genetically linked to the regulation of insulin signaling in Caenorhabditis elegans. Here we demonstrate that O-GlcNAc cycling and insulin signaling are both essential components of the C. elegans response to glucose stress. A number of insulin-dependent processes were found to be sensitive to glucose stress, including fertility, reproductive timing, and dauer formation, yet each of these differed in their threshold of sensitivity to glucose excess. Our findings suggest that O-GlcNAc cycling and insulin signaling are both required for a robust and adaptable response to glucose stress, but these two pathways show complex and interdependent roles in the maintenance of glucose-insulin homeostasis.