The major accomplishment of this year was publication of studies examining age-related changes in tissue morphology of the C. elegans pharynx. The pharynx is a neuromuscular structure in the head that which injests, concentrates and crushes the bacterial food. The pharynx experiences significant changes in both structure and function during aging. In particular, the rate of pharynx muscle pumping declines during aging. In addition, structural deterioration is evident in the aged pharynx. However, it was not known whether these two factors are correlated, or if the functional declines would be the result of other changes in cell function that could not be detected visually. Finally, it was not know whether structural declines themselves were correlated with age. To address these questions, we took advantage of a computational approach for image analyses developed at the NIA. With this approach, it was possible to study the progression of structural aging in the C. elegans pharynx, as reflected in Nomarski images of the pharynx at time points across the adult lifespan. This analysis revealed that structural decline during aging occurs in stages. That is, the structural changes associated with pharynx aging proceed in a step-wise fashion between discreet structural states that can be recognized using mathematical transformations of these images. This finding suggests a model for structural aging in which cellular deterioration competes with cellular maintenance processes. Cellular maintenance processes may attempt to stabilize cellular structure during aging. At some point, we hypothesize that deterioration processes overcome the maintenance processes and cause cellular structure to collapse to a more aged state. We also examined whether structural and functional aging could be correlated. Using image analyses and mathematical transforms of image data, we found that pharynx function was weakly correlated with pharynx structural decline. This is consistent with the idea that functional aging in this organ is reflective partly of muscle deterioration and partly of other processes that are not evident in Nomarski images. These findings provide a context for developing futher experiments for identifying the cellular processes that are most significant for maintaining cellular structure and function during aging. The laboratory also continued work on other projects that will be ready for publication in the near future. A major focus of current work is to identify endocrine pathways that coordinate aging and stress responses throughout the body. One study was undertaken to identify downstream pathways through which DAF-2 insulin receptor and AGE-1 PI3K signaling within a subset of cells regulates development and aging throughout the body. Our previous work suggested that DAF-2 and AGE-1 signaling regulated an endocrine output that controls aging and development in collaboration with DAF-16/FOXO, which is the major direct target of DAF-2 and AGE-1 signaling. To identify this parallel pathway, transcriptional microarrays were used to compared global gene expression in animals lacking AGE-1 PI3K signaling and two strains with AGE-1 PI3K-signaling restricted to specific tissues. This analysis identified specific transcripts that are regulated by endocrine outputs of AGE-1 PI3K signaling. Using RNA-interference and promoter deletion analysis, we identified the signaling pathways that couple to AGE-1 PI3K to regulate these targets. This study is complete and is being submitted for publication. A second focus of our current work is defining molecular pathways that regulate the allocation of metabolic resources between somatic maintenance and other processes, such as reproduction. Aging can be slowed by processes that increase the maintenance and repair of the adult soma. Stressful conditions, such as limiting nutrients, trigger activation of these repair processes. Stress also impedes the distribution of resources to more costly processes, such as reproduction. Two active projects seek to identify pathways that regulate resource distribution under replete and stressful environments. One investigation has examined the factors that regulate synthesis of vitellogenin yolk proteins by intestinal cells. In reproductive adults, vitellogenins are synthesized by the intestine, transported to the gonad and stored by oocytes as a food source for developing embryos. Signaling by the DAF-2 insulin pathway regulates intestinal vitellogenin synthesis through unknown mechanisms. Our work has elucidated factors required for vitellogenin gene expression in response to DAF-2 signaling and other stimuli. This work is nearly complete and will be ready for publication soon. In related work, we are examining cellular responses to nutrient stress. In several publications, we described a novel response to nutrient stress that could be visualized in C. elegans intestinal cells. This response is termed, FIRE, for Fasting-Induced Redistribution of Esterase activity. Under replete conditions with adequate nutrients, intestinal cells contain many cytoplasmic vesicles that are detectable by in situ esterase activity. When nutrients are removed, the cytoplasmic esterase activity is depleted and appears to redistribute to a nuclear, or perinuclear, localization. Using RNA-interference techniques, we have identified genes that regulate this cellular response to nutrient stress. These genes also affect growth, suggesting they provide a link between nutrient levels and growth processes. We are also examining the effects of aging on the FIRE response to determine whether FIRE-regulating genes might be altered during aging.
| Wolkow, Catherine A (2010) New haystacks reveal new needles: using Caenorhabditis elegans to identify novel targets for ameliorating body composition changes during human aging. Interdiscip Top Gerontol 37:84-93 |
| Love, Dona C; Ghosh, Salil; Mondoux, Michelle A et al. (2010) Dynamic O-GlcNAc cycling at promoters of Caenorhabditis elegans genes regulating longevity, stress, and immunity. Proc Natl Acad Sci U S A 107:7413-8 |
| Shamir, Lior; Wolkow, Catherine A; Goldberg, Ilya G (2009) Quantitative measurement of aging using image texture entropy. Bioinformatics 25:3060-3 |
| Johnston, Josiah; Iser, Wendy B; Chow, David K et al. (2008) Quantitative image analysis reveals distinct structural transitions during aging in Caenorhabditis elegans tissues. PLoS One 3:e2821 |
