What causes aging is far from clear, but the theory of "antagonistic pleiotropy" postulates that aging is a consequence of the inverse correlation between age and selection pressure. Such a correlation allows positive selection of mechanisms with early-life beneficial effects, in spite of potential late-life detrimental effects. Understanding when and how such mechanisms become detrimental is crucial for understanding both the principles and constraints directing the evolution of aging, as well as the aging process itself. We recently identified a novel example of antagonistic pleiotropy. The current project will characterize this mechanism at the molecular level. In the nematode Caenorhabditis elegans the conserved protein KGB-1 provides protection during development against heavy metals and protein folding stress, but becomes detrimental during early adulthood by sensitizing animals to environmental stress and shortening their lifespan. Although little is known about KGB-1's targets and interactions, our recent work suggests that some of the age-dependent changes occurring following KGB-1 activation are mediated by age-dependent regulation of the longevity-associated transcription factor DAF-16. This project will: 1) characterize genetically age-dependent interactions between KGB-1 and DAF-16, as well as interactions between KGB-1 and proteins of the insulin signaling pathway, which regulates DAF-16; 2) identify, through genomic analysis, yet unknown targets of KGB-1 in developing larvae and in young adults, focusing on transcriptional targets and their regulators. Use of the genetically tractable C. elegans model organism allows pursuing the project's goals in the context of a whole animal, and provides an opportunity to flesh out a fundamental feature of the evolution of aging. Understanding aging is of increasing importance as biomedical advances increase human lifespan. The project will provide opportunities for training undergraduate and graduate students in scientific research, among them individuals from typically underrepresented groups, encouraging students to participate in scientific meetings and earning them, when appropriate, authorship on publications.
Our work aims to characterize a switch that we identified in the contribution of Caenorhabditis elegans stress-activated JNK signaling. Activation of this evolutionary conserved pathway during development was found to provide protection from environmental stress, but a similar activation during early adulthood compromised stress resistance and further shortened lifespan under normal conditions. A similar dichotomy is documented for the contribution of JNK signaling in humans, wherein JNK activation is important for stress protection, but can also exacerbate an array of aging-associated pathologies, including neurodegenerative diseases, tissue damage following stroke, and insulin resistance. The basis for the dichotomy in humans is yet unknown, but our results in the worm model suggested that the outcome of JNK signaling may be hard-wired to age. Our interpretation was that the age-dependent reversal in the contribution of JNK signaling was an example of a fundamental principle thought to underlie the evolution of aging, namely Antagonistic Pleiotropy. The Antagonistic Pleiotropy theory suggests that inverse correlation between age and selection pressure allows positive selection of mechanisms with early-life beneficial effects, in spite of potential late-life detrimental effects. Collectively, such mechanisms could be the ones determining aging characteristics of a species. The identified switch in the contribution of JNK signaling thus offers an opportunity to flesh out this theory and by characterizing the JNK switch and its implications for aging, shed light on the molecular underpinnings of Antagonistic Pleiotropy. Our work identified two mediators of the effects of the JNK homolog KGB-1 in different ages. We found that KGB-1 antagonistically regulated the transcription factor DAF-16/FOXO, an evolutionarily-conserved determinant of aging and longevity: KGB-1 activation in developing animals promoted DAF-16 function, but activation in adults attenuated it. In agreement, DAF-16 was found to be responsible for KGB-1-dependent age-specific contributions, although not all. These results demonstrated a novel interface between environmental stress and the regulation of aging. Moreover, they showed that the outcome of interactions between stress (through KGB-1) and aging (through DAF-16) are age-dependent. This study was published in ‘Aging Cell’ (Twumasi-Boateng et al 2012) and was highlighted in ‘Faculty of 1000’. Results were also addressed in talks given at UC Berkeley, UC Irvine, UMass Amherst, and in C. elegans and aging conferences. Since DAF-16 was not sufficient to explain all kgb-1-dependent phenotypes, we sought to characterize age-specific KGB-1 targets, both at the transcriptional level and the protein level. Microarray gene expression analysis identified a robust kgb-1-dependent ‘regulon’, including genes that were regulated in an age-dependent manner, and identified fos-1, a stress-activated transcription factor, as a mediator of kgb-1’s beneficial contribution to stress protection in developing animals, but not in adults. Similarly, characterization of KGB-1’s protein-protein interactions identified KGB-1 interactors, among them JUN-1, FOS-1’s partner in transcription regulation. Current work is focusing on characterizing the specific roles of DAF-16 and FOS-1, as well as identified KGB-1 targets, in KGB-1’s contributions to age-dependent phenotypes. Advances made in understanding kgb-1-dependent DAF-16 regulation in different ages point to involvement of gonad-derived hormones. Current studies focus on the role of gonadal signaling in a) inducing the KGB-1 switch, and b) in determining its interactions in different ages and their outcome. Results obtained with the support of the EAGER award shed light on a fundamental principle determining the outcome of stress responses. Identifying DAF-16 and FOS-1 as mediators of age-specific KGB-1 contributions is an important step toward therapeutically targeting detrimental mechanisms downstream to JNK activation without impairing beneficial functions. Our results also begin to address the mechanistic underpinnings of antagonistic pleiotropy, by demonstrating that age changes the function of an essential protein network. The emerging hypothesis is that onset of reproduction and the associated changes in energy allocation (reproduction versus maintenance), instills pleiotropy, probably in more than one pathway, and thus could be responsible for the appearance of antagonistic pleiotorpy as a developmental program. Work on the project provided educational opportunities focusing on the evolution and mechanisms of aging: It was the dissertation project of Kwame Twumasi-Boateng, a PhD student that graduated last year, who with the help of the high-profile publication secures a postdoctoral position. Kwame, who immigrated as a child from Ghana is well on his way to fulfill his goal of becoming an independent researcher. The project further provided research experience opportunities for six undergraduate students, four of which earned authorship on the paper. A new graduate student, Dena Block, is continuing the project focusing on the role of gonadal signaling in antagonistic pleiotropy, and a postdoc, Song-Hua Lee, is expanding analysis of KGB-1’s interactions. Working with them are five undergrads. Our studies of aging mechanisms also served as the basis for outreach activity, which targeted 5th grade elementary school students. This involved discussions on species diversity, how simple model organisms could teach us about human disease and its treatment, and used aging research to demonstrate that.
