An energy-sensitive pathway of cold-induced metabolic remodeling in threespine stickleback

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Adjustments in metabolism are necessary to meet changing energetic demands that result from processes such as exercise, temperature fluctuations, and diseases such as cancer. One of the most striking examples of alterations in metabolism occurs in fish in response to temperature. Because fish are ectotherms, with body temperatures equivalent to their environment, some species may experience body temperature changes as great as 15-20oC diurnally or seasonally, requiring adjustments in metabolism to maintain activity and swimming performance. Although metabolic remodeling in response to temperature has been well documented in several fish species, little is known about how it is regulated. While some components of the regulatory pathway are similar between fish and mammals, others differ, providing an opportunity to expand understanding of how metabolism is regulated. This project will identify the signaling pathway involved in temperature-induced changes in metabolism in the threespine stickleback fish. Stickleback are ideal for these studies because they inhabit thermally variable environments and their genome has been sequenced, making molecular biological studies more tractable compared to other species. High-school, undergraduate, and graduate students will participate in this research, obtaining training in physiology, biochemistry, and molecular biology. Native Alaskan high school students will be involved through independent studies as part of the Rural Alaskan High School Honors Institute, a six-week college preparatory program at the University of Alaska, Fairbanks. Results from this research will provide a better understanding of how metabolism is regulated, a process essential to the health of all organisms.This project investigates mechanisms of phenotypic plasticity, specifically the role of sirtuins, NAD+-dependent deacetylases, in driving metabolic reorganization in response to temperature in the threespine stickleback, Gasterosteus aculeatus. The hypothesis will be tested that sirtuins activate c-MYC, a potent regulator of cell growth and metabolism, and that differences in chromatin packing among different tissues will affect c-MYC binding, resulting in tissue-specific metabolic remodeling that is reflected in the degree of thermal compensation at the organismal level in aerobic metabolic scope. Stickleback will be acclimated to three temperatures (5, 12, or 20oC) for 10 weeks. Maximal activities of key metabolic enzymes, mitochondrial respiration rates in permeabilized cells, aerobic metabolic scope, and levels of adenylates, sirtuins, and c-MYC will be quantified in liver and glycolytic and oxidative muscles. Levels of sirtuins will then be manipulated in vivo in animals at 12oC and these parameters quantified, along with the expression of select mitochondrial genes. Gene targets of c-MYC will be identified using chromatin immunoprecipitation coupled with high throughput sequencing (ChIP-Seq), and a c-MYC promoter and reporter construct will be used to assess c-MYC DNA binding activity in vivo during thermal acclimation. This project will determine how changes in metabolism at the cellular level contribute to whole-organismal metabolic remodeling and identify components of the signaling cascade driving tissue-specific metabolic remodeling, creating an integrated understanding of metabolic remodeling that spans molecular, cellular and organismal levels. Broader impacts include graduate student training and research opportunities for Native Alaskan high-school students participating in a six-week summer college preparatory program.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.