Cold stress, protein, brown adipose tissue, and human skeletal phenotype

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Biological anthropologists are interested in understanding how modern human populations have adapted over time to a wide range of environments, including different climates. The goal of this project is to understand how a specific kind of fat, called brown adipose tissue or brown fat, helps humans keep warm in the cold, and how the combination of diet, exercise, and brown fat affects the way the skeleton grows in people who are adapted to different climates. The bones of people alive today are less strong than the bones of our ancestors. This trend is probably partly the result of decreased exercise, but the researchers want to understand whether changes in temperature (such as living in heated homes) and/or diet also contribute. This research will advance the career of a female scientist and two female graduate students, one of whom is African American. The investigators will present workshops on bone health to high school students about how diet, temperature, and exercise affect bone health and develop a hands-on bone measurement activity with the University of Michigan Museum of Natural History.This proposal tests a new model called TEMPS (Thermogenesis, Energy, Mechanical loading, Protein, and the Skeleton) to integrate the effects of temperature, diet, and exercise on skeletal phenotype. The research will focus on how a type of fat called brown adipose tissue, or brown fat, helps develop strong bones. Brown fat burns energy to produce heat, and individuals with more brown fat also tend to have stronger bones, although it is not clear why. The study will test the hypothesis that eating a high fat/high protein diet made it easier for human ancestors to move into cold climates by providing fatty acids and protein for non-shivering thermogenesis, and that this diet, combined with cold stress and exercise, contributed to bone strength in cold-adapted populations. The researchers will use a combination of controlled experiments in mice and comparative studies in human skeletons to test their model. They will study skeletal growth in young mice raised at cool, standard, or warm temperatures and fed either standard or high-protein diets. Some mice will also have cage wheels for exercise. The researchers will collect data from mice including food intake, body mass, brown fat mass, bone mineral density, bone size and shape, and bone strength. These data will be compared to microcomputed tomography data from museum skeletons of cold- and heat-adapted humans, to see if they show similar patterns. The results will show whether cold exposure, high protein diet, and exercise make bones stronger, and identify new ways to maximize bone mass in young people, in order to reduce osteoporosis later in life. The data will also improve our understanding of skeletal development in hominins such as humans and Neanderthals that are adapted to colder or warmer climates.