Calorie restriction has been show to extend lifespan. A key aspect of calorie restriction is a shift in systemic metabolism from carbohydrate to lipid metabolism. The hypothalamus is a crucial regulator of systemic metabolism and has been directly implicated in the aging process of mice. We uncovered that cell-selective impairment of hypothalamic Agouti-related peptide (AgRP)-expressing neuronal circuitry, part of the hypothalamic melanocortin system, in ad libitum fed mice, results in accelerated aging phenotype of many tissues, including the immune system and bone. We also found that males of mice strains with impaired AgRP neuronal circuitry have shorter mean lifespan when ad libitum fed. Taken together these results gave impetus to the central hypothesis of this proposal, which is that the AgRP system is key mediator in calorie restriction-induced extension of lifespan. We will test our hypothesis through the following specific aims:
Specific Aim 1. To test the hypothesis that calorie restriction prevents declining functioning of hypothalamic AgRP neurons in chronological aging. In our preliminary studies we found that AgRP neurons manifest aging associated decline in mitochondrial integrity in ad libitum fed mice. We also observed that calorie restriction promotes AgRP mRNA expression and suppression of POMC mRNA levels. We showed that the input organization of the melanocortin system is shifted by calorie restriction to a constellation that enhances AgRP neuronal activity and suppresses POMC cells. We hypothesize that calorie restriction suppresses deterioration of AgRP neurons during chronological aging, and that this effect is mediated by intracellular pathways regulating mitochondrial dynamics and ROS generation. We will test this hypothesis by analyzing the effect of calorie restriction on AgRP neuronal activity, mitochondrial dynamics and ROS production in control and transgenic mice, in which specific processes of mitochondrial fission, fusion or ROS control is cell-selectively down or up-regulated.
Specific Aim 2. To unmask if hypothalamic AgRP neurons are critical for lifespan promotion by calorie restriction. We will utilize multiple lines of transgenic animals in which AgRP neuronal function is selectively up- or down-regulated. Groups of animals will be maintained for lifespan assessment and whole body necropsy will be carried out at the time of death in each. In other control and experimental cohorts, we will analyze the effect of calorie restriction on systemic metabolism and behavior of mice. We will also assess pancreatic beta cell-, adipose-, liver, muscle and immune system parameters of control and experimental animals. The execution of these studies will shad new light on integrative physiology and molecular principles of calorie restriction-induced alterations in heath- and lifespan.
