Ilia N. Karatsoreos, Ph.D. - US grants

? DESCRIPTION (provided by applicant): Aging is a natural process, occurring in all organisms. While this process may be normal, the costs of age- related pathologies are enormous. The NIH estimates the cost of treating people with age-related dementia of being in excess of US$600 Billion. Disrupted metabolic function is a hallmark of aging. Metabolic disorders, including Type II Diabetes, have increased prevalence in aged populations, with over 25% of the US population over 65 having Type II Diabetes, reaching a cost of over US$100 Billion. Age-related dysregulation of metabolism includes increased adiposity, dyslipidemia, insulin resistance, and reduced glucose tolerance. It is known that metabolic interventions, including caloric restriction and exercise, positively impact both lifespan and healthspan. Given the relationship between aging and metabolism, animal models that result in altered metabolic function may be leveraged to provide new models for aging research. To this end, we propose to use a model characterized in our lab that results in environmentally driven metabolic dysregulation that seems to mimic metabolic changes observed in aging. Our model is elegant in its simplicity, in that we cause metabolic dysregulation by housing mice in a shortened day of 10h light and 10h darkness as compared to the normal day of 12h light and 12h darkness. We have shown this results in chronic misalignment of hormone and behavioral rhythms, metabolic dysregulation (including weight gain and hyperinsulinemia), changes in neural structure in the prefrontal cortex, and cognitive abnormalities. Further, this occurs in a short time frame of only 4-6wks. An additional benefit of this model is that misalignment of internal biological rhythms to the externa environment is also a hallmark of aging. The objective of the current proposal is to determine the feasibility of using environmental circadian disruption to produce an accelerated aging phenotype, particularly in the context of peripheral and brain metabolism. We propose a series of integrative experiments to test the hypothesis that environmental metabolic dysregulation by disrupting clocks leads to accelerated aging. We will compare our model to normal aging with respect to peripheral metabolism, brain function and local metabolism, and determine if our model shortens lifespan. Given that disruption of corticosterone hormone rhythms is observed in aging and our model, we will explore if restoring young like rhythms of corticosterone in aged mice can improve metabolic function, and increase lifespan. Future experiments using this model will provide new insights into molecular, cellular, and physiological processes underlying normal aging.

The rotation of the Earth provides one of the most salient environmental signals: the circadian (daily) alternation of night and day. Nearly all terrestrial organisms, from single-celled to multi-cellular species, possess internal biological clocks allowing for synchronization of internal processes with the environment. In mammals (including humans), a master circadian clock in the brain synchronizes other clocks throughout the brain and body, maintaining temporal organization in the whole organism. The importance of these clocks becomes apparent during times of temporal disruption, with the degradation of circadian rhythms associated with numerous negative health effects. However, to fully understand how "broken" clocks cause negative effects, understanding how they promote optimal function under normal circumstances is necessary. The goal of this research is to understand how circadian clocks promote normal functioning of brain circuits important in complex behaviors like decision making, attention, and cognitive flexibility. A mouse model is used to investigate how normal or disrupted circadian rhythms regulate the size, shape, and function of neurons in the brain, and how these changes affect cognition. Advanced techniques in the measurement of brain chemistry, imaging, 3-dimensional reconstruction of neurons, and pharmacology is used to help understand how circadian clocks maintain normal function, and how disrupted clocks lead to negative outcomes. An integral component of this award engages rural and urban undergraduate students in outreach involving the Mobius Science Center and Children's Museum in Spokane, helping increase awareness of how biological clocks affect physiological function, from the simplest organisms, to our own brain.

Significant inroads have been made in understanding the cellular and molecular function of the suprachiasmatic nucleus (SCN) circadian clock. However, the fundamental role of circadian rhythms in brain areas underlying complex behaviors, such as the prefrontal cortex (PFC), remains illusive. Using environmental circadian disruption as a tool, this research determines how circadian rhythms modulate normal PFC function at the behavioral, physiological, structural, and biochemical levels. This research builds upon our findings that circadian disruption impairs cognitive flexibility and causes atrophy of PFC neurons. The overarching hypothesis of this project is that circadian rhythms promote normal PFC function primarily through modulation of glutamatergic signaling, since glutamate is crucial for optimal PFC function. Circadian disruption effects on the PFC is determined by examining PFC mediated behaviors, and through the use of implantable biosensors to determine effects on extra-cellular PFC glutamate in real time. To establish a causal role for glutamate, pharmacological manipulation of PFC AMPA and NMDA signaling is undertaken. Confocal microscopy and 3-D reconstruction of PFC neurons is used to investigate circadian changes in neural morphology and dendritic spines, primary sites of excitatory signaling. Biochemical studies determine how normal and abnormal circadian rhythms drive membrane trafficking of glutamate receptors, providing another substrate on which circadian rhythms may act to modulate PFC function. The third and final experimental aim is to determine whether changes in a rhythmic hormone (corticosterone) mediates these effects, which would provide a mechanism by which normal and disrupted timing cues are relayed to extra-SCN brain regions.

ABSTRACT: Obesity and its co-morbid pathologies cardiovascular disease and diabetes are significant and growing public health problems. Obesity occurs as a result of interactions between multiple organs (e.g. liver, muscle, adipose), genetic factors, physiological factors (e.g. insulin, cytokines, and glucocorticoids), and environmental factors, particularly those associated with modern life (e.g. diet, lack of exercise, stress). Growing evidence suggests one of the most insidious of these environmental factors is the change in our circadian (daily) rhythms, driven by inappropriately timed exposure to light, shiftwork, and a 24h ?always-on? society. Both epidemiologic and experimental data, including work from our own laboratory, support a role for circadian disruption in metabolic dysregulation. As such, manipulating environmental light-dark (LD) cycles could serve as a powerful tool to probe the mechanisms of environmentally driven metabolic dysregulation. Importantly, the mechanisms that link environmental circadian desynchronization (CD) to metabolic dysregulation remain unknown, limiting our mechanistic understanding of the role of circadian rhythms in the development of obesity. This proposal builds upon our published findings in mouse showing CD caused by shortening the LD cycle from 24h to 20h (LD10:10) results in weight gain, hyperinsulinemia, and other aspects of metabolic syndrome. Our focus now is to determine the mechanisms by which this environmental challenge leads to obesity. New data from our lab demonstrates that the endocannabinoid (eCB) system may be an important link between circadian rhythms and metabolic dysregulation. This is strengthened by recent data in humans that show rhythmic profiles of eCBs in the blood, that sleep/circadian disruption can alter these rhythms, and that over-activity in the eCB system is associated with obesity. The objective of this proposal is to mechanistically determine if the eCB system is an essential factor by which environmental and genetic circadian disruption contribute to changes in metabolic function, including increases in adiposity. We will use state-of-the art behavioral and metabolic phenotyping, gene expression and mass spectrometry to assess outcomes, and targeted pharmacology and tissue specific genetic manipulations to probe the mechanistic links between eCB signaling, circadian desynchronization, and metabolic dysregulation.