Brain Energy Metabolism and Sleep in Adults

Alzheimer's disease (AD) is rapidly progressing in the elder population and the pathophysiological changes in the brain start at least 1-2 decades before the disease onset. During this period of slow progression, individuals may notice subtle changes in the memory and this subset of the population is termed as Mild Cognitive Impairment (MCI). MCI is a pre-clinical stage of Alzheimer's disease (AD) in which individuals have memory complaints but are functionally independent and not yet clinically diagnosed with dementia. New modalities for potential identification of the progression of the disease, include different biomarkers, state-of-the-art technologies like sleep tracking and magnetic resonance spectroscopy (MRS) may provide additional, essential tools to facilitate early detection of disease, which may allow for earlier intervention and provide a potential gauge for a response to treatment.

The first goal of this research project aims to understand the variations in the brain energy and phospholipid metabolites as measured by magnetic resonance spectroscopy at 7 Tesla across three groups: cognitively healthy adults, MCI, and AD. The brain requires a lot of energy in the form of adenosine triphosphate (ATP) to support the neuronal activity, and it has a rich source of phospholipids to maintain biological functions. Therefore, abnormalities in the mechanism of energy supply and phospholipids can affect a wide range of function in the neuronal cells. Previous literature using 18FDG PET scan has shown impairments in brain glucose metabolism associated with cognitive decline in MCI even before the individual presents with clinically apparent cognitive dysfunction. Thus, measuring the ratio of energy metabolites ATP-to-PCr (ATP/PCr) and Pi-to-PCr (Pi/PCr) offers a promising way to predict the active status of the resting brain.

Additionally, the levels of phospholipids start to decrease by the age of twenty (20), and more pronounced decline is noticed after the age of 80 years. Thus, aging and diseased brains are more susceptible to the changes in the levels of phospholipids metabolites which can lead to neurodegenerative disorders. Two classes of phospholipid metabolites that can be studied using 31P MRS are phosphomonoesters (PMEs) and phosphodiesterase (PDEs). PMEs are the essential building blocks for cell/neuronal membrane synthesis whereas PDEs are the metabolites from the breakdown of the cell/neuronal phospholipids membrane. A higher ratio of PMEs-to-PDEs can, therefore, reflect as an improvement in brain health leading to neurogenesis, with the opposite suggesting neurodegeneration. Thus, 31P MRS has opened a window to measure various neurochemical metabolites non-invasively, which could provide detailed information about important high-energy phosphate metabolites, as well as phospholipid metabolites in real time. 7T Ultra-high magnetic field MRI scanner, which is now increasingly accessible worldwide and enables fast and accurate BEM measurement, may provide a comprehensive approach for aiding in the diagnosis of the neurodegenerative process from cognitively normal adults to MCI and AD and also monitoring the treatment responses to newer drugs.

Secondly, disturbance in sleep patterns can impact the brain's energy metabolism by altering the ratio of brain energy and phospholipid metabolites, thereby causing impaired brain cognitive functions. Aging is a significant moderator of sleep quality and may affect non-REM slow wave sleep (SWS), which facilitates the clearance of toxic material like amyloid protein. Stable sleep helps restore the neurobiological and neurophysiological responses about energy requirements impacting the changes in the concentration of brain energy and phospholipid metabolism. Currently, data are lacking regarding the relationship between sleep, brain energy requirement and its effect on the performance of cognitive domains to healthy aging, MCI, and AD.

Thirdly, BEM is regulated by specific genes that support the continuous energy requirements for the electrical activity of the brain. Hence in this research, we are interested in investigating the effect of two genes APOE ε4 and ABCA7 on brain energy and phospholipids metabolites in the three groups. It is essential to understand this connection as genes regulate the synthesis of appropriate protein/enzymes like ABCA7 transporter protein for glucose metabolism leading to energy production.