DESCRIPTION (provided by applicant): Type II diabetes mellitus (T2DM) is a common metabolic disease and an established risk factor for cognitive dysfunction in the elderly population. However, the pathological mechanisms that underpin the development and progression of DM-related deficits remain unclear. Recent investigations1-4 have altered the traditional model of cerebrospinal fluid (CSF) hydrodynamics. The brain lacks specialized organ-wide anatomic structure to facilitate lymphatic clearance although the brain has complex architecture and high metabolic activity. However, a newly identified glymphatic system has been shown to modulate the CSF-interstitial (ISF) exchange, which facilitates clearance of interstitial solute from the brain parenchyma. Impairment of the glymphatic system is involved with the development of neurodegenerative conditions, including Alzheimers disease and sleep disorders, etc2, 4. Although the impact of the glymphatic system is being investigated in Alzheimers disease and sleep disorders, with promising results, there are no reported data related to diabetes and the glymphatic system. Using a model of T2DM in middle-aged rats and noninvasive MRI methodologies, our preliminary data indicate that compared with age-matched non-DM rats, the T2DM rats reduced clearance rate of interstitial Gd-DTPA agent from brain parenchyma by approximately 84 % and increased clearance time by 4.2 time of Non-DM rats in the hippocampus, leading to accumulation of Gd-DTPA agent in these regions and consequently high MRI signal intensity in T1 weighted MRI (T1WI). In parallel, ex-vivo confocal imaging analysis revealed that in Non-DM rats, the concentration of interstitial Texas Red-conjugated dextran (TR-3, MW 3kD) reached a plateau in the brain interstitium approximately 3h after injecting TR-3 into the cisterna magna and after that TR-3 began to clear and was almost completely cleared from brain parenchyma at 6h after the injection, whereas in middle-age T2DM rats TR-3 accumulated in the hippocampal interstitium with time and exhibited strong fluorescent signals at 6h after the injection. These ex-vivo data are consistent with in vivo MRI findings, indicating that T2DM impairs the glymphatic clearance of interstitial solutes in the brain. In addition, T2DM rats exhibited microvascular thrombosis and blood brain barrier (BBB) leakage in the hippocampus in immunofluorescent analysis and also showed spatial learning deficits compared to Non-DM rats. Based on our novel preliminary data, we will employ MRI and 3D confocal microscopy to evaluate for the first time, temporal and spatial profiles of paravascular CSF-ISF exchange throughout the brain during the development of T2DM. We propose to further develop MRI protocol and analysis modeling as an effective means to evaluate the function and status of the glymphatic system (Aim 1). We will then use the optimized MRI protocol and analysis to explore the relationships between impairment of glymphatic system, vascular damage, and functional deficits during develop of DM (Aim 2). Data generated from this application will provide new insights into the progression of DM associated impairment of the glymphatic system.

PUBLIC HEALTH RELEVANCE: This application pioneers the investigation of impairment of a system that removes metabolic toxins from the brain, the glymphatic system, during the development of diabetes in aged rats. Magnetic resonance imaging (MRI) protocols will be optimized to characterize and monitor glymphatic dysfunction and will be confirmed using laser scanning confocal microscopy (LSCM). Advanced MRI will permit non-invasive measurement of the dynamics and temporal impairment of the glymphatic system induced by diabetes. These studies will shed light on aged brain dysfunctions due to diabetes.