Michael Giannetto - PhD Candidate, Advisor: Maiken Nedergaard, MD, DMSc
The brain is the most metabolically active organ in the body, yet it lacks a traditional lymphatic system for waste clearance. Instead, the brain utilizes the glymphatic system, a network of fluid filled spaces surrounding blood vessels, termed perivascular spaces (PVSs), which facilitates movement of cerebrospinal fluid (CSF) into the brain along arteries and waste clearance out of the brain along veins. Astrocytic endfeet comprise the outer boundary of the PVS and serve as a point of regulation for CSF flow into the brain. CSF flow in pial artery PVSs is well characterized to follow the same direction as blood flow driven by cardiac pulsations, and CSF flow is increased by large arterial dilations associated with neuronal activity. However, the function, and even existence, of the PVS along capillaries remains unclear. Additionally, the physiological function of pericytes, mural cells that cover capillaries, remains controversial. Some groups claim pericytes are important in blood flow regulation while others have demonstrated they are irrelevant to blood flow, but instead could maintain the extracellular matrix and phagocytose waste. Capillaries make up the bulk of vasculature surface area in the brain, with no brain tissue further than 30 micrometers away from a capillary, and capillaries are continuously covered by pericytes. Thus, capillary PVSs and pericytes are well positioned to clear waste but remain understudied. In this proposal, I will determine if there is directional fluid flow in capillary PVSs, test if pericytes contribute to capillary PVS function, and finally test pericyte and capillary PVS function in aging.
Aim1, I will test the hypothesis that fluid flow in the capillary PVS is directional, following the same direction of blood flow, similar to CSF flow in arterial PVSs. I will utilize in vivo 2-photon imaging of secreted fluorescent protein to label capillary PVSs and measure fluorescent recovery after photobleaching.
Aim 2 will test whether pericytes play a role in clearing waste or maintaining the structure of the capillary PVS. I will use approaches developed in Aim 1 combined with inducible genetic manipulations of pericytes to ablate them or impair their phagocytic and cell matrix maintaining functions, then measure capillary PVSs and glymphatic flow.
Aim3, I will test the hypothesis that capillary PVSs and pericyte dysfunction contribute to glymphatic impairment. I will use the same methods to label capillary PVSs to determine if functional fluid flow decreases, the structure of capillary PVSs changes, or pericyte functions decrease in a cohort of aged mice. I will then attempt to rescue pericyte function in aged mice using PDGF-beta supplementation to improve glymphatic function.
Ultimately this project will answer longstanding questions concerning function of pericapillary PVSs and pericytes, and determine their effect on the glymphatic system in normal aging.
Feb 08, 2023 @ 2:00 p.m.
Medical Center | Ryan Case Method (1-9576)