Blood-brain-barrier and white matter mechanisms underlying dementia

Abstract White matter (WM) damage has increasingly been recognized as an important contributing factor to neurodegeneration and dementia, however, little is known of the specific molecular and cellular events underlying the pathogenesis. Clinically, chronic hypoperfusion is often associated with WM changes in small vessel disease. We previously demonstrated that mice deficient in endothelial nitric oxide synthase (eNOS) spontaneously develop chronic cerebral hypoperfusion in multiple areas that precisely match to the most vulnerable areas of hypoperfusion in early demented patients, surrounded by elevated ROS and neuroinflammation, microbleeds, cerebral amyloid angiopathy in middle aged mice, followed by hippocampal neurodegeneration in older age. Moreover, these mice develop WM changes (e.g., myelin and oligodendrocyte loss) at middle age, accompanied by marked astrogliosis and selective loss of pyramidal neurons in cortical layers 2/3 and 5/6. We found upregulated bone morphogenic protein BMP4 in pericytes in these mice at younger age, preceding myelin loss, and pericytes are the most vulnerable cell type to hypoperfusion among the others in neurovascular unit. We therefore hypothesize that pericyte degeneration is the earliest pathological event in WM in eNOS-deficient model, preceding blood-brain-barrier breakdown, astrogliosis, myelin loss and neocortical neurodegeneration; pericyte-BMP4 is a critical initiating factor to these events. Three Aims are proposed. Aim 1. We will use optical histological approach to image pericytes in whole brain after clearing to determine when and where pericyte losses occur in eNOS model, and the cell-cell communication in neuro-glial vascular units. Aim 2. We will profile expressional changes of BMP4 in different cell types using BMP4-CFP reporter mice as well as validate BMP4 protein upregulation in WM pericytes in human brain cortical samples of a large cohort of vascular dementia cases. We will also block overactivated BMP4 signaling at early age by Noggin infusion to CNS and fully characterize gene alteration on microvessels by RNAseq analysis. Positive outcome will identify novel molecular mechanism and molecules as potential therapeutic targets for WM disease. Aim 3. Neurophysiological determination of white and gray matter functions in eNOS deficient mice. We will conduct in vitro electrophysiology (brain slice recording) to detect WM axonal functional abnormalities in corpus callosum and patch clamping for cortical neuronal abnormalities in intrinsic membrane excitability, action potential properties and excitatory synaptic circuits in cortical layer 2/3 and 5/6, as well as in vivo electrophysiology-tetrode spike recording in freely moving mice. Successful completion of these tasks will provide direct evidence for a causative role and mechanisms of WM and vascular changes in WM and cortical dysfunction and functional loss in neurodegenerative diseases, a highly under-explored area.