PERICYTE CONTRACTILITY BY OPTOGENETICS REGULATES CAPILLARY DIAMETER AND BLOOD FLOW

Abstract

Pericytes are vascular mural cells that wrap around capillaries and are essential for blood-brain barrier formation and maintenance, and perform multiple functions at the neurovascular unit including regulation of 1) BBB permeability and bulk flow fluid transcytosis, 2) capillary diameter, 3) cerebral blood flow (CBF) velocity, 4)angiogenesis (the formation of blood vessels from existing vessels) and subsequent microvascular stability and network architecture, 5) phagocytotic clearance of toxic metabolites from the CNS, 6) pro-inflammatory responses, e.g., leukocyte trafficking, and 7) multipotent stem cell activity. However, whether or not pericytes are contractile cells has been a continuous debate dating back to 1873 when Rouget first described them. Recent studies found that a pericyte marker in cerebral spinal fluid, soluble platelet-derived growth factor receptor-β, is an early biomarker of human cognitive dysfunction (Nation et al., Nat. Med., 2019). Therefore, understanding the physiological roles of pericytes is imperative, especially since they degenerate in Alzheimer's disease. Here, we test the hypothesis that capillary level pericytes are contractile cells, and that their contractility is altered by amyloid-beta. We used a novel pericyte-specific Cre mouse using a double-promoter approach with both the Pdgfrβ and Cspg4 promoters, and crossed to a Cre-dependent channelrhodopsin (ChR2) mouse with a YFP reporter gene, termed Pericyte-ChR2, or crossed to a Cre-dependent archaerhodopsin (ArchT) mouse with a YPF reporter gene, termed Pericyte-ArchT. Furthermore, we are testing the impact of amyloid-beta on pericyte contractility. First, we confirmed that ChR2 and ArchT are only expressed in pericytes by performing immunofluorescent staining with anti-CD13 antibody and which colocalized with the YFP reporter gene. Using the Pericyte-ChR2 mice, we performed optogenetics experiments in vivo and found that stimulation of ChR2 caused pericytes to contract, the underlying capillary to constrict and restricted blood flow. Using Pericyte-ArchT mice, we performed optogenetics experiments in vivo and measured changes to pericyte contractility and underlying capillary diameter, and are assessing whether amyloid-beta alters contractility. Pericytes are contractile cells. Discovering the functional role of pericytes will have important implications for pathological conditions and neurodegenerative diseases in which pericytes degenerate including Alzheimer's disease, amyotrophic lateral sclerosis, Parkinson's disease and Huntington's disease.