REGULATION OF CAPILLARY HEMODYNAMICS BY THIN-STRANDED PERICYTES - PROJECT SUMMARY Capillaries are the sites of gas exchange between circulating red blood cells (RBCs) and the surrounding tissue. Pericytes are perivascular mural cells and play a vital role in regulating blood flow within the microvasculature. Based on their general morphology, contractile kinetics, and location along the capillary tree pericytes can be categorized into different subtypes. Ensheathing pericytes are found on the most arteriole- proximate segments of the capillary network, have multiple densely-packed enwrapping projections, and can dynamically constrict capillary vessels. Thin-stranded pericytes are found deeper in the capillary network, have long, thin processes that extend 100-200 microns from the cell body, and have fewer and smaller capillary enwrapping projections. Preliminary data presented here show that thin-stranded pericytes are capable of a constriction in response to increasing intraluminal pressure but through an unknown mechanism. In the current application, we propose to characterize the ion channels, intracellular signaling pathways, and contractile machinery responsible for generating the slow pressure-induced focal constrictions by thin-stranded capillary pericytes. In addition, we will test the hypothesis that the long extending processes of thin-stranded pericytes function to sense changes in intraluminal pressure and neuronal activity and are capable of generating and propagating electrical signaling back to the cell body to stimulate constriction. Lastly, we will determine whether this process is essential for tuning the transit time of flowing RBCs with the capillary network; a process that facilitates the local release of O2 at specific points within capillary networks. To address these hypotheses, we will employ our newly developed ex vivo pressurized retina preparation, an application ideally suited for studying pericyte-dependent constriction of capillary vessels, with several other state-of-the-art approaches, including advanced optical imaging, electrophysiology, optogenetic stimulation, and genetically engineered mice. Completion of the proposed work will address many of the controversies in the field, provide valuable insights into pericyte physiology and identify new therapeutic targets for the regulation of capillary blood flow.
