My research program is focused upon the novel role of erythrocyte based signaling in matching regional blood flow to metabolic need. The RBC transport portfolio is newly appreciated to include 3 gases (O2, CO2, NO), and RBCs appear to serve as vascular control elements by exerting O2 - responsive control over the bioavailability of vasoactive effectors in plasma. My lab explores the biochemical and molecular events critical to this process.
Our fundamental working paradigm is that RBCs serve as a regulatory node in hypoxia- and redox- responsive signaling by either quenching or initiating thiol-based transfers of nitric oxide (NO) groups (transnitrosation reactions) that cascade through plasma and subcellular compartments in response to alterations in tissue O2 tension. These low mass S-nitrosothiols participate in hyper-acute regulation of vascular tone as well as modulate inflammatory signaling and the gene-regulatory response to hypoxia in vessels. The proposed mechanism within RBCs is that Hb conformational transition appears to govern thiol-based transactions between NO equivalents and RBCs in the microcirculation. Specifically: R-state Hb quenches, and T-state Hb deploys, net NO bioactivity. Thus coupling the release and capture of NO by RBCs to tissue O2 gradients subserves the matching of NO bioactivity to perfusion sufficiency. Notably, it appears that disordered NO flux in RBCs may subvert physiologic and cellular controls. Since transnitrosation signaling appears designed to tune physiologic responses to O2 gradients and local redox signatures in the microcirculation, this process is therefore particularly vulnerable to disruption during periods of sustained hypoxia or oxidative stress. Unmasking disruption in erythrocytic nitrosative signaling may provide mechanistic insight into the perfusion insufficiency and maladaptive physiologic and cellular responses in the microcirculation that characterize many forms of critical illness, and thus – inform novel therapies for these conditions. Query is modeled on many levels from isolated proteins - cell culture - isolated organ - whole mouse - to studies in humans.
More specifically, the long term goal of the studies in my lab is to define the role of red blood cells (RBCs) in the spread of vascular dysfunction during oxidative stress, as exemplified by the development of secondary lung injury. Impaired pulmonary vascular control occurs early in respiratory failure complicating systemic inflammation. This pulmonary vascular dysregulation is characterized by loss of coupling between regional vascular tone and oxygen gradients (e.g. ventilation – perfusion mismatching). While nitric oxide (NO) signaling has been implicated, there is no clear mechanism linking remote inflammation to downstream lung injury. New data suggest that NO groups circulate and signal remotely through serial NO-thiol transfer reactions. Our recent data suggests that these reactions 1) are linked to RBC O2 content; and 2) actuate vasoactivity of NO groups harbored within RBCs, by export to plasma thiols. This signaling reinforces coupling between physiologic cues and vascular tone. We speculate that vascular dysfunction may spread from foci of oxidative stress to the lung through modification of critical thiols in RBC membrane proteins and in plasma.
We use both in vitro biochemical methods and in vivo perfusion models to 1) study the role of RBCs as biochemical links between inflammation remote to the lung and dysregulated pulmonary blood flow and; 2) define the cellular and molecular events critical to this process. We hypothesize 1) that RBCs are injured by transit through vascular beds under severe oxidative stress; 2) these RBCs lose O2 - responsive control of NO transfer reactions in plasma; and consequently, 3) the downstream pulmonary vascular bed loses coupling to environmental inputs.
As a result of the studies in the Doctor Lab we hope to improve mechanistic insight into normal coupling between regional pulmonary vascular tone and local O2 gradients, and to develop an understanding of how RBCs may propagate dysfunction across vascular beds. Achievement of these goals may inform novel therapies for critically ill patients with respiratory failure.
Principal collaborations (at Wash U) are with the Baker Lab (Center for Computational Biology) for mathematical modeling of transnitrosation cascades in plasma, with the Frazier Lab (Biochemistry), with whom we are exploring S-nitrosothiol regulation of thrombospondin signaling, and with the Wash U Proteomics Center (Townsend, with whom we are working to identify SNO-adducted proteins in erythrocyte membranes.