Name of Applicant (Last, First, Middle): BAHOU, Wadie F. Project Summary/Abstract Research proposed in this grant application builds on extensive genetic, biochemical and animal studies designed to further characterize and validate biliverdin IX reductase (BLVRB) as a novel cellular target regulating human platelet production in situations of stress hematopoiesis, with concomitant effects on erythroid development and repopulation. Although heme degradation is largely studied as a processing pathway designed to clear pro-oxidant (free) heme generated during cellular senescence (or metabolism), heme catabolic enzymes are also known to maintain function(s) in cellular signaling and cytoprotection, and tetrapyrrole byproducts biliverdin (BV) and bilirubin (BR) function in redox reactions as potent buffer(s) against oxidant stress. We now challenge existing dogma, hypothesizing that redox-regulated activity involving heme catabolism functions in a unique metabolic pathway controlling hematopoietic lineage fate with divergent effects on erythroid/megakaryocyte balance. Research goals are accomplished through two synergistic specific aims, designed to (1) delineate cellular mechanisms of BLVRB-regulated Mk/Erythroid redox coupling and cytoprotection in vitro, and (2) define and expand upon mechanisms of lineage-restricted speciation and cytoprotection in vivo, collectively designed to dissect Blvrb-regulated perturbed pathways controlling E/Meg lineage speciation from MEPs during stress hematopoiesis. Basic science implications are broadly relevant to (1) metabolic and bioenergetic consequences of hematopoiesis, (2) heme-regulated redox chemistry, and (3) novel cellular target validation. Clinical/translational implications are designed to enhance our understanding of mechanisms of disease pertaining to stem cell metabolism, aging, anemia and platelet production. Unique reagents and cell lines generated and characterized include (1) murine models of Blvrb- and Blvra-deficiency, (2) iPSC models with targeted BLVRB knock-outs, (3) biliverdin IX (and IX, IX) isomer detection and production methodologies. All proposed studies are formulated on pre-existing studies in subject cohorts, and proposed experiments are predicated on reagents and expertise currently available or in advanced development among the research team. PHS 416-9 (Rev. 6/09) Page Continuation Format Page