Study design for testing role of SMC CYB5R3 in SCD-associated PH.Cyb5r3^fl/flMyh11-CreER^T2 and Cyb5r3^wt/wtMyh11-CreER^T2 mice were lethally irradiated (500-550 rad twice) and transplanted with BM (2-4 million cells) from SS donor mice to create SS/R3^fl and SS/R3^wt chimeras, respectively. At 8 to 10 weeks posttransplantation, peripheral blood was sampled to test engraftment to donor Hb phenotype. Chimeras testing ≥80% engraftment, assessed by Hb electrophoresis, were fed a tamoxifen diet ad libitum for 2 weeks, and thereafter switched back to regular chow and aged for an additional 3 or 12 weeks before measurement of hemodynamics by RV microcatheterization. At 3 weeks CYB5R3 knockdown (solid timeline), animals were 5 weeks SS phenotype (dashed timeline) and a total age of 19 to 24 weeks. At 12 weeks CYB5R3 knockdown (solid timeline), animals were 14 weeks SS phenotype and a total age of 29 to 34 weeks. Complete blood counts were assessed at 8 to 10 weeks posttransplant, before a tamoxifen diet and again at time of RV catheterization. ≥80% ΔHb, time point at which animal is at least 80% engrafted to SS phenotype and used to calculate number of weeks with humanized HbS circulating red cells; BMT, BM transplant; D₋₁, 1 day before starting 2-week tamoxifen diet; RV Cath, right ventricle microcatheterization; T_i R3 KD, completion of tamoxifen treatment and initial time point of CYB5R3 knockdown.