TMPRSS6 inhibition increases endogenous hepcidin and improves PV disease severity. (A) Schematic of experimental design. (B-C) Liver Tmprss6 (B) and Hamp1 (C) mRNA expression relative to Hprt; control + NTC, n = 9; PV + NTC, n = 16; PV + TMP, n = 18. (D) Serum hepcidin; control + NTC, n = 4; PV + NTC, n = 7; PV + TMP, n = 8. (E-H) HCT (E), HGB (F), MCH (G), and RBCs (H); control + NTC, n = 6; PV + NTC, n = 14; PV + TMP, n = 17. (I) Kidney Epo mRNA expression relative to Hprt; control + NTC, n = 9; PV + NTC, n = 16; PV + TMP, n = 17. (J-K) Terminal erythropoiesis in the BM (J) and the spleen (K) determined by flow cytometry. Based on CD44 expression and FSC-A, Ter119⁺ cells were gated into 5 distinct populations: I, proerythroblasts; II, basophilic erythroblasts; III, polychromatic erythroblasts; IV, orthochromatic erythroblasts and reticulocytes; and V, RBCs; BM: control + NTC, n = 7; PV + NTC, n = 13; and PV + TMP, n = 19; and spleen: control + NTC, n = 7; PV + NTC, n = 5; and PV + TMP, n = 7. (L-M) Spleen (L) and BM (M) Erfe mRNA expression relative to Hprt; spleen: control + NTC, n = 9; PV + NTC, n = 8; and PV + TMP, n = 8; BM: control + NTC, n = 8; PV + NTC, n = 11; PV + TMP, n = 16. (N) Serum ERFE; control + NTC, n = 7; PV + NTC, n = 7; and PV + TMP, n = 8. (O) MCV; control + NTC, n = 6; PV + NTC, n = 14; and PV + TMP, n = 17. (P) Serum iron; control group, n = 2; PV groups, n = 4. (Q-R) Liver (Q) and spleen (R) nonheme iron content; liver: control + NTC, n = 9; PV + NTC, n = 16; PV + TMP, n = 18; spleen: control + NTC, n = 5 and PV groups, n = 11. Kruskal-Wallis test for panels B,D,G,I,L-N,P,R, ordinary one-way ANOVA for panels C,E-F,H,O,Q, or two-way ANOVA with Tukey correction for multiple comparisons for panels J-K. ∗P < .05; ∗∗P < .01; ∗∗∗P < .001; ∗∗∗∗P < .0001. NTC, nontargeting control siRNA; TMP, TMPRSS6 siRNA.